ZoomZoom-RCU

[8D] Hello all,

I am in the process of building an 80" wingspan bird, and am in the middle of wing construction. My quandry is in the spar department. Having never built anything of quite this size I was wondering if anyone here could give me some tips as to whether what I am proposing will be strong enough. It is a foam core wing with lightening holes cut span wise inside the structure. I am thinking due to the inherent strength of the foam, that I will neeed only one decent sized spar to handle the wing load, as I can see no real element of torque happening on the Trailing edge. (The foam keeps it very stiff). So, I'm thinking for a front spar, two full length pieces of 1/8th or 1/4 inch ply, laminated together, and almost, but not quite as deep as the cross section of the wing. This of course at 25% MAC. Think this will haul the load of a 10 to 14 lb plane? Let me know what you guys think. And TIA!

ZZ.

Dr1Driver

I'd use two 1/4" wide, 3/8"-1/2" tall spars, depending on the type of flying you'll do. Sheet and cap strip the wing like any other. Use bass or spruce. Also use a balsa trailing and leading edge.

Dr.1

ZoomZoom-RCU

Thanks DRI Driver. By "use two" do you mean two separate spars? Or two strips of 1/4" material laminated into one spar? And if two separate spars are reccomended, what should the placement be in the wing? Also, what purpose does the balsa trailing edge serve on a foam wing? Just curious. By the way its funny you should be the first responder as this AC is a Fokker DVIII.

Thanks for your help! ZZ.

GreaTOne_65

I agree with DR, about the size of the spars. I built an 85" airplane 15 yrs. ago, used a foam core, I cut slots top and bottom and glued the spars in, then sheeted the wing from the spar forward, then used a 2 in. wide sheet from trailing edge forward. I then laid 3/8ths in wide balsa strips at the rib locations and cut out the foam inbetween. The airplane has been crashed 3 times, and every time the wing and tail feathers come through with flying colors, so all I have to do is fix the fuse, and take her back to the field.

Hope this helps, good luck.

Dale

ZoomZoom-RCU

Wow Great One! How heavy was that wing when you got done!! It had to weigh like a tank!! No wonder it survived repeated crashes. Thanks for the input though. It always amazes me at how many ways there are to skin the proverbial cat. I was just looking at a site where a guy was building 85" wingspan birds with foam board, ie hollow on the inside. All he uses for a spar was yardsticks laminated together, 4 thick in the center section and tapering out to one thickness at the wing tips. Since mine isn't hollow, (ie has a solid core with lightening holes), a similar spar should work in my opinion. the foam is the denser blue type, not the flexible styrofoam(white foam) so a lot of beefing up shouldn't be necessary. Its quite stiff and torque resistant. As it stands my plan is for one laminated spar of three to 4 layers of 1/4 inch ply, tapering to the ends, and located at approx 25% MAC. I haven't determined the sheeting type yet. Likely a composite of glue and fiber that will harden hard but light. I'm going to do a weight stress test on the spar first. Does anyone here have a clue as to how many pounds I should test this with? I'm thinking 2 to 3 G's would run around 25 to 30lbs. I dont think I'll be pulling this in a WWI type anyway. Does anyone here know a good way to stress test the spar?

Thanks Again

ZZ.