138 THE APPEARANCE OF JAWS v. 3 



corresponds to a motion of 3 m.p.h. in water. The lateral force was 

 measured when the body was made to yaw at various angles. The 



+0-2 

 + 0-1 



-15 -ipl^^ f 



-0 



-0-2 



+5° +10° +15° 



D 



+ 5" oX S+Yo° +iV 



-0-5 



Fig. 94. A. Results of yawing test on model of Mustelus without fins. The lateral force 

 is plotted as a light full line, drag force as a light broken line; yawing moment about 

 centre of gravity as full heavy line. Abscissae show the angle of attack in degrees, 

 ordinates the lateral force and drag in pounds weight, yawing moment in in. -lb. X ^j. 

 n. Yawing test similar to (a) but with the fins behind the centre of gravity in place. 



C. Yawing test with all median fins in place. 



D. Pitching test on model of Mustelus with all fins intact and pectoral fins set at an 

 angle of incidence of 8°. Lift force is shown as a light full line, drag force as a light 

 broken line, pitching moment about the centre of gravity as a heavy full line. 



(From Harris.) 



results showed that the equilibrium in this plane is quite unstable; a 

 slight turn off the direct course would produce a turning moment 

 tending to increase still further the deflection (Fig. 94). This is a 

 well-known property of all airship hulls, and is known as the 'unstable 

 moment' of the hull. It is corrected in the airship by the addition of 



