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SU27 ACS & FCS


vparez
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Hi all,

 

I noticed a lot of problems with the ACS (autopilot). It seems to fight a lot with either the natural stability of the airplane or with the fly-by-wire system (FCS). Most notably it it over-controls initially and then oscillates until much later it finally stabilizes the axis. This seems to me indicative of a very aggressive gain setting of the controller (a PID controller?).

 

I observed this problem not only with the pitching but also when stabilizing the roll. For example, if you engage altitude hold, it definitely oscillates a lot around the pitch axis, but also around the roll axis.

 

I believe that there are also issues with the FBW system since in free flight it tends to over-stabilize the plane in the roll axis. If you bank the airplane a bit suddenly but not a lot, the plane goes back to horizontal, instead of stabilizing at the bank angle you input (after you let go of the stick).

 

Not to mention that the general trim characteristics of the airplane are very much reminiscent of an I-16... If SU27 performs like this in reality... wow, what a failed controller design...

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