Weissinger and Maass 



The tangential velocity induced by y is 



u,. = +Vg/2 . 



(1.10) 



(B) Moderately thick airfoils (see Fig. 3). At zero incidence the boundary con- 

 dition can be satisfied approximately by putting a source distribution of strength 



q(0 = 2 — [Vt(^)] 



(1.11) 



on the chord. This relation can be found immediately from continuity consider- 

 ations and, in this form, is also correct for more general flows where v de- 

 pends on ^. The tangential velocity induced at the chord is 



:-C : 



if 



In J. 



q(g^') 



1 ^- r 



d^' 



"' f-?':' f/ljg&-0 'a r.J ^ ; U' ■ .' 



(1.12) 



Fig. 3 - Two-dimensional airfoil 

 theory. Syminetrical airfoil at 

 (a) zero incidence, (b) nonzero 

 incidence [actually, for the con- 

 figuration in (b) the vortices ro- 

 tate in the opposite direction]. 



If the profile is cambered and at incidence, u = Ug + u^ is very often considered 

 as the induced surface velocity. Near the leading edge, this is not very accurate 

 because u^ becomes infinite. If the velocity vector (V cos a + u, 0) is multi- 

 plied by the surface tangent, a better approximation 



Vl + [y'(^)]2 

 is obtained for the surface velocity. 



{Vcosa +u +u } , y(^) = s (^) + t (^) , 



(1.13) 



1216 



