Cool, someone's playing with the 747. This model hasn't had a lot of tweaking yet beyond the engine thrust bugs that Jim Wilson dealt with a few months back.
Manual Bessler wrote: > Here are a few things I wanted to ask about the 747-yasim: > > Does it model the thrust reversers ? > What about Speedbrakes/Spoilers ? No, no, yes. The spoilers control is mapped to the /controls/spoilers property, which doesn't have a default input binding. I have it wired to one of the thumbwheels on my Saitek throttle. Thrust reversers and speedbrakes wouldn't be hard to support, I've just been lazy. The Boeing obviously doesn't have a speedbrake, but the A-4 and Harrier should. There are still some (much harder) issues with drag scaling that I'd like to get fixed first. None of the planes need a brake right now, since they all sit way behind the power curve during approach and dump speed really fast. > Bouncing: > * Landing is relatively hard, esp. since it bounces much. Part of this is due to a blindingly stupid bug with ground effect that I discovered this weekend. It should interpolate the effect from zero at one span height to one at ground level, but it did the opposite. You got full effect instantly at about 200 ft, and the aircraft sorta bounced in midair, spoiling the approach. I don't have this checked into CVS yet, but it'll be there today or thereabouts. Another factor is the lack of automatic wing spoiler deployment, which helps a lot to keep the airplane from getting airborne again after a hard landing. This would require just a tiny amount of C++ code right now: watch the /gear[n]/wow properties and set the /controls/spoilers to 1.0 when they transition from false to true. This would be a great application for interactive scripting from the aircraft definition; a feature that has been long talked about but not yet moved on. And finally, I agree. The default gear damping is a little too light. YASim computes a default damping coefficient automatically, based on the weight of the plane and the placement of the gear. But it's not going to work perfectly for all aircraft. There needs to be a per-gear tunable for spring and damping coefficients, but there isn't yet. This is like the reversers/speedbrakes issue -- something unimplemented only due to my laziness. > * Prior to takeoff, if I keep pressing 'b' and let the engines spool up > to full throttle (or less), the front gear starts bouncing quit a bit > after I release the brake. Well, pumping the brakes during the takeoff is hardly standard procedure; I'm not sure what the real aircraft would do. :) The joystick trigger is mapped to the wheel brakes, by the way. You can use this to get constant braking instead of pounding on your keyboard. The wheel bounce issue is real, though. In my copy, I got better results by changing the compression distance of the nose wheel strut from 2m to 1m in the Aircraft-yasim/747.xml file. This has the effect of making the nose gear much stiffer, reducing the pitch change from gear oscillations. Try this, and see if it feels better. I have no idea what the compressibility of the real thing is -- I made the 2m number up too. >(BTW: the parking brake doesn't seem to work w/ the 747) Uh, true. This is trivial to fix, just add a mapping from the parking brake property in the 747.xml file. Everywhere you see: <control-input axis="/controls/brakes[n]" control="BRAKE"/> add a: <control-input axis="/controls/parking-brake" control="BRAKE"/> I don't know why this wasn't done to begin with. Maybe it's because I'm not sure how the parking brake functionality is handled on a 747; I'm sure it's more complicated than this, but this is a start. > Another thing: It does not seem possible to start fgfs with the 747's > engines off. This is true. The YASim jet model doesn't handle starting and stopping behavior. Unlike piston engines, starting procedures and behavior for turbines are very complicated, and vary widely from engine to engine. The idea behind YASim is to provide good and sane behavior for all aircraft, or at least as many as practical. I suppose I could wire up an "eye candy" starter, which spooled the engine up and down from zero while diddling the temperature and fuel flow variables in a vaguely plausible way. But features like realistic engine start aren't possible for this code; they'll need to wait for someone with the patience and dedication to model one specific engine (and electrical system, and APU, and...). :) > Why are the four engines mapped to two thrust[n] properties instead of > four ? Would it work if I map them to 4 throttles ? There are only default input bindings for two throttles. While I was happy leaving spoilers out of the default configuration, a 747 with its two starboard engines fixed at idle is kind of a showstopper. :) It will work just fine to map them to as many properties as you like. You can map any joystick/keyboard input to any property, and any property to any single YASim input. You can even have multiple properties mapped to the same input -- they sum to get a final number. 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
