Re: [Flightgear-devel] Fwd: Re: Bug in JSBSim FGPropeller.cpp
I just tried FG rebuilt with that update, with P-38L when pushing the throttle and pulling and pushing the aircraft reaction is better the aircraft heading is now close to be stable. Same here with the Seneca. And debugging the moments shows that they are now symmetrical as desired. Cutting either one of the engines gives the equal yaw for both sides - perfect. I think, thats it! Thanks your help, Torsten - 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
Re: [Flightgear-devel] Fwd: Re: Bug in JSBSim FGPropeller.cpp
On Tue 7 August 2007 22:37, Berndt, Jon S wrote: 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. I haven't been able to look too closely at this, yet, but I have a suspicion. If you look in the function FGPropeller::GetPowerRequired() there is this line at the end of that function: vTorque(eX) = -Sense*PowerRequired / (RPS*2.0*M_PI); This calculates the torque caused by the propeller as it beats against the atmosphere, and it does account for the sense that the propeller turns in. Now, look in the function above it, Calculate(), and you will see this, where the moment is calculated for the propeller: vMn = fdmex-GetPropagate()-GetPQR()*vH + vTorque*Sense; Do you see what is happening? The torque is getting multiplied by the sense, again. I suspect that the equation should simply be: vMn = fdmex-GetPropagate()-GetPQR()*vH + vTorque; Can you try this out? Jon Hello Jon I just tried FG rebuilt with that update, with P-38L when pushing the throttle and pulling and pushing the aircraft reaction is better the aircraft heading is now close to be stable. When testing it with F4U-7 (french corsair) i continue to get the welcome right torque effect more or less according to the throttle position. I cannot answer instead of Torsten, may be you you have pointed to the right place. That update gives a positive result. Regards -- 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
[Flightgear-devel] Fwd: Re: Bug in JSBSim FGPropeller.cpp
-- Forwarded Message -- 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 CCWon 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
Re: [Flightgear-devel] Fwd: Re: Bug in JSBSim FGPropeller.cpp
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. I haven't been able to look too closely at this, yet, but I have a suspicion. If you look in the function FGPropeller::GetPowerRequired() there is this line at the end of that function: vTorque(eX) = -Sense*PowerRequired / (RPS*2.0*M_PI); This calculates the torque caused by the propeller as it beats against the atmosphere, and it does account for the sense that the propeller turns in. Now, look in the function above it, Calculate(), and you will see this, where the moment is calculated for the propeller: vMn = fdmex-GetPropagate()-GetPQR()*vH + vTorque*Sense; Do you see what is happening? The torque is getting multiplied by the sense, again. I suspect that the equation should simply be: vMn = fdmex-GetPropagate()-GetPQR()*vH + vTorque; Can you try this out? 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
