A friend lent me an OA rig so I could learn to weld. Lots of good material in the library and on the NGs. But all that welding is done on a welding bench, at a comfortable height. Apparently one does not have to get near an airframe to get a certificate to weld 4130 with OA.
How does a welder learn how to weld on a built and covered fuselage (say on fabric/steel)? How does he know how much fabric has to be removed to insure his heating doesn't screw up glue adhesion? How does he learn how to protect the nitrate from going up in flames from sparks? How does he learn the tricks to weld all around a splice without standing on his head or laying on his back?
Normally, when there is such a major repair to an airframe that requires welding, it probably needs a recovering anyway. Not always true, of course.
The only way to learn how to weld tubing and in clusters is practice practice practice. There are also jigs that lets you rotate a fuselage so you can get at the cluster in a comfortable position
Just a suggestion, but you might want to take a welding class from a local community college. It'll speed up the learning process, and should save you money in the long run. I know I went through *far* more metal/rods/wire that the class cost me.
I also scrounged some stainless flex-tube and storage rack out of the trash. (I almost got a milling machine, too, but the head of the welding department wanted it sold for scrap instead of letting me haul it out of the trash.)
Cy - the point I was making was the welder is faced not with a bare fuselage on a turning jig, but if he were faced with a covered a/c with engine and landing gear. How does he handle that? - Mike
Practical welding can involve welding in all kinds of awkward positions, like upside down, head first, under a pipe in a ditch and lots of other strange positions depending on what you are doing. You can learn how to weld in a class or at the bench. You learn how to be a welder by applying that knowledge in the field. You learn how to tackle new situations by asking knowledgeable folks, watching them, or using your head, trying something and seeing how it works. As far as welding a fabric covered airframe, you remove nearby flammable materials and/or cover them with fire resistant material, and then have a firewatch standing by with an extingiusher. Heck, plumbers sweat pipes in walls with wood studs all the time. It is pretty much the same concept.
:I also scrounged some stainless flex-tube and storage rack out of the :trash. (I almost got a milling machine, too, but the head of the :welding department wanted it sold for scrap instead of letting me haul :it out of the trash.)
And you didn't immediately tell him that you were paying $.010 for scrap? As a UCI alum, I'm ashamed...
Which community college did you do it at? (I'm just down the block from Santa Ana, and I've been thinking about taking their welding series)
Short of that, are there good book(s) that you could teach yourself?
I seem to recall practicing clusters with short sections, and putting a tire valve in it, and see if your welds will hold pressure. I think I saw that in BengalisIs (sp?) books. Is that a common practice to test the welds?
The second part, IIRC, is tearing it apart, to check penetration and strength of the welds.
Step one is to see if the welds are airtight, because aircraft welds should be, so corrosion (rust) does not eat away the tube, with no visible warning.
Mike I think you're approaching this the wrong way. welding requires some practise, quite some practise, to develop the fluency and quality of weld. like you I was repairing a vintage fuselage. I did all the preparation work myself and then enlisted the services of a certified and experienced aircraft welder. he did a truely stirling job of the welding ...but only after telling me to piss off out of the hangar because my watching him was making him nervous :-)
best decision I made actually was getting that welder in. he bought with him 30 years of practical hands on experience, something that I could have achieved myself of course, but in another 26 years.
focus on finishing a truely quality restoration, not on doing it all yourself. use other peoples expertise as well.
Yup. Finch's "Welder's Handbook". Well written, easy read. Also, just visit your library. Although after trying and if unsatisfied, visit an EAA Chapter.
Part of the tube cluster test after welding involves sawing the tubes cluster along its center line. This alows a visual inspection of the root for each side of the entire joint. From this half cluster you can cut out bend test coupons. Depending on how the bend test fails you can determine if you have adaquate fusion on both sides of the joint; and if preheat may be required.
One method used to extend the life of welded aircraft structures was to pour in a gallon or so of boiled linseed oil after all welding had taken place and the structure passed a leak test. It is a time consuming task involving rolling the structure as it is being tilted to ensure full coverage of the interior of the tubes.
There is a publication out there that goes into great detail of fabricating weldments for the tubular weld test just don't remember the name off hand. I do have one reference I was able to find but it is the tentative code for welding aircraft structures dated 1944.
They proposed the use of a piece of 1/4" x 6" flat bar 6" long. Three tubes would be notched and coped to slide over the flat bar and form a Y type connection with the third tube center on the two tubes forming the Y. After the weld is completed the weldment was cut across the the flat bar around the 2 1/2" mark exposing the ends of the tubes; allowing inspection of the interior .
I had posted a pdf file many years back to a web site I forget the name of but it was titled welding tubular structures or something along those lines. It may still be out there.
So there I was trying to finish up welding on the last engine mount flange to my Delta's fuselage. By the time you get to the engine mount flange, the Delta has grown to a considerable size and I had it up on sawhorses. All the tubes coming back from the firewall to form a closed box. The only way to get inside the box in through a lot of longerons and diagonals.
Well, I had managed to get my head wedge up between a couple of the bottom diagonals. My right hand snaked the torch around the longerons, and my left hand wrapped around the front bottom crossbrace to bring in the filler rod. The metal was hot and flowing and the bead was running smooth. Then my filler rod got short. Not the whole rod, just the part on the weld side of my hand. It had taken several minutes to get wedged into this position, and I didn't want to kill the weld bead just to feed more filler rod. Thinking quickly, I grabbed the back end of the rod in my mouth, pulled my hand up further and continued the weld. "Smart", I thought to myself, as the bead rolled on.
Most of you have already guessed what happened.
Melt. Fill. Melt. Fill. Advance. All in a steady staccato beat. More a habit than thought. And then, as I reached the end of the filler rod, for some indiscernable reason, I decided that I could slide my hand all the way to the rear of the rod if I grabbed the other end in my mouth.
I'm not sure if the burn mark is still discernible across my tongue, but I do know that there isn't much worse that having your head caught in your airplane when you need to scream.
Later, I learned the proper way to advance your filler rod without the aid of gravity is to dip it in the weld pool and let the pool cool just slightly. It'll solidify just enough to allow you to slide your hand back. Bring the heat right back in and keep going.
the other trick of the trade is to put a quarter inch kink in the cold end so that you can immediately see which end is cold on the bench. brother in law welder told me that one after the second bandage appeared on the left hand one day. they dont hurt immediately but by god they do hurt a moment later.
a weld lump that goes down your shirt and ends up in your socks gets exciting as well :-) Stealth Pilot
Almost like my one experience. I had a piece of slag go between by jeans waistband and my tucked in shirt.
I am pretty sure the shirt burned through very quickly, without a significant temperature loss to the lima bean sized piece of red hot metal. My skin did start to cool it, and I decided that this was a *bad thing.*
Even though I was standing out in my back yard, in full view of neighbors, I very quickly unbuckled my pants and dropped them. Modesty was not high on my list of concerns, at that moment. Only then was I able to release my lima bean piece of pain, to continue it's journey to terra firma.
I still proudly wear my momento of that day. My lesson of the day, is to weld or cut with your shirt hanging out, or wear a leather apron. At least most of the stuff will be shed like water.
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