Aircraft Maintenance Technology

APR 2014

The aircraft maintenance professional's source for technological advancements, maintenance alerts, news, articles, events, and careers

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M I L I TA R Y 26 April 2014 AIRCRAFT MAINTENANCE TECHNOLOGY E very aircraft, whether business, commercial, or mili- tary, is an expensive asset and downtime is expensive. Most aircraft are repainted about every seven years to inspect for corrosion and improve aesthetics. Besides full aircraft, parts such as nacelles, radomes, and f light controls are often removed for repair then repainted off-aircraft. Composite aerostructures in particular require special care, as substrate damage is very costly. Composites are in progres- sively greater use on modern aircraft (787, A350) and there are 20,000 planes in the commercial f leet. Military aircraft, particularly the F-22, F-35, and C-17, have a significant share of composites as well. Prior to painting, every surface must be prepared so that the new paint will adhere properly. Currently, while some surface preparation tasks are per- formed with chemicals (aluminum fuselages are often stripped this way), all of the composite surfaces, and some of the alumi- num ones, are abraded manually with random orbital sanders and coated abrasive discs. Sometimes the goal is to remove all the Whole Lotta Sanding Going On The technology will prevent exposure to vibration and dust, will help the operator sand faster and more consistently, yielding the best possible fnish in the least amount of time. By Robert Kent old paint (to reduce weight and/or inspect for corrosion) before new paint is applied, and sometimes the goal is just to reactivate the surface so the top coat will adhere well. Sometimes, vacuum systems are integrated into the process, facilitating dust collec- tion at the source to minimize operator exposure. Both finish quality and material removal rate are driven by several factors, including abrasive type, tool speed, sweep rate, and contact pressure (a function of how hard the artisan is push- ing and whether the sander is f lat on the surface or tilted). Skilled artisans can accommodate these factors in real time — e.g. as an abrasive disc wears, an artisan can sweep more slowly or push harder. Ideally, every artisan would be sanding exactly the same way so the resulting finish is as consistent as possible. Technical and ergonomic issues One major challenge is that industrial-duty pneumatic sand- ers weigh a lot, particularly with attached hoses, and expose the operator to harmful vibration. Holding a heav y vibrating tool out in front of you, or up over your head, is an ergonomic nightmare. Aircraft are large enough that there is a lot of reach- ing involved, and awkward postures also contribute to the high injury rates in many shops. Injury risks include hand- arm vibration syndrome (H AVS) and repetitive stress injury (RSI). These lead to a high incidence of shoulder, arm, wrist, and hand surgeries, dramatically affecting the worker's quality of life, not to mention their overall productivity. The sander's weight and vibration make it difficult for the arti- san to keep the sander f lat on the surface. A tilted sander leads Military customers value the technology's ability to prevent worker exposure to hexavalent chromium and vibration, to address the challenges of chemical agent resistant coating (CARC) paint, and to reduce flowdays. TEMPLE ALLEN AMT_26-27_MilitarySanding.indd 26 4/3/14 1:57 PM

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