Stall Characteristics Stall Characteristics

   Because of engineering design variations, the stall characteristics for all airplanes cannot be specifically described; however, the similarities found in light general aviation training type airplanes are noteworthy enough to be considered. It will be noted that the power on and power off stall warning indications will be different. The power off stall will have less noticeable clues (buffeting, shaking) than the power on stall. In the power off stall the predominant clue can be the elevator control position (full up elevator against the stops) and high sink rate. When performing the power on stall the buffeting will likely be the predominant clue that provides a positive indication of the stall. For the purpose of airplane certification, the stall warning may be furnished either through the inherent aerodynamic qualities of the airplane or by a stall warning device that will give a clear distinguishable indication of the stall. Most modern airplanes are equipped with a stall warning device.

   The factors that affect the stalling characteristics of the airplane are: balance (load distribution), bank (wing loading), pitch attitude (critical angle of attack), coordination (control movement), drag (gear or flaps), and power. The pilot should learn the effect of each on the stall characteristics of the airplane being flown and what should be done to effect the proper correction. It should be reemphasized here that a stall can occur at any airspeed, in any attitude, or at any power setting, depending on the total number of factors affecting the particular airplane.

   A number of factors may be induced as the result of other factors. For example, when the airplane is in a nose high turning attitude, the angle of bank has a tendency to increase. This occurs because with the airspeed decreasing, the airplane begins flying in a smaller and smaller arc. Since the outer wing is moving in a larger radius and thus traveling faster than the inner wing, it has more lift and causes an overbanking tendency. At the same time, because of the decreasing airspeed and decreasing lift on both wings, the pitch attitude tends to lower. In addition, since the airspeed is decreasing while the power setting remains constant, the effect of torque becomes more prominent, causing the airplane to yaw.

   During the practice of nose high turning stalls, to compensate for these factors and to maintain a constant flight attitude until the stall occurs, aileron pressure must be continually adjusted to keep the bank attitude constant. At the same time, back elevator pressure must be continually increased to maintain the pitch attitude, as well as right rudder pressure increased to prevent adverse yaw from changing the turn rate. If the bank is allowed to become too steep, the vertical component of lift decreases and makes it even more difficult to maintain a constant pitch attitude.

   Whenever practicing turning stalls, a constant pitch and bank attitude should be maintained until the stall occurs. Whatever control pressures are necessary should be applied even though the controls appear to be crossed (aileron pressure in one direction, rudder pressure in the opposite direction). During the entry to a power on turning stall to the right in particular, the controls will be crossed to some extent. This is due to right rudder pressure being used to overcome torque and left aileron pressure being used to prevent the bank from increasing.