BOLT ON WING MOUNTING (converting from rubber band) - RC Groups
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Aug 15, 2012, 10:49 AM
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BOLT ON WING MOUNTING (converting from rubber band)

in reference to my future building projects, I want to convert from rubber band to bolt on wings... projects are a Paragon and OLY IIs..... please post drawings, links, pictures of conversions.. Would like simple super strong & light mounting systems to resist strong winch launches... thanks for your help.

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Aug 15, 2012, 02:38 PM
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One popular system is to make a reinforced hole in the forward bulkhead, and put a mating pin, very securely, in the l.e. of the wing. Then you slightly reinforce the t.e. and put a nylon bolt there. It probably doesn't take much of a bolt, particularly if you are willing to replace it often. Maybe #8 for the Oly and #10 for the Paragon? (Probably more for wings with some sweep or even just straight trailing edges.) However, I suspect you'd have to extend the bulkhead with the aircraft you are talking about. And not so great in a cart wheel.

Graupner used to use two M5 nylon screws for the wings in the Electro Junior, as I recall. (maybe 90 inch span?) That's similar to a #10 in english threads. This was a two piece wing, and the screws were near the joiner rod and only a couple of inches apart. Guaranteed to shear in a bad cart wheel, which might save the fuse. I suspect you might want to go a bit larger, and you'd want to change the screws now and then.

For any nylon screw, if it breaks you can use a heated screwdriver to melt into it so you can back it out.

If memory serves, there is a discussion of how to do a bolt on wing for a Chrysalis over at D J Aerotech.

No need for a super strong wing mount unless you are making the wings much stronger than stock.
Aug 15, 2012, 05:10 PM
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doc993's Avatar
Please be care full of nylon screws.I've had two sets fail on me causing some maddening damage.Once on landing, and once on a tap tap winch launch.The screws were 10/24's I finally converted to steel.If I do it again I'll use 1/4 20 nylon.
Aug 15, 2012, 08:01 PM
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R2R's Avatar
I've used this setup: install a 3/8 in ply block in the fuselage butted against the fwd bulkhead and fuse sides under the LE. Install a 1/4 in thick ply block under the TE. Drill and tap both blocks for a 1/4-20 bolt. Reinforce the drill points in the wing with thick ply blocks at the LE and TE. Drill matching holes in the wing. Bolt down with two 1/4-20 nylon bolts for crash forgiveness, steel for bullet-proofness.
Aug 15, 2012, 08:43 PM
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Originally Posted by doc993
Please be care full of nylon screws.I've had two sets fail on me causing some maddening damage.Once on landing, and once on a tap tap winch launch.The screws were 10/24's I finally converted to steel.If I do it again I'll use 1/4 20 nylon.
What size sailplane ?
Aug 15, 2012, 09:39 PM
Full Scale Piper Cub Driver
Piper J3's Avatar
I use two 1/4 wood dowels in leading edge and a single 1/4-20 nylon bolt in TE for my E-Paragon. Also use a nylon flat washer under the bolt head to spread forces and protect film covering. Works like a charm...
Aug 15, 2012, 09:52 PM
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How old were the screws, how many times flown, and what kind of glider?

While I've had very good luck with nylon screws, any data on where the limits are is good to have.

My Cumic (100 inch version) had a 1/4-20 nylon bolt on the trailing edge that survived many crashes. IMHO, that's TOO strong.
Originally Posted by doc993
Please be care full of nylon screws.I've had two sets fail on me causing some maddening damage.Once on landing, and once on a tap tap winch launch.The screws were 10/24's I finally converted to steel.If I do it again I'll use 1/4 20 nylon.
Aug 15, 2012, 10:24 PM
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Hey there Wylie,

Don't know if this is much good to you, it was a one piece wing and I will assume you won't be doing that with a Paragon or Oly?

Skybench 2m Lil Bird, which had a very similar wing build as the gliders you mentioned but I did it as a one piece, being only 2m. This system took really punishing launches of open F3J competition type pressure (yeah the whole wing was very modified for high launch and zoom pressure, spar carbon etc) and worked nicely with nylon bolts, of course. It was a terrific little thermal sailplane and will be sorely missed.

The pics aren't that great but give an idea, the front bolt mounting plates were laminated ply/epoxy and butted against the mainspar centre join. With a two piece wing your mounting plates could be on opposing wings and slightly offset of centre, the plates and bolts need not interfere with the wing joiner system.

Other ways to skin thy cat though. like a reinforced LE front dowel through a fuse bulkhead/former and a rear nylon bolt fastener as mentioned already.
Last edited by atmosteve; Aug 15, 2012 at 10:58 PM.
Aug 15, 2012, 10:46 PM
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doc993's Avatar
Hi all .It was on my crimson.And they were bought at the hard ware store so age ?Tapping into hard wood or ply works very well, but consider the weight of your plane, and the strength you need to launch.I think !/4 20 should be enough for most planes. The poor landing was clearly my fault, and the damage was not too bad.But the failed launch cost me some down time It was a real learner.My next plane will be lighter.
Aug 16, 2012, 03:35 AM
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A mounting system I'ce used is one large bolt right next to.the spar. This can go into a tee nut in the same block of wood that th tow hook goes into. It's a good idea to use something high friction on the wing saddle so that a twisty launch won't skew the wing. Flying with a wing twisted 30 degrees is upsetting, though it can be done if you have ailerons and not much dihedral. Advantage is far less stress in cartwheel.landings. Mantis uses 1/4 inch steel bolt. (3 meter span).
Aug 16, 2012, 08:18 AM
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Thanks all ...for the info

Steve that is what I'm looking for,,, ways to design or copy from previous builds... Thans mate

Wylie aka The Coyote
Aug 16, 2012, 11:53 AM
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ozmo01's Avatar

Nylon screw tip

Most of us have learned this by example or (me) experience it the hard way.

Tip #1
Do not over tighten nylon screws. Screw them down until in place then just a 1/4 (or less) turn to snug.

Dropping your stored nylon screws in hot water once in while is good for 'em.
Nylon works better with a certain amount of moisture. Guys do this with nylon props all the time. Why not with hardware?
Aug 17, 2012, 04:00 AM
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Ozmo01; Tip#2, never thought of that one!

Does the liquid heat help re-form bent threads for people who were naughty with their screwdriver? Blind nuts are usually metal and it is easy for folks to overtension their screws.
Aug 17, 2012, 01:40 PM
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If you messed up the threads, replace the screw!
Aug 17, 2012, 04:37 PM
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ieyasu's Avatar
Here's an old RC Groups post with some bolt sizing advice.

I have included some photos of what I did for my Paragon. It's got a 10-24 forward of the trailing edge and a 1/4-20 in front of the spar. I used hard balsa gussets to reinforce things. I'm not sure it's as strong as it would need to be to winch, but I didn't build a winchable spar, either. The plane hasn't had a hard landing yet, but it's doing okay so far... If I had it to do again, I would've put a 10-24 behind the leading edge instead of going over the spar--I *want* the screws to break, not the wing or fuse. The wing on my Paragon is too thick at the spar for a #10 screw to reach down to the thread block in the fuse though, so I had to go with the 1/4" size.

I'll note also that my DJ Aerotech 2m Chrysalis uses 2x #8 nylon screws as per the design, located near L.E. and T.E. That thing has had hard landings, and never broke a screw.

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