TM  55-1510-221-10 CHAPTER   3 AVIONICS Section  I. GENERAL 3-1. INTRODUCTION. Except for mission avionics, this chapter covers all avionics equipment installed in the RC-12H air- craft.  It  provides  a  brief  description  of  equipment covered, the technical characteristics and locations. It  covers  systems  and  controls  and  provides  the proper  techniques  and  procedures  to  be  employed when  operating  the  equipment.  For  more  detailed operational information consult the vendor manuals that accompany the aircraft loose tools. 3-2. AVIONICS EQUIPMENT CONFIGURATION. The  aircraft  avionics  covered  consists  of  three groups of electronic equipment. The communication group  consists  of  the  interphone,  UHF  command, backup   VOW,   VHF/AM-FM,   VHF   command   and HF  command  systems.  The  navigation  group  pro- vides the pilot and copilot with the instrumentation required to establish and maintain an accurate flight course  and  position,  and  to  make  an  approach  on instruments under Instrument Meteorological Con- ditions (IMC). The navigation group includes equip- ment  for  determining  altitude,  attitude,  position, destination, range and bearing, heading reference, groundspeed, and drift angle. The transponder and radar   group   includes   an   identification,   position, emergency  tracking  system,  a  radar  system  to  locate potentially dangerous weather areas, and a radar sys- tem  to  differentiate  between  friendly  and  unfriendly search radar. battery,   left   and   right   generators,   and   external power. Power is routed through two 50-ampere cir- cuit  breakers  to  the  avionics  power  relay  which  is controlled   by   the   AVIONICS   MASTER   POWER switch  on  the  overhead  control  panel  (fig.  2-12). Individual  system  circuit  breakers  and  the  associ- ated avionics busses are shown in fig. 2-22. With the switch  in  the  ON  (forward)  position,  the  avionics power  relay  is  de-energized  and  power  is  applied through   both   the   AVIONICS   MASTER   POWER No. 1 and No.2 circuit breakers to the individual avi- onics   circuit   breakers   on   the   overhead   circuit breaker panel (fig. 2-26). In the OFF (aft) position, the  relay  is  energized  and  power  is  removed  from avionics  equipment.  When  external  power  is  applied to the aircraft, the avionics power relay is normally energized, removing power from the avionics equip- ment.  To  apply  external  power  to  the  avionics equipment, move   the   AVIONICS   MASTER POWER switch to the EXT PWR position. This will de-energize   the   avionics   power   relay   and   allow power to be applied to the avionics equipment. NOTE b. Single-Phase AC Power. AC power for the avionics  equipment  is  provided  by  two  inverters. The  inverters  supply  115-volt  and  26-volt  single- phase AC power when operated by the INVERTER No. 1 or No.2 switches (fig. 2-12). Either inverter is capable of powering all avionics equipment requir- ing  AC  power.  AC  power  from  the  inverters  is routed through fuses in the nose avionics compart- ment. All  avionics  equipment  require  a  3-min- ute  warmup  period.  The  weather  radar has  an  automatic  time  delay  of  3  to  4 minutes. 3-3. POWER SOURCE. a.  DC  Power.  DC  power  for  the  avionics equipment is provided by four sources: the aircraft c. Three-Phase  AC  Power.  Three  phase  AC electrical power for operation of the inertial naviga- tion system and mission avionics is supplied by two DC  powered  3000  volt-ampere  solid  state  three phase inverters. The three phase inverters are con- trolled by two three-position switches located on the mission control panel (fig. 4-1) placarded No. 1 INV - OFF  -  ON  -  RESET  and  #2  INV  -  OFF  -  ON  - RESET. 3-1