In a message dated 11/16/2003 7:41:18 AM Central Standard Time, [EMAIL PROTECTED] writes: OK, I bite. What do you put on the paper? Cal Posthuma
CAL - I figger out where 37% of the MAC is at the wing root. That's where the CG should be on all the gliders I ever flew. That's a touch forward of neutral, which works for me. Your favorite CG may be forward or aft of this, but the important thing is that once you find the sweet spot for one plane it will be at the same spot on the next plane, as long as you don't radically depart from the typical TD layout and try a canard or flying wing. It's not hard for the typical straight trailing edge tapered wing. I am not qualified to teach math or geometry, but here's roughly what I do. What I put on the paper is a rough sketch of the wing planform. Then I do a bit of rudimentary geometry and change the shape to an equivalent size rectangle. Since the TE is straight the TE of the rectangular wing is the same. The areas of the real wing and the rectangle need to be the same. The span needs to be the same. The root chord of the rectangle will be less, and the tip chord will be greater. The chord of this rectangle is the MAC. 37% aft of the leading edge of this rectangle is the spot. 63% forward of the trailing edge is the same spot. The leading edge of the real wing is forward of the LE of the equivalent rectangle, but the trailing edges are the same. I can measure from the TE of the real wing and have the right place. If the trailing edge is swept forward or aft it complicates the process slightly, but you do basically the same thing. For elliptical shapes I need to drag out the Machinery's Handbook and a calculator, or just pretend it's a quad taper wing and call it good enough -- it's still pretty close. Close enough for this government worker anyway. happy trails - Rob RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
