Beechcraft aircrafts roll by themselves

[robertoga 1]

Hello,

I come from Flight Simulator, and have iniciated myself in XPlane 10 few days ago. I find it a challenge, and am sure I am going to find coming dificulties.

One of the first is that Beechcraft planes do roll themselfes to the left; it does happen also with Cessna 172. At the moment, I have only flown with these three aircrafts.

Would anybody know the cause?

Thanks

XPlane 10 in Windows 7 Pro, Core 2 duo 2,63 GHz, nVidia Geforce GTX 550i 1 GB

[jcomm 5,890]

The cause is - overdone torque effect on all prop aircraft in X-Plane10, ported from X-Plane9.

 

It's realistic, on powerfull, WW2-type aircraft, and the best models for FSX do that too - take A2A's p51d as a good example - but a Cessna 172, and specially a Baron58 should not roll this way. Instead, where there is excessive roll due to torque, there is less yaw due to slipstream than expected, and area where again FSX does a better job, even if not very good...

 

Well, we can hope this get's fixed one day... Meanwhile use aileron trim - irrealistic for thos e aircraft, unless under emergency or unbalance (weight) situations, but it works....

[Murmur 3,941]

The cause is - overdone torque effect on all prop aircraft in X-Plane10, ported from X-Plane9.

 

It's realistic, on powerfull, WW2-type aircraft, and the best models for FSX do that too - take A2A's p51d as a good example - but a Cessna 172, and specially a Baron58 should not roll this way. Instead, where there is excessive roll due to torque, there is less yaw due to slipstream than expected, and area where again FSX does a better job, even if not very good...

 

Well, we can hope this get's fixed one day... Meanwhile use aileron trim - irrealistic for thos e aircraft, unless under emergency or unbalance (weight) situations, but it works....

 

What about your old story about the Cessna Wagon? I understood pilot needed fuel imbalance to "trim out" the roll torque at high engine power...

 

http://forum.avsim.net/topic/384613-the-cessna-ag-wagon-pilot/

 

Marco

[jcomm 5,890]

... I don't find it realistic the way it is now ... not on a C172, not on a Piper Warrior, certainly not on a twin like a Baron 58...

 

OTOH I would like to see a lot more justification for the use of rudder instead of aileron / aileron trim, namely, the ball in our turn coordinators clearly asking for right rudder, sometimes all the way accross a high power climb...

[Murmur 3,941]

... I don't find it realistic the way it is now ... not on a C172, not on a Piper Warrior, certainly not on a twin like a Baron 58...

 

OTOH I would like to see a lot more justification for the use of rudder instead of aileron / aileron trim, namely, the ball in our turn coordinators clearly asking for right rudder, sometimes all the way accross a high power climb...

 

Yes the general consensus is torque induced yaw is too low (MortenM encountered this problem while modeling his Piper Archer for X-Plane 9, there's an old thread on the .org).

 

However, there's one thing I don't understand: you say that in a twin, torque induced roll should be even lower than in a single. But in a single, the helical slipstream hits the vertical (and horizontal) stabilizers, and this should produce a counter-torque (clockwise in a clockwise rotating engine) balancing the torque of the engine (anti-clockwise torque).

 

Instead, in a twin, the helical slipstream only hits a very short span of the wings and nothing else. So according to this reasoning, torque induced roll in a twin should be higher than in a single. What do you think?

 

Marco

[jcomm 5,890]

Yes the general consensus is torque induced yaw is too low (MortenM encountered this problem while modeling his Piper Archer for X-Plane 9, there's an old thread on the .org).

 

 

And the way Morten found, just like others, around this limitation was to use artificial stability control inputs defined in PM, to create a moment, by artificial aileron deflection, opposing the overdone torque effects...

 

On a twin, say CW, and provided you're flying coordinated (slips will agravate the effects of asymmetric propwash hitting the tail on a twin), there is still propwash hitting the tail and causing a yaw moment to the left, and of course there is still mechanical torque from the engine and from the airflow drag, but the rest of the fuselage is less affected by asymmetric propwash effects (it's balanced), and the inner sections of both wings are still hit by propeller propwash, only, both compensate in some way because if the main propwash stream hits their lower surface then on the right wing this will contribute to a roll moment to the left, while on the left wing it will be opposite... OTOH, if it's the upper surface that is hit, then there is contribution to right roll from the right wing and to left roll from the left wing...

 

It's not the best explanation I know, and a sketch would certainly help...

--

[Murmur 3,941]

On a twin, say CW, and provided you're flying coordinated (slips will agravate the effects of asymmetric propwash hitting the tail on a twin), there is still propwash hitting the tail and causing a yaw moment to the left, and of course there is still mechanical torque from the engine and from the airflow drag, but the rest of the fuselage is less affected by asymmetric propwash effects (it's balanced), and the inner sections of both wings are still hit by propeller propwash, only, both compensate in some way because if the main propwash stream hits their lower surface then on the right wing this will contribute to a roll moment to the left, while on the left wing it will be opposite... OTOH, if it's the upper surface that is hit, then there is contribution to right roll from the right wing and to left roll from the left wing...

 

It's not the best explanation I know, and a sketch would certainly help...

--

 

Here's how I see it:

 

 

 

If that is the case, in a single, one should have more yaw and less banking, since most of the banking (roll) torque should be balanced by the opposite torque induced on fuselage, wings, tail. In a twin instead, that should not be the case, so one should have more roll torque and less yaw (since in a twin the propwash does not hit directly the vertical stabilizer, that should be the main source of induced yaw). What do you think?

 

Marco

[jcomm 5,890]

Marco,

 

the argument you use for the singles is perfect - and also the one I've been using with Austin.

 

Regarding the twin example - and you picked an even easier twin, because of the "T" tail :-), if the spiraling slipstream hitts both wings (each engine) from the down side (your leftmost arrows in your sketch), then, the left wing will be pushed up and so will the right wing. Actually the "moment will be a little more effective" on the left wing because of the longer arm from the CG... the difference being probably negligible...

 

OTOH if the propwash slipstream hitts both wings on their uppper surfaces then the left wing will be pushed down and so will the right wing, although this turn around the arm will be a bit longer on the right wing...

 

Appart from torque only, the spiraling slipstream resultant on both wings will tend to overcome any roll tendency....

 

RW twin pilots (non Counter-rotating) know about this and comment that you end up using a lot less right rudder on takeoff / climb than on a single...