J-20 5th Gen Fighter Thread V

[Engineer]

It's interesting how they came to their different design decisions. CAC decided to challenge itself with the FCS to reduce the number of compromises they had to make, while SAC ended up going with a more conservative approach.

Actually, it was SAC's design that was way more challenging. There are too many control surfaces the FCS needs to take into account. Even the engineers themselves were unsure. PLAAF asked whether the plane can fly on date X, and the engineers couldn't answer "definitely yes".

You are right about CAC's design having less compromises though. SAC's triplane design incurs more drag, more weight, and less stealth just for a few extra degree of controlability. By giving up that few degrees, CAC's design did better in the other three parameters.

 

[latenlazy]

Actually, it was SAC's design that was way more challenging. There are too many control surfaces the FCS needs to take into account. Even the engineers themselves were unsure. PLAAF asked whether the plane can fly on date X, and the engineers couldn't answer "definitely yes".

You are right about CAC's design having less compromises though. SAC's triplane design incurs more drag, more weight, and less stealth just for a few extra degree of controlability. By giving up that few degrees, CAC's design did better in the other three parameters.

Well, SAC's FCS would have been challenging in different ways. I would say SAC's would have to account for more moving surfaces, which could complicate the aerodynamics, but more control surfaces also meant a broader range of potential flight characteristics. SAC could have hit some performance parameters with a greater margin for error. CAC's FCS design, on the other hand, especially with the aggressive relaxed stability and vortex generation, probably required a lot more fine tuning and design optimization. It was a riskier gambit.

 

[Quickie]

Actually, it was SAC's design that was way more challenging. There are too many control surfaces the FCS needs to take into account. Even the engineers themselves were unsure. PLAAF asked whether the plane can fly on date X, and the engineers couldn't answer "definitely yes".

You are right about CAC's design having less compromises though. SAC's triplane design incurs more drag, more weight, and less stealth just for a few extra degree of controlability. By giving up that few degrees, CAC's design did better in the other three parameters.

CAC's design should have higher max AOA than the SAC's design. CAC's design uses a multi pronged approach to increase the AOA, vortex generators at the air inlets, the LERXes and canards, whereas the SAC's design only has the LERXes and canards.

 

[Air Force Brat]

This is some of the pictures from the research paper of the Snowy owl.
View attachment 21430 View attachment 21431 View attachment 21432

Both these aircraft will offer fine high angle of attack performance, the SAC design might actually achieve higher alpha than the CAC design, due to the additional "leverage" in pitch, the SAC design has larger verts, a little farther forward, where the CAC has smaller "all flying verts" further aft, with the additions of ventral fins for longitudinal stability and control.

In any regard the FCS of each of these aircraft would be, and will be very "busy", I would actually love to see some of the J-20s high alpha testing as we did on the F-35, the absence of same will leave many questions yet unanswered?

I use the word "leverage" because once you go after "supermanueverability" you must force the aircraft to do things outside of its envelope, you must have additional leverage, that is why canards were a part of all of our initial high angle of attack experiments, and the reason that fighter aircraft all still operate with a vertical tail. Tailless designs will not be able to apply that leverage, and will never achieve similar levels of supermaneuverability without that vertical surface?? very simple physics

 

[Quickie]

Both these aircraft will offer fine high angle of attack performance, the SAC design might actually achieve higher alpha than the CAC design, due to the additional "leverage" in pitch, the SAC design has larger verts, a little farther forward, where the CAC has smaller "all flying verts" further aft, with the additions of ventral fins for longitudinal stability and control.

The CAC design has the vertical stabilizers further aft in order for it to be in the air stream at very higher AOA. A position that is a little farther forward may not allow the smaller vertical stabilizers to catch enough air stream for control and stability at very high AOA.

 

[Air Force Brat]

The CAC design has the vertical stabilizers further aft in order for it to be in the air stream at very higher AOA. A position that is a little farther forward may not allow the smaller vertical stabilizers to catch enough air stream for control and stability at very high AOA.

The RC Powers J-20 is stabilized by gyros, not airflow at high-angle of attack, in the case of the J-20, it should have outstanding longitudinal stability due to the ventral fins, which should provide stability at very high alpha. There are many who cry about those vents, but they are significant and indeed signature to CACs design.

So while interesting and partially helpful, those gyros are providing most of the slow flight stability, and are irrelevant when applied to the J-20, as the J-20 is not gyro stabilized, but aerodynamically stabilized.

 

[Quickie]

The RC Powers J-20 is stabilized by gyros, not airflow at high-angle of attack, in the case of the J-20, it should have outstanding longitudinal stability due to the ventral fins, which should provide stability at very high alpha. There are many who cry about those vents, but they are significant and indeed signature to CACs design.

So while interesting and partially helpful, those gyros are providing most of the slow flight stability, and are irrelevant when applied to the J-20, as the J-20 is not gyro stabilized, but aerodynamically stabilized.

Actually the gyro is only a component of the flight control system for both the RC model and real sized J-20. Both are aerodynamically controlled through all the usual control surfaces of either a real aircraft or a RC model.

There was a video by the same company showing how well the RC J-20 model flew at high alpha compared to the RC models of a few well known modern jet fighters with some of them crashing. It seems that for some reason they have removed it from YouTube. Obviously, all of them are using the same gyros.

 

[Engineer]

CAC's design should have higher max AOA than the SAC's design. CAC's design uses a multi pronged approach to increase the AOA, vortex generators at the air inlets, the LERXes and canards, whereas the SAC's design only has the LERXes and canards.

Lower, actually.

The CAC design has the vertical stabilizers further aft in order for it to be in the air stream at very higher AOA. A position that is a little farther forward may not allow the smaller vertical stabilizers to catch enough air stream for control and stability at very high AOA.

At very high AOA, vertical stabilizers aren't going to do anything regardless of whether they are placed more forward or more aft. This is where the ventral fins come in.

 

[Air Force Brat]

Lower, actually.


At very high AOA, vertical stabilizers aren't going to do anything regardless of whether they are placed more forward or more aft. This is where the ventral fins come in.

Roger That!

 

[lcloo]

2016 fly again.