Hi Rob,

Just wanted to ask about unstayed masts and possible ways of reducing the cost and complexity to build.

As far as i can tell, we use carbon for these masts mostly due to the high modulus, rather than the high strength. This is so that we can avoid an excessively flexible mast whilst keeping the diameter as small as possible. Sure carbon is lighter too, but i believe its the defelection which is driving the design and so is directly related to the "E" and "I" - "material modulus of elasticity" and "area moment of inertia" respectively.

So i had a think about things, and the biggest drama related to infusing these heavy carbon UD laminates... the rest of it seems pretty straight forward. Also the cost of so much carbon is pretty high. So then i thought, why not make the bottom of the masts from UD glass, of thicker wall and transition the laminate around a carbon C-spar somewhere above deck level so we can maintain the stiffness higher up on the mast - where the quantity of carbon is much less anyway. With the largest loads at the deck bearing, the really heavy carbon laminates down there add up to most of the carbon in the mast - whereas the flexibility problem relates to the entire length.

 So ive been reading some stuff from the aircraft homebuilders and seen what they are upto. They are onto this pultruded carbon rod which they use for the spar caps. They mostly use glass for the shear webs in their wing spars. This pultruded carbon rod is almost TWICE the strength of standard UD carbon laminate,  its 1900Mpa minimum in compression,2100Mpa tension - so we only need half as much to do the same work. As it comes in rectangular rods/bars on a long large coil or spool, you simply roll it off the spool and cut the lengths you need, and glue the rods together with neat epoxy.... presto you have a spar cap of super strength. Seems a very simple task to wet lay or vacuum bag a tapered C-spar using this stuff - the aircraft guys are doing it everywhere...

So then take the C-spar of carbon, and put it inside a glass skin mast to stiffen it. Very minimal use of carbon, and only a tad heavier than an all carbon mast. All glass laminate is easy to infuse, bond the c-spar in as you build the rest of the wing in 2 halves.

Just wanted to know if youve investigated anything along these lines, and if so what have you found which might make this impossible of otherwise impractical?