On Thursday 03 Nov 2005 17:09, Andy Ross wrote: > Curtis L. Olson wrote: > > However, I know Andy's intension was to produce "plausible" > > behavior across all flight regimes as best as can be guessed > > at, and there is clearly a bug where stalls come *way* to > > early in the negative aoa regime. > > Yes, this is a real bug. It's not the "stall" per se, I > think, but a discontinuity somewhere in the lift curve. Every > time this comes up I end up re-reading the (admittedly hairy) > Surface.cpp code looking for it, and get lost. The stall > handling itself, though, is fairly transparent and looks > clean. Something else is going on. > > I should probably take some time and write up a test rig that > graphs the lift curve that emerges from the model, but that > requires generating a Surface object with real world > coefficients, which requires running it through the solver on > a real model, which has interactions that kinda obscure the > "pure" behavior of the Surface. Ick. :( > > Andy
This is an interesting topic to me as I've seen it many times while tuning YASim configs but it seemed sort of reasonable behaviour to me. If the AoA of a wing decreases from a positive value (below it's stall angle), through zero, into negative it seems to me that you are not creating a situation where turbulent air passing over the wing un-sticks from the aerofoil surface. Instead you still have good flow but the direction of lift changes. If you imagine a situation where there's no gravity and you have a symmetrical aerofoil you will get equal lift from equal amounts of +ve or -ve AoA but in opposite directions, which is how rudders and sails work. When you throw in real wing aerofoils and gravity I would expect to see some discontinuous behaviour at -ve AoAs. Dunno what exactly :) LeeE _______________________________________________ Flightgear-users mailing list Flightgear-users@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-users 2f585eeea02e2c79d7b1d8c4963bae2d
