making bombs for fun
 

flying a warbird in a scale like fashion is what makes these models realistic. with diving straffing passes, sweeping low turns and victory rolls is what makes flying a warbird enjoyable. one of my favorite things to do is to drop simulated bombs or fuel tanks. in this thread i thought i would show my effort to develop a large bomb that looks something like a 1000 lb wwII bomb for my meister p-47. the bomb will be molded out of fiberglass and although not exact scale shape or size should look good for the plane. i am going to jump into the middle of my project and show how i made a fiberglass mold. when i first started the plug i just took a piece of foam and cut and sanded to shape covered with a heavy fiberglass cloth. i thought i would just put a layer of body filler on the fiberglass sand smooth and prime but this was such a difficult shape to work with to get right i decided to chuck the plug into a metal lathe apply body filler where needed then machine the filler to shape in the lathe. when finished this turned out rather well. i then primed and put a finish coat of automotive clear coat to hold up to the mold making process.
in the pic i cut out of a thin piece of aluminum the shape of the bomb that fits very close to the plug and centered the plug into the hole.
[img][/img]

RE: making bombs for fun
 

this next pic shows the bottom side of the form. after the plug was waxed it was set into the form halfway and with a hot glue gun the plug was held into place on the bottom for the fiberglassing process. on the top side you will see some green oil based modeling putty applied in the crack to keep any resin from leaking to the bottom.[img][/img]
in the next pic this shows half the mold layed up. i fist used a 1.4 oz cloth with epoxy to make a thin coat without any air bubles. this is a gel coat the finish you will see from the inside. after that i applied 4 layers of heavier cloth for strength.[img][/img]

RE: making bombs for fun
 

after one side was cured the base parting surface was removed, the other side was rewaxed then cloth was layed up as in the first side. the layup for the other side was made with the first side as the parting surface. in the pic this is the finished mold ready to start making bombs.[img][/img]

RE: making bombs for fun
 

mike, donnie here finally got my p-47 build page up check it ou:Dt

RE: making bombs for fun
 

zipnz1,
I have been making bombs by the same molding technique you have posted. I have had a lot of success joining the halves with the following method: I use "Mountains in Minutes", a two part polyurethane foam that is sold to the model railroad guys. After molding the two half shells in fiberglass, I trim them flush with the mold then pop them loose. The shells are then returned to the mold. I mix up some polyurethane and pour some into each half of the mold then clamp the mold halves together.(You need dowel pins to align the molds). I leave a vent hole at the trailing edge of the bomb. The polyurethane will expand and glue the two halves together in perfect alignment. When the cure is finished(just a few minutes) open the mold and remove the assembled bomb. Then I drill a couple 1/4" holes and epoxy in short lengths of wooden dowel as screw anchors for the attaching bracket. I have been making the shells from two or three layers of 1 1/2 ounce cloth. the bombs are light enough that I have not broken one yet. I make the fins out of glass too. I laminate a couple layers of glass cloth and resin between two peices of plate glass then cut fins from the resulting homemade "G-10." The circular fins on British bombs can be made with fibreglass and resin over a mandrel (Broomstick, pipe, bottle, etc)
Chuck

RE: making bombs for fun
 

not bad at all

I saw a yuoung bloke a few years back who made smake eye retarded bombs by spring loading the fins. They were kept retracted by pressing on the bomb pylon till released. He used to do a pass at about 40 ft and drop about 4 of these at once.

Looked very cool, shame no explosion at the end but that is a bit naughty though sure there are some who have tried it!! Not this black duck though.

cheers
PEter

RE: making bombs for fun
 

chuck, i like your idea of filling with foam, but i never knew it would be possible to seam the halves together with the mixture of it. i think i will try it out. as for the fins i hav'nt decided what to make these out of, it has to survive bieng dropped repeatedly. was thinking of a thin plywood, fiberglass laminate, or maybee even a thin flexible sheet foam from a craft store.

mike

RE: making bombs for fun
 

i made my first set of bombs and they worked well but i am going to have to work on the durability factor. my biggest problem is i was not able to locate any of the 2 part polyurethane foam described by chuck. i have since found the materials online but i needed it by last weekend so i tried "great stuff" in a can used for home insulation. this resulted in failed experiment #1. in my first attempt with the foam i just filled the bomb up with the foam and let it sit a day. the back end was hard so i tried dropping the bomb about 2 feet, that resulted in all the foam except the top 2 inches to colapse into a liquid mess in the bottom of the bomb. after cleaning out that mess i tried again spraying 1 inch then letting it harden then repeating over and over till full. here is a couple pics of my first finished bomb. they don't look overly large because of the size of the airplane, but they are about 15 inches long.[img][/img]

RE: making bombs for fun
 

here is the result of a few bomb runs. the last run dropped from a higher altitude pretty much killed one bomb. one thing that worked out rather well was the fins. they were folded out of a thin aluminum and a few bombing runs bent them up a little, but i was able to bend them back into shape rather easily. on my last run i destroyed one bombs fins, but that was my falt. i scribed a line very lightly with a exacto knife and that caused the bends to fail under stress. i plan on molding another pair of bombs laying up an extra layer of cloth on the nose and filling them up with a 2 part urethane foam and then get out for more testing.

mike
[img][/img]