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Composite Spars

Composite Spars

Composite Spars

I'm constructing some 40ft carbon fiber spars 3in Outer dia. The only autoclave I have access to is 8ft so if I want to use prepreg I need to do it in smaller sections. I'm worried how this would affect load however, so am looking into wet-layup.

Does anyone have tips on how to wet lay-up a carbon-fiber tube this long? My main concern is finding a mandrel and how to suspend it without bending.

Thanks- Dan

RE: Composite Spars

Bending is less of an issue if you work the piece with its axis vertical.

That in turn presents a real estate problem, but all you really need is a decent sized atrium....

Mike Halloran
Pembroke Pines, FL, USA

RE: Composite Spars

Assuming you don't want to deal with vertical wet layup, another alternative is to put the horizontal mandrel under tension. Note that you can't eliminate deflection from gravity this way, you can just reduce it.

Or, work with it; you could pre-camber the mandrel to sag to absolutely straight when the resin kicks, but that requires a good estimate of the weight of everything, including the mandrel. ... so your second spar can be straight.

Mike Halloran
Pembroke Pines, FL, USA

RE: Composite Spars


Since the spar has a small diameter, why don't you construct an oven from something like a steel pipe just big enough to fit the spar & mandrel into? There are many excellent out-of-autoclave pre-pregs available which can be cured/post-cured with just an oven cycle.

And if you want compaction pressures beyond what vacuum bagging will provide in an ambient pressure oven, there are adhesive tapes that can be wrapped around your mandrel-tooled layup which shrink when heated and will provide substantial compaction pressure.


Hope that helps.

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