How do you scale down the wing area?

[Frank B]

This might be very simple, but I'm not sure about the calculations.

I want to scale down an AT-6 Texan from 36.5" wingspan to 31.5" wingspan. The wing area of the first one is 188 sq.in, so what will the wing area be on the smaller one?

Do I just scale it down by the same percentage, or do I calculate an average cord and scale that down, or...?

[AndyKunz]

31.5" / 36.5" = 86% - that's a linear measurement (ie, multiply everything by that much when you are drawing it).

Wing AREA is a two-dimensional thing, so you multiply

(span x 86%) x (chord x 86%) =
(span x chord) x (86% x 86%) =
(original wing area) x 74%

Your 188 sq in scales down to 140 sq in.

Weight is a cubic factor - your target weight will be about 63% of the original's weight (this is why big models fly better, aside from Reynolds).

Andy

[Frank B]

Thanks a lot Andy.