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Below is an excerpt from the FAA's Airplane
Flying Handbook - FAA-H-8083-3B (cpt4,
pages 3-4)
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It should help
you understand the underlying "what, why,
and how" of this maneuver.
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If you want to
read the entire chapter:
Chapter
4: Maintaining Aircraft Control: Upset
Prevention and Recovery Training
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Slow Flight
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Slow flight is
when the airplane Angle of Attack (AOA), is
just under the AOA which will cause an aerodynamic
buffet or a warning from a stall warning device
if equipped with one. A small increase in AOA
may result in an impending stall, which increases
the risk of an actual stall. In most normal
flight operations the airplane would not be
flown close to the stall-warning AOA or critical
AOA, but because the airplane is flown at higher
AOAs, and thus reduced speeds in the takeoff/departure
and approach/landing phases of flight, learning
to fly at reduced airspeeds is essential. In
these phases of flight, the airplane's close
proximity to the ground would make loss of control
catastrophic; therefore, the pilot must be proficient
in slow flight.
The objective of maneuvering in slow flight
is to understand the flight characteristics
and how the airplane's flight controls feel
near its aerodynamic buffet or stall-warning.
It also helps to develop the pilot's recognition
of how the airplane feels, sounds, and looks
when a stall is impending. These characteristics
include, degraded response to control inputs
and difficulty maintaining altitude. Practicing
slow flight will help pilots recognize an imminent
stall not only from the feel of the controls,
but also from visual cues, aural indications,
and instrument indications.
For pilot training and testing purposes, slow
flight includes two main elements:
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1. Slowing to,
maneuvering at, and recovering from an airspeed
at which the airplane is still capable of maintaining
controlled flight without activating the stall
warning-5 to 10 knots above the 1G stall speed
is a good target; and
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2. Performing
slow flight in configurations appropriate to
takeoffs, climbs, descents, approaches to landing,
and go-arounds.
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Slow flight should be introduced with the airspeed
sufficiently above the stall to permit safe
maneuvering, but close enough to the stall warning
for the pilot to experience the characteristics
of flight at a very low airspeed.
When practicing slow flight, a pilot learns
to divide attention between aircraft control
and other demands. How the airplane feels at
the slower airspeeds aids the pilot in learning
that as airspeed decreases, control effectiveness
decreases. For instance, reducing airspeed from
30 knots to 20 knots above the stalling speed
will result in a certain loss of effectiveness
of flight control inputs because of less airflow
over the control surfaces. As airspeed is further
reduced, the control effectiveness is further
reduced and the reduced airflow over the control
surfaces results in larger control movements
being required to create the same response.
Pilots sometimes refer to the feel of this reduced
effectiveness as "sloppy" or "mushy"
controls.
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Performing the Slow Flight Maneuver
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Slow flight should
be practiced in straight-and-level flight, straight-ahead
climbs and climbing medium-banked (approximately
20 degrees) turns, and straight-ahead power-off
gliding descents and descending turns to represent
the takeoff and landing phases of flight. Slow
flight training should include slowing the airplane
smoothly and promptly from cruising to approach
speeds without changes in altitude or heading,
and understanding the required power and trim
settings to maintain slow flight. It should
also include configuration changes, such as
extending the landing gear and adding flaps,
while maintaining heading and altitude. Slow
flight in a single-engine airplane should be
conducted so the maneuver can be completed no
lower than 1,500 feet AGL, or higher, if recommended
by the manufacturer. In all cases, practicing
slow flight should be conducted at an adequate
height above the ground for recovery should
the airplane inadvertently stall.
To begin the slow flight maneuver, clear the
area and gradually reduce thrust from cruise
power and adjust the pitch to allow the airspeed
to decrease while maintaining altitude. As the
speed of the airplane decreases, note a change
in the sound of the airflow around the airplane.
As the speed approaches the target slow flight
speed, which is an airspeed just above the stall
warning in the desired configuration (i.e.,
approximately 5–10 knots above the stall
speed for that flight condition), additional
power will be required to maintain altitude.
During these changing flight conditions, it
is important to trim the airplane to compensate
for changes in control pressures. If the airplane
remains trimmed for cruising speed (a lower
AOA), strong aft (back) control pressure is
needed on the elevator, which makes precise
control difficult unless the airplane is retrimmed.
Slow flight is typically performed and evaluated
in the landing configuration. Therefore, both
the landing gear and the flaps should be extended
to the landing position. It is recommended the
prescribed before-landing checks be completed
to configure the airplane. The extension of
gear and flaps typically occurs once cruise
power has been reduced and at appropriate airspeeds
to ensure limitations for extending those devices
are not exceeded. Practicing this maneuver in
other configurations, such as a clean or takeoff
configuration, is also good training and may
be evaluated on the practical test.
With an AOA just under the AOA which may cause
an aerodynamic buffet or stall warning, the
flight controls are less effective. The elevator
control is less responsive and larger control
movements are necessary to retain control of
the airplane. In propeller-driven airplanes,
torque, slipstream effect, and P-factor may
produce a strong left yaw, which requires right
rudder input to maintain coordinated flight.
The closer the airplane is to the 1G stall,
the greater the amount of right rudder pressure
required.
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Maneuvering in Slow Flight
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When the desired
pitch attitude and airspeed have been established
in straight-and-level slow flight, the pilot
must maintain awareness of outside references
and continually cross-check the airplane’s
instruments to maintain control. The pilot should
note the feel of the flight controls, especially
the airspeed changes caused by small pitch adjustments,
and the altitude changes caused by power changes.
The pilot should practice turns to determine
the airplane’s controllability characteristics
at this low speed. During the turns, it will
be necessary to increase power to maintain altitude.
Abrupt or rough control movements during slow
flight may result in a stall. For instance,
abruptly raising the flaps while in slow flight
can cause the plane to stall.
The pilot should also practice climbs and descents
by adjusting the power when stabilized in straight-and-level
slow flight. The pilot should note the increased
yawing tendency at high power settings and counter
it with rudder input as needed.
To exit the slow flight maneuver, follow the
same procedure as for recovery from a stall:
apply forward control pressure to reduce the
AOA, maintain coordinated flight and level the
wings, and apply power as necessary to return
to the desired flightpath. As airspeed increases,
clean up the airplane by retracting flaps and
landing gear if they were extended. A pilot
should anticipate the changes to the AOA as
the landing gear and flaps are retracted to
avoid a stall.
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