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Concorde engine intake "Thrust"

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Concorde engine intake "Thrust"

Old 11th Sep 2010, 13:52
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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.
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Old 11th Sep 2010, 14:37
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Concordeski

Superb stuff guys.

Can't signoff without questioning how Concordeski designers solved the problem!
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Old 11th Sep 2010, 18:33
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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 ?
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Old 12th Sep 2010, 01:31
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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.
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Old 12th Sep 2010, 08:26
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Landroger
Its a bypass? 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.
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
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Old 12th Sep 2010, 08:43
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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
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Old 12th Sep 2010, 08:49
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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
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Old 12th Sep 2010, 08:59
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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

Last edited by M2dude; 12th Sep 2010 at 10:13.
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Old 12th Sep 2010, 11:48
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And to think these were all done without the modern CFD codes
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Old 12th Sep 2010, 15:15
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Originally Posted by M2dude
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.
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Old 12th Sep 2010, 19:50
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Phew! Thanks Dude!

Many thanks dude, there is light indeed at the end of the tunnel - and not simply because it is on fire! 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?

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?

Thanks again for the extra info about the intake.

Roger.
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Old 12th Sep 2010, 20:24
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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
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Old 12th Sep 2010, 22:59
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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.

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Old 12th Sep 2010, 23:14
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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

Last edited by M2dude; 12th Sep 2010 at 23:46.
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Old 12th Sep 2010, 23:32
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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.
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Old 12th Sep 2010, 23:41
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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?
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.

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
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Old 12th Sep 2010, 23:53
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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 ?
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Old 13th Sep 2010, 10:07
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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.

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Old 13th Sep 2010, 11:18
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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
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Old 13th Sep 2010, 11:24
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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 ?
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