TM 55-1520-240-23-4
5-1
ROTARY-WING HEAD AND CONTROLS
(Continued)
5-1
DROOP STOPS
The droop stops limit blade droop. Each pitch-varying
housing is supported by a droop stop. Forward and aft
heads have fixed droop stops. These are installed on
the bottom of the pitch shaft to limit droop at zero rotor
speed. These fixed droop stops rest directly against the
hub. The centrifugal droop stop assembly is mounted on
a splined plate under the aft rotor head. The droop stop
contains three balancing arms. These are connected by
springs to lugs on the hub oil tank. Interposer blocks on
the balancing arms are positioned between fixed blocks
and the hub. As rotor speed increases, the centrifugal
droop stops swing out. This moves interposer blocks
clear of the pitch shafts and allows more freedom for
blade droop. As rotor speed decreases, the springs pull
the arms in toward the hub. This positions the blocks
between the hub and pitch shafts to reduce droop angle.
SHOCK ABSORBERS
Each head has three shock absorbers. They are
connected between lugs on the pitch-varying housing
and brackets on the blades. The shock absorbers limit
lead and lag motion of the blades. Each shock absorber
has a vent valve. The valve is opened for extreme cold
weather operation. Changing the vent valve position
allows the shock absorber to be used on forward or aft
head.
5-3
