Here's a quick review of YASim -- I've been following the first few releases, and 0.1.3 (not yet in FlightGear CVS) is the first that seems stable enough to use. I tried the YASim C172, since that's the plane we've had for the longest in FlightGear, in both JSBSim and LaRCsim versions.
The YASim C172 flies fairly well. Take-off works, and p-factor is about the same as in the FLY! C172 -- i.e. you need a lot of right rudder to keep the nose straight during a power climb. Levelling off at 3000' ASL, however, I had trouble establishing a cruise above 100kt at about 85% throttle -- I'd expect 110kt - 125kt, depending on the engine. Where YASim differed most was the stall. I cut the throttle at 3000' then held altitude with the elevators while the plane bled speed. Stall was *very* different than in any of the other simulated C172's I've tried (LaRCsim, JSBSim, FLY!, and MSFS) -- instead of the nose falling until I picked up speed again, the left wing suddenly dropped out from under me and the ground started spinning towards me at an alarming rate. I didn't recover until 1000' ASL (about 600'AGL), which was a little too close for comfort. Is that right for a C172 with neutral rudder and aileron? It was quite dramatic, in any case. Given that YASim models airflow over surfaces, I expected a more fluid feel to the controls (i.e. more like a boat than a car), but it felt much the same as the JSBSim C172 -- the plane responds instantaneously to all control inputs, as if it had virtual tires firmly in the air. I'd like to hear from the pilots on the list about how real C172s feel in the air -- is there a tiny, fraction-of-a-second lag between control input and response and air pressure builds up on the control surfaces? YASim's gear code, like JSBSim's, has trouble handing wind while on the ground. While sitting on the ground with a 20kt crosswind and full brakes, YASim will still weathervane into the wind, while JSBSim will bounce around with the nose hitting the runway. I didn't land the C172 during this review, so I do not know whether YASim supports ground effect yet. The greatest weakness in YASim right now is the powerplant. Unlike JSBSim, LaRCsim, and FLY!, YASim does not allow you to start the engine, does not allow you to lean it in flight to get extra power (leaning just cuts the RPM proportionally to the mixture), and doesn't give a useful EGT or fuel-flow display. That shouldn't be taken as a major criticism -- YASim's lifespan in FlightGear is still measurable in days, and it's astounding how fast it has caught up with the other FDM's in many areas. Adding better powerplant support won't be hard, and hopefully, others will volunteer to help Andy with it. All the best, David -- David Megginson [EMAIL PROTECTED] _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
