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Question on making leading edge skins

Iflylower

Iflylower

Registered User
Memphis, TN
I've seen some other threads...they talk about extended leading edge skins, or thickness of skins.

I have access to a bender and a shear. I want to make the simple leading edge skins. A friend of mine has a setup with 2x4's and pvc to make his skins.

Is this "pre-formed leading edge" necessary?
Can I cut the skins, bend the spar flanges, make the rib cut-outs on the wing and attach? Will they form up well, or do they need to be a "pre-formed leading edge" to work properly?

I don't suspect they need to be formed, but I don't want to find out too late and cause more work.

Thank you very much!
 
That's what I'm going to do---- use lots of straps.

check your messages

DW
 
Thanks for the pics Tim. Nice Bender.

Thanks for post DW.

I've seen the straps, I've seen the Dakota cub "plywood tightener" and also the really nice metal strap contraption that Steve Pierce uses on tightening leading edge skins for install.

My only question, and I guess Tim is a proponent of bending, is "Does the skin have to be pre bent?" Can one get away with no prebending, can I do a poor man's wrap around a 1.5" PVC in the right place?

What do you think?
 
Iflylower said:
What do you think?
Click to expand...

If I were building experimental I would be using the 3M adhesive transfer tape to afix my leading edge skins to the ribs. A few screws for security too.

No bending before install.


Laugh at me if you want.... But the only reason I would ever build an experimental would be to use some modern technology.

Tim
 
In my opinion, the only reason for pre bending the skin is so it will be easier to make the final bend when you are securing the skin to the wing. I used cargo straps. Had I known about Steve's tool at the time I installed mine, I would have used his.
 
pre bend....

you might just collapse your ribs between spars(piper light ribs) if you straps get so tight trying to do it flat....
takes allot of pressure to where i am scared with prebent ones, I can't even imagine what you will be doing...

would think the screws would be pulling out of ribs too.....(piper light ribs)

think there IS a reason most all of them are made prebent....... don't think you will be saving any time, or money!

Edit: i should add that i am talking hard 2024. T3.... .020"....
 
Prebend yes.

The aluminum will try to straighten itself out after you have fastened it to the ribs if you don't. So it will bulge out between the ribs and fasteners, and try to pull the fasteners out of the rib caps. It will also be difficult to maintain a nice radius the full length of the leading edge. The better way is to bend the tight leading edge radius with your friend's 2x4s and PVC then, make a slight reverse curve on the rest of the skin top and bottom. This will make the skin lie down nice and straight by counteracting it's tendency to straighten out when you pull it to the ribs.
 
Even prebent is a bear. You'd find that out in short order. I made a jig of which I need to photo for Marty and I can post it here. maybe tonight. It's pretty slick and bends like the factory. It's a press break style make of wood.
 
Fortysix12
Hope you get a photo of your bender posted--- would like to see it.
 
Don't even try without pre bending the leading edge radius. If you need to know a simple way, just ask.

Don
 
I did some J-3 metal spar skins out of .020 T3 - prebent. I believe the inboard skins are identical to the Super Cub skins, and screw to the spar. Pre-bending was a real bear, and it took a lot of force, even with giant clamps, pipes, etc.

I really like the idea of a slight reverse bend - that's where I had most of my problems. The sheet metal screws will not do a good job of pulling it down on to the ribs.

But Piper used .016, and it was quite soft - so if you use that, maybe pre-bending is not necessary. I'd recommend the .020 half hard, and pre-bent with the above reverse curves. Great idea!
 
I'm working with .020 2024. I sheared all my leading edge skins today.

I guess I'll bend the flanges and "pre-bend" the skins when I get back in the shop. Thanks for the input. I was worried about deformation between the ribs - that's why I asked. I never even thought about the screws being pressured or pulled out of the ribs.
 
The the Leading edge press I made for my 18 wings.
Moms_Camara_013.jpg

Moms_Camara_011.jpg

Moms_Camara_012.jpg
 
wirsig said:
This is how I did it.
Chad's Vacuum forming
Click to expand...

This is a great idea. I like it. You deserve a great big gold :Gstar: :Gstar: for this one. How much spring back did you get on the radius? Do you think that it is necessary to pop rivet the skin to the pipe or could you have accomplished the same thing by just attaching the ends to the pipe?
 
A little math/measuring is involved when setting up to press a leading edge skin.
First measure where you want the skin to terminate past the front spar plus any down turns to determine the over legth required for the part. I had Aircraft preshear my demensions and it worked out well I used .025. Besure to put your down turns in first-not sure if this the correct terminlogy,angles at the trailing edge of the leading edge skin to add regitity strength. In my case with the wood wing I didn't need any and only created a slight bevel using a hand held beveling tool. Next very accurate measuring helps in locating the center of the leading edge radius so that it is more or less where you want it when installing the part. This line will be located dead center at each end skin and located DC of the Schedule #40 steel pipe, I referenced the inside of my opening using a MM machinist rule adjusting and centering until I was ready to start pressing the part. Rotate then nuts at even rate until the pipe is down flush with the top of the lumber,no need to go any further. Before removing the skin tape close the tailing edges of the skin to reduce the possibility of skin snapping out of the jig and creating a small wrinkle. (I speak from experience but if happens don't worry about it becuase it's minor and after you cover it disappears). Carefully remove the skin evenly if possible. This jig is available to anybody who wants it. Come get it in Clearwater. When your done pass it on.
 
Leniuk said:
What is the outside diameter of that #40 pipe??
Click to expand...

I want to say it's 2.09 in. This gives you almost perfect radius for the cub leading edge. The nice thing is if you want to make a smaller radius, then install shims on either side and go for a smaller piper O.D.
 
What 46/12 did was great. But two 2X2's, some screws to screw them to a wood table and the 1 3/4" madrel is all you need to achieve the same thing.

Don
 
don d said:
What 46/12 did was great. But two 2X2's, some screws to screw them to a wood table and the 1 3/4" madrel is all you need to achieve the same thing.

Don
Click to expand...

Don, you are correct. This litttle gem of a monstrosity was fabricated from a telephone conversation. I wasn't sure of the side load when building the tool so I went overkill not knowing better. It is way to big and heavy, the only thing I can say about it is it will serve many for years. It needs to be on wheels. :)
 
skywagon8a said:
How much spring back did you get on the radius? Do you think that it is necessary to pop rivet the skin to the pipe or could you have accomplished the same thing by just attaching the ends to the pipe?
Click to expand...

It's at 90 when all said and done. I didn't try it w/o the rivets but I wanted to make sure my break point didn't move when it sucked down. It usually only takes one suck to get it to shape but I didn't seal up the end good enough the first time.

I just watched my vid again, at the very end I take the LE off the pipe and show the amount of spring back.
 
wirsig said:
skywagon8a said:
How much spring back did you get on the radius? Do you think that it is necessary to pop rivet the skin to the pipe or could you have accomplished the same thing by just attaching the ends to the pipe?
Click to expand...

It's at 90 when all said and done. I didn't try it w/o the rivets but I wanted to make sure my break point didn't move when it sucked down. It usually only takes one suck to get it to shape but I didn't seal up the end good enough the first time.

I just watched my vid again, at the very end I take the LE off the pipe and show the amount of spring back.
Click to expand...

I guess that I didn't word my question correctly. I was wondering about the radius itself. What size pipe did you use in comparison to the curve of the leading edge? Or how much smaller is your pipe than the radius of the leading edge? I would think that after the sheet is sucked down to the pipe it would spring back to a larger size.
 
I used 1-1/2". It worked pretty well w/ a bungee on every rib but I'd use 2" if I do it again. Kind'a had to fight it a little.
 
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