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By: - 8th June 2002 at 17:58 Permalink - Edited 1st January 1970 at 01:00
RE: F-15 with thrust vector?
[updated:LAST EDITED ON 08-06-02 AT 05:59 PM (GMT)]It was done a long time ago, and no, it was simply a test. It's not American way to slap on something, get a performance gain, and introduce it to the fleet. That would be too expensive, need to re train the whole fleet, etc....The Russians always slap on something and want to sell it asap even when it's not proven, shows you how desperate they are. By the way those canards are the tails of an F18!
By: - 8th June 2002 at 22:23 Permalink - Edited 1st January 1970 at 01:00
RE: F-15 with thrust vector?
It's also not the American way to save taxpayer's dollars and evolve the plane into something more cost effective either, and instead rely on a strategy of phased obsolescence. An evolved aircraft would not only cost less, but training and integration costs would be much less than to attempt to deal with an entirely new and unproven plane.
The flat nozzle system used by the American technology demonstrators are less efficient and weigh considerably more than the rounded nozzle system used by the AL-31FP. Furthermore, it's only 2D (so is the swivel on the AL-31FP), with only one axis, unlike the full swivel (dual axis) axisymetrical thrust vectoring system (AXEN) demonstrated on the AL-31FN that was shown at Zhuhai 2000.
Here is a more interesting technology experiment.
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By: - 9th June 2002 at 01:35 Permalink - Edited 1st January 1970 at 01:00
RE: F-15 with thrust vector?
It was a study done in the late eighties as a result of part of the USAF ATF requirement for the a/c to be able to take off and land on a reduced length runway resulting from bomb damage. I cannot remember the name of the programme, but the Eagle was modified first with canards, then the 2 dimensional thrust vectoring nozzles with thrust reversal. This Eagle was one of the first a/c to employ such a system. The programme was considered successful, such that the requirement was written into the ATF spec. When it became obvious that an ATF equipped with such a capability would be too expensive, they dropped the requirement. As we all know, the F-22 retained the 2 dimensional vector capability, giving Lockheed an edge in the ATF flyoff.
By: - 9th June 2002 at 05:39 Permalink - Edited 1st January 1970 at 01:00
RE: F-15 with thrust vector?
another one.....
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By: - 9th June 2002 at 07:21 Permalink - Edited 1st January 1970 at 01:00
HIMAT..
Didn't have vectored thrust.
By: - 9th June 2002 at 14:45 Permalink - Edited 1st January 1970 at 01:00
RE: HIMAT..
In fact, a 3D thrust vectoring version was also tested. Long before any Flanker variant. ;-) The programme was called F-15 ACTIVE. The pics show the modified engines good.
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By: - 9th June 2002 at 14:49 Permalink - Edited 1st January 1970 at 01:00
RE: HIMAT..
btw KabirT: Your pic shows the 3D version aswell. Didn't see it earlier. The 2D nozzles looked like the Raptors and featured thrust reverse too.
By: - 9th June 2002 at 15:27 Permalink - Edited 1st January 1970 at 01:00
RE: HIMAT..
Agreed, that is indeed a 3D thrust vector nozzle.
By: - 9th June 2002 at 20:43 Permalink - Edited 1st January 1970 at 01:00
RE: HIMAT..
[updated:LAST EDITED ON 09-06-02 AT 08:47 PM (GMT)]you see, the problem here is how much ignorance there are, and when people first saw a russian fighter with TVC people automatically assume they did it first because they don't see it elsewhere. In fact the Americans have the most experience in TVC. The axis symmetric TVC design was around since the early 90s. It is truely axis-symmetric and very light weight design too. The Russians have admitted being late in this field and only those who don't know assume they are advanced just because they saw it at some trade show. Besides motion, there are others concerns on a advanced TVC design. The weight of the unit is very important, and again, the US is at the forefront, with their units being much much lighter. Infact, the US have already tested "stealth" versions of both nozzle and Fan blade for a face mounted engine. About 2D versus 3D...that yaw direction doesn't buy you too much for the amount of weight penalty, that's why the F22 (and Boeing's JSF) uses 2D only. Remember, it also have to be very stealty and very efficient in cooling for reduced IR signature. Like always, there are trade offs. What i would give the Russians credit is that their TVC is mechanically very simple, but very crude too. Their axis symmetric version (not the one for the Su30MKI) first shown recently have the "feathers" split out, where the American design seals and conforms much much better.
The HIMAT is highly configurable and i think it uses a J85 engine. I wouldn't be surprised that it was also mounted with TVC sometimes during its career. The data from the HIMAT is not reported (classified) at all, except all i've heard is that a lot of "advanced" manuevering concepts for the US comes from the HIMAT experiences. Very successful program.
By: - 9th June 2002 at 20:55 Permalink - Edited 1st January 1970 at 01:00
TVC...
I've forgot to mention that a while back i was explaining that TVC is only used at low speed and why. The reason is that at supersonic speeds, aerodyanmic methods are still the king. Being easier and lighter. However, 3D TVC can work (and desired in terms of performance) at supersonic speeds only if the engine mounts are strong enough and light enough. So far it's still not...at least to what aeroengineers consider as a good tradeoff...hence another reason why the F22 is still 2D. Remember one important series of tests for the F22 a while back "thrust reversing at supersonic speeds"...it most likely includes thrust vectoring at supersonic speeds. It was very subtle and not many noticed the significance.
By: - 10th June 2002 at 00:04 Permalink - Edited 1st January 1970 at 01:00
RE: TVC...
If your TVC nozzles happen to be pretty light, chances are, they're not very durable either (made of carbon fibre). Seems to me there is a reason why the US reverted back to the flat nozzle. And contrary to what you said, I don't see any reason why the Russian units are heavier as you supposed, or that their sealing is less effective, or that they don't test their units as well or rush them to make a showpiece.
Here are the words of Viktor Chepkin himself of Saturn Lyulka. Note that the interview was done in 1998, and thus Russian research on TVC goes back at least 12 years from that year.
"This is a mere technological task. A real problem is controlling the thrust vector. We have been trying to solve that problem for 12 years.
- What problems did you face while developing a swiveling nozzle?
- A lot of spears had been broken in choosing the very system of thrust vector deflection. The Americans went one way, we chose another, quite different to boot. While developing the swiveling nozzle, we encountered a most formidable problem - that of the seal between the moving and static parts of the nozzle. The exhaust gas pressure here reaches seven atmospheres with temperature running as high as 2000 degrees centigrade. The sealing of the point where two parts of the engine - the static and moving ones - meet, must be ideal, since the gas leakage here means a fire on board the aircraft. The second important problem is how to provide reliable control of the nozzle itself. Fancy that: during the take-off, the nozzle at an altitude of 15 m deflects on its own into the pitch position. In 1-1.5 seconds, the crash will be bound to happen. At a low speed, the pilot is absolutely unable to counter the sudden negative pitching moment, since the alteration of the thrust vector at full reheat is enormously powerful exceeding the effectiveness of the aircraft control surfaces.
Thus, developing the TVC version of the AL-31F engine, we had to solve most complicated technical problems and look for ways to ensure the highest degree of reliability of the system as a whole. Many a year of theoretic and experimental research resulted in successful resolution of those problems, and, for two years now, the AL-31FP-powered Su-37 fighter performs brilliantly at international airshows displaying magnificent maneuverability. Which is not the case with its foreign counterparts. There have not been any American or European combat aircraft featuring TVC engines at public airshows, though their development has been going on abroad for quite a while. Maybe, there is nothing to show yet...
- The AL-31FP boasts an axial exit nozzle. That is to say the nozzle is circular. It is known that your overseas counterparts used to try to solve the thrust vector control problem via the use of a flat nozzle that should be easier to swivel. What do you think of that?
- 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.
AL-31F turbofan engine
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.
Su27 fighter powered by AL-31F engines
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. "
By: - 10th June 2002 at 20:27 Permalink - Edited 1st January 1970 at 01:00
RE: TVC...
[updated:LAST EDITED ON 10-06-02 AT 08:29 PM (GMT)]Crobato, you are using a Russian source to say about American technology? If i use American source to say about Russian technology, everybody here would cry foul. As to the attitude of "not showing meaning nothing to show", that's very unprofessional in the military technology field. Showing what you consider advanced is not practiced with US military hardware too much, unless that component is ready for export. Which unlike Russians and French and many others, US weapons exports are limited by politics not availability. A more technical example, the stresses the guy said sounds scientific, but he's not addressing the issue of supersonic conditions where the stresses at the nozzle is not the concern, but it's the stresses for the engine as a whole, all the way to the mounting pins. As to adding very little weight, how much is very little. Again, no comparison is made to how much the F22 nozzle weighs, which you can't it's classified. Again, without data, you assume it must mean the Russians are better because some guy told you it "weighs little bit more". Very exact science there. Aerospace is a field very very deep in details, without much you really can't compare too well except using your own scientific judgement...unless you have the benefits to see some real data. You know a rocket engine swivles right? You do know about it's operating conditions right? There's some hint on it's practicality merit, in the context that many rockets are unreusable. But, like always, Russians are very good in mechanics, so i could be wrong. But then again, not too advanced from what i know about it.
By: - 10th June 2002 at 22:35 Permalink - Edited 1st January 1970 at 01:00
RE: TVC...
It just obvious for me that you really didn't read the article closely. Are you going to assume that you know the mind and data of the people of Saturn-Lyulka and know what they ignored? Can you ask why politics have decided to use flat swivel nozzles instead of axial nozzles? As for rocket engines, that's different. If you read the article closely, the nozzles of rocket engines can afford to be burned out in one use, while those of jet engines have to last like 1500 hours or so.
By: - 10th June 2002 at 22:50 Permalink - Edited 1st January 1970 at 01:00
RE: TVC...
[updated:LAST EDITED ON 10-06-02 AT 10:53 PM (GMT)]>It just obvious for me that you really didn't read the
>article closely. Are you going to assume that you know the
>mind and data of the people of Saturn-Lyulka and know what
>they ignored?
Exactly my point, i didn't say based on your report blah blah blah about the Russian system, i said based on what i know of on the Russian system.
>Can you ask why politics have decided to use
>flat swivel nozzles instead of axial nozzles?
Again, it is not why "politics" use flat nozzles, that's rediculous of course. The point is that what people outside of US, outside of the industry only knows what is available when it's export released, which means that the technology YOU get to know is already OLD. That is politics. What you don't know and not necessary classified is a huge amount of data categorized as "export/reprint restriction documents". You obviously haven't and won't see that. In this light, many defaults to what ever "others" said. But if i know exactly what "others" are saying because i know what their charts look like and i know what "our" charts look like, well....I know I know, you guys always want sources, but sometimes you have to take somebody's word for it, if not, it's ok too, everybody have the freedom to believe what they want, but my point is everybody have the basic tools of basic scientific knowledge and decide for yourself.
>As for rocket
>engines, that's different. If you read the article closely,
>the nozzles of rocket engines can afford to be burned out in
>one use, while those of jet engines have to last like 1500
>hours or so.
Exactly the point again, trying to adopt something from other existing designs for a similar but not the same purpose means that optimization is not as thorough as possible. It is truly not the state of the art. I may be somewhat "un-nice" sometimes, but it seems to me that many times people jump on a few pieces of english and rewrite my sentences. Sorry, i should remember that sometimes it is second or third or fourth or more language to others. I would probably be in the same situation if i visit for example some Spanish speaking boards.
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By: KabirT - 8th June 2002 at 16:28
this pic shows an F-15 with thrust vectoring capabilities? When was this tested and what was the outcome? What was the main reason behind this test? USAF planning to induct some types like these at that time?
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