porosity of seams / Flexi performance

Hello all,
        Here's the story... my friend dave & I have built two
10foot Flexifoil clones, after I built a 6foot one a few months
ago. We built most of them together, and in theory they should
behave identically - but they don't. I'm trying to figure out why...

Actually, I lied - they're not quite identical. The two diferences,
apart from `normal manufacturing tolerances', are:

1) Dave made his too long (wide) by 6cm or so. In order to use the
standard flexi spar, He has made a couple of extension couplers
(steel & aluminium) between the centre CF spar and the outer GF
spars. His couplers are together longer than 6cm, and so the ends of
the spar stick a bit out beyond the end of the kite. His spar is
also heavier than normal.

2) We (accidentally) changed the pattern of the ripstop, which has
a sort of wide arrow on one side, and is solid ripstop on the other:



(R = red, G = green - bear with me ;-)

The difference in  flight is that dave's spar seems to bend more,
and more uniformly, than mine - this I could understand, especially
because the couplings have some slack. However, his is also (grr!)
faster and more manouvreable than mine, by a noticable degree. (~30%?)

The obvious thing to do would be to try his `extended' spar in my
flexi: however he had to cut slots in his tunnel to get the (larger)
couplers in, and I'm reluctant to do this. The other thought I had
is that if the seams are porous, than the fact that mine is on the
top and his on the bottom might make a difference. I used lapped
double seams (I think that's what they're called!)

I ask for thoughts and comments on the above. Anyone with multiple
flexis - how does performance compare? Might the weight and/or bend
of the spar make all that much difference? Is there another aspect I
haven't thought of ??

                john nicoll
john nicoll (jkn@ohm.york.ac.uk)

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