Equipment,

One stable (ie, single line)kite, One small lightweight parachute of similar area to the kite, One set of car keys, One big open space with a breeze, One mobile telephone.

Method,

Attach car keys to the kite string with about 150 feet of string to the kite. Tie the parachute to the keys with a short line (about 4 to 5 feet). Launch the kite. Run towards the kite (downwind) such that the kite continues to fly but you feel a headwind, ie, slower than the high altitude breeze but faster than that at ground level. Let go of the keys and parachute. Use thje mobile telephone to call your wife for a spare set of keys. Drive home and ponder on todays lesson.

This works although I did not use car keys.

A wind gradient engine is exactly analogous to a sailing boat. A sailing boat requires a shear layer, either air-water, air-grouns, air-ice, or, if different wind speeds can be experienced by the same craft, air-air. Replace the parachute with a controllable aerodynamic device (another kite, etc) and you now have a viable machine.

Sea birds use exactly this principle by flying between the shear layers to exchange momentum (dynamic soaring). There is nothing physically wrong with the principle and there are many theoretical ways of achieving a similar result. Hang on to your car keys!

Unfortunately, these ideas are neither original (I first heard conceptually similar ideas in 1989), likely to produce a particularly fast machine, or mine. However, someone should have a proper go...

Jon Howes.