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

New and old developments in aviation technology.
  • Author
  • Message
Offline

firstimpulse

Senior member

Senior member

  • Posts: 313
  • Joined: 12 Jan 2012, 18:21

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.
Offline

haavarla

Banned

  • Posts: 873
  • Joined: 28 Jul 2009, 19:36

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.
Offline

popcorn

Elite 3K

Elite 3K

  • Posts: 3212
  • Joined: 24 Sep 2008, 08:55

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?
Offline

Prinz_Eugn

Forum Veteran

Forum Veteran

  • Posts: 928
  • Joined: 03 Aug 2008, 03:35

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.
"A visitor from Mars could easily pick out the civilized nations. They have the best implements of war."
Offline
User avatar

linkomart

Active Member

Active Member

  • Posts: 229
  • Joined: 31 May 2010, 07:30
  • Location: Sweden

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

my 5 cent
Offline

firstimpulse

Senior member

Senior member

  • Posts: 313
  • Joined: 12 Jan 2012, 18:21

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?
Offline
User avatar

linkomart

Active Member

Active Member

  • Posts: 229
  • Joined: 31 May 2010, 07:30
  • Location: Sweden

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
Offline

munny

Forum Veteran

Forum Veteran

  • Posts: 589
  • Joined: 13 Jan 2010, 01:39

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

Return to Technology

Who is online

Users browsing this forum: No registered users and 0 guests