On Wed, 2004-02-04 at 19:54, Curtis L. Olson wrote: > Andy Ross wrote: > > Curtis L. Olson wrote: > > > >>The real fun comes from practicing with only one engine running > >>[...] There are some real world effects that are important for > >>training which I don't think we model well on existing twins. > >> > >>The main one that comes to mind is that with an engine out there is > >>a minimum speed you must maintain > > > > > > That's no doubt true, but hopefully it's more a lack of tuning than it > > is a fundamental flaw. For the specific case of YASim: the asymmetric > > thrust effects should be more or less correct as-is, because it > > applies the force at the location of the engine. The blue line speed > > is almost certainly wrong, but should be relatively easy to find by > > tuning the rudder effectiveness only. > > > > If anyone with ME experience wants to take a few hops in the DC-3 or > > (YASim) C310 and provide feedback, I'd be happy to try tuning the > > models. > > It very well could be a model setup issue at which point it's probably > beyond my ability to debug, but with the JSBSim c310, I took off, climbed > to a comfortable altitude and speed, and chopped the throttle on my right > engine. Then I slowly pitched up to bleed off speed little by little. As > the speed bled off, I held my heading with rudder and kept the wings level > with aileron. > > From the readme: > > Minimum single-engine control speed (Vmca): 75 KIAS > > However, I was able to fly right through this until I got the stall horn, > (about 60 kts?) and all the time, the rudder had plenty of effectiveness to > hold heading. In the real thing (assuming the README is correct) at about > 75 knots the rudder loses enough effectiveness to hold heading against the > one good engine at full throttle and you begin an uncontrollable yaw. This > doesn't happen right now in the JSBSim C310 anyway.
It sounds like it's got too much rudder power or too much directional stability. It could be the propulsion, too, but if the performance is about right then it's probably the aero. > > I'm sure this is just a matter of tweaking the configuration file. But > this is an important behavior to have reasonably correct in small twins. > > I also tried this with the YASim C310. I see a definite yaw effect from > the engine, but I think I am getting to the stall point there too before > I'm getting to the point where the rudder looses effectiveness against the > engine. At about 80 kts (yasim version) the rudder can't quite hold > heading by itself, but I can add a bit of bank towards the good engine with > ailerons and hold my heading until I stall. At the point of the stall in > the real aicraft, the good engine would definitely dictate the direction of > the spin. I find in the yasim model, the aircraft can stall/spin into the > good engine about as easily as the other way. > > In both cases it's probably just the models that need tweaking, but in > their current form, I don't think they are very useful for engine out training. -- Tony Peden <[EMAIL PROTECTED]> _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
