Carbon Fibre spreaders for Carbon wing mast?

[Corley]

I've just recently had a wing mast section designed for me by Chris Tucker (thanks Chris) just wondering what the best approach is for bonding spreaders to the wing mast blank I'd assume a composite fittings bonded to the exterior of the mast would be the way to go I was thinking I'd go with the 4mm gaboon ply core that Chris specced for the mast. I'd assume you could use the gaboon as the spreader core material with a similar scantling to the mast. The mast is approximately 9metres tall and designed to suit the kraken 25 I'm restoring. Gary you have a similar mast on your Flash Harry what approach did you take??

[Gary Baigent]

Corley, There are no spreaders on Flash Harry's wing mast. If your chord and thickness ratios are around 450mm x 140mm (same as Harry's), you shouldn't need diamonds. In fact you could get away with 120mm thickness on a 9 m mast ... but less than that would require extra support, just IMO.

[Corley]

Thanks for the reply Gary, when I discussed the need for spreaders with Chris he recommended them, the wingmast section I have is nowhere near as extreme as Flash Harry's being approx 175 x 65. Do you find that you have much deflection with Flash's much thicker section when under load?

[Gary Baigent]

In savage wind with full sail, FH's mast will bend alright - but nothing that ever worries me, I mean, you expect it to.
Yes, your mast is a smaller section, definitely will need diamonds. Maybe paulownia or white cedar core (preferable to gaboon ply, I think) with some layers of uni directional carbon overlaid for the airfoil shaped spreaders; you're going to need a spacer through the mast too .... or if you don't like that idea, you could beef up the spreader/mast base section with some box weave carbon in tapering layers to take the compression loads and spread them around the mast.

[fastwave]

U need to have a bar inside the mast to handle the compression load. Otherwise the mast will collapse. You could also enforce the area by extra laminate in a ring aroung that section, but heavy and ungly. Best way is to cut holes on the side of the mast and slot a continuous spreader through. Bond it with some local reinforment. Downside is that there is not adjustability, unless you use some tricks. Works only with inline spreaders

[Corley]

I assume you would need to add a fair amount of reinforcement around the aperture which is cut in the mast to accept the spreader to take the loading and the interruption of the uniaxial carbon fibre would a tape do? or would a number of layers be required over a larger area to spread the stress?

[fastwave]

You can get away with a reduction near the ends of the panels. If it is bonded in correctly the load also gets transfered through the spreader as well. Also you need to make sure that teh spreader does not start splitting the mast when it tries to move fore aft or up and down. Unidirectional laminated are very bad in that respect. Best to put a few +/-45 layers around the area. Also regarding how much reinforcement you need, that is a tricky question. Not that simple. Masts are one of the most tricky things to design and they come down on a regular basis.

[Gary Baigent]

Fastwave, when I talk of laminating in uni-directional carbon, I mean it to be used not only in one direction, but also in +/-45 degrees, or in whatever angles are required to take or spread the loads. To layup in all one direction in areas where there are multiple direction loads, would be just asking for trouble.