Concorde engine intake "Thrust"

[b377]

It is stated that the engine intakes produce 70% (?) of the thrust during some portions of the envelope. It sounds as if the plane is sucking its way through the air. Can anyone elucidate on this?

WRT the doppelganger thread readers of the SUN in the UK will know that Concorde in fact had two APUs - just that the crew never read the ACM or were never told anything about it.:)

[lomapaseo]

It is stated that the engine intakes produce 70% (?) of the thrust during some portions of the envelope. It sounds as if the plane is sucking its way through the air. Can anyone elucidate on this?


I don't recall hearing he term "thrust" before, but perhaps they are talking about the ram jet effect of pressure recovery balances throughout the engine.

[b377]

OK the exact frasing is 63% (not 70%) as follows as per link:

"During the Supersonic cruse only 8% of the power is derived by the engine with the other 29% being from Nozzles and an impressive 63% from the intakes. " CONCORDE SST : Powerplant (http://www.concordesst.com/powerplant.html)

[Brit312]

b377

I think you will find that because the engine's compressor can only handle incoming air at subsonic speeds ,then when the aircraft is at Mach 2.0 the 14 ft long intake has to slow the air down in rough figues from 1350 mph to
350 mph .

As the figure in your web site shows it does this by creating a number of shock waves in the forward part of the intake with the last shock wave[ where the air goes from supersonic to subsonic] being between the two intake ramps

In slowing the air down it also increases it's pressure , and I think the compression ratio was 7 to 1 but could be wrong. This was like having another compressor on the front of the engine with no need for turbine at the back

You can think of it like a piston engine with a turbo charger in the air intake so making the engine more powerful because it pre- compressed the air for the engine

Hope it helps

[M2dude]

Guys, another interesting Concorde thread (:D:O:ok:).
OK, the thrust thing. YES, the numbers are just about correct, what we have is propulsive thrust that without a perfectly matched engine/intake would not be present. The divisions of the thrust are (Quoted from the publication "The Concorde Air Intake Control System").

The engine itself now only generates 8% of the total thrust, a mere shadow of its subsonic glory. The now divergent secondary nozzle produces a sizeable 29%, this being produced in a similar way to how the intake subsonic diffuser produces its thrust. (The main difference in the case of the secondary nozzle is that instead of a subsonic decelerating flow, we now have a supersonic accelerating flow). A huge 75% OF THE TOTAL THRUST is produced by the intake subsonic diffuser section, this being due to the huge rise in static pressure that is occurring in this section. The 'negative thrust' from the forward ramp section this time is 12%, produced by the supersonic compression forces acting on the divergent section of the intake, resulting in an intake thrust component of 63%. So it can be seen that the vast majority of the Mach 2 thrust forces are transmitted to the airframe not via the engine mountings, but via the mountings of the intake, and to a lesser extent the TRA nozzle. It might seem that the two cases, and in particular the latter one, are very demeaning to the role of the engine, but nothing could be further from the truth. By the laws of conservation of energy, thrust (or any other force for that matter) cannot be created out of thin air, the whole process is about maximising the powerplant thrust that is potentially 'on tap'. (O.K. I know, this entire subject is about providing thrust from thin air!!). Without the engine, the entire process of course falls apart and all components of the powerplant produce exactly the same amount of thrust - ZERO!! It is also doubtful if any engine currently in existence could do the supersonic job anywhere near as effectively as the OLYMPUS 593. (Not bad for a design that can be traced back over fifty-four years!). The 593 produces the necessary gas flows to produce these stated levels of thrust, and in the final analysis all powerplant thrust of course is really generated by the engine, what we have been looking at how this thrust is transmitted to the airframe.
I hope that this clarifies things guys, regards to all.

Dude :O

[b377]

Brit312

The way it is stated in the web site its almost like you're getting a free lunch - like the engine delivering only 6% while the rest comes with the territory!

The compresion process as described - a ram air effect - some how, to me at least, suggests a drag force rather than something producing thrust...

btw, you must know all about Proteous engines? Very fond of the 312 myself having spanned the Atlantic ocean on them as a kid.

[b377]

M2dude

As clear as mud but I'll give it another read.

My previous post was written before I read yours and already hinted at the perpetual motion or free lunch situation that develops if the pressure rise-drop along the engine isn't accounted for correctly.

After all kerosene burning furnishes the power = drag x air speed.

[awblain]

There was a similar discussion last year, Can Vmg exceed the V of a jet exhaust?, in which ChristiaanJ (I think) reasonably criticized my dislike of the `free lunch'-type of description of supersonic intakes, owing to having been there and knowing the load-bearing structure of the concorde intakes.

The pressure of the air increases going backwards through the intake, and this produces a net forward force on the intake ramp. As M2dude's quote rightly states, the engine is enabling this to happen. Turn off the fuel and the thrust from all bits of the intake-engine-nozzle system no longer occurs.

[john_tullamarine]

Intake/Nacelle/etc thrust - think pressure distributions over the surfaces associated with the airflow. A clever design will milk a great deal of benefit from the net force.

[Landroger]

Hang about - hang about!!!:eek: :ugh: :=:O I'm sorry ..... do WHAT?? :confused:

Look, you must forgive me - I'm not an aero engineer, just a humble MRI/CT scanner engineer and I am having very serious problems understanding this.:ugh: Okay I understand perfectly that the 593, capable as it is, cannot accept supersonic air.

I further understand approximately that the intake is a prize winning work of engineering genius all on its own and that it is capable of leaching a whole 1000mph from the incoming air, so the 593 can do its thing. I also - just - understand that the aerodynamics of the nozzle does a huge amount of magic to the raw jet exhaust and appears to produce a thrust gain over and above the 593.

So far so good. :hmm::)

I was holding it all on the island because I reasoned that all that air going in has to go somewhere and if it was being slowed down, it must therefore be compressed - like another very powerful front end stage to the compressor. Then, I thought, that the compressor would be compressing compressed air so, although the engine gain would be the same, the result would be dramatically greater. Yes? :D Or no? :sad:

If not, by exactly which mechanism is real thrust being generated and, more importantly, transmitted to the airframe?

I love this aeroplane and since M2Dude, ChristiaanJ, Bellerophon, BS312, Exwok and all the other 'Concorde family' contributors have pitched in so generously, it is really coming alive. But she's damn complicated. :confused::eek:

Roger.

[bearfoil]

Great respect, see the Pratt and Whitney J58 mounted x2 on the Lockheed SR-71.

I think first flight was ~early 60's.

Great thread..........

[M2dude]

I hope that this diagram just might make matters a tiny bit clearer. It clearly shows how the propulsive thrust is divided up among the various components, particularly the intake. As the airlow travels through the carefully controlled and complex inlet shock system, it exhibits a 600% rise in Static Pressure Ps, this huge pressure rise reacts against the divergent wall of the intake, giving us colossal amounts of thrust. Take a look at this quote from ' The Concorde Air Intake Control System:
A good impression of the efficiency of any engine/intake combination can be gathered by looking at overall intake pressure recovery, as this will determine compressor face total pressure, itself being a major parameter in determining powerplant thrust. The following example is given for the A/C just before Top of descent, Mach 2.0, ISA +5 (This equating to temperatures of Ts = -51.5 ºC, Tt = 127 ºC) and altitude = 60,000'
Freestream Total Pressure = 8.14 P.S.I.A
Freestream Static Pressure = 1.04 P.S.I.A
Freestream Dynamic Pressure = 7.10 P.S.I.A.
Compressor Face Total Pressure = 7.63 P.S.I.A
Compressor Face Static Pressure = 6.42 P.S.I.A
Compressor Face Dynamic Pressure = 1.15 P.S.I.A.
Compressor Face Total Temperature = 127 deg's. C

Analysis of the above-described case shows that there is:
A SIXFOLD INCREASE IN STATIC PRESSURE !!!
AN INTAKE PRESSURE RECOVERY OF ALMOST 94%. THIS IS AN EXCEPTIONALLY HIGH FIGURE, PRODUCED WITH A STATIC PRESSURE INCREASE OF 5.38 P.S.I.
A REDUCTION IN DYNAMIC PRESSURE OF 6.78 P.S.I. NO HEAT ENERGY IS LOST IN THE COURSE OF THE COMPRESSION PROCESS
The pivotal part of all of this is a staggering 94% recovery of the freestream total pressure (the pressure coming at the intake), this is what enables the engine to move the required amount of airflow, enabling the intake, engine and nozzle to provide the thrust required for supersonic engine operation without the use of reheat and with staggeringly low fuel flow values.

Dude :O http://i991.photobucket.com/albums/af32/riconc1/Concorde/Thrust.jpg[/font]

[M2dude]

http://i991.photobucket.com/albums/af32/riconc1/Concorde/Nozzle.jpgThis diagram shows just how the action of the two nozzles is able to help provide so much thrust at Mach 2. The 'cooling air' from the engine bay into the nozzle annulus s the secondary airflow that was diverted the intake ramps, and this gives the high pressure efflux an aerodynamic cushion to expand against from within the divergent secondary nozzle buckets. This gives a dramatic reduction in the thrust that would otherwise be wasted due to the high pressure efflux over-expanding/flaring against the very low static air pressure.

Dude :O

[M2dude]

Guys, apologies if it seems that I'm trying to hog things here, I'm just attempting to help clarify an extremely complex and bewildering subject.
Just imagine for a second that we are flying (or attempting to fly) at Mach 2, but instead of having a convergent/divergent intake, we just have a hole at the front. (This is termed 'a pitot intake'). Contrary to common folklore supersonic air will not enter the engine, this is a fallacy. The velocity of air entering a jet engine compressor is defined by engine mass-flow demand and the cross sectional area of the L/P compressor, you cannot force air into a jet engine at a velocity it does not require. (You can certainly force the engine to surge, and possibly drive the inlet into unstart by attempting this though). The Olympus 593-610 at Mach 2 ISA +5 had a demanded compressor Mach number (Mn1) of 0.46, this is fixed. With just a pitot intake, what WILL happen is that to satisfy the demand of the engine a single normal shockwave will form across the face of the intake, resulting in subsonic flow downstream of the shock. (A normal shock will always without exception produce subsonic downstream air). Now the pressure losses involved with a normal shock are proportional to the 'strength' of that shock, where there is only a single normal shock is utilised, over 40% of the propulsive thrust would be lost at Mach 2. (Due to enormous compressor face distortion, the engine would also be unstable to the extreme. As Mach number increases this loss also increases, to the point that if we were able to fly at Mach 3 there would be no available thrust left at all. This installation would also have huge aerodynamic drag, due to air spilling over the intake lip.
To minimise all these losses, a convergent/divergent intake is usually used for supersonic aircraft, but unless this can be made to adjust to varying engine demand and Mach number changes, this intake will be efficient at one Mach number only, and poor flow/efficiency will result at all ‘off design’ Mach numbers. (Lockheed seem to have done an incredible job with the fixed inlets on the F22 Raptor however). Designing a variable inlet in itself is not too difficult, but if you want a design with maximum possible efficiency (no reheat or afterburning) together with totally automated surge protection and operating stability, the task is truly daunting, and before Concorde quite frankly not achieved anywhere.
What any convergent/divergent intake achieves is to use a series of relatively weak oblique shocks to progressively slow the intake air down (Oblique shocks ALWAYS produce supersonic downstream airflow) the unavoidable normal shock is designed to be as weak as possible, and should occur as close as possible to the narrow throat of the intake. The now subsonic air will progressively slow down as it travels through the divergent section of the intake, up to the compressor face. Any time that intake matching is not perfect, large losses quickly occur, with air spilling over the lip of the inlet, and surge/unstart also likely to occur if things go too far off song. (The intake system of Concorde actually sensed the position of the normal shock, and allowed it’s perfect placement by varying the intake surface).
Due to the onset of writer’s cramp/mental fatigue coupled with a desperate need for beer, this will have to do for now guys, I just hope it makes it all a little less ‘clear as mud’

Dude :O

[b377]

M2dude

Thanks for your effort. Clearly the answer rests on the interpretation of the axial pressure profile; not as simple to explain as a momentum exchange in a rocket engine or mass flow at subsonic speeds.

Wonder how much of this was learned from the use of the 593s on the 1950s Victor bombers albeit these were not supersonic?

[Mr Optimistic]

yep, there was a huge thread on this last year focused on ice cones I believe. Switch off the fuel and see how much thrust the intake gives.

[HarryMann]

SR-71's J58 SFC quoted at 0.9 lb/lf-hr (dry)

Oly 593 quoted at 1.19 or similar (dry)

Presume these figures are not comparable, if Olympus reckoned to be the most efficient of the dry supercruise engines - think this discrepancy is that J58 is fundamentally a wet ramjet in cruise, and a smaller core? (OLy usually quoted as the largest core fo any gas turbine?)

[Machaca]

The J58 intake and exhaust inlets and outlets create 83% of total trust at M3.2 at 80,000 ft. It first flew in 1963 powering the YF-12A, precursor to the SR-71.

Wikipedia:
The J58 is a hybrid jet engine: effectively, a turbojet engine inside a fan-assisted ramjet engine. This was required because turbojets are inefficient at high speeds but ramjets cannot operate at low speeds. To resolve this, the airflow path through the engine varied, depending on whether ramjet or turbojet operation was more efficient, thus the term variable cycle. To create this effect, at speeds over 2000 mph the nose cone of the engine was pushed about 2 inches forward to improve the air flow in the ramjet cycle.

Air is initially compressed and heated by the shock wave cones, and then enters 4 stages of compressors, and then the airflow is split: some of the air enters the compressor fans (core-flow air), while the remaining flow bypasses the core to enter the afterburner. The air continuing through the compressor is further compressed before entering the combustor, where it is mixed with fuel and ignited. The flow temperature reaches its maximum in the combustor, just below the temperature where the turbine blades would soften. The air then cools as it passes through the turbine and rejoins the bypass air before entering the afterburner.

At around Mach 3, the initial shock-cone compression greatly heats the air, which means that the turbojet portion of the engine must reduce the fuel/air ratio in the combustion chamber so as not to melt the turbine blades immediately downstream. The turbojet components of the engine thus provide far less thrust, and the Blackbird flies with 80% of its thrust generated by the air that bypassed the majority of the turbomachinery undergoing combustion in the afterburner portion and generating thrust as it expands out through the nozzle and from the compression of the air acting on the rear surfaces of the spikes.
http://i337.photobucket.com/albums/n385/motidog/SR71_J58_Engine_Airflow.jpg

[M2dude]

b377
Wonder how much of this was learned from the use of the 593s on the 1950s Victor bombers albeit these were not supersonic?
The Handley Page Victor Mk1 was powered by four Armstrong Siddely Saphire turbojets, and was underpowered like hell. The Mk2 was powered by four Rolls Royce Conway turbofans, was a far more capable aircraft and was the fastest of all the V Bombers.
The Avro Vulcan Mk1 was powered by four Bristol Siddely Olympus turbojets, the Mk1 by four Olypus Mk1 1 engines, rated at 11,00lb static thrust and the Mk2 by four 22,00lb thrust Olympus 301 engines. Now allthough the Olympus 593 shares the same name and twin spool turbojet layout, they were in reallity light years apart. The 593, although a development of the earlier engine became an almost total re-design, and was a direct development from the Olymus 320 engine, powering the polititian murdered but absolutely superb BAC TSR2.
Machaca
Thanks for the superb diagrams for the J58 powerplant. The SR71 (one of my top 3 ever favourite aircraft) was without doubt Kelly Johnson's finest creation, and still remains on the record books as the fastest conventional eaircraft ever built. The axisymmetric intake is in fact a potentially more efficient design than the two-dimentional intake used on Concorde, and is really essential for any Mach 3+ design. (The Mig 25 used a two dimentional intake, but was a crap design that only achieved very brief high speeds by use of brute foce and ignorance).
There are two fundimental problems with axisymetrical inlets, that of unstart and also instabily in sideslip conditions. There were many sideslip induced unstart events with the SR71, even aircraft losses occured as a result. There was a club in the SR71 community, known as the 'split helmet club'. This was where as an intake surged or unstarted, as a result of the violent yawing the crew member's bone dome would strike the side of the canopy violently and crack open. To be a member this had to have happened to you. (There were MANY members). I read an article by an SR71 test pilot saying that an unstart was 'like being in a train wreck'.
So you can see that this effect was not really desirable for a passenger aircraft carrying 100 passengers). For a note on unstart we have here another extract from the Concorde Air Intake Control System:

UNSTART
Occurs when the intake shock system is expelled from the intake resulting in almost instant engine surging due to enormous flow distortion. Merely throttling the engine will not resolve the problem, as the shock system will not re-establish itself without movement of the intake surfaces. The phenomenon has plagued almost every variable geometry intake ever flown, with the definite exception of this one.

For these reasons an axisymmetric design was ruled out for Concorde, and it was deemed that the inlet had to be both more or less immune from the effects of sideslip, as well as being a self starting design. (Originally the control laws were tweaked to compensate for side slip disturbences, but eventually an aerodynamic solution was found, and side slip signalling/compensation was relegated to blank lines of code in the system software).
But in spite of the above, I have nothing but respect and admiration for the SR71. :ok:

Dude :O

[Landroger]

Bear with me Dude, I think your drawing in post #12 has done it for me, but I'm prepared to be embarrassed yet again. :) :uhoh:

Its a bypass? :O The "power" is generated by the action of shock waves slowing the air mass and passes around the 593 to mix with the core engine exhaust within the buckets? So, it is the opposite of a High Bypass fan, in that a core of 'relatively low' velocity air from the 593, is surrounded by a tube of very high velocity/energy air from the intake?

I refer to the 593, buckets and intake as components, because the whole assembly is 'The Engine'. Is that how you see it? Please say I've got it, because its been doing my head in since the statistic (75% thrust from intake) was first mentioned. :D

ROger.

[barit1]

The thrust produced by the intake is not only a supersonic phenomenon.

A well-designed subsonic inlet will also - due to static pressure rise in the divergent annulus - create some thrust.

The effect even occurs in a radial engine with the NACA cowl (http://en.wikipedia.org/wiki/NACA_cowling). I once ferried a prewar a/c with the cowl removed - it was 15 kt slower without the cowl fitted.

[b377]

Superb stuff guys.

Can't signoff without questioning how Concordeski designers solved the problem!

[Mr Optimistic]

On the wetted surface theory elucidated above, a simple unknotted toy balloon will be thrust about the place and this is calculable, in theory, by looking at the unbalanced pressure acting on the inside wall. So the front of a rubber toy balloon produces thrust. Are you sure a good intake design is not more about reducing losses ?

[barit1]

There are both drag and thrust benefits of the NACA cowl.

Externally, the cleaner surface (compared to cylinder heads etc.) is certainly a drag reduction.

Internally, the divergent (diffuser) flow field increases static pressure on the inside of the forward cowl, which is a thrust felt by the cowl mounts. If these mounts should break, the cowl is free to shift forward, and will in fact strike the trailing edge of the prop blades.

Theoretically, some additional thrust should be available from the internal air, heated (and expanded) by cylinders etc., then accelerated out the exit annulus. I'm not aware of this ever actually achieved in an aircooled engine, although the liquid-cooled P-51/Merlin combination seems to have done it.

[M2dude]

Landroger
Its a bypass? http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/embarass.gif The "power" is generated by the action of shock waves slowing the air mass and passes around the 593 to mix with the core engine exhaust within the buckets? So, it is the opposite of a High Bypass fan, in that a core of 'relatively low' velocity air from the 593, is surrounded by a tube of very high velocity/energy air from the intake?
Not quite Landroger, but really close. The Concorde intake design is what is known as a 'two stream' intake. What this means is technically the inlet capture area itself is fixed, with 'unwanted' subsonic air passing over the ramp surfaces. Now this basic design is not uncommon, F14, F15, Tornado, MIG 25 etc., but the spilled subsonic air in these designs is ejected overboard, giving very little in the way of secondary benefits, and in fact the secondary airflow at all is technically a small waste of energy. What is totally unique about the Concorde design is that the dumped secondary airflow is used to radically enhance the performance of the secondary nozzle exhaust, If you look at the diagrams in post #13 you will see that the jet eflux is nicely following the contour of the wide open secondary nozzle buckets. Without the cushioning airflow coming off the intake ramp bleed, the high pressure exhaust gas (16 PSI) as it meets the very low pressure ambient air (only 1.04 PSIA at 60,000') would flare outwards acutely, wasting a large amount of thrust. The inake thrust gets generated from the huge increase in static pressure, acting on the divergent wall of the intake and ramp assembly.

I refer to the 593, buckets and intake as components, because the whole assembly is 'The Engine'. Is that how you see it? Please say I've got it, because its been doing my head in since the statistic (75% thrust from intake) was first mentioned. :D

Yes Landroger, you certainly HAVE got it. The important concept to grasp is that you have to consider the powerplant as the 'engine' if you like. It's the intake, engine and nozzle assembly that were able to work together in such perfect harmony, but each component was totally codependant on the others.

Dude :O

[M2dude]

barit1
Your information on the NACA cowls, particularly the P51 are both fascinatating and enlightening, thank you for adding another dimension to this thread. It's so easy to forget what an amazing design the Mustang was, I remember reading a fascinating article a few years ago on the very area that you describe, The air inlet design was totally unique, and was lrgely responsible for the high performane of this amazing aircraft.

Dude :O

[M2dude]

b377

Can't signoff without questioning how Concordeski designers solved the problem!
They never did. The original TU 144 engine was an apalling lump, and the intake was crude, both aerodynamically and in terms of it's control system. One of the major problems with the TU144 was it;s inabity to supercruise without the use of afterburning, due entirely to inadequate control on inlet airflow as well as a far too simple NK144 engine.
Keep posting away here b377, you've started a really interesting thread.

Dude :O

[M2dude]

Mr Optimistic

On the wetted surface theory elucidated above, a simple unknotted toy balloon will be thrust about the place and this is calculable, in theory, by looking at the unbalanced pressure acting on the inside wall. So the front of a rubber toy balloon produces thrust. Are you sure a good intake design is not more about reducing losses ?

A good intake design is ALL about minimising losses, remember without a good intake, nomatter how good the Olypus 593 was, the 68% total thrust that came from the intake would not have been fully realised, the poorer the inlet design, the greater the losses of the powerplant as whole are. But a poor engine design will also not allow the intake to do it's work either, it is total co-dependance, the reduced losses translating into greater overall thrust and SFC. Try and think of it all as a powerplant, rather than intake, engine and nozzle; each of these components provide the thrust forces, but as we have said before, without the engine itself every part of this powerplant provides equal thrust: ZERO.
As far as having a problem with the whole thrust thing, the intake mounting assembly was designed to absorb and transmit the thrust forces from the intake assembly to the airframe, I'm afraid this is fact my friend.

Dude :O

[Mr Optimistic]

And to think these were all done without the modern CFD codes

[DozyWannabe]

Now this basic design is not uncommon, F14, F15, Tornado, MIG 25 etc., but the spilled subsonic air in these designs is ejected overboard, giving very little in the way of secondary benefits, and in fact the secondary airflow at all is technically a small waste of energy.
Which is presumably one of the factors in why those designs can't supercruise (not that supercruise was considered a must-have in a fighter of that era), and one of the reasons that once the old girl was supersonic, none of them could catch her.

[Landroger]

Many thanks dude, there is light indeed at the end of the tunnel - and not simply because it is on fire! :D The whole concept of 'Supercruise' is quite stunning and the thought occurs; was it played for, or a happy outcome of the way the design froze? :rolleyes:

They never did. The original TU 144 engine was an apalling lump, and the intake was crude, both aerodynamically and in terms of it's control system. One of the major problems with the TU144 was it;s inabity to supercruise without the use of afterburning, due entirely to inadequate control on inlet airflow as well as a far too simple NK144 engine.

Your comments about the Tu144 are astonishing and quite unexpected. I had heard, over the years, that Concordski was a triumph of the Soviet state and a very close competitor to Concorde. You are saying though, that it could not maintain Mach 2 without reheat?

Having said that, I also read that there were external clues - to those that really know aeroplanes - that Concordski was actually a donkey. The canards, for example? :eek:

Thanks again for the extra info about the intake. :ok:

Roger.

[ChristiaanJ]

To come back a moment to the difficulty of visualising how intake and exhaust provided "nearly all" the thrust, and the engine "next to nothing"....

Think a moment of various marine and industrial gas turbines (Olympus and others).

What does the engine do in those installations? It is a 'gas generator', and all the power in the exhaust is extracted by a separate turbine.
As a matter of fact, the thrust of those engines is practically zero, since having thrust in a stationary installation would just be a waste.

On Concorde at Mach 2, the situation is really not all that different...

By sucking a huge amount of air through a very sophisticated inlet, it sets up pressures in that inlet, that provide about 75% of the thrust.
By blowing that same amount of air, with added heat energy from the fuel, out of the other end, through another sophisticated convergent-divergent nozzle, we produce yet more thrust.

The engine itself produces very little thrust, but by 'sucking' and 'blowing' on the right components front and back it creates the right conditions for those components to produce the thrust we're looking for.

I hope this makes some sense?

CJ

[M2dude]

MrOptimistic

And to think these were all done without the modern CFD codes

Oh, being devised 'centuries' ;) before C++ was only a tiny issue. The problem was that having decided that an analog intake system would never be able to provide the level of control and stability required for certification, the technology almost had to be invented. In 1970, when relatively late on, in project definition terms, it was decided to use 'throw 'away' the analog system and replace it with a completely new digital one, there came a problem; there was no such thing as an airborne digital control system, and so one had to be 'invented' in Bristol. The control units were to be built by the Guided Weapons Division of what was then the British Aircraft Corporation, and so it made sense that the 'digital computer' part was adapted from a guided missile system. (I'm 90% sure that it was based on the Sea Dart SAM).
The control unit's processors were based on TTL logic, as this gave superior speed and better voltage transient tolerance than the CMOS chips that were then available. Trouble with THAT was that TTL runs really hot, and cooling the eight control units was a bit of a nightmare originally. But in spite of all these and many more electronic mountains to climb, this revolutionary system was developed and test flown for the first time within TWO YEARS of the 'go digital' decision. To me that still seems one hell of an achievement.

Dude :O

[M2dude]

DozyWannabe
Which is presumably one of the factors in why those designs can't supercruise (not that supercruise was considered a must-have in a fighter of that era), and one of the reasons that once the old girl was supersonic, none of them could catch her.
Not really DW, it was not so much due to the simpler secondary airflow systems, more to do with the design of the engine and intake, and only Concorde achieved the following: The engine itself should be able to operate with a more or less constant turbine entry temperature and with the HP and LP spools operating as close as possible to their individual surge boundaries throughout the entire flight envelope. The intake itself had to operate at a pressure recovery of 94%, no other intake to date had even come close to Concorde, and typical figures of 65-70% are still common. Without all this you did not get the required level of propulsive thrust and supercruise is just not possible without afterburning/reheat. The Concorde intake was also unique in producing far less secondary induced aerodynamic drag than other designs.
The 'old girl' as you call her really was amazing though, wasn't she? :)

Dude :O

[Mr Optimistic]

No-one would dare take that kind of risk now under fixed price rules. Had forgotten about TTL. Of course you would need 10^-9 now, don't suppose safety was quite the game it was now.

[M2dude]

Landroger
The whole concept of 'Supercruise' is quite stunning and the thought occurs; was it played for, or a happy outcome of the way the design froze? :rolleyes:

It was both 'played for' from the very beginning and was certainly a happy outcome. But development of the intake was not completed until three years AFTER the aircraft entered airline service, after hundreds and hundreds of flight test hours. It was really quite a small team of designers at BAC Filton that developed the aerodynamics and control systems, a team of twelve extremely talented individuals, the leader being the great Dr Ted Talbot.
Your comments about the Tu144 are astonishing and quite unexpected. I had heard, over the years, that Concordski was a triumph of the Soviet state and a very close competitor to Concorde. You are saying though, that it could not maintain Mach 2 without reheat?
Yep, that aircraft was a total dog. :eek:

Roger I'm so glad that my blurbish explanations are making a little sense, the subject drives me nuts too, and I started doing it thirty six years ago.

I quite like ChristiaanJ's analogy on explaing how an inlet can provide thrust, but the precise shockwave geometry that the Concorde intake required in order to do what it did best, was little more than mind numbing in terms of complexity and control; It is really difficult to imagine if it could ever be bettered aerodynamically, even now.

Dude :O

[Mr Optimistic]

Fair try but it still seems a bit perpetual motion machine to me.

In the frame of reference where the engine is stationary, work is done on the entering gas to slow and compress it. The pressure rise over free stream sure enough gives a forward force on the intake structure (pressure higher inside than out). If the thing was a sealed unit the same would still be true (except the forward force would be greater though nothing like the net force acting backwards (aka drag)). The engine does work on the gas and expels it at higher speed and maintains a delta-P between the front and rear faces such that the pressure at the front is maintained below full recovery. So momentum taken from the air at the front and more given back at the, erm, back and it is the lower pressure at the front face compared to full recovery which underlies the force accounting does it not ?

We had this discussion last year, same principle as rocket motor, the hole in the back is the big trick and yes, if you look at the forces it is the higher pressure on the casing at the front which transmits the NET force, but who ever says that a rocket motor casing provides thrust ?

[M2dude]

Mr Optimistic
This is one of those arguments that you could make go around and around for ever. The facts of the matter are this:
The intake DID provide a sizeable amount of thrust at Mach 2, but if it makes it easier to realise think of it in terms of the engine provides ultimately all of the thrust, and a large amount is projected through the intake assembly. Without the intake, the engine would not have been able to manifest this thrust in any way. However without an extremely capable and sophisticated Rolls Royce Olympus 593 being able to be operated at maximum supersonic efficiency, this thrust would still not have been realised by the engine.
We have an extremely complex powerplant arrangement here that took years to develop and gave phenomenal performance, these are facts.

Dude :O

[M2dude]

Below is quite a nice simple but clear diagram of the powerplant as a whole, showing a VERY simplified diagram of the shock system within the intake as well as the complex path for the secondary airflow, from over the intake ramps, through the secondary air dors into the engine bay and then finally into the secondary nozzle annulus.

Dude :O
http://i991.photobucket.com/albums/af32/riconc1/Concorde/Powerplant.jpg

[Mr Optimistic]

The issue is one of terminology but not semantics. The idea of thrust from the intake leaves just one small step to the intake sourcing thrust and then to why do we need the hot and heavy thing just behind. This was a question here last year. Physics v engineering I guess. Should we make this an annual date ?:8

[b377]

Going full circle to the start of thread where I remarked that Concorde 'sucked its way through the air' it obviosuly wasn't too far from fact.

Still when one thinks about thrust one imagines what happens in subsonic flight where the propelling force comes from prop-wash,
jet-wash or down-wash in the case of a wing. All these involve momentum exchange iaw Newton to produce thrust.

I suppose part of the cognitive problem wjhen talking about 'intake' produced thrust is that it sounds a bit like 'one hand clapping' as one looses clarity of the momentum exchange process which is a prerequisit for thrust generation.

I suppose that the satisfactory explanation one was hoping to get was one that related the deceleration/compression of the incoming flow in the intake to a momentum exchange process that ledi to thrust.

There are of course other propelling forces that do not rely on momentum exchange such as tyre traction which requires friction and the dreaded drag forces produced by viscous friction.

[Brian Abraham]

Mr Optimistic, Kelly Johnson of SR-71 fame described the the power plant as a pump to keep the intake alive (producing the thrust). Take it as a given that 2dude and christian know what they are talking about.

[Mr Optimistic]

Indeed I do.

[Landroger]

Roger I'm so glad that my blurbish explanations are making a little sense, the subject drives me nuts too, and I started doing it thirty six years ago.

I quite like ChristiaanJ's analogy on explaing how an inlet can provide thrust, but the precise shockwave geometry that the Concorde intake required in order to do what it did best, was little more than mind numbing in terms of complexity and control; It is really difficult to imagine if it could ever be bettered aerodynamically, even now.


It is getting clearer all the time, many thanks to you both, but I have to take the math as read. :uhoh: I have my grandfather's grasp of the mechanical (electronics was before his time, but those too :)),but not my late father's self taught grasp of mathematical concepts. They just give me a sensation very closely allied to vertigo. :eek:

Your latest diagram at #39 has, I think, finally wrapped it up about as far as I am going to be able to cope with. :uhoh: In return I could try and explain how MRI scanners work :ugh:, but it would be a long way off piste and is just as much brain damage. :D

What I find so neat - I'm sure it is beautiful if the maths are included - is the way the design team 'conjured' the shock waves. :ok: The edges, dump gates and ramps are sort of obvious, almost simplistic in a sense, but the secret is all in the way these engineering 'magic wands' conjure a series of invisible, yet powerful 'force fields'. Force fields not directly connected to the doors and ramps necessarily, but the whole witches kitchen interacting to produce .... the thrust rabbit out of the intake hat. :ok:

I know engineers are regarded as soul less nerds, but the things they create are truly beautiful. Very few in Britain would disagree that Concorde is a beautiful thing to look at, like the Spitfire and the fan blades on a Trent 900, but how many could understand how beautiful she is on the inside?

There I go, waxing lyrical on a technical forum. :O I'll get my hat. :)

ROger.

PS: Thanks again guys, I just can't stop reading these threads. :)

[Mr Optimistic]

...well, perhaps one of these super light things to some extent but not with the combination of elegance and power.

[ChristiaanJ]

....the cognitive problem when talking about 'intake' produced thrust....You're hitting the nail on the head. It's a cognitive problem.

Nearly all that is taught about jet propulsion (or aircraft propulsion in general) treats the engine, or rather the propulsive system, as a "black box", with mass going in, energy being added by the fuel, and basically the same mass coming out with added momentum.
Yes, in that case Mr Newton has the correct description of what's going on.
F= m x a !
The simplistic thrust formula T = m' x (Vo - Vi) is just another way of stating the same thing.

It's when you start looking in detail of what happens inside that "black box" that the "cognitive problems" start.

You're now suddenly dealing with a far more complex description of how and where the momentum exchange happens.
The basic F= m x a, while globally still perfectly valid, is no longer much use when you try to "get your head around" what exactly happens inside that "black box".

Inside the "black box", thinking in terms of pressure distribution, and in particular the forward components of those pressures, is an easier way of understanding what is going on.

I'm not a "propulsion" engineer, and I'm the first to admit when I first saw "the intake produces 75% of the thrust", that my first reaction was "huh"??? too.

And yes, it did take me more than a moment to work out what I now tried to say just above.

Luckily, the structural design engineers that designed the engine nacelle, and more specifically the intake, knew about this.
Because indeed, at Mach 2, those 75% of the actual propulsive force of the "engine system" was transferred to the wing structure and from there to the rest of the aircraft... by the intakes.
Just as well they were bolted on properly....

CJ

[ChristiaanJ]

It is getting clearer all the time, many thanks to you both, but I have to take the math as read. :uhoh: I have my grandfather's grasp of the mechanical (electronics was before his time, but those too :)),but not my late father's self taught grasp of mathematical concepts. They just give me a sensation very closely allied to vertigo.Roger,
A lot of it is not maths as such, but "getting your head around a concept".
Like supersonic flow, shock waves and all that.
I was lucky, I suppose... I learned all that when I was still a teenager, from somebody doing a few very simple demonstrations in a flow of water over a slightly inclined glass plate lit from below.
The same with electronics... my grandfather was a radio amateur (1920's !!), my father was an electrical engineer. It rubbed off very early on.

....I could try and explain how MRI scanners work...Again, it's not just being an engineer, but being able to explain a concept in clear terms.
BTW, I know how MRI scanners work... after my early retirement I went into writing documentation for medical imaging software....

What I find so neat - I'm sure it is beautiful if the maths are included - is the way the design team 'conjured' the shock waves. :ok: The edges, dump gates and ramps are sort of obvious, almost simplistic in a sense, but the secret is all in the way these engineering 'magic wands' conjure a series of invisible, yet powerful 'force fields'. Force fields not directly connected to the doors and ramps necessarily, but the whole witches kitchen interacting to produce .... the thrust rabbit out of the intake hat. :ok:Thanks, Roger.
It's usually only engineers that will recognise a particularly neat engineering solution as "beautiful".....

I know engineers are regarded as soul less nerds, but the things they create are truly beautiful. Very few in Britain would disagree that Concorde is a beautiful thing to look at, like the Spitfire and the fan blades on a Trent 900, but how many could understand how beautiful she is on the inside?So true... sad, really that so few people can see the beauty in a truly well-done design, apart from rare exceptions such as Concorde or the Spitfire, where beauty of form join beauty of design.

There I go, waxing lyrical on a technical forum. :O I'll get my hat. :)Please put your hat back on the hat-rack.
Because whether technical or not.... we've all been waxing lyrical here, one way or the other.
With Concorde, we did something special.
Apollo took men to the moon.
Concorde took us to the other side of the Atlantic in three-and-a-half hours, and in the end did so for twenty-seven years.
No, it didn't all work out, sure.
Apollo was abandoned, Concorde saw only sixteen aircraft built.
But I think we're all proud of what we DID achieve.

And as to Concorde.... she was beautiful in every way.

CJ

[Shaft109]

The concept (on a very, very basic level) of the Concorde powerplant / intake nozzle combination I keep having is basically squeezing the end of a hosepipe to 'focus' the forces already present.

Would that be close to the truth?

[b377]

I think we can summarise all these muzings by stating that regardless of what component ( nozzle, intake, engine support) communicates the thrust ( force) to the airframe, the bottom line is that the POWER required for flight = drag X air speed comes from INSIDE the engine-core burning fuel.

The "intakes" may be doing the pulling but the energy: every Joule or Watt-sec or Newton-meter for the intake to do that work has to come from the engine fuel burn and there can be no other way unless this thread has successfully falsified Newtonian mechanics.

To say that the intake produces the thrust is not the same as saying that it produces the power, the engine-core does that. But if the engine (balck box) is taken to comprise of all its subcomponents: nozzle, intakes, compressor, turbine, burners etc then the thrust is generated by the 'engine'.

I think the cognitive problem lies here. Thrust on its own means very little if one talks about the power required for flight there can be no doubt that it comes from inside the engine and no where else.

In this case intake_thrust x airspeed= engine_core fuel burn engery x efficiency factor. (ignoring thrust contributions from nozzle etc which also exist of course)

[ChristiaanJ]

b377,
Most of the problems lie in the fact that, when discussing a subject such as this, a lot of terms such as thrust, force, power, momentum, energy, etc. are used very loosely, and as a result the discussion can easily go off on a tangent, if the terms, and their context, are not defined very clearly beforehand.

You're right, the aircraft is finally propelled by the chemical energy in the fuel being released in the engine.

But you have to be careful with the term "power"... as discussed in an earlier thread, for instance: what is "power" for a Concorde?
When it is standing at the start of the runway, with all four engines at full dry thrust, you have about 120 000 lbf thrust, but the power is... zero, because that force isn't moving.

In our current context, nothing stops one from defining the "power" of the intake as the 75% (at Mach 2) of the forward-acting force on the propulsive assembly, multiplied by the speed.
With that definition, 75% of the propulsive power comes from the intake. Nothing wrong with that statement.

The mistake being made is considering the intake as a closed system, and then considering the thrust of the intake as "free power".
This is wrong, of course... nothing would work without lots of fuel being burned each second in that engine right behind the intake, to maintain the airflow, even if the engine itself produces little thrust (8%) in the process.

Maybe we could say, that the "power", in the sense of forward-acting force x speed, is "expressed" (or finally does its "work", if you like) for 75% in the intake.

Its really a matter of semantics, or terminology... saying the intake 'produces' the power is indeed misleading, as you say.

CJ

[ChristiaanJ]

A minor snippet about the SR-71 (also see page 1).

On Concorde at Mach 2, the engine itself provides only about 8% of the total thrust.

On the SR-71 at Mach 3, that percentage is even less.
And in certain flight conditions, the engine itself no longer produces any thrust at all, but some drag.
Result? Instead of the engine 'pulling' the aircraft along, it's now the aircraft that 'drags' the engine along, and yes.... the engine moves rearward in the engine mountings !!

CJ

[b377]

ChristiaanJ (http://www.pprune.org/members/105267-christiaanj)

I fully agree... my simple expression for power says just that.

i.e. at constant forward speed the thrust just compensates for drag and the power required is thrust x air speed = total drag x air speed.
i.e. thrust= drag.

The power lost to the "induced" drag component of total drag goes into putting the air in motion as down-wash from the wing to keep the plane in the air. Parasitic drag heats the air and a/c skin. The latter losses represent all the power the engine has to provide to maintain constant forward speed. But of course the engines also have to provide the power to run electricity generators and supply bleed air etc...that is extra.

75% of the thrust ( not power) requirement to compensate for drag is provided from the intake assembly.

[bjornhall]

Let's make this a tad more complicated still. ;)

From "thrust (force) = drag (force)", does it follow that "power (developed by engine) = power (lost due to drag)"? Or, for that matter, is the opposite implication true?

Hint 1: If we stand right behind the aircraft with its engines on take off power with reheat, can we hear the engines? Is it perhaps also a little windy? If we step close enough, or drive a small car behind the aircraft, would anything noteworthy happen? :E

Hint 2: If we were able to position ourself right behind the engines with the aircraft in cruise (i.e. when thrust force does actually equal drag force), is it likely that the engines would be inaudible and the exhaust would not be felt?

What I am getting at is of course that the engines also do work on other things than the aircraft. Therefore the engine will develop more power than that being lost due to drag, whether induced drag or the other kind.

Edited to add: Great minds think alike... :) And some are 1 minute faster than others... :} ;)

[b377]

what is "power" for a Concorde?
When it is standing at the start of the runway, with all four engines at full dry thrust, you have about 120 000 lbf thrust, but the power is... zero, because that force isn't moving.


absolutely true.

If you push against a wall you do no work on the wall as it does not move, but your muscles are still expending the same engergy - you get tired, muscles heat up, heart works harder to pump against contracted muscles etc.. basically effort wasted.

Concorde with its brakes on and engines running at full tilt at the end of the runway does not gain kinetic energy so it takes no energy from the engines - but the engines still do substantial work if not the same, after all its burning the same amount of fuel, but it all goes into moving fast air as jet blast (jet-wash) noise, heat etc.

[b377]

[the engines also do work on other things than the aircraft

yes that is part of the efficiency figue - heat, noise, bearing friction, and turbulent motion in the jet-wash itself that just increases the entropy of the world.

[M2dude]

Wow this subject has generated one hell of a lot of debate, but intake 'thrust' really became a truly fascinating subject once the SR71 became reality. (Keep the posts coming guys, this is great).
What I've tried to suggest before (in my own confusing way :E) is that the nozzle and inlet components should maybe considered as part of the whole 'engine' if you like, and this rotating bit is where the chemical energy conversion ,lighting of the fires occurs and sucking and blowing occurs.
For a supersonic aircraft, how good your whole 'engine' in this context is relies on solely how well designed the 'front bit', the 'rotating middle bit' and the 'back bit' are, and how they work together. Weakness in any one of these three is gonna cost you performance and/or fuel (and trans-Atlantic range is just not possible; ask Tupolev).
The mistake being made is considering the intake as a closed system, and then considering the thrust of the intake as "free power".
This is wrong, of course... nothing would work without lots of fuel being burned each second in that engine right behind the intake, to maintain the airflow, even if the engine itself produces little thrust (8%) in the process.

Well said ChristiaanJ, I think this is the main 'thrust' of the argument (sorry 'bout the pun :p).
75% of the thrust ( not power) requirement to compensate for drag is provided from the intake assembly.
Not forgetting of course the 12% negative component due to to front ramp loading, giving us 63% net thrust. (numbers are really mind blowing I know).
In all my ramblings I've not even mentioned the incredible complexities of arranging and generating the inlet shock system, and how controlling the intake was as complex as any single system that I personally seen on ANY aircraft, old or new. And all this done with slide rules, protractors and the backs of hundreds of cigarette packets, without any mathematical modelling in sight. (And also some oil lamps and diesel oil, but that's another story).

Dude :O

[bearfoil]

shaft109

Now it can be told. Imagine your hose has a fitting that varies the water spray. It is set on "fan", a wide chord of accelerated water. See It? Now imagine that instead of exiting the nozzle, it is reversed, and entering instead. Each drop makes its way to the inlet and barges in with all its mates. Consider that it (the hose) has a forward velocity, creating a dynamic system. The "Cone" of entering water (air) is larger consistent with the size and setting of the "system". It is not incorrect to say that the entering air creates (potentiates) a very low pressure (energetic) cone for the nozzle, hose and airframe to enter.

Nomenclature is all, unless you have envisioned this new system before, and can enfold it into prior bias of the pilot mind (guilty). For one, the top of the wing lifts the a/c, for another it is the bottom pushing. I hope ChristiaanJ appreciates my hose "chops", I mean it in good humour!

Bear

[ChristiaanJ]

bearfoil,
IF I follow your way of describing things... what you describe is what happens at low speed, when indeed a 'cone' of air is sucked into the inlet.
Once supersonic, to use the popular old-fashioned way of describing it: there no longer is any "warning" for the air ahead of the intake, and the intake neatly slices a squarish "pipe" from the arriving airflow and performs its magic.

bjornhall, b377, et al,
This thread really started off on the problem of getting ones mind around the question on how an intake could actually produce thrust.
We seem to have that sorted out to a large extent.

What happens to the energy actually being liberated by the burning fuel is a slightly different story, and there your reasoning is perfectly right... some ends up being used to power the engine accessories, some ends up as hot air, literally, some ends up as noise :ugh:

At Mach 2, most of it is still used to move the aircraft.

CJ

[ChristiaanJ]

In all my ramblings I've not even mentioned the incredible complexities of arranging and generating the inlet shock system... I think you already did.
....and how controlling the intake was as complex as any single system that I personally seen on ANY aircraft, old or new. And all this done with slide rules, protractors and the backs of hundreds of cigarette packets, without any mathematical modelling in sight.You may have mentioned this already in the other 'Concorde question' thread.
(And also some oil lamps and diesel oil, but that's another story).I suppose you're talking about Casablanca?
Maybe we could add that story here, now that most of us agree an intake can produce thrust?

CJ

[bearfoil]

ChristiaanJ

The only part I left off (arguably) is the part about the size and shape of the cone being relative to setting and configuration of the "system". This means velocity, and at velocities in excess of a specified value, the shape is as you describe. "Down the Rabbit Hole, Alice." I leave this hole at the end of every essay. One must allow the student some room to extrapolate, reason, and experience the "Aha!", No?

Arrogant enough?

Your water sheet on glass, was that in re: Laminar flow?

bear

[ChristiaanJ]

[B]ChristiaanJ
Your water sheet on glass, was that in re: Laminar flow?
No. It was a very simple way of demonstrating subsonic and supersonic flow by way of a 2D analogy of wave effects in a very thin sheet of water running down a more-or-less inclined sheet of glass.
It was so simple I replicated it (as a teenager) in a washbasin....

It is very much like the long-spun-out analogies we tend to use to describe the "sound barrier", and shock waves and the sonic boom, like dropping a stone in a pond, then moving a stick along a water surface at various speeds, then looking at a skiff in a canal, and looking at the waves hitting the bank.

But that simple gadget "showed it all".... even the differences between thin and thick wings by placing different 2D shapes in the stream.

Since then, for me the "sound barrier" was no longer a mystery, even if I didn't learn the maths until much, much later.

Oh, and it also told me, even then, about the difficulities of building transsonic windtunnels....

CJ

[M2dude]

ChritiaanJ
My point was we had not shown just how complex and difficult the Concorde intake aerodynamics were in these posts. I have mentioned NOTHING about the complexities of the generation of the generation of the shock system as I thought it might be a little 'heavy' in the context of this topic, but in defference to you, maybe I will for the benefit of everyone ELSE here:
http://i991.photobucket.com/albums/af32/riconc1/Concorde/ShockComplex.jpg
The above diagram shows a broad view of the intake at Mach 2 cruie. What is not shown here is, if you like, the 'very first' shock; this comes off the wing leading edge, reducing the local Mach number (Mo) to around Mach 1.9 for an inner intake, Mo for the outer intakes is a little lower.
Here are some extracts from The Concorde Air Intake Control System.. You may also want to refer to my previous 'whole powerplant' diagram:
[quote]
Assume Mach 2 supersonic cruise conditions, with the intake operating critically. Underwing local Mach Number is assumed to be Mach 1.9 (a good average for the inboard and outboard intakes). The ramp angle is assumed to be 9.5 degrees (about 45% on the Manual Control Panel's ramp position indicator). As the entry airflow enters the intake it encounters the 1st shock, which at normal Mach Numbers is just forward of the cowl lip. As well as the air experiencing a reduction in velocity, it is turned downwards to follow the profile of the fixed (7 deg') wedge compression surface. The Mach Number at this point has now fallen to approx' Mach 1.65. As the shock is not 'on lip' there is a small amount of airflow lost over the lip known as 'Supersonic Forespill', this generating moderate losses in the way of form drag etc. In fact the losses incurred by this spill drag equates to about a tonne of fuel burnt (or a corresponding reduction in payload), but to allow the intake to cope with aircraft Mach overshoots, without surging this unfortunately is a necessary evil.
As the airflow meets the 2nd and 'Fan' shocks, it is subjected to further turning down, following the forward ramp profile, which produces a 5.75 deg' total turn-down by the bottom of the ramp. (So the air is subjected to the initial 7 degree turn down plus a turn down that depends on the actual ramp angle and a 5.75 deg' turn down imposed by the curve in the ramp profile). The Mach Number after the second shock has fallen to approx' Mach 1.57, and after the final stage of the fan shock to approx' Mach 1.37. Transition of the airflow through the fan shock produces a staccato increase in Ps and reduction in velocity. What is particularly interesting about this process, known as 'isentropic turning', is that there is absolutely NO LOSS in Pt (Total pressure) as a result, making the utilisation of an isentropic fan shock an extremely efficient way of carrying out the compression process. As the downward inclined airflow meets the cowl lip, which itself is inclined upwards at 12 deg's, the 4th shock is formed. Because of the relatively low local Mach Number at this point (M1.37) and the fairly shallow approach angle of the airflow relative to the cowl lip (3.25 deg's, see below), a strong oblique shock is produced. This shock is inclined upwards towards the bleed slot (the gap between the ramps) and this slot has the effect of modifying the shape of this shock into a gentle curve, the upper component of this shock helps force the secondary airflow into the bleed gap. The total airflow turndown at this point now is the initial 'fixed wedge' 7 deg's plus the combined turndown as a result of the 9.5 degree ramp angle, and the 'isentropic turn' of 5.75 degrees]. We therefore at this point experience a total turndown of 7 + (9.5 - 7) + 5.75 = 15.25 degrees]. (As the ramp angle is taken relative to the local horizontal and not the 7 degree wedge, we subtract 'wedge angle' from ramp angle). This airflow then, at an incident angle of 15.25 degrees relative to the horizontal. The approach angle of the airflow onto the cowl lip is therefore 15.25 - 12 = 3.25. (This producing our nice 'strong oblique' shock rather than a normal shock). Our oblique shock has the effect of starting to turn the airflow back into line with the engine, in fact to within about 5 degrees] of the local horizontal.
Now for some real confusion; Although we have produced an oblique shock, as far as the local airflow at the base of this shock is concerned, a small amount of the shock is in fact normal and we therefore end up with a mix of just supersonic air (upper region) and just subsonic air (lower region). In fact, because of the curved nature of the shock, we end up with a progressively varying mix of Mach Numbers in the downstream section. As a result of the coalescing of these supersonic/subsonic airflows, we end up with a few very weak near normal shocks that radiate rearwards from the 4th shock, these shocks collectively being known as ‘the terminal shock’. The terminal shock is about half intake height and stands over the bleed slot and can be considered as a ‘virtual’ single weak normal shock. The downstream airflow is now mixed and finally subsonic, having fallen to about Mach 0.98. ]Beyond the terminal shock, the subsonic (only just) airflow continues its journey to the engine, through the divergent (diffuser) section of the intake. As well as functioning as a conventional subsonic diffuser (as the airflow passes through the duct, it's velocity progressively reduces and it's static pressure simultaneously increases), this section also has the effect of causing the primary flow to turn the final 5[/font]o[FONT='Arial','sans-serif'] back into line with the engine. As far as the primary airflow is concerned it has now come to the end of its journey to the engine face, but before we deal with the secondary airflow, we now have to dispel a little Concorde folklore:
Contrary to popular belief, MN1 engine compressor face Mach Number) has NOTHING directly to do with intake operation as such, being entirely dependent on engine mass flow and compressor face cross sectional area. If the intake goes 'off tune' for any reason, MN1 remains the same, only the losses incurred in the course of producing that Mach Number would increase markedly. Even if the intake ‘wasn’t there’ this Mach Number would still be the same. (There would be a massive normal shock across the face of the compressor and probably barely enough P1 left to produce any real thrust at all). As far as our intake is concerned, at the compressor face and assuming 'design' engine mass flow, the engine airflow MN1, will be at Mach 0.49.
The now subsonic secondary airflow passing over the rear ramp is channelled to the four secondary air doors by some carefully designed cascade ducting. The secondary flow now finally completes its journey by travelling through the engine bay as cooling air and exiting via the gap between the primary nozzle and the secondary nozzle structure. This air is now used to give the rapidly expanding exhaust flow a relatively high pressure cushion and so limit this expansion, reducing 'flaring' of the exhaust efflux and hence the massive potential loss in thrust. Together with the divergent nozzle of the open secondary nozzle buckets, the secondary airflow helps to maximise nozzle thrust
Local sensing of under-wing airflows is not practical, in termes of accuracy and predictability, and so local manometric data was used to accurately synthesise the flow field conditions, and the use of only one internal intake static pressure tapping was required to accurately predict the precise shock system geometry.
So we can see tha there is nothing at all simple about creating this amazing shockwave cocktail, and the control of all this was also something else, and if we go off song even slightly, then reduction in powerplant efficiency and/or surge will result.
In the ideal world, our intake would just operate in a critical manner, but superimposed on this 'performance requirement' are limitations placed on the control pressure ratio, the variable limits for maximum and minimum ramp angles, as well as maximum engine mass-flow demand. All of these variables change with intake local Mach number; the intake acually limiting engine N1 at high Mach number, low temperature conditions. Oh, and changes of aircraft incidence have also to be instantly compensated for, particularly at very low Alpha. Incidence will both alter the capture airflow AND affect intake local Mach number.
I hope that MOST people here find the above descriptions useful and interesting; to me it is one mind-blowing subject.
The 'oil lamps and diesel oil' story in a future post, and no ChristiaanJ, it's not just about Casablanca, perhaps you will allow me to explain ?

Dude :O

[john_tullamarine]

It was a very simple way of demonstrating subsonic and supersonic flow by way of a 2D analogy of wave effects in a very thin sheet of water running down a more-or-less inclined sheet of glass.

Another useful water analogy is the hydraulic jump.

Use the tap/faucet in your kitchen sink to impact a jet of water onto the smooth, horizontal sink surface. The water jet radiates as a thin film of water until it enters the hydraulic jump region. Here, there is a flow discontinuity with the ring of the jump being analogous to a normal shock wave in a compressible gas. Plenty of pictures on the net of jumps.

Main generic things to keep in mind with intake flow -

(a) a normal (perpendicular to the flow direction) shock wave is bad news for flow parameters with lots of losses and so forth

(b) you have a normal shock as you transition through the transonic region whether you like it or not

(c) the trick is to use a series of oblique shocks ahead of the normal shock to step the flow changes progressively so that the abrupt changes across the final normal shock are reasonably minimised. This is the artform inherent in intake design and geometry.

(d) while doing the bits in (c), the designer can pick up lots of useful pressure distributions on the tinwork which is what the intake thrust discussions are all about.

[M2dude]

Loved your analogy John, and agree 100% with your far more elequent than my 'shockwave summations'. (As you say, you get the normal shock whether you like it or not).
But you sir are in trouble with my wife; I was just demonstrating your water analogy (basically showing off again) and ended up soaking her, and drowwned the kitchen floor. :O:uhoh::O

Dude :O

[john_tullamarine]

ended up soaking her, and drowwned the kitchen floor.

Oh dear ...

.. however, as with the majority of good men of long married character and self preservation knowledge, I'm sure that you grovelled in the approved manner, wiped up the mess ... and the universe returned to normality ...

[Pugilistic Animus]

I hope that MOST people here find the above descriptions useful and interesting; to me it is one mind-blowing subject.

Beautiful--the Concorde threads are Beautiful:{...and it illustrates that the Great Art of Aerodynmics is Experimental:ok: a little twist here a little waxing and polishing,..., a little area cut away from there...and it---- Still Flies :D:D:D

[M2dude]

John tullamarine
. however, as with the majority of good men of long married character and self preservation knowledge, I'm sure that you grovelled in the approved manner, wiped up the mess ... and the universe returned to normality ...
Oh yes, I found that although only relatively recently married, the art of being humble still prevails. :)
Pugilistic Animus
Thanks very for your comments Pugilistic, in my personal opinion the air intake design is one of the most fascinating parts of the whole Concorde tapestry.

If I may, I would now like to mention the 'some oil lamps and diesel oil' story. This is a true story told to me by Dr Ted Talbot, the father of the Concorde Intake, brilliant aerodynamicist and all round amazing gentleman. Ted had been invited in 1975 to speak to the US test pilots at Edwards Air Force Base in California, and after he landed he was invited to take a tour through one of the top secret hangars there, and in this hangar were a few glistening Mach 2.5 design B1A development aircraft. Now Ted had heard that Rockwell were having major difficulties with the engine intakes, and obviously had more than a passing interest in such things, and was allowed to take a close look. Just above and slightly forward of each intake he observed several beautiful made precision total pressure probes mounted under the wings, and although he had a good idea what they were for, said nothing at the time.
That evening, Ted gives his presentation speech to the assembled Test pilots, explaining in fair detail how the Concorde engine intake operated, and that the fact that unlike most other supersonic designs, the engine power was more or less freely variable at Mach 2 and above, even to the extent that if necessary the throttle could be closed all the way to the idle stop. There allegedly many gasps of amazement and disbelief in the room at this, and one B1A pilot was heard to ask his boss 'why the hell can't WE do that John'?. (It should be borne in mind here that the 'traditional' way of slowing down Mach 2+ aircraft is not to touch the throttles initially, and just cut the afterburners. If you don't do it this way many designs will drive into unstart and even flame-out).
After the audience had asked Ted several questions about Concorde, Ted was then invited to ask the assembled USAF and Grumman personnel about the B1A programme, which would be honestly answered within the confines of security considerations. Ted said that he only had one real point to raise; 'I see that you are having major difficulties with wing boundary level interference at the engine inlets'. There was now a gasp of horror from various members of the USAF entourage, 'That's top secret, how the hell do you know that?'. Ted chortled 'it's easy, I saw that you have a multitude of precision pressure sensors under the wing forward of the intakes, that I assume are to measure the wing boundary flows'. Ted then unhelpfully comes up with 'Oh, and you've got the design completely wrong, your intakes are mounted sideways, and that allows the intake shocks to rip into the wing boundary layer, which will completely screw up your inlets at high supersonic speeds. That in my opinion is where most of your problems lie, with wing boundary level interference, but I think that your probes for measuring boundary layer are beautiful, we never had such things'. According to Ted there was not so much uproar at the meeting as much as horror and amazement that this (even then) quite senior in years British aerodynamicist had in a few seconds observed the fundamental design flaw in an otherwise superb but top secret aircraft, and could even see what they were trying to do about it. Ted was asked, 'so you had no boundary layer issues with Concorde then?' Oh we had a few, mainly with the diverter section mounted above the intake' replies Ted, 'but we sorted out the problems relatively easily. 'You said that you did not use precision pressure probes under the wing to measure boundary layer flow fields, so what DID you use then?', asks a Rockwell designer. 'Some oil lamps and diesel oil' replies Ted. The room is now filled with laughter from all those assembled, but Ted shouts 'I am serious, it's an old wind tunnel trick. You mix up diesel oil with lamp black, which you then paint over the wing surface forward of the intakes, where it forms a really thick 'goo', which sticks like glue to the wing'. The pilots in particular seem quite fascinated now, and Ted goes on; 'You fly in as cold air that you can find (we flew out of Tangiers and Casablanca) and flew as fast as you could. As the skin temperature increases with Mach number, the diesel and lamp black 'paint goo' becomes quite fluid, and start to follow the boundary layer flow field. You then decelerated as rapidly as possible, and the flow field 'picture; is frozen into the now again solid 'goo'. After we landed we just took lots of pictures, repeated the process for several flights until we know everything that we needed to know about our difficulties. After doing some redesign work we then repeated the exercise again several times, eventually proving that we'd got things right'. The audience asked Ted if this technique might help them with the B1A, but he replied that although it might help them with accurately illustrating the problem, in his opinion it was irelevant, 'because the intakes are the wrong way round'.
The B1A intake problems were never resolved, and in 1977 the project was cancelled, due to performance and cost issues. However the project was reborn as the B1B, not entering service until 1986. Although an amazing aircraft, with astonishing low altitude performance and capability, it is a fixed intake design, limited to Mach 1.6 at altitude. Ted was right it seems.

Dude :O

[M2dude]

Hi Ventus45
There was no real 'magic' as far as the intake mounting to the wing goes. There were just four heavy duty attachments as well as a sliding transition ring between the intake and engine compressor case. The attachment links on the intake itself were also allowed to move fore and aft a little The two rearmost attachment points ran along the centre line of the intake assembly and were totally enclosed within a large arrow shaped diverter, the large seal of which butted up against the wing lower surface.

Dude :O

[Pugilistic Animus]

I don't even have further comments that story is unbeatable---boundary layer mapping with lampblack and diesel fuel vs high tech probes...there must be a million How many aerodynamiacists does it take to----jokes for that one :ok::D
M2dude
Thanks for relaying that anecdote---LOL :}:}:}

[bearfoil]

The SR-71 was developed in 1959-60. Cocktail napkins and slide rules. Johnson drank Scotch and water, the Concorde is more than beautiful, she is a totem of genius.

She also blazed trails the Blackbird never had to face, but credit where credit is due.

Mr. Pratt, Mr. Whitney, Ampersand.

M2dude that story is priceless, I envy your experience with CONCORDE

bear

[Machaca]

Viscous fluids are an excellent method for visualising flow and boundary layers, no matter the budget:

http://i337.photobucket.com/albums/n385/motidog/ViscousFluidFlowTest.jpg

[M2dude]

bearfoil
She also blazed trails the Blackbird never had to face, but credit where credit is due.
Absolutely credit where it is due. The YF12/SR71 was without doubt Kelly Johnson's finest creation. (I'll let you into a secret, it was the SR71 inlet that first got me 'hooked' into the world of shockwave management).
As I said in a previous post, you will find nothing but respect in the family of Concorde for the SR71.

Dude :O

[ChristiaanJ]

As I said in a previous post, you will find nothing but respect in the family of Concorde for the SR71.And vice-versa....
At the 1974 Farnborough airshow, the crew of the SR-71 that had just done a record New York-to-London flight, was treated to a flight in Concorde.

Since they could hardly "pay back in kind", they reciprocated by treating us all at Fairford to our own "private airshow".

I've never forgotten that.... seeing that alien shape in the sky, that already had been flying routinely at Mach 3+ before Concorde first flew.

CJ

[M2dude]

I remember it well CJ; I seem to remember that the guys flew in pre-production aircraft 101 (G-AXDN), and were full of praise about Concorde and the fact that they flew for the first time at 60,000' WITHOUT a pressure suit. (And in the case of SR71 crews this was more akin to a full blown spacesuit).

Dude :O

[Pugilistic Animus]

at about 63000'-the blood boils :\

[M2dude]

OMG I regularly went up to 63,000' on test flights, without too much blood bubbling I'm pleased to report. The physiological effects of altitude was well known to most of us, and dictated just about everything about the design philosphy for the environmental systems on Concorde.
These test flight excursions at 63,000 were when we used to check the intake surge margins by doing a near zero G pushover at Mach 2 from a zoom climb. (Which I mentioned in another Concorde thread). At the top of the 'bunt' the throttles would be pulled back, to prevent overspeeding; at the point of zero alpha the local Mach number at the intake face would be far higher than any other time, as well as wing flow distortion would also be at maximum, so hence the surge margin check. With all this going on you really did ask yourself if this was really an airliner. :D

Dude :O

[Flight_Idle]

This thread reminds me of when I was a young airman (Airframes) & I asked some engine guys "Where does the thrust act in a jet engine". They can't have been very bright because they just told me the 'Change of momentum' business.

I then got hold of a flying AP & it had a diagram of the forward & rearward gas loads in a RR Avon engine (With & without reheat) that cleared things up for me.

It would be interesting to see all the forward & rearward gas loads in the Concorde intakes, engines, nozzles ect, after all, something is 'Pushing' somewhere, it just needs to be split down into sections to see where.

I can understand manufacturers having commercial secrets, maybe that's why they don't publish this information on the internet, but it all boils down to simple forward & rearward gas loads somehere in the works.

[Pugilistic Animus]

M2dude it's just an honor to hear you write about this subject man...:ok:


You were pressurized though?:\

[rjtjrt]

I have often wondered about depressurisation in Concorde.
Above 40,000ft involves pressure breathing if no pressure suit.
Was there a provision for flight deck crew to pressure breath in event of explosive decompression?
It was speculated in my av med course that Concorde was designed in a way that "explosive" decompression was not taken into account but we had no real idea or information.
John

[AC Busted]

Regarding the decompression risk, was that the main reason Concorde had small windows?

[lomapaseo]

The Concorde laid the ground work for the scientific basis of some of our airworthiness assessments today.

To say it another way, since the airplane was so different in its enviroment, some extra thought went into how to make it safe.

Today when we look at supersonci high altitude flight, we also have to look at potential decompressions and how to get the plane down quick enough to save the passengers. No real harm in a few healthy passengers passing out, but we would like them to wake up for the landing. Thus the size of the hole that lets the air out has to be considered vs the probability of the hole being made.

So a consideration is made of uncontained engine failures as well as a window out, etc. Because of this a limitation had to be placed on the size of the engines in diameter, simply due to the size of an engine disk being ejected.

I suppose that other what ifs could enter into this but they would all be veted by the historical probability of them occurring.

That of course brings one back to the arguments was the Concorde really safe enough?

In my view it was considered a leader in safety for its design period, not withstanding a couple of surprises to us in its service life. It simply had less surprises.

[ChristiaanJ]

Decompression is already discussed in the other Concorde thread.

Have a look here :
Concorde question, post #68 (http://www.pprune.org/tech-log/423988-concorde-question-4.html#post5885694)
and the few posts before and after that.

And yes, decompression was definitely taken into account!

The critical case was considered to be the loss of a cabin window with only three of the four air conditioning / pressurisation packs operating.
With a near-immediate emergency descent, cabin altitude would have reached 40,000 ft for about two minutes, which is survivable with pure oxygen without pressure breathing.

I wasn't personally involved, but obviously tests were performed to measure the air loss with the appropriate pressure differential.
And yes, that's why the windows are so small. They are slightly bigger on the prototypes, either because the tests hadn't been done before the construction of the prototypes started, or because the certification requirements were narrowed afterwards.

I don't know about the uncontained engine failure case (never happened either), but I suspect it was considered the resulting shrapnel would have resulted in several smaller holes, with a total area not bigger than that of a cabin window.

lomapaseo is right, in that many of the existing certification and airworthiness requirements for subsonic aircraft were either inapplicable or inadequate, and in the end a huge document, the TSS (Transport SuperSonique) Standards was written specially for Concorde.

CJ

[EXWOK]

RJTRT -

Yes, the flight crew had pressure breathing apparatus.

I believe the EROS masks we're all so familiar with were developed for Concorde??? Anyway - that's what we had, with the addition of a couple of supplementary 'pull' straps to ensure the mask remained firmly attached in pressure-breathing mode. The system was automatic - if the pressure altitude was above 42000' you were px breathing, below that you weren't.

Every other year we'd go on a rig during SEP to practice it, and it was really not that big a deal. A bit odd and a bit harder to speak but no issues.

There would have to have been a pretty serious event to the cabin to >42000', mind.

As for uncontained failures, don't forget the Olympus' were in pretty substantial housings - I know of one fairly severe fire which burned for a few minutes, resulting in huge damage inside the nacelle but none out of it.

Wasn't 202's divider robbed to go on AB after the latter had a fairly big failure of an engine? Again - no question of airfram damage outside the cowlings.

In this respect I reckon the Conc was more robust than many conventional designs.

[M2dude]

When intakes go wrong
We've talked quite a bit here about surges and such, so I thought it might be useful to look at what was involved with Concorde 'when things went wrong', in that direction as well as a few other intake horror stories.
The variable air intake control system on any supersonic aircraft is fraught with pitfalls, and downright dangers, the main areas of concern are those of surge and unstart.
A surge, resulting from the breakdown of stable compressor flow, can occur in just about any type of gas turbine engine, however with a supersonic aircraft the effect are really dramatic; The typical characteristics can be really quite disturbing. We get a loss of thrust, an increase in turbine entry temperature and most alarmingly of all a short sharp inlet overpressure, followed by a fairly small longer duration under-pressure. The problem is with any such surge is that unless the cause of that surge is corrected, then the whole process can repeat again and again.
Unstart is far more serious than a simple surge; the inlet shock system is expelled forward of the inlet, with severe 'surge like' effects. Unless changes are made to the intake geometry itself AND ALSO engine demand is reduced, the inlet and engine will not recover and very severe cyclic yawing forces will continue to act on the airframe.
In the case of a Mach 2 surge on Concorde, the most commonly occurring event would be due to a control system malfunction. (The malfunction itself could be an intake ramp going slightly off schedule, a mis-matched engine N1 and N2 at a given temperature or even wing-induced flow distortions. Above Mach 1.6, a surging engine would always cause it's neighbour to surge also. The dynamics of all this, 'a typical surge' are as follows (again quoting from 'The Concorde AICS':
An engine surge is the result of a breakdown of stable airflow in the L/P or H/P compressor sections of an engine. Intake induced surges are exclusively L/P in nature and are brought about by excessive airflow distortions/induced turbulence that can be caused by a number of reasons. A surge will usually result in a sudden sharp rise in EGT, a brief dip in N1 and an almost total collapse of P7 (LP turbine exit total pressure). More dramatically some quite severe over-pressure pulses are generated, that travel forward, into and out of the front of the intake. (During Mach 2+ intake development flying, if an engine surged when the aircraft was operating in darkened conditions, balls of flame could be seen from the flight-deck that were actually OVERTAKING the aircraft at a colossal speed!!). A single surge is relatively short in duration, only about 200 m/sec' or so but can place both the engine and the intake structure under severe trauma. During a typical surge, there is an initial over-pressure of around 50 m/sec' duration that peaks at approx' 10 PSIG, being followed by an under-pressure of about 150 m/sec' duration, peaking at about -2 PSIG. After this point the engine will either recover or the surging will repeat, surges often do tend to be oscillatory in nature and typically repeat at about 8-10 Hz. When you consider the relatively high cross-sectional area of the ramp surfaces, it can be appreciated that very severe peak loads are induced into the whole ramp mechanism from these over-pressures. In the case of oscillatory surging, the effects are even more serious. (The ramps in this case being 'hammered' with severe oscillatory air loads that result in 'organ reed' vibrations of the ramps, at very high peak structural loads).
The surge drill used by Concorde crews involved reducing power on the affected engines, until the surging stopped, and when the power was re-applied this was done quite gingerly. (I will leave it to the guys to tell you all how not easy this wa, but the thing was that this well rehearsed drill did in fact work well, and normal service was normally resumed afterwards.
As far as unstart went on Concorde, well I#m pleased to say that there was no such thing :). The intake was designed from the outset to completely self-starting, and so unstarts were fortunately completely unheard of.
I'll continue the surging saga and things that went bang in the night in my next post.

Oh, and ps:
EXWOK
Wasn't 202's divider robbed to go on AB after the latter had a fairly big failure of an engine? Again - no question of airfram damage outside the cowlings. In this respect I reckon the Conc was more robust than many conventional designs.
It was OAF, and you are quite right. (OAF's damaged titanium centre wall was removed, 202's was first modified to airline standard and fitted to OAF, the centre wall from the retired French pre-production aircraft 102 was fitted to 202 (to enable the aircraft to remain airworthy) and finally the damaged OAF centre wall fas fitted to 102 in the museum SO THAT THE ENGINE DOORS COULD AGAIN BE CLOSED. (A neat game of musical centre walls). I may have repeated in another thread that when this event happened (as the result of a first stage LP compressor blade loss in 1982 that an FAA inspector was quoted as saying the no other commercial aircraft could have survived the same titanium fire that OAF did.
EXWOK, as far as your statements regarding the safety of our aircraft go, I'm with you 1000%.



Dude :O

[bearfoil]

M2dude

I know this is the CONCORDE thread, and Blackbird was a twin that operated at 3+, so I'll not stay long, but only share what her pilots have shared with me.

Bird burns a one-off fuel, I think J-8. It will not light on start up without a hypergolic chemical reaction with injected ethyl Borate. I am unfamiliar with airstart, but believe it to be impossible following an unstart. If one engine unstarts, the Yaw is nearly 90 degrees, and instantaneous. Rather than wanting to be in dense air, the only hope is to be at thin air, and hope the a/c does not tumble. I have heard estimates that after unstart, the event is 50% fatal. There is a "club" where one's trophy is the helmet, worn at loss of sym thrust. The helmet strikes the side glass and folds in two. I think it is the "crease club".

Her pilots, (there are but two seats) are well trained for all possibilities, and have an edge over CONCORDE in that they have weighed the odds. The commercial ship is engineered to closer risk taking, and her limits also dance at the "edge".

One last SR-71's Size. Don't get the impression she is dainty, she has the shadow of a 727 classic. The Blackbird may have wider limits, but the Concorde put money in the Bank. The Blackbird "stole" two or three Banks per mission.

[NW1]

I was always impressed with the groundschool's instructors comment that the a/c could maintain (*maintain*!) a cabin altitude of 15,000' with the a/c at FL600 and 2 windows blown out (all 4 airgroups working). Would've been a bit breezy I should imagine.

[ChristiaanJ]

I was always impressed with the groundschool's instructors comment that the a/c could maintain (*maintain*!) a cabin altitude of 15,000' with the a/c at FL600 and 2 windows blown out (all 4 airgroups working).NW1,
It's not impossible that your instructors were wrong....

http://img.photobucket.com/albums/v324/ChristiaanJ/Decompression.gif

This graph is from Chris Orlebar's book "The Concorde Story" (redrawn by me, because the original was too pale to scan properly).

It tells a very different story... after a window blowout you very quickly started an emergency descent, and in the worst case (only 3 airgroups working), the cabin altitude would still peak at about 40,000 ft for about 2 minutes.

I think we'll have to look at our flying manuals to setlle the question!

CJ

[NW1]

Christiaan - possibly. But even Chris's book's (4-groups working) graph shows the cabin peaking only at just above F220: and that's with the engines at idle with the resultant low bleed pressures. At full dry power, FL600, I could believe the manufacturer's claims on this one. It doesn't really matter - the point is they designed the aircraft not to be exposed to rapid depress to FL600 as that wouldn't be survivable - the small windows and over-engineered air groups meant that the only way the cabin would "pop" to zero diff at ceiling would be following a structural failure the like of which would make what happened next moot...

[M2dude]

bearfoil
Thanks for you interesting post regarding the 'HABU', just like Concorde the SR-71 deserves and has it's own truly unique place in the realms of aviation history. (It really IS my second favourite aircraft of all time). We were always told that the 'I survived an unstart' club was called the Split Helmet Club; any S-R71 guys around can maybe clear this one up. I think that you will find that the fuel was JP-7; your points regarding igniting the stuff are I think correct, at least that's what I read.
The first really good look that I got of an SR-71 was at the Smithsonian hanger at IAD, before it was opened to the general public, and I have to admit that I was surprised what a big beasty she is. (But an absolutely awesome one too).
Please feel free to chip in here anything that you'd like to about the SR-71, I'm sure readers of this particular thread will find it as fascinating as I do.

Dude :O

[M2dude]

NW1
It always amazed me just how 'tight' the airframe was in this regard. I remember that during construcion we used to do a pressure sustained leak check at 15 PSIG!!! (No one on board of course). She was totally amazing structurally , and if you were lucky enough to do any C of A renewal test flights you'll remember just how long that cabin altitude could be maintained at a fairly comfortable level with ALL air groups (packs to the rest of the world) shut down.
For pressure control, instead of using the 'traditional' motorised Boeing type outflow valve, she used four (I know, we only used two at a time) wonderfully designed pneumatically operated Normalair Garret (now part of the American Honeywell Group) discharge valves. These were not only lighter and far more elegant than the 'modern' units, they were INFINATELY more reliable than the units fitted to the 744 and 777. (As a 777 driver I'm sure you agree). But the real beauty with these things is in the deatail; for example if for some God-forsaken and unknown reason the entire 'guts' of the valve blew out at 60,000', the cabin altitude would be limited to no more than 15,000', due to the design of the frame of the outlet nozzle. (The flow of air through the divergent nozzle section produced. yes you've guessed it, a normal SHOCKWAVE across the divergent neck, choking down the flow).
Yes, they really DID think of everything with our wonderful aeroplane.

Dude :O

[ChristiaanJ]

Re the SR-71 JP-7 fuel I cheated, and copied Wikipedia, but it explains an issue mentioned earlier about relights.

"When the engines of the aircraft were started, puffs of triethylborane (TEB), which ignites on contact with air, were injected into the engines to produce temperatures high enough to ignite the JP-7 initially. The TEB produced a characteristic puff of greenish flame that could often be seen as the engines were ignited. TEB was also used to ignite the afterburners. The aircraft had only 20 fluid ounces (600 ml) of TEB on board for each engine, enough for at least 16 injections (a counter advised the pilot of the number of TEB injections remaining), but this was more than enough for the requirements of any missions it was likely to carry out."

One last SR-71's Size. Don't get the impression she is dainty, she has the shadow of a 727 classic.She's 107.5 feet long, just over half a Concorde....
But yes, dainty she isn't.
And for my UK friends (or rather the few who may not know this yet), the only SR-71 in a museum outside the US is at Duxford in the American Air Museum.
And very much worth a visit.

CJ

[M2dude]

There were many concerns regarding the design integrity of the system, where performance and stability had to be both predictable and safe. The designers at British Aerospace (and to an extent Rolls Royce also) had hundreds and HUNDREDS of flight test hours ahead of them; remembering also that a digital control system had to be 'invented' and flight testing begun in less than two and a half years; the original analog system being totally discarded as far as development went.
The biggest worry for the intake design team was however the STRUCURAL integrity of the intake itself, in the event of engine surging, and this was a worry that was well justified by events. In 1971, the French prototype 001 was undergoing tests when on cancelling reheat (At Mach 1.9, not 1.7 as was the eventual 'norm') the associated engine suffered an N1 overspeed and surged, along with it's neighbour. (001 like it's British sister 002 used the original Ultra Electronics constructed analog intake control system; the digital system being still two years away from taking to the air). Unfortunately in the case of this surge, the intake design was found to be seriously under engineered and the surge over-pressure spike caused the failure of the entire forward ramp attachment assembly. A large section of the forward ramp was blown forward and over the top of the wing (we are doing Mach 1.9 remember) and pieces of the rear ramp were swallowed by the engine, which was already in deep surge. The engine was seriously damaged and flamed out, but miraculously was re-lit at Mach 1.5, of course only to surge again, and was then shut down manually.
After the above event the structure was substantially improved mechanically, in order to prevent any such surges causing failures within the linkages and hinges. The biggest surge fear was always the over-fuelling surge which produced the highest overpressures of all, and it was always a concern that the structure could suffer terribly from such an event. Although the electronic engine control system was carefully designed to avoid such a thing, in normal airline operation it was hoped that this would never happen; IT DID!!:
In early 1977 a Concorde (NOT British Airways) was flying at Mach 2 when the crew noticed a mismatch on engine parameters; the fuel flow of one of the engines was depressed compared to the other three. Unfortunately it was decided instead of following normal procedures that a little 'experimentation' would be tried, and the F/E pulled the N1 overspeed protection system circuit breaker. There was a loud bang, and the aircraft was buffeted by some quite severe yawing forces, the autostabilisation system working flat out to prevent violent yawing of the aircraft. The engine was subsequently shut down as a precautionary measure and luckily the aircraft landed safely. Although there was a little damage to the frame of the intake, generally the structure had stood up well to a very serious event brought about quite honestly by abject stupidity. (There was a malfunction of the overspeed system, causing the system's own 'butterfly’ valve' to partially close off from it's normal wide open position in order to limit the fuel flow. In response the 'normal' engine control system's butterfly progressively opened to attempt to keep N2 on schedule. The overall effect was a wide open normal fuel valve and the overspeed one, in 'series' with the other guy partially closed off. When the F/E tripped the C/B the overspeed valve, that for obvious reasons was not rate limited in any way, to fly back to it's normal wide open position in about 150 milliseconds. So we have two valves, and both of them are wide open, and before the 'normal' valve has a chance to react, MAXIMUM fuel flow is fed to the engine, hence the violent surge.
There was another violent event that was in many ways far more serious: In late 1977 another NOT BA aircraft was undergoing maintenance at CDG, and part of this maintenance input was to replace an intake hydraulic actuator. Now this rather substantial unit lived high in the roof of the intake, just above the forward ramp and drove two screw jacks, winding in and out at ether side. The two screw jacks were coupled to the twin torque tubes (that rotated and subsequently moved the ramps up and down) with a pair of trunnion blocks, these being secured to the screw jacks with a large nut and bolt. The trunnion blocks were very substantial, being designed to absorb any shock loads that an engine surge could provide. Unfortunately the engineers in Paris forgot to fit, yes THEY LEFT OUT the two trunnion blocks, and the only thing attaching the two torque tubed to the actuator were the nut and bolt. (In this condition the thing would have rattled around like crazy, it's a 'surprise' that no one spotted it. (Or even not to mention followed the maintenance manual). The aircraft departed from CDG for JFK, and miraculously attained Mach 2 cruise without incident, that is until there was a system defect on the adjacent intake; this defect was a failure of the servo valve that operated the spill door that was located in the floor of the intake. (There were several servo valve failures in the early years of operation until modifications remedied the problem). The spill door would normally only ever open at top of descent when the throttles were reduced for decelleration, or in the event of an engine shutting down. Now the control system had quite adequate and sophisticated protection for such an falure event, and, due to the same spill door servo being mechanically common to both control channels, (but with independent control windings) froze the intake as both channels failed, preventing any further movement of the surfaces. I seem to remember that the crew drills just allowed a single reset attempt; every time you did a reset, all failure were over-ridden for just over 100 milliseconds, to give the system a chance to get online. While this time delay is in effect, the door was allowed to drive open, before the protection system freezing things up again. Unfortunately, the F/E performed a completely unauthorised rapid series of multiple resets, ech time the door travelling downwards, each time pushing the terminal shock system further aft in the intake, until the inevitable happened and the engine surged. Quite naturally this induced a 'sympathy' surge into it's neighbour intake, the one with the trunnion blocks missing. The surge loads hit the ramps, and without the two vital trunnion blocks in place, the two attachment bolts (which were never designed to absorb such punishment) sheared. The two ramps then freely fell downwards, the front ramp hitting the floor of the intake violently, shattering the honeycomb structure as well as seriously damaging the intake lower lip. Pieces of intake went straight into the compressor, taking out the engine and it's associated temperature probe. (Which unfortunately at the time was being used by the adjacent engine). Fortunately the aircraft, although with serious intake damage, was close enough to JFK to make an emergency descent, and land safely. The intake itself was so badly damaged that is had to be returned to Filton for repair. (Where all Concorde intakes for both countries were built on a separate production line, and fortunately in this case that line was still making intakes). It was highly fortunate that the intakes were still being constructed in late 1977; the wrecked assembly spent several weeks back in the assembly jigs. But things could have been far worse; it was lucky in this event that this pattern of poor maintenance and airmanship did not cause more serious damage.
The intake things that went bang in the night story IS TO BE CONTINUED

Dude :O

[M2dude]

BA themselves had a serious incident, but unlike the OTHER airline this was not as a result of pathetically poor maintenance or airmanship, but of a strange defect coupled with a design anomaly. In the early 1990’s the ramp actuator brake assembly of #2 intake of G-BOAD detached in flight and travelled rearwards, seriously damaging the engine itself, which of course had to be shut down. This defect had never happened before and was attributed to a random failure, until three weeks later the same thing happened again. The aircraft was of course grounded until a fix was found (we could not even find out why this happened). It was known that a feature of the system called ‘HOLD’ would freeze the intake for a brief period (400 milliseconds) in the case of certain failures, inhibiting failure indications and control lane switching at the same time and it was postulated that maybe here maybe lay a clue. (just a theory at this point). Although no static failures could be detected (using specific electronic test equipment) we tried it during an engine run, and found that with a little vibration there was a high frequency repetitive failure of the spill door position resolver, which was replaced. The subsequent engine run proved good, with no further failure indications, and a test flight carried out with the same test equipment fitted, again with without any further failure indications. (It was a great flight too, just me, the three crew and my very large yellow test box at the rear of the aircraft). The aircraft was now allowed safely back into service, and when the offending spill door resolver pack was inspected in the overhaul workshop, a dry soldered joint was confirmed. Analysis showed that the failures were at just the right frequency to allow the ramp actuator brake to be applied, but after the HOLD time delay period expired the failure had cleared, and so the brake was released again, with no other indications, but a fraction of a second later the process would repeat itself. It was estimated that in the three week period between failures over a quarter of a million brake applications had been made, eventually the attachment bolts of the brake assembly failed as a result of metal fatigue. It was a horrible coincidence that this one little soldered joint could fail at just the right frequency to cause such mayhem; eventually stronger bolts were fitted to all aircraft and regular bolt replacements were routinely implemented.
During the first couple of years of Concorde airline operation there was a serious structural issue regarding the intake assemblies. Serious cracking was discovered at the ramp hinge area, and the cause was found to be an aerodynamic resonance issue in the Mach 1.4 to 1.8 flight regime. A short term fix was to strengthen the structure, coupled with a change to the control laws in this speed band. (The change to the intake software did have a performance penalty however). The long term fix was a profiled rear ramp leading edge, and more software changes coupled with a performance enhancing modification to fit a lower, thinned bottom lip to the intake.
The intake was nothing more than an aerodynamic balancing act, where you not only knew and controlled the position of the terminal shock system to within fractions of an inch you also hat to ensure that maintaining critical operation (the normal shock being at the narrowest part of the intake convergent/divergent duct) did not compromise other factors such as ramp angle and control schedule limits variable limits that could result in flow distortion and surge. The system always controlled everything to give you maximum performance, but would move slightly away from this point when necessary to preserve engine flow stability and safety; as was said before, a surge was always the result of something going slightly off 'tune' and was never just ‘one of those things’.
To find the root cause of a surge required a fair bit of forensic analysis; unlike AF, BA had a superb Plessey PVs1580 digital flight data acquisition and recorder (AIDS) system that monitored all the intake parameters; this enabled us to find the cause most of the time, by reading data from the Quick Access Recorder after the flight. (A fair bit of Midnight oil burned though; I still have bags under my eyes ). I remember that originally the singular most important parameter, inlet void pressure, was only sampled once every four seconds by the AIDS system, but once we showed that this was like an ETERNITY when you were trying to track down an engine 'hiccup', we got the sampling rate increased to once per second. Although even this was not ideal, it generally did prove to be sufficient for us.
One small drawback of the thinned and lowered bottom lip was a susceptibility to small pop surges at top of descent, when the throttles were retarded. You just had to be a little careful, and I seem to recall that the initial 'throttle back' minimum limit was 18 degrees throttle angle; zero being max throttle. These surges were very mild and did no damage, but as with all surges post flight engine and intake inspections were required, (no problems werer ever found) together with the usual forensic investigations, ‘just in case’.

Dude :O

[Feathers McGraw]

Just found this thread after a pointer in another Conc thread.

In all the 40 years I've been reading about Concorde, I've never found any of this sort of information before.

Seriously this all needs to be copied over to one of the specialist Concorde sites and tidied up for permanent display. It's a complete treasure trove and it needs preserving.

Amazing information about the SR-71 too, I've been a 'Sled' fan for a very long time too....

[M2dude]

Thanks Feathers, glad you enjoyed the thread. The 'black art' of Concorde always was a fascinating subject. I always found ithe idea numbing that this more or less 'set it and forget it' system could achieve so much and contribute so much to the performance of Concorde. Never in the world both before or since could a variable intake give such a large amount of stability and efficiency, time after time. A tribute to the twelve British and two French designers; well done lads and lass. (The two Aerospatiale guys were responsible for the intake/wing aerodynamic interface, true masters of their craft).

Dude :O

[Feathers McGraw]

I suppose that with the exception of the the SR-71 engine installation, no other aircraft had need of an intake control system that maintained performance in such a tight set of constraints. But yes, truly an impressive piece of engineering and all done with a tiny fraction of the computing power available to the modern designer.

[Mr Optimistic]

Magnificent stuff. Thanks.

[ChristiaanJ]

I suppose that with the exception of the the SR-71 engine installation, no other aircraft had need of an intake control system that maintained performance in such a tight set of constraints.Yes and no.
Yes, in the sense that just about any aircraft going up to Mach 2 and beyond needs some type of variable intake system.
No, in the sense that most of them have a far less sophisticated intake control system than Concorde or SR-71, with only Mach number and throttle setting as inputs.

The Tornado was originally designed for Mach 2+ and used variable intakes. Legend had it that the Tornado AICS had a family relation with the system on Concorde, but since it was developped by a German firm (Nord Micro), that's unlikely.
Also, most of the later Tornados were limited to Mach 1.3, so the AICS and the ramp actuators were removed.

CJ

[barit1]

Ditto the production B-1B, vs the pre-production B-1A.

[M2dude]

The Tornado was originally designed for Mach 2+ and used variable intakes. Legend had it that the Tornado AICS had a family relation with the system on Concorde, but since it was developped by a German firm (Nord Micro), that's unlikely.
And here lies a very true tale: When the Tornado airframe and systems 'carve up' was done in the early 1970's,the aerodynamic responsibility for the variable intake went to MBB in Germany. Now the last time that this particular company was involved with air inlets was in World War 2, so some ideas for problem solutions were required here. The only real place for MBB to go in Europe for help was good old BAC in Filton. The method of aerodynamic shockwave control and feedback used for the Concorde 'two stream' intake was totally unique, and BAC were only too happy to help out their German brethren (kinda dumb really as we shall soon see). After the Tornado intake was (finally) developed in the mid 1970's MBB realised that there was no existing patents on their (copycat) design, and so they applied for and obtained these necessary patents. The next part is pure comic opera; MBB then approach BAC for financial compensation with regard to this copyright infringement, (yep!! BAC design and develop the Concorde intake, give all the necessary knowledge and 'know how' to MBB for the Tornado and then are required to PAY THEM for the pleasure??). No money in fact ever changed hands, there was of course no justifiable case here, but there is a bit of poetic justice; the final Tornado intake was a very poor design, with excessive levels of fuselage boundary layer ingestion and shockwave control. The RB199 engine (a totally 'political' design, with a never to be repeated, for a supersonic engine that is, 3 shaft layout) was already down on thrust, but now had even worse Mach 2 performance due to a wholly inadequate intake design. (MBB had the design principles thanks to BAC, but were totally out of their depth when it came to applying these principles into a practical intake). The eventual 'locking out' of the Tornado intake ended up being no big deal.
(Not sure if this was done with the F3 though).
Fortunately for the western world, the Tornado was (and still is) a superb low level performer, but would have been a so much better Mach 2 aircraft if the powerplant (including the intake) was left to expertise and not politics.

Dude :O

[ChristiaanJ]

M2dude,

Thanks for a very interesting story, that puts it all into context !

You may want to glance at this old PPRuNe thread re the Tornado :
Is the Tornado GR4 still supersonic? [Archive] - PPRuNe Forums (http://www.pprune.org/archive/index.php/t-249417.html)

It would seem your guess about the F3 was right.

CJ

[M2dude]

Thanks ChristiaanJ, that Tornado thread was absolutely fascinating to read. The poor old Tornado was so down on thrust; a little more thought and effort in the powerplant design would have resulted in an otherwise good aeroplane becoming a GREAT aeroplane. (I stll remember the case of an F3 being left standing by Concorde during transonic acceleration).

Dude :O

[speedbirdconcorde]

As Feathers said...

"In all the 40 years I've been reading about Concorde, I've never found any of this sort of information before.

Seriously this all needs to be copied over to one of the specialist Concorde sites and tidied up for permanent display. It's a complete treasure trove and it needs preserving."

Totally agree. If only we could get Dude, Christiaan, Exwok, Bellapheron and all the Concordians to somehow have their stories documented and thus preserved. So many stories and names I have never heard of - could keep on reading till the cows come home. But seriously....as Feathers said....its a complete treasure trove and it needs preserving......

[M2dude]

Thanks speedbirconcorde, possibly food for thought indeed. This particular thread I think deals with one of the most mystical and definately most 'clever' of all of the various 'Concorde Magic' aspects; that is how a 14' long box can end up providing 63% of the 'welly' pushing you through the air at Mach 2. After nearly 37 years of my own personal involvement in the project, it still fascinates the hell out of me. :ok:

Best Regards
Dude :O

[Landroger]

Another great 'dollop' of my favourite 'indulgence'. Reading these two Concorde threads, especially this one - even though it makes my brain ache and my eyes wobble. :uhoh:

Dude wrote;
To find the root cause of a surge required a fair bit of forensic analysis; unlike AF, BA had a superb Plessey PVs1580 digital flight data acquisition and recorder (AIDS) system that monitored all the intake parameters; this enabled us to find the cause most of the time, by reading data from the Quick Access Recorder after the flight. (A fair bit of Midnight oil burned though; I still have bags under my eyes ). I remember that originally the singular most important parameter, inlet void pressure, was only sampled once every four seconds by the AIDS system, but once we showed that this was like an ETERNITY when you were trying to track down an engine 'hiccup', we got the sampling rate increased to once per second. Although even this was not ideal, it generally did prove to be sufficient for us.

This raises a couple of observations, one is really a question and is this; The Plessey Data Logger you coveted Dude, was surely only as good as the thermocouples, strain gauges and pressure transducers to which it was connected? Also the quality - or validity - of the data acquired from them was really only as good as the locations decided upon by the engine/intake group? Does it then follow that the production Concorde (BA and AF?) was routinely fitted with a whole outfit of sensors that were not normally monitored unless you and your mates needed to know something specific? (I've just realised there are about four questions there, but you probably know what I'm getting at?:))

The observation is; a picture is beginning to emerge of one airline who cherished and took care of an extraordinary asset, while another, broadly speaking, did not. :( Yet another remarkable aspect of Concorde, that the same aeroplane should have been held in such diametrically opposed regard. :confused:

Dude also wrote;
the final Tornado intake was a very poor design, with excessive levels of fuselage boundary layer ingestion and shockwave control. The RB199 engine (a totally 'political' design, with a never to be repeated, for a supersonic engine that is, 3 shaft layout) was already down on thrust, but now had even worse Mach 2 performance due to a wholly inadequate intake design. (MBB had the design principles thanks to BAC, but were totally out of their depth when it came to applying these principles into a practical intake).

This highlights yet another example of how British Industry/ government have habitually managed to snatch defeat from the very jaws of victory, especially in aviation. I am currently re-reading Genesis of the Jet - the story of Sir Frank Whittle and the struggle he had to bring his revolutionary creation to life - and although one is very proud that Sir Frank was one of the good guys ( a Brit :D) the story is ultimately quite depressing. The attitude of the government of the day, British Thompson - Houston's reluctance and Rover's deviousness all conspiring to delay what should have been a war winner. :ugh:

One thinks of the TSR2 which, on the limited amount of flight data acquired by the single flying airframe, appears to have been an aeroplane in the same astonishing mould as Concorde. With later digital electronics the TSR2 would have made an unbeatable bomber, allowing the money and effort 'squandered' (?) on MRCA to be spent on an agile interceptor replacement for the 'Electrifying' Lightning. :{

One also thinks of the P1154 and later, the offer of joint development on a supersonic AV8B succesor. All of these and many more until even reading about them becomes too depressing and frustrating. :ugh: :ugh:

Finally, Dude wrote;
This particular thread I think deals with one of the most mystical and definately most 'clever' of all of the various 'Concorde Magic' aspects; that is how a 14' long box can end up providing 63% of the 'welly' pushing you through the air at Mach 2. After nearly 37 years of my own personal involvement in the project, it still fascinates the hell out of me.

I completely agree and what is more, your fascination mirrors my own with my day job. Although MRI scanners are my day job, I still - after more than twenty years - look at some of the images it can produce and think; " That is bl00dy clever!" :) I still haven't got over the 'novelty'.

Thanks once more to all the Concorde respondents - amazing stuff. :ok:

Roger.

[M2dude]

Landroger
Does it then follow that the production Concorde (BA and AF?) was routinely fitted with a whole outfit of sensors that were not normally monitored unless you and your mates needed to know something specific? (I've just realised there are about four questions there, but you probably know what I'm getting at?http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/smile.gif)
Actually Roger the Plessey PVS1580 system generally used 'spare' outputs from existing system sensors as far as the powerplant went, the one exception to this being T3 (HP compressor delivery temperature) which had it's own dedicated thermocouple. An engine surge would be 'indicated' on the recorder playback as a spike in EGT (Exhaust Gas Temperature), Pv (Inlet Void Pressure - a static absolute pressure measurement above the fwd intake ramp) as well as a collapse in P7 (Exhaust gas total pressure). The surge itself might only be evident for one to three recorded frames, before the engine recovered. The E/O would usually give you a head start by pressing an 'event' button on the system control panel, which put a marker on the recording. You then needed to decide (by looking at the frames immediately BEFORE the surge) whether the engine or the intake caused the surge in the first place. (Not always easy and straightforward). The recorded frames were generally one second samples, so there could often be quite a bit of 'searching' involved.
The observation is; a picture is beginning to emerge of one airline who cherished and took care of an extraordinary asset, while another, broadly speaking, did not. http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/sowee.gif Yet another remarkable aspect of Concorde, that the same aeroplane should have been held in such diametrically opposed regard
I see your point Roger, but personally I found that it was more a case of one airline not taking matters (and the aeroplane) for granted and approaching everyday Concorde 'life' in a disciplined and professional manner and the other, very clearly, not. I remember one visit to CDG where I was horrified by the state of the aeroplanes there: The airframes were generally filthy and festooned with repair 'patches' (one large one over the main passenger entry door looked absolutely awful) and the flight deck panels had at least one broken switch and a couple of cracked instrument glasses. (I thought 'surely they don't actually FLY the aircraft like this?' .... they did!!). When I witnessed with my own eyes how aircraft defects were being investigated I could only wonder if 'they' had any clue how the aeroplane really worked. It was blessed relief when I returned to LHR that evening, and could see two gleaming Concorde aircraft in the hangar.
One thinks of the TSR2 which, on the limited amount of flight data acquired by the single flying airframe, appears to have been an aeroplane in the same astonishing mould as Concorde. With later digital electronics the TSR2 would have made an unbeatable bomber, allowing the money and effort 'squandered' (?) on MRCA to be spent on an agile interceptor replacement for the 'Electrifying' Lightning.
I can only agree with you here Roger, the story is one of complete political and industrial madness; the designer and manufacturer of the finest quality and most capable aircraft in all of Europe being relegated to a producer of mere sub-assemblies and spare parts for certain European 'partners' :ugh:
(Who must now be rubbing their hands together in glee at this short sighted British stupidity). As has been said here before; 'WHAT A WASTE'
I completely agree and what is more, your fascination mirrors my own with my day job. Although MRI scanners are my day job, I still - after more than twenty years - look at some of the images it can produce and think; " That is bl00dy clever!" http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/smile.gif I still haven't got over the 'novelty'.

Oh I can echo that 1000%. After having an MRI done last year (a very sick Dude indeed) I was absolutely AMAZED at the quality and detail of the resulting images. (Being a true engineer of course I drove everybody at the hospital nuts, wanting to know all the ins and outs of this incredible (but rather LOUD) machine). Truly amazing stuff Roger, I can see your attraction here.

Regards
Dude :O

[goarnaut]

I realize this thread is two years old...but I just came across it and would like to clear up some of the misconceptions here about what causes the high amount of thrust produced by the Concorde inlet duct...

The reason is very simple and it has to do with the fluid impulse principle...the air entering the inlet duct has a very high momentum (mass flow times velocity)...but it slows down inside the duct from about M2 to ~M0.5...as a result there is a large decrease in fluid momentum...

Since momentum must be conserved...the aircraft gains that much forward momentum...which is thrust...

This momentum change happens in every stage of the engine...the inlet...the compressor...the combustor...and the nozzle...the total thrust of the engine can be computed by computing the impulse (the change in momentum) at each station in the engine...

Even in subsonic flight a diffusing inlet that slows down the flow will produce a thrust impulse...the compressor also...and the burner...the turbine produces a net drag force...and so will the nozzle...

The basic math is that the net Force (in the longitudinal x axis) produced on the engine inside wall is equal to the (mass flow times velocity at the inlet...plus the pressure times area at the inlet)...MINUS... (the mass flow times velocity at the outlet...plus pressure times area of the outlet)...

Fx = (mdot * V1 + P1 * A1) - (mdot * V2 + P2 * A2)

Looking at the right hand side of that equation we have the intake duct opening as the first term..and the fan face as the second term...in order to make thrust in the forward direction we need Fx to end up with a negative value...which means the second term must be bigger...

The mass flow-velocity product decreases as the flow slows down in the duct...but the pressure-area product ends up much bigger so we end up with the second term being bigger than the first term...and we have a change of momentum to the left (ie negative impulse) and we get thrust...

So while it is true that flying at M2 we can greatly increase the static pressure going into our engine by converting dynamic pressure to static pressure...that does not tell us why this causes thrust...the reason is the change of momentum...or impulse...

By itself an increase in pressure ratio will result in somewhat more thrust...and a six-fold increase in static pressure would result in about a 40 percent increase in thrust...compared to an engine that is at atmospheric pressure...but that does not tell us which components of the engine are actually making thrust and which ones are making drag...only a component-by-component breakdown of the impulse will give us the answer...

[CliveL]

I realize this thread is two years old...but I just came across it and would like to clear up some of the misconceptions here about what causes the high amount of thrust produced by the Concorde inlet duct... I’ve also just come across this thread after two years, and although I for sure don’t want to repeat any of the millions of electron-volts expended in the excellent discussions I thought it might be of interest to have some additional comments ‘from the inside’.
The first thing I would like to say is that we always thought of the total system as “powerplant”. As in any aircraft powerplant (engine) the forces on the various components vary – some produce drag, others thrust. Part of the intake had a thrust component, part had drag. Similarly with the engine itself and the propelling nozzle. It is really a bit misleading to say that “the intake produced thrust”. For us it was just one component of the powerplant that gave a thrust .- and we weren't particularly bothered whether that came from pressures on the diffuser walls or momentum changes, What mattered for us was that the intake efficiency (pressure recovery and intake external drag) was as high as possible. (not intake drag as high as possible of course). I can't stress too highly that the powerplant had to be considered as a whole!



Dude’s remark:


The important concept to grasp is that you have to consider the powerplant as the 'engine' if you like. It's the intake, engine and nozzle assembly that were able to work together in such perfect harmony, but each component was totally codependant on the others. was absolutely on the mark. Other things I found interesting:


Post #15 B377
Wonder how much of this was learned from the use of the 593s on the 1950s Victor bombers albeit these were not supersonic? Not a lot!
Post #31 Landroger
The whole concept of 'Supercruise' is quite stunning and the thought occurs; was it played for, or a happy outcome of the way the design froze? Very definitely played for !
You are saying though, that it could not maintain Mach 2 without reheat Yup!
Post # 33 M2Dude
The problem was that having decided that an analog intake system would never be able to provide the level of control and stability required for certification, the technology almost had to be invented. In 1970, when relatively late on, in project definition terms, it was decided to use 'throw 'away' the analog system and replace it with a completely new digital one, there came a problem; there was no such thing as an airborne digital control system, and so one had to be 'invented' in Bristol. The analogue system wasn’t thrown away exactly – we retained the inner ‘analogue’ system that did the closed loop dynamic control of ramps etc. and wrapped a digital system around it to define the control ‘laws’ to which the intake operated.

Post #39 Mr Optimistic

Of course you would need 10^-9 now, don't suppose safety was quite the game it was now. Actually Concorde was the first civil aircraft to be certificated using this 10^-9 approach, although the rules were of course contained in TSS Standards not enshrined in FARs. Also we adopted a far more pragmatic ‘engineering’ way of working than the almost blind faith in numbers that seems to be the case today!
Post #56 M”Dude
For a supersonic aircraft, how good your whole 'engine' in this context is relies on solely how well designed the 'front bit', the 'rotating middle bit' and the 'back bit' are, and how they work together. Weakness in any one of these three is gonna cost you performance and/or fuel (and trans-Atlantic range is just not possible; ask Tupolev). Post #66 Pugilistic Animus
and it illustrates that the Great Art of Aerodynmics is Experimental - a little twist here a little waxing and polishing,..., a little area cut away from there...and it---- Still Flies Ain’t that the truth!
Post #56 again
And all this done with slide rules, protractors and the backs of hundreds of cigarette packets, without any mathematical modelling in sight. Also true, but only two of the team smoked (mind you they made up for the others)
Post #67 M2 Dude
If I may, I would now like to mention the 'some oil lamps and diesel oil' story. True, but we also did the ‘Hi-tech’ bit. I thought people might be interested in the actual flow visualisation results we got from the lamp black and diesel fuel trick:


http://i1080.photobucket.com/albums/j326/clivel1/scan0031.jpg

Post #100 M2Dude
The next part is pure comic opera; MBB then approach BAC for financial compensation with regard to this copyright infringement, (yep!! BAC design and develop the Concorde intake, give all the necessary knowledge and 'know how' to MBB for the Tornado and then are required to PAY THEM for the pleasure??).
but there is a bit of poetic justice; the final Tornado intake was a very poor design, with excessive levels of fuselage boundary layer ingestion and shockwave control.
In fairness to MBB, one should say that the Tornado had conflicting design requirements in that there was a need for efficient subsonic performance to give loiter (CAP) endurance, so they were forced to compromise a bit on the purely supersonic efficiency.


Hope I haven’t hogged too much space!

[goarnaut]

Clive...thanks for chipping in with some very interesting info...


Always good to hear from one of the design team members...just curious about a couple of things...what was the mass flow per engine at M2 cruise...?...and what about the jet velocity out the tailpipe...?...my rough estimate puts it at ~300 lb/s and ~ 1,100 ft/s over and above the freestream velocity...


That would put propulsive efficiency at ~80 percent...which means engine thermal efficiency would be just over 50 percent...


Some other interesting figures...total flight power at M2 would be over 140,000 thrust hp...nearly three times the flight power of a triple seven...fuel burn would have been most impressive at over 13 lb per second...compared to 5 for the triple seven...


The triple seven's GE90 engine is good for a TE of ~50 percent...and propulsive efficiency of ~0.8...really quite amazing that a Mach 2 transport could still be the high water mark after all these decades...


Regards,


Gordon.

[chris weston]

I'm fascinated by this thread too chaps, addicted to is a better way of putting it.

I know it's not Concorde but how will Bloodhound SSC be addressing these problems do we think?

1,000 mph at 0 agl must be some challenge too and not exactly "off the shelf"....

CW

[goarnaut]

It was mentioned earlier that the Tu144 did not supercruise...and that Soviet designers never did solve the technical challenges in creating an efficient engine inlet...

In the spirit of fairness and accuracy...this is not correct...it is true that the initial version of the airplane was not ale to supercruise...due to using inefficient Kuznetsov turbofan engines... instead of more efficient turbojets which are better suited to supersonic cruise...the Russian designers were aware of this but there was not a suitable turbojet engine available at the time...


The D model of the airplane switched to Kolesov RD36 turbojets when those became available...and was able to cruise at M2 without reheat...SFC of the Kolsesov engine was comparable to the Olympus at ~1.2...although the Kolesov was a bigger more powerful engine with `12,000 pounds of cruise thrust compared to the Olympus's 10,000...


The more efficient engines greatly increased the range of the airplane to 3,500 nm...largely closing the gap with Concorde's 3,900 nm range...an extended range model was in the works that would have exceeded Concorde...when the program was cancelled in 1983...


The original intake ducts were not as efficient as Concorde...but this was rectified with subsequent models...starting with the S model that preceded the D...


In the 1990s Nasa obtained a Tu144LL which was a D model retrofitted with Kuznetsov fan enngines due to the fact that the more efficient Kolesov jets were no longer in production...a comprehensive flight test report is available from Nasa...


http://dcb.larc.nasa.gov/DCBStaff/ebj/Papers/TM-2000-209850.pdf (http://dcb.larc.nasa.gov/DCBStaff/ebj/Papers/TM-2000-209850.pdf)

(http://dcb.larc.nasa.gov/DCBStaff/ebj/Papers/TM-2000-209850.pdf)
The report notes that "the engine inlets appeared insensitive to sideslips (up to 4.5 degrees) or to pitching moments..."...this points to good inlet design...something that is not always present in supersonic aircraft...for instance the F14 which was known to have compressor stalls at high yaw angle...



Overall the Tu144 is a bigger and heavier aircraft than Concorde and was able to reach a higher speed...M2.4...although cruise was at M2...the prototype used a lot of titanium although this was cut down on production models...unfortunately...


Regards,


Gordon.

[CliveL]

Gordon,

Without doing a lot of sums (which I have probably forgotten how to do), the best I can offer is:

58000 ft, M 2.0, Ambient temperature - 52 deg C, Ambient pressure 1.2 lb/sq.in
Engine intake conditions
Total pressure 8.5 lb/sq.in, Total Temperature 127 deg C, Mass flow 189 lb/sec.
Fuel burn 9700 lb/hr
Jet pipe exit (not final nozzle) Total pressure 16 lb/sq.in, Total Temperature 687 deg C
Engine thrust 8050 lb.

The jet pipe nozzle was choked of course and the petal angle was 10 deg, but I don't have the value of the actual area handy.

Clive

[goarnaut]

I had estimated the compressor inlet area at ~1 m^2...based on the engine static mass flow of ~450 lb/s...and an assumed inlet Mach of 0.5...


Seeing as cruise mass flow is a lot less...perhaps some of my assumptions were off the mark...


Also surprised to hear a cruise thrust figure of just 8,000 lb...a Concorde website with lots of info gives 10,000 lb per engine...Wikipedia gives a Lift to Drag ratio of ~7 at M2 cruise...which would imply that ~50,000 lb of total thrust would be needed...since maximum weight is ~400,000 lb...fuel weight is ~200,000 lb...and fuel flow with max power and reheat is ~50,000 lb/hr...


This means even if it takes a full hour at the maximum fuel flow the airplane would still weigh at least 350,000 lb by the time it reached cruise speed and altitude...since thrust must equal drag in straight and level unaccelerated flight...it means 50,000 lb of thrust would be required...


Looks to me like there is a fair bit of confusing information floating around...hope you can clear some of that up...would like to do a full cycle analysis on the engine at cruise power...that SFC figure of 1.2 is very impressive...


Regards,


Gordon.

[Crabman]

First, thanks for resurrecting this most interesting thread. At one point I thought I was getting this, but clearly I wasn't.

Gornaut states that momentum is being transferred from the supersonic incoming air flow to the engine (and hence to the aircraft). I can't visualize it. Isn't the momentum already in the aircraft?? (It is the aircraft that is moving through the air, not the other way round.)

As I read the discussion, it seems we are getting the ultimate free lunch (which I know isn't right). I'm sure that if we turn off the fuel flow, the net thrust must drop to zero. So how can we say that 63% (or whatever) of the thrust is coming from the inlet duct.

I'm really trying to understand this.

[HazelNuts39]

Crabman,

Perhaps post #5 explains:
in the final analysis all powerplant thrust of course is really generated by the engine, what we have been looking at how this thrust is transmitted to the airframe.

[Mr Optimistic]

Gornaut states that momentum is being transferred from the supersonic incoming air flow to the engine

That would be drag as something has to slow the air down. This thread caused endless discussions a while back. The way it was originally phrased you would think you had the basis for a perpetual motion machine, ie just bend metal into a sophisticated shape and off it would fly ! Need to take a holistic view of the whole power plant to really get the picture, hence the quotes above. My view was that it was really about the efficient recovery of pressure for the intake but what do I know: certainly the intake on its own isn't a prime mover or the active source of any thrust.

[goarnaut]

The math is quite straightforward and can be found in any good engine text or fluid mechanics text...but that does not help us understand the physical principles behind it...


I have already given the momentum equation involved which is a statement of Newton's Second Law of Motion...which we mostly know as F = mass times acceleration...


In fact the Second Law tells us that a force results from a change of momentum...In differential form F = m * a becomes...F = m * dV / dt...which means a mass that experiences a velocity change (differential of V with respect to time) is experiencing a momentum change...


Of course momentum must be conserved...just as mass or energy must be conserved...if a car collides with another car it loses its momentum as it stops...but the other car gains momentum as it is shoved forward...


Same thing with a flowing fluid... if it goes into a control volume such as an engine intake with a certain amount of momentum...and then loses a good part of that momentum...what happens to it...?...it is transferred to the control volume...ie the engine...which is attached to the airplane...


An impulse is simply a change of momentum...when we accelerate a hot gas stream out the tailpipe we impart a change of momentum to that mass flow...the result is reacted by the engine which is attached to either an airplane or a test stand...in either case a change of momentum in the forward direction means thrust...

If we were to take an engine inlet duct (a diffusing duct that has a smaller hole at the front than at the back) and bolt it to the floor inside a wind tunnel... and then blow air at 500 mph through that duct...what do you think would happen...?


If we allowed the mount to slide back and forth...which way would it slide...forward or backward...?


What if we turned the duct around and now had the big hole at the front and the little hole at the back...?...which way would it move now...?...isn't this how a wind sock works...?...which way does it want to go...?...back of course...


And have you ever seen a wind sock where the wind is blowing into the little hole...?...and coming out the big hole in the back...?...of course not...


So why would that intake duct that is shaped just like a wind sock that is turned around front to rear want to move back...?...of course it is going to move forward...


The reason is that the impulse (change of momentum) gets bigger as we go from front to back...

Now we can work out an example like the illustration...we have an airplane flying at 250 m/s...and the inlet opening is 1 m^2...the mass flow is 100 kg/s...let's say the opening at the aft end of the duct is 1.25 m^2...which has the effect of slowing down the flow and increasing static pressure...at the same time the flow loses momentum as it slows down...


We recall that Force = mass flow * velocity...so the force at the front of the duct is 250 m/s * 100 kg/s = 25,000 newtons...a little over 5,000 lb of force...


If the flow slows down to 125 m/s at the aft end...its total force will now be 125 m/s * 100 kg/s = 12,500 N...(mass flow does not change of course...owing to conservation of mass)...


So the fluid flow has lost 12,500 lb of force...but we need to account for all the forces acting on that control volume...we see that there is pressure from the wall pushing on the fluid that is equal and opposite to the pressure of the fluid that is pressing on the wall...since pressure acts exactly perpendicular to any wall...we see that a lot of the arrows are canted in the forward (thrust) direction...this gives us a clue that the sum total of all those little arrows is going to end up as a net forward force...


We can integrate all the pressure forces across that surface and expend a lot of math...or we can just do a simple multiplication of the pressure times the area of the inlet and outlet respectively...that will give us the answer...


So we see that our static pressure at FL350 is 22,500 N/m^2 (22.5 kPa)...and our intake area is 1 m^2...so the total pressure force pushing back is 22,500 N...


At the aft end our pressure is 1.5 times higher...this is a subsonic plane and slowing down the flow from ~M0.8 to ~M0.4 will result in a static pressure increase of that amount...


Our duct exit is 1.25 m^2...so our total force at the back is 22,500 N * 1.5 * 1.25 m^2 = ~42,000 N...So we have gained nearly 20,000 N from the pressure on the engine duct inside surface...!...


We subtract the 12,500 we lost from the flow slowing down...and we are still ahead y more than 7,000 N...an engine of that mass flow would make perhaps 30,000 N total thrust so that would be a good part of it right there...nearly ¼... of total thrust...


So yes the engine inlet is making thrust...that is very real...it is just that we are used to thinking purely about thrust as mass flow times velocity coming out of the tailpipe...and that is the simplest way to account for the sum total of all the physical forces going on in the engine...


However...if you want to do a more thorough line-by-line accounting...then we must start at the tip of the engine and do this impulse analysis for each component...we would then go on and do this for the compressor...the burner...the turbine...and the jet nozzle...and we would find that the net thrust still remains the same...but it is the physical forces of pressure and momentum and impulse that do their work at each point along the way...


Regards,


Gordon.

[Lyman]

Source/Site

Power/Work

I think unpacking any aeronautical question leaves room for almost absurd conjecture. Of course the nacelle does not provide power. It is the site, instead, of the Work. Or at least most of it, in modern Turbofan engines. Powered aircraft need, well, power. This happens well aft of the Work.

The Wrights used unducted fans. The power came from a combustion engine that provided mechanical energy to the fans.

Given extreme latitude in architecture, how is the Concorde different from the Wright Flyer? Distance from power to work?

I am still trying to suss the Wright's accomplishments. There were few shoulders to stand on, they made their own engine, for goodness sake.

The idea is to move mass, energetically enough to gain useful work, after all. It is an attempt at lazy magic that pulls people into heated discussion that requires a suspension of the basic Laws.

Mr. Optimistic has busted out the thread, imho.

[goarnaut]

http://i46.tinypic.com/1w4n8.jpghttp://tinypic.com/r/1w4n8/6

[peter kent]

Perhaps it helps, just for a moment, to view the engine as a flow inducer. This is the term used by 'Kelly' Johnson to needle P&W J58 engineers. This merry banter should be seen for what I'm sure it was, just that.

However there is merit in viewing the engine as such since another angle on any issue can only help to get a better picture.

This particular view imo helps to come to terms with the ever-increasing relative contribution of the intake to the total thrust.

At the same time though the engine is producing ever more gross thrust from an ever-increasing release rate in its engine and jetpipe combustors. Everything can be traced back to the fuel. The burning fuel induced the flow which, by virtue of its finer details, must produce forces in some direction or other.

Imagining what's going on in the combustors should help prevent downplaying the loser in the relative stakes.

On a slightly different tack:

Would the inlet momentum drag be zero when the flight speed is the same as the engine entry speed, say M0.5, assuming, of course, that the intake design flow was matched to the engine flow at that flight speed?
After all, if I watch a plane go right to left at M0.5 the compressor face is going left at M0.5 and the air is going right at the same speed, ie is stationary like it was before the plane appeared.

Alternatively, if I'm sitting on the Rosemount probe and looking ahead I see air approaching at 0.5 and if I look behind I see it going away from me into the compressor at 0.5, again no speed change.

[goarnaut]

The flow going into the compressor or fan is going to be at its design speed as long as the engine is turning at its design rpm...even when the airplane is standing still on the ground the engine will be sucking mass flow into the engine at about its design speed...


We can always do the math if we know the mass flow and the compressor (or fan) face area...and the design flow speed at the compressor face...which is almost always going to be ~ M0.4 to M0.5...


If we have a compressor inlet area of 1 m^2 and the flow speed is M0.5...which is ~ 170 m/s at sea level temperature...and knowing that SL air density is 1.23 kg/m^3...we know that mass flow is going to = 170 m/s * 1.23 kg/m^3 * 1 m^2 = 209 kg/s...


If we fly faster or slower that mass flow does not change...the engine is going to take in what the compressor can swallow...nothing more...of course as we go higher the air gets thinner and the density at FL350 is only ~1/4 of what it is at SL...


So if we are flying at M0.5 at ~SL the air flow in front of the engine inlet is going to be moving faster...due to the fact that the same 209 kg of mass flow moving at 170 m/s at the compressor face of 1 m^2 has to go through a smaller hole at the front...that is maybe 0.75 m^2...


Again we calculate that and get mass flow of 209 kg/s divided by area of 0.75...divided by air density of 1.225 = ~228 m/s...so even though our airspeed is M0.5 (170 m/s) and the speed of the flow at the compressor face is (M0.5) 170 m/s...the engine is sucking in the air in front of the engine due to the small “straw” opening...


So inside the duct we still see some static pressure rise as the air slows down from 228 m/s to 170 m/s...although this is not that much...we can calculate the static pressure rise as the kinetic energy from the moving flow that we have converted into pressure energy...kinetic energy being velocity squared divided by two...


The difference in speed is 58 m/s so that is a kinetic energy of ~1,700 m^2/s^2...the temperature of the flow would increase by the energy divided by the specific heat of air...which is ~1,000 J/kg per degree so we would get a temp rise of ~1.7 degrees...if the air was at 250 K to start with it means the temperature ratio ends up as ~252 / 250 = ~1.01...Pressure Ratio = Temp Ratio to the 3.5 power at these moderate temperatures...so the PR increases by 1.01^3.5 = 1.03...


Which means we get ~3 percent increase in pressure going through that diffusing duct...we can see from this that the more we slow the flow down the greater our temp rise...and the lower our starting temp to begin with...the higher our temp ratio...and therefore the pressure ratio as well...


So with Concorde where we slow the flow down from M2 to M0.5 we get a big temp rise...from minus 51 C to plus 127 C...a swing of 178 deg...we use absolute temp scale to get our temp ratio so temp compressor face of 415 K divided y freestream temp of 237 K gives TR of 1.75...


The pressure increase is the temp ratio to the 3.5 power so that is 1.75^3.5 = 7.1-fold pressure increase...that is the ideal isentropic (lossless) pressure increase...the actual static pressure increase in the airplane ends up as ~6.4 so the duct efficiency at recovering pressure is 6.4 / 7.1 = 0.9...90 percent...which is good...


However we see that this pressure increase results in the intake making thrust because it causes a large swing in momentum in the forward thrust direction when we take all forces in the intake into account...not because the increased pressure makes the jetpipe speed faster...although this occurs also...but now we are talking about a different way of accounting for the thrust...


So to wrap up a few loose ends...we see that it is useful to go through each component of the engine and figure out if its contribution is a net drag or thrust...but that does not change things...the whole thing needs to work together...without the fuel being burned the whole process comes to a stop...


So when we stand back and say “the intake produces x amount of thrust...”...well yes..but so does the compressor and the burner...and the turbine will produce a net drag...etc...it is just one way of looking at what is going on in the physical sense...


It was mentioned that the mass flow coming in to the engine is a net drag...and yes that is called ram drag and is the mass flow of the engine times the freestream velocity (aircraft speed)...but this is another method of accounting where then subtract that ram drag from the total thrust produced by the mass flow times its jet velocity out the tailpipe...


So if the airplane is flying at 250 m/s and the mass flow is 100 kg/s...then the ram drag is 25,000 N...and if the speed of the jet blast is 750 m/s then the gross thrust is 75,000 N from which we subtract the ram drag and get net thrust of 50,000 N...which is why thrust = mass flow * jetpipe speed minus freestream speed...



It is another way of accounting for the forces going on...and the most simple way...the important thing is you can't mix and match different ways of doing the bookkeeping...if you start with one method then stick with it and don't mix concepts...


Regards,


Gordon.

[CliveL]

Gordon,

Not wanting to go over old ground I wasn't going to do any more on this, but w.t.h. the golf course is unplayable, the river unfishable and its raining again ....


I had estimated the compressor inlet area at ~1 m^2...based on the engine static mass flow of ~450 lb/s...and an assumed inlet Mach of 0.5...I make the compressor inlet area just about the same, and checking the mass flow from intake supply conditions a value of 189 lb/sec at FL580 looks about right also. The intake efficiency derived from the figures quoted would be around 94% which is also correct. That makes the compressor inlet Mach Number about 0.45.


Also surprised to hear a cruise thrust figure of just 8,000 lb...a Concorde website with lots of info gives 10,000 lb per engine...Wikipedia gives a Lift to Drag ratio of ~7 at M2 cruise...which would imply that ~50,000 lb of total thrust would be needed...since maximum weight is ~400,000 lb...fuel weight is ~200,000 lb...and fuel flow with max power and reheat is ~50,000 lb/hr...You need to be careful with that 8050 lb figure - it is the thrust produced by an Ol 593 operating behind an intake that supplies 189 lb/sec mass flow at a total pressure of 8.5 psi. It does NOT include the thrust generated through the expansion of the flow in the secondary nozzle. Add on the 25~29% often quoted for this contribution and you are up to the 10,000 lb mark.

The actual cruise L/D was 7.5. Any Concorde pilot reading this could confirm, but I would expect that by the time the aircraft cruise climbed up to FL580 it would be at around 300,000 lb, which would fit well with the 10,000 lb per powerplant.

Looks to me like there is a fair bit of confusing information floating around...hope you can clear some of that up...would like to do a full cycle analysis on the engine at cruise power...that SFC figure of 1.2 is very impressive...PM me if you need more detail

Going back to that 8050 lb thrust it is the thrust you would get from an engine and intake working together. The engine won't work without the intake and the intake won't work without the engine, so it is a bit pointless to consider them as separate units. As you suggest in a later posting, there are thrust and drag variations on the various components inside the engine proper (thrust on compressors and combustion chambers, drag on turbines etc) and nobody apart from the engine stressmen cares a stuff about those distinctions.

Better, I suggest, to consider the intake and engine together as a single powerplant and think of the intake as a zero stage compressor, or more accurately as a pre-diffuser set ahead of the first stage of the compressor.

That way you get to see the intake "thrust" as just another split in the breakdown of powerplant force distribution.

Again as you say. its all in the book keeping, and as an accountant friend of mine is fond of saying "What answer do you want?"

[goarnaut]

Okay...the numbers are starting to come together like they should...

I made a math boo-boo in calculating cruise mass flow...but now I get ~177 lb...oh well...that's in the ballpark at least...


It doesn't change the fact that thermal efficiency is well over 50 percent on this engine...something the high bypass fans are only now reaching...although with the smaller mass flow propulsive efficiency would end up at ~75 percent...still pretty good...I put overall efficiency right at 40 percent...again where the top airliners are at today...



What do you think about a bigger mass flow and lower jet velocity to increase propulsive efficiency...?...I will try sending you a PM...any data you can provide would be most appreciated...


Regards,


Gordon.


PS: I had to smile at your comment about all this drag and thrust stuff being important only to the structure guys...I'm sure you meant no slight...and it is a fact of course that their role is very much secondary...but it is a bit funny nonetheless...I'm sure they would point out very earnestly that if they did not do their job...that a lot of those carefully designed engine bits would come flying off the airplane long before it ever reached Mach 2...

[Crabman]

Gornaut, I agree that the maths are straightforward . But I also agree that it can be somewhat unhelpful without some intuitive understanding of what is being described. I did find your diagram very helpful as to what the point of the calculations were.

I went back and reread post #5 which does indeed explain it very well. In light of that explanation (and CliveL's remark "nobody apart from the engine stressmen cares a stuff about those distinctions"), isn't the phrase "produced by" a little misleading. I can understand that 63% of the thrust is transferred to the aircraft through the inlet duct. But, couldn't I just as easily calculate and say that (obviously I'm making this up): 23% of the thrust is transferred through attachment bolt A, 15% through attachment bolt B, and 25% through attachment bolt C. I don't see where I would ever say that 23% of the thrust was produced by attachment bolt A.

This discussion (which is fascinating!), sort of reminds me of the story of the man who upgraded his car with: a carburetor that claimed fuel savings of 40%, spark plugs which saved 30%, tires that saved 30%, and an exhaust which saved 20%. He had to stop every few miles and drain his fuel tank.

[CliveL]

Goarnaut
My remark wasn't meant to denigrate anybody's work, and with hindsight I can see that the same criticism of my words could be applied to all those people who struggle to improve the efficiency of all the component parts of an engine. They all care very much.
What I really meant to say was that people OUTSIDE the engine companies don't really care about the fine distinctions.

Crabman
I can understand that 63% of the thrust is transferred to the aircraft through the inlet duct
That was exactly the message I was trying to convey

[NW1]

Brilliant conversation!

I've got to say that the numbers and physics can be brain-numbing. And this just emphasises the achievement of all those brown-overalled slide-rule operators who didn't let common sense get in the way, and made an airliner do Mach 2, and go from London to New York in under three and a half hours whilst burning about the same amount of fuel as a 747-2.

The Blackbird was a phenomenal achievement, a magnificent aircraft, but to achieve supersonic flight with an airliner, using more restrictive legislation (TSS) than existed for blunties at the time was nothing short of miraculous. Our equivalent of the Apollo programme.

But as a simple pilot who lived under those brown overall coat-tails (and was bloody luck to do so), <<without the use of reheat and with staggeringly low fuel flow values>> brought back to mind one of my most treasured memories of the experience (apart from those nights in pubs around Filton):

You plugged in reheat (the proper name for afterburners) at 0.95. She climbed at Vmo. M 1.0 went past without a gin & tonic spilt down the back. The ramps dropped at (from memory - Dude?) M1.3. But the real cool bit was at M1.7. You had a burn of about 12000 KGS/HR per engine. You cut the reheat. The fuel flow dropped to about half that - 6 tonnes per hour / engine. She didn't drop out the sky. She just carried on reaching - at FL500 hitting M2.0 - and just did what the designers intended - cover distance at about 20 nms/min. No fuss. No reheat. Day in - day out.

I suppose that's the practical experience of this thread's title.

Brilliance. Pure, original physics and engineering brilliance.

Hey ho.

[TURIN]

goanaut, any chance you could resize that image at post 119 please. It's doing my head in just trying to follow the maths never mind scrolling back and forth at the same time.

Thanks again to all the contributors. :ok:

[goarnaut]

NW1...it's good to hear from you...your numbers fill in some blanks...How long did it take to reach cruise altitude...?...


Crabman...the inlet is not transferring the thrust force from the engine to the airframe...that's the job of the engine pylon...the inlet is actually making thrust...think it through logically...the engine adds momentum to the mass flow and hurls it out the back with greater force than it came in...the engine is hurled forward as a reaction...momentum is conserved...


Now why don't we put that same kind of nozzle on the front of the engine instead of a diffuser...?...the flow would likewise speed up increasing the momentum going INTO the engine...but what would happen...?...how would the engine react...?...if the flow going OUT is speeded up and the engine moves forward...then logically if the flow coming in is speeded up then the engine will move backwards...we get drag...not thrust...


That is why you don't see a nozzle on the front of the engine...so continuing in this logic...if the flow COMING IN is now slowed down...what happens...?...how does it all balance out...?...remember momentum must be conserved...where does it go...it can only be forward or back...there are no other choices...


Turin...you can decrease your browser resolution by simultaneously pressing ctrl and minus keys...

[Crabman]

goarnaut:

the engine adds momentum to the mass flow and hurls it out the back with greater force than it came in...the engine is hurled forward as a reaction...momentum is conserved... That much, at least, my simple mind understands. That is how I always viewed the situation. That is the way I'll need to continue viewing the situation.

the inlet is actually making thrust This is the wording that I find confusing. I can understand that some (most) of the thrust is being "actualized", "transferred", or [... fill in another word..] due to momentum changes in the airflow which are occurring in the inlet duct which are transferred to the walls of the inlet duct (and/or passed along with the airflow to the next stage), which are transferred to the engine structure which are transferred to the craft through the engine pylon. I also can understand that this (plus and minus changes to the momentum of the airflow) is occurring all through the engine.

My problem is this. From the point of view of the aircraft, all the thrust is coming from the pylon. I still think it would be an odd usage to say that the engine pylon is "actually making thrust".

I'll bow out now and continue reading this thread. I don't want to appear obstinate or argumentative. Many thanks to you and CliveL (and also to M2Dude who earlier attempted to explain this).

[CliveL]

Crabman

My problem is this. From the point of view of the aircraft, all the thrust is coming from the pylon. I still think it would be an odd usage to say that the engine pylon is "actually making thrust".I see where you are coming from, but Concorde didn't have a pylon. On subsonic aircraft all the powerplant loads are transmitted to the airframe via the pylon as you say. But the Concorde powerplant had three distinct components, the intakes, the engines and the secondary nozzles, and all three were attached to the airframe separately.
I tried, and failed, to find a suitable illustration.
Since the components are individually attached, it seems not extraordinary to think about how the powerplant forces are shared between them. This is why people talk about the thrust transmitted through the intake attachments. That, for me, is not saying that the intake makes thrust - it just carries its share of the powerplant forces.

[peter kent]

Clive,
Belated thanks for the shockwave explanation. Inevitably I must spend time with the basics.

Gordon,
Thanks for your explanation.

I always thought the intake momentum drag was one of the costs of bringing the air aboard. Hence the appearance of flt velocity in the expression.
However, since the air never slows down beyond about M0.5 at the engine face the air is never brought to rest relative to the aircraft. Does this mean that the momentum drag is really a function of axial vel at compressor entry also?
Have I gone off the rails here or is it something to do with airframe, ie inlet, and engine accounting?

[goarnaut]

If you prefer... think of the inlet making a forward force...that's all it is...and that force is very real..the mechanism of it is that the diverging duct shape decreases flow speed and increases pressure...that increased pressure yields a forward force...after all force is pressure time area...


Since the outlet of a diverging duct has a bigger area than the inlet...and since the pressure is also increased...the result has to be a force pointing forward...there can be no other outcome in the physical world in which we live...


A converging duct...nozzle...is the opposite...I think you have stumbled on that “transferring” thrust part...that wording is unhelpful and does not actually have any place in this explanation...there is no transferring going on...the forward force is made right there in the duct...


Now of course it is true that the duct by itself cannot move the airplane forward...we need the entire engine and all of its bits...but the same is true for any other component...the gas generator without the nozzle will make no thrust...


So the bottom line is that if we look at the engine component by component...each of them makes either thrust or drag...doesn't change the fact that we still need each and every one of them...


I just pulled a good engine book off my shelf and looked this up...Aircraft Propulsion by Farokhi...Fluid Impulse is covered in chapter 2 and there is a whole section on it...with worked examples for each engine component...the inlet...compressor...burner...turbine and nozzle...there is a drawing that shows which components are making thrust and which ones drag...the inlet...compressor and burner all make thrust...while the turbine and nozzle make drag...


Now I agree with Clive that this is not hugely important to break things down in this way...but it is the physical reality and we must appreciate that...


As far as the Concorde inlet is concerned the goal was to have good aerodynamic performance...a diffuser is a difficult item...the flow is moving from low pressure to high pressure...an adverse pressure gradient...going uphill if you like...which can cause flow separation and the resulting turbulence eats up energy that we wish to recover as pressure...


So those were the design goals...I'm sure Clive and the team spent zero time thinking about how much “thrust” was going to be made in the inlet...that part we have no control over...it is just the way it works out if we do a proper job in recovering as much pressure as possible...


My aim here was just to shed a little light on this because it is fascinating...like many physical phenomena...it is another example that there is nothing for free in nature...when the air flow going at M2 gives up its momentum...it is the engine that gains...similarly if we inject cold fuel into a hot combustion chamber the fuel heats up and vaporizes...but the surrounding air loses the exact same amount of heat that the fuel gained...and the air temperature goes down...it is always a 2-way street...the action reaction thing...


I hope I have been able to help a little...if you still want to keep working through it I am certainly willing to help...


Regards,


Gordon.




.

[TURIN]

Turin...you can decrease your browser resolution by simultaneously pressing ctrl and minus keys...


Yes, I appreciate that but then all the text gets reduced and my eyes are not what they used to be. :{

[goarnaut]

Clive mentioned that the engine structural designers were probably the only ones calculating the component thrust and drag...you can be sure that is the very first thing they did...


In order to keep the engine together you have to know how much force is pulling in what direction...think about the burner and turbine interface...the burner is attached to the compressor...which is attached to the inlet duct...all of which are pulling forward with great force...and then you have the turbine making a drag force and pulling in the opposite direction...how strong do you make those bolts that hold things together...?...


So this stuff is more than just a curiosity...it is very real and that engine would have flown apart on the test stand if someone did not calculate all this in advance...


Regards,


Gordon.

[goarnaut]

Yes...ram drag is what we subtract from the gross thrust...ram drag is freestream speed (aircraft speed) times mass flow...so that is why thrust = mass flow * (jetpipe exit speed – freestream speed)...


However...if we want to do a control volume analysis of the engine...then we do it as mentioned...btw we can also do the whole engine as a single control volume and we will get the thrust the exact same way as I did for the inlet duct...using the same math...


And again it helps to make a sketch...we see from such a sketch that we can again use the impulse method to calculate thrust...


Let's say again we have a mass flow of 100 kg/s...and an inlet area of 1 m^2...at the nozzle the area is 0.5 m^2 and the pressure is let's say 2 times the atmospheric pressure...the speed of the jepipe exit is 500 m/s...the aircraft is flying at 250 m/s...~M8 at FL 350...


The simple formula for thrust is mass flow times jetpipe velocity...minus ram drag which is mass flow times freestream V...so our ram drag is 25,000 N...and our “gross” thrust is 50,000 N...from which we subtract ram drag of 25,000 N and we have net thrust of 25 kN...


We can get the same result if we now do a control volume analysis and take into account the pressure times area at the front inlet and aft nozzle respectively...the atmospheric pressure is 22.5 kN/m^2 so the front pressure pushing the engine 22.5 kN/m^2 * 1 m^2 inlet area = 22.5 kN...


The nozzle pressure is double...but the area is smaller by half...so it is a wash...we then take our inlet momentum (ram drag) and our exit momentum and we find that we have 25 kN thrust...


We could do this control volume thing for each component and still will get the same net thrust at the end...


The important thing is not to mix and match ideas...pick one bookkeeping method and stick with it...




Regards,


Gordon.



PS: being an Ontarian myself...I'm curious if you are related to the TV newsman of the same name...?


http://i49.tinypic.com/1t0cra.jpg

[goarnaut]

http://i49.tinypic.com/sdl00h.jpg

[CliveL]

Peter,

Have I gone off the rails here or is it something to do with airframe, ie inlet, and engine accounting?

It's just the accounting. Normally to calculate thrust one takes the momentum change from freestream conditions (ahead of the intake) to the exit conditions just behind the jet pipe nozzle or fan. Between those two 'stations' the momentum is fluctuating as the flow goes through intake diffuser/compressor stages/ combustion chambers etc. Momentum drag is calculated from that initial state ahead of the powerplant.

[Lyman]

Hello, Sir.

How far in front of the intake is freestream?

[peter kent]

No relation Gordan. I've disappointed a few people tho'(dentist,etc)

[Brian Abraham]

goarnaut and CliveL, you two gentlemen seem to have the background to be able to answer this question. Many assert that airflow through a turbine engine may reach and/or exceed sonic conditions with respect to the rotating components. I would have thought that unlikely, what with shock waves bouncing around inside the rotating bits. Would it be safe to assume that the temperature rise as the air passes through keeps the airflow subsonic?

Many Thanks.

[goarnaut]

Brian...yes the tip speed of the compressor and fan will almost always be supersonic in a modern turbine engine...typically from M1.2 to M1.7...even a turbocharger compressor will go supersonic at its higher pressure ratios...



The reason is that high wheel speeds are necessary to achieve high rates of work...remember kinetic energy is a function of speed squared...and compressor and turbine work are a function of rotational speed...so the higher our wheel speed the greater the work output per given mass flow...


The sonic shock waves do contribute to losses of course...although the shock energy actually helps to compress the air...the axial gas speeds through the compressor and fan will generally be ~M 0.4 to M 0.5...


The axial gas speed through the first turbine nozzle guide vane ahead of the turbine wheel will usually be choked...ie Mach 1...although this will typically increase to just slightly over sonic speed just aft of the NGV...about M1.1 or 1.2 at most...as the annulus increases in size...giving a bit of converging-diverging nozzle effect...


The turbine wheel tip speeds are generally subsonic...about M 0.8...or M 0.9...however since the speed of sound increases with temperature...and at hot section temps it will be more than double that of freestream speed of sound...the turbine actual speed in m/s (or ft/s) will be similar to the cold section...


It is really quite something to stop and consider the amazing power that modern gas turbines produce...a single turbine wheel of ~0.75 m diameter will make close to 40,000 hp...with a mass flow of about 100 kg/s through the engine core...about the size of a 50,000 lb thrust fan engine you would see on a widebody airliner...


Regards,


Gordon.


PS:One more thought about the intake thrust...the very first post said it best...with the intake making over 60 percent of thrust...the airplane is basically “sucking” its way through the air at M2...that's it in a nutshell...

[CliveL]

How far in front of the intake is freestream?

Not closer than the point at which the streamtube that contains the engine flow is first affected by the forward influence of the intake. Otherwise as far ahead of the intake as you wish to define it.
For subsonic intakes the closest point will vary with the ratio of engine mass flow to intake capture mass flow for that flight Mach number and intake area.If in doubt go further forward.
For supersonic intakes it will be the point of the cone for axisymmetric intakes or the leading edge of the ramps if 2D

[Tomtech]

Hello All,
I have been reading and studying for many, many years the topic of "Supersonic Inlet Thrust. I do not hold a degree in Aeronautical Engineering or physics, but feel that I have my head around the physics of propulsion, at least to a degree.

I am not posting to irritate others or create a flame war, I only seek the truth, and there is MUCH confusion regarding the issue of how supersonic inlets work, even among the engineering staff at NASA. I know, because I have spoken with them and exchanged much mail and documents regarding this interesting issue.

First of all, in trying to get of grasp of this, one must have an understanding of supersonic and subsonic fluid flow. Supersonic fluid flow is not magic, but it behaves very differently than fluids at subsonic flow, and the transition from one to the other must be kept in mind too. To state that "Most of the thrust of the SR-71 or Concord" comes from the intake is a misunderstanding of jet propulsion. Yes, there is positive pressure recovery in the inlet, and yes it is greater than free stream static pressure. Jet engine propulsion creates thrust thru momentum change, accelerating gas out of the exhaust. The "positive pressure" in the inlet system or that acting on the rear faces of compressor blades is what is know as "PRESSURE THRUST". It is used to explain rocket and jet propulsion to high school students. It is a VERY INEFFICIENT way of producing thrust, and is avoided by engineeers.

If you look at rocket nozzle designs, you will see a different flow regions the relationship of "pressure thrust" to change in momentum. Engineers would like to convert all pressure thrust to a change in momentum, however some pressure thrust will always be created. It is NOT the lions share of thrust, even in the case of the SR-71 or the Concord. The supersonic inlet on the SR-71 is very efficient and it is thru that (at high mach speeds) it performs the lions share of compression, freeing up compressor stages of the J58 engine. At the 4th or 5th stage (can't remember which one), 6 bypass ducts pass the compressed air directly into the afterburner inlet, so a large portion of the airflow is acting as a ramjet engine. One could state that (at high mach) the inlet is responsible for the compression and ramjet action, BUT it is NOT producing the greatest portion of total thrust anymore than the Pistons in you car create the greatest portion of the horsepower generated.

This misconception has been perpetuated and is a misunderstanding of how the entire propulsion system works together. When some state that "The engine falls back in it's mounts while the intake system transmits forward thrust to the airframe", you should be willing and able to offer proof. DO the math, you will not find "positive pressure" in the inlet system "pushing" on the rear end of inlet components, or doors to amount to "75% or whatever number" of the total thrust. If you are careful to study ALL of the inlet system, you will find, again at high mach much of the "overpressure" air in the inlet is dumped overboard thru ducts and vents, as the inlet can take in more mass flow than the J58 can effectively deal with with some bypassed around the core and mixed in the complicated exhaust system again with it's blow-in doors and de-laval type noxzzle.

I am not posting to offend anyone, I like most everyone here am interested in the exact workings supersonic inlets, and propulsion. If, I have overlooked anything or failed to take into account forces not considered, please call me on it and educate me. The supersonic inlets and exhaust systems on the SR-71 are extremely interesting and work together, but it is not "Sucking itself thru the sky. I find it incredibly that all of this was conceived, worked out and tested in the 1950's with slipsticks.................
Tomtech

[goarnaut]

Tom...please refer to my previous posts in this thread...I have even drawn little sketches to illustrate the physics...I do have a degree in aerospace engineering and I work in the industry...

It is no secret how an intake produces thrust...this subject is covered in all textbooks...here is a book from Rolls Royce that has an entire chapter devoted to this...you can view the entire book online here...

Rolls Royce - The Jet Engine (http://www.scribd.com/doc/51618999/Rolls-Royce-The-Jet-Engine)

Go to Chapter 20...Thrust Distribution...Figure 20-1 on page 208 shows the thrust distribution in the engine...the compressor...diffuser...and burner each make a forward thrust force...or gas distribution as the book calls it...

The turbine section and the jet nozzle make a rearward force or drag...when you subtract all the drag forces from all the thrust forces you end up with the engine's overall thrust...

This is the principle I have tried to explain in detail...it has to do with the fact that the sum of momentum and the pressure times area product is greater at the aft end of the compressor and diffuser and burner...than it is at the forward end...creating a force in the forward direction...

An engine inlet is a diffuser...that is why it makes a forward force...please read the chapter and try to do the math in there and you will understand how it works...

Regards,

Gordon.

[Tomtech]

Gordon,
Many thanks for replying to my post, I will, when I have time look at the materials you mention. No disagreement on the inlet being a diffuser. I think the mail area of confusion lies in the statements that point to the inlet static pressure being much above the outside static pressure, no argument there. The aircraft is not standing still, the inlet or the entire engine is not "thrusting against static pressuer outside the aircraaft". It is, rather thrusting against the "ram pressure", whic is MANY times geater than static pressure. It is the energy in ram pressure that the inlet can recover and convert to pressure rise, this, is one measure of inlet performance. As the (mach 3.1 or so) air is slowed thru a series of shocks, (in the case of the SR-71) it is terminated in the inlet section. The diffusion process builds pressure but at the expense of DRAG. Inlets produce drag, not thrust. You are not thrusting against outide pressure (which at 50,000 feet ain't much), but against the RAM pressure. If you want to say the the air compressed by the Sr-71 that is bypassed and fed to the afterburner inlet produces the majority of thrust, so be it, I am sure that is correct. I have "done the math", seems like everyone posting is not familiar with PRESSURE THRUST, which is covered in elementary text on any type of jet or rocket propulsion. To go even further and state that the engine is just processing airflow, while the inlet is doing the lion's share of the work is a false statement. It was stated by Kelly Johnson himslef, but later he was corrected by engineering and he, among friends admitted he was initailly wrong. Yes, I have done the math, and adding up and summing drag and positive pressures inside the engine is not necessary or even correct, unless you want ot calculate Pressure Thrust. In the end it is momentum exchange in the exhaust gases that creates thrust, and yeah, some state the "exhaust system " produes X amount of thrust. All propulsion components work together to provide thrust. I will study the book you mentioned, and try to see what you are saying. Again, thank you for the response, I know you for sure have done the math, and I will continue to educate myslef in this area. I will get back with you when I have done some more studying. I still find this an extremely intersting subject!

[Tomtech]

Gordon,
I have taken time to look at the book you referenced. I must say, I hope, as a practicing engineer you are not using that material, it was written for the "Sunday Reader". In turbojet engineering school, you would have worked out velocity triangles for axial flow compressors? Well, the bulk of energy put into the air is swirl energy, that is slowed (diffused) by the stator blades, resulting in compression correct? The stator blades absorb forces in the rearward direction releiving what the compressor "rotor" blades put into the foward direction (Pressure thrust again). Yeah, there is an overall foward pull on the compressor shaft. If so much "foward thrust" was generated by the compressor blades, then the Harrier would be moving foward while it is in hover? The book even shows gas flow for the Harrier. I have seen thrust distributions for turbojet engines before in far greater detail than the Rolls Royce book, If I get a chance, I will dig thru some and foward them to all for study. I am not trying to poke fun, I am glad you took the time to respond, as I my learn something. I will be back, thank's for taking time to read and think.

[CliveL]

Tomtech,

As one of the original Concorde inlet design team and as someone who has spent a fair bit of time recently trying to unpick the intricacies of the SR-71 design, I have to disagree with you gently.

The 'split' of Concorde's cruise propulsive forces generally referred to first appeared in Ken Owen's "New Shape in the Sky" many years ago. The data was given to him by members of the design team, and I think it is stretching things a bit to suggest that they 'misunderstood' jet propulsion principles.

I won't try to answer for the SR-71, but on Concorde (this is after all a Concorde thread :)) the intake, engine and final nozzle all had their own attachments to the airframe so it is reasonable and possible to enumerate their relative contributions. They all produced thrust. How you divide the total up between them is a matter of book-keeping conventions and as any accountant will tell you those are convenience variables!

Specifically, the 'split' will depend on how one divides the momentum drag out between the components. I can't remember (if I ever knew) the book-keeping that went with the Ken Owen's picture, but any reasonable division results in a considerable part of the total thrust acting on the intake mounts and another sizeable chunk on the final nozzle mounting.

What I think you may be missing is that although, of course, the thrust is obtained by imparting momentum to the mass flow through the engine, and although the design objective is to make sure that the static pressure of the flow exiting the final nozzle is as near ambient static as possible, the forces which must be applied to that mass to accelerate it to its final velocity are reacted as pressures on solid surfaces on the aircraft (or engine of course). In fact all forces on the aircraft (other than gravitational) ultimately come from pressures acting on solid surfaces.

So "pressure thrust", far from being an undesirable, is in fact an essential.

I'm going to be away for a few days, but if you feel you want more detail feel free to PM me.

[Mr Optimistic]

I think some ealier posts had the view that the engine could be deconstructed into individual parts which could be characterised separately with the total engine being the sum of the parts.

[Tomtech]

Gentlemen,
Well, I have gone back over all the fine posts made on this forum and re-introduced myself to aircraft propulsion and must offer my apology for my prior post (#143). I STAND CORRECTED and thank all of you for having patience with me. My misunderstanding was thinking of the intake as lone device "creating" thrust, not, rather as contributing to thrust by virtue of the great pressure recovery at high speeds. Also, I will take this time to correct myself, I completely miss applied the term "pressure thrust". As Gordon, and others have pointed out, ALL reaction forces in the engine and intake must be eventually felt as pressure forces distributed throughout the engine, intake and exhaust. I was using the "pressure thrust" term of positive pressure at the exhaust opening, which was not fully expanded to velocity, thereby contributing to thrust, but not as efficiently if it were converted to gas velocity. It was my miss application of the term that led me to a "serious miss understanding" of propulsion. I feel I have moved my understanding forward by quite a leap, and have you all to thank. I will read more in an effort to rid myself of ignorance and thank you all again for putting up with my lack of understanding and taking time to post and offer diagrams, it helped me much.
Tom