Rudder trim vs dihedral effect

[AKar]

Well, it is certainly possible to simulate "properly" various trim systems, including tabs that fly the control surfaces and direct springs. On FSX platform at least the good old Project Tupolev comes to mind. They actually simulated tabs and THS independently. DCS also does reasonable job. Obviously, when using spring-centered sticks, the simulation of control feel remains subjective, because simulation of both the control forces and displacements need to be "translated" into single combination of both which is what the controller offers. There is no one right way to do this "translation" properly, and one needs to balance in between controller displacement vs stick displacement, and controller displacement vs applied stick force to get the feel subjectively right. That is, to simulate control forces, one can't have one-to-one relationship in between controller position and the airplane's stick position, but to retain some feel of the displacement, one can't consider the controller position as control force input alone either.

-Esa

[Nick - A2A]

I recall also reading somewhere that MS Flight did a much better job with its trim simulation than FSX, but I never really experimented with that platform much. Trim in FSX sure can get weird though: I think it was you Esa who posted an external screenshot (this was ages ago) showing the—let's say 'eccentricity'—of the elevator in something like the default Cessna maintaining level flight with trim tab fully deflected?

RealAir made good steps in making the animations much more convincing in terms of a trim tab that actually moves the control surface, but I'm not sure this went beyond being just an animation thing. Anyway, if A2A ever manage to bring any cunning external coding to the trim simulation in FSX/P3D, it'll certainly be welcome.

Cheers,
Nick

[AKar]

It could have been this:



The plane would be A2A 182. In FSX/P3D, the trim tab has control authority of its own, which is certainly incorrect when discussing an aerodynamic trim tab (okay, not quite to be precise, but the order of magnitude and direction of effect are wrong!).

Similar test with DCS Mustang gave these results (oh my have they improved the graphics since! ):



Significant nose-up effort is required on the joystick, but the control authority and elevator position remain correct.

-Esa

[Eseem]

Nick's right on the money, I'd very much like a rudder trim that makes the rudder do ruddery stuff, rather than some strange single-axis trickery. As it is now, the rudder trim just remains centered in all phases of flight, because the only thing it does in my aircraft is momentarily affect turn coordination, and then the aircraft disregards it and creeps back into coordinated flight with level wings. Is this something that can be given attention in an update, or is this beyond fixing due to FSX's shortcomings?

[mallcott]

Nick's right on the money, I'd very much like a rudder trim that makes the rudder do ruddery stuff, rather than some strange single-axis trickery. As it is now, the rudder trim just remains centered in all phases of flight, because the only thing it does in my aircraft is momentarily affect turn coordination, and then the aircraft disregards it and creeps back into coordinated flight with level wings. Is this something that can be given attention in an update, or is this beyond fixing due to FSX's shortcomings?

Now you understand the foregoing. P3D is the same. Deliberate uncoordinated flight is very difficult to maintain as the two control surfaces - rudder and rudder trim - `fight`.

[AKar]

For spring-based rudder trim (or any other trim for that matter), a working solution would simply be to alter the "curve" for the rudder control so that the center position is changed with the trim. This way, the rudder trim would work though the primary control as it is supposed to. Of course, the amount of curve bending would take some dynamic pressure feedback to get the back-driven controls just right; for constant control force applied via spring pressure, the rudder displacement would get smaller with increasing dynamic pressure increasing the hinge moment on the surface.

-Esa