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Fuel has been a popular choice for thermal system designers to use for absorbing aircraft accessory heat load due to its consumable nature. However, the shortcoming of using fuel as a heat sink is the dependency of environmental conditions. This deficiency has plagued the current United States Air Force fleet operation especially performing ground hold and low altitude attack mission during hot days. A Northrop Grumman led industrial team, commissioned by AFRL Power directorate through the INVENT program, has vigorously explored potential technologies to assist air force to enhance the mission capability. The results show various promising technologies not only can extend the hot day operational limit but also can potentially have an unrestricted capability. This paper describes the results from the study performed by Northrop Grumman for an advanced unmanned air vehicle (AUAV) for potential technologies and discusses the modeling approach in support of the analytical process.

A number of technology breakthroughs in the past ten years rekindled the concept of a more-electric aircraft. High-power solid-state switching devices, electrohydro-static actuators (EHAs), electromechanical actuators (EMAs), and high-speed generators are just a few examples of component developments. These developments have made dramatic improvements in properties such as weight, size, power, and cost. However, these components cannot be applied piecemeal. A complete, and somewhat revolutionary, system design approach was needed to exploit the benefits that a more-electric aircraft can provide. Traditional-mounted auxiliary drives, and bleed air extraction will disappear, to be replaced with integral engine starter/generators and electrically driven actuators and pumps. A five-phase Power Management and Distribution System for a More-Electric Aircraft (MADMEL) program was awarded by the Air Force to Northrop/Grumman Military Aircraft Division in September 1991.

A dc-dc converter and a dc-ac inverter have been developed for More Electric Aircraft (MEA) use. They are both highly compact and are designed to operate from 270 Vdc input power and produce output power that meets requirements for fighter aircraft, including compliance with MIL-STD-704E and MIL-STD-461D guidelines. Both units are designed to be cooled with Poly Alpha Olefin (PAO) at 30°C maximum inlet temperature and to operate for 30s after a loss of coolant flow before shutting down. Both units incorporate under/over voltage, short circuit, and over temperature protection. The dc-ac inverter also has over/under frequency, dc content, waveform distortion, and zero voltage content protection. The dc-dc converter provides 5.6 kW at 29±0.5 Vdc with an efficiency of 85%. It weighs 9.1 lb and is 6″ long by 5″ wide by 5.5″ high (165 in3). The dc-ac inverter provides 8 kVA of three phase power at (115±1.5)/200 Vac and 400 Hz with an efficiency of 75%.