composite props

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Postby ozzie » Sun Jan 15, 2006 3:59 am

G'day, i had a chance today to grab a carbon fibre prop blade from my neighbour at the strip. short story on this blade is that the (trike) owner fired his ballistic chute off when he became disoriented in poor conditions, unfortunatley he forgot to shut down the engine and damaged all three blades. this was the worst of the three. one was chipped but intact and the second was slashed still intact. the one in the photo obviously took the first hit of the thick cable bridle. the cable had enough damage that if it was any smaller in diameter it would have failed. (no wonder he was quite for a week or so).
So the construction is open for the world to see. this prop was made in Sth Africa. it consistes of two skins of laid up carbon fiber for the top and bottom surfaces. a single laminated foam and carbon fiber spar made up of 3 foam strips about 1/8 thick and 4 layers of carbon fibre. the spar running from root to tip at the centre of the chord. the laminates stand vertical to the chord line . this gives the blade it's stiffness. the root has a molded knob for the hub. the two blade halves encompass the knob. the tip has a recessed metal leading edge.
all parts glued together with epoxy. three photos of this.
a second type of composite that i hoped to photo was the Bolly composite that hit the barbed wire fenc. it was made of machined solid blue foam with a layer of carbon fibre over the top. ala surfboard way. the sth african, for comparison is how you make a surf ski. just for your interewst ozzie
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Postby ozzie » Sun Jan 15, 2006 4:12 am

second veiw
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Postby ozzie » Sun Jan 15, 2006 4:19 am

third.
the spar laminates.
the creamy coloured strip is the dry epoxy glue.
this spar is glued into the knob and also takes the torsional loads to stop the blade from pulling out of the hub/knob.
so thats the secret of why there so lite. 1% c/fbr 1% foam, 3% epoxy glue, 5% metal for the tip, and 90% air. per mass/vol.
no wonder engines run smoother last longer ect ect.
the extra performance may possibly come from the horsepower saving from not having to spin a heavy wooden prop around not to mention the associated gyro forces on the crank ect.
might just duck down to waxheads and get some foam blanks and try to do some better ones for my pioneers.
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Postby flyalaz » Wed Jan 18, 2006 3:41 pm

Hey Ozzie,

Did you get those links I sent you?

Karl
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Postby ozzie » Thu Jan 19, 2006 4:35 pm

karl yes thanks i will go over them on the weekend when i have (hope) some spare time ozzie
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Postby crazyneosimpson » Tue Jan 24, 2006 1:46 am

Ozzie,
Thanks for the look inside the prop, I noted it was the flat surface to part from the cambered leaving the spar behind.
Was there a mechanical reason for this or is there more reinforcement to the cambered surface?
I've made a few props now, but have not had one fail yet to see the result. I'm not bragging, it scares the hell out of me to think what one and a half blades could do, even on a test stand!
I've always been more concerned about reinforcing the underside which deals with the highest tensile forces, it seems this is made the other way.

Is the underside simply bonded as this appears?

This is my latest pattern, 44" and pitch adjustable, by far the smallest I've ever made.
Carl
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Postby ozzie » Tue Jan 24, 2006 2:52 am

G'day Carl.
It seems that when the cable hit the leading edge the bonding let go and the cable just rode under the botttom surface. peeling it off and folding it over at the root. it looks like it took at least three more good wacks before the engine stopped. the cable never tangled around the shaft. but hooked up some near and he came down nose first. looking at how the bonding seperated from the carbon fibre blade, showed no real mehcanical or chemical bonding between the blade and bonding material.
i'd like to find the remains of the bollyprop as it hit a wire fence at full power and even tho it was destroyed seemed to be able to sustain 'battle damage' better and not shatter like the other. the bolly being machine foam solid core. the difference in weight is nothing.
ground adjustable is great way to go just find the parameters and then you can set it for whatever flying you are doing that day. Ozzie
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Postby crazyneosimpson » Tue Jan 24, 2006 3:19 am

Ozzie
My first three props were foam filled leading edge only. The foam work took longer than the rest of the layup.
These lazair props are just too thin for me to be playing with foam, thats why I like the idea of just bonding the pieces together.
I was contemplating laying the spar into the flat side and bonding to the curved shell which is already stronger.
Carl
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