Strength of Foam for Wing Cores?

[green66]

Hi all,

Concerning sheeted foam wings --- Is there a practical way, or accepted rule of thumb, to determine the required compressive modulus of the foam to avoid bending-induced buckling of the top sheeting? I know the wing's thickness, sheeting thickness / properties, and anticipated bending moment.

Thanks in advance.

[John Boren]

I guess it depends on what type of airplane you are going to use the form wing on. If you are building a simple 40 to 90 size sport flyer, 1/16 balsa skin should be fine. If you are going to build a Weight carrying type plane then it might be wise to add a small spar on the top and bottom of the wing. If your building a giant scale plane then use 3/32" balsa sheeting. The wing thickness is also important, the thicker the wing the stronger it's going to be. Also since most of the loads are in the inner 1/4th to third of the span you can beef up the center section and really not worry much about the outer span of the wing.

John Boren