The F- 18 aircraft radar liquid cooling system (fig. 1-15) circulates liquid coolant to remove heat from the radar transmitter high-voltage RF energy modules. Coolant heated by the transmitter is routed through a closed loop system to a heat exchanger. The heat exchanger subjects heated coolant to cooling air, and the coolant is returned by a pump. (A temperature control valve is integral to the heat exchanger to maintain a minimum coolant temperature level.) One of three sources of air is induced across the heat exchanger to provide coolant temperature control. During normal flight operations, ram air is induced across the heat exchanger by an electrically powered ram air scoop. At high ram air temperature conditions (hot day- low altitude or high speed- high altitude), the ram air scoop is closed by a signal from the air data computer, and conditioned air from the air cycle ACS is delivered to the heat exchanger. For ground operation, with aircraft weight on wheels, a cooling fan supplies cooling air to the heat exchanger. When cooling air is supplied from the air cycle ACS, a coolant temperature sensor operates through the ACS temperature/ flow controller to modulate an airflow valve and limit preconditioned air to the heat exchanger. The coolant is filtered and the system monitored for filter contamination, ram air door actuator position, low pressure, high temperature, and coolant quantity. A system servicing panel and quick-disconnect fittings are located in the left fuselage. Quick-disconnect fittings are also provided in the coolant lines at the radar transmitter high-voltage module to aid in transmitter replacement by a preserviced unit. The radar liquid cooling system is made up of a liquid-to-air heat exchanger, a liquid coolant

Figure 1-15.- Radar liquid cooling system.

pump, a ram air valve, a ground cooling fan, a coolant filter, a low-pressure sensor, a high-temperature sensor, a coolant temperature sensor, and an airflow valve.