On Thursday 18 Feb 2010, syd adams wrote: > I have the same problem with the Citation X and Yasim... at mach > 6.2 and above , the center of lift starts to move rearward and > the nose starts to drop. > the autopilot has a mach trim ,I just haven't figured out how to > simulate that. > Cheers
Does this nose-down attitude develop at all altitudes, or only at relatively low altitudes? At only 0.62 Mach I doubt it's a Mach tuck problem but may instead due to fundamental aerodynamics;-) Within the sub-sonic regime, the lift generated by the wing depends upon both it's speed and the density of the air it's flying through: for a given Mach you need to increase AoA as you increase altitude, to maintain the same amount of lift. What it sounds like to me is that the aircraft has too much lift with the result that to maintain level flight at relatively high speeds at relatively low altitudes the AoA has to be reduced to -ve values. This was a relatively common problem with many of FG's early YASim aircraft, especially before the inverted wing incidence bug was fixed (Lol), and I hit it big time with the B-52F. However, it actually turned out that at relatively low altitudes (< ~10000 ft iirc) the real life B-52's speed has to be limited to < 310kts for precisely this problem, not so much due to structural or power limitations but that to be able to fly at it's rated altitude and speed the wings have to generate so much lift that at low altitudes this excessive lift can only be countered by reducing the AoA of the airframe to -ve values (and in the B-52 this is exacerbated by the fact that the wings needed to be set at an incidence of +6 degrees anyway so that the AoA wasn't ridiculously high at its cruising altitude). The consequence of this is that if you look at a lightly loaded B-52 in low level flight it'll be flying with a distinctly nose-down attitude, even at the lower limited speed. Check the Vmax speeds for the Citation-X, at the altitudes you're flying at, as you may be exceeding them. If this isn't the case then it may be that the C-X actually cruises with a higher AoA than you've tuned for and you need to tweak the FDM config to increase it. LeeE ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
