Date:	Thu, 8 Jul 1993 09:36:57 -1000
From:	sasaki@das.harvard.edu (Marty Sasaki)
Message-Id: <1993Jul8.193840.1680@das.harvard.edu>
Organization: Division of Applied Sciences, Harvard University
Subject: Stretched sails

A stretched sail can dramatically change performance. I saw this
firsthand with the kites that Storm Front flew last season. These were
MDM-4's, which are stable dart-shaped kites, designed for team flying.
At the time, I was making MDM-4's using a highly bent standoff. The
standoff acted like a spring so that as the sail stretched, the
standoff just uncoiled a bit, and the additional stretch was not
really noticed.

I made 5 kites, four for the team to fly, and one for me to fly
individually. About half way through the season, we added a fifth
member to the team for ballet flying, and out came my individual kite.

The individual kite had maybe 20 hours on it, while the team kite
probably had around 200 hours on it. The bridle had to be lowered
about one inch in order to get the speeds to match.

No matter what you do, you won't get back the original speed, although
lengthening the spreaders (surprisingly, lengthening the upper speader
has a more profound effect than lengthening the lower spreaders) will
get some of the performance back.

Ripstop polyester (like Icarex) does hold out the promise for lower
sail stretch. I have no long term expereince, but short term
experience has shown Icarex to be a nice material in terms of stretch.
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Marty Sasaki            Harvard University           Sasaki Kite Fabrications
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