300 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 19 3 2 



main wing is fully spread the feathers of this tiny winglet are also 

 spread so that they present the greatest amount of superficial area 

 to the atmosphere; that is, they are ready for action. 



When the main wing is at a fairly small angle of incidence, and 

 there is no risk of a stall, the bastard wing serves no active purpose. 

 It is so shaped that it forms part of the leading edge and therefore, 

 with that part of the wing, is subject to pressure from the air stream. 

 This pressure keeps it in position, and it does nothing more than 

 fill in the slight " reentrant curve " in the leading edge of the main 

 wing which can be seen in Figure 36. 



When a wing is at normal angles of incidence, the area of pressure 

 on the leading edge covers the whole breadth of the bastard wing, 

 but as the incidence is increased the area of suction moves forward 

 and sucks the bastard wing upward. 



Figure 37. — Left wing of a woodcock seen from below and in front, 

 showing the bastard wing in the " slot-closed " position. A-B, 

 total length of the bastard wing 



This may seem to be rather an astonishing statement, but it should 

 be borne in mind that the air which passes over the top of a wing 

 can not exert any upward suction until it has passed over the summit 

 of the curve, or camber. 



The upward force which the suction exerts may perhaps be added 

 to by muscular action in accordance with Headley's observation, and 

 may also be augmented by that part of the air stream which passes 

 under the leading edge of the main wing, for there is a little pocket 

 formed between the front of the bastard wing and the " reentrant 

 curve " mentioned above into which air must press with increasing 

 force as the angle of incidence gets greater. In Figure 37 this pocket 

 is shaded black. But one thing seems certain, and that is that the 

 opening of the wrist slot is mainly automatic and that it is brought 

 about in the same way as the opening of a Handley-Page slot. 



Once the initial upward movement has started, a stream of air 

 passes between the main and bastard wings and assists the suction in 

 its work by pressure from beneath. Having formed part of the 

 curved-down leading edge of the main wing, the bastard wing, when 

 acting on its own, finds itself to have a considerably smaller angle of 

 incidence than its parent (fig. 38), therefore it remains effective and 

 unstalled when the main wing has passed the stalling angle. 



