I've recently tested the DG-101G which is (I think) the first JSBSim
glider I've been flying in Flightgear. I've noticed a rather strange

In Local Weather, I added some amount of turbulence around a thermal
proportional to the strength to simulate the fact that a thermal is not a
laminar rise as wave lift. In a thermal, the DG-101G turned out to be
essentially out of control for magnitude-norm of the turbulence set to
just 0.18.

Now, I determined the amount of turbulence to be added to a thermal by
test-flying with the ASK-13 and comparing with my real flight experience -
and in the ASK-13 the value seems about correct. However, the ASK-13 is a

I've first suspected that something is fishy with the DG-101G, but since
I've flown all sorts of aircraft through the thermals (as a side note,
it's really interesting that the F-16 instrumentation allows nicely to
trace the thermal rise profile - I hadn't expected that). Of course, an
F-16 isn't thrown so wildly around as the DG-101G for the same magnitude
of turbulence , but then it has 100 times the mass - but there seems to be
some sort of pattern that JSBSim aircraft are affected much more by the
same value of magnitude-norm of turbulence than YASim aircraft.

If anyone else could try confirm that?

If the observation is real, it's sort of bad, because it means that one
can't really draw up a thermal which works realistically for both JSBSim
and YASim. Well, one could make FDM-dependent statements into Local
Weather, but I feel that's somewhat beyond the scope of a weather system.
So maybe a better potential fix would be a Flightgear-wide FDM dependent
scale factor such that a given value of turbulence magnitude really means
the same for all FDM engines and the weather system can simply set it.

* Thorsten

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