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Subject: Re: [Flightgear-devel] Bug in JSBSim FGPropeller.cpp Date: Tue 7 August 2007 21:03 From: "gh.robin" <[EMAIL PROTECTED]> To: FlightGear developers discussions <flightgear-devel@lists.sourceforge.net> On Tue 7 August 2007 20:00, Torsten Dreyer wrote: > > > May be i don't understand your remark, and i could be wrong, > > > > > > but all aircraft propeller have not the same rotation direction , > > > some are CCW on the same aircraft > > > some are CW on others aircraft. > > Correct - and some aircraft have both of it: one CW and one CCW. > > > > Sure there is no problem with P-38L one propeller is given > > > <sense> -1 </sense> > > > The other is given > > > <sense> 1 </sense> > > > > > > so, Sense could be -1 or 1 which is significant for the propeller > > > effect. > > > > > > it is very important to keep in that calculation the Sense. > > Yes - also true. > > > In addition to, if these effect seems to be more than you espect it is > > possible to reduce the value with <p_factor> </p_factor> with zero > > there is no effect. > > Since the engines of the P-38L and the Seneca are turning in opposite > directions, the p-factor of both propellers are compensating each other. > Thats why aircraft with counterrotating props are made: they are easier to > fly! > > Try yourself: Get the P-38L in the air and fly full throttle straight and > level, open the property-browser for controls/flight. I need a right > aileron deflection to keep the wings level. If I reduce power to idle, the > aircraft turns sharply to the right with that aileron setting. > This should not happen on aircraft with counterrotating props. Yes there is some differences needed to keep the right heading , when we modify the throttle value, but it is not exactly what you are describing. When tuning the FDM during developpement: I experienced a stable flight , waiting for the supercharger being stopped (five minutes after take off) I opened both property browser jsbsim/propulsion/engine[0] and /jsbsim/propulsion/engine[1], i could notice some diff in between blade-angle , thrust coefficient of both propellers engines (i don't know why) If i reduce the throttle value the aircraft change slightly his heading, the aircraft stability is modified, because of the speed which decrease quickly, that modification could be: turn on the left, or turn on the right. At that stage i modify again the aileron deflection to keep the right heading. If i increase again the throttle, i get again a stability problem, and the ac turn to right or to left. I did not conclude it is due to a torque effect. I have an other aircraft the F4U-7 only one propeller , the engine and propeller values are close to these we have with the P-38, the torque effect on the F4U-7 is very high, and .........that is right. So i can say we don't have any torque effect with the P-38L, we have more or less a stability problem when the speed and the thrust are modified. Regards BTW: i have just finished the Noratlas 2501 which is only two engines , propeller both the same <sense> ( viewed from the pilot CCW). with <p_factor> 60</p_factor> I do not notice a very significant torque of the aircraft -- Gérard ------------------------------------------------------- -- Gérard ------------------------------------------------------------------------- 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
