scott@opus.UUCP (Scott Wiesner) (02/05/85)
A few possible problems have been given regarding my model's set-up. > (1) CG too far aft. Not really. With the tank full, I suspect the CG was quite a bit forward from the "dry" CG. With the tank empty, the plane was "just a touch" nose heavy. > (2) A poorly chosen airfoil, airfoils with sharp leading edges have > undesireable stall charisterics (like WHAMO ), there are also > airfoils that have VERY poor lift moments. Though I can't speak to the lift moment question, the leading edge was incredibly blunt. > (3) The wing had a lot of wash-in. I don't believe there was ANY wash-in or wash-out. The plane was built quite straight. No trim was required for level flight at full throttle. > (4) Elevator had too much throw (very easy to overcontrol). The elevator had plenty of throw, but anything other than VERY large manuevers caused a snap. > (5) Elevator push rod was too flexable (assuming that it pushed for up > elevator). All pushrods were quite stiff. Even if the it were too flexible, I don't think this would be a cause for the snap rolls. > (6) An asymetrical wing (did it always snap the same direction?) different > airfoils on right and left wing will produce wierd effects. I'm not sure about this one. It did always snap in the same direction, but I'd think this problem (asymetrical wing) would have cause a lot of trim problems, of which there were none. The theory I'm most likely to believe is that the plane was too nose heavy, requiring a fair amount of elevator deflection to cause any pitch change. The "extra" amount that was causing the snaps was causing the tail to stall out, which resulted in the snap. -- Scott Wiesner {allegra, ucbvax, cornell}!nbires!scott