Trims and Forcefeedback

[Furio]

Originally Posted by zipper

Trim can vary by weight, but much more significantly by CG and speed. For best speed you want to be loaded at the aft limit because the stabilizer produces less downforce* at that loading than at the forward limit (the stab always produces downforce in a normally loaded conventional aircraft).

This is true in theory, but at the price of a reduced stability. P51 emptied rear tank before attempting any aerobatic manoeuvre.

Originally Posted by zipper

Some aircraft nose up sharply when flaps are lowered - some don't. That would be a function of the stabilizer size and distance from the wing and the type of flaps.

This is true for the immediate reaction of plane (more common in high wing design). Fact remains that you must re-trim – PRESTO – nose down and maintain a steeper glide.

Originally Posted by Furio

This is true in theory, but at the price of a reduced stability. P51 emptied rear tank before attempting any aerobatic manoeuvre.

That was because when the fuselage tank was full the CG was AFT of the aft limit - not AT the aft limit. The aft limit is set by minimum stability requirements and the Air Force threw that out the window for range.


This is true for the immediate reaction of plane (more common in high wing design). Fact remains that you must re-trim – PRESTO – nose down and maintain a steeper glide.

Again, different aircraft behave ... differently. The flaps by themselves cause a severe nose down force that is countered by the downwash behind the wing (created by the flaps) landing on the stab. The size of the stab and its position in the downwash are major factors in trim settings. I've flown planes that I've trimmed in the downwind leg and not had to retrim before touchdown. As the planes slowed on base and final rather than retrim noseup I simply fed the flaps down and maintained neutral trim. Not all planes are like this.

ha - my first response got caught in the quote ...

[Furio]

Originally Posted by zipper

That was because when the fuselage tank was full the CG was AFT of the aft limit - not AT the aft limit.

The P51 was just an example. Stability is reduced while the cg goes aft and, beyond aft limit, we cannot talk anymore of reducing stability but of increasing instability. All of this to say that playing with cg for obtaining more speed is something acceptable for racing, but I doubt it can be a wise choice – or a realistic one – in an operational plane loaded for war.

Originally Posted by zipper

Again, different aircraft behave ... differently. The flaps by themselves cause a severe nose down force that is countered by the downwash behind the wing (created by the flaps) landing on the stab. The size of the stab and its position in the downwash are major factors in trim settings. I've flown planes that I've trimmed in the downwind leg and not had to retrim before touchdown. As the planes slowed on base and final rather than retrim noseup I simply fed the flaps down and maintained neutral trim. Not all planes are like this.

You’re right, different planes behave differently, and I also flew with planes that showed pitch-up at flaps lowering. But generally speaking, the effect of flaps in landing position is to generate more drag than lift and – again, generally speaking – planes steepen their approach with flaps down.

Returning on topic, trim is presently simulated with moderate realism, and this is perfectly understandable and acceptable. Any attempt to simulate it with force feedback should try to simulate stick force variation with trim changes. It's no easy task, and I sincerely wish good look to anyone attempting it!

[flyingblind]

I'm looking at building another stick from scratch and the thought I had on trim was to have a means of rotating the pot or hall sensor body so that the center point could be moved in game so setting trim via the hardware rather than software. This may give a more realistic solution? But obviously no good if you are using a bought stick unless you can modify it in some way although I think at least one stick, not sure which one, has trim wheels but again don't know if they control trim via hardware or software.