Canadian Hydrofoil Program. Hydrodynamics and Simulation 



for a port anhedral foil of angle ^ , T 



'J) 



AP ' AP 



for a stbd. anhedral foil of angle I\ , 



-A.o 



r = r 



i AS 



L^ , D^ and M^ may be evaluated by the methods of References [9], 

 [10] , [ll] and [1Z] . 



Steady State Performance 



In the steady state, equations (1) to (3) become 



!(L.x. cos T. + D.z. - M. cosT.) + (x_ cot7 - z_) 

 x ii l li l i T T 



(8) 



2D. 



i 



2L cos r + cot 7 2 D = W (9) 



i i i 



Since dynamic pressure is constant Lj_ , D-[ and Mi are 

 functions of immersion depth (h) and angle -of -attack (a) alone. 

 For an all-fixed foil system, furthermore, knowledge of h and a 

 for a single foil element enables all other h's and a 's to be de- 

 termined. Hence (8) and (9) contain only two unknowns : h and a 

 of a reference foil element. Because of the non-linear nature of these 

 equations the solution must be obtained by an iterative technique. 



Figure 11 illustrates the accuracy obtainable using the above 

 procedure. Predicted curves of BRAS D'OR trim, keel clearance 

 and weight- drag ratio are presented, along with trials measurements 

 of these quantities. Estimated measurement accuracies are —/a, 

 for trim, i 1 ft. for keel clearance and + 1.5 for W/D. The ac- 

 curacy of the resistance prediction is of particular importance ; the 

 fact that measured drag is higher than predicted is probably due lar- 

 gely to the one to three foot waves encountered during most calm 

 water trials. 



Calm Water Stabilit y 



Foilborne stability in calm water is most easily assessed by 



301 



