vacuum bag composites

Well, looks like I'm not going pre-preg so thought I'd start a different thread for just composites in general.

For my first try I am going to try to make a 1 inch (od) carbon fibre tube that will serve as a embedded spar (front and rear) in my first try at my HS. Am going to try to use 2 pieces of 2 inch thick 2 lb pqf blue extruded styrofoam. One slab will be upper half and the other slab will be the lower half and I will attempt to "route" out channels in both halves for the spars and other "frame" parts plus the short flexabile tubes that will house the Push-Pull cables for my twin rudders. This will then be glued together and hot wired to shape and covered with maybe two layer of carbon fibre BID.

Construction of the rudders is still in the "thinking" stage. If anyone has tried this before and run into a lot of trouble, would appreciate some critique and advice before I try to invent the wheel again.

Tony

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Well I will start chapter 1 paragraph experiment 1. Had heard that a old refrigerator compressor (the sealed unit type ) could be made into a good "vacuum source" SOooooo
I hunted around town intil I found a dealer in used appliances and sure enough he had a bunch of junk appliances out back behind the shop, washing machines, airconditioners dryers and ----REFRIGERATORS!!!

Now I got there about 15 minutes before closing so he made me a deal, normally he must connect a "refigerant recovery machine" to the unit and bleed off the gas, but since it was so close to closing he said $10 bucks and load in the my pickup and take it away, probably could have got one for nothing if I had waited long enough but I wanted to experiment NOW.

About 30 minutes later back at the hangar I now have a nice QUIET VACUUM pump. For my $10 and about 30 minutes of work I got a comprsssor, mounts, starter capacitor and power cord with plug. A little additional work with the extra tubes and I will have a nice neat vacuum system. Will now progress to making the resin trap for the intake line so you don't get resin in the compressor and I will have saved a BUNDLE.

Tony

Great thread Tony!!!!

Way to scrounge and save money.

I've help build two sailboats using vacuum bagging and none of them leaked I've help build one without vacuum bagging and the port bow leaked into the interior foam.

It was just a pinhole took a year or more to fill up and you could not see it from the exterior with aircraft we don't have that concern.

Hi John

I find that I am frequently thinking "outside the box" simply because I CAN'T FIND THE BOX !!

Tony

Welllll, I know I like the way you think and look forward to following your build.

This vacumm compressor is a great deal ONLY if it ends up working but supposedly it has been tried and proven

Tony

Yep, that what my friends, used then and my Nephew is using not to build RC sailplanes.

They work very well with the weight of the atmosphere pressing down it could crush 55 gal drum if you hook it up to it.

"Crush a 55 gallon drum" !! wow will try to be careful, as stated in earlier post my first attempt at vacuum bagging will be making a carbonfibre tube for a spar, will try to do this on either a 3/4 inch steel tube mandrel or a 7/8 inch steel tube mandrel . My biggest concern at the moment is getting the steel tube out after I have done the bagging and curing. My present idea is to wrap the steel tube in about 2 or 3 layers of Saran wrap and hope that after it is done I can twist the steel tube and shred the Saran wrap and pull the tube out. Anyone got some other suggestions ????

Tony

While talking about low cost, the students at the University of BC cut large diameter holes in the side walls of 4 used clothes dryer and joined them in a long row with large diameter sheet metal tubes between. They then use it (them) to cure the composite wings.

They probably also removed the drums from the dryers.





Dave

Now that is flat a$$ brililant , talk about thinking outside the box !!!

Tony

Never thought about using old clothes dryers as a control source of heat for curing, but would sure work, would be great for smaller pre-preg parts !!

Tony

Tony there is relief agent made for each resin you spray on and or special material.
I saw them making light-polls out of carbon fiber.
They used a relief agent and they used threads of carbon fiber not woven fabric.
They had a bobbin stand with 10+ or more spools of thread on them it look like a giant lathe the threads were all run through a plate with holes that then when under a metal rod that was under the resin. It was dipped twice by running it up over another rod and back under another rod under the surface of another pool of resin and the the thread came together through one hole in a plate and warped around the mandrel putting extra wraps around the base for more strength and the look they wanted.
They did not vacuum bag it they simply kept the mandrel turning for 12 hours so no drips could form and it was perfectly round.

They would pull it off the mandrel with a machine that would could down from the roof. It was a motor with to small tires on each side of an electric motor. The tires were at an angle so they would eventually pinch the tubing and an shoot it off the poll about five feet and then humans could just pull it off.

The most interesting thing was these polls were straight and the would shoot steam through them and heat them up then put a curved press and champ them into shape pass cold water and it would set that shape for life.

HI John

Yes I saw a fiberglass sewer pipe being made almost exactly the same way except the had some kind of collapseable mandrel but esed the same multi bobbin wraping you described . The reason i don't think I can use a spray on release agen it that even the "mandrel drawn tubing is a "little out of round and if you vacuum bag this composite it will fit like a skin and you need to be able to rotate the mandrel to "tear it loose", hence the need for something that can be sheared and have enought clearance to pull out the mandrel .

Tony

Unless a solid mandrel is tapered or you use a collapsible one, you can pretty much forget about removing it. It can be done with a dissolvable mandrel.

Or you can layup ½ of the tube on each half of the airfoil….shaped kinda like an omega….with its >=1" wide flanges ply-thickness inlayed into the foam. This would be done just before the airfoil halves are bonded together…..which will also bond the two tube flanges together….you see….

Do some research on the Gossamer Condor and Albatross, man powered aircraft. They used carbon fiber spars, the first ones being made by laying up the carbon over an aluminum tube, curing, then burning the aluminum tube out by placing the spar in a pvc pipe filled with acid. Later spars were fabricated in some way that allowed the aluminum tube to be removed mechanically.

.

As Alan said...aluminum eaten away by acid....foam eaten by acetone, paper or cardboard tube softened with water….anything that won't hurt the composite. This may be the way to go for the lightest tubes….

RotoPlane said:

As Alan said...aluminum eaten away by acid....foam eaten by acetone...........................................

Click to expand...

A friend fabricated some strut fairings out of fiberglass laid over blue, hot wired foam cores and once the resin cured the plan was to melt the foam out with gasoline. Holy Melted Mess Batman, blue foam when dissolved turns into blue liquid s**t that is near impossible to get out, in fact the fairings were scraped. Hotwire the foam out in some way.

.

Maybe, you can cut and fit one of these items
http://dragonplate.com/ecart/categories.asp?cID=19

1) They sprayed the mandrel with something before they wrapped it.
2) I didn't notice if the mandrels were tapered however, I did not ask and I did not know to look for that.
3) I wonder how they got it off the mandrel so easily? It literally pop off when the tires hit it!

@Tony
How did they get the pipe you saw off. Sewer pipe could not be tapered?

Another way I've seen with mold removal is the mold or mandrel is sprayed with mold release as John said and after curing air or water is pumped through holes in the mold….you can hear the part snapping as it releases.

A friend tried to dissolve Styrofoam with gasoline….it melts the foam more than it dissolves it….acetone almost makes it disappear, but where possible, remove all foam you can before using the acetone.

I would go with the pultruded tubing that Mark linked, especially with the smaller diameter tubes. If this HS is in one piece, I wonder if one even needs a tube spar…plus it is hard to attach the spar to the airfoil skin and it tends to be heavy. If needed for strength, spar-caps are easy to make, strong and light…