On 12/02/2007 10:18 AM, Roy Vegard Ovesen wrote: > My question then is reduced to: why doesn't more FDM modellers use these > features of JSBSim and YASim to create cotrol surfaces that seem to have mass
Probably because in most cases, it would a very unrealistic way to deal with the reported problems. > The problem that I am addressing is the fact that an object can not move from > one position to another in an instant. Nobody is arguing that they should move "in an instant". They can, however, move rather fast. The timescale is not long compared to the inverse framerate of the sim. Any filter that would be noticeable on this timescale would be unrealistic. > The problem that I am addressing is the fact that an object can not move from > one position to another in an instant. Why? Because it looks bad? If the pilot rapidly moves the control surfaces, it not only looks bad; it *is* bad. However, that doesn't mean it can't happen. http://www.ntsb.gov/publictn/2004/AAR0404.htm > That would of course require an > unlimited amount of force. Before we can discuss the laws of physics, you need to figure out what *you* are talking about. a) damping [from the subject line] ??? That's a stick force proportional to X dot. b) mass [above] ??? That's a stick force proportional to X dot dot. c) "big aircraft with huge control surfaces" [previous msg] ??? That can give rise to a stick force proportional to X. d) slew rate limiting in the hydraulic system ??? That's something yet again, not mentioned until now. e) programmed slew rate limiting in the autopilot ??? Since very few of our users have force-feedback joysticks, there is no realistic way to model (a), (b), or (c) ... and attempting to model any of those with the suggested low-pass filter is a bad idea ... worse than no filter at all. Item (d) makes more sense; it should be modeled by the FDM on the few aircraft that actually exhibit a significant amount of this behavior. Item (e) should be modeled within the autopilot. Real autopilots are sure-as-shootin slew rate limited. > I mentioned the "5" key only as an example. I am not proposing to put a > filter > on that command. Too bad; that would have been a sensible proposal. The "5" key is essentially in the autopilot category; it should feed a smooth signal to the control system. This is *not* considered a limitation on how the control system responds to inputs; it is a limitation on the output from the autopilot and autopilot-like systems. ========================= To repeat: 1) In the overwhelming majority of aircraft, Asking the FDM to low-pass filter the controls (to any significant degree) is unrealistic. 2) In the few aircraft where there is a significant limitation in the fly-by-wire system, sure, go ahead and model it. This will require a lot more than a low-pass filter. 3) As the proverb says, pilots are judged on their smoothness, not on their quickness. Smoothness is built into the pilots; it is not usually built into the hardware. ------------------------------------------------------------------------- SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
