I'd like to add a bit more about my pylon racer that was twitching down at high speed. I spent a fair amount of time trying to figure this problem out and had many many many "expert" suggestions along the way. The suggestions included items such as - the servos are not "Holding" center properly, radio glitch, the CG is too far aft, the fuse is flexing etc etc. Well, I went out and spent BIG bucks on the most expensive std size digital servos I could find with the best centering numbers available and guess what. NO CHANGE at all. I added some carbon fiber to stiffen the fuse - NO CHANGE. Switched from a Futaba radio to Spektrum, NO CHANGE. As I mentioned in the earlier post I moved the CG forward a bit and while that seemed to help it, it also introduced problems that were unacceptable for the intended purpose of the plane. (It also had the side effect of slowing the speed slightly) Changing the tail incidence fixed the problem which, after much thought, I suspect was some form of turbulence hitting the stab and causing the twitch. Whatever the cause, changing the stab incidence added stability to my racer. We're talking about a plane that was traveling between 120 and 130 mph so whether or not it would affect one traveling much slower I have no clue. These extremely fast Pylon Racers normally "Groove" extremely well with everything set at 0-0-0 on the incidence angles. This type of plane, AMA - 424/428 AKA Q500, with a Jett or Nelson engine will run between 180 and 190 mph and they usually just go EXACTLY where you point it hence the term "Groove". In the end some really sharp racers over in the pylon forum came up with the stab angle change and viola problem solved. Why? I have no idea, it doesn't make sense. But it worked for mine as well as theirs.