Michael Selig writes: > Some "real" numbers on the 310 are in one of Roskam's books, and > those same numbers are in the fgfs base package here: > ~fgfsbase/Aircraft-uiuc/Cessna310/aircraft.dat
Yes, I took my numbers from Roskam as well. > Personally, given the ability of fgfs to do a fairly high-fidelity > simulation (one of it's strengths), I'd stick w/ the published numbers. That applies only if we're starting from the same assumptions as Roskam. Roskam probably assumed fuel in the tanks when he estimated the moments with his AAA software (remember that his numbers are not from actual flight tests). Normally, that wouldn't matter so much, since fuel tanks tend to be on the inboard portion of the wings, close to the centre axis. The 310, however, is a special case: each wingtip tank holds 50 gallons of fuel, or approximately 300lb; since they're on the wingtips, each tank has an arm of about 88 inches from the centre axis, creating a very significant moment. JSBSim, on the other hand, assumes no fuel in the tanks, and does an additional calculation of the moment for the fuel when the tanks are full. Hence our (possible) problem. > Chances are that the 310 has a yaw damper as part of the autopilot > system. JSBsim has yaw damper functionality, and the current UIUC > code (yet to be given to Curt) has this too. Rather than tweaking > the aero and mass data, I suggest adding the yaw damper. The yaw damper would have to be disengaged in turbulence (and many other flight conditions), so we still need a flyable plane without it. Fortunately, yaw instability is the least of the problems -- pitch and roll instability are much more serious. There's also no reason to include yaw dampers in the individual FDMs -- we should be able to handle that in our FlightGear autopilot module. Roskam's pitch numbers are also worth investigating. He gives the 310 a Cmalpha of only -0.137 in cruise, compared to -0.613 for the 182 -1.89 for the Beech 99. That makes his 310 model surprisingly unstable in the pitch axis. On the other hand, in his climb condition (5 degrees alpha), he gives a linear Cmalpha of -0.339, and in his approach condition (6.6 degrees alpha, probably with flaps and gear down), he gives a linear Cmalpha of -0.619. We don't have enough information to factor out the flaps and gear from the last value, but these still suggest a steepening curve rather than a straight line -- i.e. the 310 is relatively unstable only in a small range around 0 alpha. All the best, David -- David Megginson, [EMAIL PROTECTED], http://www.megginson.com/ _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
