I will Email you a sketch of some thoughts on viable wind gradient engines if I can get your Email address to work (it didn't last time). This could be great fun given a serious push. The main methods are:

1. Dynamic soaring analogy, probably via a rotary wing

2. Simple wind-gradient engine (needs to be big), probaly two kites in ragged formation.

3. A wind-turbine approach where the lower part of the turbine is in the slack low speed flow and the upper part is in the energetic upper flow.

4. A separated turbine approach where two wind turbines are interconnected, one low and one high, one driving and one providing power. This would result in two aircraft in ragged formation and is probably impracticable due to control reasons.

I favour (1) or (2) since both could be achieved simply at low cost.

Give it a bit of thought and change the world! Also, persuade Richard to find a way of posting sketches on his site.