On-wing diagnostics monitor engine performance

Greg Reed, Technical Editor -- Test & Measurement World, 11/1/2004

Manufacturers of aircraft engines are always on the lookout for ways to measure and evaluate the performance of their products. One recent addition to turbine aircraft engine diagnostics is a module that tests engines while mounted in flight position.

Developed by VI Engineering (Farmington Hills, MI; www.viengineering.com) for one of its customers, the breadbox-sized module works with LabView software from National Instruments (Austin, TX; www.ni.com). Technicians use the module, which is mounted with tie-down straps and anti-vibration gear, to perform periodic maintenance tests on an aircraft's engine.

Technicians can install and set up the unit in about 2 hrs. It then performs engine diagnostics and real-time data collection in about 20–30 min of engine operation. The unit advances the engine through a preprogrammed sequence of RPM and temperature set points, logging steady-state engine data at each point as well as collecting historical data for the duration of the test. Over the life of each aircraft engine, diagnostics logging of performance is expected to improve routine maintenance by pinpointing specific engine hardware that needs replacement.

The test system produces real-time data with a plug-and-play data-acquisition device. The unit does not require a user interface or need to communicate with a remote computer. Device input and output is achieved with a compact flash card, LEDs, and DIP switches.

Two LEDs indicate the engine status after power up and also communicate the test status and any errors to the technicians. Three user-configurable DIP switches set the device to input configuration data and run tests.

As the system boots up, it checks for updated setup and calibration files on the compact flash card, begins data acquisition and FIFO data buffer for pre-trigger scans, and then waits for the first trigger condition to be met. Upon meeting the first trigger, the pre-trigger scans are saved and the historical datalog begins streamlining data to the compact flash card.

If the system meets an error condition, the LED will turn red and the application will abort. An "Extract" mode transfers the current setup and calibration files from the system to the compact flash card.

An I/O module enables two types of measurements on a pair of incoming pulse strains for figuring phase difference and RPM of the engine. The data file structure and format, recorded on the compact flash memory, can be exported to an Excel spreadsheet for analysis.

In responding to customer needs, major aircraft engine manufacturers look for automated solutions that address test and measurement concerns. This system replaces a manual test checklist previously performed by technicians looking at gauges on the plane.

Since data collection by hand entry is cumbersome, real-time data collection affords easier gathering and recording and also offers analysis capabilities. Units can be made available at the point of sale for all customers, and airplane technicians can operate this toolkit without specialized training.