J-20... The New Generation Fighter III

Originally Posted by latenlazy

I stand by the notion that the J-20 will need TVC for both stealthier cruise flight and supersonic maneuverability. I COULD be wrong on that, but I haven't heard anything yet that would dissuade me.

I respectfully concur!

Originally Posted by latenlazy

I don't think that's the only argument for why the J-20 needs TVC. Having TVC can also help minimize deflections during cruise flight for signal management purposes and aid in supersonic maneuverability when using control surfaces induce drag penalties. None of these reasons assume that the J-20 will fly like an airliner without it. The first one assumes that TVC can help preserve stealthy flight because the J-20 is a VLO platform, and the second assumes that TVC can offer some benefits over control surfaces in the supersonic regime because the J-20 is meant to supercruise. I have not yet heard an argument for why these are not valid reasons.

The first reason is already rebutted many times. A large enough deflection that can hurt RCS would mean the aircraft is maneuvering for its life, at which point the aircraft has long been seen and RCS is meaningless. The rebuttal for the second reason was in my very last post. Namely, the deficiencies that proponents of TVC claimed to rectify don't really exist on a canard configuration in the first place.

Originally Posted by Engineer

The first reason is already rebutted many times. A large enough deflection that can hurt RCS would mean the aircraft is maneuvering for its life, at which point the aircraft has long been seen and RCS is meaningless. The rebuttal for the second reason was in my very last post. Namely, the deficiencies that proponents of TVC claimed to rectify don't really exist on a canard configuration in the first place.

On the first point, you originally brought up that point to refute that canards were not inherently detrimental to stealth. That is a good point, but canards not being detrimental to stealth does not mean deflections are not detrimental to stealth. Canard deflections are as detrimental to stealth as any other form of control surface deflections.

On the second point, you haven't really refuted the supersonic maneuverability claim. The crutch of that claim is the notion that control surface deflections (canards, tail planes, etc) induce greater drag penalties at supersonic speeds than vectored nozzles. You're either going to have to show me that control surface deflections don't induce so much drag that they make TVC favourable, or else show me that whatever the net benefits/costs of TVC, taking the drag penalties for surface deflections at supersonic speeds is still the better option.

IMO since flattening the nozzles reduces thrust but also suppress IR signature, they should design a circular TVC for J-20 that can be flattened, if such a one is in the works. That way the pilot can have the option of lowering his IR sig on approach or rounding his nozzles to squeeze every juice out of the engines when needed.

Originally Posted by no_name

IMO since flattening the nozzles reduces thrust but also suppress IR signature, they should design a circular TVC for J-20 that can be flattened, if such a one is in the works. That way the pilot can have the option of lowering his IR sig on approach or rounding his nozzles to squeeze every juice out of the engines when needed.

i don't think that's a feasible engineering

besides, you need a heavy and thick nozzle shielding like the ones on F-22 for it to act as IR suppressor, the shape of the nozzle just happen to be flat as it only employs 2D TVC

IMO a flat nozzle won't happen on the J-20, the position of engines are way too aft for such modification

Originally Posted by latenlazy

On the first point, you originally brought up that point to refute that canards were not inherently detrimental to stealth. That is a good point, but canards not being detrimental to stealth does not mean deflections are not detrimental to stealth. Canard deflections are as detrimental to stealth as any other form of control surface deflections.

That point is a rebuttal to the argument that deflection hurts RCS. Please read it again, as I even have the word "deflection" in my reply.

Originally Posted by latenlazy

On the second point, you haven't really refuted the supersonic maneuverability claim. The crutch of that claim is the notion that control surface deflections (canards, tail planes, etc) induce greater drag penalties at supersonic speeds than vectored nozzles. You're either going to have to show me that control surface deflections don't induce so much drag that they make TVC favourable, or else show me that whatever the net benefits/costs of TVC, taking the drag penalties for surface deflections at supersonic speeds is still the better option.

I already did. See points #2 and #4 on post #4189. Hence I said what I have said in my previous two posts.

Another argument going against TVC on the J-20 is that TVN will require lengthy testing which will delay the entry date of the aircraft. This is because TVC is an unproven technology for China with no known flying hours on a technology demonstrator. People who do not like J-20 would obviously be happy to see such a delay, but not so for PLAAF who wants to deploy the aircraft on 2017 if possible. If you optimistically assume WS-15 becomes available on 2015 and only requires two years to complete tests on the J-20, then PLAAF's expectation could barely be met. There is little reason to make things more complicate with untested technologies and delay the delivery date by years.

btw, this intrigued me, for all the J-20 photos we've seen, i don't remember any clear shot at the engine nozzles

What are you talking about?

well certainly not my standard, besides i remember a better one than that, an early photo of J-20 in taxi

edit : i think this is as clear as you can get, and perhaps it can illustrate why i opined against F-22 like 2D nozzle

Originally Posted by Engineer

The S-47 actually uses triplane configuration. So even though the aircraft has tailplane, the aircraft is not traditional configuration.

I know, and that's not what the translated quote said. All it said was that there was no plane with FSW and tailplane.

But that's just the translation, which is why I asked if they meant something more specific, like "There is no plane with FSW and tailplane in a traditional configuration", or something similar.

Since I can't read Chinese, would someone mind revealing if the original Chinese was more specific, or if the translation is as good as it gets?

Here is my attempt, but it will be great if another person can provide an alternate interpretation.

Canard can enhance the advantages brought forth by use of forward swept wing. The nature of forward swept wing requires the wing root to be placed near the tail of the aircraft. This makes placement of tailplane awkward, but placement for canard is very natural. Existing aircraft with forward swept wing all uses canard configuration. Furthermore, interactions between canard and wing can improve flow along the wing root, which reduces the strength of shock wave, thereby enhancing lift while reducing drag.

Originally Posted by Engineer

That point is a rebuttal to the argument that deflection hurts RCS. Please read it again, as I even have the word "deflection" in my reply.

We'll have to agree to disagree then (about deflections hurting signals management)

I already did. See points #2 and #4 on post #4189. Hence I said what I have said in my previous two posts.

Another argument going against TVC on the J-20 is that TVN will require lengthy testing which will delay the entry date of the aircraft. This is because TVC is an unproven technology for China with no known flying hours on a technology demonstrator. People who do not like J-20 would obviously be happy to see such a delay, but not so for PLAAF who wants to deploy the aircraft on 2017 if possible. If you optimistically assume WS-15 becomes available on 2015 and only requires two years to complete tests on the J-20, then PLAAF's expectation could barely be met. There is little reason to make things more complicate with untested technologies and delay the delivery date by years.

Points 2 and 4 make comparisons to tail planes, not tvc. Point 3 discusses the benefit of having both canards and tvc.

We know they at least have tested tvc before. Furthermore nothing prevents parallel development or introducing the feature later on. If they're willing to do that with a new engine, they could certainly do that with tvc itself. New technology hasn't nor shouldn't be prevented from being introduced to new designs. Personally I think there is plenty of time for them to test it on the J-20 and still get to the intended date of production. We are already contemplating the PLAAF's backup options in case the ws-15 isn't ready. It would not be unnatural to consider tvc installed onto the ws-15 as part of that uncertainty.

Originally Posted by Engineer

Here is my attempt, but it will be great if another person can provide an alternate interpretation.

Canard can enhance the advantages brought forth by use of forward swept wing. The nature of forward swept wing requires the wing root to be placed near the tail of the aircraft. This makes placement of tailplane awkward, but placement for canard is very natural. Existing aircraft with forward swept wing all uses canard configuration. Furthermore, interactions between canard and wing can improve flow along the wing root, which reduces the strength of shock wave, thereby enhancing lift while reducing drag.

Thank you very much. That is a lot more specific. Can't debate anything there.

Never seen this image before ....