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becoming excessive. However, if the turn rate
becomes excessive prior to the landing, simply
execute a takeoff and return for another landing.
11-12
LANDING—STUCK NEUTRAL OR RIGHT PEDAL
The landing profile for a stuck neutral or a stuck right
pedal is a low power approach or descent with a
running or roll-on landing. The approach profile can
best be described as a steep approach with a flare at the
bottom to slow the helicopter. The power should be low
enough to establish a left yaw during the descent. The
left yaw allows a margin of safety due to the fact that
the helicopter will turn to the right when power is
applied. This allows the momentary use of power at the
bottom of the approach. As you apply power, the helicopter
rotates to the right and becomes aligned with the
landing area. At this point, roll the throttle to flight idle
and make the landing. The momentary use of power
helps stop the descent and allows additional time for
you to level the helicopter prior to closing the throttle.
If the helicopter is not yawed to the left at the conclusion
of the flare, roll the throttle to flight idle and use the
collective to cushion the touchdown. As with any
running or roll-on landing, use the cyclic to maintain the
ground track. This technique results in a longer ground
run or roll than if the helicopter was yawed to the left.
UNANTICIPATED YAW / LOSS OF TAIL
ROTOR EFFECTIVENESS (LTE)
Unanticipated yaw is the occurrence of an uncommanded
yaw rate that does not subside of its own
accord and, which, if not corrected, can result in the
loss of helicopter control. This uncommanded yaw rate
is referred to as loss of tail rotor effectiveness (LTE)
and occurs to the right in helicopters with a counterclockwise
rotating main rotor and to the left in helicopters
with a clockwise main rotor rotation. Again, this
discussion covers a helicopter with a counter-clockwise
rotor system and an antitorque rotor.
LTE is not related to an equipment or maintenance malfunction
and may occur in all single-rotor helicopters
at airspeeds less than 30 knots. It is the result of the tail
rotor not providing adequate thrust to maintain directional
control, and is usually caused by either certain
wind azimuths (directions) while hovering, or by an
insufficient tail rotor thrust for a given power setting at
higher altitudes.
For any given main rotor torque setting in perfectly
steady air, there is an exact amount of tail rotor thrust
required to prevent the helicopter from yawing either
left or right. This is known as tail rotor trim thrust. In
order to maintain a constant heading while hovering,
you should maintain tail rotor thrust equal to trim thrust.
The required tail rotor thrust is modified by the effects
of the wind. The wind can cause an uncommanded yaw
by changing tail rotor effective thrust. Certain relative
wind directions are more likely to cause tail rotor thrust
variations than others. Flight and wind tunnel tests
have identified three relative wind azimuth regions that
can either singularly, or in combination, create an LTE
conducive environment. These regions can overlap,
and thrust variations may be more pronounced. Also,
flight testing has determined that the tail rotor does not
actually stall during the period. When operating in
these areas at less than 30 knots, pilot workload
increases dramatically.
MAIN ROTOR DISC INTERFERENCE
(285-315°)
Refer to figure 11-10. Winds at velocities of 10 to 30
knots from the left front cause the main rotor
vortex to be blown into the tail rotor by the relative
wind. The effect of this main rotor disc vortex causes
the tail rotor to operated in an extremely turbulent environment.
During a right turn, the tail rotor experiences
a reduction of thrust as it comes into the area of the
main rotor disc vortex. The reduction in tail rotor thrust
comes from the airflow changes experienced at the tail
rotor as the main rotor disc vortex moves across the tail
rotor disc. The effect of the main rotor disc vortex
initially increases the angle of attack of the tail rotor
blades, thus increasing tail rotor thrust. The increase in
the angle of attack requires that right pedal pressure be
added to reduce tail rotor thrust in order to maintain the
same rate of turn. As the main rotor vortex passes the
tail rotor, the tail rotor angle of attack is reduced. The
reduction in the angle of attack causes a reduction in
thrust and a right yaw acceleration begins. This acceleration
can be surprising, since you were previously
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