Just look at Doug’s two videos: on the first one, you can see that the longer shaft length generates a higher catenary sag effect than on the second video. And I didn’t see any significant difference in elevation angle with rotors at rest or in rotation.
This is confirmed on one (see below) of your videos: we can see at 0:50 and at 1:58 that without rotation the elevation angle of the rotor remains the same or even higher than with rotation. Thus when rotating at 1:20 and 2:15, the rotor loses elevation angle and descends due to the additional drag which is not compensated by the assumed and sufficient additional lift. The lifting kite does all or almost all the lift work.
As the lifting kite is at one end and the anchor (PTO) is at the other end, the catenary sag effect will increase with the length of the shaft.
That said you could take my comments then start a preliminary study to confirm or infirm them, or rather to detail them. Then you can decide what direction is better for Daisy: scaling, or improving it for a possible market.
