MD Helicopters CSP-900RMM-2, Servicing And Maintenance

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CSP − 900RMM − 2 MD Helicopters, Inc.
Rotorcraft Maintenance Manual
Page 1
Revision 17
25-60-10
EMERGENCY EQUIPMENT
DESCRIPTION AND OPERATION
1. Rescue Hoist
A. Description
The Rescue Hoist System provides a means for
lowering and raising personnel from an
airborne helicopter. Operation is from either
the crew station or pilot station. The system is
comprised of a Hoist Assembly, Pendant
Control Assembly, Electronic Variable Speed
Controller; interconnection Electrical Control
Pendant Cable, and a Pilot Display Assembly.
Hoist Assembly is a multiple layered type
drum design with a cable capacity of 245 feet
of 3/16” dia. 19 x 7 const. (Spin Resistant
type). Reduction gearing is the planetary type.
Drive train includes a fail-safe mechanically
actuated load brake. Hoist is driven with a 28
VDC electric motor, which includes a totally
enclosed fan cooling and an integral motor
brake.
Limit switches are directly coupled to the hoist
drum to control cable fully extended and
intermediate cable positions (hook approach to
aircraft and approach to cable fully-extended
switch). A cable fully retracted switch is built
into the cable level-wind nut assembly to
assure proper homing of the hook when hoist
is not in service. Redundant switches are used
and the mechanical mounting techniques
employed ensure fail-safe operation.
In the operation of the hoist, the cable rate is
automatically slowed to a safe speed whenever
the hoist is operated in the cable zone con­
trolled by the fail-safe redundant intermediate
switch.
The Hoist also incorporates a cable payout
potentiometer driven by the output of the limit
switch drive mechanism and provides a signal
(proportional to the length in feet of cable
extending from the hoist) to the cable payout
display on the control pendant.
A cycle (events) counter is included which is
operated by a magnetically actuated reed
switch to count drum revolutions. Divide this
number by 334 to determine full hoist cycles.
Variable Speed Controller is a highly efficient
speed control which incorporates the latest
(PWM) Pulse Width Modulated speed control
techniques. Hoist speed control is accom­
plished by a speed command applied to the
controller from either the variable speed
operator control or the constant speed priority
override pilots control switch.
Internal power MOSFET switching elements
control the amount of average DC voltage
applied to the hoist motor. The greater the
deflection of the thumbwheel on the hoist
operators Pendant Control Assembly, the
greater average DC voltage applied to the
motor, hence, faster hoisting speeds.
The Controller Assembly being greater than
95% efficient dissipates minimal power. A heat
sink on the side of the controller is used to
remove heat from the controller and installa­
tion must be either horizontal with heat sink
facing up or vertical. The controller incorpo­
rates digital electronics which process the hoist
limit switch information and limits the hoist
speed if an intermediate switch is actuated
and inhibits further hoist movement if a stop
switch is actuated.
Controller's digital electronics control the
priority of the control inputs from the hoist
operator or the pilot control. The pilot has
complete priority over the hoist operator and
the hoist is automatically set to the 600 lb
mode. Pilot's command is fixed-speed with
automatic slow downs and stops when the
cable extremes are reached.
The controller processes cable position
information from the hoist. Position informa­
tion is absolute and will continue to provide
cable position information if power is inter­
rupted. Cable position information is processed
and digitally transmitted to hoist operator's
control display and pilot's display assembly.
Cable payout information is for reference only
and should not be used for helicopter position
information. The cable payout cannot account
for cable stretch due to hook loads, therefore,
there is a tolerance at the full-in or full-out of
plus or minus 3 feet.