It looks like the main problem with the 747-100 configuration file is the ground effect factor in the <drag> section. Here it is:
<FACTOR NAME="kCDge" TYPE="VECTOR"> Change_in_drag_due_to_ground_effect 11 aero/h_b-mac-ft none 0 0.048 8 0.515 16 0.709 24 0.815 32 0.882 40 0.928 48 0.962 56 0.988 64 1.0 72 1.0 80 1.0 </FACTOR> The property used is called h_b-mac-ft. This is what is actually calculated in FGAuxiliary: FGColumnVector3 vMac = Propagate->GetTb2l()*MassBalance->StructuralToBody(Aircraft->GetXYZrp()); hoverbmac = (Propagate->GetDistanceAGL() + vMac(3)) / Aircraft->GetWingSpan(); Which is basically the altitude AGL divided by the wing span. Using a chart like this one: http://home.comcast.net/~davidculp2/groundeffect.png We see that ground effect starts at a height of about one wingspan. In the 747-100 config file the ground effect is occurring at 64 wingspans, which for a 747 means it occurs everywhere under 12000 feet. So, the author is off by a factor of 64. A better factor would be: <FACTOR NAME="kCDge" TYPE="VECTOR"> Change_in_drag_due_to_ground_effect 9 aero/h_b-mac-ft none 0 0.048 0.125 0.515 0.250 0.709 0.375 0.815 0.500 0.882 0.625 0.928 0.750 0.962 0.875 0.988 1.000 1.0 </FACTOR> I've flight-tested it and the drag looks much better. What's the protocol for fixing configs? Dave _______________________________________________ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d