Military VTOL/VSTOL aircraft are required to operate in areas where it is impractical to provide ground support equipment to supply types of power needed for system checkout, emergency and standby power, and main engine starting.
To provide this capability, the Secondary Power System must be considered on an integrated basis as a major aircraft subsystem which incorporates an auxiliary power unit (APU) that will provide an alternate source of power, in flight and on the ground, for aircraft hydraulics, pneumatic drives, APU starting, environmental control, main engine starting, electrical power generation, power transfer to accessory gearbox for shaft-driven accessories, plus the power distribution system to interconnect these components.
This paper discusses the application of this integrated concept and the associated analyses of operating characteristics of major components. Appropriate interface and compatibility with the total air vehicle is illustrated. Significant parameters such as power, weight, efficiencies, product assurance characteristics, etc., are compared.