302 



ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1932 



" extensor " muscles, which are designed to pull upward on it, come 

 into play in the opening process more than has been suggested; but 

 the most likely duty of these muscles is to damp down the movements 

 of the bastard wing and " steady " it in the closed or open position, 

 just as the springs of the Handley-Page slotted wing device do. 

 Shufeldt says of the " flexor " muscle that it is sufficiently powerful 

 to retain the bastard wing in the closed position when the wing is 

 folded. 



The considerations which govern the length of the bastard wing in 

 different types of birds form a most interesting study. Like the 

 wing-tip slot, this other form seems to be influenced chiefly by the 

 aspect ratio, for birds with long, narrow, pointed wings, like the 

 sea birds, and such birds as the golden plover and woodcock, have 

 smaller bastard wings than the short-winged types, such as the game 



FiGDUE 39.- 



-Bastard wing of a blackcock. A, seen from below and in 

 front ; B, from above, slightly foreshortened 



birds; though, again, such matters as wing loading, size of bird, speed 

 of flap, span loading (weight carried per unit of length between 

 wing tips)^^ and habits of living may have a certain influence as 

 well. Figure 40 and the left-hand bird in Figure 41 show examples 

 of the bastard wing in action, and the right-hand bird shows the 

 appearance of a wing when the slot is closed. 



It would be rash to come to any conclusions as to the lessons that 

 are to be learned from the antistalling devices of birds without care- 

 ful consideration of the influence that flapping flight may have upon 

 their design; but two things seem to stand out clearly: (1) That 

 the ideal glider is one that has great span, high aspect ratio, and 

 pointed wing tips, like an albatross, and (2) that such a glider would 

 probably be but little improved by the presence of any form of anti- 

 stalling device, either on the main wing or on the control surfaces. 

 But if practical considerations, such as structure weight, housing, and 

 handiness for operation, dictate a smaller span, then it is worth while 



" Data on these matters will be found in the table. 



