Re: [Flightgear-devel] Bouncing JSBSim aircraft

[Bertrand C. <bco...@gm...>]

2010/11/28 Gijs de Rooy <gij...@ho...>:
> Yeah, problems is fixed! I had --model-hz=30. Setting it to 120 (so it
> was omitted from the commandline by FGRun) fixed the problem.
>

(...snip...)

> After takeoff, bouncing stops. After landing, bouncing continues.
> When braking, the intensity of the bounces increases significantly.
> Apparently not all JSBSim aircraft bounce (see list below).
>

To make a long story short, this kind of behaviour is driven by the
eigenfrequencies of the system. They are the frequencies at which a
system "naturally" oscillates. A very rough estimate of these
frequencies can be obtained by the square root of k/m where k is the
sum of the stiffnesses of all the gears and m is the mass of the
airplane. It is thus obvious that this frequency varies from one
airplane to the other. As far as I remember, the simulation rate must
be as greater as possible than these frequencies otherwise bouncing
issues may arise. Hence the disappearance of the issue when you set
the simulation time rate back to its default 120 Hz.

> Cheers and thanks for the "help"!

You are welcome :-)

Cheers,

Bertrand.