Installation of a modern, pulse-Doppler radar into the F-5 causes a significant increase in the heat loads in the forward fuselage. Even the most powerful Environmental Control System (ECS) that was installed in the F-5 is unable to provide sufficient cooling to handle this increase in heat load. Even if the temperature of the ECS output air could be reduced, there is insufficient pressure to drive the cooling air through the radar components. A typical solution to this problem is to add dedicated cooling fans increase the flow of cooling air through the radar boxes. Unfortunately, the power required to drive these fans adds an additional heat load that must be cooled, creating a very unattractive “law of diminishing return” as greater and greater power is required to provide smaller and smaller benefits.
To address this problem, Tiger Century Aircraft (TCA) has developed a compact Auxiliary Cooling System (ACS) that utilizes a small air-cycle machine located in the forward fuselage and powered by an existing ECS air output source. The ACS provides cooled primary air to an ejector that is mounted in the gun bay plenum where it mixes with cooled air exiting from the cockpit. The output of the ejector provides forced air cooling directly to selected radar components. The ACS vents overboard through the existing gun-gas purge door.
The ACS generates an output of 2kW of cooling. This capacity exceeds the heat load generated by the addition of the modern pulse-Doppler radar by a comfortable margin. Importantly, the ACS does not have an adverse effect of the performance of the F-5 ECS. The ACS weighs less than 21 pounds and requires only 0.4 cubic feet of volume.
A prototype ACS was installed in an F-5E as part of an evaluation of the modern, 4th generation radar. The installation is seen in the photograph at the right. The ACS was subjected to a series of 20 flights and performed flawlessly. In addition to its successful application to the F-5, the ACS can easily be adapted to other aircraft that require increased cooling for a specific system that is being added to support a special mission. Possible systems include radars, infra-red sensors and cameras.