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very nice
We have used a slightly modified Corvette tow point that mounts in a similar fashion but is a bit longer so it shifts the center of motion a bit farther away from the rear valence.

Good Job. Thanks for sharing
 

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Discussion Starter #3
very nice
We have used a slightly modified Corvette tow point that mounts in a similar fashion but is a bit longer so it shifts the center of motion a bit farther away from the rear valence.

Good Job. Thanks for sharing
Hadn't thought about that. Good point. still have some aluminum left, may make them longer.
 

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You might want to make it out of something a little more stout if you actually plan to use it. As drawn it'd fail at just over 3,000 lbs of tensile force - and that's a smooth, slowly and evenly applied 3,000lbs.

It'll start to bend well before that which is less than ideal if you're trying to secure it to a trailer for a long trip.
 

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Phil,
While what you say is true, these are most likely to be used to load a car onto a trailer when it cant be driven on. So you are not putting anywhere near 3000 pounds loading on them. On level you are overcoming the rolling resistance plus some initial inertia. Going up the ramp, the load is a function of the geometry of the ramp.
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its the normal force acting on the ramp plus rolling resistance. I have not done the calculation but its probably in the low hundreds of pounds.

The Corvette hook I use is basically the same geometry but the thickness is less. Its steel.
 

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Loading it on a trailer sure, but what happens when someone doesn't use it to gently tow on a flat (or near flat) surface with a car on four wheels? Tow straps releasing sudden busts of stored potential energy aren't fun for anyone within their reach.

Or when using it as a tie down to the rear - what starts a trip as a secured car might not finish it that way if it bends.

3k is a good working load target. The actual failure point should be 2 or 3 times that if you really want to rely on it (most commonly available steels have 2-3 times the yield strength of 6061 BTW.)
 

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My books say that 6061-T6 and 1020 steel have essentially the same yield strength (40-45 ksi), so I don't think material choice is the real issue. But I think you will have at least as much risk from shearing the bolts or breaking them in an off-axis load as you will with the ring itself breaking, and probably more.

I would never use something like this to tie a car down, because the loading is almost always going to be off-axis making it very likely to bend from just the stress of normal towing. That doesn't even consider what is going to happen if there is an incident during the tow and it has to keep the car on the trailer.
 

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Discussion Starter #8
I built these just get the car on a trailer or rollback without destroying the fascia. When I have hauled cars on a trailer (maybe twice in my life) I always hooked the tie downs to an unsprung portion of the vehicle, such as an axle or the tires.
 

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I built these just get the car on a trailer or rollback without destroying the fascia. When I have hauled cars on a trailer (maybe twice in my life) I always hooked the tie downs to an unsprung portion of the vehicle, such as an axle or the tires.
That sounds much better. My confusion came from "hold down" in the thread title.
 

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Discussion Starter #10
As an aside, I got a spec on the drawing wrong. The bolts are 8-1.25x30 NOT 8-1.5x30. Sorry bout that.
 

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Discussion Starter #11
That sounds much better. My confusion came from "hold down" in the thread title.
If that is not complicated enough, try securing a cessna 182 on a rollback when the wheelspan is the same width as the rollback and there is nowhere to hook anything securely to anything else and then driving it home on the interstate. Talk about sweating bullets!!
 

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If that is not complicated enough, try securing a cessna 182 on a rollback when the wheelspan is the same width as the rollback and there is nowhere to hook anything securely to anything else and then driving it home on the interstate. Talk about sweating bullets!!
I have always thought that airplanes were pretty well equipped to be tied down. Apparently not.
 

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Discussion Starter #13
I have always thought that airplanes were pretty well equipped to be tied down. Apparently not.
You are right, They actually are well equipped, on the tarmac. Trouble is that the tiedown points are on the wings, which were removed for transport, and at the tail, which hung out at least five feet past the back of the rollback.
 
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