Your instructor will demonstrate the stability characteristics of the T-34C aircraft by trimming
for straight and level balanced flight. He will then place the aircraft in various attitudes and
permit the aircraft to return to straight and level balanced flight, demonstrating the necessity and
ease of proper use of trim. As discussed earlier in this chapter, the T-34C is capable of
equilibrium flight in all airspeeds and configurations that you will encounter. That is, for all
changes in power, airspeed, and configurations, the aircraft is able to maintain a "hands-off"
straight and level balanced flight condition, but will require a CHANGE IN TRIM SETTING
for those changes. Further discussion on the use of trim will occur later in this chapter.
An aircraft is said to be trimmed if all moments in pitch, roll, and yaw are equal to zero. The
establishment of equilibrium at various conditions of flight is the function of the controls and
will be accomplished by pilot effort and trim tabs. Pilot effort is necessary to establish
equilibrium conditions and trim tabs will be used to hold the desired conditions (i.e., reduce
During training, trim will be of extreme importance and trimming rapidly and properly will
become a habit. The necessity to trim the T-34C cannot be overemphasized. When all of the
pilot's energy is consumed fighting the controls, little is left over for flying the aircraft and
maintaining situational awareness.
3. Control. Control is concerned with the maneuverability of the aircraft. Although the T-
34C aircraft is "inherently stable" due to its positive and static and dynamic stability, it is not so
stable as to inhibit aircraft maneuverability. Since the T-34C is a primary trainer, it was
designed to have controls capable of aerobatic flight, yet not so sensitive as to make the aircraft
difficult to control or allow aircraft limits to be easily exceeded. Generally speaking, control
forces are highest in the directional axis (ailerons). The magnitude of these forces varies
depending on the airspeed, trim setting and the amount of deflection. At higher speeds, controls
become difficult to deflect due to higher dynamic pressure impinging on the control surfaces.
Although the higher dynamic pressure makes the controls more effective, resulting in a greater
aircraft reaction for a given control deflection, the forces required to obtain that control
deflection are higher. Trim setting affects control forces in that the further the aircraft is flown
from its trimmed airspeed, the greater the forces required (in all axes) to maintain balanced flight
conditions. These forces serve as physical cues to the pilot that the aircraft has deviated from its
trimmed airspeed. The T-34C is capable of equilibrium flight in nearly all airspeeds and
configurations that you will encounter. That is, for nearly all changes in power, airspeed, and
configurations, the aircraft is able to maintain a hands-off straight and level flight condition, but
will require a change in trim setting for those changes.
In earlier discussions it was shown that an airplane would fly as long as the wing is creating
sufficient lift to counteract the load imposed on it. When the lift is completely lost the airplane
stalls. Remember that the direct cause of every stall is an excessive angle of attack. There are
any numbers of flight maneuvers which may produce an increase in the angle of attack, but the
stall does not occur until the angle of attack becomes excessive.
2-8 INTRODUCTION TO T-34C AERODYNAMICS