I was interested in how the actual helicopters implement advanced control functions like these and found a paper detailing the testing done on the Comanche control system for the prototypes. I found that they implement Hover-Hold, Altitude-Hold, and one more, Velocity-Stabilization.
Hover-Hold was limited to horizontal and axial motion, no vertical control was implemented because it was intended to be used in conjunction with Altitude-Hold. Our Hover-Hold does all three axes.
The Comanche Altitude-Hold has two modes, below 300 ft it uses the radar altitude like ours currently does, above 300 ft it uses the barometric altitude. I might add the barometric part into ours. The professional system also doesn't concern itself with station keeping, heading keeping, or speed control, all it does is maintain altitude. The professional system also uses a manual control lever, which is used to perform the Bob-Up maneuver as described in the Enemy Engaged manual. We now have an automated version of that. You can also use the incremental hover height adjustments (Alt-J and Alt-K) similar to the lever control described in the paper.
Velocity-Stabilization from what I can tell was only for forward speeds, lateral control was not considered. I've implemented a form of Velocity-Stabilization when you select Altitude-Hold in our control system already. It attempts to keep your speed up to about 50 knots on the low end, and below about 110 knots on the high end. You can be anywhere in that range and it doesn't interfere, and you can over-ride it by simply moving the control stick. The paper didn't go into enough detail on how it functions, so I don't have any more changes in mind at this point. It's mostly for use as a long-distance cruise control, which isn't really too much of an issue with our sim anyway.
I suppose we could separate out each control function like they've done in the professional system, but I don't really see the advantage of that. I really like the controls the way they function now.
I just thought you guys might like knowing that our sim is on par now with the actual flight control systems of the more advanced helicopters.