I wrote: > Curtis L. Olson wrote: > > With the latest YASim changes, the J3 Cub won't converge for me (and > > others.) > > Confirmed. Sorry, I didn't test this one.
OK, fixed. The model was almost converging, but wasn't getting close enough to the threshold. It was oscillating around the right values, but each iteration moved to far to be considered "done". This is a problem with this kind of heuristic. Just moving the solution "precision targets" a tiny bit was sufficient to fix the problem. I should probably make this number settable in the configuration file, for aircraft that run into problems. It affected the Cub because it's small and light -- relative changes in performance per-AoA and per-knot (i.e. the first derivatives of the solution functions) are higher. The problem is therefore "stiff", in the lingo of computation differential equations. One exacerbating factor that I noticed is that the Cub we model has a *monster* elevator. Holding the aircraft at its stall AoA requires only 35% back stick. Is that really correct? I changed the "lift" parameter on the hstab from 1.7 to 1.3 and seemed to get better results. I've never flown one, though, so I hesitate to check the change in. As above, this makes the "moment per elevator" derivative bigger and the problem stiffer. 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
