Roll Bar bend

I've seen a couple RV-4's (and maybe others) with a non-Vans Roll Bar that was bent instead of welded at the top. The material is 1.50"dia X .049"wall 4130 tube.
Does anyone have a source for the bend ???
I've been chasing vendors and am getting quotes of $500 plus 20' of material and lead times of 8 weeks for just one bend.

I would check for a muffler shop that does custom exhaust, they use hydraulic tube benders that use dies that encapsulates the material to eliminate kinks.

My -4 has a rounded roll bar. While it looks nice, it is several inches shorter than the stock Van's plans. I think it has to be in order to achieve the necessary bend radius. I have actually been considering replacing it. In the event of going over on its back, all the height possible on the rollbar will be a good thing.

Roll bar

The roll bar in my RV4 was fabricated by a shop that builds roll cages for racecars.

Two problems exist. The severity of the bend at the top makes it very difficult to fabricate. We ended up doing this by bending two pieces as tight as we could without any crushing, and then cut and welded in an internal sleeve at the top to join the two pieces. If that doesn't makes sense, you can contact me and I'll try to explain better.

The second problem is that since it isn't pointed at the top (a radius bend instead of an acute angle) it ends up being wider near the top. So the tip over canopy can interfere. That's why they tend to be a bit shorter.

https://static.wixstatic.com/media/...1/c26698_1975153838d14b8eb295f4956203c4d3.jpg

I've been considering this for a non RV airplane. You might find it worthwhile.
http://www.showplanes.com/ecom-prodshow/WD_814fb.html

Thanks for the input so far but none applies.
I'm scratch building a Rocket including a canopy system of my own design; a combination fixed windscreen and flip over. The layout work is done and I can accommodate the shortcomings discussed (height etc.). The standard mandrel bend radius for the 1.50 X .049 is 3.50"CLR (Center Line Radius). My experience with muffler shops is that their equipment is not fine enough to handle the thin-wall. Similarly, race car shop bending roll-cages are bending much thicker wall DOM and are not using a mandrel.
Still looking for a tube bending shop.

larryj said:

...Similarly, race car shop bending roll-cages are bending much thicker wall DOM and are not using a mandrel.
Still looking for a tube bending shop.

Click to expand...

When I need 4130 bent I shop it out on mfg.com. But it's been a while since the last batch, so I can't remember who did it.

As to the wall thickness, you kind of have to decide whether you are making what the Miata guys call a "show bar" or an actual piece of rollover structure.

Thanks, Bob K.

Roll bar bends

You might give this a look.
http://secure.chassisshop.com/partrelate/C42-290/

larryj said:

Thanks for the input so far but none applies.
I'm scratch building a Rocket including a canopy system of my own design; a combination fixed windscreen and flip over. The layout work is done and I can accommodate the shortcomings discussed (height etc.). The standard mandrel bend radius for the 1.50 X .049 is 3.50"CLR (Center Line Radius). My experience with muffler shops is that their equipment is not fine enough to handle the thin-wall. Similarly, race car shop bending roll-cages are bending much thicker wall DOM and are not using a mandrel.
Still looking for a tube bending shop.

Click to expand...

Header manufacturers have the correct Eaton or Pines benders and ball mandrels ("spoon" mandrels won't give you the quality you're looking for on thin wall DOM tubing)

I did one for my Rocket and ran into the same problem. Ended up going with heavier material, mild steel, and had a pipe bending firm do the bends for me. Added ~8 pounds as compared to the stock setup.

I wanted to close this thread; here's what I ended up with.
I was first trying to find a shop that would / could put a 3.5" CLR (Center Line Radius) bend in 1.50"dia x .049"wall 4130 tube; this is the tubing Vans uses for a stock RV-4. I was willing to go up to .058:wall taking into account the increased weight of the Rocket but was really trying to keep the piece weight down (I've gone to a lot of work to keep my aircraft weight down; making concessions where increased weight/strength are helpful). I first contacted several aerospace manufacturing shops and this proved to be the wrong path. I then got hold of a local hot-rod shop and they were happy to work with me. The compromise I made is in wall thickness; I had to go to 1.625"dia x .083"wall. This gains about 1.5lbs but I can rationalize this added strength because of the design of the Roll Bar. I've seen earlier posts on the Roll Bar subject and remember Dan H making the observation that the Roll Bar is put in a bending moment from the diagonal side-brace up. My design will move the side-brace higher thus lessening this moment but it is still a weak point of the design. So the thicker wall Roll Bar is of some benefit. Long winded post, sorry.