Stability and Control - P-330

CHAPTER TWO

T-34C CONTACT

forced aft. This results in an opposite (forward) force 90 further along the prop arc, in

the direction of rotation (the right side of the prop). Conversely, as the bottom of the

prop arc is forced forward, the left side of the prop precesses aft. That force will be

particularly noticeable during takeoff if an abrupt change in attitude is made. The

amount of force created by this precession is directly related to the rate at which the

propeller axis is changed.

Propeller slipstream. The third factor that causes the airplane's left yawing tendency is

the corkscrewing of the propeller slipstream, acting against the side of the fuselage and

tail surfaces. The high-speed rotation of an airplane propeller results in a corkscrewing

rotation to the slipstream as it moves rearward. At high propeller speeds and low

forward speed, as in the initial part of a takeoff, the corkscrewing flow is compact and

imposes considerable side forces on the airplane. As the airplane's forward speed

increases, the corkscrew motion of the slipstream loosens or elongates, resulting in a

straighter flow of air along the side of the fuselage towards the airplane's tail.

When this corkscrewing slipstream strikes the side of the fuselage and the vertical tail

surface at airspeeds less than cruising, it produces a yawing motion, which tends to

revolve the airplane around its vertical axis. Since in the T-34, propeller rotation is

clockwise as viewed from the cockpit, the slipstream strikes the vertical tail surface on

the left side, thus pushing the tail to the right and yawing the nose of the airplane to the

left.

Asymmetrical loading of the propeller. The fourth factor which causes the left yawing

tendency is the asymmetrical loading of the propeller, frequently referred to as P-factor.

When an airplane is flying with a high angle of attack (with the propeller axis inclined),

the bite of the downward-moving propeller blade is greater than the bite of the upward-

moving blade, meeting the oncoming relative wind at a greater angle of attack than the

upward-moving blade. Consequently, there is greater thrust on the downward-moving

blade on the right side and this force causes the airplane to yaw to the left. At low

speeds the yawing tendency caused by P-factor is greater because the airplane is at a

high angle of attack. Conversely, as the speed of the airplane is increased and the

airplane's angle of attack is reduced, the asymmetrical loading decreases and the

turning tendency is decreased.

204.

STABILITY AND CONTROL

Most types of naval aircraft have been designed with satisfactory handling qualities in addition to

adequate performance. In particular, the T-34C is stable enough to maintain uniform flight

conditions, recover from disturbances (such as turbulence), and minimize pilot workload. It has

sufficient controllability to achieve the desired performance. However, there are certain

conditions of flight which produce the most critical requirements of stability and control. These

conditions must be understood and respected to accomplish safe and efficient operation of the

aircraft.

2-4 INTRODUCTION TO T-34C AERODYNAMICS