Simulation Study of an Aircraft's Environmental Control System Dynamic Response

Abstract

SIMULATION was made of the environmental control system (ECS) of a high-performance aircraft. The ECS provides temperature control for the cockpit and avionics equipment bays, throughout the flight performance envelope of the aircraft. This is achieved by bleeding hot air from the engine, cooling part of it, and mixing the hot and cold flows. The sensors, controller, and valves of the system were modeled, as well as the heat exchangers and expansion turbine. The simulation was programed in CSMP, on an IBM 370/165 computer and operated over an array of conditions representative of the whole operational envelope of the ECS. Dynamic response was compared to specification s and sensitivity of performance to system parameters was measured. A partial evaluation of the simulation was achieved by using some available laboratory test results and comparing these with simulation results from the same conditions. The rationale, models, program, and results are presented in this paper. Content The environmental control system (ECS) of a highperformance aircraft is required to perform complex tasks. Consequently, it is complex in design. The ECS must supply proper temperature air to the cabin and to the avionics equipment, within the entire performance envelope of the aircraft and within the entire scale of external conditions of temperature and pressure. There are specifications on the dynamic behavior which require the system to stabilize within seconds and to not exceed specific inlet temperatures to the cabin and equipment which would be harmful to the pilot and to the avionics. Proper flow levels must be maintained and it is necessary that no severe pressure changes reach the cockpit, which would be uncomfortable to the pilot. To verify the design of the ECS for a high-performance aircraft, a simulation was made which portrayed the dynamic performance of the system. It was intended to study stability, study sensititivity, identify possible problem areas in the design, and serve as a tool to evaluate the dynamic effects of any future design changes. A discussion of the system follows. System Description. The ECS provides temperature control for the cockpit and avionics equipment bays, throughout the flight performance envelope of the aircraft. This is achieved by bleeding hot air from the engine, cooling part of it, and mixing the hot and cold flows. Transient changes into the ECS occur when the pilot alters the engine throttle setting and/or when altitude changes occur. A functional flow diagram of the ECS system is shown in Fig. 1. The rate of flow of bleed air from the engine is