Stringers over cabin and welding questions

[james gevay]

I've just started fitting the stringers over the cabin and the first bend starting at the top of the windshield aft to the first cabin former is a tight bend to make. The former I'm talking about is 12" aft from the windshield.

I'm afraid of trying to make the bend and cracking the former, which is only 1/2" X 1 1/4" spruce. How did you guys do the same thing? Did you soak the wood in hot water or steam it first and clamp it in there and let it sit until it dries? The rest of the bending seems fairly easy to do.

The bottom of my rudder TE was rusted out so I cut about 1' out from the tail post to just under the bottom rib. Questions; Is it permissable to use the inner sleeve method to make the repairs on such small tubing? The TE is 5/16" OD and 1/4"OD tubing will fit inside.

I already have some 4130 and have bent the curve for the 2 pieces to fit together. If that method is acceptable, then is it possible for someone to make such small welds on the tubing?

Also the old tubing was brazed on at the tail post, I know your not supposed to weld over brazing but I ground off all the brazing and it looks like I'm down to bare metal. Do you think that will still be a problem to weld?

Thanks, Jim

[joea]

Jim,

No ideas on forming the wood.

Regarding the brazing, as far as I know, Aeronca never brazed anything and everything was welded. My gut feeling is that someone out in the field did this and this does not make me very happy. If you found one site like this, pls look for others and make sure that there are no other repairs like this on the airframe.

I could clean off the old brazing as best as possible and give it a try but you very well might end up having to replace that section of tubing. Hope some others will chime in here but brazing should not be anywhere near your airframe tubing in areas like this.

Joe

[james gevay]

Joe, yes this was a field repair as there was evidence of a fabric patch on the bottom of the rudder. I'm sure they didn't want to recover the rudder and just peeled enough of the fabric back to braze the TE on. I checked the rest of the fuselage and there was no other brazing. If I have to I could make a small patch about the size of a 50 cent piece and have that welded on the tail post, and avoid welding directly on the old brazed area and then weld the TE to that.
Some years ago I saw a local plane that had some brazing done on some fittings on the lower longerons. I don't know much about welding but I knew that wasn't right. It's amazing what half baked repairs get done on these kinds of planes over the years. Jim

[joea]

Jim,

I can understand a "jury rig repair" out in the field to get the plane back to a shop and done right but other than that I do not take chances like this.

Good that you found it and can do it right!

Joe

[15A]

Jim,

Get an Oxy-Acetlyne tourch and heat up the old braze area red hot and wire brush the remaining braze off. Brush it AWAY from you while it's still in its molten state. You don't want any left on. The flux that's used to braze wreaks havok with the finish, and shouldn't have been there to begin with. Clean the area and use 4130 welding wire for filler rod. You can get this at a welding supply house in small spools for a mig gun.

Remember, when welding any metals together, you should try to keep everything as clean as possible.

Joe

[Jody Wittmeyer]

Jim, get you a piece of pipe that the 2 outside stringers will fit into. Only has to be @ 4' long. Cap one end and put the stringers in it. Put some water in it. @ a gallon. Use a torch to heat the tube and turn the water into steam. When most of it has steamed out, take the stringers out and put them in place. You can use zip ties or safety wire to keep them in place. They will handle like a wet noodle. When they dry, they will retain their shape and you can secure them in place.

[DELCOM]

What I did and seemed to work great was to refine the fit of the stringer at the forward part of the cabin wood and make all preparation to pemanantly attach, but before I made the permanantl attachment I clamped the stringer in place and proceeded to the next aft position where the stringer lays into the cabin wood. Here again I preped the fit and proceeded on to the next aft connection. By doing it this way when it came time to make the final attachment to the forward most attachment point the stringer was already in place in position 2 and 3,thus minimizing the strss on the freshly glued and pined stringer attach points. I might point out that after the dry clamping of the forward connection and laying the new stringer into the second position I spent a day or so lightly misting the stringer with a bottle of water at the same time pulling it slowly into place with increasingly more taunt bungee cords.
Also if I remember right I placed a small block of wood under the cabin wood cross brace that the stringer is notched into and stood it on top of the steel cross tubing to supply additional suppot to the cabin wood so as not to bow the cabin wood cross brace. When it was all done I then removed the small block of wood.

At least it worked for me..........good luck

Del in Columbia Ca.

[David Johnson]

Guys, please don't use 4130 filler rod. It's way too hard and is usually used when the whole assembly will be heat treated after welding. We tig and like ER70S-2 most of the time. David J.

[15A]

OK, I'll go with that!
I usually like to use similar metals when welding. I also use ER70S-2. And I have used my tig machine with it. But I learned the old school way that the oxy-acetlyne heats a larger area, distributing the heat further out with less chance of cracking. I love the way the tig is so controllable and fine. But this is an area that will go back and forth depending on personal preferance!

[james gevay]

Thanks for all the replies and pictures. Yeah, I kind of thought I would have to use the model airplane technique and make the wood wet, I just needed some confirmation I wasn't going to mess up my stringers. I don't want to have to order and make new 12' stringers.
My second question was if the inner sleeve method is acceptable, is it possible to weld a new section of TE onto the tail post? I know that it's accepted on larger tubing, but is it possible to do on the small TE tubing?
I'm trying to stay away from big bumps or patches that show. Here's a picture that hopefully explaines it better. Thanks, Jim

[David Johnson]

James, AC 43.13 is the best source of information about tubing repairs. It shows the specs for internal splices, length & size information, as well as where and how big to make the rosette welds. I would not want to try this with the torch! But tig will work real good for this. Tubes too small. It will always be cut at a 60 degree angle or fishmouth on a 60. Never straight across. I have repaired the lower tail post with an outer sleeve and fishmouth on the upper side. It does leave a bump. Internal splices are real neat... Remember, Aviat(Pitts) uses tig and last I heard, no post weld heating! David J.

[joea]

Also, you can download a copy of AC43-13 off of the internet. The FAA site has this here as do other sites.

Its a very good resource and APPROVED methods of repair. Its hard to go wrong with AC43.13 unless the manufacturer says otherwise.

[james gevay]

Thanks David, thats what I wanted to know... if it's possible. I was thinking of a torch but TIG sounds better. I'm not a welder so I didn't know what would be the best way to do this. I did buy one of those Smith Airline torches, the small kind but I haven't taught myself to weld yet. I don't think I'll be good enough to do something like this so I'll find someone at the airport to do it. Yes, I have a copy of 43.13 and use it for guidance. Thank you David and Del for helping and posting photos, they are a big help to me. Jim

[Nathan K. Hammond]

The hard part will be the roset welds. With an O/A rig, it will want to spit and splatter from the heat and flow, even with a #1 tip. The other promblem you might run into is undercutting the metal; at least thats what always happens to me. With some practice on scrap you should be able to do it though. TIG would certainly make it a bit easier. Internally sleeved is fine legally, but your IA has the ultimate authority of how it's repaired.

You'll like that Smith, it's a handy tool to have around.

nkh