Aerial Locomotion 



19 



Two i6-celled Tetrahedral Kites, the one on the 

 right protected by a beading of weed around the 

 outer edges. 2, 3, 4. Oionos Kite with fixed tail. 

 2 Front view. 3. Bottom view. 4. Top view 



SO that there would be no tendency to 

 a recovery of position, but the very re- 

 verse. The pressure of the wind would 

 tend to increase the tipping action and 

 favor the production of oscillation and 

 a tendency to upset. The lifting power 

 of the wind upon a surface inclined at 

 10° is less than at 20°, and greater at 

 25° than 20°. The more the wings 

 are opened out and the flatter they be- 

 come, the more essentially unstable is 

 the arrangement in the air. 



Mow suppose the wings to be raised 

 until they are nearly closed, or at all 

 events till they make a small angle with 

 the vertical (say 70° from the horizon- 

 tal), then, if from any cause the cell 

 should tip so as to elevate one wing 

 (say to 75°) and depress the other 

 (say to 65°), the lifting power of the 

 wind will be increased upon the de- 

 pressed wing and diminished on the 

 elevated wing ; for the lifting power of 

 the wind is greater at 65° than at 70° 

 and less at 75°. Thus the moment a 

 tipping action begins the pressure of 

 the wind resists it, and an active force 

 is invoked tending to restore the struc- 

 ture to its normal position. The more 

 the wings are raised and the more they 

 approach the perpendicular position, 

 the more stable essentially is the ar- 

 rangement in the air. 



The dividing line between these two 

 opposite conditions seems to be drawn 

 about the angle of 45°. As the tetra- 

 hedral wing surfaces make a greater 

 angle than this with the horizontal, 

 they constitute an essentially stable ar- 

 rangement in the air, whereas a hori- 

 zontal surface represents the extreme 

 of the undesirable unstable condition. 



AUTOMATIC STABILITY 



These considerations have led me to 

 prefer a structure composed of winged 

 tetrahedral cells alone, without hori- 

 zontal surfaces either large or small, 

 although the lifting power is less than 

 when horizontal surfaces are employed, 

 because the factor of safety is greater. 

 One of the chief causes that have led to 

 disasters in the past has been a lack of 

 stability in the air. Automatic stability 

 under varying conditions is surely of 

 the very first consequence to safety, for 



