wip AFCS off flight missing pitch transients from thrust inputs

cw4ogden · August 11, 2024

Thrust (collective) inputs should make significant changes to the aircraft's pitch attitude AFCS off. Pulling in thrust should cause a pronounced nose downward moment. Reducing thrust should cause the nose to pitch upward. This is caused by the fact the forward and aft rotor system are mounted at different angles. 9 degrees of forward incline on the front, 4 degrees on the aft.

This angular difference causes the aft rotor's lift vector to be more vertical than the forward system's, and therefore any change to collective pitch will add more lift to the aft head than the forward head, and vice-versa. The difference in lift vector manifests in a rolling moment about the pitch axis. Pull thrust, nose goes down, lower thrust, nose comes up.

The same aerodynamics happen AFCS on, but are largely (but not entirely) mitigated by the AFCS.

Edited August 11, 2024 by cw4ogden

47_Driver · August 11, 2024

6 hours ago, cw4ogden said:

Thrust (collective) inputs should make significant changes to the aircraft's pitch attitude AFCS off. Pulling in thrust should cause a pronounced nose downward moment. Reducing thrust should cause the nose to pitch upward. This is caused by the fact the forward and aft rotor system are mounted at different angles. 9 degrees of forward incline on the front, 4 degrees on the aft.

This angular difference causes the aft rotor's lift vector to be more vertical than the forward system's, and therefore any change to collective pitch will add more lift to the aft head than the forward head, and vice-versa. The difference in lift vector manifests in a rolling moment about the pitch axis. Pull thrust, nose goes down, lower thrust, nose comes up.

The same aerodynamics happen AFCS on, but are largely (but not entirely) mitigated by the AFCS.

Can definitely tell you've flown the real thing if you know all this. I've noticed that the module with the AFCS on seems to fly like a watered down AFCS off. Not quite as bad, but I was messing around in level flight, trimmed up real nice, and as I added power the nose would dip just like it should AFCS off. Opposite would happen when I took power out, nose would pitch up. So it seems they've got some of the fundamentals down for what the aircraft should do, they just need to build on that and make it to where the AFCS actually does its' job at suppressing those things. I've had to break the habit of trying to fly the module as I would fly the real aircraft, at least in its' current state, and I've been having fun with it. Definitely tough to do cause everything looks so true to life lol, but for now I think that's the solution for those of us who know how it should actually fly.