rednekk58

Hey All,
Looking for experience, opinions, or great ideas!
I'm trying ti design an EDF, my first other than a flat delta to test the fan. The wing panels are 20’ long, with a root chord of 13 '' NACA0010. Tip is 9" chord NACA0012 with a 8" leading edge sweep. four 1/16 balsa ribs, I-beam tapered spars. 5/8 to 1/2 root to tip (front spar) made from 1/8 thick basswood. Capped top and bottom with 1/16 X 1/2 wide basswood. Rear spar is tapered 3/8 to 1/4. Capped with 1/16 X 3/8. All bass wood. Have bottom 2mm depron sheeting installed on bottom of panel with retracts cut in. Will also rough in the servos. After the panel is sheeted on top with 2mm depron, I plan to coat once with 3/4 oz glass.
Here's the question I'm thinking. Should I "X" support between ribs spar to spar? Bottom rear on spar cap to top front under spar cap maybe, then reversed in next bay for extra rigidity? Maybe bamboo skews? Trying to keep it light. Maybe forget the braces and use two coats 3/4 glass?
Hoping to install aileron servo where shown.
Pics will help what I’m trying to explain. I hope.

Thanks Al

BMatthews

What you've got sounds fine as is. At these sizes the depron will supply all the skin stiffness you need to avoid warping. No need to add X braces.

However I would suggest you skip the glassing step. It'll add way too much needless weight at this size. Suggesting you skip adding a few bits of wood in favour of even adding a second layer of glass is totally off the mark. The glass and bonding agent, be it epoxy or water based varnish or ? would add WAY more than the few bits of wood and glue would add to the weight.

I would also suggest you figure out how to join the outer panel spars to the center section spars more effectively than with a butt joint. If you can't get any proper joiners in there at this point due to your construction progress than one thing you can do is go ahead and finish it with just simple butt joints. After it's done then slice out small 3/16 x 1 1/8 inch sections at the joints from the depron and use 1 inch long fibers of a heavier grade of fiberglass and epoxy to fill in these outer surface "joiners". To add the glass wet the cutouts with epoxy and then lay in the 1 inch long strands into the wetted areas and pat down with a scrap stick to mush things around and get the epoxy to wet out the glass. Use enough glass to fill the slots to just under 1 mm and then add a cap of depron. After it cures slice off the protruding caps with a sharp knife. You'll want to use fibers unwoven from 6 to 8 oz cloth to get them thick enough. I definetly do NOT recomend using the 3/4 cloth for this application. Other suitable fibers would be kevlar or carbon. But unravel a bit of it and use the long fibers to get the most advantagious fill for this. Each "cap" should have 30 to 50 fibers in them depending on the fiber sizes. Doing it this way the "caps" can also be added with the bend at the joint line to best line up with the spar stock.

Other than this joiner issue and the need to forget about the overall glass clothing I like it.

rednekk58

Thanks B.M.,
Too late , added bracing already. Seemed to stiffen the wing quite a bit. For the panel joint, I planned on using plywood blocks in front of front spar and rear of rear spar. Holes drilled spanwise, aligned. Epoxying in CF tubes when ready to join panels. Would really like to have the panels skinned before joining. I never even thought about chopped glass, that is a good idea also. I could prepare pockets before skinning.
I won’t glass entire wing unless it doesn’t seen stiff enough..
Any other ideas?
Thanks Again
Al

BMatthews

Just fly it. Seriously, you'll find that even 2mm depron will stiffen it up quite a bit. It'll be like a full chord D box.

rednekk58

Thanks again,
Maybe I should turn this into a build thread. Gonna need help with the rest of the plane too! This is kind of a design as I go. I commute 2 hours a day, time spent on mental design notes. (Not much to right on [sm=spinnyeyes.gif])


Not quite a "D" box. I Beams stop short from top and bottom of rib.
Not trying to discredit or insult you, but have you built like this before?
Would low temp heat shrink covering help stiffen it if needed?

I've designed / scratchbuilt planes, but nothing this light with an airfoil, or EDF for that matter. Designed a FF delta to try the EDF. I've used flat foam (electric) or balsa, ply, and sheeteed foam (glow). All prop jobs.
Here are some pics of the wing joiners. (third pic is dry fit)
Thanks for your interest. Gets my *** in the work shop!

Anyone one else is welcome to chime in.