Aircraft and other vehicles are often kept in service beyond their original design lives. As they age, they become susceptible to system malfunctions and fatigue. Unlike future aircraft that will include health-monitoring capabilities as integral parts in their designs, older aircraft have not been so equipped.
The Adaptable Vehicle Health and Usage Monitoring System is designed to be retrofitted into a preexisting fleet of military and commercial aircraft, ships, or ground vehicles to provide them with state-of-the-art health- and usage-monitoring capabilities. The monitoring system is self-contained, and the integration of it into existing systems entails limited intrusion. In essence, it has “bolt-on/bolt-off” simplicity that makes it easy to install on any preexisting vehicle or structure. Because the system is completely independent of the vehicle, it can be certified for airworthiness as an independent system.
The purpose served by the health-monitoring system is to reduce vehicle operating costs and to increase safety and reliability. The monitoring system is a means to identify damage to, or deterioration of, vehicle subsystems, before such damage or deterioration becomes costly and/or disastrous. Frequent monitoring of a vehicle enables identification of the embryonic stages of damage or deterioration. The knowledge thus gained can be used to correct anomalies while they are still somewhat minor. Maintenance can be performed as needed, instead of having the need for maintenance identified during cyclic inspections that take vehicles off duty even when there are no maintenance problems. Measurements and analyses acquired by the health-monitoring system also can be used to analyze mishaps. Overall, vehicles can be made more reliable and kept on duty for longer times.
Figure 1 schematically depicts the system as applied to a fleet of n vehicles. The system has three operational levels. All communication between system components is by use of wireless transceivers operating at frequencies near 433 MHz. Electromagnetic-interference tests have demonstrated that the radio frequency emissions from the transceivers do not influence civilian aircraft communication and navigation systems.
The first level of the system includes one or more remote data-acquisition units (RDAUs) placed at different locations within each aircraft or other vehicle. An RDAU acquires, stores, and analyzes sensor data. The user has the capability to define the number of inputs, type of sensors, sensor input characteristics, aggregate sampling rate, and acquisition period duration. This information is used to configure the sampling interface and its associated multiplexed eight-channel analog-to-digital converter. An RDAU can analyze measurements from each channel individually or from all channels fused together. Programmable data-acquisition circuitry and expert-system software trained to performance baselines in each RDAU make it possible to adapt the system to many types of vehicles and structures. The RDAU has been tested at temperatures from –50 to +55 °C. Pressure testing has verified that RDAUs could be used in non-environmentally-controlled spaces on aircraft at altitudes up to 50,000 ft (15.24 km). Vibration tests have verified that RDAUs can operate during vibrations representative of those of commercial aircraft. The final vibrations used in the tests had an amplitude of 20 times normal Earth gravitational acceleration and a frequency of 2 kHz.
The second level of the system includes a command-and-control unit (CCU) in each vehicle. The CCU regulates the health monitoring activities in the vehicle. The CCU is a computer-based subsystem that controls communications to and from all RDAUs; regulates all RDAU measurement, collection, and analysis; and retrieves the results of all data-collection and analysis performed by the RDAUs.