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X-Brace

Binty

Registered User
South Island, New Zealand
Im looking for some info on the overhead X-brace as one has been installed in our cub from way before we bought it.
 
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No doubler - a mod added to the existing tube. My understanding is it was added to keep the right flap/wing area from coming into the cabin in the event of a crash and hitting the passenger. Size: .875 x .035 tubes
 
Here are a couple of not so great pictures. Like Chris said, 7/8"x .035" wall tubes. I was in an accident where the right wing hit the ground and the rear spar carry-thru tube collapsed behind my head and the fuselage side caved in. The "X" brace will let the wing fold up and help keep the cabin structure in tact. I have installed it in everything from PA15, 16, 17 and 18. Atlee Dodge has the STC.

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Actually the X brace tubes are .875 x .049.....the short .50 tube(shoulder harness holder) is .035, all are 4130
 
Nanook is correct. I tried going off memory and that is always bad. I knew I got a bunch of 7/8" x.049' wall drops from Air Tractor for a reason.
 
The existing diagonal can fail in buckling due to compression loads in a crash and bend down into the cabin. At least that is what happened to my Cub when a previous owner crashed it. Not as severe as Steve's crash, but more of a knock and you can imagine what would happen.

From memory the original diagonal is only 1025 on an original Piper fuse, so the amount of strength this adds in this area is enormous.

When I first started buying stuff from Atlee Dodge he'd include the X-brace STC and a hand-written note; "This is a freebee. You must do this mod". That the guy would care that much about someone in little old New Zealand was enough; all I had to do was cut the tubing to length!

Cheers, Andrew.
 
The original diagonal is Piper part #10562-81, and calls for 7/8" x .035 1025. Not sure what Atlee calls for in the STC, but using 7/8" x .035 4130 will give you a 30-40% increase in strength by nature of the material alone over the original Piper engineering. Not sure where the .049 is coming from (again, unless that is what Atlee calls for)
 
Actually the X brace tubes are .875 x .049.....the short .50 tube(shoulder harness holder) is .035, all are 4130

What’s the preferred method of attaching the shoulder harness to the .5” tube? Atlee’s attachments won’t work for a .5” tube.

Does a thimble with a cable and nicopress sleeve work? Any other ideas?

Thanks
 
The original diagonal is Piper part #10562-81, and calls for 7/8" x .035 1025. Not sure what Atlee calls for in the STC, but using 7/8" x .035 4130 will give you a 30-40% increase in strength by nature of the material alone over the original Piper engineering. Not sure where the .049 is coming from (again, unless that is what Atlee calls for)

Column buckling strength of 1025 and 4130 is basically the same. 4130 is only stronger in tensile.


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Reading through this thread it seems a no brainier to do an x-brace. How are the carbon cubs able to get away with a V-brace? Does the V also protect against these issues or are there other changes to the airframe cub crafters made to protect against these issues which allows them to get away with just a V brace?
 
Add two tube to the upper deck simulating the cross tube that is already there. You will have a tube from the left front wing attach fitting to the right rear and another tube from the front right wing attach fitting to the left rear.
 
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