Please let me know how can i calculate the incidence angle of a sailplane wing without incidence meter.

I suppose is something related with trignometry - arctang but i don't know the formula.

From : Don Stackhouse

Yes, it involves trigonometry, but it's quite simple. Support the fuselage on a flat, level surface, shimmed so that whatever reference line on the fuselage that you want to measure the incidence from is exactly parallel to the surface.

Now, measure the distance vertically from the surface to the chord line at the leading edge of the wing, and again at the trailing edge, then subtract the trailing edge distance from the leading edge distance.

Divide this result by the chord of the wing at that location. Find the arcsine of that ratio. The resulting angle is the incidence that you're looking for.

Regarding your recollection of arctangent being in the formula, not arcsine: For small incidence angles (less than about 5 to 8 degrees or so), taking the arctangent of the ratio will give you essentially the same result. However, if you're measuring the chord of the wing along its airfoil's chord line, the arcsine is technically the correct function. However, if you measured the "projected chord" (i.e.: you measured the chord parallel to the reference surface instead of parallel to the chord line of the airfoil), then arctangent would be "mathematically correct".

Don Stackhouse
DJ Aerotech