Shenyang next gen combat aircraft thread

Schwerter_

Schwerter_

Junior Member
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secretprojects said:
I guess a more productive line of discussion is - why use tiperons at all? Its an unconventional solution.

I don't find a lot of research happening in the West at least, and most mentions are in the context of hypersonic designs, and effectiveness at low and highly supersonic speeds.

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I've poked around a bit on this topic and it seems that the simplest (albeit almost certainly not the whole picture) explanation is that 601 has been studying this form of control surface for well over a decade and found some good things going for it.

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This is a paper from 2010 on AMWs and tailless aircrafts, and the author Zuo Linxuan is currently deputy director of 601.

Quick summary:
  • symmetrical pitch-up causes a reduction in lift, increase in drag and creates nose-up moment (essentially working as airbrakes)
  • Only turning one side creates yaw moment while having little effect on CL, although it comes with substantial roll and pitch moments
  • AMWs' yaw moments are weakly coupled to both AoA and sideslip angle, which means it remains effective during aggressive maneuvering
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This isn't written by anyone directly related but still contains some interesting points on splitting rudders
  • More suited for high aspect-ratio flying wings while AMWs are considered by this paper to be more suitable for low aspect-ratio ones.
  • Moment on splitting rudders increase drastically with the increase of airspeed (due to aerodynamic center being far aft of the axis of rotation) which means that it's only suitable for low-speed use.

My personal takeaway from this is that 601 probably chose the AMWs because they have a better understanding of it due to years of prior research, and that it is better suited for high-speed use and remains effective in aggressive maneuvering, both of which are important points mentioned in Sun Cong's paper detailing 601's vision of 6th gen fighter's air combat philosophy.
 
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Nx4eu

Nx4eu

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secretprojects said:
Having one of my members who's an interesting guy, a regular poster with an interesting history in the industry being essentially made fun of here wasn't nice.

My forum secretprojects.co.uk has been around for 19 years and has some very knowledgeable members, though not many China Aviation experts. Which is why I also hang out here and other places.

I was actually a member here back in 2006 and other forums as 'overscan' or 'aerospacetech'.
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This is exactly the reason why I acted like so in my response, I agree your forum has many knowledgeable members. However I sometimes read comments from your members that are a bit dismissive to Chinese aviation, often due to the lack of knowledge in Chinese aviation.

The environment between this forum and your forum as you can tell are quite different. I see your forum as slightly more professional on the technical side, which is why my comment was not as rash while responding to him on there, however on this forum, there exists a bit more of a sense of Chinese nationalism which you could probably tell.

The notion that a former engineer for the B-2, and YF-23 implied that Shenyang Engineers installed useless control surfaces that flap around and do nothing on their aircraft would seem like a pretty arrogant American opinion from this forums perspective wouldn’t you agree?

This is why I think forum members should keep discussions in one forum separate from another, as not many are in both and may not see the nuance of responses.
 
T

taxiya

Brigadier
Registered Member
Mearex said:
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interestingly at this moment in the video the right wingtip seems to be deflecting downwards which should cause the right wing to lift, making the aircraft roll to the left when it's rolled to the right. Perhaps it's trying to counter the right-rolling moment caused by the left wingtip deflecting downwards earlier in the video.
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The wing tip tilting creates moments in yaw, pitch and roll all at once. Besides the roll you mentioned. The aircraft will also pitch down because the wing tip is located behind the center of mass.
Mearex said:
As cool as all moving wingtips look, it does take more work to induce a pure yaw moment compared to split air brakes like on the J-36 because split air brakes are symmetrical and don't induce roll. Makes you wonder why Shenyang chose the former. I'm also still hoping that its flat nozzles can have yaw TVC. That will truly be alien.
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This paper is saying that all moving wing tip is a good choice for high speed tailless flying wing design. I think it implies that split-flaps are not good enough for extreme demand on maneuverability after vertical stablizer is removed.
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another paper recommended all moving wing tip together with TVC for the design
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Both papers are from early therotical research by BUAA. This seems to mean that it is not choices by SAC or CAC to compete for the same role, but PLAAF and AVIC choose both designs for different missions. I guess SAC fighter is somewhat replacing J-20 and focuses on maneuverability (more traditional role), which J-36 is filling a totally new role as a central hub. The two together with UAVs would make the complete fighting network.

Once again, as PLA observers we need to drop the inertial thinking formed by US observation. There is no US style competition in PLA weapon programs. Instead PLA gather everyone for ideas and assign A to do one thing and B to do another thing. "competition" only exists during pre-study/conceptual study phase. PLA will not waste money on people doing the same thing.
 
S

secretprojects

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The US ICE program Phase 2 in 1997 concluded the all-moving wing tip (AMT) was the best control surface for manoeuvrable tailless fighters.
Three AMT variations were tested that included small and large unskewed tips with chordwise hingelines and a third skewed tip with a swept hinge line. On the skewed tip, the pivot trunion was swept aft such that the AMT-wing break was aligned with the opposite leading edge on the land-based configuration (250 hingeline sweep) or the opposite wing-fold line (100 hingeline sweep) on the carrier-based configuration. Skewing the pivot trunion aft improved AMT control effectiveness because favorable side forces were generated when the control surface was deflected trailing-edge down. These side forces acted aft of the aircraft center-of-gravity and thereby increased AMT yaw effectiveness by combining with the yawing moment increments produced by the drag forces on the device. On the land-based configuration, the skewed AMT generated 25% to 30% more yawing moment per unit of control surface area than the unskewed AMT over a large AOA range, which meant that a smaller surface could be used to obtain the same level of control power. AMT deflection generated yaw control power throughout the AOA range that was tested, and favorable rolling- and pitching-moment increments were produced for most of these AOAs. AMT yaw effectiveness was not significantly affected by either sideslip or rotation rate, which is a highly desirable trait. AMT deflections provided sufficient control authority for spin recovery when deployed against the direction of rotation. Based on these results, the AMT was judged to be the best overall effector of all the concepts investigated during the ICE program for full-envelope operation of a highly maneuverable tailless fighter.
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Agree that everything points to Shenyang's design being intended for high manouverability.
 
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