Lifting Rings

[N3UW]

I am planning on eventually putting my Patrol on floats. As I am getting ready to rivet on the skins, I am thinking about installing lifting rings onto the wing. Has anybody out there done that? I looked at the lifting rings on the Cessna 180 and they connect through the front and rear spar attach fittings. I am considering fabricating a steel piece that attaches to the front and rear spar near the root. I would have 4 brackets. 2 on each wing attached to the rear of the main and rear spar. I would attach them to the spars with bolts through existing rivet holes between the ribs under the 0.032 skin. The bracket would fit between the neighboring rivets to the right and left. I am considering fabricating them basically as an inverted L with the long side of the L against the spars. At the top of the L I would weld in a nut to accept the actual removable lifting ring. The top of the L would be supported by a triangular piece running the length of the long side of the L. Any thoughts?

[Zzz]

That's pretty much how it's done on Cubs, or so I learned when researching the same topic a while back. I'm not planning on putting mine on floats, but I do like the option of lifting it with a hoist for gear/wheel work. Here's the lifting eye that Atlee Dodge sells. Pretty simple design that just uses the spar attach bolt.

[alaskabearhawk]

Don't do any mods or additions to the spars. Just use the existing spar attach bolts. Here's what Rob Taylor did. He made a total of four, one for each attach point.

[Battson]

I would tend to use the wing attach bolts, rather than attaching straight to the spars. Let the bolts spread the load between the fuse and wings, rather than concentrating the total load on the spar.

[Chewie]

Did he load test them?

[Battson]

Don't do any mods or additions to the spars. Just use the existing spar attach bolts. Here's what Rob Taylor did. He made a total of four, one for each attach point.

I wonder about that design, whether it might bend under load and deform / crack at the weld? Maybe I am being too conservative... I would tend to copy a certified design.

[N3UW]

Don't do any mods or additions to the spars. Just use the existing spar attach bolts. Here's what Rob Taylor did. He made a total of four, one for each attach point.

Thanks. I like that design. Much easier also. With the spreader bar attached it would not put any twisting force on the bolts.

[whee]

I wonder about that design, whether it might bend under load and deform / crack at the weld? M

I wonder about it also. When you get to the point of building them AKbearhawk it would be interesting to see one put in the tensil test machine if you still have access to it. The Atlee Dodge design will put a torsion load on the wing attach fittings which I don't like, but it probably won't hurt anything. I will likely use something like the Atlee Dodge rings on mine because I can add them after the fact as long as I install a bolt with a little extra length.

[alaskabearhawk]

I sincerely doubt those lifting eyes aren't strong enough to lift 500lbs each. If they were made of mild steel (they are not) they could probably lift at least 1000lbs each and using 4130 more than double that. I do have access to the tensile test machine. It would be an interesting test for sure. I might just do that someday.

[Battson]

I sincerely doubt those lifting eyes aren't strong enough to lift 500lbs each. If they were made of mild steel (they are not) they could probably lift at least 1000lbs each and using 4130 more than double that. I do have access to the tensile test machine. It would be an interesting test for sure. I might just do that someday.

My concern wasn't about the tensile strength of the steel.
The concern was about the tang's ability to resist bending created by the off-centre lifting point welded between the two tangs (the little arms which attach to the wing bolt).
The way the arms are oriented means they have basically zero 4th Moment of Area in the plane of bending, which means they will try to straighten themselves under load, instead of trying to resist the bending force. So they have to transfer all their bending force to the web, which resists the bending. Also, all that resulting bending force has to go through weld to get to the lifting point.

Like you say, it's probably 100% fine because it's over-built. I wouldn't have included a weld personally, it creates weak points in the HAZ and at the cracks where he didn't weld in the underside.

[Zzz]

Those lifting eyes are always used with a spreader bar device, which keeps the compression load off the carrythrough spar and the fuselage. It's easy enough to prevent torsional loads. Plus, it's a static load. It's not like they're being subjected to work cycles.

[marcusofcotton]

I sincerely doubt those lifting eyes aren't strong enough to lift 500lbs each. If they were made of mild steel (they are not) they could probably lift at least 1000lbs each and using 4130 more than double that. I do have access to the tensile test machine. It would be an interesting test for sure...

I agree with Paul, plenty strong and an interesting test.

[Robert440]

If anyone wants an unofficial down and dirty material test done free of charge I have an old school steam gauge/hydraulic Vega Material Tester with test fixtures in my shop. It's the kind you used to see in shop class when you were in high school. I use it for pressing bearings in and out but the testing fixtures are all still there and in great shape.

[Battson]

If anyone wants an unofficial down and dirty material test done free of charge I have an old school steam gauge/hydraulic Vega Material Tester with test fixtures in my shop. It's the kind you used to see in shop class when you were in high school. I use it for pressing bearings in and out but the testing fixtures are all still there and in great shape.

That is a cool offer.

[S Lathrop]

I thought it would be fun to take a look at Lift Rings as an exercise with the latest version of Solid Works. The one in the picture will just hold 1250 lbs.. in .080 mild steel or 1600 lbs. in 4130 (28% more) The loads and fixture were with 3/8 diameter rods of the same material as the clevis.