Interesting thing I found in the comments section in a post by Sweetman.
"Andrei,
canard can deflect to unload itself from stalling, so the drastic lost of pitch-up moment should be avoidable. However, it is true that there is a limited authority for the canard to provide pitch-up moment if its AoA is limited.
This is where the canted vertical tails come in, at least based on the 2001 Chinese technical paper by chief designer Sung that I just came across, it seems to be what the Chinese designers are going for.
The vortices generated by the LERX and canard creates very strong side slip -- for the non-aerodynamic fluent, this means the flow is spreading/radiating outward from the centerline when you view it from top of the aircraft -- on the flow above the tail. This creates postive AoA on the outward canted vertical tails and the lift force would point downward, creating a pitch up moment.
In fact, based on the paper, the way they are blowing two vortices over the wing was creating so much side slip that this pitch-up moment became the main challenge in maintaining longtitude stability and this new design would have a more relaxed longtitude stability than anything they have attempted.
Now how much this actually happens in real life full-scale aircraft I am a little skeptical, but I think it could happen. In fact, some of the configuration choice may have been dictated by this possible vertical tail pitch-up moment. For example, fully movable vertical tail could be used to adjust AoA and unload them, setting the main wing very far back give longer moment arm for the pitch-down from wing, the two vertical fins by the engines could be compensating the need to make vertical tails smaller to minimize pitch-up moment.
Looking at all the pictures of J-20 take-off and landing so far, one would also notice both vertical tails were toed-in somewhat, so it would also support that they are trying to align the two surface toward the side slip to reduce incidence and keep this pitch-up at bay.
In the end, I think if all the control surfaces worked as the Chinese computational modeling and wind tunnel testing suggested, J-20 could be more maneuverable than what we have given it credit for. I think the risk is still high at this stage, though, (even though the paper is 10 years old) and I would not be surprised if it needs more aerodynamic refinement as the tests continue."
Read the comments. They seem pretty interesting.
EDIT: Except for later on, where it just becomes a Rafale vs the world bashfest...-_____-;
"Andrei,
canard can deflect to unload itself from stalling, so the drastic lost of pitch-up moment should be avoidable. However, it is true that there is a limited authority for the canard to provide pitch-up moment if its AoA is limited.
This is where the canted vertical tails come in, at least based on the 2001 Chinese technical paper by chief designer Sung that I just came across, it seems to be what the Chinese designers are going for.
The vortices generated by the LERX and canard creates very strong side slip -- for the non-aerodynamic fluent, this means the flow is spreading/radiating outward from the centerline when you view it from top of the aircraft -- on the flow above the tail. This creates postive AoA on the outward canted vertical tails and the lift force would point downward, creating a pitch up moment.
In fact, based on the paper, the way they are blowing two vortices over the wing was creating so much side slip that this pitch-up moment became the main challenge in maintaining longtitude stability and this new design would have a more relaxed longtitude stability than anything they have attempted.
Now how much this actually happens in real life full-scale aircraft I am a little skeptical, but I think it could happen. In fact, some of the configuration choice may have been dictated by this possible vertical tail pitch-up moment. For example, fully movable vertical tail could be used to adjust AoA and unload them, setting the main wing very far back give longer moment arm for the pitch-down from wing, the two vertical fins by the engines could be compensating the need to make vertical tails smaller to minimize pitch-up moment.
Looking at all the pictures of J-20 take-off and landing so far, one would also notice both vertical tails were toed-in somewhat, so it would also support that they are trying to align the two surface toward the side slip to reduce incidence and keep this pitch-up at bay.
In the end, I think if all the control surfaces worked as the Chinese computational modeling and wind tunnel testing suggested, J-20 could be more maneuverable than what we have given it credit for. I think the risk is still high at this stage, though, (even though the paper is 10 years old) and I would not be surprised if it needs more aerodynamic refinement as the tests continue."
Read the comments. They seem pretty interesting.
EDIT: Except for later on, where it just becomes a Rafale vs the world bashfest...-_____-;
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