To demonstrate this in flight, an attempt can be made to turn to the right without using the rudder
pedals. As right aileron pressure is applied, the airplane rolls into a right bank and tries to turn to
the right. But the adverse yaw, or the drag on the downward deflected left aileron, pulls the
airplane's nose to the left. The airplane banks, but it turns hesitantly and sideslips. This is
undesirable and corrective action should be taken by applying right rudder pressure.
When right rudder pressure is applied simultaneously with right aileron pressure, it keeps the
airplane from yawing opposite to the desired direction of turn. In fact, the rudder must be used
because the ailerons were used. Therefore, neither of those controls should be used separately
when making normal turns.
Rudder. The rudder controls movement of the airplane about its vertical axis. This is the
motion called yaw. Like the other primary control surfaces, the rudder is a movable surface
hinged to the vertical stabilizer. Two rudder pedals control movement of the rudder-left and
right. Its action is very much like that of the elevators, except that it moves in a different plane;
the rudder deflects from side to side instead of up and down. When the rudder is deflected to one
side, it protrudes into the airflow, causing a horizontal force to be exerted in the opposite
direction. This pushes the tail of the airplane in that direction and yaws the nose in the desired
direction. When rudder is used for steering during ground taxiing, the propeller slipstream
provides the force to yaw or turn the airplane in the desired direction. (The T-34C does NOT
have a steerable nosewheel.)
As mentioned earlier, the primary purpose of the rudder in flight is to counteract the effect of
adverse yaw and to help provide directional control of the airplane. In flight, the rudder does not
turn the airplane; instead, the force of the horizontal component of wing lift turns the airplane
when the wings are banked. As in the demonstration of turning by use of ailerons alone, this can
be verified by flying straight and level and then, after taking the hands off the control stick,
trying to turn to the right by applying right rudder pressure only. At first it may seem to work
pretty well. The airplane will turn to the right, but it will also skid to the left (a skid in a turn is
an unbalanced flight condition caused by insufficient angle of bank for a given radius of turn).
Since the airplane possesses inherent stability, it will tend to stop the skid by banking itself to the
If the pilot were now to neutralize the rudder, only a shallow banking turn would result.
However, inasmuch as the purpose of this demonstration is to make a turn using only the rudder,
continue to hold right rudder pressure. Since the airplane is slightly banked to the right, the
rudder will force the nose of the airplane downward to the right. The reason for this is that
yawing is the only movement the rudder can produce. As a result, the nose yaws downward, the
airspeed increases, and the airplane starts losing altitude. At the same time, the airplane, being
stable, attempts to stop the increased skidding by banking more steeply. The more steeply it
banks, the more the nose is yawed downward by the right rudder action. The net result of
holding rudder alone is a descending spiral unless back elevator pressure is applied. Thus, it can
be seen that rudder alone cannot produce a balanced turn. Coordinated application of aileron,
rudder, and elevator pressure will produce a balanced flight condition.
USE AND EFFECT OF CONTROLS 3-3