Integrated Environmental Control System and Liquid Cooling System for F/A-18 E/F Aircraft

Ever increasing demand for air and liquid cooling in high performance fighter aircraft, such as the F/A-18, presents a challenge for aircraft environmental control system (ECS) design. Traditionally, the air-to-liquid cooling ratio has been about 4 to 1, and the liquid cooling system design typically consisted of a liquid transportation loop with a pump/reservoir and a single liquid-to-air or liquid-to-liquid heat exchanger. The heat sinks have been typically ram air, conditioned ECS air, or fuel. Of these potential heat sinks, ECS air usually has the highest aircraft penalties but has been utilized where the other heat sinks could not meet system temperature requirements. Ram air usually requires an external scoop, and the cooling flow and temperature available is highly dependent on aircraft flight condition. Direct fuel usage usually imposes operating temperature limits but can be very low in penalty to the aircraft when the added heat can be burned by the engine. With the advent of advanced development aircraft radar, the aircraft liquid cooling demand is projected to increase over four times. In addition, these advanced radars require significantly cooler liquid delivery temperatures in order to provide sufficient reliability to make them cost effective. Using a traditional design approach on the liquid cooling system, this increase in demand would drastically impact the sizing of the ECS and/or ram air scoop, or impose unacceptable increases in coolant delivery temperature for a significant amount of operating conditions. This trade study led to the selection of a system which integrates the liquid cooling system, the fuel thermal management system, and the environmental control system. This integrated system minimizes the aircraft performance penalty while maximzing the heat sink usage, and is inherently simple and low risk.