Making Fiberglas Tanks

First off, of course, is the fiberglas cloth. ... resin and hardener you will need to lay up the glass cloth .... mix some resin and fill the lightening holes until there is a ...
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Making Fiberglas Tanks By Col. Marion D. Unruh, EAA 122 Pretty Prairie, Kans.

N problem for the homebuilder. In order to get as much capacity as possible, you come up with an odd shape and

O DOUBT about it, gasoline and oil tanks are a real

this means seams and joints. Even a good welder has his problems with buckling and warping on a job like that. So you start thinking of fiberglas. You find someone that

has used it and after talking to him for 30 minutes it sounds real practical—also simple and easy. Well—it is, and it isn't! Two weeks and $15 after my first go at it, I learned a few things that I think might save the uninitiated some time and money—both of which are hard to come by for the average homebuilder.

In case you have never worked with fiberglas, you can waste a lot of time and materials learning how to handle the stuff. It is really not too difficult if you have a few items of equipment ready and at least an idea of

how to proceed. First off, of course, is the fiberglas cloth. It comes in coarse and fine weave, treated and untreated. A cloth with 18 to 20 threads per inch, about .013 to .015 thick and

chrome complex or VOLAN A-C treated is ideal. Polyester Resin, a hardener, and the fiberglas materials are complete. Your dealer can approximate the amount of resin and hardener you will need to lay up the glass cloth you buy from him. You will need enough cloth to cover your mold at least three times and allow a little extra for seams and patches. When applying sheet strips over

the edges, you will be mixing up batches of about tablespoon size. To insure uniform mixes of the resin, get a hypodermic syringe for measuring. Experiment until you

get a mix of proportions of resdn and hardener that sets up and cures properly. Graduate these proportions on a Dixie cup so you can mix from a tablespoon full to a nearly full Dixie cup. (Unless you have help, a cupful is

about all one person can apply before it hardens). Two or three dozen Dixie cups for hot drinks are needed because you can only use them once. The hot drink cups are necessary because the mixed resin generates heat. Two \Vz in. to 2 in. cheap paint brushes are also needed. You

need two because you will be using one and will have one drying after washing in acetone. Styrofoam, one inch thick will do, enough to make the mold, and Elmer's glue to glue the mold together. A gallon of acetone to wash brushes and your hands, a small can of Johnson's

paste floor wax, and a good supply of clean rags (believe me—you will NEVER have enough rags) are all necessities. The above materials are about all you will need to

make a tank, with the exception of the inlets and outlets. There are a number of materials for use in making

the metal inlet and outlet fixtures. Aluminum is, of course, ideal for it is light and relatively corrosion resistant — but requires more skill than steel to weld. Brass can also

be used, but a fixture made from brass will weigh about the same as steel. I used .049 steel sheet and .049 x 3A in. steel tubing for the oil tank. The filler neck and cap came from an automobile gas tank. Be sure to get a non-vent type. For the oil tank drain, I used .250 dural, drilled a % in. hole and threaded it with pipe threads for the drain plug. The drain plug fitting is about 3 in. in diameter, with the edge tapered to about 1/16 in. thickness from the edge of the drain hole. Typical dimensions for one of the fittings are: Flange (from .049 sheet steel) 2% in. dia., % in. outlet

hole, Vz in. lightening hole. Weld a V& in. band around the end of the tubing to help prevent the hose from slipping off. See drawing. Cadmium plate the fitting to prevent corrosion. (Continued on page 6)

i= Left—Typical oil tank fitting. Material 4130 steel .049 thick. Right—Oil tank drain fitting. Material .250 Dural. SPORT AVIATION

5

MAKING FIBERGLAS TANKS . . . (Continued from page 5) . . . . . . . .

The next step is to make a mold to support the fiberglas during initial stages of fabrication. I used styrofoam.

While visiting with Tony Spezio, he said he used corrugated cardboard. Just remember that the mold has to be

strong enough to support the fiberglas yet fragile enough so you can tear it out. There are other methods for doing the job. For example, Bill Leighnor used a plaster mold and made the cloth lay-up over it. After the first two layers, he cut the top or "lid" off, removed the mold and replaced the top. By using this method, he was able to insert an aluminum baffle. First of all make the mold Vs in. less than the dimensions of the finished tank. The average thickness of the tank will be about half that, but corners and edges will have two or three extra layers of glass — and this adds up to nearly double the average thickness. A standard table circular saw with a finish cut blade will do a wonderful job of cutting the styrofoam. For curved pieces use a standard wood cutting band saw. To prevent the two pieces from slipping while glue is setting up, just

stick some long TEE pins (or any pin that is long enough) into the joint to hold the pieces in place. Not much pressure is required on the joint, bucking bars are about the

right weight to lay on top of a glued joint. Even bricks come in handy. Building up the mold takes a little time since usually only one side or end at a time can be glued in place. Set up time for the glue is about two hours— depending on temperature and humidity. Remember that

all the mold has to do is support the fiberglas so one inch thick styrofoam is fine. When the joints of the mold have set up enough so there is no danger of their coming apart, pull all the pins and sand all corners and edges so that they have at least a Vi in. radius. From here on (after the styrofoam mold is completed) there are several methods of laying up the fiberglas over the mold. Sealing the mold with wax or some other material to protect it from the resin or using a resin that will not attack the styrofoam seem to be the accepted way to proceed. I tried this without too much success. I'm not saying this won't work for I've seen tanks made this way. The following method was most satisfactory for me. To begin with, I made a single layer of fiberglas on some dural sheet. To make up a sheet of fiberglas, wax the dural sheet with Johnson's paste floor wax for a releasing agent. After removing the fiberglas sheet be sure to sand off the wax. From this sheet cut out the top, bottom, sides, and ends of the tank. The bottom and one side were held in place on the mold with pins around the edges. Then a strip of fiberglas cloth about two inches wide and as long as the edge was laid over it and resin applied. After the fiberglas had set up, the other side of fiberglas sheet was pinned in place and so on with the ends and top until the mold was completely covered. This method eliminates the use of compound curves, but single curvature shapes are no problem. After the fiberglas dries, sand it until it is smooth. This completes the first layer of fiberglas. You are now about ready to glue the fixtures to the tank. Mark where the inlet and outlet fixture holes will be on the tank and cut them out. A sharp pen knife will do the job. There are a number of Epoxy adhesives to use in gluing metal to plastics. The Borden Company's

Elmer's Epoxy Glue is what I used—and it is still hold-

ing. Be sure both the fiberglas and the fixture are clean and free from wax or dirt! To prevent the adhesive from

getting into the fixture openings, plug them with wood plugs thoroughly waxed. After the Epoxy glue has set, mix some resin and fill the lightening holes until there 6

MAY

is a flat surface across the fixture. Also, add resin around the outside edge of the fixture. After the resin sets, smooth it with a file and sand paper. If you do this before

applying the fiberglas patch, you practically eliminate

the possibility of a void. Now cut patches large enough to cover and extend y2 in. to 2 in. over the fixture. Whenever you apply a layer of fiberglas, voids are always possible. There seems to be no satisfactory way to prevent them or to eliminate them after they develop. However, they should be eliminated before applying the next layer of cloth. One method is to cut them out with a knife or file and then fill them with a mixture of resin and shredded fiberglas cloth. Sand the tank smooth and you are ready to apply the second overall layer of cloth or mat, I used mat for a second layer and found

it worked and laid in place far easier than cloth. There seems to be a difference of opinion as to the strength of

mat versus cloth. My only answer is that the tank with a

layer of mat is doing the job. After the second overall layer the tank is strong enough to support itself without the mold. Cut a hole about 6 in. in diameter in the end or side (or any place you can get your hand in) and dig out the styrofoam. Sand the inside edges of the seams smooth, inspect the interior of the tank to be sure it is clean. Cut a cover for the hole from the fiberglas sheet. It should overlap about y2 in. Apply it to the hole with resin. Smooth the edges by sand-

ing and apply a fiberglas cloth patch that overlaps the hole patch by about two inches. Again sand the tank smooth and apply the last overall layer of fiberglas cloth. Sand the last layer, remove the waxed plugs and test the tanks for leaks. You can test for leaks by plugging the openings with wood plugs and wrapping the plugs with electrician's plastic tape. In one of the plugs drill a hole the size of a welding torch tip prior to inserting it in the fixture opening. After all the openings are plugged, screw the tip into the torch and slowly open the oxygen regulator to 3 Ibs. Immerse the tank in water to locate any possible leaks—if there are no leaks, you have it made! With a little thinking and planning, integral tanks in plywood (or fiberglas) covered wings should be no problem. I honestly believe fiberglas has many applications for the homebuilder that have either not been explored or if so, the findings have not been reported. The above is only one.

THREE "FLYING FLEAS" . . .

NX18266, 71 hp Rover engine, completed Palwaukee, III. airport, Dec., 1937. NX18240, powered with one of the

first Continental 50 hp engines, June, 1938, Palwaukee. NX18218, 40 hp Continental, now rebuilt as M.E.2Y, X43993, originally built at the old Curtiss Airport at

Glenview, III., now the center of the Great Lakes Naval

Air Station. For further information write Frank Easton,

EAA 4392, R. 2, Salem, Ohio,