Date: 27 Feb 1993 16:27:23 GMT
From: martin@patricia.verfahrenstechnik.uni-stuttgart.de (Martin Hepperle)
Message-ID: <1mo4pb$hvc@info2.rus.uni-stuttgart.de>
Organization: Institute A for Mechanics, University of Stuttgart, Germany
Subject: Flexifoil wobbles on my nerves

I have a rather small FlexiFoil kite (approx. 80 cm span) which
does something I don't like:
It does not keep it's angle of attack constant, but "wobbles"
up and down when the wind load is getting stronger.
The frequency of these changes in angle of attack is about 5-10 Hz.
To me it looks like separating flow at higher alfa -> lift is
dropping -> reduction in alfa -> flow reattaches -> higher alfa ->...

Is there a trick to avoid this (adding lead to the lead-ing :-)
or trailing edge or something like that) ?
The larger FlexiFoil seem to have no problems with this phenomen.

Martin.

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Date: Sun, 28 Feb 1993 01:47:34 GMT
From: steveth@netcom.com (Steve Thomas)
Message-ID: <1993Feb28.014734.20140@netcom.com>
Organization: VisionAire, San Francisco, CA
Subject: Re: Flexifoil wobbles on my nerves

In article <1mo4pb$hvc@info2.rus.uni-stuttgart.de> martin@mecha2.verfahrenstechnik.uni-stuttgart.de writes:
>I have a rather small FlexiFoil kite (approx. 80 cm span) which
>does something I don't like:
>It does not keep it's angle of attack constant, but "wobbles"
>up and down when the wind load is getting stronger.
>The frequency of these changes in angle of attack is about 5-10 Hz.
>To me it looks like separating flow at higher alfa -> lift is
>dropping -> reduction in alfa -> flow reattaches -> higher alfa ->...
>
>Is there a trick to avoid this (adding lead to the lead-ing :-)
>or trailing edge or something like that) ?
>The larger FlexiFoil seem to have no problems with this phenomen.
>
>Martin.

You probably have sand or dirt inside the sail.  I had some sand indside one
of mine once and observed the exact same behavior.
-- 
_______
Steve Thomas
steveth@rossinc.com

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