Washout?

[William]

Does anybody know how to calculate the amount of washout for a swept wing?
Nothing too complicated but just to be able to get it somewhere near!

William

[Ollie]

See:
http://aero.stanford.edu/WingCalc.html
put your wing configuration into the program and run it. Vary the wash out until the blue line is a nice elliptical curve from the root end to the tip end for the highest coefficient of lift (highest unstalled angle of attack) that your airfoil can produce at the root end of the wing. If the blue line does not decrease fast enough near the tip, the tip will be overloaded and tip stall tendencies will result.

[Sail 'n Soar]

Originally posted by Ollie
See:
http://aero.stanford.edu/WingCalc.html
put your wing configuration into the program and run it. Vary the wash out until the blue line is a nice elliptical curve from the root end to the tip end for the highest coefficient of lift (highest unstalled angle of attack) that your airfoil can produce at the root end of the wing. If the blue line does not decrease fast enough near the tip, the tip will be overloaded and tip stall tendencies will result.

You really need to consider the full range of flying conditions. The calculator on the Stanford site is a great design tool for simple taper wings. The best measure of "a nice elliptical curve" is an "e" very close to 1.0. 1/e * 100% represents the induced drag of the specific configuration relative to the ideal elliptical lift distribution. Note that for a wing with any wash in or out, e will change as a function of angle of attack - it is not constant.

With that in mind, the second design goal is to have a benign stall characteristic. You want to have CL max at or toward the wing root at angles of attack where CL >= CLmax. At near stall angles of attack a stall-benign lift distribution is more important than an e close to 1.0. If your design has the max CLachieved out toward the tips your plane is likely to fall off to one wing or the other at stall, rather than straight forward.