Carbon Shortage

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Dust

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from everything i have read - this is a bad idea, the carbon would take all the load - i would interleave them like aero composites does on their props

temp - for epoxy is important, but solvable. heat workspace during work hours, store epoxy in light bulb heated box, tent layup to heat during cure
 

mstull

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Cold Cure

You can use Jeffco Fast epoxy laminating resin at cool temps. It is available from Aircraft Spruce. Jeffco is amazingly temperature tollerant... nontoxic too. The cloth will wet out slower if the resin, room, cloth, and/or mold is cool, but it will still work. You can warm the part by bringing it in your house after it's all layed up... even days later... to harden it up. As with all epoxys, you should post cure at around 140 degrees for at least 20 minutes. This prevents the part from sagging in the hot sun next summer.
 

Aviatrix

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So Dust,

You are saying that when I shape the cowl out of foam, and start applying layers of fiberglass on top of the foam, with a layer or two of carbon on top the resulting cowl will be weak?
 

Dust

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the carbon is the stiffest material and will take ALL of the loads, the glass will just be there for the ride
 

mstull

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Aviatrix,

I've used different reinforcement materials in the same layup quite successfully, including E and S fiberglass, carbon, and kevlar. A ply of carbon on each side of some fiberglass plys will make the whole layup much stiffer and stronger than using all fiberglass. It is a good way to save money, and still get a layup that's nearly as strong and stiff as all carbon. Using all carbon would come out much lighter. Generally the different reinforcement materials compliment each other by adding their good traits.

For any given reinforcement... strength is proportional to the number of plys... and stiffness is proportional to the square of the thickness. When you bend/stress a layup, the outer plys, on both sides, take almost all the load. The inner plys serve mainly as a spacer between them... like the vertical part in an I beam.

Some amazingly stiff, strong and light structures are made of a ply of fiberglass or carbon on each side of end-grain balsa core. The balsa won't delaminate like styrofoam cores will. I'm using balsa scrimmed with very light fiberglass for the non-structural ribs in my new wing... and balsa with carbon on both sides for the structural ones.
 

Falco Rob

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mstull,

I don't mean to be a smart arse, but if a rib in non structural, why is it there !!

Perhaps I'm missing something in the definition of structural !

Cheers,

Rob
 

mstull

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Good question. Most aircraft ribs, especially in ultralights, are really flimsy, intended just to hold the airfoil shape, and the little bit of lift from the fabric that touches each one. If the aircraft is covered with a shrunk fabric, like Stitts PolyFiber, the tip and root ribs have to be much stronger to withstand the tremendous span-wise pull of the fabric. Those would be structural. If the plane has wing tanks, some of the ribs might have to be strong enough to support them... structural.

My aircraft and wing designs are quite unique. My plane doesn't really have a fusalage. The cockpit, engine, empennage, main gear, and everything else, bolt to the wing. So in addition to the tip and root ribs needing to be strong, some ribs have to support the engine, cockpit, empennage, etc. At high G loads, those forces can be huge. There's also vibration loads for the ones that support the engine, that are surprisingly huge. So I'm using three different kinds of ribs. The tip and root ribs are styrofoam core to get lots of thickness, so they don't bend from the side pull. The other structural ribs have two plys of carbon on each side of 1/4" balsa. You can't break them, bending them over your knee, with all your might. My ribs also get plywood rib caps of 1/32" or 1/16" birch, adding to their strength, and allowing PK screws, instead of rib stitching.
 

Dust

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Originally posted by mstull
Aviatrix,
A ply of carbon on each side of some fiberglass plys will make the whole layup much stiffer and stronger than using all fiberglass.

The balsa won't delaminate like styrofoam cores will. I'm using balsa scrimmed with very light fiberglass for the non-structural ribs in my new wing... and balsa with carbon on both sides for the structural ones.
ok i understand using glass as a core and carbon fiber as a skin.

sorry falco and aviatrix - don't like wood in airplanes. balsa cores can rot and no way to inspect, but the falco IS a work of art and beauty - nice and fast too

on the ribs - they are all structural, but they just don't carry the loads that you envision, if they did, the fabric coverred planes would not be strong enough. the rib is meant to transfer the skin loading to the spar
 
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Aviatrix

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I'm confused.

Foam delamination? Balsa core?


The steps to make the a-plane cowling say to glue a big block of insulation grade foam to the front of the plane,
then carve the foam up in the desired cowl shape, then slap some mold release on the foam,
then start slapping layers of cloth and resin over it.

Once the resin cures pop of the cowling for surface prep for paint, etc.
 

Dust

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Troy, Michigan
no core material for the cowl that i know of - maybe some hard points?

the cores that are being talked about are for ribs and other stuffff.


BTW - leave the cowl on the mold at elevated temps for a week, i mean 90 or so degrees. let cool to room temp and then remove.

it will stay more stable afterward.

no need to post cure a cowl - the engine heat will do it for you later and then freeze it in perfect position
 

Aviatrix

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Ah, okay.

I got a little confused about the core talk, when in my application my "core" was more of a form or mold.

Thankfully I have a heated garage wich during the winter is usually set to 65 degrees.

I shudder to think of the bill I'll have if I do the cowl during winter,
but with my roadmap, chances are the cowl will be one of the final things I do,
so ambient temps will be in the 50-60 degree range so warming up the cowl shouldn't be that hard to do then.

Thanks again for the tips.
 

Dust

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Location
Troy, Michigan
i think ambient should be at least 70 and keep the epoxy heated to about 95 and then turn off heat and use small heater to keep tented parts warm
 
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