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Aeronautical Supplier Puts the Brakes on Defects

You can rely on the laws of physics to stop a plane; the trick is making that stop both efficient and safe. For more than 20 years jet plane manufacturers have turned to the Dee Howard Co.'s braking systems to help accomplish that feat. To produce even better systems faster and less expensively, Dee Howard has turned to FARO Technologies' FaroArm portable measurement arm.

 Given the incredible speed and inertia produced by today's commercial jets, braking systems for jet engines are as technically sophisticated as they are crucial. These braking systems, or thrust reversers (TRs), are curved metal flaps that open up at the rear of an engine pod and redirect the high-powered air flow to curb the plane's forward motion. FARO's 3-D articulating coordinate measuring arms have helped Dee Howard produce its TRs more efficiently.

 Dee Howard has set industry standards for TR design in safety, dependability, quick deployment (one-second operation), efficiency and low maintenance costs. However, keeping up with the latest engine designs requires manufacturing to tighter tolerances and schedules. To this end, the company needed to improve its inspection processes on several fronts. It needed to increase the speed and accuracy of its measurement techniques, maintain a more detailed paper trail to satisfy federal aviation standards for record keeping on critical safety components, and meet customers' testing requirements when working with prototype aircraft.

 In the past, measuring the neck of the TR was difficult and time-consuming. Dee Howard quality control engineers used a two-part mechanical fixture to measure every unit. The engineers used a micrometer and had to input the results manually into a computer program, which then calculated the average area of the unit. Because these measurements are a post-manufacturing engineering requirement, engineers couldn't rely on sample testing--and this tedious process was required for every TR produced.

 Dee Howard still measures the dimension of every unit; however, the process now takes about 20 minutes as opposed to three hours. "The time saving is astronomical, not to mention the accuracy," notes Bill Awbrey, a Dee Howard quality control lead inspector. "Instead of measuring the 36 points that were taken before, now we're taking hundreds of points."

 The FaroArm is an internally balanced device made of aircraft-grade aluminum, with precision bearings and rotary transducers at each of its six joints. It sets up quickly, mounting on either a fixed surface or portable tripod, and folds to fit into a portable case. The arm's freedom of movement provides a base spherical measurement envelope of up to 12 feet, but this range can be increased indefinitely as the user moves the unit to a new location and realigns the target datums. After purchasing an 8-foot FaroArm in September 1995, Dee Howard has since acquired a 12-foot model.

 In addition to the measurement of finished products, Dee Howard also uses the arm for tooling inspection. The inspection program regularly looks at specific critical dimensions and compares those values to those previously recorded to detect any change. That process, as well as the necessary record keeping, is now faster, more accurate and more sophisticated with the FaroArm.

 The TR narrows near the aft portion, where exhaust gas would exit in normal operation, to a neck whose cross-sectional area is critical to the system's long-term performance, which in turn makes its accurate measurement just as crucial. "If the area is too small, it can create back pressure that can severely limit the life of the TR," says Awbrey. "Conversely, if it's too wide there are other effects, including reduced apparent thrust, poor fuel economy and higher exhaust gas temperatures."

 For this and many other tasks, Dee Howard now uses the FaroArm. The FARO probe sends data to an onboard digital signal-processing unit that translates each recorded location into 3-D coordinates. Probe calibration only takes about five minutes and is only required when the operator changes probes.

 Quality control engineers at Dee Howard continue to set new standards in their field, just as they continue to find new uses for their FaroArms. Awbrey foresees increased cooperation between manufacturing and engineering, and continuously improving tooling and subassembly accuracy. The FaroArm is now an integral part of Dee Howard's drive to make great thrust reversers better, he notes.