Free-flight tests on kites in the 24-ft wind tunnel

Abstract

Tests were required to be made on six kites over a greater range of wind speed than for previous large-tunnel tests. The kites used during the investigation were (A) 3-ft Cody kite Mk. II, (B) 3-ft reversed Cody or Dyco kite, (C)3-ft Haldon kite, (D) 2 X 3-ft Cody storm kite with lateral cross-bracing, (E) 2-ft Cody kite Mk. III with bifurcated inner bridle and (F) 2-ft Cody kite Mk. III with longitudinal bracing. Tests were made over the whole stable range of the kites and up to the highest safe wind speed. The kites were flown from a pylon and values of lift, drag and incidence of the forward and rear bridles were measured. Attempts were also made on two of the 3-ft kites (A and C) to improve their stability at higher wind speeds and low incidences. The maximum value of (L-W)/D was below 2.5 and values of Cz, based on the fabric surface area, excluding the vertical panels, were not greater than 0.9. The unmodified kites are unsuitable for high wind speeds. At low incidences, the kites tend to fall away from their flying position at speeds above 70 ft/sec, but this can be temporarily delayed by diagonal cross-bracing to lift the centre of the leading edges of the front lifting panels, and by tying the wing tips together. At high incidences, bending of the bamboos may disrupt the kite and it is recommended that a bifurcated bridle, which picks up at four points on each lower longitudinal, be used to prevent this bending. The parallel-rigged wing canes tend to take up a negative incidence as tile lower longitudinals bend under load, and thus cause bending of the transverse bamboos. This can be avoided by using cross-rigging, the wing canes then taking up a slight positive incidence. The flapping of the vertical panels, which limits the usefulness of the kites at higher speeds, can be moderated by stiffening canes sewn in the fabric in a fore and aft direction.