On Thu, 2003-03-20 at 03:22, David Megginson wrote: > Erik Hofman writes: > > > We have three FDM's of which two of them use windtunnel/flight-test > > data and one is based on physical dimensions of the aircraft. The > > latter is a bit less accurate but is easier to design a working > > aircraft for. > > To be fair, YASim is not necessarily less accurate, though it does use > a solver to fill in many of the blanks.
It depends entirely on how you want to define accurate. The coefficient approach used in JSBSim and LaRCsim/UIUC makes it possible to duplicate the unique characteristics of a particular aircraft throughout the normal flight envelope. It is, however, more difficult to get reasonably good behavior in spins, stalls, and turbulence. The YASim approach makes it easier get the latter behaviors about right. In terms of unique characteristics, however, you can only match them at a couple of places in the flight envelope. Everywhere else, you take what you get. >In fact, YASim is currently the only FDM that performs calculations > for each lifting surface separately -- YASim figures out the angle of > attack, lift, and drag for each surface then calculates moments from > the differential lift and drag, while JSBSim uses a single angle of > attack for the entire aircraft and simulates the differences in lift > and drag using a long series of moment coefficients. Both are fine in > regular flight, but YASim's approach is likely to work better for > stalls, spins, and other aerobatic maneuvers outside of the regular > flight envelope. Note that it's far from perfect so far, but at least > the potential is there (likewise, it would be much easier to simulate > something like a tailplane stall from icing in YASim). > > JSBSim could do the same thing by providing an option to specify > separate coefficients and relative orientations for each lifting > surface. Then, if the right wing were producing more lift than the > left, you would have a left roll; if the right wing were also > producing more drag, you would have a right yaw; and so on. > > > All the best, > > > David -- Tony Peden <[EMAIL PROTECTED]> _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
