Scan Patterns

T-34C INSTRUMENTS

CHAPTER TWO

Continue lowering the nose to set the attitude of 2 down and trim left rudder, nose up. When

stable, reset P.A.T. and continue to scan for wings level descent.

How to Trim. The generally accepted sequence for trimming the aircraft is: rudder,

elevator, and aileron. The rudder trim is usually initiated first because it seems

difficult for most pilots to hold the ball centered with rudder for an extended period

and secondly, yaw affects both nose and aileron trim. Thus, if rudder were trimmed

last, both nose and aileron would have to be retrimmed to some extent.

To trim, first set a maneuvering attitude on the gyro and center the ball using light

pressures on the controls. Use peripheral vision to note ball centered. Note the

pressures needed to hold this new balanced attitude and move the trim tabs smoothly

until the pressures are removed. Relax hand and foot pressure on controls to see if

the attitude remains. Do not let go of the stick; simply relax. If the aircraft needs

further "fine" trimming, you will feel the attitude wanting to change and can then trim

out the final pressures. Note that most students tend to undertrim and move tabs too

slowly. Do not be afraid of overtrimming slightly. Fine or final trim will also correct

that.

This trimming sequence will take much less time than it does to read about it and it is

the key to precision flight.

Confirming Attitude With Crosscheck Scan

Once we have established an attitude and trimmed it, we must crosscheck it with the proper

instruments to verify correct attitude.

Aircraft instruments are not absolutely accurate. The attitude gyro is subject to precessional

errors in turns and accelerations and must be crosschecked with other instruments. In addition,

the small size of the gyro makes it difficult to see small changes in attitude.

To explain the scan sequence, we shall use an analogy. Compare attitude flying with the tuning

of an old car radio. We set an initial attitude on the gyro just as we set the desired frequency

with the station selector buttons. Neither is necessarily perfect, so we crosscheck the attitude

with other instruments, just as we would dial back and forth across a frequency range for best

reception. Then we "fine tune" by checking performance in the aircraft, for example, a little

more power for airspeed in straight and level. Just as we would adjust volume prior to receiving

the best signal, it is likewise useless to check performance instruments prior to establishing and

crosschecking an attitude.

202.

SCAN PATTERNS

In order to determine the aircraft's attitude quickly and effectively, you must know what

instruments to scan for a particular maneuver. The following section lists the correct instruments

or scan "pattern" for every situation. It is mandatory that the student commits these patterns to

memory.

BASIC INSTRUMENTS GENERAL PROCEDURES 2-5