On 06/18/2007 04:06 AM, Stefan Seifert wrote: >> If you want to know exactly why FGFS poops out at approximately >> 62,000 feet, look at line 88 of Environment/environment.cxx
> Just for my understanding: this table is only used for instrumentation, > isn't it? > Both JSBSim and YASim have their own atmosphere models including such > tables where JSBSim goes up to 259186ft and YASim to 18900m (62008ft). That's an interesting question. I said there was a mess, but I barely hinted at how big a mess it is. Here are a few more hints: 1) Do you consider the MAP (manifold absolute pressure) instrument to be "instrumentation"? In the c182r, the MAP instrument looks at the mp-osi property, as it should. The mp-osi property is driven by the FDM (i.e. JSBSim). At 100,000 feet, I observe that map-osi property reads 0.32 with the engine turned off, which is a sensible value, vastly more sensible than the "environment" and "static" pressures. So there's not a clean division between "instrumentation" and "other". 2) But wait, there's more. The FDM's model of the atmosphere model is blissfully ignorant of the properties of the actual air mass. If you change the local barometric pressure, the MAP that you observe (with the engine off) should track the barometric pressure, but it doesn't. You can easily verify this while sitting on a runway with the engine turned off. Changing the barometric pressure affects the altimeter but not the MAP. 3) Tangential remark: the c182r engine continues to run at 100,000 feet. In fact with the throttle at idle, the engine spins up to thousands of RPM. It's quite comical. 4) By the way, did you ever wonder what "osi" means, in the context of the mp-osi property? The only documentation I can find on the subject is here: http://baron.flightgear.org/pipermail/flightgear-devel/2003-May/017373.html The only problem is that it is 100% false. 5) I'm not even going to ask why a single copy of FGFS has at least three different atmosphere-models (one in the Environment directory, one for JSBSim, and one for YASim). *) Note that it is /not/ a cause for concern that the altimeter has its own model. The altimeter necessarily models an ideal atmosphere, whereas the Environment (and the FDMs) should be modeling the real atmosphere. They have some things in common, but they are not the same thing. A pilot who thinks that pressure altitude is equal to true altitude is asking for trouble, possibly fatal trouble. ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
