222 The National Geographic Magazine 



wind, increasing the head resistance 

 without counterbalancing advantages. 



TRIANGULAR CELLS IN KITE CON- 

 STRUCTION 



Iii looking back over the line ( f ex- 

 periments in my own laboratory, I 

 recognize that the adoption of a trian- 

 gular cell was a step in advance, con- 

 stituting indeed one of the milestones 

 of progress, one of the points that stand 

 out clearly against the hazy background 

 of multitudinous details. 



The following (Fig 3) is a drawing 

 of a typical triangular-celled kite made 

 upon the same general model as the 

 Hargrave box kite shown in Fig. 1 . 



A triangle is by its very structure 

 perfectly braced in its own plane, and 

 in a triangular-celled kite like that 

 shown in Fig. 3, internal bracing of any 



fig. 3 



character is unnecessary to prevent dis- 

 tortion of a kind analogous to that 

 referred to above in the case of the 

 Hargrave rectangular cell (Fig. 2). 



The lifting power of such a triangular 

 cell is probably less than that of a rect- 

 angular cell, but the enormous gain in 

 structural strength, together with the 

 reduction of head resistance and weight 

 due to the omission of internal bracing, 

 counterbalances any possible deficiency 

 in this respect. 



The horizontal surfaces of a kite are 

 those that resist descent under the influ- 

 ence of gravit}', and the vertical surfaces 

 prevent it from turning over in the air. 

 Oblique aeroplanes may therefore con- 

 veniently be resolved into horizontal 

 and vertical equivalents, that is, into 

 supporting surfaces and steadying sur- 

 faces. 



The oblique aeroplane A, for exam- 

 ple (Fig. 4), may be considered as 

 equivalent in function to the two aero- 

 planes B and C. The material compos- 

 ing the aeroplane A, however, weighs less 

 than the material required to form the 

 two aeroplanes B and C, and the frame- 



work required to support the aeroplane 

 A weighs less than the two frameworks 

 required to support B and C. 



In the triangular cell shown in Fig. 

 5, the oblique surfaces ab, be, are equiv- 

 alent in function to the three surfaces 

 ad, de, ec, but weigh less. The oblique 

 surfaces are therefore advantageous. 



The only disadvantage in the whole 

 arrangement is that the air has not as 

 free access to the upper aeroplane ac, in 

 the triangular form of cell as in the 

 quadrangular form, so that the aeroplane 



fig. 5 



ac is not as efficient in the former con- 

 struction as in the latter. 



While theoretically the triangular cell 

 is inferior in lifting power to Hargrave's 

 four-sided rectangular cell, practically 

 there is no substantial difference. So 

 far as I can judge from observation in 

 the field, kites constructed on the same 



