Thanks everybody. That's all great stuff.
if you can find a way of increasing the rate of disc response to cyclic input you will succeed in producing a less stable hover
I've managed to do that already. It doesn't increase the helicopter's instability, only it's responsiveness. It's half the problem cracked though.
put in about .5% of control for each 10 deg per second angular rate (in the same direction as the rate)
That's an interesting idea. I'll give it a try. I had been wondering whether I could override its self-stabilising tendency by requiring a negative input to counteract a previous positive one. i.e. If slight forward cyclic had been applied then relaxing the joystick wouldn't level the helicopter, (as it does at present, after a delay), but a back cyclic input would be required. Though some decay would be implemented. That would cause a great deal of pilot induced oscillations until people got used to it.
It feels to me like the MS helicopter model's stability feels more like an r/c model with the Bell-Hiller mixer and large paddles than a full-sized one does, (in the hover anyway.)
I'll be sure to post a link so you can try out my software when it's ready.
Si