LE & Control Surface Construction Questions

[atjurhs]

Hello All,

I am trying my hand at a "mostly scratch" built plane (which means that I have a set of wing-form drawings to work from but no real set of plans) and need a little advice on building techniques for the LE and the Control Surfaces.

The wing is approximately 122inches and a constant 14inch chord (it's a flying wing design).

Question (1) I plan to D-Sheet over the ribs and or the LE? Currently the LE trianangular stock that I have is balsa which will be easy to shape and sand, but will it be sufficiently strong enough?

Question (2) Would running the D-Sheeting atop and bottom the LE greatly increase the strength or will the butt-joint work well enough?

Question (3) Is 1/32nd balsa suffienctly strong enough for the D-Sheeting or do I need to use 1/20th or 16th?

On to the Control Surface contstruction question:

Question (4) I planning to construct Control Surfaces (elevons) using very thin 0.014inch CF sheeting, balsa triangular ribs, and a 3/32nd inch balsa LE spar. This way I can make the Control Surfaces' shape match the very thin airfoil. The question is, has anyone ever used this build method before and was it successfull, or will the resulting elevons be too flexy?

[ChuckA]

How long do you expect the model to last? I have found that anything less than 1/16 will be too easy to damage during ground handling. I add the leading edge as the last step in fabrication. This way, I can inspect the top sheeting glue joints and reglue if necessary before adding the leading edge. I leave the sheeting a little long and sand to a straight edge with a long sanding block. It also makes it easier to add washout. I just clamp the wing to a flat surface with the desired washout while the leading edge glue sets.

[schrederman]

I have always lapped my D-Tube sheeting over my leading edge piece after planing and sanding. However, Chuck's method has always been around, but I never tried it, even changing kits up to match my building style. Reason - I just never knew why people built this way, and I just did what was familiar. Chuck's adding the reason gives me reason to try it. That's what I like about these boards - you can always learn something!

Chuck's also correct about 1/16 sheeting. I use 1/20 on tails to help with weight, but wings are always done with 1/16 or thicker.

Thanks, Chuck...

Jack Womack

[rogerflies]

I like the way it was done on the old Airtronics (Saggitas, Cumic, etc) with the sheeting lapping over a trapezoidal piece of spruce. It was quite strong, and it was easy to sand it to the correct form. It's pretty easy to cut the trapezoidal stick with a bandsaw.

Roger

[atjurhs]

Well it sounds like Chuck and Jack covered questions 2 & 3 and Roger made a comment about balsa vs. spruce for the LE (question 1), but more info on question 1 and ANY info on question 4 is still requested.

Thanks, Todd

[fly1milehi]

1. It will be sufficiently strong enough if the rest of the wing (ie the spar) is strong enough also. My opinion is that hard balsa is sufficiently strong enough but it still "dings" pretty easily being loaded into the car/truck/basement and also dings up on landing zones that happen to have uncontrolled weed growth... So spruce is tougher and holds up longer.

4.Im not quite sure I understand your proposed method. If you are planning a solid sheet of .014 carbon sandwhiched by balsa ribs/sticks on both sides then NO I dont think it wont be strong enough. On that length of wing span and im guessing only about a 2 inch cord for the elevons I would think that a solid balsa elevon wrapped in carbon tissue would be about right.

Does you wing design have some sweep, or is it a Plank? Have you looked up any flying wing threads? Sounds like an impressive scratch build!! should be cool
Greg

[Robglover]

Todd -

1. - It will be plenty strong enough until you hit something with it and then it won't be strong enough, but neither would anything else.

4. - Never tried that yet.
Rob

[atjurhs]

Greg,

Actually the design is a plank design that is a result from highly modified WindLord plans.

As to #4, actually you've got the build design/method just backwards. What I'm thinking of doing for the elevons is sandwiching balsa "ribs" and a balsa LE between an upper and lower sheets of CF. BTW, I am planning to make this bird a full-house, so each elevon is about 30inches in length.

[fly1milehi]

okay that makes more sense for the elevons than what I was thinking or understanding. Seems like it would be plenty rigid with the CF on the top and bottom over a balsa structure. Sounds like a paint only finish since I cant imagine trying to monokote over solid CF. But since I havent ever tried that you should go for it!
greg

[ChuckA]

I have experimented with several ways of getting thin trailing edges using fiberglass and spruce for the sharp edge but have gone back to old fashioned balsa. Balsa trailing edge found at the hobby shop is too thick for modern airfoils so I have to shape my own. I built a jig with two 12 inch long 2 inch wide strips of 3/32 inch flat iron I bought at the local hardware store. (Yes, there are still a few of them around). The strips of flat iron are bolted together with a 1 inch offset. I place a standard 1/4 by 1 inch piece of hard balsa trailing edge stock in the jig and sand it down to a 3/16 by 1 inch trailing edge with a much thinner edge. I harden the thin edge with instant CA and wrap the monokote around the sharp edge. It stands up very well in normal flying if I can keep from damaging it before covering. I have though about reinforcing the sharp edge with carbon fiber but the CA and monokote has stood up so well that I haven't bothered. The jig does wear down and has to be reworked after a couple of models but I can bolt the iron strips together in a different way and use them several times. The jig can be used to shape thiner trailing edges by adding layers of masking tape to the jig to shim the balsa to give the desired thickness.

The trailing edge is sized for the root rib, however I have found that the same trailing edge stock also works on tapered wings. Haven't checked the modern airfoils but the Eppler airfoisl such as the E205 and E387 are almost the same thickness one inch from the trailing edge for chord lengths from 6 to 12 inches.