John Wojnaroski wrote: > Indicated Airspeed (IAS) > Calibrated Airspeed (CAS) > Next comes Equivalent Airspeed (EAS) > Finally TAS > > Bottom line question for the FDM' rs: Would you take a few moments > to comment/explain how your models handle the various airspeeds.
The FDM interface treats CAS and IAS identically -- the calibration error, as you point out, is poorly defined and will vary between installations. All FDMs simply report a single "calibrated airspeed" value; if other code wants to model the vagaries of a given ASI, then it's welcome to. :) It's also worth pointing out that the FDMs work, internally, with a real, 3D velocity. So TAS is what you get natively as the projection of velocity along the aircraft's X axis; everything else is computed from that. EAS is really simple -- it's just the true speed multiplied by the square root of the density ratio; it corresponds directly to a given dynamic pressure (which is the space in which force constants like drag coefficients are measured). CAS gets hairy. At low speeds, it's identical to EAS. At higher speeds, it needs to be corrected for compressibility; and at supersonic speeds it needs to be corrected for shock wave effects. I have a good handle on the first two, but the shock stuff is beyond me. JSBSim had code for doing this, so (after verifying that it agreed perfectly at sub-mach numbers) I just used that. :) Andy -- Andrew J. Ross NextBus Information Systems Senior Software Engineer Emeryville, CA [EMAIL PROTECTED] http://www.nextbus.com "Men go crazy in conflagrations. They only get better one by one." - Sting (misquoted) _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
