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ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 32 



same effect as a large movement in an unslotted one ; and, further, a 

 slotted wing tip can go on giving lateral control at far greater angles 

 of incidence of the main wing than a solid one can. It is the auto- 

 matic twisting of the emarginated parts of the primary feathers 

 toward the line of the air stream and the angle of " no lift " that 

 achieves this desirable result. 



There is a parallel to this controlling device in a certain man-made 

 flying machine called the " pterodactyl " ^ (the word means " wing 

 fingered"). It is really, with all due respect to its designer, only 

 an experiment as yet; but it may well be the prototype of big things 

 to come, for it can be made to perform efficiently in the air at lower 

 speeds than can be used with any other modern fixed-wing aeroplane. 

 Its best trick is the same controlled stalled descent as was described 



on page 281, with this small 

 difference, that, in the ptero- 

 dactyl, the controlling sur- 

 faces at the wing tips are 

 not twisted toward the line 

 of the air stream by means 

 of air reaction; instead, 

 they are moved by the pilot 

 himself. They consist of 

 swiveling flaps which, in 

 form, are prolongations of 

 the wing tips, and so have 

 nothing in front of them, as 

 the ordinary aileron has, to 

 disturb the flow of the air 

 before it reaches them. They can be moved, like ordinary ailerons, 

 in opposition to each other, by means of sideways motions of 

 the control stick; but they can also be made to move together by 

 pushing the stick backward and forward. Tlius, when a controlled 

 stalled descent is being made, the pilot, by pulling the stick back, 

 can turn both flaps so that their front edges are lowered and their 

 trailing edges raised, a movement which brings them into line with 

 the air stream. Then, if lateral control is required, sideways move- 

 ments of the stick will make them work like normal ailerons, in 

 opposition to each other. 



Figure 24 shows what the pterodactyl looks like when it is carry- 

 ing out such a flight. The fact that it is tailless has no bearing on 

 the present discussion; but it may be as well to say here that the 

 control flaps, being set so far back on the machine, can be used in 



FiGDRB 24. — The Pterodactyl tailless monoplane. 

 A sketch taken from a photograph to show the 

 position of the controllers in a stalled descent * 



*The pterodactyl described has been superseded by a new type (1931) whose control 

 surfaces are not designed to operate in the manner described. 



