On Sat, 2010-03-20 at 12:32 +0000, Alan Teeder wrote: > -------------------------------------------------- > From: "Erik Hofman" <e...@ehofman.com> > Sent: Saturday, March 20, 2010 10:04 AM > To: "FlightGear developers discussions" > <flightgear-devel@lists.sourceforge.net> > Subject: Re: [Flightgear-devel] Bounce at startup. > > > Alan Teeder wrote: > >> I am (trying) to develop a model with JSBSim. > >> > >> At the moment the aircraft jumps violently into the air at startup and > >> then > >> bounces around on the runway until it sorts itself out. > >> > >> Is there a way of setting the initial height so that it is more or less > >> in > >> balance or is there something else that I need to look at? > > > > This normally happens when the gear spring coefficients are not set > > properly. > > > > Try looking at a configuration for a similar aircraft that sits steady > > at the runway and adjust spring_coeff and damping_coeff accordingly to > > see if it solves the problem. > > > > Erik > Thanks Eric, but the U/C (numbers from aeromatic) seems stable. > > It looks like an initialisation problem.
I have to agree with both of you. At initialization the aircraft is not perfectly positioned in respect to the ground so it gets dropped/lifted by the ground contacts. However, if the ground contacts are properly set these reactions will be minimal. Its really hard to make a specific recommendation without seeing the FDM in question, or at least a minimal FDM that demonstrates the problem. > If I start and switch immediately to rear view, the gear extends, and when > it reaches "down" the plane is thrown upwards! By design a gear doesn't support weight until it reaches >0.99 of extension. This was done so the gear would collapse rapidly if it was retracted on the ground. In FGLGear code the gear is initialized to "down" In Aircraft/controls.cxx gear is initialized to "down" In preferences.xml gear is initialized to "down" As near as I can tell the gear is always "down" on the c182rg model during initialization. I verified this by adding a line to source/src/FDM/JSBSim/models/FGLGear.cpp FGLGear::GetBodyForces if (t<30.) cout << "Gear is down : "<<GearDown <<endl; Cheers, Ron ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
