On Thursday 24 February 2011 11:41:43 Geoff McLane wrote: > Hi, > > Re: http://www.geoffair.net/tmp/tilted-001.png (updated) > > Thanks Ron, and Stuart, for the tailwind c172.xml > change. As stated, all tests so far on this are great... > with due care can now taxi, takeoff and land with a > modest tail wind ;=)) > > Is there any 'documentation' I can read on why > putting <sin> ... </sin> around the > <property>aero/alpha-rad</property> > did the trick?
I have a few spare moments, maybe I can shine a bit of light... Traditional aerodynamics texts concern themselves with the normal flight envelope. To simplify things they tend to use linear equations that work within the few degrees alpha +/- that make up that flight envelope. Our c172p was written with those simplifications in mind. For example, the pitching moment was expressed as a negative linear function of alpha. That means the higher the alpha angle became the more pitch down force was applied. For alpha angles below stall this is a pretty close approximation, however, for larger values of alpha the approximation rapidly breaks down. Causing, as noted, huge values of pitching moments for alphas near 180 degrees. The sine(alpha) function is fairly linear and equal to the radian alpha angle measurement in the normal flight envelope the textbook functions are written for, but it increases less rapidly above 15 degrees alpha, peaks at 90 degrees and falls back to zero as alpha approaches 180 degrees giving us reasonable behavior for all alpha angles. I'm not claiming aerodynamic truth, just reasonable behavior. > Just so maybe I, or others, could try to be more > helpful next time, if there is one ;=)) Hope that was helpful. Thanks, Ron ------------------------------------------------------------------------------ Free Software Download: Index, Search & Analyze Logs and other IT data in Real-Time with Splunk. Collect, index and harness all the fast moving IT data generated by your applications, servers and devices whether physical, virtual or in the cloud. Deliver compliance at lower cost and gain new business insights. http://p.sf.net/sfu/splunk-dev2dev _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
