I discovered today that the WD-641 roll bar for my RV-7 slider was 3/8" too wide, thus I consulted the instructions:
"It can be adjusted quite easily by hooking one end behind something and pulling (to make it wider) or by putting one end on the floor and leaning against it (to make it narrower). Go slowly. It is easy to do too much."
So I leaned it against the floor and put every ounce of my pathetic 150lbs against it, and absolutely nothing happened. I then went and got a truck ratchet strap, wrapped that around the posts as low down as I could get it, and cranked as hard as I could whilst still leaning on it, yet nothing happened (ok, it bent now, but not enough to get even a fraction of plastic deformation). It is apparent that when building an aeroplane, one must calibrate their definition of "easily".
Thoughts were now running through my head of getting the tractor out and pressing it with the hydraulics, but then I remembered I had a 1 ton chain hoist somewhere. Thus, I found that, along with some 6.5Ton shackles big enough to go around the roll bar, three different sizes of poly water pipe (1 1/4, 1 1/2 and 2") which were slit and used to distribute the load from the shackle (along with some tape to protect the powder coat). The shackles were positioned low on the rollbar, about an inch or so above the start of the gussets. The setup was placed on the bench to which I had drawn my reference marks, and I started tensioning the chain hoist, bending the roll bar in one inch increments, then unloading it and checking against my marks. I got to 4 inches of elastic displacement, and still no plastic deformation, so I went to 5.5 inches, and sure enough, I got exactly my targeted 3/8" plastic defection within 1/32". In hindsight, I should have started at 4 inches deflection, then began increasing at half inch increments as I approached my limit, so I consider myself lucky to have achieved my target with a 1.5" step.
I suspect I had about 500-800lb force on the hoist until it began plastically deforming (a guess based on how much force I had to put on the drive chain), so be warned when you do this, there is a lot of stored energy. You will also see in the picture that I had some zip ties to hold the shackles in place. Once the assembly starts deflecting, there is not load on these, but they are handy to stop the shackles slipping off the poly pipe before you have tension built up. In all, the chain hoist solution gives you a highly controllable way of adjusting the bend in the rollbar, and I would definitely use this method again in the future.
Anyway, I posted this because I couldn't find much information myself on how to bend the roll bar inwards. The chain hoist was just a Harbor Freight 1ton cheapo I purchased 15 years ago, but note the amusing warning label on the back.
Cheers,
Tom.
"It can be adjusted quite easily by hooking one end behind something and pulling (to make it wider) or by putting one end on the floor and leaning against it (to make it narrower). Go slowly. It is easy to do too much."
So I leaned it against the floor and put every ounce of my pathetic 150lbs against it, and absolutely nothing happened. I then went and got a truck ratchet strap, wrapped that around the posts as low down as I could get it, and cranked as hard as I could whilst still leaning on it, yet nothing happened (ok, it bent now, but not enough to get even a fraction of plastic deformation). It is apparent that when building an aeroplane, one must calibrate their definition of "easily".
Thoughts were now running through my head of getting the tractor out and pressing it with the hydraulics, but then I remembered I had a 1 ton chain hoist somewhere. Thus, I found that, along with some 6.5Ton shackles big enough to go around the roll bar, three different sizes of poly water pipe (1 1/4, 1 1/2 and 2") which were slit and used to distribute the load from the shackle (along with some tape to protect the powder coat). The shackles were positioned low on the rollbar, about an inch or so above the start of the gussets. The setup was placed on the bench to which I had drawn my reference marks, and I started tensioning the chain hoist, bending the roll bar in one inch increments, then unloading it and checking against my marks. I got to 4 inches of elastic displacement, and still no plastic deformation, so I went to 5.5 inches, and sure enough, I got exactly my targeted 3/8" plastic defection within 1/32". In hindsight, I should have started at 4 inches deflection, then began increasing at half inch increments as I approached my limit, so I consider myself lucky to have achieved my target with a 1.5" step.
I suspect I had about 500-800lb force on the hoist until it began plastically deforming (a guess based on how much force I had to put on the drive chain), so be warned when you do this, there is a lot of stored energy. You will also see in the picture that I had some zip ties to hold the shackles in place. Once the assembly starts deflecting, there is not load on these, but they are handy to stop the shackles slipping off the poly pipe before you have tension built up. In all, the chain hoist solution gives you a highly controllable way of adjusting the bend in the rollbar, and I would definitely use this method again in the future.
Anyway, I posted this because I couldn't find much information myself on how to bend the roll bar inwards. The chain hoist was just a Harbor Freight 1ton cheapo I purchased 15 years ago, but note the amusing warning label on the back.
Cheers,
Tom.