Straighten bent tube idea

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Built2Fly

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I had a recent minor incidence with my airplane resulting in two tubes on the fuselage being bent. One is 3/4" OD and the other is 5/8" OD. I watched some YouTube video on how to bend back those tubes, and I still have some questions maybe some of you can help.
  1. These two bents are on connected tubes. Could I bent both back together? Or do I have to cut one open, bend the other back, and then weld the tube that has been cut open?
  2. How hard is it to bend back 3/4" OD tube? Can it be easily done with just wood blocks and clamps, or do I need some serious leverage and strength to get it done?
Thanks a lot for your help.

Adam
 

wsimpso1

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I had a recent minor incidence with my airplane resulting in two tubes on the fuselage being bent. One is 3/4" OD and the other is 5/8" OD. I watched some YouTube video on how to bend back those tubes, and I still have some questions maybe some of you can help.
  1. These two bents are on connected tubes. Could I bent both back together? Or do I have to cut one open, bend the other back, and then weld the tube that has been cut open?
  2. How hard is it to bend back 3/4" OD tube? Can it be easily done with just wood blocks and clamps, or do I need some serious leverage and strength to get it done?
Thanks a lot for your help.

Adam
I am accustomed to cutting out damaged tube sections and splicing new in. Best to check 43.13 chapter on tubes and welded structure…
 

TiPi

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I had a recent minor incidence with my airplane resulting in two tubes on the fuselage being bent. One is 3/4" OD and the other is 5/8" OD. I watched some YouTube video on how to bend back those tubes, and I still have some questions maybe some of you can help.
  1. These two bents are on connected tubes. Could I bent both back together? Or do I have to cut one open, bend the other back, and then weld the tube that has been cut open?
  2. How hard is it to bend back 3/4" OD tube? Can it be easily done with just wood blocks and clamps, or do I need some serious leverage and strength to get it done?
Thanks a lot for your help.

Adam
for them having been bent means they are the weak point. Straightening these tubes will make them weaker if that is what you want. If you want the same strength, replace them.
 

Yellowhammer

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As our esteemed colleague Wsimpso 1 pointed out, It is vitally important that you take the time to read the Advisory Circular 43.13-1B chapter 4-91 titled Repair of Tubular Members which includes welded structures. I just so happened to be reading through that very same chapter today and remember clearly what it says about repair of fuselage tubes that have been bent or any other type of damage incurred.

Way too much information to convey in this post but once you read it you will see what I and Wsimpso 1 mean by his/our recommendation.

The Circular has every conceivable type of repair for tubular members found in aircraft with tube structures. Not one mentions just straightening out a bent or dented tube. A few more steps are to be taken along with the proper welding rods used, patchwork steel used, and, also very important, it calls out the re-tempering process that MUST be done to bring the tube back to its original temper. If it is welded it looses it and that step cannot be ignored.

Hope this helps and best of luck to you on your repairs. Please let us know which method you choose to repair it with. Pictures as well would be helpful to others in the same boat.

-Yellowhammer
 

cvairwerks

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Lots of SRM's show field fixtures to remove slight bends from structural tubes. There are limits to how much bend can be removed, due to one tube being bent can cause bends in others. You need to lay a strait edge on every tube within two connections of the bent ones and verify there hasn't been damage or misalignment elsewhere.
 

Built2Fly

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A lot of good suggestions. Thanks.

I don't have a good picture, but here is a drawing of the frame. As you can see, this is a pusher, so the engine, wings and other flying surfaces are all on the back side. The bend is on the front, which is just a cage for the pilot. So the ultimate strength and alignment is not that critical.

The blue arrow points to a 3/4" tube. It is bent down slightly, like maybe 1/2 inch. Barely visible by eyeballing, but it affects my window panel alignment, so I'd want to get that fixed.

The green arrow points to a 5/8" tube. It is bent inward about 1-1/2 inch. I think it affects the nose alignment slightly (which I can adjust the nose cone to get rid of). However, the side skin is attached to that tube. So I want to have this straightened and I feel that it may not be too hard.

My question is that all these are welded together in one piece. Could I bent it in place without cutting it loose (maybe hard to do, because all the structured rigidity) or maybe there is a trick to do it? At the last resort, I can always cut those and realign that way. But I felt that there might be a way to do it in place. Just am trying to figure out how.

Your ideas and experiences would be very helpful.




fuselage.png
 

TFF

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They are going to be pretty hard to bend. A floor jack pushing on a block of wood might shove some of it back, but not all the way. Of course you have to push against something that’s not going to move and hold the fuselage too. I remember a friend flipped our racing kart and bent it when we were kids. To try and bend it back, I jacked up my mom’s Grand Torino wagon and put it on top. Didn’t budge. Years before I had a torch and other things. What will you be happy with as a fix? A torch will make it easier to bend, but you are changing the strength. Each bend is a stretch even if it’s straight. My plane the Cabane struts were tweaked. I heated them and reset them. Then I welded a finger patch over the joint. The original guy was just going to leave it and muscle it into place.
 

proppastie

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I don't have a good picture
So seems like it is a tail dragger rather than a nose dragger.....how did they get bent....?......and if it was flight related and or the tubes protect the pilot you probably should repair them properly.
 

Peterfyg

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I have straightened out trailer frame tubes. You need a rigid beam to clamp at either end, either outside to pull or inside to push. The ends have to be spaced off the tube to over bend to allow for springback. You can pull with a clamp or ratchet strap, or push with a jack. Wouldn't do that for anything flight critical.
 

dog

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cut a v groove in a piece of 2x4,whatever,longer than the bend,tie it on to the bowed out side, secure the frame to a wall or tree,apply
hammer to wood,if it does not move the tube,
then heat the bend to a dull red(as seen in a dark shop)and hold your wood block,apply hammer to smoking wood
if you have not done this sort of thing before on lesser metal things,often,then seek help,as the force and technique required will add a new bend
as easily as subtracting the one you have now
 

Built2Fly

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Great ideas on using a torch and heat. I will try the block/clamp method I learned in another video, and maybe try the heat method if that doesn't work. I will let you know how it goes.

For your curious kind, it is a Titan Tornado. Just another stupid ground hanger incidence that something run into something. Not much impact to make these small bends, so hopefully it would not be that hard to bend back.
 

Kyle Boatright

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I have an ancient video that shows fixing tubes like that using boards that are routed out to a v shape and used to sandwich the bent tube and compress it back into shape. I think there are a couple of ways to do that and apply leverage that will straighten the tube without beating on it. Personally, I find that when I take a hammer to things, bad stuff happens.
 

Yellowhammer

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A lot of good suggestions. Thanks.

I don't have a good picture, but here is a drawing of the frame. As you can see, this is a pusher, so the engine, wings and other flying surfaces are all on the back side. The bend is on the front, which is just a cage for the pilot. So the ultimate strength and alignment is not that critical.

The blue arrow points to a 3/4" tube. It is bent down slightly, like maybe 1/2 inch. Barely visible by eyeballing, but it affects my window panel alignment, so I'd want to get that fixed.

The green arrow points to a 5/8" tube. It is bent inward about 1-1/2 inch. I think it affects the nose alignment slightly (which I can adjust the nose cone to get rid of). However, the side skin is attached to that tube. So I want to have this straightened and I feel that it may not be too hard.

My question is that all these are welded together in one piece. Could I bent it in place without cutting it loose (maybe hard to do, because all the structured rigidity) or maybe there is a trick to do it? At the last resort, I can always cut those and realign that way. But I felt that there might be a way to do it in place. Just am trying to figure out how.

Your ideas and experiences would be very helpful.




View attachment 128778



Id just replace those members if you could.
 

Larry650

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Find a custom bicycle frame builder in your area. If it can be fixed, they will know how to do it. And they work with very thin chromoly all day long.
Some of those guys can straighten a multi-thousand dollar racing bike frame using hardwood blocks and a bench vice.
 

bmcj

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The diagram posted looks suspiciously like a Titan Tornado. Everything forward of the bucket is for streamlining, and (somewhat) pilot protection.
You are correct, it does look like a Titan Tornado.

So seems like it is a tail dragger rather than a nose dragger.....how did they get bent....?......and if it was flight related and or the tubes protect the pilot you probably should repair them properly.

The Titan Tornado is a nosewheel plane. The photo cuts off part of the nose where the nose wheel would mount, but it does show steering linkages going forward from the pedals, lending credence to the Tornado supposition. There’s not much in the way of diagonal trusses in that area, so I’m assuming those tubes are either lightly loaded or loaded in tension. Still, consult 43.13 and other experts for there opinion. If they are structural, you need to know what you are doing when it comes to heating or bending.

Is your blue arrow pointing to the (center) windshield support tube or the side tube opposite the green arrow?
 
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