Concorde engine intake developed "Thrust"
 

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.:)

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.

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

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

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").
I hope that this clarifies things guys, regards to all.

Dude :O

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.

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.

See also: "Can Vmg exceed the V of a jet exhaust?"
 

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.

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.

Thrust from the INTAKE????
 

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.

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..........

The Division of Powerplant Thrust in Concorde
 

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: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/a...rde/Thrust.jpg[/font]

http://i991.photobucket.com/albums/a...rde/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

And one more thing....
 

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

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?

last year
 

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.

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?)

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:
http://i337.photobucket.com/albums/n...ne_Airflow.jpg

b377
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:
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

By George, I think he's got it.
 

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.

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. I once ferried a prewar a/c with the cowl removed - it was 15 kt slower without the cowl fitted.

Concordeski
 

Superb stuff guys.

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

I think the problem is the word 'thrust'
 

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 ?

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.

Landroger
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.

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

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

b377
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

Mr Optimistic
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

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

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.

Phew! Thanks Dude!
 

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:

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.

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

MrOptimistic
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

DozyWannabe
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

M2Dude
 

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.

Landroger
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.
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

CJ
 

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 ?

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

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/a...Powerplant.jpg

I agree
 

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