From the original post at x-plane.org:

 

"

Realistic Flight Model

Originally used in professional simulators

Airframe, flight model, speeds, performance and handling as close to realistic as X-Plane permits.

Checklist and performance charts included

 

 

Works with x-plane 9.70 and 10+"

 

 

http://forums.x-plan...&showfile=18484

 

One of the pilots I talked to regarding torque-induced roll was a 1900D captain working for a portuguese airline. He was very helpful and provided lot's of interesting information, including the fact that appart from the use of rudder to counter some left yaw when power is applied, there is no need for aileron input regarding any torque effects. Aileron trim can be used under fuel imbalance or engine-out situations though...

 

I really look fwd to test this aircraft in XP10 ;-) If it still has torque roll, I will apply the Art Stab trick to it :-)

So, who's going to be the first to test this one and let us know if it's indeed that good?

I'll try ASAP... maybe tonight, but not for sure because I'm far from my PC right now.... This one and the Sbach300 are both in my priority list :-)

It's the X-Plane 8 model by STMA. Wasn't bad at the time, but I haven't used it in years.

That's disappointing to know :(

Yes, tested it, just as my other suggestions from yesterday...

 

X-Plane must have potential... I have to believe... :-(

That's disappointing to know :(

 

No, not really. It WAS a nice one, a good one. And STMA donate their older planes to the Community. That's a nice offer and nothing to be dissapointed about, imho. Some people still enjoy those old birds.

Yes, tested it, just as my other suggestions from yesterday...

 

X-Plane must have potential... I have to believe... :-(

 

I thought (as per your statements) that some of Goran's aircrafts have a good flight model (I assume without the torque roll "bug") without using the art stab "cheat". So it can be done?

Murmur,

 

I thought (as per your statements) that some of Goran's aircrafts have a good flight model (I assume without the torque roll "bug") without using the art stab "cheat". So it can be done?

 

both the dc3 and the sundowner are certainly a lot better than any default in x-plane10, or the two Carenados I bought too, but they still have the persistent roll torque effect.

 

Of course we should be careful about the subject of torque roll because, most RL aircraft are equipped with either trim tabs or canted engines or vertical fin, mostly to overcome slipstream yaw effects than to overcome torque effects (*** at the end of this post...)

 

I haven't yet found the exact source (with formulas) to convince me about what John Denker writes here on the last two points. This sort of roll from engine torque is, for instance, perfectly modeled in DCS World's p51d, but also in all of the Aerofly FS prop aircraft. A fellow Extra 300 portuguese pilot (who also owns a Pitts S2b) confirmed that indeed torque roll was felt *** ONLY *** when making changes to power (either increasing / decreasing), but as far as the new power setting was attained and stabilized there would be no additional effects.

 

The problem with X-Plane is that torque roll persists beyond the power changes even at straight & level flight, and we have discussed here various possible explanations for that effect. When airplane designers take care to choose their wing airfoils, sometimes different along a wing, they can use tweaked CL or Drag/AoA curves to try some forces to counteract the "torque budget", or use modified Radii or Gyration to make the roll axis more sluggish... Combined with trim tabs these changes can lessen the effects of the bug in X-Plane (I still think it is a bug or a simplification causing it...) that causes the persistent roll from engine/prop torque on prop aircraft.

 

The other approach as you know as well is to use the Art Stab section. In fact this one even allows for an almost "perfect" solution for the way too sensible behavior of aircraft on ground under cross-wind conditions by setting a LOW SPEED region of Art Stab activation.... and for me this is a way better approach than using truck like undercarriages for airplanes do have more sideways drag than they should...

 

Goran's aircraft are certainly a lot better than many others I have tested, but still not perfect, not by his fault, but because of X-Plane's problems / limitations...

 

(***) Of course, if you make changes to AoA / Speed / flaps or other lift augmentation devices, torque as well as slipstream will again pump in....

I really start thinking about an engine torque on or off tick box in the joystick menue. Realistic or not, it must be useable.

I haven't yet found the exact source (with formulas) to convince me about what John Denker writes here on the last two points. This sort of roll from engine torque is, for instance, perfectly modeled in DCS World's p51d, but also in all of the Aerofly FS prop aircraft. A fellow Extra 300 portuguese pilot (who also owns a Pitts S2b) confirmed that indeed torque roll was felt *** ONLY *** when making changes to power (either increasing / decreasing), but as far as the new power setting was attained and stabilized there would be no additional effects.

 

I'm still not 100% sure it's a bug. John Denker (a pilot himself) writes:

 

"Airplane designers have long since learned about this propeller drag rolling moment, and they take steps to compensate for it. For instance, they set the left wing at a slightly higher angle of incidence than the right wing. This is called, unsurprisingly, asymmetric incidence. It is especially useful to apply this trick to the part of the wing that flies in the propwash, so that the effect increases as engine power increases. On a Piper Cherokee, the roll-wise trim is easily adjustable on the ground — in the flap extension mechanism for each flap there is a turnbuckle that allows the flap to be raised or lowered until the roll-wise trim is just right."

 

Now, how many X-Plane aircraft designers know about this aspect and use asymmetric incidence, engine cant, etc?

However, I'm not even saying that there is NOT a bug. It's possible that even using these "realistic" tweaks, the roll tendency would not be completely canceled out at every airspeed/power combination. MortenM once wrote (when modeling his Archer) that the propeller helical propwash is underestimated in X-Plane, since using an engine cant of 3 degrees right (the engine cant on the real Archer), the X-Plane model would yaw to the right on takeoff roll, while the real one yaws to the left (despite a 3 degrees engine cant to the RIGHT!).

 

However, I'm trying to tweak the B1900 and I managed to get some improvements, although still no 100% perfect.

 

Marco

However, I'm trying to tweak the B1900 and I managed to get some improvements, although still no 100% perfect.

 

Marco

 

Tell us how you did it ;-)

 

Also, I seldom mention ELITE v8 lately, but in that sim they managed to get the sipstream effects very realistically for the various aircraft models in the package. You have left yaw during takeoff or other high power / low speed situations, and right yaw when on low power (i.e. during a descent...). These come both from the reversal of force / pressure distribution on the prop(s) but also from the fact that most aircraft use trim or other techniques for cruise flight, and when they are on other regimes those "tweaks" show thgeir effect

Tell us how you did it ;-)

 

Adding additional wings downstream of the props, on the outside of each, to compensate for the varying torque and the supposedly underestimation of helical propwash. Of course it's absolutely equivalent to modyfing airfoils on that part of the wing, I'm using the "unrealistic" hidden wings only beacuse it's much faster to experiment than modyfing airfoils.

 

If I get good results I'll upload the modified aircraft.

 

Marco

Also, I seldom mention ELITE v8 lately, but in that sim they managed to get the sipstream effects very realistically for the various aircraft models in the package. You have left yaw during takeoff or other high power / low speed situations, and right yaw when on low power (i.e. during a descent...).

 

Problem is, yaw should induce roll. What happens if you don't compensate for this yaw? Will the aircraft roll progressively to 90 degress?

Problem is, yaw should induce roll. What happens if you don't compensate for this yaw? Will the aircraft roll progressively to 90 degress?

 

Yes of course they will roll too :-) But the yaw comes 1st, and if you use the correct rudder input, because even if you do not notice it, the ball tells you to do so, the roll will never start...

 

In Xplane if you use the correct countering input - right rudder (*) - , you'll be in a sideslip with your ball to the left asking for left rudder - nonsense....

 

On most sailplanes torque from the rotating slipstream from the tug, specially if you're low behind it, will cause roll :-) So, gliders can suffer from torque roll :-) (but not in x-plane :-(

 

(*) Assuming CW rotating prop as seen from the cockpit on an aircraft with the prop ahead of the cabin....

 

P.S.: Just 1 more thing! I'm glad you picked the 1900d for your experiments. I confess I liked the model, although I have to set my throttle axis properly because, just as it is, it goes down from beta range to reverse without having to hit the default key used in x-plane for reverse thrust...

 

Looking inside PM revealed a good deal of aileron trim (right trim), prepared for cruise. When you set power for descent a noticeable right bank results...