Making My Own Carbon Fiber Gear

Here is the result of my second attempt to make my own Carbon FIber Landing Gear. Most of the techniques I used is from Windy Urtnowski's instructional tape on "Making Carbon Fiber Parts".


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More on my web page:
http://www.aeromaniacs.com/Carbongear.htm

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Isn't that pretty. I've made my own also. Cool, huh?

Is really not that pretty, still requires a lot of sanding.
I used wax paper as the peel ply or release film on my first gear.
On the second, I used pack tape as a peel ply. Finish looked better, but not perfect. I will try the non-porous release film with bleeder cloth on top. Maybe even use the vacuum bag method.
How did you get a finish on your gear?

Heman,

When I built my mold, I made a plug from some balsa and glassed it then polished it up. I used a hard mold material (Quik Mold) from Tap Plastics and made a top and bottom piece. When I pulled the plug from the mold (using a lot of wax and mold release), it was quite smooth. Makes for a very nice gear finish. I plan to make a new mold with a different shaped landing gear as this one was made originally for a specific plane.

I will try to make a Silicone mold using a product called POYO. It is a putty, so it will hold up on vertical surface.

Heman,

I use silicon for molding things like cowls and decks and such, but I think you may be happier with a hard mold for a landing gear. It allows you to use some pressure to compress the mold and squeeze out excess epoxy. Much like a prop mold.

Try something like this: http://www.tapplastics.com/shop/product.php?pid=74&

Qwik Cast is pretty easy to work with.

If you put pressure, as with a vacuum bag, on a cloth part in a silicone mold, the pressure will push the weave into the compliant mold, making a bumpy surface. I made six cowls this way, and the guys who finished them were annoyed.

Howard Rush

Howard,

Yea, a vacuum system would work fine. I kinda liked the pressure mold with two hard surfaces. I just used clamps to put it together. Worked pretty well overall.

I plan to make a new mold for the gear for my next PA plane since it will a kinda different gear.

A pressure mold with two hard surfaces is probably better.

Howard Rush

You might try bending a piece of sheet aluminum to use as a mold and then vacuum bagging the part the part to the mold. Use mold release or Teflon film on the aluminum. Using the aluminum as a female mold is more difficult than using it as a male mold, but it puts the nice surface on the upper side of the gear. I make carbon gear, but I use entirely different materials and a different process.

I'll send you some stuff.

Howard Rush

The carbon fibre and resing respond well to increased temperature as the resin will penetrate far better when it is warm. In your language about 90 deg F is good. The team race guys use 14 thou mylar as a backing for the cloth when they laminate the wings, no problems with sticking and a great surface finish.
Regards,
Andrew Heath (aussie F2A)

aluminum mold would be my choice or possibly galvanized steel.
i use both in racecar and modle airplane work.for landing gear i would stack 3(or more) layers of aluminum and bend it up all at once.discard all but the 2 outside and you get a male and female mold for the thickness of the discarded material.
neither needs release agent with polyester resin dont know for epoxy but shouldnt.
pva(poly vinal acohol)is quick and easy to use mold release agent.
light satin finish and water soluble.

be careful with loose carbon thread peices(cut offs ect)
unlike glass the body dosnt break it down and slivers may penatrate and move through/around in your body and damage something.putting tape on cut offs before cutting helps.

Randy,
For various reasons, I HAVE to make my own landing gear on my next plane,(has something to do with the Saito 72). While I have Windy's video showing how to do it, I know your work tends to be first class,(your Saito 56 venturi). So, if you have any pictures on how you make your gear, I would sincerely appreciate checking them out. [photo not recovered: sipcof.gif] P.S. this is me looking at Randy's photos

Milt,

Well, I thought I had some pictures but I can't seem to find them. The shop is a bit thick with dope fumes right now so I want to let it settle in there a bit before going back out or I would take some now.

The process I use is pretty simple. Build the gear out of balsa. Get it shaped the way you want it. Then glass it, sand and polish it up. This is the plug. Build a box out of 1/4 aircraft plywood that the plug will fit into. Cut it in half so that the plug fits right along the cut line (I'll take some pictures later and post them). You have to be sure that you have holes through the box on the top and bottom so that you can pour the mold material in. I used modeling clay for the next part. I put the plug in one half and packed clay around it. Get it packed in so that one half of the plug is exposed. I used a dental tool to smooth the edge. Once that's done, shoot some PVA mold release on the half you just worked on and let it set a bit. It's a good idea to stuff the other half of the box with balsa scraps so that a lot of the volume is filled without actually touching the plug when you put the mold together. Saves a lot on molding material later. Once you have your balsa scraps glued in, fit the mold together and seal up the opening all along the cut line. This is important. You have to make sure that the molding material doesn't leak out the cut line so be SURE you have it sealed all the way around. I use cheap silicon for this. Put a bead all the way around and let it dry. When it is dry, set the box down with the side that has the plug and the clay on the bottom. You did put the holes in the box so you can pour the molding material in, didn't you?

If the plug is packed into the side that will be the "bottom" of the gear (side that faces the ground when the plane is on the gear) then the holes should be right at the top. Three or four of them. If it's the other side, then you'll have to pour the molding material into what is nominally the gear leg. Hope that's clear. When you make the box, be sure you have good sized holes at what is the area off the end of the gear leg. Anyway, I use Tap Plastics Qwik-Cast as a molding material. It's pretty easy to work with, leaves a nice, smooth finish and sets up pretty quickly. Mix the stuff up and pour it into the holes (either those you drilled in the “top” or into the gear leg holes depending on which side you did first). Helps if you use a funnel for this. It's less messy. I usually set the whole thing on a big sheet of wax paper just in case of accidents.

Once the molding material is set up, cut off the silicon and pop the mold apart. Carefully pry the plug out of the clay and fix it into the completed mold side. Wax it up really well, polish and shoot PVA mold release on it. Let it set for a bit then do the same thing the other way. Fill in the voids in the other half of the mold with balsa scraps again and be sure you don't touch the plug. Put the mold back together. Seal it up with silicon again and let it dry. Once the silicon is set, pour molding material into the other half (again, either through the drilled holes or the gear leg holes). The stuff only takes about 20 minutes to set, so there isn't a hole heck of a lot of working time. Once set, clean off the silicon and pull it apart, pry the plug out and polish up your new mold. There is sometimes some clean up. If you didn't get the cut line absolutely straight or is there were irregularity in the clay surface, you may have some clean up, but no big deal. It's not that critical. It's also possible to put in a couple of square chunks of material (scraps, old kingpins you have lying around, whatever) into the clay so that they extend into the other half of the mold giving you a sort of locking system. That way, when you put the mold together, you have a pin and keyway to lock it together, but that's just frills.

When you lay up the gear, wax the mold real well with mold making wax and polish it up. I then spray PVA again. This is probably redundant, but I'm a belt and suspenders man. I use both and take no chances. Then I lay up the gear using CF cloth and tow. Don't over stuff the mold, but get in just a bit more CF in there than you think you really need. It's important to make sure that the stuff is pushed into all the little corners and crannys. I use West Systems epoxy to make landing gears. Once all the CF and epoxy is in there. I put the mold together and use big, sliding “C” clamps the squish it down. Make sure it is tight along the cut line. Then put it aside.

Once it is cured (24-48 hours in moderate temperatures). Pop the mold apart, pull your gear and there you are. Mine come out with a nice, shinny finish. I use a "post cure" oven of sorts. It's really just a Styrofoam cooler with a 75 watt light bulb in it and at thermostat. I set it to 150F and put the gear in (suspended with strings) and turn on the light. I leave it in the for 24 hours, then pull in out and let it cool for an hour or two then put it back in for 24 hours.

So that's it. Hope the explanation is clear. Feel free to ask questions. It's not the only way to do it, but the process works pretty well for me. Haven't had a gear break yet and I've had at least one go into the pavement full bore (don't ask).

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This is not my mold, but it is a fair example. Very similar to what I have with the box removed.

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VERRY NICE WORK Randy!
would you like to make real molds off my prototype racecar molds/plugs?
just kiddin

NICE WORK!

David

Randy,

I was all over the west systems site to see if post curing was something they recommend. I couldn't see where they discussed it or even suggested it. I know that epoxies can typically be post cured but I had just made the 75 gear and couldn't risk the failure if post curing damaged the gear. Ie made it brittle or something.

What are the characteristics of post curing that you see from your efforts? Are the gear more springy, stiff? or what?

Thanks for the tips on the gear mold I may call you to get more details.

Thanks

B

Bruce,
Pro-Set resins by Gougeon Bros. require post cure http://www.prosetepoxy.com/ . It's what I use on my carbon layups. Post-curing resins not formulated for it will do no good and will likely degrade their properties.

Pro-Set resins have very good, but not extreme, mechanical properties. They are easy to work with and readily available. The difference in strength and stiffness between West Systems (also a Gougeon Bros. product) 105/206 (resin/hardener) and Pro-Set 125/229 is very noticeable.

Epon resins, like Howard and Dan Winship use, are the next step up. This is what you want for props.

Derek

Bruce,

On Howard's advice, I called a West Systems rep. He claimed that post curing would aid in mechanical binding and create a piece more resistent to cracking. I have no idea if it makes any difference at all. But the gears seem to hold up well.

As Derek notes, it could be that it does nothing, but I've stuck with it and have seen no adverse effects.

I've use 105 resin and 209 hardner. I recently picked up some 135 resin and 224 hardener that I plan to try. This is the stuff that Derek mentions. Should be interesting.

edit for typo

Heman,

check out the following, I used screw on plates with a formed plastic piece for the top finish. This worked really well and resulted in a usable gear the first time. It reduced the amount of epoxy in the lay up since it was largely squeezed out from the clamping pressure.

http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=253271&mesg_id=253271&listing_type=search

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Today is warm, so I decided to lay-up another gear. This time I add one layer of Kevlar tape.

Also, I am using porous release film (#V275) from Aerospace Composite and bleader cloth on top.

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Heman,

See, there's the problem. You're having too much fun!

Looks good.

UPDATE!

Thanks for all of your input. Here is my newest mold using Silicone Putty. First I made a cradle to hold the putty. This allow me to use a lot less material. Its was not as easy to work with as I thought it would be. The stuff is really sticky and dries way to fast on the first try. So, the my next attempt I put 1/3 less hardener.



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Heman,

that's the idea. I don't use silicon for this sort of thing because I want to be able to squeeze the two mold forms together and put some pressure on parts while it cures. Squeezing a silicon mold just causes deformation.

On the other hand, as long as you don't squeeze it, it should work fine.

When I make cowl molds, I usually make them out of silicon, the when the mold is ready, I pour hard mold material in and make a sort of plug out of the hard molding material. It allows me to lay the carbon fiber into the silicon, then insert the plug. Gives a nice, even CF cowl.

Fun stuff, huh?

Heman,
Sent you a PM.

I built this cradle for the silicone, so that it is no more that 3/8" thick. This allow me to use a lot less silicone and it is more supported.