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Carbon fiber intake runners

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n3480h

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#1
Some of you are aware that I am building an experimental aircraft. The engine is a 2287cc VW aeroconversion which typically uses steel tubing for the intake runners between the carb and the head intake ports. I decided to try my hand at making my own carbon fiber intake runners. The primary goal is to reduce the total weight of the aircraft by about 4 pounds, since lighter aircraft perform much better than the heavy ones. The pics are of a 90° elbow section and a "test" coupler/transition tube. They are much lighter, very stiff, and very glossy. At the very least, they will never rust.:rofl:

Tom

Carbon Elbow.jpg Carbon Transition.jpg

Carbon Elbow.jpg Carbon Transition.jpg
 

12bolts

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#2
Tom,
"make" as in manufactured the carbon fibre tube? I would love to see how you did that

Cheers Phil
 

n3480h

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#3
Tom,
"make" as in manufactured the carbon fibre tube? I would love to see how you did that

Cheers Phil
It's all voodoo and wizardry, Phil. :rofl: Ok, it's not all that. Here's a video showing how to make a straight tube: https://www.youtube.com/watch?v=jwExI_vnchE&feature=youtu.be
It gets a little more difficult for the curved tubes. My forms were the original mandrel bent steel intake tubes, polished, and with several layers of PVA mold release sprayed onto them. The first carbon sleeve was formed over the tube, wet out, and a treated Viton shrink sleeve was shrunk over the assembly. The layup was allowed to cure. The ends were then trimmed and the carbon was slit lengthwise - which allowed removal from the steel tube. The slit in the "skin" was then glued back together with super glue. The skin then becomes the form and additional layers of CF are formed over it. This produces a tube with a slightly larger diameter, but in my case this is ok since my 2287cc VW engine is somewhat beefier than stock. A final coat of resin is applied over the finished and sanded tube to produce the super glossy finish. Since these intake runners will be subjected to atomized fuel, vinylester resin was used for all layups. Vinylester resin has superior resistance to petroleum and heat, and has been proven to work in this application.

See? Nothing to it. This is not the only way to do this, but it's the way that worked for me.

Tom
 

Ebel440

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#4
Very nice I have been thinking of making a plenum type intake for a vw bug but that wouldn't be needed for quite some time as I still need to get the case done and do all the assembly. I have made tubes before by making Styrofoam cores then laminating the sleeve and dissolve the foam out with acetone. It can be an easy way to get complex shapes.
 

6literZ

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#5
Looks amazing!

Composite work is tedious work, as just as much work goes into the plug, the mould and the final part.

When you're at Airventure in your homebuilt everyone will compliment you on the fine work!
 

cjtoombs

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#6
My only worry for your application is the glue joint where you put the runners back together. In the event of a backfire, or under G loading my worry is that that glue joint would fail, leading to a massive vacuum leak that would render the engine inoperative. I would test some glue joints for both lateral loading externally and pressure loading internally. For an automotive application, it wouldn't be that big a deal, but for an aircraft, loosing an engine at the wrong time can be a life ending experience.
 

Ebel440

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#7
I wouldn't really worry about the seam it's only in one layer and covered with more carbon fiber from what I'm reading.
 

n3480h

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#8
That is correct, only the first layer is cut, and that layup is then used as the form for three additional layers which are not cut. However, the concern has some validity in that there could be pinholes in the resin matrix - not likely, but possible - and this is why the tubes are pressure tested before use. With a total of four layers, they are unbelievably strong. As a benchmark, I know of a builder who has successfully flown with fiberglass intakes (not as strong) for many hours with no problems. I used CF because it is much stronger . . . and prettier.

Tom
 

n3480h

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#9
Not sure how to edit in the new format, but this needs to be said: A backfire in flight would be an indicator of poor tuning, excessive component wear or poor adjustment of that component, or inferior parts. All of these conditions are "pilot error" in my opinion, and the aircraft should never have left the hangar.
 
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