Canadian Hydrofoil Program. Hydrodynamics and Simulation 



A major concern of the experimental program was upper sur- 

 face design, with the objective of inhibiting and controlling intermit- 

 tent flow reattachment. The leading edge was made as fine as practic- 

 able and, to enforce reattachment to occur in stages and hence re- 

 duce the severity of accompanying lift increases, two additional break 

 points were incorporated in the upper surface, at 66% and 87% chord. 

 A major problem of the initial manned model trials was that the an- 

 hedral foils served as fences to inhibit the spread of ventilation down 

 the dihedrals, leading to cyclic pitching at speeds close to intersec- 

 tion emergence. This was overcome by adding another large upper 

 surface spoiler to the anhedral sections in the neighbourhood of the 

 intersection. 



The most comprehensive set of quarter scale towing tank data 

 was obtained at the National Physical Laboratory (NPL) under 

 Froude- scaled conditions, providing good definition of bow foil cha- 

 racteristics. (Figures 6 and 7). Data points have been coded to show 

 the spanwise extent of leading edge ventilation down the dihedral foils 

 from the upper surface. (For all test conditions of interest, the ca- 

 vities behind the midback spoilers remained consistently ventilated.) 

 Spanwise extent of leading edge ventilation is indicated by the degree 

 of openness of the points, e.g. : 



100 % fully open 



50 % 50% open 



0% fully closed I 



Figure 9 shows that the lift-curve slope decreases gradually with in- 

 creasing rake angle as ventilation spreads down the leading edge of 

 the dihedrals. 



The most interesting quarter scale tank tests took place at 

 the Lockheed Underwater Missile Facility (LUMF) , where both ca- 

 vitation and Froude numbers were scaled. Cavitation scaling was 

 found to have no significant effect on flow state, lift or drag. An 

 equally significant finding was that lift values obtained at NPL were 

 much higher than at LUMF (Figure 8). These differences were later 

 shown to be due in large part to deterioration of the foil surfaces and 

 leading edges during the time interval between the two series of tests. 



It was possible to estimate full scale bow foil lift characteris- 



297 



