Bladders, anyone?

[davidfee]

I mentioned this in a thread in High Performance, but figured it deserves its own thread in here.

I've recently begun experimenting with bladders, initially to help press fuselage seams down but, eventually with the intention of doing a kind of "pressure molding" for fuselages. Ultimately, I'm sure I will need a more custom-fitted silicone bladder, but for my first experiments I'm just using a length of carbon tube and a section of polyethylene tube that my porous release film came in. It's not the best, but this was fast and easy... and cheap. The carbon tube goes in the bladder and fills it up with air provided by my airbrush compressor (connected via flexible rubber hose).

Have any of you guys used bladders on fuse molds? Can you provide any pointers?

thanks,
-David

[Ward Hagaman]

I read a thread about someone using a partially inflated balloon and then vacuum bagging the whole mold. Pretty ingeneous. It would be nice to have a cast latex or silicone balloon a little undersize to lay up a carbon sock on and then insert everything into the mold and then bag it.
Have you done any fuses with the bag yet?

[davidfee]

Yes, I've done a couple tests. The first one worked perfectly... the second one not so perfect. On the second, I was testing to see how fast I could make the fuse. That is, could I slap the whole thing together with the epoxy still very soft (usually, I let the halves "gel" before I join them). Anyway, the bladder revealed that I had too much epoxy in the layup and resulted in some "puddles" inside the fuse. Now I know I can make them lighter in the future! ;)

I think the form-fitted silicone bladder is the way to go... latex will usually stick.

-David

[GregG]

It would be neat to get a bladder that would inflate and apply pressure from one end 1st. That way it could help squeegie out any remaining excess epoxy resin. Perhaps a silicon tubing with diminishing wall thickness would work?

[Ward Hagaman]

Makes you think of clown balloons, doesn't it?

[davidfee]

I tried a clown balloon a couple years ago... they are too flexible and they just get longer instead of increasing in diameter. They "escape" rather than applying pressure, in my experience.

Good thought, though!

-David

[GregG]

Perhaps a piece of surgical tubing? You may need more than 10 psi for that though.

[Ward Hagaman]

I think that any pressure bladder would need to be captured all around; I'm picturing a fuse mold with no cutouts, with even the tail boom opening sealed. The clown balloon would be partially inflated and tied off, just fitting into the closed mold. Then the whole mold would then be put in a vacuum bag and then Bingo! 14 psi is seen inside the balloon. The thread I saw used multiple balloons--maybe a bigger one in the front and a more cylinderical one for the boom area.

[davidfee]

Hmm... would require heavy modifications to my existing molds. Further experimentation is required. ;)

[SchiessCo]

You might also consider a section of bicycle inner tube with the ends sealed. Depending on the size of your fuselage, you could use a road bike or mountain bike tube.

[davidfee]

I just worry about natural rubber and latex sticking to the epoxy. Silicone I know will not stick.

-David

[Ward Hagaman]

I heard about a high-tech molded carbon kayak blade that used a balloon and just left it in the molded part--latex balloons are by nature pretty light. :)

[GregG]

How about using a piece of silicone surgical tubing placed inside a piece of silicone that has been cast inside the fuse mold? Sort of an inflatable silicone male plug.

Coat the fuse mold with a thick application of gel coat and allow that to dry thoroughly. After the gelcoat finishes drying fill each fuse half with the liquid silicone. Insert the silicon tubing into the center of the liquid silicone so that it will be floating in the center of your custum bladder when it's cured. Bolt the fuse mold halves together and allow excess liquid silicone to ooze out. Once this drys you could remove your bladder (male plug) and clean the gelcoat from inside the mold.

Just an idea.... :D

[Robert Burson]

Warbirds LTD. has mastered building and using internal bladders. Ron _______ is the gentlemen, but stop production 1 yr ago. His planes were RC combat with Kevlar fuz.

[davidfee]

Thanks for the contact, Robert.

I found a website which goes over the process... looks like what I need to do is make an undersized plug by casting plaster (or something) in my mold, with an offset made by coating the inside of the mold with sheet wax, or something else if I get more creative. The undersized plug is then coated (dipped) with silicone (latex in the case of the website) and then, when cured, the bladder is removed from the plug.
http://www.latextechnology.com/composit.htm

Sounds like a plan. ;)

-David

[dcairns]

I did something similar, but going the opposite way on a large fuselage. I had a hollow "tube": of blue foam that I wanted to vacuum bag the fiberglass onto:
http://www.thecairns.com/pss/HPIM0837.jpg


So I laid up the glass and and put a bag on it. The only trick is getting the bag into the hollow of the tube to prevent collapse of the foam. It worked rather well on a large fuselage. Not sure how easy it would be on smaller projects.

The "outside" bag
http://www.thecairns.com/pss/HPIM1051.jpg

The "inside" bag
http://www.thecairns.com/pss/HPIM1053.jpg

Mylar sheet to keep things smooth, just like on a wing.
http://www.thecairns.com/pss/HPIM1054.jpg

Gave a pretty smooth surface to work with.
http://www.thecairns.com/pss/HPIM1057.jpg

I found it easier to use a wing bag "tube" than the gooped together plastic sheets shown in the pictures above. With the tube, you seal one end, put the fuselage inside, stuff the rest of the bag down inside the fuselage and back out again and then seal the bag. I didn't figure this out till the last time I did the process on this project, :rolleyes: but that is the way you learn stuff :D
http://www.thecairns.com/pss/HPIM1236.jpg

[davidfee]

Thanks dcairns! I bagged a hollow foam fuse once, forgetting about the airspace inside. CRUNCH!! This tip would have saved me!

-David

[davidfee]

More on bladders:

I still haven't made a real bladder, but I did one more experiment with my plastic tube. I did the layup as usual and then used the bladder to press the seams down. It worked great, with no mishaps. However, it appears I still used too much epoxy on the seams. ;)

-David

[Prof. Maneuver]

You might also consider a section of bicycle inner tube with the ends sealed. Depending on the size of your fuselage, you could use a road bike or mountain bike tube.

Sorry I'm a little behind the power curve here. The above will give you the much coveted rubber lined fuselage; handy if you require water proofing, excessive weight and the desire to have all pieces in a crash nicely collected for disposal ;) ;) .

In other words, the rubber sticks real well!

Steve Manganelli