Turn Indicator and Balance Ball

CHAPTER ONE

T-34C INSTRUMENTS

Turn Indicator and Balance Ball

A complete description of this instrument can be found in NATOPS. In a practical

aerodynamic sense, the balance ball indicator (Figure 17) shows directly and

immediately the longitudinal alignment of the aircraft, nose to tail. This information

enables the pilot to detect and eliminate aircraft yaw by trimming the ball to the

center of the inclinometer (while holding the aircraft attitude constant on the attitude

gyro), thus maintaining balanced flight.

Use and Limitations. The turn needle (Figure 17) is a wing attitude crosscheck

instrument in constantrate turns. The needle is calibrated for a fourminute turn;

that is, if the aircraft is in a turn with one needlewidth deflection, it will take four

minutes for the aircraft to turn 360. This means that a oneneedlewidth deflection

of the needle yields a turn of approximately 1 per second. If a twoneedlewidth

deflection is maintained, the aircraft will turn twice as fast, or at 3 per second. At any

given airspeed, a specific angle of bank (AOB) may be set on the gyro, which will

give an exact needlewidth deflection if in balanced flight (ball centered). If in

unbalanced flight, we would have difficulty coordinating the gyro attitude and turn

indicator for a specific turning rate.

Similarly, if the wings were level and the ball displaced, a yaw (turn) develops in a

direction opposite from the displaced ball, adversely affecting heading control.

If the ball is displaced to the right or left, which will occur when a slip or skid takes

place, it indicates unbalanced flight. This condition may be corrected by application

of rudder pedal pressure on the side to which the ball is displaced. When the ball is

again centered, use rudder trim to relieve control pressure. During the trimming

operation, the pilot must ensure the attitude is controlled by observing the miniature

airplane on the gyro. If the attitude (nose and wing) is not held constant during the

rudder trimming operation, the aircraft nose will yaw as rudder pressure and/or trim is

applied and the wings will attempt to roll in the direction of the yawing moment.

Therefore, the pilot should trim the balance ball only when stabilizing the nose and

wing attitude on the gyro. Finally, check the ball position and repeat the trimming

steps if necessary.

1-10 INTRODUCTION TO BASIC INSTRUMENTS