Shenyang next gen combat aircraft thread

[enroger]

Here are my observations after analyzing the video more closely. The all moving wingtip as we know generates both yaw and roll authority. And seemingly, deflection of a single wingtip seems to generate as much roll moment as opposite deflections of ailerons. During the banked turn, the aircraft is maintaining it's bank angle while constantly changing the yaw force applied to the aircraft, as without a vertical stabilizer the aircraft is inherently unstable in yaw at low speed. This wingtip deflection will generate a roll moment opposite in direction of the yaw moment, which requires aileron correction to keep a stable bank, the aileron correction applies more adverse yaw on the same side as the wingtips, which means it cannot stay deflected for long periods of time, this you can see likely causes the wingtips and ailerons constantly moving in a pattern during the turn. I drew a diagram below to help myself understand, if there are any issues with my observations, please do tell me.
View attachment 152446

What you're describing is a cyclic motion. But with proper control law the amplitude should damp down and converge to zero as less and less yaw input is needed. So I still say we will see less flapping in the future with better control law, or maybe such behavior only manifest at low speed so less efficiency and the impact on stealth can be tolerated as long as it doesn't occur in more relevant flight regime.

This wingtip deflection will generate a roll moment opposite in direction of the yaw moment, which requires aileron correction to keep a stable bank, the aileron correction applies more adverse yaw on the same side as the wingtips, which means it cannot stay deflected for long periods of time

I don't quite get this paragraph. Adverse yaw maybe opposing the intended yaw input but in terms of magnitude adverse yaw moment will be smaller than the yaw moment created by AWT + aileron deflection. Therefore it should not be a big problem so can stay deflected

 

[Nx4eu]

What you're describing is a cyclic motion. But with proper control law the amplitude should damp down and converge to zero as less and less yaw input is needed. So I still say we will see less flapping in the future with better control law, or maybe such behavior only manifest at low speed so less efficiency and the impact on stealth can be tolerated as long as it doesn't occur in more relevant flight regime.



I don't quite get this paragraph. Adverse yaw maybe opposing the intended yaw input but in terms of magnitude adverse yaw moment will be smaller than the yaw moment created by AWT + aileron deflection. Therefore it should not be a big problem so can stay deflected

Basically what I mean is that when the AWT is deflected, the ailerons seemed to be deployed in a way to counter the roll force generated, meaning it only needed the yaw force from the tip. Saying adverse yaw was confusing, but the yaw from aileron is small yes, but it acts in the same direction as the yaw generated from the AWT.

I can’t exactly explain why it’s alternating back and forth so much but I was just trying to describe the events of the video.

 

[enroger]

Basically what I mean is that when the AWT is deflected, the ailerons seemed to be deployed in a way to counter the roll force generated, meaning it only needed the yaw force from the tip. Saying adverse yaw was confusing, but the yaw from aileron is small yes, but it acts in the same direction as the yaw generated from the AWT.

I can’t exactly explain why it’s alternating back and forth so much but I was just trying to describe the events of the video.

If I understand correctly, you mean yaw from aileron reinforce yaw from AWT, thus causing too much yaw, hence needing counter yaw from opposing side to cancel it out? Sorry if I'm being obtuse here

 

[Nx4eu]

If I understand correctly, you mean yaw from aileron reinforce yaw from AWT, thus causing too much yaw, hence needing counter yaw from opposing side to cancel it out? Sorry if I'm being obtuse here

Basically yes. That’s what I’m seeing in the video though I am not sure entirely.

Usually in banked turn, rudder would be used to counter adverse yaw. But in this case the AWT is the main yaw control, but to use it for yaw, ailerons are needed to counter the roll which generates the adverse yaw on same side. Which is why I believe they cannot be stayed deflected constantly.

I know it just sounds like I’m repeating same thing again and again. I’m just trying to word it better into more clear way every iteration.

 

[enroger]

Basically yes. That’s what I’m seeing in the video though I am not sure entirely.

Usually in banked turn, rudder would be used to counter adverse yaw. But in this case the AWT is the main yaw control, but to use it for yaw, ailerons are needed to counter the roll which generates the adverse yaw on same side. Which is why I believe they cannot be stayed deflected constantly.

I know it just sounds like I’m repeating same thing again and again. I’m just trying to word it better into more clear way every iteration.

If it really is the case it should be easy to adjust control law to take into account the extra yaw from aileron and tone down the AWT deflection so as to produce just the right amount of yaw.

It's an interesting observation, though personally I think they'd have already taken this into account from all the CFD simulations and wind tunnel tests. In any case I predict we'll see far less fluttering in the near future

 

[taxiya]

I wonder why they didn't use the skewed AMT if it superior
View attachment 152452

It is only superior for the two configurations (land and carrier based) in the ICE study. It's advantage over unskewed AMT is due to higher side force generated. But it is bad for RCS reduction. The paper said that the turnion line is aligned to the wing folding line on the other side for RCS reduction purpose. These measures increased more reflection angles.

The ICE configurations are either delta wing or canard and single engined. SAC's aircraft is different in layout, noticably the lambda wing and wide spaced twin engines. In SAC's configuration, there may not be much side force needed because the air flow between the twin engines' hump improves stability, kind of like vertical stablizer. Using unskewed AMT would improve stealth.

Things like aerodynamics are extremely complicated, there is no "always right" solution. One small change here will lead to recalibration everywhere.