Lee Elliott wrote: > 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 >
I would look at some polar graphs. Stuff happens at those AOAs, but it is usually continuous. Even the stall regimes are continuous, though they do have a much greater slope. I haven't ever seen graphs of deep stalls though, so I have no idea what happens there. Josh _______________________________________________ Flightgear-users mailing list Flightgear-users@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-users 2f585eeea02e2c79d7b1d8c4963bae2d
