re: [Flightgear-devel] Re: Default startup aircraft
Dave Perry writes: Three comments/concerns for the recent changes to the flight model: 1. The nose pitch-up when adding flaps seems extreem. If I don't change the elevator trim a lot, the plane actually stalls. If I recall correctly, the Piper Tri-Pacer had a slight pitch up with added flaps. But the Cessna 172 nose pitches down a little and you have to make minor trim changes more like the c182 in FlightGear. In my experience (still under 100 hours in type), the C172 always pitches up at slow speed when you add flaps, and you could, in fact, stall the plane if you went to full flaps at approach speed and weren't fast enough on the elevator. That said, I agree that the pitching moment is too violent in the current 172P aero model -- even adding 10deg flaps sends the nose shooting for the sky. I had just used Roskam's numbers (for the 182), but I'll tone it down a bit. 2. The adverse aileron yaw is too much at modrate speeds. In fact, since these changes, the wing leveler auto pilot will cause ever increasing aileron oscillations leading to a crash with the c172p. I'll look into this one. What do you mean by 'moderate' speeds? You should be seeing a lot of adverse yaw below 70kt. 3. The rate of descent with full flaps seems less than it should be. I'll check this as well. Thanks for the input, David -- David Megginson, [EMAIL PROTECTED], http://www.megginson.com/ ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Re: Default startup aircraft
Curtis L. Olson writes: I've never tried this in a real C172, but I can see that for a real pilot, pushing forward on the yoke to hold the nose down after applying flaps could become an almost unconcious act. Yes, after the first couple of approaches, the newly grey hair on your instructor is a good reminder to get on the elevator fast. On the other hand, the first 10deg isn't so bad. If you're trimmed for about 85-90kt and drop the first notch of flaps, you'll get very close to a 70kt approach speed. 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
Re: [Flightgear-devel] Re: Default startup aircraft
David Megginson writes:
Dave Perry writes:
2. The adverse aileron yaw is too much at modrate speeds. In fact,
since these changes, the wing leveler auto pilot will cause ever
increasing aileron oscillations leading to a crash with the
c172p.
I'll look into this one. What do you mean by 'moderate' speeds? You
should be seeing a lot of adverse yaw below 70kt.
The following changes to newauto.hxx allows one to adjust the 'gain'
for this interactively with the autopilot adjuster widget :-)
This widget could be extended to 'tweak' the elevator controls
in a similar manner
// accessors
inline double get_MaxRoll() {
return fgGetFloat( /autopilot/config/max-roll-deg );
}
inline double get_RollOut() {
return fgGetFloat( /autopilot/config/roll-out-deg );
}
inline double get_MaxAileron() {
return fgGetFloat( /autopilot/config/max-aileron );
}
inline double get_RollOutSmooth() {
return fgGetFloat( /autopilot/config/roll-out-smooth-deg );
}
inline void set_MaxRoll( double val ) {
fgSetFloat( /autopilot/config/max-roll-deg, val );
}
inline void set_RollOut( double val ) {
fgSetFloat( /autopilot/config/roll-out-deg, val );
}
inline void set_MaxAileron( double val ) {
fgSetFloat( /autopilot/config/max-aileron, val );
}
inline void set_RollOutSmooth( double val ) {
fgSetFloat( /autopilot/config/roll-out-smooth-deg, val );
}
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Re: [Flightgear-devel] Re: Default startup aircraft
Dave Perry writes: I like the c172p-3d 3d model and 3d cockpit a lot. Three comments/concerns for the recent changes to the flight model: 1. The nose pitch-up when adding flaps seems extreem. If I don't change the elevator trim a lot, the plane actually stalls. If I recall correctly, the Piper Tri-Pacer had a slight pitch up with added flaps. But the Cessna 172 nose pitches down a little and you have to make minor trim changes more like the c182 in FlightGear. I have some experience with a very high fidelity C172 model (commercial) based on real, instrumented flight data. Even at speeds as slow as 90 knots the model will come close to looping unless you add a lot of down elevator. I've never tried this in a real C172, but I can see that for a real pilot, pushing forward on the yoke to hold the nose down after applying flaps could become an almost unconcious act. When you are flying from mouse/keyboard it's just not the same and these sorts of effects can be surprising. Even just with flying with a yoke and having your hands on it, you really don't need to add much down force to keep the nose from ballooning. I have no opinions on #2 and #3 right now. Regards, Curt. 2. The adverse aileron yaw is too much at modrate speeds. In fact, since these changes, the wing leveler auto pilot will cause ever increasing aileron oscillations leading to a crash with the c172p. 3. The rate of descent with full flaps seems less than it should be. What do the rest of you think, especially those with recent real c172 time? It has been several years since I flew the c172. Regards, Dave ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel -- Curtis Olson IVLab / HumanFIRST Program FlightGear Project Twin Cities[EMAIL PROTECTED] [EMAIL PROTECTED] Minnesota http://www.menet.umn.edu/~curt http://www.flightgear.org ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Re: Default startup aircraft
On Wed, 2002-12-11 at 21:24, Curtis L. Olson wrote: Dave Perry writes: I like the c172p-3d 3d model and 3d cockpit a lot. Three comments/concerns for the recent changes to the flight model: 1. The nose pitch-up when adding flaps seems extreem. If I don't change the elevator trim a lot, the plane actually stalls. If I recall correctly, the Piper Tri-Pacer had a slight pitch up with added flaps. But the Cessna 172 nose pitches down a little and you have to make minor trim changes more like the c182 in FlightGear. I have some experience with a very high fidelity C172 model (commercial) based on real, instrumented flight data. Even at speeds as slow as 90 knots the model will come close to looping unless you add a lot of down elevator. I've never tried this in a real C172, but I can see that for a real pilot, pushing forward on the yoke to hold the nose down after applying flaps could become an almost unconcious act. When you are flying from mouse/keyboard it's just not the same and these sorts of effects can be surprising. Even just with flying with a yoke and having your hands on it, you really don't need to add much down force to keep the nose from ballooning. I've never noticed a nose-up tendency when I pull on the flaps. But, I tend to pull them on slowly and gently - and at a lower airspeed (= 90mph for landing). The flaps in the C172 make you go down, not up. OTOH, when you have full flaps down and you hit the throttle (in a go-around type situation), the nose almost shoots up into the air. It takes a lot of forward force on the yoke to keep the plane level with the ground. The lack of nose-up when I'm pulling on the flaps may just be because I'm correcting for the nose-up without thinking about it. I'll try to note this (along with the left-roll tendency) the next time I go flying. -Luke -- Luke Scharf, Jack of Several Trades http://www.ccm.ece.vt.edu/~lscharf ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
