Scratch Designed/Built Sailplane Fuselage - Page 3 - RC Groups
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Oct 23, 2012, 03:53 PM
was geht , müssen unten kommen
Keenan smith's Avatar
Two Small nylon Thumb Screws
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Oct 23, 2012, 04:04 PM
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Nodd's Avatar
Yeah I'll probably use nylon screws to hold the wing down to the wing-saddle. My question is how do I attach the wing saddle to the pylon upright & have it be strong enough?
Oct 23, 2012, 04:28 PM
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mhodgson's Avatar
I would glass the top of the saddle to get the dihedral angle fixed. I would then screw (and epoxy)the saddle to the pylon with small screws, countersunk one would be best. Then glass the underside of the saddle with the layers going down the side of the pylon. Extra layers across the joint area would also be needed.
does that make sense?
Oct 23, 2012, 05:19 PM
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Nodd's Avatar
Yeap that makes perfect sense. Glassing the joint would be simple enough.

I'm worried that won't be strong enough though. With 2½ meters of leverage acting on a 1/4" joint, I'm thinking fiberglass may just end up cracking. I'm wondering if I should be looking at a metal or carbon fiber angle joint of some kind? An L or T shaped bracket maybe?
Last edited by Nodd; Oct 23, 2012 at 06:44 PM.
Oct 23, 2012, 08:05 PM
Registered User
Hi, Nodd.

I would think that a few small CF rods bedded in epoxy and milled fiberglass would work well. You could notch them and make the dihedral bend as long as they are well bedded in the plywood pylon. For that matter, if you want continuous strength, it would be hard to beat good hard steel music wire. 1/8" perhaps? 2 or 3 molded into the bottom of the wing saddle should do the trick.

Steel is heavy but would be perfect for the kind of load distribution you are looking for and, for the size of structure involved, would not be much heavier than a carbon construct. I think it would be easier to fabricate and, if you decide it won't work after you have bent your steel rods? You are out a few pennies worth of steel rather than several dollars worth of composite!
Oct 23, 2012, 10:46 PM
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Nodd's Avatar
Good suggestions for the wing-saddle, thank you. I still have lots of other stuff to do before I tackle that job so will think on it some more, appreciate the advice.

I spent a couple of hours today rounding off the pod...

You'll notice I deliberately didn't round off the line running along the lower edge. I kinda like the ways it looks, helps accent the pod's curves...

Looks a little like a flying boat hull in some ways. Remind me not to try landing on the water though...

Those that have seen my other build threads will be familiar with my canopy making process. First I start by outlining the canopy...

Then on goes the two liter soda-bottle...

Starting along the bottom the bottle is heat-shrunk around the fuselage...

Draw some dots with a permanent marker before removing then cut her out...

Rough cut the fuselage...

Sand to the template & test fit...

Now she's starting to look more like a sailplane, getting excited.
Last edited by Nodd; Oct 23, 2012 at 10:57 PM.
Oct 24, 2012, 02:22 AM
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mhodgson's Avatar
A bracket would be a good idea, perhaps where the wing bolts go through. Either carbon or alloy. Carbon might be easier and lighter.
One final option would be to widen the pylon with balsa fairings either side and give it a symmetrical cross section. This would not increase drag much, in fact the shape shape might reduce drag in turns/side slips but would give a wider seat for the wing and could be used to hide any bracket?
Oct 24, 2012, 09:08 AM
Registered User

Wing Bracket


Here is my idea. Hope it helps.

P.S. Loved the Piper sailplane. It was worth the wait.

Oct 24, 2012, 12:45 PM
was geht , müssen unten kommen
Keenan smith's Avatar
you could glue the wing saddle to the pylon with Epoxy and then fill out the underside of the join with an epoxy/Balsa Dust mix...

Oct 26, 2012, 10:15 PM
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Nodd's Avatar
Wow more great ideas.

I love the diagram Bandit. Thank you so much for taking the time to put that together. I'm going to use some aspects of that for sure.

mhodgson I agree brackets are probably the way to go here. I also really like your suggestion to add balsa fairings to thicken up & shape the pylon some.

3DDF I think you're on the right track also with the filleting suggestion.

[ ( { brackets } ) ]
So I took a leisurely stroll around the Home Depot today & stumbled upon these nifty little steal brackets...

I really like these as they have a bump that should add significant strength...

These are a little longer, no bump but they still feel really strong...

I'm liking the look of that. Simple, relatively lightweight & should be very strong...

These look like they'd work nicely too...

So not sure which of the two I'll use but I figure if I glue the brackets to a plywood wing-saddle then embed the whole thing in fiberglass I should be good to go...

The brackets are fairly lightweight but I can see maybe drilling some lightening holes here & there. That'll save some weight & give the fiberglass/epoxy more to grab a hold of. Simple, strong, sounds like a plan to me. Talk me out of it if you like.
Oct 27, 2012, 10:10 AM
Cumulus Altimus
FASTBEN's Avatar
what a great design she is a looker .
Oct 27, 2012, 10:17 AM
was geht , müssen unten kommen
Keenan smith's Avatar
Go For It!!

BTW Call me K

Oct 28, 2012, 03:55 PM
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glidarflyar's Avatar
Woa.... steel brackets? in a glider?

How much do they weigh? You know, epoxy and glass cloth can be layered to give tapering strength where it's needed. Simply cut different size pieces and lay them into the corner.

In fact, you can create a dual purpose assembly in that corner by layering in a couple of cloths, then a wood fairing piece, then cloth that covers the wood extending however far out the wing support you choose to go. The glass would also serve another purpose going down over the pylon to fuselage joint.

Most glider designs avoid interior right angle joints if possible. Interference drag is a killer.
Oct 28, 2012, 04:07 PM
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glidarflyar's Avatar
Originally Posted by Nodd
The brackets are fairly lightweight but I can see maybe drilling some lightening holes here & there. That'll save some weight & give the fiberglass/epoxy more to grab a hold of. Simple, strong, sounds like a plan to me. Talk me out of it if you like.
Glass cloth and epoxy by itself should be way more than required. Remember pictures of free flights from the early days? Ones with pylons? They didn't even use glass cloth.

If you're going to use those metal things, consider making them more "holes" than metal. They will still be far stronger than needed. They'll also create stress risers around their unyielding perimeters. The glass cloth and epoxy reinforcement around their edges strong enough to deal with the small areas probably would be strong enought to support the wing to fuselage loads without needing the steel.

Putting too strong reinforcements into structures often leads to more strength being needed around those reinforcements. One leads to the next, and next. Consider how strong the wing is going to need to be right where those strong supports end.

Whichever way you go, it'll be entertaining to see it go.
Oct 28, 2012, 07:40 PM
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Nodd's Avatar
Stubborn Bugger
I've not weighed the brackets but they're nothing I'm worried about, especially once I've "Swiss-cheesed" them. I'm getting lots of suggestions to just use fiberglass & I do intend to FG the heck out of the joint but I want something else in there too.

Fiberglass is good stuff no doubt but from experience I know it also has its limitations. For example look at what happened to my fiberglass four meter sailplane after a moderately bumpy landing...

Fiberglass is rigid & cracks, metal is substantially inflexible but when it does move it just bends. I think a combo of both will be perfect for this application.

I know you folks already know this stuff but I'd like to explain my thinking here:
This all comes down to leverage. Archimedes famously said, "If you give me a lever long enough and a place to stand, I can move the world." While I have no Earth moving aspirations, my understanding is because I have just 1/4" of pylon to work with here Vs a normal fuselage with its wide wing mounting area, there's going to be a lot more force on this joint than usual...

I did a little math & was astonished to learn...

So with that in mind, yeah I'm going to stick some steal in there along with some fiber-glassing.

So here's a rough diagram of what I'm building...

Anyway not sure exactly when I'll get to this. Situated directly in the path of hurricane Sandy I'm expecting some "interesting" weather over the next few days. At the very least I expect I'll lose power for a while, will have to see how I feel about working in the dark *grin*. Anyway see you all later this week I hope. Stay safe.
Last edited by Nodd; Oct 28, 2012 at 09:13 PM.

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