Andy Ross writes: > Hrm... well that throws a wrench into the "static spring force while > stopped" idea. Maybe it could be salvaged by doing the static spring > computation only in the (1D) transverse direction...
Again, I'm wondering if this is an aerodynamic problem (aside from the bouncing-around-sitting-still thing). Because of its lifting surfaces, a plane is certainly more vulnerable to the wind than a car, even when it is sitting on the ground; however, the coefficients we use in JSBSim are designed to deal with a relative wind near or above the plane's stall speed, coming straight onto the nose +- about 20 deg vertically or horizontally. They probably do a pretty crappy job of modelling (say) a 15 kt gust hitting the plane from 90 deg when it's sitting on the ground. I expect that the same applies to the assumptions made by YASim's solver. I don't speak physics/math/engineering, but I'm going to try to fake it and suggest that there's a strong <jargon>discontinuity</jargon> in the effect of relative wind on the aircraft once the wind falls more than a little below the stall, particularly when the wings are no longer bearing much of the aircraft's weight. Neither JSBSim's coefficients nor YASim's solver deal with that continuity well -- in the first case, there's probably very little data available; in the second case, it may not be possible to extrapolate it from the aircraft's in-flight performance. Here's something that would help: let's look at the total forces and moments acting on a the plane sitting on the ground during, say, a 20 kt crosswind. If they're moderate, then it's a weak-gear problem; if they're excessive, then it's an aerodynamic problem. For example, depending on tire pressure (etc.) I'd guess that it takes somewhere between 100-200 lb of force (is that the right term?) to start a small single-engine plane rolling on level pavement -- easy for two adults, difficult for one. Once the plane's moving on dry pavement, one person can keep it going by pulling moderately hard. All the best, David _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
