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Jan 24, 2017, 09:24 PM
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installing wing tube sleeve w/dihedral

I am building a 1/4 scale cub that I would like to install a small wing tube for ease of wing installation and to strengthen the fuse sides. The ribs are not cut out for any tube sleeves. I am not sure how to drill the ribs so that the wing will have the dihedral that is required with the cub. I havent built the wing yet so I can stack the ribs. Any advise?
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Jan 24, 2017, 09:55 PM
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AntiArf's Avatar
There's not much dihedral with a Cub, which would make this work. You could install a slightly oversized tube in the fuse, and then using short bushings or o-rings to enlarge the diameter of the wing tubes for a snug fit. The idea is that the bushings or o-rings would fit just into the beginning of the fuse tube, and the clearance between the wing tubes and the oversized fuse tube would allow for the dihedral to be set by the wing struts. This method would allow for all the wing rib holes to be drilled identically.
Jan 25, 2017, 01:28 PM
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wizard of odd's Avatar

I'd approach the tube holes from the wing side. Two options come to mind:

1. The dihedral on a typical Cub would be around one degree. Decide where the holes in the wing ribs need to be, then cut them out maybe one millimeter oversize, or use the "next size up" drill to drill the holes. Make a set of thin plywood bushings that are a snug fit on the sleeve. Build the fuselage and wings. Install the sleeve in the fuselage so it's level. Slide the wings onto the tube with a bushing at every rib station. Prop up the fuselage and wings so it looks right, then use a bushing at every rib station to glue the sleeve to the rib.

2. Scan the ribs, trace on a computer, work out the hole locations and then print templates of each rib with the correct drilling centre marked. Use the templates to make the ribs.

It would be ideal if you could drill the holes first before cutting out the rib profile, to prevent the drilling process from splitting the wood. Use a Brad point drill or a Forstner bit in a drill press to make the holes in the ribs- there's no hope of getting it right when using a regular drill bit or drilling free handed. Better yet, have the ribs laser cut, if possible.
Last edited by wizard of odd; Jan 26, 2017 at 08:04 PM. Reason: typo
Jan 26, 2017, 06:33 PM
Registered User
As above sorta :-)
Find / Buy.. sections of telescoping (slide fit) CF tubings.. Likely of ~1" diameter IMO onna 1/4 scale cub )
Personally I'd prefer to incorporate all this into the things' Main spar.. But?
Cut the outer/bigger one to an exact width to the Cubs fuse sides . Fit it perfectly perpendicular to the Cubs' two axis
ie; vertical and longitudinal ...Important that.
Fit the smaller diameter bits of CF tube into the first 2 , 3 or? ribs of the cubs' wings.
Shim adjust until everything is Precise! then Zap the CF tubes into their preprepped rib holes. Job done.
IF cautious drill holes for small sheet metal type screws to lock the tubes together once setup at the field ... Inconsicouously from the wings' underside
Jan 27, 2017, 11:13 AM
DPlumpe's Avatar
Easy. Offset the hole in the second rib so that rib slides on the wing tube sleeve a tad higher than the first rib. Similar with third higher than the second, fourth higher than third, etc, depending on how far the sleeve extends into the wing.

The Sine of 1 degree (dihedral angle) is 0.0175, so for every inch spacing between ribs, offset the hole .0175 inches lower (so the rib sits higher) than the previous rib. Thus, if the second rib is spaced 2-1/2" from the root rib, cut it's hole 2.5x.0175 = .0438" lower. That's a tad under 3/64".

Actually, Paul Matt's 3-view says the rear spar is 1 degree dihedral and the front spar is at 45 minutes dihedral. The Sine of 45min is 0.0131. If the wing tube is located between the front & rear spars, you might pick a number between .0131 and .015?

-Dave Plumpe
Jan 28, 2017, 11:21 AM
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E-Challenged's Avatar
Make the tube holes in the first three ribs over size, Make ply rings that fit the tube. Insert the tube plus rings into the uncovered wing. Set proper angle of tubes and glue rings to ribs securely, then glue tubes to rings. Oughta work!
Jan 28, 2017, 01:37 PM
Registered User
Using Rings is Clever... Nicely thought.

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