Quote:
Originally Posted by Sleepless
AutoPower and others have solved this issue with the main loop needing to be up on the seat ledge with a welded in plate and bolting to that.
I'd be uncomfortable using any bar that bolts to the floor in these cars as it is extremely flimsy. It would take too much convincing that it won't punch though...
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True. At the risk of being too blunt, that's not the problem we're trying to solve here. If you weld in plates and bolt to them, now you've got the permanent chassis mods of a weld-in cage, with all the safety and stiffness of a bolt-in.
With a large enough landing plate distributing the load, you can get some surprisingly large forces.
Hypothetically, let's say we've got a 4" x 6" landing plate. That's got a perimeter of 20". If our material is 0.020" thick (just a worst-case guess, I'm not at the shop right now), that's a cross-sectional area of 0.400 sq. in.
Mild steel typically has an ultimate yield strength of 36,000 psi, which means its shear strength is somewhere around 20,500 psi.
20,500 psi * 0.400" = 8200 lb to punch that one landing plate through, almost 4X the weight of the entire car on that one plate. A 3" x 3" landing plate would only take 4920 lbs to yield.
Now, that's not entirely accurate given the myriad of variables involved, but it does give you a ballpark estimate of the forces involved.
We've all seen those pictures of the Mustang that had the Autopower punch through the floor pan at Hallett. I couldn't find up-close pictures of the landing plates with a 5 minute google search, but the consensus seemed to be those landing plates were too thin, and too small. That's a totally solvable problem, and why we're putting so much emphasis on getting a good landing plate design.
Jake