Molded Leading Edge PLanking

Derek,

Good for you for trying out this great method of sheeting a wing. The advantages are many and the work involved...although seeming to be a lot...is not much more than the conventional methods and the finished product is much superior.

The basic answer to your question is that the grain should be parallel to the leading edge. Doing so simplifies the molding process and is less apt to result in a molded sheet with a twist.

The best solution and one I routinely use when sheeting leading edges which require more than a single three inch sheet of balsa is to us three pieces glued into a single sheet for molding. A middle piece which molds over the more acute radii of the leading edge itself and an additional sheet for the remainder of both the top and bottom.

The central piece is that which wraps around the leading edge itself. This is always A grain and parallel to the leading edge. The width of this piece depends on the radius of the leading edge. If it's sharp it need only be an inch or so and if blunt as much as three inches might be preferable.

Attached to this "central" leading edge piece will be a top and bottom sheet whose grain is parallel to the spar. Because these sheets need not mold over a significant radius the grain direction is less important for molding purposes and can thus be aligned so as to obtain greater rigidity. It is also possible to use B grain or even somewhat flexible C grain for these pieces which will further enhance the strength of the final product.

If you choose to use "variable" grain method such as this two inch spacing is more than adequate between ribs. Two and a half is probably just fine. If the entire leading edge sheet is soft A grain you might want to use two inches as the maximum and could consider somewhat closer spacing especially if you intend to use a high shrink dope which could cause some dipping between the ribs.

I am guessing that with this method there is no LE solid piece like the diamond or no builtup pc. like Morris' lincoln log method. Is this correct?

If so, what method do you use to jig the LE?? I could slot the ribs just for the fixture I suppose and remove it prior to applying the sheet molding, or just leave it in?

Thanks,

Tim

Tim

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(The above image was uploaded to the PAMPA FTP site from one of our South American friends..)

Molded LEs are the cat's meow. Once you have the mold (mine is foam on a strip of plywood), and master the technique of joining three sheets, the rest is trivial.

L.

Tim

Tim

I am always looking at wing construction methods. Could you please explain how you build your wing for your latest purple plane? I guess what I really want to know is how you Jig it up. What is the method of jiging the wing? Do you use a leading edge spar or not?

I just built a lost foam wing. Best method I have tried so far. I built another one to make a 4s plane around. I used laser cut ribs on that one. Wow it was awesome and easy and fun to build that wing in one evening. Only thing I dont like about it is I have to have a new cradle for each type of wing.

Just curious about how you jig it up.

DMoon

Hi Doug,

Although I've recently built several wings using the lost foam system the one on the purple pond scum ship was built on an adjusto-jig. Although the lost foam system has a lot of advantages (in particular the ability to make accurate ribs at pretty much random a selection of angles!) it isn't as handy to build on as the suspended jigging of the adjusto-jig. I like the fact that by rotating the jig I can work on any part of the wing from the same standing position. I routinely work on the leading edge components for a while and then rotate to work on the back end while glue or whatever dries on the front. It is a very accurate system but probably not quite as good as the lost foam system. I'm continually adjusting the fixture before, during and after each project. Not a big deal but not as dead nuts as Bobby's foam system on a good flat building board.

Derek,
I have made a few wings with molded leading edges. The above info is good. To that I would add that I think 1/16" is too thin. Personaly, I use .077 (5/64") or 3/32". I mold around a foam buck with plain old strips of bedsheet. I don't use amonia, just plain ole' bath water. Rib spacing is about 2 1/4". I don't like hollow leading edges , so I stick a bit of 1/16" x 1/4" between ribs at the leading edge to form a "T" section when the mold is glued on. I do this at least as far out as anyone is likely to hold my airplane.
To get straight molds, I wrap the balsa first, then wrap again over aluminum angle to insure straightness.

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To insure a straight wing, I build on 3/8" x .055 x 6' aluninum jig tubes. When ready to sheet the leading edge, pull the molded leading edge tightly to the wing and secure it with masking tape then glue it with CA or Tightbond, running it down the intersection of rib and molded sheeting. Glue only when the wing is securely tied down to a jig.

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Hope this helps.
Al
P.S. Don't wrap too tight. It isn't necessary and excessively tight wrapping will crush your foam buck.
A.R.

If you are concerned that 1/16 is too thin, try to layers of 1/32. It is the same thickness, but much easier to mold, and when two layers are glued together it adds tremendous strength, even though the grain is running in essentially the same direction. Matt does this with his turtle decks, etc. (as well as leading edge sheeting) and doesn't use formers in the turtle decks. Doesn't need them.

Leonard Neumann

L.