To protect the flight controls, pressure can go
Q3. What does the approach power compen-
to only one stage of the main rotor servos during
sator use to compensate for differences in
fold operation. One hydraulic system must be shut
ambient temperatures?
off by the SERVO switch on either collective stick
grip. Pressure switches operate relays to ensure
that only one hydraulic system is on. Relay
BLADEFOLD SYSTEM
operation permits master power to the bladefold
control panel only when one hydraulic system is
on.
Learning Objective: Recognize operating
principles and characteristics of helicopter
The 28-Vdc rotor brake pressure switch senses
bladefold systems.
rotor brake condition. The pressure switch
actuates a relay, which applies a signal to the
Bladefold on the H-60 helicopter is an
bladefold control panel. This signal is for the
bladefold control panel indexing logic. The
electromechanical system. The bladefold index
ROTOR BREAK-APPLY-RELEASE indicators
drive unit positions the main rotor head before
folding. There are four bladefold actuators--one
on the bladefold control panel advise pilots when
for each blade. A tail rotor blade positioner
to apply or release the rotor brake.
actuator positions the tail rotor for pylon and
FOLD SEQUENCE
stabilator folding. The blade deice distributor
assembly on the main rotor contains sequencing
The first step in folding the main rotor blades
electronics and power switching circuits for
is to index the rotor head to a known position.
bladefold and pitchlock actuators.
The bladefold index drive unit accomplishes this
Power goes to the main rotor distributor
task. A de-operated linear actuator in the unit
through the main rotor slip ring. The bladefold
engages the indexing motor output gear to the
control panel contains system operating controls
rotor brake disc gear. An index command from
and status/cue light capsules.
You can manually fold the pylon by using a
the bladefold index drive unit drives rotor head
to indexed position. A 2.5-degree maximum
folding pole. A lockpin switch on the pylon
cutaway segment of an index slip ring in the slip
indicates when the pylon is locked in flight
ring assembly senses this position.
position. The tail cone-pylon fold point has a
With the BLADEFOLD switch in the FOLD
crack open switch. This switch indicates pylon
position, and the rotor brake disengaged, the rotor
disconnection from the tail cone. Two stabilator
lockpin switches indicate when stabilator lockpins
can drive in either the clockwise or
counterclockwise direction. The rotor will drive
are locking the stabilator panels in flight position.
in the direction of the shortest distance to the
In addition, switches on each rotor hub
indicate fold or spread status, and pitchlock
index position. To do this, index drive slip ring
engage or disengaged status. The switch signals
construction is in two segments separated at the
index position, 180 degrees from index position,
go to the bladefold control panel and distributor.
and by providing a reversing relay in the index
MASTER POWER DISTRIBUTION
drive unit.
The index motor rotates at 0.5 RPM. As the
DC power for the system is from the No. 2
rotor head reaches the 1.0-degree index position,
index drive motor power switches off and the
dc primary bus. This power goes through the
weight-on-wheels and low oil pressure relays.
drive motor brake de-energizes, applying the
brake. Power removal and brake application
Bladefold cannot operate unless the helicopter is
prevent the rotor head from overshooting the
on the ground and the rotor head not moving.
The transmission pressure switch energizes the
index position.
When rotor head position is on the insulated
transmission low oil pressure relay. With both
weight-on-wheels and rotor head stopped, the
area between index drive slip ring segments 180
degrees from the index position, head rotation will
28-Vdc master power goes to the blade deice
be counterclockwise toward the index position.
junction box.
The index unit can also act as a backup system
The 28 Vdc at the blade deice junction box
to the rotor brake. You can use the index unit to
goes to two hydraulic system interlock relays.
engage the brake disk and to hold the rotor head
These relays actuate by pressure switches in the
stationary when performing maintenance on the
No. 1 and No. 2 hydraulic systems.
