777-200LR Flight Test Journal: Archives

30 September 2005

Measuring it all

Richard Lamarre, lead instrumentation engineer on WD001

Luidel Bernitt, lead instrumentation engineer on WD002

The heart of what the Validation Instrumentation group does in flight testing the 777-200LR is to take measurements - sometimes in the tens of thousands - on all parts and systems of the airplane.

We measure practically everything; pressures, temperatures, positions, accelerations, loads, flows, video, electrical and digital buses. We start with measurement specifications that tell us what needs to be measured, the measurement range, the sample rate and the accuracy of each measurement.

After receiving the specifications, we make drawings and diagrams, as engineers do, which eventually go to a flight test manufacturing engineering planning group, where they become detailed plans to build and install the test parts. Next, the flight test manufacturing group uses those plans to install the test parts in the airplane. Then, with the help of manufacturing, we have to do a rigorous functional test of every measurement. As the program continues, we maintain the instrumentation every day.

The very last part of the program is refurbishment, where we work with manufacturing to take everything out and restore the airplane to its pristine shape and deliver it to the customer. So we are involved at the very beginning with design and go all the way through to the end.

We're involved in a lot of detail work, too. We design sensor installations all over the airplane. All of these sensors need wiring, and the wiring needs to be supported and go through bulkheads and ribs as it gets out to the wings, engines, tail, and down to the landing gear. We have to design access provisions for all of that wiring. For larger test programs there can be many miles of "orange" test wire routed throughout the airplane.

Once it all gets into the main cabin, the wiring is connected to racks which contain equipment for signal conditioning, multiplexing, power, communications, tape recording, video, engine monitoring, gross weight and center-of-gravity and data analysis and monitoring.

The flight test instrumentation can vary a lot between airplanes. There's even a huge difference between WD001 and WD002, the two 777-200LR Worldliners. Whenever the airplanes fly, instrumentation engineers are onboard. It's almost a never-ending job. When the airplane lands after a test flight, we actually begin preparing for the next day. We start reloading the data systems with new databases and repairing things that were broken in flight, and later begin to preflight the airplane and make sure everything is running. We cover about 20 hours worth of time a day.

Other flight test teams also report instrumentation problems. We troubleshoot the sensors, wiring, signal conditioning and the entire circuit from end to end to see what's broken. Usually sensors or something else fails every night. Don't forget some test flights can be pretty dramatic, with buffeting encountered during stalls, windup turns, zero or negative-Gs, performance landings and brake testing. Obviously we need a lot of spare parts. We carry a bunch of spare transducers and have a full inventory; almost anything you'd want. In the field we have to keep flying every day. We take truck loads of support equipment with us for testing at remote locations like Edwards Air Force Base, Calif.

It's amazing to look back to the start of the 200LR flight test plan - almost two full years ago. That's how long it takes to get ready. We started planning 23 months ago for WD001, and our first flight was just this past March. It's a pretty massive undertaking. Coming to the end feels like a weight being lifted from our shoulders little by little. However, when one test program ends, another begins.