On Fri, 15 Mar 2002 14:42:27 -0800 Andy Ross <[EMAIL PROTECTED]> wrote:
>Sigh... grab a calculator. Type "2", then "0", then "sin". :) >The answer to this question: > > How far from the original position is the tip of a gear strut at 20 > degrees of AoA (or bank, or whatever)? >...is "34% of its length". Draw it out, if it is not clear. For >small angles, that distance goes as the sine of the angle. The sine >of 20 degrees is 0.34. QED. Andy can draw. Andy can do trig. Andy can write "QED". Either you are missing my point, or I am missing yours. This 34% has no bearing on anything - at least given the way JSBSim models gear/ground interactions. I am absolutely clueless on what you are trying to get across. It appears to be totally irrelevant. >The point of doing separate gear intersection testing >is to get proper results when the ground is *not* flat. We *already* >get proper results with flat ground. For Pete's sake, I *know* this, and I am *not* assuming the ground is flat. I've been trying to get across to you that we *can* assume that: 1) *FOR THE PURPOSES OF CALCULATING FORCES* and MOMENTS given our simulated world that the strut *compresses* along a vertical axis only. 2) For the purposes of calculating correct aircraft *orientation* (repeat O R I E N T A T I O N ... look it up at m-w.com) we can assume that the strut compresses vertically. 3) If we have the ground elevation (E L E V A T I O N) at each gear point, then we can correctly orient (O R I E N T) the aircraft on the ground on NON-FLAT runways - EVEN if we span polygons. We've discussed this and investigated it ad nauseum long before you even became involved in this project. >You can't fix the flat ground assumption by making the flat ground >assumption. Again: if we're going to do it, we should do it right and >not wrong. We already have "good enough". If we need better, we can >only go to perfect. You're not making any sense. You're completely missing the point. Given a *NON-FLAT* polygon, how do we place the aircraft on it properly so the gear doesn't sink in on one side and sit above it on the other? The answer is that you give each gear the blasted elevation at that gear. How can I make it any plainer? >Ah, here's an actual feature. But the solution is wrong. If you want >a tilted aircraft, then use the normal vector for the ground plane >(take a look at the YASim code for this if you want). You don't need >to do per-gear stuff for this. And in fact you don't want to, because >of the stair-stepping effect I mentioned earlier. You can do better >with a single plane. Andy, this doesn't work. You cannot simply have a single surface normal and calculate the delta height and angle at any point because the aircraft may span more than one polygon. We went over this long, long ago. At that time we wanted to do a per-gear elevation, but we decided it was too computationally expensive (IIRC). If we can do this now, as Norman mentioned, it's an attractive way to go. Jon _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
