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Real-time Tactical Aircraft Fuel Ullage Oxygen Sensor System for Inerting Operations

Description:

OBJECTIVE: Increase survivability of advanced tactical aircraft as protection against fuel tank explosion and lightening strike vulnerability throughout the flight envelope by using a real-time oxygen sensor measurement system for fuel-tank inerting. DESCRIPTION: Higher levels of oxygen present in the air/fuel vapor space (ullage) of tactical aircraft fuel tanks increases risk of explosion and fire due to ballistics, lightning strikes, and other system failures. Oxygen content of this ullage must be controlled to levels of 9 to 12 percent by volume. In order to displace oxygen in the tanks, nitrogen-enriched air (NEA) from an inerting system, often called the Onboard Inert Gas Generation System (OBIGGS), is pumped into the fuel ullage. A real-time oxygen sensor system is desired for adaptive closed-loop feedback control of NEA from the OBIGGS pack in energy optimized aircraft. This will reduce the demands on the environmental control system when tanks are already inert. This reduction will enable more efficient use of engine bleed air for cooling flows for avionics, aircrew, electric power generator, fuel, and propulsion systems. Ideally, a fuel tank ullage oxygen sensing and monitoring system should also provide a real-time fuel tank temperature and pressure measurement for thermal management system calculations, determining liquid fuel thermal capacity remaining in the fuel tank. Current sensors are applicable to cargo aircraft operating under different mission profiles. These current systems have not been fully matured and integrated into tactical aircraft systems, and are not fully environmentally qualified electronics units with appropriate aircraft interfaces. New generation sensor systems, to include the sensing probe and electronics unit (EU), must be redesigned and fully evaluated for current and next generation tactical aircraft needs, as well as integrated into the aircraft electrical and fuel inerting control systems. Emphasis should be placed on total system development. The desired system will not only provide active control incorporating multiple sensor feedback in closed loop, but also provide feedback to the cockpit for pilot awareness. The complete sensor system must provide accurate, reliable operation over temperatures and pressures experienced in advanced tactical aircraft fuel tanks in the flight envelope, be intrinsically safe, and survive under shock and vibration loading during takeoff, landing, and mission profiles. Anticipated temperatures range for the sensor probe from -45 degrees F to 215 degrees F (the electronics unit must operate from -60 degrees F to 160 degrees F) and pressures range from atmospheric down to 50,000 ft in altitude. It must be lightweight (less than 5 pounds), durable, low cost, able to interface with aircraft electrical and control systems (IEEE 1394"Firewire"), and must have low power consumption. The sensing probe must be compatible with fuel and fuel vapors. In addition, while not a critical requirement, if the sensing system is designed to incorporate a bulk fuel temperature/pressure sensing capability, it is highly desired that this be incorporated into a single compact unit, i.e., one sensor system versus two. PHASE I: Design and demonstrate feasibility of a new generation oxygen sensing system for fuel tank inerting and lightning suppression at pressures and temperatures experienced within a tactical aircraft flight envelope. Control and operation of a feasible sensor system can be shown by laboratory investigations. PHASE II: Complete full development of a production representative sensor system and demonstrate in a simulated relevant tank environment. Abbreviated testing of the sensor system under MIL-STD must be conducted and qualification testing of sensor interface must be completed. A full-scale, simple-to-operate working unit is desired for delivery to the Air Force at the completion of this program phase. PHASE III: This technology is also directly applicable to commercial aircraft. It is encouraged to develop commercial partnerships for transition into commercial aircraft as well as with prime contractors to the military and their suppliers. An oxygen sensor system should be developed as an end product. REFERENCES: 1. Ritter, K.J. and T.T. Wilerson,"High Resolution Spectroscopy of the Oxygen A Band,"Journal of Molecular Spectroscopy, 121: 1-19, 1987. 2. Smith, R.J. and Casey, William L.,"Dart: A Novel Sensor for Helicopter Flight Safety,"Photonics Spectra, 110-116, July 1992. 3. Silver, Joel A.,"Frequency-modulation Spectroscopy for Trace Series Detection: Theory and Comparison Among Experimental Methods,"Applied Optics 31 (6), 707-717, 1992. 4. Technical Performance Measurement requirements for a tactical aircraft sensing system. [Will be provided in SITIS after Pre-Release.]
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