Sec. it.S 



FORCE AND FLOW DATA FOR HYDROFOILS 



81 



08 06 04 OZ 



X-Diatonce from LE, Froction of Chord c 



Fig. 44.G Typical Chordwise Pressure Distri- 

 bution ON Face and Back op a Symmetric Hydro- 

 foil AT AN Angle of Attack 



At the nose the dynamic pressure equals the ram 

 pressure 0.5pC/« or LOOg. On the back of a sym- 

 metric section working at a small angle of attack, 

 the pressure coefficient usually drops very rapidly 

 with distance abaft the nose, to a value of 0.0 

 at 2 or 3 per cent of the chord. Within from 5 

 to 20 per cent of the chord length from the leading 

 edge it increases numerically to a large negative 

 value. Then it diminishes with distance abaft 

 the nose, until at about 0.9 or more of the chord 

 length the pressure coefficient may reach zero 

 or have a small positive value. On the face 

 of the section, in a typical case with a small angle 

 of attack, the pressure coefficient drops from its 

 value of LOO at the nose to a small positive value, 



which it holds for most of the chord Icnglh from 

 nose to tail. 



Pressure-distribution curves for shaft-strut sec- 

 tions in the form of thick symmetric hydrofoils 

 are given by M. S. Macovsky, W. L. Stracke, and 

 J. V. Wehausen in TMB Report 879, issued in 

 January 1948. Two typical sections were tested, 

 having a common thickness ratio of 1/6. One was 

 the Bureau of Ships standard strut section, with a 

 pointed tail, and the other the TMB-EPH 

 (Ellipse-Parabola-Hyperbola) section, with a 

 rounded tail. The pressure distributions were 

 measured for angles of attack of 0, 5, 10, and 

 15 deg. 



Fig. 44.H Shapes and Characteristics of Seven 

 Symmetric Hydrofoils for Which the Pressure 

 Distribution Is Given in Fig. 44.1 



Fig. 44.1 Chordwise Pressure Distribution on 

 the Surfaces op the Seven Hydrofoils op Fig. 44.H 



Many similar diagrams and other data on the 

 distribution of velocity and pressure around 

 airfoils and hydrofoils are published in the tech- 

 nical hterature. Among the sources may be 

 mentioned: 



(1) Zeitschrift fiir Flugtechnik und Motorluftschiffahrt, 

 26 Apr 1913, Vol. IV, No. 8, Fig. 9, p. 92. A series 

 of 56 diagrams show the pressure distribution over 

 the face and back of eight sections of the blade 

 of an airscrew at eight dilTerent radii, from 0.25 

 to 1.00 iJniai ■ The measurements were made at 

 seven values of the real-slip ratio, from -f-O.ll to 

 -1-1.00, and from -0.06 to -0.15. As is to be 

 expected, the distribution of pressure over face and 



