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lostagain View Drop Down
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Posts: 2595 		Direct Link To This Post Topic: GVWR>GAWR and Stabilizer Issues
    Posted: 08 Jan 2019 at 10:19am
Sounds like a plan.  But then I'd have to get the metal guy to not only cut the pipe, but to bend a crown into it? Right?
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Posts: 5290 		Direct Link To This Post Posted: 08 Jan 2019 at 9:59am
If you do go to the trouble to measure it I'd suggest lifting the trailer off its wheels first so you can get the crown dimension with the axle unloaded. Then if you crown the angle to match things should line right up under load. 
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lostagain View Drop Down
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Posts: 2595 		Direct Link To This Post Posted: 08 Jan 2019 at 9:55am
My axle is about 3" inches in diameter.  Since I broke my arm at the end of Dec., I'm in no condition to crawl under and measure it right now. Cry  I have no idea who the manufacturer is, except to say it's likely to be one of the two common brands.  When the weather warms up and my arm heals, I'll take a gander below and see if I can find a label.  Maybe I should just call FR and see what was originally installed.  Since it's probably never been replaced, that should answer the question.

Where would I find a piece of steel pipe split in half without getting into going to a metal fabricator to cut one for me?  Would the round half pipe configuration be sufficiently resistant to bending to make it worth it?
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StephenH View Drop Down
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Posts: 6417 		Direct Link To This Post Posted: 08 Jan 2019 at 9:41am
I did find some online, but none of the correct dimensions for this purpose. I did not measure, but there was a little bit of crown visible. I don't think it was more than about 1/2", but I would really have to measure to be sure.
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Posts: 5290 		Direct Link To This Post Posted: 08 Jan 2019 at 9:33am
StephenH, I've never seen a v bottomed U bolt but yes if there was one that would be good. Or you could weld up some custom clamps but I'm not convinced its necessary. 

If your axle is crowned you'd probably want to crown the angle a bit to match. We'd probably have to ask a metal shop what that would cost to do. Angle iron gets bent all the time but I've mostly seen it bent parallel to one of the flats.   

I don't notice any crown in my axle but I haven't looked carefully. Could be mine has already started to fail, or its got more weight on it. About how much of a center crown do you have?

I calculated the 3/8 bolt size based on only a single thread engagement, so it's really way overkill even with standard nuts, but more threads can never hurt. 

lostagain, interesting that you have a round axle. Vikingr's 172 has pretty much the same axle as StephenH and I do. Who is the manufacturer? 

With a round axle you might be better off thinking about using a piece of steel pipe cut in half lengthwise rather than an angle to reinforce it. What is the OD of the round axle?  You should be able to buy off the shelf u bolts to clamp it. 

I just looked at the 3 x 3 x 3/16 angle, which seems about right for reinforcing the 3 x 3 x 3/16 inch Lippert box tube axle, while not adding a lot of weight. Your case might be totally different, your configuration might or might not even be subject to axle failure. Have you had any signs of it?  
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Posts: 2595 		Direct Link To This Post Posted: 08 Jan 2019 at 8:10am
ummm, errrr, I just went out into the pre-dawn chill to confirm what I recall, that my axle is round.  I was actually thinking  of standard U bolts, not square ones like you'd find on a leaf spring.  The round part would rest against my round axle and the retainer plate passing over the angle iron.  The issue I had with that was that the retainer plate wouldn't fit up against the angle iron completely as it would have to be bent with a right angle in it to touch the angle iron and would need additional bends where the bolts go through at 45ยบ or so.  Or am I, once again, trying to put round pegs into a square hole?

Another dumb question:  Has anyone calculated the various potential sizes of angle iron and what additional strength they would impart to the axle once installed securely?  For me, if I were to engage in such a modification, I would not be looking to significantly increase the load capacity of our 172, but to give it a little more strength for forest service roads and such when loaded within the defined limits.  If I put a 1 1/2 inch angle with about 1/8th thickness angle iron would I be wasting my time or would it add enough strength to make it worth the bother.  It's a lot of work wallowing around under a trailer for an old geezer my age.
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Posts: 6417 		Direct Link To This Post Posted: 08 Jan 2019 at 7:43am
Originally posted by offgrid

Ha Ha lostagain. Not laughing at your idea of using square u bolts, just laughing 'cause I beat you to it by 22 minutes Tongue.

The reason I was mentally resisting them at first is because with the diamond orientation of the axle you need to have two of them at each point to symmetrically hold the angle to the axle, so its a little weird. But it should still work I think.  The holding capacity of each u bolt in the direction of force is derated to cosine(45 deg)= 71% so two together would be about 1.4x the the holding force of a single u bolt used normally. 
It would be nice if there were such a thing as a V bolt used with a V plate, washers and nuts. I don't know if such a thing exists, but it would make things easier, I think.
The only issues I'd take with your summary of the situation is first that there isn't just the one weak point, the stresses on the axle are continuous. The points just outboard of the axle attachment brackets are most likely to see the most stress over time but that doesn't mean they're the only points to worry about. 

Second, I'm not sure what you mean by "get pushed away from the bend site"? The bending forces are upwards on the wheels so the axle ends are getting pushed upwards while the midsection of the axle is getting pushed downward. By clamping the to the axle at the ends the two parts should stay in intimate contact over their whole lengths under load. You could add more clamps inboard if you wanted to but I don't really think they're necessary. 
When I look at the new axle, I can see a little upward bend in the middle section. Would an angle iron need to be bent to match the initial shape of the axle? Would adding a straight piece of angle iron tend to start a bending stress on the axle if an initial matching of the shape is not done?
StephenH, I think the hose clamps you found should work but I'm now leaning toward trying square U bolts if we can find the right size. They would probably need to be 3/8 inch to have enough thread area to carry the load and have a 3.5 inch opening to slide over the 3 inch axle plus the 3/16 in angle.

These would probably work. We'd need bolt plates, nuts and washers as well. 

https://store.uboltsdirect.com/SecureCart/ViewCart.aspx?mid=0D3EC8DE-C0FA-487C-81A3-BB423F37A886&sctoken=164be636ce8a4f7da159cd2aa91502b4&optionId=1012189971,&bhjs=1&bhqs=1

I saw the 3/8" deep nuts and washers offered as an option. I like the idea of the deep nuts as they would have more threads.
StephenH
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Posts: 5290 		Direct Link To This Post Posted: 08 Jan 2019 at 7:05am
Nope, you can't weld to torsion axles. There are rubber cords inside there that would burn up. 

When Lippert and Dexter make them all the welding is done before inserting the rubber. The rubber cords are compressed and frozen (in liquid nitrogen I think) then everything is inserted and allowed to warm up. 

The axle ends bend up under load, the center section of the axle between the frame attachments bends down.  
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Posts: 1088 		Direct Link To This Post Posted: 08 Jan 2019 at 6:59am
This discussion brings me back to a question I asked a while back--does the axle bend up or down ? it would seem to me that you could weld the 3x3 angle to the axle and it would stop the bend regardless of the directin.  Is it not possible to weld to the hollow axle instead of U bolts?
Vann

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Posts: 5290 		Direct Link To This Post Posted: 08 Jan 2019 at 6:35am
Ha Ha lostagain. Not laughing at your idea of using square u bolts, just laughing 'cause I beat you to it by 22 minutes Tongue.

The reason I was mentally resisting them at first is because with the diamond orientation of the axle you need to have two of them at each point to symmetrically hold the angle to the axle, so its a little weird. But it should still work I think.  The holding capacity of each u bolt in the direction of force is derated to cosine(45 deg)= 71% so two together would be about 1.4x the the holding force of a single u bolt used normally. 

The only issues I'd take with your summary of the situation is first that there isn't just the one weak point, the stresses on the axle are continuous. The points just outboard of the axle attachment brackets are most likely to see the most stress over time but that doesn't mean they're the only points to worry about. 

Second, I'm not sure what you mean by "get pushed away from the bend site"? The bending forces are upwards on the wheels so the axle ends are getting pushed upwards while the midsection of the axle is getting pushed downward. By clamping the to the axle at the ends the two parts should stay in intimate contact over their whole lengths under load. You could add more clamps inboard if you wanted to but I don't really think they're necessary. 

StephenH, I think the hose clamps you found should work but I'm now leaning toward trying square U bolts if we can find the right size. They would probably need to be 3/8 inch to have enough thread area to carry the load and have a 3.5 inch opening to slide over the 3 inch axle plus the 3/16 in angle.

These would probably work. We'd need bolt plates, nuts and washers as well. 

https://store.uboltsdirect.com/SecureCart/ViewCart.aspx?mid=0D3EC8DE-C0FA-487C-81A3-BB423F37A886&sctoken=164be636ce8a4f7da159cd2aa91502b4&optionId=1012189971,&bhjs=1&bhqs=1
1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold
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