Shenyang next gen combat aircraft thread

[enroger]

Like my previous post mentioned, AMTs behaviors are super non-linear so it’s basically incomparable to every other form of commonly-used control surface. At small deflections there is very little yaw moment: at large deflections flow separation creates large amounts of yaw moment, and roll & pitch kicks in, so holding it at a constant small deflection won’t work and holding it at a constant large deflection won’t work either, thus the observed fluttering motion.

I get your point on nonlinearity of AWT. However if the AWTs needs to constantly induce flow separation to use stall drag for yaw, it will drastically reduce flight efficiency, not to mention the impact on stealth.

Therefore the hope is either it only occur at low speed maneuver or it will improve with better control law. Otherwise if this behavior occur at leveled flight it will be bad

 

[Nx4eu]

I get your point on nonlinearity of AWT. However if the AWTs needs to constantly induce flow separation to use stall drag for yaw, it will drastically reduce flight efficiency, not to mention the impact on stealth.

Therefore the hope is either it only occur at low speed maneuver or it will improve with better control law. Otherwise if this behavior occur at leveled flight it will be bad

Movement is not that bad for stealth. Dhimas Afihandarin did radar analysis on J-20 canards where even significant deflection only had small impact to observability. The stealth of Small movements in AMT can be easily managed.

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[Schwerter_]

I get your point on nonlinearity of AWT. However if the AWTs needs to constantly induce flow separation to use stall drag for yaw, it will drastically reduce flight efficiency, not to mention the impact on stealth.

Therefore the hope is either it only occur at low speed maneuver or it will improve with better control law. Otherwise if this behavior occur at leveled flight it will be bad

The impact on aerodynamic efficiency is not necessarily significant. The same paper also found that deflecting AMTs on one side only (for yaw control) have minimal impact on CL curve, and L/D at low and high AoAs also experience little change. AMTs do mess with drag coefficient and by extension maximum achievable L/D, however since tailless designs inherently have less drag to begin with, the additional drag created by AMTs may well be small enough to still provide a net benefit compared to tailed designs.

As for stealth, such extreme levels of deflection should only occur at very low speeds or during very aggressive maneuvers (or both), which are hardly the scenarios where stealth is of any great significance. At higher speeds AMT deflection will most likely not be as aggressive simply due to the aerodynamic forces being proportional to the square of flow velocity.

 

[donnnage99]

Movement is not that bad for stealth. Dhimas Afihandarin did radar analysis on J-20 canards where even significant deflection only had small impact to observability. The stealth of Small movements in AMT can be easily managed.

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That's just frontal rcs which makes sense given that the edge alignment still deflect rcs return to the sides and not back at the emission source

I'm curious how movements of canards effect from other angles outside of straight head on.

 

[iewgnem]

I get your point on nonlinearity of AWT. However if the AWTs needs to constantly induce flow separation to use stall drag for yaw, it will drastically reduce flight efficiency, not to mention the impact on stealth.

Therefore the hope is either it only occur at low speed maneuver or it will improve with better control law. Otherwise if this behavior occur at leveled flight it will be bad

Dynamic pressure scales to airspeed squared while aero force is linear to CS deflection or AMT alpha, you should only need ~1/10 the amount of deflection to achieve the same moment (both through lift and drag) at cruise vs takeoff/landing.

Also with minimal side slip during cruise yaw axis is probably in a neutral to slightly stable equilibrium, so you won't need nearly as much yawing moment compared to during the maneuvers seen in the video. So it's really a non-issue.

Also let's not forget J-50 also have multiple traditional trailing edge control surfaces that can be differentially actuated to increase drag on one side without affecting roll. Won't be enough at low speeds but at high speeds should be more than enough.

Also the way people traditionally think about it is probably not how the control law was derived either, its probably done with state space control (at least, could be even fancier) with a the entire system and every actuator modelled in state matrices then optimal control deflections of all actuators solved together in real time.

 

[a985010812]

这些有多准确？
没有官方消息的话 只能算推测

 

[Schwerter_]

Dynamic pressure scales to airspeed squared while aero force is linear to CS deflection or AMT alpha, you should only need ~1/10 the amount of deflection to achieve the same moment (both through lift and drag) at cruise vs takeoff/landing.

Also with minimal side slip during cruise yaw axis is probably in a neutral to slightly stable equilibrium, so you won't need nearly as much yawing moment compared to during the maneuvers seen in the video. So it's really a non-issue.

Also let's not forget J-50 also have multiple traditional trailing edge control surfaces that can be differentially actuated to increase drag on one side without affecting roll. Won't be enough at low speeds but at high speeds should be more than enough.

Also the way people traditionally think about it is probably not how the control law was derived either, its probably done with state space control (at least, could be even fancier) with a the entire system and every actuator modelled in state matrices then optimal control deflections of all actuators solved together in real time.

I cannot imagine the complexity of that state space matrix man, and I’m also happy that I’m not in charge of developing that xd

 

[qwerty3173]

I cannot imagine the complexity of that state space matrix man, and I’m also happy that I’m not in charge of developing that xd

For a simplified model of a conventional aircraft there are six main control surfaces and it seems possible but with both 6gen having about 12 or 13 control surfaces I doubt that the state space can be properly stored in a hard drive. Some novel way of simplifying is necessary.

 

[latenlazy]

For a simplified model of a conventional aircraft there are six main control surfaces and it seems possible but with both 6gen having about 12 or 13 control surfaces I doubt that the state space can be properly stored in a hard drive. Some novel way of simplifying is necessary.

Realistically speaking there will be redundant envelopes in the state space matrix that won’t need to be kept. Part of the point of the flight testing is to confirm which envelopes are redundant or suboptimal and which are ideal for the flight characteristics you care about, and then determine the right eigenvectors for the flight control system. At the end of the day it’s all about mapping and compression.

 

[Schwerter_]

For a simplified model of a conventional aircraft there are six main control surfaces and it seems possible but with both 6gen having about 12 or 13 control surfaces I doubt that the state space can be properly stored in a hard drive. Some novel way of simplifying is necessary.

I’ve only done state space stuff for aeroelasticity, and even for just a wing with TE flaps it’s an absolute nightmare, and the design team has to work with the 4 pairs of TE control surfaces, LE slats (or flaps), AMTs and TVC nozzles. I would just jump off of a bridge instead but hey that’s probably why I’m not the one designing a 6th gen fighter