Monday, February 9, 2009

Stall Characteristics

Because of engineering design variations, the stall
characteristics for all airplanes cannot be specifically
described; however, the similarities found in small
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 a high descent 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
airplanes are equipped with a stall warning device.

The factors that affect the stalling characteristics of the
airplane are balance, bank, pitch attitude, coordination,
drag, and power. The pilot should learn the effect of the
stall characteristics of the airplane being flown and the
proper correction. It should be reemphasized 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.

Anumber 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 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 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 power-on 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 keep the ball centered and 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 cls 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.

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