wing joiner for foam wings

[kevin6Q]

Hey All,
I just realized that all of my foam wings have been built as one piece. I have no experiance with wing joiners for foam core wings. I've seen all of the Drela styles and was hoping for something as simple as a wire rod in a tube. How do I reinforce the tube to keep the foam from compressing and tearing away? The planned wing is for a Gentle Lady so I have plenty of thickness to work with. Thanks, Kevin 6Q

[Ollie]

What is the size of the wing? How are the load forces along the span by the wing structure?

Begin by:
"1. One half of gross weight of fuselage times distance from wing root to center of wing area. This gives you the bending moment.
2. Now divide the moment by the depth of the spar minus one cap thickness at the wing root.
3. You now have the load on the spar caps at the wing root at one 'g'.
4. Multiply this cap load by the design load factor times a safety factor. Usually this is 5.3 x 1.5. "

From:
http://www.homebuiltcentral.com/site/960757/page/468057

Or:
http://www.charlesriverrc.org/articles/design/oliverwilson_quicksparstrengthcalc.htm



Then I could suggest some joiner designs after you calculate forces and moments.

[seerspaz]

"... distance from wing root to center of wing area."

Meaning on one half (side) of the the wing? How do you find the center of the 'wing area'?

Sorry if this is a basic question.

Spaz

[fhhuber506771]

Generally, you can insert tubes in the foam core similar to inserting tubes in the wood structure wings. The larger the expected loads, the larger the diameter of the tube for the joiner wire or aluminum or CF joiner tube.

The tube being inserted in the Gentle Lady size wing... I would use 1/4 inch ID 1/64 wall CF tube... or maybe just CF arrowshaft. (which is about that size...) If I remember correctly.. the center joiner tube recommended in the kit for the Gentle Lady was 6 inches... I'd use 8 inchse into the foam wing. For glung it in I woudl plug the end of the tube to be inserted, then mix 50-50 yellow glue and polyurethane glue (Gorrilla Glue or similar) as it will expand and firmly lock the tube in place.

due to the loads expected on the 2 meter wing with appx 10 inch chord...(I forgot the measure of the GL wing... been a while) I'd balsa sheet the center 8 inches (each side) and the "D-Tube" portion (forward 3 inches of the wing top and bottom, tapering from the polyhedral break to 1 inch at the tip) and I'd sheet the rear 1/2 inch top and bottom full span. For ease of core cutting... I would use 1/4 inch "cap strips" spaced as if it had wing ribs. (this way the core can be cut as if the whole wing were to be sheeted) If the joiner was permanent I would lay a 2 inch wide 0.5 oz fiberglass joiner reinforcement on in addition to the CF (arrowshaft) joiner. If its to be "broken down" for transport.. I would use a snug fitting music wire.

The foam wing could be lightened by cutting out mose of the foam that wasn't sheeted or cap stripped... (for the Gentle Lady wing) This aproximates the way that the Hobbe Hawk" wing was made (except you have a polyhedral break.. and they had a Bow due to the way the wings had the sheeting laminated on in a mold) Those wings were strong enough they were demonstrated by having a truck drive over them.

[Sparky Paul]

Hey All,
I just realized that all of my foam wings have been built as one piece. I have no experiance with wing joiners for foam core wings. I've seen all of the Drela styles and was hoping for something as simple as a wire rod in a tube. How do I reinforce the tube to keep the foam from compressing and tearing away? The planned wing is for a Gentle Lady so I have plenty of thickness to work with. Thanks, Kevin 6Q
.
Use a 1/16" plywood full depth spar at the wing high point, out about 12 inches on each side..
You'll probably be using a 1/4" steel wire joiner.. get a brass tube to fit.
Shouldn't need more than 8" per side.
Epoxy your joiner tube to the rear of the spar, along the centerline of the spar, and the whole thing in a slot in the wing.
Fill in the gap between the spar and the top of the wing and the bottom of the wing with firm balsa.
Sand to contour.
Add a hard balsa or liteply root rib, with a hole for an anti-twist joiner a few inches aft of the spar.. this can be a 3/16" wood dowel that goes about an inch into each wing half.
It wouldn't hurt to fit a balsa leading edge, about 1/2" deep and 3/8" wide, full span to handle the "arrival" events.. sanded to the foam contour.
White glue/aliphatic resin will work for this.
I'm presuming you plan to sheet the entire wing with 1/16" balsa.. do that.
Epoxy or contact cement.. Both foam friendly, of course.
A slight weight savings can be accomplished with balsa sheet from the leading edge to the high point out to the tip, then capstrips every 3 or 4 inches, and a 1-1/2" wide sheet to the tips for the trailing edges, top and bottom.
Cover to suit.

[Ollie]

Spaz,
"Meaning on one half (side) of the the wing?"
Yes.

"How do you find the center of the 'wing area'?"
Try finding it by questimating its center. Within an inch is good enough. I estimate it's half wing area center point from 19" from the wing center line. Don't calculate the half wing area center point. If you are good at darts, throw a dart at the wing plan. ;)

[kevin6Q]

Thanks All,
I was planning on using Kevlar and CF for the skins. I have a bunch of it and I've never sheeted a wing before using anything but the fabrics. Sorry for not mentioning this in the original post. All of my wings thus far have had no spars; just skins. I have yet to fold one up (those who have and those who will) and it looks like I will have to come up with a spar system to share the loads of the joiner system. I have a bunch of CF arrow shafts so these will be incorporated as per the replies. The root rib will help the foam compression issue. Thanks again and I'll keep you posted as to how it works or doesn't. Kevin 6Q

[Sparky Paul]

On contemplating this, I wouldn't bother.. it's only a GL.. the labor involved would be seriously greater than building the kit.
But if I did do it, I'd do it this way...

[jirvin_4505]

Drawing on some experience with bagged 3m wing with built in spars - joiner box is built in similar to the Drella system.

I think you just have skin? _ Drawing on the oldy but golden source for bagged wings - "The Waco newsletters- anybody got the complete set? im missing a few" the 2m design has plug in wing tips - I think and uses ply sub ribs. Similar to description on the favonius site (can't remember URL?)

for a GL even 1/4" mwire into subribs would probably do it in the centre section.

I have used joiner tubes blocked in onto 1/16 ply full depth sub spar on 2.5 meter veneered wings no other spar. Spar extended obout 1/2 way out the centre panel - all vague I know!

some hints looking at the arthobby wedsite
http://www.arthobby.com/gliders/specs/plan/boar_P.html

Ollie I like the precise nature of your reply - there must be ball park figures for a 2m glider?

regards Jeff