Malavard 



Following the decomposition of the movement, the function k(y) is also split into 

 two parts: kj and kj. We see that the arbitrary choice of this function is sup- 

 ported by 025 3-nd that s^-i is completely defined by its overall boundary condi- 

 tions. The solution of the boundary value problem of ij depends on the choice 

 of kjCy), which finally amounts to the choice of the thickness distribution of the 

 hydrofoil. In the most general way, the choice of kjCy) is essentially dictated 

 by the structural point of view. The drag coefficient is available by considering 

 the kinetic energy on the Trefftz plane. 



An example of the possibilities offered by this method is presented in Figs. 

 18a and 18b. The planform of the two wings is trapezoidal, the aspect ratio is 

 K = 4, the taper ratio is 1/3, and the swept angle back of the line situated at 

 25% of the chord is 15°30'. The local distribution chosen is constant along the 

 chord and optimal over the span for the immersion depth d/s =0.2. The cal- 

 culations were made so that in each section the thickness relative to the local 

 chord should not be lower than 1.6% at 10% from the leading edge. The choice 

 of a lower Cl, 0.3 instead of 0.5, led, in the case of Fig. 18b, to a higher lift- 

 drag ratio, 9.52 instead of 6.9. 



Design of a Supercavitating Wing with Strut and Walls Effect — This special 

 study was carried out in order to verify analog experimental results. The con- 

 figuration of the testing channel (Fig. 19a) is taken into account in the calcula- 

 tions by considering the strut and walls effects. The latter are easily repre- 

 sented by rheoelectric analogy, since the zero normal velocity on the walls is 

 conveyed by a zero normal derivative of the potential. The introduction of the 

 strut does not complicate the problem, which is devoid of lifting effect. The 

 strut sections are obtained by the introduction of an appropriate distribution of 

 potential on the projection of the strut and the cavity of its sections on the y = 

 plane. The method of solution is similar to that described in the Design of a 

 Supercavitating Wing, above. 



Figures 19b and 19c show clearly the influence of the strut on two wings of 

 the same planform with the same load distribution. In the first case, where the 

 length of the strut is equal to that of the central chord, considerable thickening 

 of the sections near it can be noted. In the second case, the width of the strut is 

 imposed to 70% of that of the central chord, the central section is thinner, and 

 this permits a lift-drag ratio 25% higher than that of the preceding illustration. 



Hydrodynamic Characteristics of a Flat Wing with Strut and Walls Effect — 

 We have already indicated the difficulties involved in the solution of the direct 

 problem. In the subsection on the Hydrodynamic Characteristics of Supercavitat- 

 ing Hydrofoils in Unbounded Flow, a method applicable to two-dimensional cases 

 was described. In three-dimensional situations at a = o it seems possible, 

 granting a plausible approximation, to remove these difficulties. With this ob- 

 ject, consider the expression of the drag coefficient c^ 



4V 2s2 J VBn 



392 



