Secondary Flight Controls-Trim Devices

T-34C CONTACT

CHAPTER THREE

After learning how the airplane will react when the flight controls are used, the pilot must learn

how to use them properly. Rough and erratic usage of all or any one of the controls will cause

the airplane to react accordingly; therefore, the pilot must form the habit of applying pressures

smoothly and evenly.

The amount of force the airflow exerts on the control surface is governed by the airspeed and the

degree that the surface is moved out of its neutral or streamlined position. Since the airspeed

will not be the same in all maneuvers, the amount of control surface movement is of little

importance. However, it is important that the pilot maneuver the airplane by applying sufficient

control pressures to obtain a desired result, regardless of how far the control surfaces are actually

moved.

The pilot's feet should rest comfortably against the rudder pedals. Both heels should support the

weight of the feet on the cockpit floor with the ball of each foot touching the individual rudder

pedals. The legs and feet should not be tense; they must be relaxed just as when driving an

automobile. The pedals should be adjusted so that the pilot with full throw of the rudder still has

a slight flex in the knee.

When using the rudder pedals, pressure should be applied smoothly and evenly by pressing with

the ball of one foot just as when using the brakes of an automobile. The rudder pedals are

interconnected and act in opposite directions; when pressure is applied to one pedal, pressure on

the other must be relaxed proportionally. When the rudder pedal must be moved significantly,

heavy pressure changes should be made by applying the pressure with the ball of the foot while

the heels slide along the cockpit floor. Remember, the ball of each foot must rest comfortably on

the rudder pedals so that even slight pressure changes can be felt. Care must be taken NOT to

apply any brake pressure inadvertently (i.e., when in the landing pattern).

During flight, it is the pressure the pilot exerts on the control stick and rudder pedals that causes

the airplane to move about its axes. When a control surface is moved out of its streamlined

position (even slightly), the air flowing past it will exert a force against it and will try to return it

to its streamlined position. It is this force that the pilot feels as pressure on the control stick and

the rudder pedals.

302.

SECONDARY FLIGHT CONTROLS - TRIM DEVICES

The secondary flight controls are the trim tabs. They are used for trimming and balancing the

airplane in flight and to reduce the force required of the pilot in actuating the primary flight

control surfaces. These tabs are really small airfoils attached to, or recessed into, the trailing

edge of the primary control surfaces. When an airplane's flight conditions (attitude, power,

airspeed, loading, and configuration) are changed, the control pressures required to maintain the

new flight conditions are affected by the resulting changes in aerodynamic forces. To relieve the

pilot of this tiring effort, the T-34C is equipped with trim tabs with which to trim the airplane for

balanced flight.

A trim tab is a small, adjustable hinged surface, located on the trailing edge of the aileron,

rudder, or elevator control surface. It is used to maintain the flight surfaces in balance in

USE AND EFFECT OF CONTROLS 3-5