David Megginson wrote: > I tried to fix this problem in JSBSim a year or two ago, and I seem to > recall that no one on the flight model list could quite figure out how > to code it back then. I also took a stab at YSBSim, and failed just > as miserably. Neither model is set up to have the propeller driving > the engine rather than the engine driving the prop.
I just hacked up a test rig for the propeller code. Feeding it numbers from the Cub's propeller (my guess for the best tested of the YASim propellers), and using 40 KTAS @ 4000 MSL as a base environment, I came up with the following: Windmill (i.e. zero torque) speed is 450 RPM. Windmill drag at that speed is 47N, about 10.5 pounds of force, or about 5 equivalent horsepower at that airspeed. > The rule of thumb for pilots is that a windmilling propeller creates > as much drag as a disc of the same size, but that's too vague for > modelling What's the drag of a 0.63 square meter (area of a 0.9m disc) flat plate at 40 knots? I wouldn't be shocked if it was in the realm of 10 lbs or so. A pickup truck (about as close to a flat plate as you can get, heh) at the same speed has perhaps 10x the surface area and requires just about 50 HP of engine power to cruise. Certainly we're within the right order of magnitude, anyway. Andy _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
