Earlier in forum we linked to a patent featuring unmanned drone towing a manned hang glider (kited manned wing) with aim of releasing the tow to effect free gliding of the manned hang glider.   We have also discussed using unmanned drone to launch kited wing intended to work as electricity-generating system.  

Along the same spirit is a contemporary article HERE. 

Multicopter towing for paragliders and hang gliders

Text and graphics by Bernd Otterpohl

There are many discussions leading to Betz's law and its validity.

In first what is Betz's law? Betz's law is note a rule, but is a physical law. This law states there is a limit of kinetic energy of wind an idealized turbine can capture through an idealized disk-shaped area section. This limit is 16/27.

Theoretically Betz's limit applies to all sorts of wind turbines.

But pratically current HAWT are closer to the idealized turbine because their rotor has roughly two dimensions, leading to a swept area roughly corresponding to the idealized disk-shaped area section, so in a configuration preventing any renewal of the wind.

If the turbine works in three dimensions, like VAWT, some renewal of the wind occurs. Said renewal of the wind could be neglected for small turbines but not for very large turbines which become far from the idealized turbine within an idealized disk-shaped area section. This has nothing to do with the eternal "beat the Betz limit" generally leading to so-called "breakthrough" but in reality fancy concepts of which one (ALT) recently discussed.

Other turbines are expected to work in three dimensions, comprising AWES. By considering the frontal airspace of wind which is swept, Betz's law could be used but only as a first approximation. JoeF provides an example for a 1 km long snake: the renewal of wind occurs, and there are also other concerns like wakes, so said snake is very far to an idealized turbine capturing wind through an idealized disk-shaped area section. 

This leads to Dabiri's work. He states the whole of a wind-farm should be considered, not the addition of parts, indicating that a single wind turbine facing the wind is more efficient in regard to Betz's law, but several turbines facing the wind lead to more important losses due to the wake effect. Resulting when the turbines are skew the whole wind-farm becomes more efficient. 

In Dabiri's work, but also for AWES or other large devices working in three dimensions, the volume of air is considered, implying the renewal of the wind and the wake effect within said volume. So this could lead to find a rule, perhaps a law, concerning a limit of kinetic energy of wind that could be captured within said volume of air. 

Clouds and AWE

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• Know clouds
• Incidents in AWE and clouds
• AWE flight planning and clouds
• Rules and governance and clouds.  Waivers. 
• Physics of clouds
• AWE opportunities with clouds
• Harvesting cloud moisture
• Identification of clouds
• Symbols for clouds
• FFAWE and clouds
• Absence of clouds
• Cloud wiki
• Video: Know Your Clouds - U.S. Army Aviation Training Film (1966)
• ... ??

• Cindy Nshuti
• Hever Moncayo
• William A. Engblom
• Diana Festa
• =================================================

• Development and Demonstration of a Flight Simulator for the Dual-Aircraft Platform Concept

  Nolan Coulter

  , 

  Hever Moncayo

   and 

  William A. Engblom
  AIAA 2018-3886
  Session: Modeling and Simulation for Unmanned and Personal Aerial Vehicle Operations
  Published Online:24 Jun 2018https://doi.org/10.2514/6.2018-3886
• ====================================

This topic thread might be used to post news on noteworthy traction AWES.

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A recent news point: 

Louis Dreyfus signs up for kite system