Thorp Air Command - T18.net

OK looking for anything I don't know here (which is a lot). Getting ready to cut and bend up some sheet for my gas tank. BTW this IS the reason I am rebuilding my plane. Went to the hangar one day with the wife for a trip Las Vegas to find gas all over the floor. The fiberglass tank had wore through the saddle and that's all she wrote. So I have the ends for the tank and this was my idea. Make 2 plywood templates to match the ends. Then build studs between the ends (so basically I have a tank frame made of wood. Then bend the sheet around it. I figured I could weld the seam while on the frame holding it together with straps. Then disassemble the frame and pull it out, and weld the sides on. What you think. Anybody with experience in this I would love to here from you.

Our first airplane had a fiberglass fuel tank. My father then tried to make one out of aluminum. In the mid 70's the aluminum welding options were not as good as today. He ended up buying a tank and not worrying about any leaks on the welded seams. Hope this helps. Terry

The only comment I would have is that you need to put at least twice the number of tack welds as you would think. I am presently building fuel & oil tanks for my current (non-Thorp) project. I found the aluminum moves quite a bit when the torch (tig) is put to it. If you have no greater than 4" between tacks it all seems to stay in alignment.

Thanks that's the sort of info I need. Have built aluminum tanks (smaller) in the past and know that to be true. Will be TIG so I hope to keep the heat down a little. I think since I have not received a lot of response I will chronicle the project with pics and dialog for those who follow. Will do the triumphs and mistakes.

The fixture I used was a couple of plywood squares, each with a large cutout, the shape of the cross-section of the tank. Make them both the same. The wrapping sheet for the tank was formed by rolling with various size PVC pipe. Once I got the net shape, the plywood pieces were placed over the metal wrap to hold it around the outside. In fact, the internal parts cut out of the plywood were forced back into place temporarily, so the sheet metal was really trapped. Once the tank wrap was tacked, the plywood centers were removed from inside and the formed tank ends were tacked on and welded. At that point the external plywood formers were removed and the rest of the welding was finished.

Nice thing about the two identical plywood squares is that on a flat work table I could be sure nothing was twisting in the process, and it was easy to flip to different sides in the process. I think I read in Bingelis' books to use only but joints for fuel tanks. Maybe lap joints could trap moisture. I wish I left room for another fitting on top. One is necessary for a vent, but in case you want to add auxillary fuel in the future, another port could be handy for topping off the main. Pressure test the final result with a rubber balloon installed. It will indicate low pressure, pop and release if you over do it. Only 2-3 psi or so is necessary. Use a regulator too. You can really damage the thin vessel or hurt yourself with any more than that.

Hope this helps.

Les Krumel,
Albuquerque

Thanks Les, so glad I posted this as I was (literally) caught thinking inside the box! I like the idea of capture from the out side. Only modification I will make is braces between the 2 frames.

I got my tank from CSA. I am NOT a welder, but the welds seemed a little ruff. I pressure tested the tank with the old balloon trick and it tested OK...however I wanted a little extra insurance once the tank was put in place (hoping not to have to remove it to fix a leak, etc.) soooo I went on the Vans Catalog site a bought a Qt can of their "Flame Master Sealant. It replaces the old Pro Seal. Prior to installing the tank I "painted on" liberal amounts of the goo to all the external seams, fuel cap weld area, vent line weld area and the weld area around fuel outlet bung. Probably not necessary, but sure makes me feel better for $40.00 + shipping. I know someone is going to tell me it only works if you had painted the inside seams !

I also recommend that anyone installing a tank cut and install an access panel over the fuel sending unit. I carefully calibrated mine before I installed the tank (according to the instructions), but after the tank was installed it still required a small adjustment. That would not have been possible without the access cover ! It only takes about an hour to install one and if you have the tank out DO IT NOW ! Once I recalibrated the guage I figger I am with about a gallon on the guage.

RB

Rich,

I had a similar situation with a tank I got from CAS several years back and sent it back on account of what you descrived. The welder Mike used to get the tank welded apparently knows how to weld, but I felt he needed more practice. As quality inspector at General Dynamic and now Lockheed for well over thirty five years, I inspected many welds, accepted some, rejected some. Hell, I even inspected and did final acceptance on the F16 Bob Highly flew in the Air Force. While I can tell you what a good weld should look like, I cannot my self weld worth a plug nickel.

I got a couple of tank ends from my friend Marc Bourget. They had been sitting around for quite some time and developed a few pitted spots and what seemed like corrossion. I cleaned the spots and what seemed like corrossion completely and with the help of a friend at work, welded the spots. I later cut the tank skin from a full size drawing my friend Robert Mardis here in Fort Worth made for me. Took the skin to a metal fabricator shop along with the drawing depicting the radiuses and when I got it back, it was formed perfect. I had my welder friend tack weld the ends to the skin, tack weld vent and fuel transfer fittings, other flanges I wanted on it and filler cap. Prefitted the tank to the fuselage, made some adjustments, took it off and we welded it all complete. Fitted the aluminum vent line, installed fuel sending unit and installed the tank which fitted perfectly.

I asked my friend the welder if he would be willing to weld more tanks if we needed them, and he agreed. I called Mike at CSA and gave him the news and told him I had a certified welder who would weld tanks for him anyway he wanted them. I would not have any monetary gain, but would be glad to serve as liason for the good of the Thorp group and even ship direct, but he wouldn't have it.

_________________
In CowTown USA,
Don D-Day
NX18DD

I really shouldn't butt in, but I will. The welder Mike used for CSA parts is a certified welder. In fact, he worked at Lockheed Skunk Works for over 30 years. Every weld he did for them was X-rayed for inspection purposes. That being a moot point now as CSA has been sold.

Don't know what welder you're refering to, but this was several years back and at the time I made my order, Mike told me the welder he was using was no longer doing it for him anymore and was in the process of finding another one. It was about 1-1/2 year from the time I ordered it ill the time I got it. The welder that put the tank he sent me together, by Mike's admission had only welded two or so tanks for him. I'm datingthis back to sometime around 2003-2005 time span. The welder he had before did do a good job and I can attest to it because actually saw a tank he had in his hangar when I visited with him back in 97 or 98.

I wasn't aware CSA had sold. May I ask who's doing it now?

_________________
In CowTown USA,
Don D-Day
NX18DD

Ah, disregard, then. The current welder is named Wayne. Not sure if I was supposed to fess up that he sold it. Suffice it to say, Mike can still supply some parts. The new owner has not picked everything up yet. He does not live in the US. I honestly do not know his name.

Glad to hear Mike and Frankie are retired ! Although when I "retired" I found I was working harder than when I was working ! Don't suppose the "new owner" of CSA will make it to KVIS this year and give a sales pitch for the business ?

RB

This week John Kerr and I flew up (as a flight of 2) to the old Norton AFB (SBD) and saw Lou and his newly aquired T-18 and his welding/fabricating shop. Hotter than a pistol on the ramp and it took us a .5 to taxi to the FBO ramp ! Remember... SDB was a C-141 base with a 10,000ft x 200ft runway with taxiways to match ! His A/C is well built and will provide many years of enjoyable flying ! He then took us to his welding shop and gave us the grand tour ! He is a very skilled welder and metal fabricator ! I was very impressed with the welds on one of his aluminum A/C fuel tanks ! It had a very nice bead on the seams and bungs ! If I had know Lou before I bought my CSA fuel tank I would have bought one from Lou. I am not bashing Mike and CSA, just stating a consumer preference. Lou has stated/posted he would work with us to fab (weld) most anything we need ( I hope that's right Lou !) I do not know what his prices are ? Maybe Lou could post a few pics of his welded tanks ? Sorry Lou...I went to your web site it does show a welded fuel tank. Sorry Bro !

http://www.dixiefriedfabrication.com/

RB

Jeez... I hope the owner isn't a Canuck. You can't trust those guys.