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AX-O 02-24-2020 12:20 AM

3D printed parts and molds: A how to guide (of my experiment)
This thread is to document a project that I have been making and maybe show other folks what they can also do. I wanted to challenge myself and learn new skills.

Please lets not go into the there is no alternate air source or not enough media to filter on the air or world is going to end because there is a carbon fiber parts in the vicinity of an aluminum aircraft. This is a project to learn new skills, fail and build.

I chose to make an air filter enclosure. The reason was because the room in the cowl is restricted to the mold line, the shape would require contours, it would force me to find a way to mount the enclosure and nicely bring that air into the fuel servo. It would also force me to learn how to use technology that i don't use.

My previous version was made out of fiber glass and was made off a wooden mold that belongs to Dave Anders. Looks like this.

After lots of research, gouge aero rules from college and some personal experience.. I came up with this. Not completely optimal but within the constraints mentioned above.

I then used a 3D printer using PLA to print a mold. The printer bed was not big enough so I had to print it in 2 pieces then join them together. I used 5 minute epoxy for that job. Each piece took approx 11 hours to print. Raw printed parts below.

I then sanded the mold with different grids of sanding paper to get rid off the ridges left by the 3D printer. And since I am vacuuming the parts, I filled the inside of the mold with pour foam.

And mounted it on a piece of wood so I could get a nice edge for joining parts later and also facilitate the vacuuming process. The plan was to pull 2 halves off the same mold then joining them using the flange. Then a strip of carbon fiber inside the part, cut the flange off, and 2 layers of carbon outside the seam.

AX-O 02-24-2020 12:21 AM

Part 2

The next phase was to plan out the work. This is similar to painting. The better work you do on the front side, the better the part ends up at the end.
I cut the carbon fiber are required to cover the mold. This particular carbon fiber is the left over stuff from my Formula One race plane. Side note: This type of fiber is Bid. But not the standard Bid. It was discovered by Paulo Iscold while building one of his race planes. A boat manufacturer had excess material and they needed to get rid of it. They made Paulo an offer that he could not refuse. The nice thing about it is that the fibers are not interweaved, they are laid on top of each other then stitched. So you can cut it and pick it up as you desired and it does not lose its shape. Paulo passed the gouge to Craig Catto and the fabric is now used on all his props. And now on to an experiment for an air filter ?box?.

Once the carbon fiber and supporting material was cut, I waxed the mold 5 times and polished the wax off.

AX-O 02-24-2020 12:22 AM

Part 3

Used West system epoxy mixed 5 to 1 with slow hardener.

Items laid on the mold were:
-3 layers of carbon fiber with multiple overlaps on the nose to make that stronger for a clamp.
-1 layer of peel-ply
-1 layer of perforated plastic
-1 layer of cotton

That was placed inside a hand made bag (plastic and tape, that was another trick I learned at Catto's place).

A vacuum was placed on the bag via a pump, approx 25 inHg. That entire assembly was placed under a moving blanket and a small portable heater was placed inside. That kept the temps inside at 118 deg during the curing process despite an OAT of 55 deg.

Little dots you see is the resin coming through the perforated plastic.

Once the part was cured, the struggle began. I had to pull the part off the mold. I started at 7 am because I was so excited. Did not even brew coffee. I quickly woke up by stabbing my index finger simultaneously by 4 carbon fiber needles. It shredded my finger pretty good. Had to put the work away for a few minutes and go into the garage so I could cry and not wake up my wife.

I reattacked the issue and was able to succeed at some point. The lessons learned from that were used on the second part and that one came off in a few minutes. Pics of the unfinished parts bellow. They are perfectly smooth inside. The is one small seam from were the 2 parts of plastic were glued but the seam is wax. so no issues to get that off. The outside waviness is due to the stitching of the carbon fiber. also some time the bagging process wrinkles the outside of the parts if you don't take extra care.

I am out of pics and work done thus far. I will finish this project at some point. Trying to finish up my engine installation. I also have to make a part on the fuel servo side.

DaveO 02-24-2020 06:27 AM

The pictures of your work did not come through for me.

Janekom 02-24-2020 01:17 PM

Really nice job so far. Please continue sharing

Gash 02-24-2020 02:21 PM

Looks like this will work really well, especially as you approach trans sonic airspeeds! :D Reminds me of the SR-71 shock cone.

sblack 02-24-2020 06:11 PM

Axel what is the reason for having the center cone making the inlet annular? I have noticed a similar center part on stock supercub intakes and always wondered why it was there.

N269SD 02-24-2020 08:37 PM

I'll bet that carbon takes a lot of resin

AX-O 02-24-2020 09:46 PM


Originally Posted by sblack (Post 1410156)
Axel what is the reason for having the center cone making the inlet annular? I have noticed a similar center part on stock supercub intakes and always wondered why it was there.

In simple terms; In subsonic flow, the shape reduces drag (drag coefficient) and ends up aligning the flow better than just a blunt object. Different reason for supersonic flow.


Originally Posted by N269SD (Post 1410186)
I'll bet that carbon takes a lot of resin

It sure does! :D Thanks for the help with the wing and tail Goose.

sblack 02-25-2020 10:37 AM

ah ok and I didn't realize from your dwg that the cone is actually the filter element! The picture tells the story.

Regarding stabbing with cured CF - I fell your pain. I redid all the empennage fairings on my 4 in CF. I had numerous punctures. It hurts! :mad:

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