TM  55-1510-221-10 CHAPTER  2 AIRCRAFT AND SYSTEMS DESCRIPTION AND OPERATION 2-1.  INTRODUCTION. The   purpose   of   this   chapter   is   to   describe   the aircraft  and  its  systems  and  controls  which  contrib- ute  to  the  physical  act  of  operating  the  aircraft.  It does  not  contain  descriptions  of  avionics  or  mission equipment,   covered   elsewhere   in   this   manual.   This chapter  contains  descriptive  information  and  does not  describe  procedures  for  operation  of  the  aircraft. These   procedures   are   contained   within   appropriate chapters   in   the   manual.   This   chapter   also   contains the   emergency   equipment   installed.   This   chapter   is not  designed  to  provide  instructions  on  the  complete mechanical  and  electrical  workings  of  the  various systems;  therefore,  each  is  described  only  in  enough detail  to  make  comprehension  of  that  system  suffi- ciently  complete  to  allow  for  its  safe  and  efficient operation. 2-2.  GENERAL. The   RC-12H   is   a   pressurized,   low   wing,   all metal  aircraft,  powered  by  two  PT6A-41  turboprop engines (fig. 2-1 and 2-11), and has all weather capa- bility.  Distinguishable  features  of  the  aircraft  are  the slender,  streamlined  engine  nacelles,  an  aft  rotating boom   antenna,   mission   antennas,   wing   tip   pods,   a T-tail  and  a  ventral  tin  below  the  empennage.  The basic  mission  of  the  aircraft  is  radio  reconnaissance. Cabin  entrance  is  made  through  a  stair-type  door (fig.  2-2)  on  the  left  side  of  the  fuselage. 2-3.  DIMENSIONS. Overall  aircraft  dimensions  are  shown  in  figure 2-3. 2-4. GROUND TURNING RADIUS. Minimum   ground   turning   radius   of   the   aircraft is  shown  in  figure  2-4. 2-5. MAXIMUM WEIGHTS. Maximum   takeoff   gross   weight   is   15,000 pounds.  Maximum  landing  weight  is  15,000  pounds. Maximum   ramp   weight   is   15,090   pounds.   Maxi- mum  zero  fuel  weight  is  11,500  pounds. AIRCRAFT Section  I. 2-6.  EXHAUST  DANGER  AREA. Danger  areas  to  be  avoided  by  personnel  while aircraft  engines  are  being  operated  on  the  ground  are depicted  in  figure  2-5.  Distance  to  be  maintained with  engines  operating  at  idle  are  also  shown.  Tem- perature  and  velocity  of  exhaust  gases  at  varying locations  aft  of  the  exhaust  stacks  are  shown  for maximum  power.  The  danger  area  extends  to  40  feet aft  of  the  exhaust  stack  outlets.  Propeller  danger areas  are  also  shown. 2-7. LANDING GEAR SYSTEM. The  landing  gear  is  a  retractable,  tricycle  type, electrically  operated  by  a  single  DC  motor.  This motor   drives   the   main   landing   gear   actuators through  a  gear  box  and  torque  tube  arrangement, and   also   drives   a   chain   mechanism   which   controls the   position   of   the   nose   gear.   Positive   down-locks are  installed  to  hold  the  drag  brace  in  the  extended and  locked  position.  The  down-locks  are  actuated  by overtravel  of  the  linear  jackscrews  and  are  held  in position   by   a   spring-loaded   overcenter   mechanism. The  jackscrew  in  each  actuator  holds  all  three  gears in   the   UP   position,   when   the   gear   is   retracted.   A friction  clutch  between  the  gearbox  and  the  torque shafts  protects  the  motor  from  electrical  overload  in the  event  of  a  mechanical  malfunction.  A  150- ampere  current  limiter,  located  on  the  DC  distribu- tion  bus  under  the  center  floorboard,  protects against   electrical   overload.   Gear   doors   are   opened and  closed  through  a  mechanical  linkage  connected to  the  landing  gear.  The  nose  wheel  steering  mecha- nism  is  automatically  centered  and  the  rudder  ped- als   relieved   of   the   steering   load   when   the   landing gear  is  retracted.  Air-oil  type  shock  struts,  filled  with compressed  air  and  hydraulic  fluid,  are  incorporated with  the  landing  gear.  Gear  retraction  or  extension time  is  approximately  six  seconds. (1.)  Landing   Gear   Control   Switch.   Land- ing  gear  system  operation  is  controlled  by  a  manu- ally   actuated,   wheel-shaped   switch   placarded   LDG GEAR  CONTR  -  UP  -  DN,  located  on  the  left  sub- panel  (fig.  2-6).  The  control  switch  and  associated relay  circuits  are  protected  by  a  S-ampere  circuit breaker,  placarded  LANDING  GEAR  RELAY  on the  overhead  circuit  breaker  panel  (fig.  2-26). 2-1