Hot New WingMill Mode
KiteLab's AWE wingmills are self-tacking high L/D crosswind foils
generally made of battened fabric. They are cheap, crash-proof, and
deliver a powerful pumping action at the ground. The latest wingmill
prototypes are now made by professional kite makers (2KiteSam and Chuck
Blevins).
It was predicted in discussion at NYU's Zhang Lab that, as these wings
scale up, the oscillation dynamics would change and likely require new
initiation principles. The old "flag flapping" trigger would at some
point stop working in slower "dimensionless wind" (same wind, bigger
wing).
The latest 3 m wingmill has proven a new tacking principle, with
enhanced power to-boot. It has a pennant tail superficially like smaller
versions, but with a stiffer low-flutter structure for amazing
high-speed flight. The new tail initiates tacking at the sweep-limit by
its mass and stiffness pitching the LE over. To do this, the sweep is
now set slightly "underhand" by line geometry, actually pulling
down hard against the pilot-lifter kite. The old overhand sweep mode
was intended to add useful lift, but this lift was redundant; the
pilot-lifter already supplied all the lift necessary.
This is the well-known power-kite paradox of pulling lower in order to
pull harder. Wubbo well summarized at Leuven the trade-off of flying too
high or low in the kite window, that we seek the sweet spot in between.
The depowered wingmill is so light and low drag that it parks with its
pilot-lifter at a quite high angle. Powered-up, the sweeping wingmill
naturally hauls the rig down into the center of the power zone. Hidden
power comes from pulling sharply against the pilot-lifter. Too big a
wingmill or too small a pilot-lifter drags the rig too low.
Measured power curves and hot video pending... old video links-
KiteLab GroupCoolIP ~Dave Santos Sept. 8, 2011 M4147 Comment and development of this topic will be occurring here.
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