1. Secondary Power Systems Auxiliary Power Units/Emergency Power Units (APU/EPU) Ram-Air Turbines (RAT) Batteries

2. Auxiliary Power Units Useful before flight Enables aircraft to be independent of ground power Generally located in the tail of the aircraft Useful during flight Provides power in case of engine failure Very important in modern fly-by-wire aircraft

3. APU Manufacturers and Weights Three main manufacturers: –Honeywell International Inc –Pratt & Whitney Canada –Hamilton Sundstrand Boeing 777 uses Honeywell 351-500 which weighs 730lbs dry Boeing 747-400 uses PW901 which weighs 835lbs dry MD-90 and A320 use Honeywell 131-9 models that range in weight from 350-450lbs dry

5. APU Design Approaches Pneumatic Link Location flexibility Decrease in overall efficiency Electrical Link Location flexibility & increased system integration Increased startup requirements Mechanical Link Limited Positioning High Efficiency Hydraulic Link Location flexibility Complex operation and ground startup Hybrid A combination of all these

6. Ram-Air Turbines Deployed in power system failure An air-driven turbine for power generation Relatively simple design Low power output Does not require stored power for startup

7. Batteries Power storage medium Batteries provide emergency power between complete main system failure and backup system startup Provides power to startup secondary power systems

8. References Pallett, EHJ. Aircraft Electrical Systems. John Wiley & Sons, Inc., New York. 1987. 3 rd Edition. Secondary Power Systems. Mechanical Engineering Publications Limited, London. 1985. Raymer, Daniel P. Aircraft Design: A Conceptual Approach. AIAA, Reston, VA. 2006. 4th Edition Fielding, John P. Introduction to Aircraft Design. Cambridge University Press, New York. 1999. Moir, Ian and Seabridge, Allan. Aircraft Systems: Mechanical, Electrical, and Avioncs Subsystems Integration. AIAA, Reston, VA. 2001