TM  1-1520-240-10            2-1-1 CHAPTER  2 AIRCRAFT AND SYSTEMS DESCRIPTION AND OPERATION SECTION  I.  HELICOPTER 2-1-1.  General. The CH-47D (fig. FO-1, 2-1-1 and 2-1-2) is a twin-turbine engine, tandem rotor helicopter designed for transportation of cargo, troops, and weapons during day, night, visual, and instrument  conditions.  (Unless  otherwise  noted,  numbers refer   to   fig.   FO-1.)   The   helicopter   is   powered   by   two T55-L-712 or T55-GA-714A shaft-turbine engines (18) on the aft fuselage. The engines simultaneously drive two tan- dem three-bladed counterrotating rotors (13 and 19) through engine transmissions (25), a combining transmission (16), drive shafting (14), and reduction transmissions (12 and 23). The forward transmission is on the forward pylon above the cockpit (1). The aft transmission, the combining transmis- sion, and drive shafting are in the aft cabin section and aft pylon sections (3 and 4). Drive shafting from the combining transmission  to  the  forward  transmission  is  housed  in  a tunnel along top of the fuselage. When rotors are stationary, a gas-turbine auxiliary power unit (22) drives a generator and hydraulic pump to furnish hydraulic and electrical power. Fuel is carried in pods on each side of the fuselage. The helicopter is equipped with four non-retractable landing gear. An entrance door (15) is at the forward right side of the cargo compartment (2). At the rear of the cargo compartment is a hydraulically powered loading ramp (26). The pilots seat (9) and controls are at the right side of the cockpit; the copilot’s seat (40) and controls are on the left side. See figure 2-1-3 for typical cockpit and controls. 2-1-2.  Gross Weight. The   maximum   gross   weight   of   the   CH-47D   is   50,000 pounds. Chapters 5 and 6 provide additional weight informa- tion. 2-1-3.  Landing Gear System. The  landing  gear  system  consists  of  four  non-retractable landing gears mounted on the fuselage pods. The forward landing  gears  are  a  fixed-cantilever  type  and  have  twin wheels. The aft landing gears are of the single–wheel, full- swivel (360_) type which can be power centered and locked in trailed position. In addition, the aft right landing gear can be steered from the cockpit by using the steering control knob on the console. Each landing gear has an individual air-oil shock strut and is equipped with tube-type tires. 2-1-4.  Landing Gear Proximity Switches. a. Two proximity switches are installed, one on each aft landing gear. Each switch is activated when its associated shock strut is compressed during touchdown. The switches improve ground handling by reducing pitch axis gain of the AFCS, by canceling the longitudinal Control Position Trans- ducer (CPT), therefore longitudinal stick input, to the Differ- ential Airspeed Hold (DASH) actuators, and by driving both longitudinal cyclic trim (LCT) actuators to the ground posi- tion. In addition to the above functions, the switch on the right aft landing gear, when activated, disables the flare dispenser to  prevent  accidental  flare  release,  and  enables  the  hold function of mode 4 transponder codes. b. On helicopters equipped with GROUND CONTACT indicating lights, activation of the proximity switches when the  associated  shock  strut  is  compressed  will  cause  the associated  GROUND  CONTACT  indicating  light  on  the MAINTENANCE PANEL to illuminate. CAUTION Should either or both GROUND CONTACT indicating lights remain illuminated after lift-off to hover, the illuminated system(s) DASH will not function properly in forward flight. If both GROUND CONTACT indicat- ing lights remain illuminated after lift-off, the AUTO function of both cyclic trim sys- tems will be inoperative and both LCT ac- tuators will remain in the GND position. c. Aft landing gear proximity switches are not actuated in a water landing. As a result, DASH actuators will respond to longitudinal stick motion, producing an apparent increase in control sensitivity. Cyclic motion of + 3/4 inch from neutral, if  held,  will  drive  DASH  actuators  hard  over.  If  longitudi- nal  cyclic movement is required for taxing, set the AFCS SYSTEM SEL switch to OFF. 2-1-5.  Steering and Swivel Lock System.   The steering and swivel lock system consists of the power steering control box with the STEERING CONTROL panel on   the   center   console,   utility   system   pressure   control module,  power  steering  actuator,  power  steering  module, swivel lock actuating cylinder, and the PWR STEER master caution capsule. The STEERING CONTROL panel consists of a three position SWIVEL switch and a steering control knob.  The  SWIVEL  switch  controls  operation  of  power steering and swivel locks.