[Flightgear-devel] YASim & sliding helicopters bug (+ ugly "fix")

[Melchior F. <mf...@ao...>]

Ever since helicopter support was added to the YASim FDM
there's an annoying bug: even when parked, with rotor off
and braked, helicopters slide happily around on the ground.

Andy knows about it and explained why it happens, but claims
that there's nothing to be fixed in the FDM code. Instead,
he suggested to place masses and weights "appropriately" in
the FDM config. Then the sliding would stop.

I've spent many hours on that, without success. And I even
doubt that is works: after all, there are adjustable pilot
and passenger weights, different loads (MG, missiles, etc.),
changing fuel level. So, how could one find a working mass
distribution for all these different states?!

I've tried a lot of other things -- most of it were ugly hacks.
Different gear (skid) parameters, masses that would only
get activated when the helicopter is parked, thrusters
that would counter any movement, thrusters that would
press the helicopter down. Nothing worked. (Oh, and I tried
to fix the gear code itself -- without success. Not that
Andy would accept a patch, I guess.)

A few days ago I found the best remedy so far: a thruster
that *lifts* the helicopter when it's parked. This stabilizes
it a lot, though when the rotor spins, all the sliding is
back.

Has anyone ever found a solution to the gear bug? Something
that's not a hack? (I'd accept an alternative FDM as well.
What about JSBSIM?  :-)

m.