Why the Russians don't use "flat" TVC nozzles

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firstimpulse

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Unread post16 Jan 2013, 17:57

From Victor Mikhailovich Chepkin himself, Director General/Designer General of Lyulka-Saturn. From 1998.

"In the late 1980s, we were engaged in the development of the flat nozzle too and conducted a thorough research. The Ufa-based Motor Scientific Production Enterprise under the guidance of Chief Designer Alexei A. Ryzhov manufactured an experimental flat nozzle that underwent a series of tests. The conclusions were as follows. Presently, the flat nozzle has two inherent snags which, in principle, have not been dealt with yet. Firstly, the turbine is round but the nozzle is flat with a distance between them being small. The distance cannot be increased because this would lead to an increase in the overall length of the aircraft, a loss of thrust, etc. While transforming the circular gas stream into the flat one, the nozzle, developed by Mr. Ryzhov, was losing 14-17% of thrust. Unfor-tunately, the gas stream cannot be "bent" as we would like it to. It has its own laws too. So far, no one has managed to transform the circular gas stream into the flat one without losing thrust. The very same snag was hit by the Americans in developing their F-117 featuring a non-afterburning engine. Such engines lose approximately 15% of thrust too. However, the F-117 is a specialised Stealth aircraft with the main requirement of ensuring "invisibility". It does not need a real good thrust/weight ratio. That is why the Americans put up deliberately with an unavoidable loss of thrust but benefited from reduced signatures.

Secondly, the other primary problem is weight. The circular TVC nozzle produces only tensile stress while the flat one exerts bending stress as well. Those stresses require special measures to be taken to ensure the nozzle strength in order to avoid deformation of the nozzle. Those measures mean additional weight. The flat nozzle made of metal is heavier than the circular one by approximately half a tonne. Mind you, the whole AL-31FP fitted with its circular swivel nozzle weighs a little bit more than 1500 kg only. So, the use of a flat nozzle implies an extra tonne at the rear of a plane (two-engine are meant here, which make up the most of modern fighters). The problem can be circumvented through the use of the "carbon-carbon" materials which have low specific weight and can stand high temperature. But they burn in the end anyway, since they are based on the very same coal. Nobody has solved the problem of preventing carbon-carbon units from burning during their operation as part of an aircraft engine. Currently, such materials covered by a thick layer of fire-resistant ceramics are used only in manufacturing the control surfaces of rocket engines. The latter are actually disposable since their operation never exceeds 40-50 seconds while an aircraft engine service life amounts to 1,000 hours or more.

So, the problem of ensuring an effective long-term protection of the non-metal nozzle is still to be solved. Thus, development of the flat nozzle encounters two problems - the loss of thrust (and it is not resolved even in theory) and the extra weight. With those two problems in mind, we stick to the circular nozzle."


So, I would assume this means the Russians are quite far behind in terms of materials and manufacturing (not surprising), or the F-22 can't use the full potenial of its engines. Or the information here is outdated.
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haavarla

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Unread post16 Jan 2013, 22:50

There are more to consider. Operational cost related to such flat nozzles, service/operational cost. And development cost/time.

Is it worth the little extra IR suppresion, the jet plume from the F-22 is still quite hot for any IR(IRIST) or other optical infrared systems to spot it.
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popcorn

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Unread post17 Jan 2013, 04:16

How credible are reports that PAK-FA will adopt rectangular nozzles in the future? Hasn't Saturn secured a patent for this tech?
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Prinz_Eugn

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Unread post17 Jan 2013, 04:56

I do remember hearing that there is some thrust drop-off from using 2D nozzles in the F-22.
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linkomart

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Unread post17 Jan 2013, 18:00

IMHO Everything that Victor Mikhailovich Chepkin says is still valid. Look at the development from F-22 to F-35. From Square to Circular (sort of).
Circular is Lighter.
Circular have less losses.
But
Circular have higher RCS and IRS....
No free lunch

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Unread post17 Jan 2013, 19:49

Haav, The Raptor has still been shown to be stealthy enough to out smart the latest IR missiles, and I believe the goes for shots fired from 6 o'clock too.
If there is a drop in thrust, I wonder if the amount of drop goes up as the engine power rating goes up? As in, 15% for an AL-31 and 17-18% from a F119?
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linkomart

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Unread post17 Jan 2013, 21:26

I'd say that the raptor have less power loss than the russian design.
IIRC the Square exhaust on the SU-27 prototype had quite high aspect ratio, where as the Raptor have a low aspect ratio.

This makes the tangential flow smaller, hence the Power drop should be smaller.

It's my 5 cent guess
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Unread post18 Jan 2013, 11:40

Starting from 7:45 into this vid there's a bit of detail on the Sukhoi experiments with the flat nozzle. Basically says that IR reduction of flat nozzles is quite significant and impressive.

http://www.youtube.com/watch?v=4Kk9UxB7eLE
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nicktheaircraftexpert

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Unread post03 Jul 2015, 03:23

firstimpulse wrote:Haav, The Raptor has still been shown to be stealthy enough to out smart the latest IR missiles, and I believe the goes for shots fired from 6 o'clock too.
If there is a drop in thrust, I wonder if the amount of drop goes up as the engine power rating goes up? As in, 15% for an AL-31 and 17-18% from a F119?


QWIP is the next generation of IR missiles and infrared sensor in general it can detect colder targets at longer ranges and has better resolution
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Unread post03 Jul 2015, 13:54

The PW-F119 was developed from the PW-5000 prototype and has always had Flat nozzles.
Static level thrust measurements on the PW-F119 has always resulted to 35,000 lbs of thrust which was the requirement for the ATF program.

With round nozzles the engine may produce a little more thrust, as the PW-F135 which is a variation of the F119 produces approximately 23% more thrust than a single F119. Of course internal modifications may also be responsible for the large increase in thrust measurement but undoubtedly the nozzle shape is also partly responsible.
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sergei

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Unread post03 Jul 2015, 20:13

As far as I understood from the explanation of the engineer from "Sukhoi"( at MAKS 2013) on the engine stage 1 use the flat nozzle do not plan.
"Too strong degradation of characteristics"
Currently T-50 has a number of advantages over the F-22 in the aerodynamic characteristics .
Which leads to F-22 engine provides less useful thrust ( Pratt & Whitney F119-PW-100 156+ kN vs NPO Saturn izdeliye 117 147kN ).
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disconnectedradical

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Unread post03 Jul 2015, 23:03

nicktheaircraftexpert wrote:
firstimpulse wrote:Haav, The Raptor has still been shown to be stealthy enough to out smart the latest IR missiles, and I believe the goes for shots fired from 6 o'clock too.
If there is a drop in thrust, I wonder if the amount of drop goes up as the engine power rating goes up? As in, 15% for an AL-31 and 17-18% from a F119?


QWIP is the next generation of IR missiles and infrared sensor in general it can detect colder targets at longer ranges and has better resolution


What? As far as I know QWIP is for long wave IR, whereas the more modern IRSTs operate in the mid-wave region. In any case, modern IR seeker heads have FPA imaging systems, so fooling them will be increasingly difficult short of DEW.

I suggest reading about IR wavelengths before spouting off without supporting evidence.

http://www.photonics.com/Article.aspx?AID=51523
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Unread post04 Jul 2015, 03:05

sergei wrote:As far as I understood from the explanation of the engineer from "Sukhoi"( at MAKS 2013) on the engine stage 1 use the flat nozzle do not plan.
"Too strong degradation of characteristics"
Currently T-50 has a number of advantages over the F-22 in the aerodynamic characteristics .
Which leads to F-22 engine provides less useful thrust ( Pratt & Whitney F119-PW-100 156+ kN vs NPO Saturn izdeliye 117 147kN ).

You know that the 156+kN is measured WITH the nozzles right? It does not have less thrust.
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sergei

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Unread post04 Jul 2015, 08:36

sprstdlyscottsmn wrote:
sergei wrote:As far as I understood from the explanation of the engineer from "Sukhoi"( at MAKS 2013) on the engine stage 1 use the flat nozzle do not plan.
"Too strong degradation of characteristics"
Currently T-50 has a number of advantages over the F-22 in the aerodynamic characteristics .
Which leads to F-22 engine provides less useful thrust ( Pratt & Whitney F119-PW-100 156+ kN vs NPO Saturn izdeliye 117 147kN ).

You know that the 156+kN is measured WITH the nozzles right? It does not have less thrust.


"less useful thrust"
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Unread post04 Jul 2015, 16:18

and how is having more thrust less useful. Your argument is pure hyperbole. It has MORE thrust. Would it have even more still with a round nozzle? Possibly, but as it stands it STILL has MORE with the rectangular nozzle. The F-22 has exceeded it's designed speed significantly. No one could ever say it is lacking in thrust.
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