Stalls -Cont. - P-330

T-34C CONTACT

CHAPTER TWO

It must be emphasized that the stalling speed of a particular airplane is not a fixed value for all

flight situations. However, a given airplane will always stall at the same angle of attack

regardless of airspeed, weight, load factor, or density altitude. Each airplane has a particular

angle of attack where the airflow separates from the upper surface of the wing and the stall

occurs. Each airplane has only one specific angle of attack where the stall occurs. The airplane

can be stalled in straight and level flight by flying too slowly. As the airspeed is being

decreased, the angle of attack must be increased to retain the lift required for maintaining

altitude. The slower the airspeed becomes, the more the angle of attack must be increased.

Eventually an angle of attack is reached which will result in the wing not producing enough lift

to support the airplane and it will start settling. If the airspeed is reduced further, the airplane

will stall since the angle of attack has exceeded the critical angle and the airflow over the wing is

disrupted.

In naval aviation, there is great importance assigned to precise control of an aircraft at high angle

of attack conditions. Safe operation in carrier aviation demands the ultimate in precision flying

at low airspeed. The aerodynamic lift characteristics of an airplane must be fully understood by

the student naval aviator as well as the seasoned "fleet pilot" for obvious safety reasons.

Additionally, mission requirements and their execution may depend on the pilot's own

capabilities and grasp of these basic concepts.

During flight maneuvers, landing approach, takeoff, etc. the airplane will stall IF THE

CRITICAL ANGLE OF ATTACK IS EXCEEDED. The AIRSPEED at which stall occurs

will be determined by weight, load factor, altitude, and configuration, but the stall angle of attack

remains unaffected. At any particular altitude, the indicated stall speed is a function of weight

and load factor. An increase in altitude will produce a decrease in density and an increase in true

airspeed. Also, an increase in altitude will alter compressibility and airflow viscosity, which will

cause the indicated stall speeds to increase.

Modern airplanes are characterized by having a large percentage of their maximum gross weight

as fuel. Most Navy inventory aircraft carry 25-40 percent of their total gross weight in this

manner. Hence, the gross weight and stall speed of the airplane can vary considerably throughout

the flight. A general "rule of thumb" is that a 2% change in weight will cause a 1% change in

stall speed. Note that for the T-34C, a full load of fuel is only approximately 18% of the

aircraft's gross weight. Fuel burnoff will consequently have a diminished effect on stall speed as

compared to most naval aircraft in the inventory.

Load factor/centrifugal force. Turning flight and maneuvers produce an effect on stall speed,

which is similar to the effect of weight. The stalling speed of an airplane is higher in a level turn

than in straight and level flight. This is because centrifugal force is added to the airplane's

weight, and the wing must produce sufficient additional lift to counterbalance the load imposed

by the combination of centrifugal force and weight. In a turn, the necessary additional lift is

acquired by applying back pressure to the elevator control. This increases the wing's angle of

attack, and results in increased lift. As stated earlier, the angle of attack must increase as the

bank angle increases to counteract the increasing load caused by centrifugal force. If at any time

during a turn the angle of attack becomes excessive, the airplane will stall. Thus, the aircraft in a

INTRODUCTION TO T-34C AERODYNAMICS 2-9