Hi,

Im designing an RC plane in which the wing planform geometry is a combination of straight rectangular and tapered wings. The centre wing is rectangular and the two ends will be tapered (similar to the cessna 172). Will the structure be strong if i make the centre wing out of balsa divinycell strips reinforced with balsa and the two tapered wings at the ends entirely out of foam (cut from a CNC machine)? Is this a good idea? Coz manufacturing a tapered wing out of balsa strips require a high degree of accuracy. Any opinion on that?

Thanks.

Ben

You could embed a wooden spar either inside the foam or slot the foam and glue one in.
Thats one option but depending on how large the wing section and how heavy the model it may not be needed.

my wing will have a wing span of approx 56in, a root chord of 9 in and a tip chord of about 5.5 in

Are you getting your ribs laser cut? If you are, it is not too difficult to design some taper into the outboard edges and still have the spar line up correctly.

The tapered sections will only be as strong as the joint to the last balsa rib unless you imbed the ends of the spar or otherwise incorporate the foam sections into the wing. I don't thing the end cemented and skin of covering alone is enough to support much of a wing panel. Were you planning om having a balsa skin over the foam? That would help some. As would carbon fiber rods or stiffeners.

Im planning to reinforce the tapered foam section with kevlar or carbon fibre. That will make it more strong, i guess.
Thanks.

Kevlar is much heavier than carbon fiber and weight is important in airplane design.