|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-
CoolIP ~Dave Santos Sept. 8, 2011 M4147
Comment and development of this topic will be occurring here.
Terms and aspects:
Commentary is welcome: