>what I need is info on how to modify (by increasing camber and washout) >a particular airfoil across the span such that tip stalling is minimized >with minimal impact on performance, and what airfoils do or do not lend >themselves >to such manipulation. Specifically, I'd like to do this with >the RG-15. (In fact I have already done it on two wings, both of which >seem to fly well, but I was more or less guessing at the amount to >increase the camber and would like to know if there is a more >"scientific" method?) A very safe way to do this is to interpolate two baseline airfoils in various proportions. The polar of the interpolated airfoil will be quite close to what you get by interpolating the two baseline polars themselves. This seems to work with any two sailplane-type airfoils. At least that's what calculations indicate. Note: A foam cutter with two different templates at the ends does this interpolation for you. On the other hand, simply scaling the camber and/or thickness of an existing airfoil is more hazardous. Scaling the camber from 2% to 4% may increase CLmax a little or a lot, depending onthe % thickness and Reynolds number. It may even decrease CLmax in some cases! One would have to run tests or calculations on the modified airfoil to be certain how it performs. There's no guaranteed simple rule to predict it. -- - Mark Drela RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
