http://www.awec2017.com/presentations-main.html then click on Fort Felker: a lot of informations.
Fort Felker (please see the attachment below or the link above): “Our largest kite to date, it has a wingspan of 26 m, and has eight onboard rotors that are each 2.3 m in diameter. For comparison, our previous prototype, Wing 7, was a 20 kW system with a 8m wingspan and with four rotors 0.7 m in diameter.”
The turbines aloft should add 1/2 drag of the wing alone in order to reach an optimal efficiency, the speed becoming 2/3. I checked this with my FlygenKite:
(please see also my comments as corrections).
But the drag of “eight onboard rotors that are each 2.3 m in diameter” (33 m²) seems to be largely above 1/2 the wing alone drag. Have you some explains please? Is it the large drag of the support of the turbines?
ch01_awec94_Felker.pdf (2.2 MB)
Another flygen AWES:
The rotors have comparable relative dimensions as M600 rotors, but there are four rotors instead of eight.
Dave Santos’ answer on https://groups.yahoo.com/neo/groups/AirborneWindEnergy/conversations/messages/25436 :
“High M600 rotor disc area is needed for E-VTOL, including safety factor. Full drag for harvesting is not the design necessity.”
Indeed E-VTOL requirement seems plausible but even half of rotors area looks to be high in regard to the wing alone, by taking into account of its high L/D ratio, so its low D.
See also on http://www.kitekraft.de/#4_System_Development with still higher values (rotor area/wing area) as mentioned previously, perhaps because of the high wing lift allowing larger rotors aloft:
Wing Span: 4 m
Wing Area: 1 m²
Weight: 30 kg
Rotor Diameter: 0.4 m
Number of Rotors: 8
Total Rotor Area: 1 m²”