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HELP! Bent J4A Cub Coupe Front Spar Lift Strut Fittings

I just reread the thread. Go with Farmer Hank’s approach on the dies. Gordon’s suggestion on a local shop is good. Those look pretty easy to make.


Sent from my iPhone using SuperCub.Org
 
J4A, did you ever find up your parts? Have you checked EBay?

Maybe put a free ad in Barnstormers.

I’m surprised that Univair doesn’t have what you need, the owner is restoring a J-4.
 
I would also use a sling girth hitched (or better yet clove hitched with a section of rope) around the upper strut rather than through that tie down eye. This is common damage. I would never use chain to tie down if you can avoid it.

You also might try Dakota or Jay at Javron to see if they can fab one for you as owner produced as well.

Good luck.


That damage is what’s caused by tying these airplanes down with chains. The chain is impossible to get really perfectly tight, as a result there’s always a bit of slack. In a wind, the plane comes up against the end of the chain with a HARD stop. Which bends things, and those are the parts that bend, and break. This has resulted in fatalities.

NEVER tie these airplanes down with chains, folks. And carefully inspect these parts on any plane you’re not very familiar with. After a fatal accident in Alaska, these parts on the Cub I was flying were found to be severely bent, and one was cracked. The last guy who flew the plane had tied it down with chains……in Kodiak.

Take a really good look at these parts.

MTV
 
Nothing yet on eBay, i got in touch with univair and they were unable to manufacture another set. I've emailed cub club to try and get some drawings but not had any reply, in the UK I'm able to manufacture my own parts however there's no way it would get approval without an original spec to go from. I might put an Ad on Barnstormers and will get in touch with Javron. Does anyone else have a lead on where I might get some construction drawings for the J4?
 
Dakota makes wings for J3 - surely they can do J4 as well or at least have access to the drawings:

https://dakotacub.com/index.php?route=product/category&path=5

Nothing yet on eBay, i got in touch with univair and they were unable to manufacture another set. I've emailed cub club to try and get some drawings but not had any reply, in the UK I'm able to manufacture my own parts however there's no way it would get approval without an original spec to go from. I might put an Ad on Barnstormers and will get in touch with Javron. Does anyone else have a lead on where I might get some construction drawings for the J4?
 
Here's a picture of my wood wing Wag 2+2. It's very similar to the J4 (with flaps hardware from SC). Not sure why you couldn't use it; it's a PMA's part but not for the J4. Main difference is how the drag wires fit; they are J3 wires.

Marty57

lift strut.jpg
 

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Here's a picture of my wood wing Wag 2+2. It's very similar to the J4 (with flaps hardware from SC). Not sure why you couldn't use it; it's a PMA's part but not for the J4. Main difference is how the drag wires fit; they are J3 wires.

Marty57

View attachment 57525

That’s the part I fabricated. A member here found me three and I ended up making the 4th. Good luck trying to find that these days. Wag discontinued it.



Sent from my iPhone using SuperCub.Org mobile app
 
You also might try Dakota or Jay at Javron to see if they can fab one for you as owner produced as well.
Be careful of the use of "owner produced". If you take advantage of "owner produced", the parts must be made in accordance to the original approved part specifications.


Nothing yet on eBay, i got in touch with univair and they were unable to manufacture another set. I've emailed cub club to try and get some drawings but not had any reply, in the UK I'm able to manufacture my own parts however there's no way it would get approval without an original spec to go from. I might put an Ad on Barnstormers and will get in touch with Javron. Does anyone else have a lead on where I might get some construction drawings for the J4?
If you can locate a drawing for this same part as used on another Piper model, look in the title box in the lower right corner. It should state there to which models that particular part is applicable. Perhaps J-3, J-5 or any other model would be the same as the J-4?
http://www.supercubproject.com/drawings/pdfs/A3310097.pdf
http://www.supercubproject.com/drawings/pdfs/A3290625.pdf
http://www.supercubproject.com/drawings/pdfs/A3290623.pdf This calls out the material spec.
http://www.supercubproject.com/drawings/pdfs/A3290054.pdf
This is a collection of drawings for the PA-18. http://www.supercubproject.com/drawings/main.aspx Some of them give reference to the J-4. You should be able to gather what you need for your plane. It appears in viewing the title box in several of these drawings, while not specifically stating so, the fitting for the J-4 is likely identical to the other early high wing Pipers.
 
Here's a pic of my spar/strut brackets.

The spacing of the bolt holes is quite different to the drawings on the PA18 (super cub project website)
PXL_20210913_134205103.jpg
 

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Here's a pic of my spar/strut brackets.

The spacing of the bolt holes is quite different to the drawings on the PA18 (super cub project website)
View attachment 57528
If I were you, I would use the drawings from Buggs' website as reference material and your bent fittings for hole spacing dimensions. While I realize you are in the UK, I would make the parts as close as possible to the originals with minimal communication with the authorities. This is assuming you can not find a drawing which is specifically calling out the applicability for the J-4.
 
In the past I had reverse engineered parts that were un-obtainable and no drawings available.
 
What am I missing here .... isn't this the same part? Listing says it fits the J3, different measurements of holes maybe?

Marty57

lift strut fitting.jpg
 

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Has J4A made a tracing with dimensions off the damaged parts? May have missed that step.

Gary

not yet, the easiest step right now would be for him to post the dimensions, and hole distances of his.

Someone here I’m sure has a J-3 and a J-5 they could get measurements off of.

Ten bucks says it’s the same one that a J-5 wood wing uses.
 
Take a look at the hole sizes, the N strut is held on by a threaded piece of wire just above the strut. I'm not sure I've seen other fittings with that style off attachment.
 
Take a look at the hole sizes, the N strut is held on by a threaded piece of wire just above the strut. I'm not sure I've seen other fittings with that style off attachment.
J-3 uses that threaded rod inside a tube and has no N strut.
 
The wood spar fittings sure look easy to duplicate. Not sure of the alloy, but I would guess 1025. A good structural engineer might suggest 4130 - might pay to ask a few questions. There is a seriously knowledgable lady on the J3 forum who has made every single piece of a J3 from scratch - bet she could help.

On the J3 there is a weld on the forward pair where the lift strut attaches. Looks really easy to do, but I would have it done by a pro. The rest is just cutting, drilling, and folding. A big brake will help a lot.
 
Take a look at the hole sizes, the N strut is held on by a threaded piece of wire just above the strut. I'm not sure I've seen other fittings with that style off attachment.

That's the same as on my 2+2 wing; the threaded rod goes through the N strut. I think the part I used was a PMA's part but no longer available from Wag. From the first picture in this post, you can see the same wire through the bent lift strut; you can see the nut and jam nut securing it in place. If all the holes and dimensions are the same, other than that hole for the threaded rod, why not weld a washer on the outside of that hole that is the correct size for the threaded rod? Guess that would be a question for the IA returning it to service after the repair.

Marty57
 
strut measurements.jpg
I took some rough measurements with a ruler to the nearest 16th. Does anybody have a J5 drawing to compare this to?
 

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The wood spar fittings sure look easy to duplicate. Not sure of the alloy, but I would guess 1025. A good structural engineer might suggest 4130 - might pay to ask a few questions. There is a seriously knowledgable lady on the J3 forum who has made every single piece of a J3 from scratch - bet she could help.

On the J3 there is a weld on the forward pair where the lift strut attaches. Looks really easy to do, but I would have it done by a pro. The rest is just cutting, drilling, and folding. A big brake will help a lot.
On the J-3 .062" 1025 steel.
http://www.supercubproject.com/drawings/pdfs/A3290623.pdf
 
Is there a good reason why you wouldn't/couldn't use 4130 instead?
No reason at all. Just be more careful in the bend radius when you make the bends. There are charts available for this purpose.
This is some discussion on the matter. https://www.aircraftspruce.com/catalog/mepages/metalinfo.php

Drawing 14172 calls for a 1/16" (.0625") radius of bend or one times the thickness of the 1025 materiel. According to the Aircraft Spruce information, they call for 3 times the thickness for the bend radius for 4130. If you follow those bend radius recommendations you should be safe. Be aware there is less likely to be cracks formed in the bend when the bend is across the grain. This is preferred when possible.
 
Could you measure the width of the channel, I do not have my J4 here. I think you will find a length of square tube will do what you need without fighting to get shop bends that do not crack along the edges or need to worry about post processing heat treat.
 
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