"Jon S. Berndt" <jonsber...@comcast.net> wrote:
>> From: Martin Spott [mailto:martin.sp...@mgras.net]
>> BUT, basically, I'd say this is not the point at all - these are
>> interesting theoretical approaches to the problem, but for the 'real'
>> user who's getting veered off the apron while he is simply doing a
>> proper run-up at a windy location, this is entirely irrelevant.
>
> If this is truly the case, and if it is due to a gear modeling fidelity
> issue, then I agree. But, the kind of problem you describe would be a
> different issue. Since wind effects are only ramped in as velocity
> increases, the example you describe above should not happen with JSBSim.
I just put the default Cessna at EDLN RWY 13 with parking brake
applied, the wind is 11009KT. It took approx. three and a half minutes
to let the aircraft slip backwards by the length of a main gear cover.
And, _no_, don't even think of it ;-)) it's definitely _not_ a proper
solution to work around such a case by clamping the aircaft to a fixed
position as long the brakes are applied :-)
>> Just for the sake of completeness: Think of a scenario on the carrier,
>> you're approaching the catapult from behind .... oh, too far, you're
>> idling the engine, letting the wind blow you backwards while you're
>> slowly manoeuvering your aircraft right into the catapult position
>> solely by nose wheel steering. That's what I call proper simulation of
>> tire ground reactions. FlightGear _could_ do that - it they didn't
>> depend decisions made at JSBSim.
> JSBSim also does not (quite yet) do blade element modeling, so it's not easy
> to do a proper snap roll. Nor do we model multiple articulated landing gear
> struts. Nor do we ...
As far as I can tell, nobody's asking JSBSim to do "blade element
modeling" - to my opinion this is mostly a buzzword. Being able to fly
an aircraft by table lookups derived from real life flight test data is
quite an appealing approach.
Instead, I'm talking about what I'd call a 'misfeature' to which a
proper fix had already been submitted (years ago) and I'm convinced
that you may apply as many workarounds, filters, whatever you like to
the current gear/ground simulation, there'll be always a relevant
corner case which remains uncaught as long as you stick to the current
approach of gear modelling.
I know that the patch which had been submitted to you uses a
fundamentally different approach at modelling the tire/surface
reactions and forces, but to my understanding this is by far the best
way to get rid of the perpetually arising discussions about ground
handling.
> Apart from that, do you have a specific proposal in mind?
My proposal is either to develop a copy of the FDM inside FlightGear
and to focus primarily on FlightGear's needs (and to try getting a copy
of the respective patch) or to have the changes applied to JSBSim's
code tree and to later merge this into FlightGear.
> We should move this to a new thread.
Feel free to do that. From my point everything's been said - the sole
purpose why I've actually been jumping into this discussion has been to
dissect and/or explain the background which has led to the current
situation wrt. gear/tire/surface modelling in JSBSim. I actually knew
about it for a long time but I wanted to hear both sides.
Cheers,
Martin.
--
Unix _IS_ user friendly - it's just selective about who its friends are !
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