Three decades of Secondary Power Unit turbomachinery technology accomplishments are reviewed and a prognosis made for its continuing importance in providing aircraft primary operating functions.
High performance aircraft of the future will demand more compact, lighter weight secondary power units (SPU's) capable of providing faster starts and rapid response over previously impenetrable flight operating envelopes. Propulsion technology advancements continue to task the design and optimization of SPU's to the point, where during a flight emergency, power must be regained in a few seconds under all flight altitudes and attitudes.
Ever increasing altitude operational requirements are limiting the viability of air-breathing SPUs, consequently hybrid units are being evolved capable of operating in both air-breathing and non-air breathing modes.
This paper highlights the primary considerations for SPU design technology and suggests profitable avenues of research and development for continuing improvement of aircraft secondary power systems.