> If the rotational rates (returned by the function GetPQR()) are zero -
> that is, at steady state - the angular momentum (vH) parameter will add
> *nothing* to the total moment (vMn). The angular momentum introduces
> gyroscopic effects.
>
> If the effect is too strong, it could be that the Ixx value for the
> propeler/engine shaft is too large. In that case, the angular momentum
> calculated would be too large and would cause the aircraft to behave
> erratically when manuevering.
Maybe I am wrong, but shouldnt these effects from the left engine compensate
those from the right engine if both are rotating in opposite directions?
>
> Can you tell more about the conditions in your test, and more about the
> problem?
I will try :-)
When you start the SenecaII and give full throttle on ground with parking
brakes set, the aircraft turns slowly to the left (because the brakes are to
weak - thats another story).
When you fly the aircraft with full throttle with wings level, a slight
aileron deflection to the right is needed (approx. 0.05) to keep the wings
level. When you idle the engines, no aileron is needed to keep the wings
level.
I put some debug code into FGPropulsion.cpp:
for (i=0; i<numEngines; i++) {
cout << "computing engine " << i << "\n";
Engines[i]->Calculate();
vForces += Engines[i]->GetBodyForces(); // sum body frame forces
vMoments += Engines[i]->GetMoments(); // sum body frame moments
cout << "Forces: " << Engines[i]->GetBodyForces() << "\n";
cout << "Moments: " << Engines[i]->GetMoments() << "\n";
cout << "finished with engine " << i << "\n\n";
}
and FGPropeller.cpp:
vMn = fdmex->GetPropagate()->GetPQR()*vH + vTorque*Sense;
cout << "PQR: " << fdmex->GetPropagate()->GetPQR() << "\n";
cout << "vH(eX): " << vH(eX) << "\n";
cout << "vMn: " << vMn << "\n";
And the output for the Seneca is
computing engine 0
PQR: -0.00243528 , -0.000488289 , -0.0360579
vH(eX): 508.722
vMn: -376.628 , -18.3435 , 0.248403
Forces: 819.428 , 0 , 0
Moments: -376.628 , -529.63 , 4889.5
finished with engine 0
computing engine 1
PQR: -0.00243528 , -0.000488289 , -0.0360579
vH(eX): -508.722
vMn: -376.628 , 18.3435 , -0.248403
Forces: 819.428 , 0 , 0
Moments: -376.628 , -492.943 , -4889.5
finished with engine 1
and the P-38L says:
computing engine 0
PQR: 0.000489925 , 3.41744e-05 , -0.00822598
vH(eX): -3114.13
vMn: -6748.41 , 25.6167 , 0.106423
Moments: 3071.39 , 0 , 0
Moments: -6748.41 , -2090.55 , 25605.2
finished with engine 0
computing engine 1
PQR: 0.000489925 , 3.41744e-05 , -0.00822598
vH(eX): 3114.13
vMn: -6748.41 , -25.6167 , -0.106423
Moments: 3071.39 , 0 , 0
Moments: -6748.41 , -3126.87 , -25605.2
finished with engine 1
As you can see, the moments second values are different on the second value,
because PQR is not zero.
Both aircraft are sitting on ground, parking brake set, full throttle.
I hope this helps
Torsten
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