FFAWE     Free-Flight AWE
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March 25, 2020, by Joe Faust
Harry Valentine's article

Idea by Harry Valentine:   Tow airships using kite system.  Anchor of tethered towing wings would by the airship.  "a kite-pulled airship"
March 6, 2020, post by Joe Faust
Facing calms with FFAWE

 I appreciated your suggestion regarding zero-wind kites.    We sometimes call the realm "calm kiting" and "calm kites."  
The upper wind is very rarely really calm.    

AWE has step-towing and towing from the ground to address some of the calm challenges.
Also, we have the ground-powered source in a tri-tether system that may keep a wing set aloft during a calm period.
As you indicated also, gliding and soaring in horizontal calms by the use of vertical thermals remains a potential solution.

And the use of changing altitudes away from a calm layer is available.

Also, FFAWE (free-flight AWE) where there are no tethers to the ground uses the asset of two strata of winds where the winds at their respective layers are in different directions or at different speeds in the same direction.