Yaw Forces

CHG 2 T-34C CONTACT

CHAPTER TWO

impeding force is needed to overcome centrifugal force so that the airplane moves in the desired

direction. The lift of the wings provides this counteracting force when the airplane's wings are

banked in the desired direction. Refer to the section on Turning Flight later in this chapter.

Since the airplane is in a banked attitude during a properly executed turn, the pilot will feel the

centrifugal force by increased seat pressure, rather than the feeling of being forced to the side as

is experienced in a rapidly turning automobile. The amount of force (G force) felt by seat

pressure depends on the angle of bank. The pilot will, however, be forced to the side of the

airplane (as in an automobile) if a turn is improperly made and the airplane is made to slip or

skid.

203.

YAW FORCES

One other force which affects the aircraft during certain conditions of flight and which will be

frequently referred to in the discussions on various flight maneuvers is torque effect or "left

turning tendency." It is probably one of the least understood forces that affect an aircraft in

flight. Torque effect is the force which causes the airplane to have a tendency to swerve (yaw) to

the left, and is created by the clockwise rotation of the engine and the propeller. There are four

factors that contribute to this yawing tendency:

Torque reaction to the engine and propeller.

The propeller's gyroscopic effect.

The corkscrewing effect of the propeller slipstream.

The asymmetrical loading of the propeller (P-factor).

It is important that pilots understand why these factors contribute to torque effect.

Torque reaction. Torque reaction can be understood by visualizing a rubber band

powered model airplane. Wind the rubber band in a manner that will unwind and rotate

the propeller in a clockwise direction. If the fuselage is released while the propeller is

held the fuselage will rotate in a counterclockwise direction (looking from the rear).

The effect of torque reaction is the same in a real propeller-driven airplane except that,

instead of the propeller being held by hand, its rotation is resisted by air. This counter-

rotational force causes the aircraft to try to roll to the left. In the case of a real airplane,

the force is stronger when power is significantly advanced while the aircraft is flying at

very slow airspeeds and high power settings.

Gyroscopic precession. The second factor that causes the tendency of an airplane to

yaw is the gyroscopic properties of the propeller. Here, we are concerned with

gyroscopic precession, which is the resultant action or deflection of a spinning object

when a force is applied to the outer rim of its rotational mass. When a force is applied

to the object's axis, it is the same as applying the force to the outer rim. If the axis of a

spinning gyroscope (propeller in this case) is tilted, the resulting force will be exerted

90 ahead in the direction of rotation and in the same direction as the applied force.

Example: As the aircraft nose is raised, the top of the propeller's plane of rotation is

INTRODUCTION TO T-34C AERODYNAMICS 2-3