180 S. Schuster and H. Schwanecke 
In case the foil pierces the surface, h, = 0 and the term shown in Fig. 31 is found to be 
i ee kak 2 
kK =) | on (h) dh. (18 ') 
Lo 
One more parameter takes care of the difference between the geometrical angle of inci- 
dence Q -eom generally defined for a system moving with the foils and the geometrical angle 
of incidence Qt eom actually existing in a system fixed relative to flow. It may be stated 
(see Fig. 18) 
geom cos $ 
a a ~ sin a 
[cos y sin Qe eam * Sim y(cos Bltan 9| 
eom 
+ sin 8 cos tell « 1@'9) 
For a nonrolling and nonsideslipping dihedral foil with the dihedral angle ®, 
Ky = cos #. 
Together with the known profile efficiency factor Kp the increase of lift for a hydrofoil 
becomes 
10 
| a ee 
08 | 2 ne 
fol Mies Lt 
06 > | 
06 / 
C 
aa 7 
0 40 
10 20 40 ” 
i 7 
hb, -o 
- af -2 [Sayan ; 
Ky, i he Jat) 
K geom = +3 
Fig. 31. Decrease of lift for a dihedral foil 
