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flight characteristics and degree of controllability of a
glider at minimum speeds. By definition, the term
“flight at minimum controllable airspeed” means a
speed at which any further increase in angle of attack
or load factor causes an immediate stall. Pilots must
develop an awareness of the particular glider flight
characteristics in order to recognize and avoid stalls,
which may inadvertently occur during the slow airspeeds
used in takeoffs, climbs, thermalling, and
approaches to landing.
The objective of maneuvering at minimum controllable
airspeed is to develop the pilot’s sense of feel and
ability to use the controls correctly, and to improve
proficiency in performing maneuvers that require slow
airspeeds. Maneuvering at minimum controllable airspeed
should be performed using outside visual reference.
It is important that pilots form the habit of
frequently referencing the pitch attitude of the glider
for airspeed control while flying at slow speeds.
The maneuver is started from either best glide or minimum
sink speed. The pitch attitude is smoothly and
gradually increased. While the glider is losing airspeed,
the position of the nose in relation to the horizon
should be noted and should be adjusted as
necessary until the minimum controllable airspeed is
established. During these changing flight conditions, it
is important to re-trim the glider, as necessary, to compensate
for changes in control pressures. Excessive or
too aggressive back pressure on the elevator control
may result in an abrupt increase in pitch attitude and a
rapid decrease in airspeed, which leads to a higher
angle of attack and a possible stall. When the desired
pitch attitude and airspeed have been established, it is
important to continually crosscheck the pitch attitude
on the horizon and the airspeed indicator to ensure
accurate control is being maintained.
When minimum controllable airspeed is established in
straight flight, turns should be practiced to determine
the glider’s controllability characteristics at this
selected airspeed. During the turns the pitch attitude
may need to be decreased in order to maintain the airspeed.
If a steep turn is encountered, and the pitch attitude
is not decreased, the increase in load factor may
result in a stall. A stall may also occur as a result of
abrupt or rough control movements resulting in
momentary increases in load factor. Abruptly raising
the flaps during minimum controllable airspeed will
result in sudden loss of lift, possibly causing a stall.
Minimum controllable airspeed should also be practiced
with extended spoilers/dive breaks. This will
provide additional understanding of the changes in
pitch attitude caused by the increase in drag from the
spoilers/dive breaks.
Actual minimum controllable airspeed depends upon
various conditions, such as the gross weight and CG
location of the glider and the maneuvering load
imposed by turns and pull-ups. Flight at minimum
controllable airspeed requires positive use of rudder
and ailerons. The diminished effectiveness of the flight
controls during flight at minimum controllable airspeed
will help pilots develop the ability to estimate
the margin of safety above the stalling speed.
COMMON ERRORS
• Failure to establish or to maintain minimum
controllable airspeed.
• Improper use of trim.
• Rough or uncoordinated use of controls.
• Failure to recognize indications of a stall.
STALL RECOGNITION AND RECOVERY
Astall can occur at any airspeed and in any attitude. In
the case of the self-launch glider under power, a stall
can also occur with any power setting. A stall occurs
when the smooth airflow over the glider’s wing is disrupted
and the lift decreases rapidly. This occurs when
the wing exceeds its critical angle of attack.
The practice of stall recovery and the development of
awareness of stalls are of primary importance in pilot
training. The objectives in performing intentional
stalls are to familiarize the pilot with the conditions
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that produce stalls, to assist in recognizing an
approaching stall, and to develop the habit of taking
prompt preventive or corrective action.
Intentional stalls should be performed so the maneuver
is completed by 1,500 feet above the ground for recovery
and return to normal, wings-level flight. Though it
depends on the degree to which a stall has progressed,
most stalls require some loss of altitude during recovery.
The longer it takes to recognize the approaching
　
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本文鏈接地址：Glider Flying Handbook(74)