Re: [a-w-h] Re: Control strategy veriable pitch

At 18:36 24/2/2002 -0700, Laurie Forbes wrote:
>
>The gravity will add to and subtract from the centrifugal force acting on
the blades as they rotate (about the horizontal axis) which will, it would
seem, cause oscillation of the blade pitch - if so, is that a particular
problem?
>
>Is it necessary to dampen the pitch movement for the above reason or to
prevent undue oscillation in turbulent winds?
>
>Laurie Forbes
>

· The Windflow 33m two-blade turbine (currently in design, and starting
manufacture, in Christchurch, New Zealand:
http://www.windflow.co.nz/windflow500/techspecs.html ) :-

http://www.windflow.co.nz/windflow500/teetering_hub.html
  has:
       Teetering Hub Animation             [uses RealPlayer]
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
This animated sequence shows the elegant simplicity of the mechanism inside
the Windflow 500 hub. The pitch change mechanism allows for teetering and
pitch-teeter coupling but is not complicated. As the actuating rod in the
centre travels back and forth, it carries the linkages which drag the blade
pitch bearings through their travel. This is the active system which
controls the pitch of both blades in unison. In helicopter terminology this
would be called collective pitch. 

Then as the hub teeters the blades pitch in opposite senses.
  In helicopter terminology this would be called cyclic pitch. However
unlike a helicopter's actively controlled cyclic pitch, the "pitch-teeter
coupling" of the Windflow 500 is purely a passive effect. It follows from
the kinematics of the linkage that the bearing attachment points must stay
in the same vertical plane, and it is this simple piece of geometry which
produces the pitch-teeter coupling.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

David.
(David MacClement) d1v9d @ bigfoot.com [remove spaces]
http://davd.tripod.ca/ ; http://davd.tripod.com/GrAPR-020201.html

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