Jim Wilson wrote: > David Megginson said: > > What happens when you reduce the fuel load? > > Hmmm...nothing because it won't reduce. I'm showing full 19k+ lbs > for three tanks no matter what I do with the "fraction" figure in > the config and can't dump during flight it either.
Yes! That's it! Actually, the bug report is bogus -- /sim/fuel-fraction works just fine to modulate gross weight, and always has (do you maybe have a typo in your configuration file?). But it got me thinking about checking the weight during solution, and that's where the problem was. For efficiency, YASim separates the computation of the inertia tensor and gross weight from the normal iteration-to-iteration operations on the RigidBody object. The recalculation is handled outside, as part of the RK4 integrator. But the solver isn't using RK4 -- it's solving for instantaneous force only. So while it was setting the fuel fraction correctly, the change in fuel weight was *not* being applied to the aircraft. Basically, every solution produced was for an aircraft at zero fuel weight. So every non-zero fuel configuration was heavier than the cruise setting and thus incapable of reaching its performance numbers. Bingo. There's another 747.xml file attached. It's needed to work with the new changes (which changed a lot -- the older model doesn't have enough tail authority to trim for cruise with the fixed code). The other aircraft seem to be OK, but I didn't fly them extensively. Folks should try them out and look for stuff that might need to be retuned. No doubt there are still bugs in there, but this definitely fixes the climb performance problems on the 747. This is actually kinda fun -- flying a fundamentally broken aircraft very carefully, and looking for tiny clues as to its performance difficulties so they can be fixed. Not at all unlike being a test pilot. :) Bring 'em on. Andy -- Andrew J. Ross NextBus Information Systems Senior Software Engineer Emeryville, CA [EMAIL PROTECTED] http://www.nextbus.com "Men go crazy in conflagrations. They only get better one by one." - Sting (misquoted) _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
