Condition-Based Maintenance Advantages for Military Applications

ESA can enhance military vehicle reliability and operational readiness by providing improved diagnostics (present condition) and prognostics (future condition) for critical electro-mechanical equipment. Military vehicles encompass aircraft, ground vehicles and ships, both manned and unmanned. ESA can be an integral part of a military Functional System Integrity Program (FSIP) and Mechanical System Integrity Program (MECSIP). Advantages gained from applying the technology include:

• Increased vehicle availability; reduced down time
• Reduced mission aborts due to equipment failure
• Maintenance man-hours saved
• Improved ability to manage and plan maintenance
• Maintenance cost savings
• Prior to deployment verify equipment condition and identify equipment needing repair or replacement
• Reduce size of war fighter's kit needed for deployment
• Improved safety

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Fuel Pump Condition Monitor

Fuel Pump Condition Monitor Developed for C-141 Aircraft (913KB)
Demonstration of C-141 Fuel Pump Condition Monitor at Wright-Patterson Air Force Base

Aircraft fuel pumps provide fuel to multiple engines from the wing fuel tanks. A total of twenty pumps are used in the C-141 Starlifter, with one primary pump and one secondary pump in the main and auxiliary fuel tank for each of the four engines and in the extended range fuel tank in each wing.

C-141 Starlifter and Auxiliary Fuel Pump

Clamp-on current probes are used to acquire motor current signals from all three phases, plus neutral. Data acquisition and analysis is performed by a laptop computer running specially developed ESA virtual instruments. Signal pre-conditioning and interfacing is handled by an I/O chassis that sits below the computer. ORNL developed ESA algorithms and diagnostic procedures based on field and laboratory testing. Together with Air Force engineering and maintenance personnel, ORNL is developing a specification for a field-ready ESA-based diagnostic instrument that can be integrated into their fuel pump maintenance processes.

Fuel Pump Condition Monitor Hardware

The C-141 Fuel Pump Condition Monitor (FPCM) is a self-contained, portable system for acquiring and analyzing fuel pump motor current data. The system is comprised of a suitcase-style hardware platform that includes a rugged laptop computer, custom-designed signal conditioning electronics, and four inductive current probes that are simply clamped-on to the fuel pump power leads (T1, T2, T3, and neutral).

Click on a C-141 Fuel Pump Condition Monitor
software screen image above for enlarged view

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Integrated Drive Generators (IDGs)

Integrated Drive Generators (IDGs) on certain aircraft experience complete failure, on average, at a rate of four per year; as many as ten have failed in one year. The causes are seizure and destruction of scavenge, drive pump, and axial gears on the generator's main shaft. Traditional re-certification tests do not detect incipient gear failure. If the $17,000 gear sets seize, the $250,000 IDG is essentially ruined. The capability to predict gear failure or incipient failure represents substantial savings for owners in replacement costs.

IDG units provide power to commercial aircraft (117/208 volts at 400 Hz) for passenger reading lights and galley microwave ovens.

To maintain their reliability, effective measures are needed to detect the onset and levels of gear wear. ORNL has demonstrated both on a test stand and on a jet that ESA techniques provide the signature attributes necessary to characterize good and worn gears. The strength of ESA is that current and voltage probes are easy to attach and use for monitoring, with no additional mounting required. Results show that even at extremely low generator loads, ESA provides excellent sensitivity to the gear-related problems.

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C-141 Electric Pitch Trim Actuator

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Aircraft Pitch Trim Actuator

An electric Pitch Trim Actuator (PTA) system, like that used on the C-141 is an ideal component for ESA-based condition assessment. PTA motor current signals were obtained by ORNL on a C-141 located on the flight line at Warner Robins Air Logistics Center on February 4, 2003, and on a C-141 PTA test stand at Ogden Air Logistics Center, on April 16, 2003, where the PTA was tested under various operating loads.

On the flight line, PTA motor current signals were easily obtained in the cockpit. When the PTA was tested under load at OO-ALC, significant fluctuations in the RMS motor current were detected that likely result from load variations caused by the PTA output gear and jackscrew. In addition, the motor current spectrum provided a direct indication of motor speed, and also included many additional frequency components that are likely to be useful in monitoring the condition of the motor, jackscrew, and other PTA components.

Close-up of C-141 T-Tail

C-141 PTA Test 2-4-03 at WR-ALC (850KB)

C-141 PTA Test 4-16-03 OO-ALC (406KB)

Aircraft Generator

On February 28, 2003, a Navy P-3C electric generator was tested at NAVAIR (Pax River). The generator output current through a constant load was monitored and analyzed using ESA methods. Many features related to generator running speed were detected in the electrical signature, including dominant peaks at multiples of eight times generator speed. These features likely result from the generator's eight poles and eight rotor bars. This preliminary test confirmed that ESA is a viable diagnostic technology for aircraft generators.

P-3C Generator Test 2-28-03 NAVAIR (1.06MB)

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Helicopters

ESA methods were used to assess the diagnostic potential of voltage signals obtained from three tachometer generators used by a Bell Jet Ranger helicopter. The results were very encouraging. A method was identified for relating features in the rotor tachometer generator output to mechanical unbalance in the main rotor. In addition, the voltage outputs from the helicopter's turbine tachometer generators were used to detect and monitor the gear mesh characteristics of several gear train components.

The Voltage Outputs From the Helicopter's Turbine Tach Generators Contain
Information on Several Gear Train Components

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Other Applications

The development of ESA has spanned over fifteen years and has benefited from the testing of a wide variety of devices:

Air Compressors Textile Plant Motors Navy P-3C Generator Electric Fuel Injectors Variable Speed Motors Multi-Axis Milling Machines Diesel Engine Starter Motors NASA Propellant Control Valve Power Plant Pumps and Valves Navy Fire and Seawater Pumps Large Chillers, Blowers and Fans Helicopter Tachometer Generators Army Tactical Quiet Generator (TQG) Gaseous Diffusion Plant Compressors Electric Vehicle Motors and Alternators Consumer Appliances and Power Tools Heat Pump and Air Conditioning Systems Army Prototype Ammunition Delivery Systems Commercial Aircraft Integrated Drive Generator Air Force C-141 Fuel Pumps & Pitch Trim Actuators

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