Stability and Control - P-330_wch50030

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CHAPTER TWO
T-34C CONTACT
forced aft. This results in an opposite (forward) force 90º 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.
c.
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.
d.
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

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