SAFETY DEVICES IN BIRDS ' WINGS — GRAHAM 301 



Another result of its smaller incidence is that the force reacting 

 approximately at right angles to its surface is directed more forward 

 than that on the main wing. Consequently, it is dragged forward as 

 well as upward, like the separated feathers which form wing-tip slots. 

 Further, the angle at which the pivot of the joint is set allows of 

 motion more easil}^ in that direction than in any other. The upward 

 and forward displacement can be clearly seen in Figure 6. The right 

 wing of the marsh harrier provides a plan view which shows the 

 forw^ard movement, and the left wing an elevation which shows the 

 upward movement. 



Nearly all bastard wings are curved down not only from front to 

 back, but also from root to tip, so that when they are in the open 

 position and the curve has been slightly reduced by the upward force 

 of air reaction, they lie nearly parallel with the leading edge of the 



A. B 



Figure 38. — I'lubable flow of the air stream through the wrist slot of 

 a blaclicocls. A, near tlie root of the bastard wing and B, near the 

 tip 



main wing and are to all intents and purposes in the same position 

 with regard to it as the auxiliary airfoil of an airplane wing which 

 is fitted with the Handley-Page device ; that is, displaced to a position 

 parallel with, above, and in front of it. 



Their action when in that position must be very much the same as 

 that of the separated tip of the first flight feather of a single-slot 

 wing described on page 280, in other words, to form an automatic 

 safety device to prevent stalling when a large angle of incidence has 

 to be used. 



The action of the closing of the slot formed by the bastard wing 

 must be just the reverse of the opening action. Put shortly, it may 

 be said that as the incidence of the main wing diminishes toward the 

 angle at which the assistance of an auxiliary to prevent stalling is no 

 longer required, the incidence of the bastard wing being already less 

 than that of the main wing, approaches the angle of " no lift," and 

 finally it experiences a downward reaction which forces it down into 

 its " stowed position " in the reentrant curve. 



It is possible that the tiny " flexor " muscle {flexor hrevis polUcis), 

 which is so arranged that it pulls downward on the bastard wing, 

 assists air pressure in this process, and it is also possible that the 



