David Megginson wrote: > Paul Surgeon writes: > > I don't know about everyone else's experience but I haven't found > > one aircraft in FG that wants to sit still on the ground even with > > the engine off. > > It might be that the problem is not ground reactions but > aerodynamics.
It's the ground reaction code. :) JSBSim and YASim do things pretty much the same way, using a coefficient of friction for gear as they slide over the ground. This integration works fine for a moving aircraft, but it's really not right for a stopped one. An aircraft with exactly zero speed would produce exactly zero force, and thus be "moved" by a wind gust, and then feel a very strong force in the opposite direction. An ideal mechanism would keep track of how much force each wheel "could" apply in the ground plane, and then calculate the right amount to apply to keep the aircraft from moving. This basically comes down to solving a bunch of simultaneous equations for each FDM iteration. It's a big mess; I'd be really scared of making this work. What I did play with at one point is a model where you basically switch gear models at slow speeds. If the brakes are on and the gear is moving below some threshold speed, then you "remember" the "nominal location" of the gear and use a damped spring kind of force model. If the spring force goes above the static coefficient limit, then you fall back to the sliding force model. This wouldn't be hard to implement, but tuning to avoid the inevitable weird behavior would probably be a mess. :) Andy _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
