radioinred
Well-Known Member
Ok guys, heres the plan. Ultralight biplane with 20 ft. span top and bottom, 4.5 ft. chord, flat bottom Clark Y type airfoil, half span ailerons on the lower wing, none on the upper. I want to make (4) 10 ft. spars by laminating (4-5) 1/2X6 in. poplar planks together with a very strong epoxy (possibly glass the spar)and use wood reinforced foam ribs. My idea for the leading 25% of the chord, in front of the spar, is to hot wire cut enough flat foam pieces to sandwhich together with a foam safe glue and make a solid foam leading edge along the span of the spar, sand for uniformity, the apply a fiberglass cover over the 40 or so (40X3 in. wafers=120in. or ten feet)leading edge foam pieces to stiffen the leading edge and protect the foam during the heat shrinking process. there will also be a second spar about 8in. from the trailing edge of each wing. I am still debating on whether or not to use in-wing ailerons or simple flaps behind the airfoil attached to each trailing edge. Riblacing and 2.7 Dacron to cover the whole frame. I still need to find a way to support the foam ribs. Maybe with .5X.5 in. poplar strips buried in the top and bottom of the ribs? The estimated gross for this project is 530 lbs. which would give me a wing loading of about 3.09 lbs/sq. foot. A few questions.... will these type of spars give me the strength i need for this kind of setup? The upper wing will fly 14 in. forward of the bottom and the two wings will have four light struts (most likely aluminum) and wire bracing. I dont think a carbon spar could provide enough rigidity considering the foam ribs. any ideas?
