Big Bag

I have been working on the last layups for the main structural element of the beams.  The akas required a lot of fairing due to the stair-step shape of the pultrusion laid on the tops and bottoms. Unfortunately this added a bit of weight and lost some of the advantage of pultrusion over regular uni.  The layers did not quite span the width of the beam.  Some of this may have been caused by rounding over the edges of the wood frame prematurely.  We had not decided to use the pultrusion until after this step was done.  I have not done all the math, but I might have been able to get layers of six rods across if I had had the full flat width of the beam.  But, that might have required rounding of the edges of pultrusion causing a loss of strength.  Future builders should definitely look carefully at the options to cut weight and fairing effort 

I ended up laying battens on the sides to dam up fairing compound.  I then sanded the tops and sides to square corners.  The corners were then true enough to run a roundover router bit down the edges getting an even, eased corner and removing some of the excess weight.

This is 6 inch diameter 14.2 oz sleeve (481 gm/sq m) rather than 11.7 oz called for in the plans.  I had my choice of 7 oz or 14.2 oz cloth, so I went with the heavier.  This again is extra weight, but it will add strength and stiffness.  The sleeve came from Soller Composites. ACP Composites is another source.  They seem to have pretty much the same product line.

The python in action.

The 6 inch sleeve was able to conform well to the variance in circumference on the beam, from 13 to 22 inches.

A shot of the 18 foot vacuum bag.  It took two of us about two hours to wet out the sleeve and bag up the aka.  I bought some extra slow hardener to give us some more time.  The shop was about 65 degrees.  Once the vacuum was on, I raised it to 78 degrees and left it overnight.  The wet beam was quite unwieldy.  It had to be flipped several times.  As with the mainsheet beams, I felt I could not get pre-wetted carbon over the beam.  I got a little paranoid with the epoxy and used plenty to ensure it was wet all the way through.  I figured the vacuum bag would remove the excess.

Overall, I am fairly pleased with the result.  The sleeve is well adhered and the weave is well filled.

I had some annoying surface wrinkles.  I think this is excess epoxy that pooled in some places.  I am able to flatten these with just a few strokes of sharp 220 paper on a flat board.  The dust is white rather than black, so I'm not sanding carbon.  Wrinkles in cloth this heavy would have been much larger. Getting peel ply and perforated release plastic on the compound curves was a pain, especially having to shift the aka multiple times.  I wish I knew more about these processes, so I could get nicer results.

Foam cowlings now have to go on one side before the last layer.  I will probably use carbon or fiberglass sleeves over the foam.  It is smoother and maybe stronger that patches of regular cloth.  The shape with the foam will be even more challenging.  Perhaps it should be infused?

With all the fairing, these steps on the two akas are taking about 80 hours.

Task time: 80 hours

Total project time: 482 hours