206 



SCIENCE. 



[N. S. Vol. XVIII, jNo. 450. 



of a rectangular 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."* 



"Triangular cells also are admirably 

 adapted for combination into a compound 

 structure, in which the aeroplane surfaces 

 do not interfere with one another. For ex- 

 ample, three triangular-celled kites, tied 

 together at the corners, form a compound 



ISlongitudinat sticto 



cellular kite (Pig. 3, A) which flies per- 

 fectly well. The weight of the compound 

 kite is the sum of the weights of the three 

 kites of which it is composed, and the 

 total aeroplane surface is the sum of the 

 surfaces of the three kites. The ratio of 

 weight to surface, therefore, is the same 

 in the larger compound kite as in the 



* Some experiments, made by us at Blue Hill 

 in 1896 with some of Hargrave's models of tri- 

 angular-celled kite, led us to think the rectangular 

 cell much superior in efficiency to the triangle, 

 owing to the sheltering of the upper surface at 

 the corners of the triangular-celled kite. 



smaller constituent kites, considered indi- 

 vidually. 



"It is obvious that in compound kites 

 of this character the doubling of the longi- 

 tudinal sticks where the corners of adjoin- 

 ing kites come together is an unnecessary 

 feature of the combination, for it is easy 

 to construct the compound kite so that one 

 longitudinal stick shall be substituted for 

 the duplicate sticks. For example: the 

 compound kites A and B (Fig. 3) may 

 be constructed, as shown at C and D, with 

 advantage, for the weight of the compound 

 kite is thus reduced without loss of struc- 

 tural strength. In this case, the weight of 

 the compound kite is less than the sum of 

 the weight of the component kites, while 

 the surface remains the same. If kites 

 could only be successfully compounded in 

 this way indefinitely, we should have the 

 curious result that the ratio of weight to 

 surface would diminish with each increase 

 in the size of the compound kite. Un; 

 fortunately, however, the conditions of 

 stable flight demand a considerable space 

 between the front and rear sets of cells; 

 and, if we increase the diameter of our 

 compound structure without increasing 

 the length of this space, we injure the flying 

 qualities of our kite. But every increase 

 of this space in the fore and aft direction 

 involves a corresponding increase in the 

 length of the empty framework required 

 to span it, thus adding dead load to the kite 

 and increasing the ratio of weight to sur- 

 face. 



"While kites with triangular cells are 

 strong in a transverse direction (from side 

 to side), they are structurally weak in the 

 longitudinal dii-ection (fore and aft), for 

 in this direction the kite frames are rec- 

 tangular. Each side of the kite A, for 

 example, requires diagonal bracing of the 



