No theory seems to exist regarding wind forces arising at standard kites. We engaged to develope it for kites in general. It says that the produced power of the kite in the soaring phase is proportional to the surface and the power of 3 of the wind speed. The maximum power is extracted when it flies with one-third of the wind speed. For the overall performance the loss is to be deducted for the sinking and retrieval phase. This is further to be optimized, particularly the folding to a minimal resistance. We expect that one can reduce that power loss to less than 20%. But since it is not expensive to increase the kite’s surface easily to almost any size, that is not a crucial problem. We measured the forces on the rope of two sled types by loading the base station into a car, driven with the desired speed , Table 1. | | | Powersled of 1,81m² face | Flowform with 3,6m² | wind velocity | | rope force with blocked kite | soaring power | rope force per m² kite face | power per m² | rope force | soaring power | rope force per m² kite face | power per m² | Beaufort | m/s | km/h | N | W | N | W | N | W | N | W | 1,0 | 0,9 | 3,2 | 0,40 | 0,03 | 2,2 | 0,0 | 1,04 | 0,09 | 2,9 | 0,0 | 2,0 | 2,5 | 8,8 | 2,93 | 0,68 | 16,2 | 0,4 | 7,69 | 1,88 | 21,4 | 0,5 | 3,0 | 4,4 | 15,8 | 9,46 | 3,92 | 52,3 | 2,2 | 24,81 | 10,90 | 68,9 | 3,0 | 4,0 | 7,2 | 25,9 | 25,33 | 17,17 | 140,0 | 9,5 | 66,44 | 47,78 | 184,6 | 13,3 | 5,0 | 10,0 | 36,0 | 48,87 | 46,00 | 270,0 | 25,4 | 128,16 | 128,00 | 356,0 | 35,6 | 6,0 | 12,5 | 44,8 | 75,75 | 88,77 | 418,5 | 49,0 | 198,65 | 247,01 | 551,8 | 68,6 | 7,0 | 15,5 | 55,8 | 117,41 | 171,30 | 648,7 | 94,6 | 307,90 | 476,66 | 855,3 | 132,4 | Table 1 Measured wind forces and calculated power on two types of free flying sleds Other measurements were performed with Rokkaku kites and sleds in the open air with real wind on a hill, because we did not have access to large enough wind tunnels.For example, with the sled Flowform on a rope length of 100m, flying at about 60m high, at wind speed of 4-5 bft (measured at 2m height) we registered a power of 150W. The indicated wind velocities are the mean values in the Beaufort's scale. A well feasible small kite of 20m² would produce an output of at least 1 kW at 6 bft. For the aerodynes, running on a rope to a lifter kite or balloon or on a mast up and down, the calculated power is outlined in table 2. | |