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ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 2 



Quoting from the Handley-Page handbook on the subject : 



The slot in the wing, extending along the leading edge and formed between 

 a small movable winglet and the main wing itself, prevents a breakdown in 

 the airflow over the plane at large angles of incidence, and so permits the wing 

 to continue lifting at angles at which stalling would previously have taken 

 place. The stream of air introduced at high speed through the slot from the 



under surface has the effect of smooth- 

 * ing out the flow of air over the plane, 

 and keeping it in contact with the up- 

 per surface, delaying the incidence of 

 the breakdown of the airflow to angles 

 so large as never to be encountered in 

 actual flight. 



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Figure H. — Probable flow of the air- 

 stream through a single wing-tip slot 

 A, section of the tip of the first flight- 

 feather ; B, of the main wing directly in 

 rear of it. 



In other words, it appears that 

 the separated part of the first flight 

 feather of the teal gives the air 

 stream a preliminary downward 

 nudge, so that when it arrives at the downward curve on the top of 

 the main wing it is able to cope with the change of direction, and 

 flow down over it smoothly, without burbling and causing a stall. 

 If this really is the case, we can presume that the part of the wing 

 which is situated behind the slot in the teal's wing, does not stall 



immediately the incidence becomes so high 

 as to cause the rest of the wing to do so, and 



i'lGURE 12. — Diagram illus- 

 trating the action of the 

 Handley-Page slot. (From 

 the handbook issued by 

 that firm.) 



FiGDRE 13. — The appearance of a 

 Handley-Page slot in the open 

 position 



that it maintains the value of the lift it is 

 giving, while the main part of the wing 

 is producing " drag " rather than lift. 

 This excellent property of the wing tips, given to them by the 

 slots, can be of use to a teal in several ways. Here is an example. 

 Think of him as he glides down to alight on a flat-calm day, when 

 there is no wind which he can use (by facing it) to reduce his speed 

 sufficiently to let him touch the water without capsizing. His wings 

 have got to produce the " braking effect " required and yet main- 



