Just had a thought, based on some of the things Chris has been saying. Not sure if this is already in the code yet, but it seems like not. From what I'm reading in Chris's comments, is that he's having to set the angle limits very low because helicopters are so "slippery" at speed.
I think what we need for heli (if not also for multis) is two angle feedforwards. The first, is the speed-vs-angle feedforward. The second is acceleration-vs-angle feedforward. The total angle feedforward would then be summed.
Now, this is still a gross over-simplification of the true aerodynamic model. The real model would have to consider the angle of the rotor disk vs. a 3-dimensional estimate of the relative airflow, and then considering the collective pitch of the rotor blades.
ie: A helicopter with 45 degrees nose-down pitch and high collective setting, if it is starting from a stand-still, will be achieving a very rapid forward acceleration. However, if the helicopter is already in high speed flight, with a rapid downward velocity (ie: it's flying at 45 degrees downward) that same 45 degree no-down pitch angle will result in nearly no accleration.
Similarly, if a helicopter were at a standstill, and then was given a 45 degree nose-up pitch, we would expect something like a 1G acceleration rearward. However, if the helicopter were already in a fast forward straight and level flight, and we commanded 45 degrees nose-up pitch, the heli would experience very rapid upward acceleration, on the order of 6G.
This is the complexity of the aerodynamic model. And why I really believe that the entire navigation system needs to be done on a 3D velocity and acceleration domain, instead of 2D North-East plus Altitude.