JasonF

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Hey everyone,
Hopefully you all can give me some tips on building a foam wing. I am trying to put together an endurance airplane that can stay up for 10 hrs. I am moving along with the powerplant but kind of stuck on the wing and whether it should be built up, or foam. Weight is clearly a concern.

If I choose to use foam, what are the best guidelines for deciding how to finish it. For example, the wing may be 80" span and 2.5" root thickness tapered to 1.5" tip thickness, chord about 14". The wing can be built as one piece, but the cores must be puchased left and right sides individually.

Is it sufficient to just butt glue the roots of the cores together and sheet the entire wing with 3/16" sheeting?

Is some form of spar necessary, either upper and lower square stock or a thin vertical strips. What are the trade offs with spar vs. sheeting. Does including spars mean that I can go with 1/16" sheeting? Are spars and balsa sheets even available in lengths greater than 48"?

How heavy can I expect a wing of this size to turn out?

Are there any websites that show photos of how to build a foam wing?

Essentially it would be nice not to have to guess what sheeting and spar combination I need, hopefully you guys can give me a hand!

Thanks

Jason

Mike James

That's a lot of questions to try and answer in one post. Use the search function at the top of the page for "foam wing", and you'll find a lot of helpful general information.

The strength issues (spars, etc.) can't be answered directly, because it depends on what you intend to do with the airplane. For comparison though, a typical sport wing for a .60 size or smaller airplane could be built from light (1 or 2 lb. density) foam, sheeted with 1/16" balsa, and covered with a film covering, and would only need the naturally-occuring box structure you get, when you combine a balsa leading edge, balsa trailing edge (where the ailerons and/or flaps are hinged) a balsa tip block, and a ply or lite ply root rib. I would include some sort of spar... A simple butt joint is weak, unless you fiberglass the center section carefully. It could be, as you mentioned, a couple of balsa sticks, epoxied into grooves in the top and bottom of the wing, or strips of fiberglass, kevlar, or carbon, epoxied under the sheeting, or a relatively short ply spar, epoxied into the center section of the wings. (occupying approximately 1/3rd of the total span) Tightly-shrunk film covering will add some strength, too.

If you can publish more details, such as expected final weight, predicted airspeed and G-loading, etc., there are those here who can get really specific with you about what you need. (I assume you meant 1/16" sheeting, although you posted 3/16" sheeting.)

Since you're going for endurance, and presumably not high G-loading, you would probably be better off with a built-up (balsa) wing, since it can be done lighter. More weight costs more fuel.

Good luck.

JasonF

My Feedback: (2)

Hi Mike,
I have built a number of kits all using built up wings, but not foam. The airplane will have a 4 pound gas engine and will need to carry 4 pounds of fuel. The rest of the weight will be airframe and electronics. I suppose I am anticipating a total weight of around 17 pounds. The wing design is not finalized, but low loading is essential. It will not be used for aerobatics or high g maneuvers, as the target is just endurance. If I order the cores, I will need to know what density foam, the sheeting thickness, and any aluminum tube or spar notches. However, I don't have any relevant experience from which to make this decision. Sorry, did not mean 3/16, meant 3/32"

Thanks again

Jason

Edwin

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I have built foam and stick wings. Foam works good in smaller planes, 60 sized and under. In larger planes, like was said, it depends. I've been helping a buddy in the club with a recently purchased used plane with an 82" ws and foam wing. Total weight of the plane with a Quadra 42 is about 17.5 lbs. I know without a doubt that the wing can be built lighter from wood since I have a plane with the same ws using a ryobi 31cc gasser that weighs just under 14 lbs. If I had built my plane per plans I could have shaved off 3 more lbs by using lite ply and reducing the reinforcement since I went gas instead of glow. I built 2 Bandito Grande's, one glow and one gas. The glow is 11lbs 10z with a saito 120. The gasser is 13lbs 14 oz with a converted ryobi weedeater motor. Both fly the same and really float on the wing very well. In my opinion, since you're doing a specific use plane, you might be able to get away with using a G-26 in a high wing J3 type of aircraft. Built up ribs in the wing would also lighten up significantly. Just thinking outloud. Sounds like an interesting project, would like to hear the results of your aircraft design.
Edwin