Wing Locating Pins & Main Pins & Spar caps.

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Foundationer

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I've got a question for you people!

I'm planning on having removable wings and joining them in a glider style - Bending loads carried by spars that overlap inside the fuselage with two big pins going into bushings to join them together then lift loads transferring into the fuselage via four pins into bushings. One forward and one rearward on each wing root. So my questions are::

1. Locating pins. Where do you buy them? Are there standard aircraft ones you can buy somewhere?
2. Fixing something like that into a composite wing root - what's the standard procedure? It's quite important that bit doesn't go wrong(!) and it's quite a lot of force into a small fixing.

Bonus question: Where in Europe sells good quality pultruded carbon? All I can find is about half the strength of Graphlite.

Any and all pointers gratefully received.

Matty
 

BoKu

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...1. Locating pins. Where do you buy them? Are there standard aircraft ones you can buy somewhere?...
If there are, I haven't found them. I make my own pins and sockets, at least for the lift pins on the root ribs.

...2. Fixing something like that into a composite wing root - what's the standard procedure? It's quite important that bit doesn't go wrong(!) and it's quite a lot of force into a small fixing...
If you're talking about a spanwise pin that is fixed into the end of the spar stub that mates to a socket on the opposite spar to react bending, I'd suggest reverse-engineering it from maintenance/repair manuals or by picking apart a broken example. On the Grobs, I think it used to be a pin welded to a plate secured to the shear web plywood by hollow rivets and then swaddled in about a dozen plies of glass. Whatever it was, it was replaced by a much beefier machined (not welded) part. The diagrams in the Grob spar spigot airworthiness directives might give you some ideas. I chose to go with two removable longitudinal pins because it was easier to fixture to the necessary degree of accuracy under relatively primitive conditions.

...Bonus question: Where in Europe sells good quality pultruded carbon? All I can find is about half the strength of Graphlite...
I'd suggest just ordering it from the US.

--Bob K.
 

BBerson

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I think Grob used off the shelf uniball bearings for sockets. And about 1" steel bar for pins welded to plates inside
 

plncraze

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Marske's Composite Manual has a few pages on this. See the Marske Aircraft website.
 

Foundationer

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My take-home is that I probably need to get something made up rather than being able to grab something off the shelf? I'll post some photos of exactly what I'm talking about Thursday once I've dragged the glider out of it's big aluminium oven.

Edit: I was talking about lift pins - just saw them on the HP24 site...
 
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Foundationer

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They taper the wrong way for what I am after. I think the photo that I will take on Thursday will illustrate what I mean better than words.
 

Foundationer

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Breathing a bit of life back into this old thread... For Lift Pins an easy way of doing it seemed to be to cut down some AN Bolts and push them into spherical bearings. Guaranteed strength parts with little modification and nice and self aligning.

Is there any reason this is a TERRIBLE IDEA?

And here are the pictures I was going to post 56 Thursdays ago of various glider wing lift pins / tailplane attach pins.
 

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Exian

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What I wonder about is how are all those lift pins installed in the root rib?
Is it simply glued in the big blocks of ply-wood, or is there also something inside the wing (nut or screw)?

For my first project, the lift pins were bolted on the wing root ribs, so there is a nut inside the wing, but this is because it was the only way to transfert the flexing moment from the pin to the rib (thin rib, without big plywood block).

If you use AN bolts, will you use a nut to create the flange that goes against the rib? I first thought of doing that, but the added thickness of the nut + washer was increasing the flexing moment in the pin too much. Also, the section of the bolt that sees the max moment is then in the threaded part (so smaller diameter, less strneght in flexion...). An unusually big bolt was need to have stress within the allowables.


On the fuselage side I installed spherical nuts to engage with the lift pins.
Old gliders used all spherical bearing, but on new ones, I see only plain bushings now.
One problem I see with sperical bearings is their bigger diameter than a bushing. On very thin glider airfoils with small cords, if you use a spherical bearing, then there is not much material left all arround to hold it! (this is a problem I have with my current project).
 

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proppastie

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Bearing on thread not a good practice. Need flange and nut so I do not understand how just cutting the head off a bolt will work.
If you weld a flange you will have to re-heattreat the bolt which will work. You might over-design the size so as welded temper is strong enough.
 
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TFF

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I think the idea is cut head off, thread the threads into the mount threads, put a nut on the back side. Probably locktite would be enough. Not the most sophisticated way, but might be enough.
 

wsimpso1

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You guys are working way too hard. Composites do not like concentrated loads. Really, look hard at BoKu's stuff. He did not invent it, there is lots of good history with that scheme in similar airplanes as well as the HP24. Big pins in big bushings work.

Billski
 

PiperCruisin

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Marske's Composite Manual has a few pages on this. See the Marske Aircraft website.
I agree. It has some good explanations of glider wing mounting methods. It is why I purchased it. He even mailed it to me when I was living in Europe.
 

plncraze

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It's been awhile since I looked at the Marske manual but I believe he had the bushings sized so he could use 4130 tube for the pin. Marske is really into the cheap and simple-no tail or engine.
 
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