NAVWEPS 00-BOT-80 
STABILITY ,AND CONTROL 
slipstream creates a normal force at the plane 
of the propeller similar to a wing creating lift 
by deflecting an airstream. As this normal 
force will increase with an increase in airplane 
angle of attack, the effect will be destabilizing 
when the propeller is ahead of the cg. The 
magnitude of the unstable contribution de- 
pends on the distance from the c.g. to the 
propeller and is largest at high power and low 
dynamic pressure. The normal force created 
thrust line is below the c.g., thrust produces a 
positive or noseup moment and the effect is de- 
stabilizing. On the other hand, if the thrust 
line is ,located above the c.g., a negative 
moment is created and the effect is stabilizing. 
A propeller or inlet duct located ahead of 
the c.g. contributes a destabilizing effect. As 
shown in figure 4.11, a rotating propeller in- 
clined to the windstream causes a deflection 
of the airflow. The momentum change of the 
261