Thermal management of military fighter aircraft electro-optics pod: an invited paper

The thermal management of electro-optics equipment mounted in a pod residing under the fuselage of a fighter aircraft represents a formidable challenge. As an add-on to the aircraft, no air- or liquid-coolant can be provided to the pod, and there is a limit to the electrical power that can be provided for cooling purposes. The operating envelope of this electronics pod is from sea level to 13.7 km (45 kft) altitude at Mach numbers from 0.3 to 0.9. The maximum allowable cooling air temperature for equipment in the forward avionics bay was 55°C at sea level and 26°C at 13.7 km (45 kft). The inlet air temperatures for the electro-optics sensor bay ranged from 4°C to 32°C with the maximum allowable inlet air temperature set at 40°C. The sensor temperature was required to be controlled within +/- 0.14°C. The liquid coolant used in the system was the dielectric oil, polyalphaolefin (PAO), and the maximum allowable liquid temperature was 70°C. The maximum aerodynamic heating load for the pod was in excess of 2000 W for high speed flight at sea level and the total heat load for the pod, including the aerodynamic heating loads, ranged from 4000 W to 5400 W, depending on the operating mode of the electro-optics equipment. The thermal management solution described in this paper is a complex one which includes the design of a ram air inlet, an environmental control system (ECS) including an expansion turbine with a compressor on a common shaft, three liquid-to-air heat exchangers, two air-to-air heat exchangers, two liquid pumps with accumulators, two fans, one air-cooling loop, two liquid-cooling loops, five air-cooled electronic chassis, and six liquid-cooled electronic chassis.