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Foam core composite propeller fabrication

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cheeka

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Has anyone tried to make a composite propeller with a closed cell foam core? Any idea how the hubs are made in conventional composite propellers?
 

Dana

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Powerfin is carbon fiber over a foam core. Fragile though; I saw a Kolb crash when the Powerfin prop exploded (due to previous gravel damage) on takeoff.

Dana
 

cblink.007

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Has anyone tried to make a composite propeller with a closed cell foam core? Any idea how the hubs are made in conventional composite propellers?
No direct experience with anybody who has self-made a composite prop. The prop is, in my opinion, one of the most critical components on an aircraft and has to endure an obscene amount of abuse, so I leave that stuff to the professionals! Now, all that being said, it would be a neat project to try one out!
 

kent Ashton

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Has anyone tried to make a composite propeller with a closed cell foam core? Any idea how the hubs are made in conventional composite propellers?
Here's a discussion. No indication this fellow actually built one but his idea sounded good. The site has changed but it's in the Wayback machine
https://web.archive.org/web/20160312124730/http://www.icon.fi/~jtki/prop.html

Then this fellow made a rather bulletproof prop, good write-up here. His tips are too wide, however. :)
https://web.archive.org/web/20150122113000/http://www.knology.net/~rv7rotary/making a prop.htm

In my experience, most "composite" props are made on a wood core with glass covering because wood is easy to shape and you don't have the extra work of mold-making and reinforcing the hub for the clamping forces.
 

TFF

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The GA props tend to be wood core covered. Probably for the hub attachment ease. The big composite props i have been around have a foam cores but they are dense. I believe they must have mold halves and partial cure them, lock them together and fill with the foam. At what point they cure the whole thing is a guess, but the foam might have heat cure too. Its closer to a hard plastic. Hub attachment inserts would need to be planned out in the construction phase.
 

BBerson

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Balsa probably easier than thin foam to carve.

The Turvamaki method was interesting. Slip some balsa into the center of the mold if solid fiberglass isn't desired.
 

Hephaestus

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Carving isn't much of an issue... CNC Hotwire or typical CNC router will do it if you're good on aligning the flip (4th axis gives some nice options though).
 

autoreply

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The GA props tend to be wood core covered. Probably for the hub attachment ease. The big composite props i have been around have a foam cores but they are dense. I believe they must have mold halves and partial cure them, lock them together and fill with the foam. At what point they cure the whole thing is a guess, but the foam might have heat cure too. Its closer to a hard plastic. Hub attachment inserts would need to be planned out in the construction phase.
Might be an idea to machine it in two parts.

Make an undersized foam core and laminate appropriate crush plate and carbon over it, but keep the entire prop say 1 mm under-sized. Laminate a thin core over it, something like Soric or so, say about 2 mm thick. Balance it and put it on a 4 or 5 axis cnc machine and machine the entire outside surface .2 mm undersized. Then add one final layer of carbon, vacuum under tight foil, paint and sand?
 
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Jan Carlsson

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Jukka Tervamäki built several props that way, for his motorglider, what was to become the PIK 20 motorglider prototype he built
 
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