Environmental Control Systems for Executive Jet Aircraft

This paper briefly presents the history of environmental control systems for executive jet aircraft and the current state of the art, and a summary of present trends. Bleed air controls, refrigeration equipment, temperature controls, interfaces with engines, and auxiliary power units are discussed. Bleed air control concepts have changed from the early systems where only one engine stage was bled and bleed air did not require precooling, to current systems incorporating precooling, bleed air switching between high- and low-stage engine ports, and double redundancy requirements for certification above 45,000 ft. Refrigeration equipment is reviewed from early simple turbine and fan units to current three-wheel and air bearing designs, through the various recirculation schemes using compound machines, jet pumps, and fans to reduce the bleed air extraction penalties and the use of high-pressure water separation, which, when combined with an air bearing turbine, completely eliminates periodic maintenance. Temperature controls are traced from early vacuum tube and relay types to current pneumatic and solid-state-driven electropneumatic transducers, with a brief dicussion of skin temperature sensors.