"pulsing" and bridle/frame adjustments
Subject: "pulsing" and bridle/frame adjustments
From: firstname.lastname@example.org.FI (Simo Salanne)
Date: Wed, 15 Sep 93 17:49:31 GMT
Mark Cottrell, Swept Wing Stunt Kites, 1990.
"So the frame is strong, stiff and light and thus
should be ideal to hang your sail on, but there is
one other nasty lurking to catch the unwary - resonance.
Many a normally well behaved commercial kite will
demonstrate the effects of resonance as the wind
speed increases. Resonance effects include wing waggling
(one wing bends up, the other down & then the cycle
repeats), cross spar jumping and pitch shrugging
(feels like sharp juddering). The problem stems from the
fact that all structures have a natural resonant
frequency - that is, the frequency at which the structure
vibrates in response to incoming energy - and since
conical rogallo sails are very good vibrational energy
generators (viz they are very noisy) it is not surprising
that so many designs show resonant effects.
Minimising resonant effects is not difficult. The ground
1. The stiffer the frame the higher the resonant frquency
viz. the stiffest frame is best. Although a very flexible
frame would absorb and damp resonance the flying
charasteristics would be horrible - if the resonant
frequency is high enough 1-vibrations are short lived
& 2-the inertia of the kite masks the effects of the
2. Do not allow any frame sub-dimension to be the same
as or an exact multiple/sub-multiple of any other frame
sub-dimension exept where absolutely necessary (the sub-
dimensions are the measurements internal to the layout
e.g. between the two leading edge connections or the top
leading edge connection to nose dimension). This needs
careful design and even a 1 cm variation in a spar can
change a waggly winged kite into a quiet well-behaved
kite and vice versa."
That's enough of retyping...
Buy Mark's booklet, The Kite Store Ltd. sells it for 3.95 GBP
and Kite Lines for 10.95 USD - it's really worth the price!
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