> There is a bug in JSBSim causing multiengine aircraft with > counterrotating props suffer from excessive yaw when engines > are running. Significant aileron deflection is required to > fly straight and level. > > I tracked down that issue and finally came to FGPropeller.cpp > line 198: > > vH(eX) = Ixx*omega*Sense; > > If I understand correctly, this is some kind of force along > the rotating axis of the propeller and it should not be > multiplied with Sense (unless someone mounts a wrong propeller...) > > Making the line > > vH(eX) = Ixx*omega; > > removes the unwanted yaw and creates symmetrical forces and moments. > > The only aircrafts using counterrotating props are the P-38L > and the SenecaII. > All others should not be affected by this patch. > > Greetings, Torsten
If this is indeed a cause of a problem such as you describe, or a bug, I would be very surprised. Here's why: If you look at FGPropeller.cpp, you will see that the vector vH does not add to the moment of the aircraft unless there is already a rotational motion experienced by the aircraft. See the equation where vH is summed into the moment equation: vMn = fdmex->GetPropagate()->GetPQR()*vH + vTorque*Sense; 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. Can you tell more about the conditions in your test, and more about the problem? Jon ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
