An analysis of the figures and references given on pages 18 and 19 of the “Parasailing Safety” document did not allow me to corroborate the enormous Cd of 2,727 mentioned here. I deduced values less than half.
Some investigations in the meantime, about not steerable square rescue parachutes and steerable square and Rogallo rescue parachutes.
This not steerable square rescue parachute seems to have a far higher drag coefficient Cd (perhaps about 3.5, guessing projected area as for other parachutes ?) than a classic parachute (perhaps a Cd of 2). But their extrapolation would not lead to kites because they have no lift.
About steerable square and Rogallo rescues parachutes: as they are steerable, they have a (very small) glide ratio. However this low glide ratio of 1:1.5, so 0.666, common to both (for the Rogallo, a likely similar glide ratio is achieved with the pre-brake device, see also the video, with a possibility to achieve 1.2, “finesse 1.2” in French by steering), can be good for AWE once extrapolated into a kite, resulting in an angle of elevation of 33 degrees and 40 minutes, avoiding too much losses by cubed cosine.
Some complements: Airborne Wind Energy System based on steerable square rescue parachute, and above all Airborne Wind Energy System based on steerable Rogallo rescue parachute (DOI : 10.13140/RG.2.2.32994.13762). For both, and with a value of 0.666 for the glide ratio, from no complete data (no projected area given) I deduced, more or less wrongly, a thrust coefficient Ct about 3.425, a drag coefficient Cd about 2.86, and a lift coefficient Cl about 1.9.
The Rogallo rescue seems more suitable for an AWE use: Rogallo parawing kites were used.
If we take a look on the specifications page 6, we can see a low sink rate of 3.93 m/s, loaded with 115 kg, with a horizontal speed of 2.62 m/s for a glide ratio of 1/1.5 (0.666), elevation angle of 33°40’), calculated Ct, Cd, and Cl similar to the values above; then a still lower sink rate of 3 m/s, loaded with 90 kg, horizontal speed of 2 m/s, calculated Ct of 4.56, Cd of 3.8, and Cl of 2.53.
These values seem very high, and I could have made a mistake somewhere, not having the value of the glide ratio for a given sink rate, nor the projected surface area, which I deduced arbitrarily.
Another point from the last example: it seems that as the load increases, the coefficients decrease. We can perhaps deduce that the force of the wind, much greater than the indicated loads, would reduce these coefficients even further.
However, if the high coefficients are real for sufficiently large units, tether-aligned devices can perhaps be an alternative (maybe simpler and consuming less space) to flexible crosswind kites, knowing that there is already a working parachute system.