Most sailboats tack (& gybe), but a special class, the Polynesian Proa, "shunts" (trades fore & aft ends) to accommodate its high performance bilateral asymmetry. Similarly a WingMill can be designed to tack or shunt. For three years now KiteLab's experimental wingmills have only self-tacked, with shunting kite flight explored by manual flying. A self shunting kiteplane was on the waiting list to demo, but emerged by accident last week when a model it did not tack as expected. A wingmill law-of-motion emerges that a longitudinally stiff kiteplane bridled near its CG naturally tends to shunt, while a longitudinally flexible kiteplane bridled ahead of its CP naturally tends to tack. Shunting is a powerful mode for an AWECS wing; a real-world example of a (rotary) shunting foil is the Aerobie flying ring where the strange foil section operates bidirectionally. This is a hot enough wing that the ring holds the record for hand thrown distance (+1000ft).

 

The little shunting kiteplane in video linked below was made in a few minutes from ordinary cardboard & a stick, & has the peculiar quality of being a conventional aircraft in one direction & a canard configuration in the other. There are a couple of secrets to its operation; the kiteplane hangs (from terrain or a lifter) as a classic mass-spring element & the fixed foils operate in-trim by the apparent wind created as the kiteplane rebounds from shunting. The wind power that excites it is extracted by damping tug.

 

Many Thanks to JoeF for hosting & posting these files!

 

 

http://www.youtube.com/watch?v=xy6FESqLVZI