Hi -- I noticed improper readings from the inclinometer ball. -- When parked, the ball was pegged to one side. -- When taxiing at low speeds (a few knots or less) the ball sometimes oscillated wildly back and forth.
I observed this in the c182 model and in the default c172 model. Tracing indicates that the problem is not within the slip_skid_ball.cxx code, but rather upstream of there, in the flight dynamics. Tracing shows huuuge and wildly fluctuating y-accel-fps_sec values. Additional evidence pointing to the FDM comes from the fact that the problem is observed with JSBSim and not with larcsim (although larcsim has other problems, such as drifting slowly sideways whille parked). Can anybody shed light on this? I suspect this bug has been around for a while, but I couldn't find any discussion in the archives. ======================= Philosophy and motivation: Some people may be wondering, who cares about taxiing anyway. Well, there are at least two ways of looking at it: -- the gamer perspective, and/or -- the flight instructor perspective. If all you want to do is fly around and look at the scenery, you don't need an inclinometer ball at all. OTOH if you want to have a realistic flight, one of the checklist items is to verify, insofar as possible, that the instruments give correct indications during preflight and taxi. In a real aircraft, if I found the inclinometer pegged, I'd cancel the flight before I even started the engine. Furthermore, there is a third way of looking at it: -- the simulated flight dynamics perspective. So far I have nothing more than a hypothesis, but my hypothesis is that there is something quite broken in the flight dynamics software. *) Perhaps somebody should be using cartesian coordinates instead of polar coordinates (which are singular at the origin). *) Perhaps somebody should be using quaternions instead of Euler angles (which are singular at the poles). That is, I suspect that this bug is not confined to taxi situations. I suspect there are in-flight situations where the same problem crops up. The fact that we can debug it on the ground may be a blessing, in a backhanded sort of way. Again: Can anybody shed any light on this? Any suggestions on where to look next? For starters, can somebody explain why some parts of the code speak of y-accel-fps_sec while other parts speak of a-pilot-y-ft_sec2 ??? ====================================== BTW, I don't want to sound too nit-picky, but the proper name for the "ball" instrument is the "inclinometer" ball. The "slip/skid" name is deprecated, because the ball measures neither slip nor skid. The distinction is significant if you are flying a multi-engine aircraft with an engine inoperative; in the desired no-slip condition the ball will be off center, correctly indicating an inclination but not indicating a slip. ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Flightgear-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/flightgear-devel
