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helicopter and the factors just mentioned. As the
airspeed increases beyond that which gives minimum
rate of descent, the rate of descent increases again.
When landing from an autorotation, the energy stored
in the rotating blades is used to decrease the rate of
descent and make a soft landing. A greater amount of
rotor energy is required to stop a helicopter with a high
rate of descent than is required to stop a helicopter that
is descending more slowly. Therefore, autorotative
descents at very low or very high airspeeds are more
critical than those performed at the minimum rate of
descent airspeed.
Each type of helicopter has a specific airspeed at which
a power-off glide is most efficient. The best airspeed is
the one which combines the greatest glide range with
the slowest rate of descent. The specific airspeed is
somewhat different for each type of helicopter, yet
certain factors affect all configurations in the same
manner. For specific autorotation airspeeds for a particular
helicopter, refer to the FAA-approved rotorcraft
flight manual.
The specific airspeed for autorotations is established
for each type of helicopter on the basis of average
weather and wind conditions and normal loading.
When the helicopter is operated with heavy loads in
high density altitude or gusty wind conditions, best
performance is achieved from a slightly increased airspeed
in the descent. For autorotations at low density
altitude and light loading, best performance is achieved
from a slight decrease in normal airspeed. Following
this general procedure of fitting airspeed to existing
conditions, you can achieve approximately the same
glide angle in any set of circumstances and estimate the
touchdown point.
When making turns during an autorotation, generally
use cyclic control only. Use of antitorque pedals to
assist or speed the turn causes loss of airspeed and
downward pitching of the nose. When an autorotation
is initiated, sufficient antitorque pedal pressure should
be used to maintain straight flight and prevent yawing.
This pressure should not be changed to assist the turn.
Use collective pitch control to manage rotor r.p.m. If
rotor r.p.m. builds too high during an autorotation, raise
the collective sufficiently to decrease r.p.m. back to the
11-2
normal operating range. If the r.p.m. begins decreasing,
you have to again lower the collective. Always keep
the rotor r.p.m. within the established range for your
helicopter. During a turn, rotor r.p.m. increases due to
the increased back cyclic control pressure, which
induces a greater airflow through the rotor system. The
r.p.m. builds rapidly and can easily exceed the maximum
limit if not controlled by use of collective. The
tighter the turn and the heavier the gross weight, the
higher the r.p.m.
To initiate an autorotation, other than in a low hover,
lower the collective pitch control. This holds true
whether performing a practice autorotation or in the
event of an in-flight engine failure. This reduces the
pitch of the main rotor blades and allows them to
continue turning at normal r.p.m. During practice
autorotations, maintain the r.p.m. in the green arc
with the throttle while lowering collective. Once the
collective is fully lowered, reduce engine r.p.m. by
decreasing the throttle. This causes a split of the
engine and rotor r.p.m. needles.
STRAIGHT-IN AUTOROTATION
A straight-in autorotation implies an autorotation from
altitude with no turns. The speed at touchdown and the
resulting ground run depends on the rate and amount of
flare. The greater the degree of flare and the longer it is
held, the slower the touchdown speed and the shorter
the ground run. The slower the speed desired at touchdown,
the more accurate the timing and speed of the
flare must be, especially in helicopters with low inertia
rotor systems.
TECHNIQUE
Refer to figure 11-1 (position 1). From level flight at
the manufacturer’s recommended airspeed, between
500 to 700 feet AGL, and heading into the wind,
smoothly, but firmly lower the collective pitch control
to the full down position, maintaining r.p.m. in the
green arc with throttle. Coordinate the collective movement
with proper antitorque pedal for trim, and apply
aft cyclic control to maintain proper airspeed. Once the
collective is fully lowered, decrease throttle to ensure a
clean split of the needles. After splitting the needles,
readjust the throttle to keep engine r.p.m. above
normal idling speed, but not high enough to cause
rejoining of the needles. The manufacturer often
　
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