Saturday, February 14, 2009

Accelerated Stalls

Though the stalls just discussed normally occur at a
specific airspeed, the pilot must thoroughly understand

that all stalls result solely from attempts to fly at
excessively high angles of attack. During flight, the
angle of attack of an airplane wing is determined by a
number of factors, the most important of which are the
airspeed, the gross weight of the airplane, and the load
factors imposed by maneuvering.

At the same gross weight, airplane configuration, and
power setting, a given airplane will consistently stall at
the same indicated airspeed if no acceleration is
involved. The airplane will, however, stall at a higher
indicated airspeed when excessive maneuvering loads
are imposed by steep turns, pull-ups, or other abrupt
changes in its flightpath. Stalls entered from such flight
situations are called "accelerated maneuver stalls," a
term, which has no reference to the airspeeds involved.

Stalls which result from abrupt maneuvers tend to be
more rapid, or severe, than the unaccelerated stalls, and
because they occur at higher-than-normal airspeeds,
and/or may occur at lower than anticipated pitch
attitudes, they may be unexpected by an inexperienced
pilot. Failure to take immediate steps toward recovery
when an accelerated stall occurs may result
in a complete loss of flight control, notably,
power-on spins.

This stall should never be practiced with wing flaps in
the extended position due to the lower "G" load
limitations in that configuration.

Accelerated maneuver stalls should not be performed
in any airplane, which is prohibited from such
maneuvers by its type certification restrictions or
Airplane Flight Manual (AFM) and/or Pilot's
Operating Handbook (POH). If they are permitted,
they should be performed with a bank of
approximately 45°, and in no case at a speed greater

than the airplane manufacturer's recommended
airspeeds or the design maneuvering speed specified
for the airplane. The design maneuvering speed is the
maximum speed at which the airplane can be stalled or
full available aerodynamic control will not exceed the
airplane's limit load factor. At or below this speed, the
airplane will usually stall before the limit load factor
can be exceeded. Those speeds must not be exceeded
because of the extremely high structural loads that are
imposed on the airplane, especially if there is
turbulence. In most cases, these stalls should be
performed at no more than 1.2 times the normal
stall speed.

The objective of demonstrating accelerated stalls is not
to develop competency in setting up the stall, but rather
to learn how they may occur and to develop the ability
to recognize such stalls immediately, and to take
prompt, effective recovery action. It is important that
recoveries are made at the first indication of a stall, or
immediately after the stall has fully developed; a
prolonged stall condition should never be allowed.

An airplane will stall during a coordinated steep turn
exactly as it does from straight flight, except that the
pitching and rolling actions tend to be more sudden. If
the airplane is slipping toward the inside of the turn at
the time the stall occurs, it tends to roll rapidly toward
the outside of the turn as the nose pitches down
because the outside wing stalls before the inside wing.
If the airplane is skidding toward the outside of the
turn, it will have a tendency to roll to the inside of the
turn because the inside wing stalls first. If the
coordination of the turn at the time of the stall is
accurate, the airplane's nose will pitch away from the
pilot just as it does in a straight flight stall, since both
wings stall simultaneously.

An accelerated stall demonstration is entered by
establishing the desired flight attitude, then smoothly,
firmly, and progressively increasing the angle of attack
until a stall occurs. Because of the rapidly changing
flight attitude, sudden stall entry, and possible loss of
altitude, it is extremely vital that the area be clear of
other aircraft and the entry altitude be adequate for safe

This demonstration stall, as in all stalls, is
accomplished by exerting excessive back-elevator
pressure. Most frequently it would occur during
improperly executed steep turns, stall and spin
recoveries, and pullouts from steep dives. The
objectives are to determine the stall characteristics of
the airplane and develop the ability to instinctively
recover at the onset of a stall at other-than-normal stall
speed or flight attitudes. An accelerated stall, although
usually demonstrated in steep turns, may actually be
encountered any time excessive back-elevator pressure

is applied and/or the angle of attack is increased
too rapidly.

From straight-and-level flight at maneuvering speed
or less, the airplane should be rolled into a steep level
flight turn and back-elevator pressure gradually
applied. After the turn and bank are established,
back-elevator pressure should be smoothly and
steadily increased. The resulting apparent centrifugal
force will push the pilot's body down in the seat,
increase the wing loading, and decrease the airspeed.
After the airspeed reaches the design maneuvering
speed or within 20 knots above the unaccelerated stall
speed, back-elevator pressure should be firmly
increased until a definite stall occurs. These speed
restrictions must be observed to prevent exceeding the
load limit of the airplane.

When the airplane stalls, recovery should be made
promptly, by releasing sufficient back-elevator
pressure and increasing power to reduce the angle of
attack. If an uncoordinated turn is made, one wing may
tend to drop suddenly, causing the airplane to roll in
that direction. If this occurs, the excessive back-
elevator pressure must be released, power added, and
the airplane returned to straight-and-level flight with
coordinated control pressure.

The pilot should recognize when the stall is imminent
and take prompt action to prevent a completely stalled
condition. It is imperative that a prolonged stall,
excessive airspeed, excessive loss of altitude, or spin
be avoided.

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