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Low-Observable Heat Rejection from Aircraft


OBJECTIVE: Future aircraft-based high energy lasers will produce hundreds of kilowatts of low-quality waste heat. Novel approaches are sought to remove waste heat under these conditions without significant impact on aircraft signature/aerodynamic performance. DESCRIPTION: The large quantities of low-quality (<40C) waste heat generated by directed energy and other electrically based technologies need to be removed from air platforms in a manner that will allow the system to meet size, weight and power constraints and not interfere with aircraft operation. Heat from directed energy systems is often generated in laser diodes with junction temperatures from 20C-30C as required for the desired pump laser wavelength. Most laser diode packages require non-electrically conductive working fluid with the current state of the art being de-ionized water which is undesirable for airborne logistics reasons. Due to the high peak heat flux of laser systems (~1MW), thermal storage is often used during system firing and a smaller, steady heat sink will recharge the thermal storage. The heat removal capacity of fuel as working fluid is at or near its capacity in future and current air platforms. Heat sinks are being sought that do not involve transferring heat to the fuel. Non-fuel heat sinks have the potential to add to the aircraft thermal signature, radar cross section or adversely impact the aerodynamic performance of the platform. The successful proposal will investigate heat sinks which do not significantly impact the thermal signature, radar cross section or the aerodynamic performance of sub and transonic aircraft and which have the capacity to continuously remove up to 100kW of heat at less than<40C at altitudes from 10kft to 40kft. PHASE I: Phase I will conduct a study examining heat sinks involving a variety of technologies, evaluating them for aircraft impact, heat removal potential, SWaP and potential for flight worthiness. At a minimum, the following should be considered: retractable fins, louvered scoops, third stream engine air, convection from aircraft skin and blow-down of engine and exhaust compatible substances. PHASE II: Phase II will build a subscale prototype system capable of being tested on surrogate heat sources in an appropriate vibration or wind tunnel facility. The Air Force Research Laboratory, Directed Energy Directorate, is able to provide testing facilities. PHASE III: Phase III will demonstrate the prototype system on a compatible aircraft with a suitable directed energy system or surrogate heat source. REFERENCES: 1. Hitzigrath, R.,"Improving Aircraft Fuel-Thermal Management,"SAE Technical Paper 932086, 1993, doi:10.4271/932086. 2. Gray, Charles N., and Shayeson, Maurice W.,"Aircraft Fuel Heat Sink Utilization," & doc=GetTRDoc.pdf & AD=AD0912902. 3. Karimi, Kamiar J., PhD, Senior Technical Fellow,"Future Aircraft Power Systems- Integration Challenges,"Carnegie Mellon University Press, 2007. 4. Swain, E.F.,"Aircraft Avionics Cooling, Present And Future,"Proceedings of the IEEE 1998 National Aerospace and Electronics Conference, 1998. NAECON 1998.
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