Re: [Flightgear-devel] Negative-drag-bug in 20 aircraft models
I'm currently maintaining the 737-300, and it has this issue as well but I wonder if a fix might make the model worse. Though it comes much closer to the Vr, it needs plenty of force on the elevator to rotate and lift off. And with that bug fixed I fear it will getting worse than now. I haven't tried what happens to each aircraft when the bug is fixed, but my guess is that the bug only is relevant to the propulsion of the model, because the property aero/coefficient/CDde doesn't rotate the aircraft, it only slows it down. All the bug does is, instead of slowing the model down, it reacts like a little boost rocket which magically accelerates the plane as soon as you pull back the yoke. During takeoff-roll the elevator deflection is almost zero, so the bug doesn't contribute to reaching Vr anyway. When the bug really is needed to rotate the aircraft, then perhaps increasing the elevator's area or angle, or increasing engine power, or checking the center of gravity is what's really needed here. But I'm only guessing! I haven't verified this, I'm sure you know how to do your maintenance job! Andreas -- Download Intel#174; Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] Negative-drag-bug in 20 aircraft models
Hello Andreas, A list of the compromised models: negative Drag 707 737-300 So each aircraft at a minimum needs a flight test and possibly some tuning for the fix. Sure! And of course I wasn't complaining - I thank you all very much for your work! If there is something I can do, tell me! I could do little test reports for the fixed models. But who will do the bug fixes, the author of the respective aircraft or some kind of CVS supervisor? Andreas I think we had this issues some while ago on the list, but wasn't fixed in FGFS cvs. I'm currently maintaining the 737-300, and it has this issue as well but I wonder if a fix might make the model worse. Though it comes much closer to the Vr, it needs plenty of force on the elevator to rotate and lift off. And with that bug fixed I fear it will getting worse than now. If you want to take a look www.hoerbird.737-300.tar.gz, which I recently sent to one of our devs with CVS-access. Cheers HHS __ Do You Yahoo!? Sie sind Spam leid? Yahoo! Mail verfügt über einen herausragenden Schutz gegen Massenmails. http://mail.yahoo.com -- Download Intel#174; Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] Negative-drag-bug in 20 aircraft models
just a quick fix like this can break an aircraft if it was tweaked to fly correctly with this bug. Okay... but if a model is tweaked this way, that would mean that the tweaking only is active when the yoke is pulled back... so there couldn't be a correct level-flight, which is a more important situation, I guess. I tried a quick flight in the L-1049 after doing this change and it would barely take off... This is probably true for other aircraft (didn't test it), but I think your experience here is a Lockheed1049-specific problem. The MAP is only 48inHg at full throttle when it should be about 56 (the Gauges don't even cover that value). When you change RatedBoost1 from 8 to 14, you get more realistic indications and lift off 25% earlier. Also make sure to set propeller pitch to max rpm. I did some comparison and found that the original version reaches take-off speed only 3 seconds earlier than the fixed version, even with the yoke pulled back during acceleration. But I'd recommend Buckaroo's SuperConstellation anyway, I just took this example because it is in CVS. (BTW: the autopilot.xml is broken as well- lines 148 to 150 need to be commented out.) So each aircraft at a minimum needs a flight test and possibly some tuning for the fix. Sure! And of course I wasn't complaining - I thank you all very much for your work! If there is something I can do, tell me! I could do little test reports for the fixed models. But who will do the bug fixes, the author of the respective aircraft or some kind of CVS supervisor? Andreas -- Download Intel#174; Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] Negative-drag-bug in 20 aircraft models
On Sat, 2010-02-20 at 18:08 +0100, andrea...@gmx.net wrote: just a quick fix like this can break an aircraft if it was tweaked to fly correctly with this bug. Okay... but if a model is tweaked this way, that would mean that the tweaking only is active when the yoke is pulled back... so there couldn't be a correct level-flight, which is a more important situation, I guess. I tried a quick flight in the L-1049 after doing this change and it would barely take off... This is probably true for other aircraft (didn't test it), but I think your experience here is a Lockheed1049-specific problem. The MAP is only 48inHg at full throttle when it should be about 56 (the Gauges don't even cover that value). When you change RatedBoost1 from 8 to 14, you get more realistic indications and lift off 25% earlier. Also make sure to set propeller pitch to max rpm. I did some comparison and found that the original version reaches take-off speed only 3 seconds earlier than the fixed version, even with the yoke pulled back during acceleration. But I'd recommend Buckaroo's SuperConstellation anyway, I just took this example because it is in CVS. (BTW: the autopilot.xml is broken as well- lines 148 to 150 need to be commented out.) I was using Buckaroo's 1049H actually, along with an engine/prop combination I'm playing with for 2.x+ flightgear. I took off from a 4800 MSL field and was never able to exceed 6000 MSL. Before the fix the aircraft would easily reach 200 knots and climb at better than 800 fpm at 180 knots. After the fix I could barely maintain 150 knots in level flight. Because the formula for elevator drag includes dynamic pressure (aero/qbar-psf), and qbar is a function of the square of the airspeed, the effects of the change won't be as noticeable at lower speeds. So each aircraft at a minimum needs a flight test and possibly some tuning for the fix. Sure! And of course I wasn't complaining - I thank you all very much for your work! If there is something I can do, tell me! I could do little test reports for the fixed models. But who will do the bug fixes, the author of the respective aircraft or some kind of CVS supervisor? It generally left up to the individual model author or if the model is maintained in the JSBSim cvs it will be synced from that database from time to time. Ron -- Download Intel#174; Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
[Flightgear-devel] Negative-drag-bug in 20 aircraft models
Hi everyone! I think I found a little bug in a couple of JSBSim-aircraft: The property /fdm/jsbsim/aero/coefficient/CDde (Drag_due_to_Elevator_Deflection) takes negative values when the elevator moves up, so the elevator face is accelerating the plane. The wrong code is found in the model.xml file: product propertyaero/qbar-psf/property propertymetrics/Sw-sqft/property propertyfcs/elevator-pos-norm/property value0.059/value /product fcs/elevator-pos-norm should be turned to an absolute value by abs .. /abs Here's an example of the bug's effect: --- When you take the Lockheed1049 and let it fly close to stall speed, yoke pulled all the way back, the elevator generates a thrust of 13kN while each of the four engines only deliver 5kN. With the bug fixed, the engines are running at 11kN each. --- A list of the compromised models: negative Drag 707 737-300 747-400 A6M2-jsbsim an2 Boeing314 Concorde DC-6B E3B F80C F-117 KC135 Lockheed1049 Malolo1 Noratlas OV10_CDF RafaleB17 Rascal110-JSBSim T-4-jsbsim YardStik - The next list contains aircraft that have the bug, but it doesn't take any effect because elevator-pos-norm is always zero. (Who can tell me why?) zero Drag- A300 A380 colditz MD11 paraglider SaabJ35Draken sgs233 victor -- And the following planes seem to have buggy code, but I somehow couldn't start their jsbsim-versions to test it: ??? HondaJet Skyranger MB326 --- Am I right? Regards, Andreas Zenner -- Download Intel#174; Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] Negative-drag-bug in 20 aircraft models
andrea...@gmx.net a écrit : Hi everyone! I think I found a little bug in a couple of JSBSim-aircraft: The property /fdm/jsbsim/aero/coefficient/CDde (Drag_due_to_Elevator_Deflection) takes negative values when the elevator moves up, so the elevator face is accelerating the plane. The wrong code is found in the model.xml file: [...] The next list contains aircraft that have the bug, but it doesn't take any effect because elevator-pos-norm is always zero. (Who can tell me why?) victor - for this one i submitted a modified version to the author a month ago, but it didn't reached CVS yet (and i don't have his mail so I can't tell what's going on) here it is: http://janodesbois.free.fr/doc/victor.tar.gz -added *-norm properties -animated aero control surfaces -working as tanker, and can be refueled too jano -- Download Intel#174; Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] Negative-drag-bug in 20 aircraft models
On Fri, 2010-02-19 at 10:20 +0100, andrea...@gmx.net wrote: Hi everyone! I think I found a little bug in a couple of JSBSim-aircraft: The property /fdm/jsbsim/aero/coefficient/CDde (Drag_due_to_Elevator_Deflection) takes negative values when the elevator moves up, so the elevator face is accelerating the plane. The wrong code is found in the model.xml file: product propertyaero/qbar-psf/property propertymetrics/Sw-sqft/property propertyfcs/elevator-pos-norm/property value0.059/value /product fcs/elevator-pos-norm should be turned to an absolute value by abs .. /abs Yes, you are correct. There is a property fcs/mag-elevator-pos-rad that gives the absolute value of the elevator position in radians. I prefer using radian or degrees for surface positions since they can be adjusted and used in a more meaningful way. A list of the compromised models: Thanks. --- Am I right? Yes, drag is a force parallel to the relative wind (direction of travel). Having it negative would imply the relative wind is somehow pulling the aircraft opposite its flow instead of trying to push the aircraft in the direction of its flow. In mathematical terms arctan(lift/drag) is always less than +/- 90 degrees. Ron -- Download Intel#174; Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
