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Noise
One of my design goals on designing a swsk (swept wing stunt kite) is
to minimise weight and minimise drag. If there is noise then there is drag.
Therefore, minimise noise. There are a number of ways to reduce noise/drag:
(1) more stand-offs. This may tension the TE (trailing Edge), altering
the TE's frequency of oscilation. You will see this on FlexiFoil's
small swsk (forget the name, is it Impulse?), which uses 4 standoffs.
(2) Tailor the LE (leading Edge) such that the sail wants to bring the
frame in to the body of the kite. The frame then wants to pull the
sail out, tensioning the TE. NOTE: this also requires a good pull
on the sail from the end of the LE. This approach is used on Phantom,
Flash Angel, Cheetah, HiProfile, ... just about every quality swsk
available in UK.
(3) Use battons in the sail, to tension the sail fore/aft. This is use in
yachts and sail boards, but it adds quite a large amount of weight to
a swsk (you need pockets, tensioners, battons, etc). This is used in the
original "King Cheetah" (Rare Air), which has 6 battons and 8 standoffs.
The kite makes no noise. Also used in Flash Angel, and quite a few others.
(4) Use a "long" stand-off from top cross spar to TE, such that it becomes
a "virtual batton" (can do the same with bottom cross spar if there is a
significant distance between bottom Xspar and TE). This is the approach I have
taken in my latest design, as it gives me a light weight design. I built
8 versions of this design to get to my current prototype (all my kites are
prototypes :-), and initial low wind trials have been promising.
(5) Put a cf (carbon fibre) whisker into the TE. This can start as a stand-off
from the bottom Xspar, curve outwards, and into the TE hem. I have seen
a number of swsk's with this (but I haven't flown them). This approach has
been adopted on the "Silent Knite" by Clarke (Windy Kites).
Patrick noise-is-a-drag Prosser
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