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Hercules Gets New APU Vol VOL. 3, NO. 4, OCTOBER - DECEMBER 1976 Second Printing Aug ust 1982 A SERVICE PUBL•CATIOt>I OF LOCKHEfO ·GEOn Gr... \ COMPANY. A DIVISION O F LOCKHEED t\IACAAFT CORPORATION •• .... - ·- ..- - r 1-' =--- - L \ . ~ Hercules Gets New APU Vol. 3, No. 4, October - December 1976 CONTENTS A SERVICE PUBLICATION OF LOCKHEED-GEORGIA COMPANY 3 Herky’s New APU A DIVISION OF LOCKHEED AIRCRAFT CORPORATION 11 Torq-Set * Screws and Tools StarTips Editor Jay V. Roy 11 Starter Servicing Associate Editors Don H. Hungate 15 Safety Wire for Hercules James A. Loftin MLG Torque Tube Yoke Assembly Art Direction & Production Anne G. Anderson DIRECTOR T.J. CLELAND Hercules Gets New APU Cover: The Hercules “Front MANAGER D.L. BRAUND Office ” emphasizes spaciousness, FIELD SERVICE & INVENTORY MGMT A.H. McCRUM comfortable seating and convenient grouping of instruments and con- CUSTOMER TRAINING A.R.LOVE trols. JETSTAR SUPPORT H.L. BURNETTE SPARES STORES & SHIPPING J.K. PIERCE MANAGER M.M. HODNETT Published by Lockheed-Georgia Company, a Division of SUPPLY PROCUREMENT R.C. WEIHE Lockheed Aircraft Corporation. Information contained in this issue is considered by Lockheed-Georgia Company to be accurate and authoritative; it should not be assumed, SUPPLY SYSTEMS & INVENTORY CONTROL C.K. ALLEN however, that this material has received approval from any governmental agency or military service unless it is SUPPLY SALES & CONTRACTS H.T. NISSLEY, JR. specifically noted. This publication is for planning and information purposes only, and it is not to be construed SUPPLY TECHNICAL SUPPORT J.L. THURMOND as authority for making changes on aircraft or equipment, or as superseding any established operational or maintenance procedures or policies. The following marks are registered and owned by Lockheed Aircraft Corporation: “ “, “Lockheed”, “HercuIes”, and “JetStar”. Written permission must be obtained from Lockheed-Georgia Company before republishing any material in this periodical. Address all communications to Editor, Service News, Department 64-22, Zone 278, Lockheed-Georgia Company, Marietta, Georgia 30063. Copyright 1976 Lockheed Aircraft Corporation. Herky's served well for many years, but in our continuing efforts to improve the Hercules, the GTC is being replaced by a more reliable APU (Auxiliary Power Unit) which is identi- fied on C-130H aircraft as GTCP85-180L. and on the L-100 series aircraft as GTCP85-185L. AiResearch, the New same manufacturer that provided the GTC for previous Hercules, also supplies the new APU. The former GTC system provides bleed air to power an ATM (Air Turbine Motor) which in turn, drives an AC generator. The new APU has a 40 KVA, AC generator APU driven directly from the shaft of the gas turbine com- pressor. The 40 KVA generator is interchangeable with the engine driven generators of the Hercules. The func- The Hercules has proven to be a very versatile airplane. A tions of the new APU are essentially the same as the prime reason for this versatility is its capability to operate earlier AiResearch Model GTC 1 with some new into remote, unimproved areas without the need for advantages. The new APU engine produces approximately ground support equipment. Much of this capability is due 20% more bleed air at a higher pressure which gives better to an on-board GTC (Gas Turbine Compressor) which pro- starting of aircraft engines at high temperatures and alti- vides high pressure bleed air for pneumatic system pre- tudes. Also, the MTUR (Mean Time to Unscheduled flight checks and engine starting. The former GTC has Replacement) of system components is greatly increased. Figure 1 3 1. BLEED AIR OUTLET 8. RELAYS 2. ENGINE EXHAUST 9. IGNITION UNIT 3. OUTPUT DRIVE PAD 10. COMBUSTOR 4. HOUR METER 11. TURBINE EXHAUST FLANGE 5. STARTER 12. 0I L COOLER EXHAUST DUCT VIEW LOOKING 6. UNIT CONTROL ELECTRICAL 13. OIL COOLER FORWARD/INBOARD CONNECTION 14. TACW GENERATOR 7. COMPRESSOR AIR INLET DUCT 15. GENERATOR COOLING AIR WITH SCREEN 16. COOLlNG FAN AIR INLET Figure 2 A U X I LIARY POWER UNIT COMPONENT LOCATIONS Although there are many similarities between the former and stopping the APU; and the other to energize circuits GTC system and the new APU, there are also some im- to open or close the bleed air valve. portant differences. Let’s take a brief look at the major components and operation of this new APU. (Reference Electrical loads on the generator are controlled from the Figure 2.) overhead electrical control panel, which includes a manual control switch for the APU generator. APU Control Panel Three indicator lights are located on the APU control The APU control panel is located in the flight station panel. They are: 4 overhead control panel. (Reference Figure 3 .) Tacho- meter and temperature gages have been added for moni- DOOR OPEN - When illuminated, this light indicates a toring the speed and temperature of the APU. Although response to the start circuit, and that the air intake engine operation is automatic, you can decrease the load door is at least partially open. or turn off the APU if the instruments indicate a problem that could cause permanent damage. START - Illuminates after door opens and the auto- matic start is initiated - Extinguishes when speed Two toggle switches are located on the APU control exceeds 35% RPM. panel : one to energize the circuits for starting, running, ON SPEED - Illuminates when the APU is operating above 95% RPM - Indicates that the APU is ready for Figure 3 service to the pneumatic and electrical systems. APU CONTROL PANEL ON THE OVERHEAD ANTI-ICING CONTROL PANEL Airflow Through the APU Centrifugal Speed Switch The air supply for the APU enters an opening just above The centrifugal speed switch is mounted on the left side the unit in the forward left wheel well fairing. A single of the accessory housing, and contains mechanically door, hinged at the back edge, opens automatically to one driven flyweights which operate three microswitches at of two positions when the APU control switch is turned approximately 35%, 95% and 110% of the APU rotor to START. On the ground the door opens to 35’; in speed. Also, air pressure taken from the APU compressor flight it stops at 15’ to prevent scooping in too much air is introduced into the flyweight cavity to actuate the from the slipstream, thereby causing a flameout. A screen 110% switch for normal shutdown of the APU. The func- over the opening prevents entry of objects over 0.250” in tion of the centrifugal speed switch is to control the size. sequence of operation of the electrical control system components. (See Figure 4.) The compressor is a two-stage centrifugal type. The first stage has two opposing inlets for two similar impellers Fuel System positioned back-to-back. The second stage is a single Fuel for the APU is gravity fed from the aircraft’s No. 2 impeller handling less volume at higher pressure. The two fuel tank. A motor-operated shutoff valve in the No.2 stages operate efficiently through a wide range of shaft drybay prevents a standing pressure of fuel to the APU and bleed air loads. when not needed, and shuts off fuel in an emergency. If SWITCH COMPRESSOR AIR ACTUATING FROM OVERSPEED LEVER TEST SOLENOID VALVE OIL SEAL INPUT FLYWEIGHT SUPPORT ELECTRICAL CONNECTOR Figure 4 CENTRIFUGAL SPEED SWITCH SCHEMATIC The second-stage discharge air is directed into the turbine circuits in the APU controls are deenergized, the fuel valve plenum. Here some of the air is bled off through the closes and the APU shuts down. bleed air duct located on the turbine plenum to provide air for the Hercules pneumatic systems. The combination Fuel Control bleed air shutoff and load control valve is located in this Operation of the fuel system is fully automatic. The fuel duct. control unit, with input from the pneumatic thermostat, protects the turbine from overtemperature during starting and during on-speed operation without a bleed load. A relatively large diameter exhaust pipe leads forward in Under bleed load operation, the pneumatic thermostat the APU compartment, and then turns 180’ up and aft to operation is automatically shifted to the bleed air shutoff exit about seven feet above ground level. Near this exit a and load control valve. section of the pipe is enlarged to form a ring shaped open- ing for jet pump action which aids in ventilating and cool- During on-speed operation of the APU, the fuel flow is ing the APU compartment. varied so that the power developed by the turbine equals load requirements as determined by an on-speed gover- shuts off fuel to the nozzle atomizer in the combustor. nor. (Reference Figure 5.) During APU starting, the valve opens at approximately 10% APU RPM, and is energized by the oil pressure se- All of the fuel pump output passes through a high pres- quencing switch. sure fuel filter. The filter element and O-ring seals should If the APU loses oil pressure or if the APU overspeeds, the be replaced at intervals prescribed in your maintenance valve circuit will be deenergized, closing the valve. manual as there is no bypass. Therefore if the filter should become clogged, it would restrict flow and could Bleed Air Shutoff and Load Control Valve result in abnormal APU operation. This double name for the APU bleed air valve is derived Fuel Shutoff Valve from its versatility: (1) When the bleed air valve switch is in the CLOSE position or the API-J RPM is below 95%, the The solenoid-operated fuel shutoff valve is located at the valve remains closed to prevent bleeding air from the com- fuel control unit outlet. When the valve is deenergized, it pressor during starting, warmup, and before shutdown.
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