GEC’s Low Profile Scales Simplify Aircraft Weighing

Originally seen in Aviation Maintenance in December 2006

Weight. It’s a constant struggle! No, not your weight, aircraft weight. Each piece of equipment added, each piece of debris or trash fallen under the seat or floorboard adds to the overall weight and balance of an aircraft. Weighing aircraft is a precise science that requires proper procedures and equipment. Jacking aircraft up to weigh them can be cumbersome and dangerous. General Electrodynamics Corporation (GEC) has developed a platform weighing system that requires less space and time to accomplish the task of weighing an aircraft.

Naval Air Systems Command contacted GEC about developing a lighter, more accurate and more portable scale for their jets. “They needed the accuracy to be one-tenth of one percent and to accurately calculate the jet’s center of gravity for performance and safety issues,” said Dick Davis, owner and CEO of GEC. The company set about achieving a platform scale that could meet the Navy’s requirements and did just that. “Most commercial scales accuracy is based on a percentage of full-scale, allowing errors of 15-50 pounds. GEC’s product accuracy is based on applied load or the actual weight applied and is accurate to one-tenth of one percent,” said Davis. The technology used in the scale also includes a self-leveling device, not a sheer beam or steel flex. The top piston of the self-leveling load cell automatically orients itself to be perpendicular to whatever force is applied to it. It can do this at an angle up to five degrees off the perpendicular. “No shims are needed,” said Davis.

“Our self-leveling transducers are tested 250,000 times without failures.” The scale also compensates for other variables such as gravity, temperature, and latitude and longitude. “If you weigh a 747 in Seattle, it will not weigh the same in Sydney, Australia, simply because of the gravitational pull of the earth,” said Davis. “But our internal software automatically corrects for these variables.” The GEC low profile scale, measures 1 and 7/8” high, and weighs only 80 pounds. Aircraft have towing restrictions that they can’t be towed over a three degree incline because connecting to the aircraft nose gear and towing it up a steep incline puts excessive stress on the nose-gear components. “We have the lowest profile in the market,” said Davis. “It takes 1/3 the space to weigh an aircraft with our product than with others.” When using a steeper inclined platform scale, ramps and bridges need to be built to accommodate the three degree incline rule.

“A four-inch scale would need a three degree angle ramp. That works out to be a 96 inch long incline vs. a 29 inch long incline,” said Davis. To weigh aircraft one scale per tire is needed. To weigh a 747 that has 18 tires, you will need 18 scales. Using the correct number of scales the aircraft is positioned and moved onto the scales. Then the aircraft is leveled. The main gear and a plumb bob are used for the leveling process. The struts are inflated or deflated to level. Once the aircraft is leveled, it is taken off the scales and then put back on. The measurement is taken and then it is taken off the scales again. “There are two ways to get the info from that point. One is to walk around and take the readings and write each one down,” said Vincent Smart, international sales manager, commercial aviation. “The other way is to use the wireless scale. The readings are sent via a wireless device and all the calculations are made and then given to you on the handheld Windows-based unit. With the wireless system, the time is reduced to 15 minutes or less.” GEC recently weighed a C-5 at 561,000 pounds. They used 28 scales, one scale per tire, at Edwards Air Force Base. The aircraft was weighed three times. The measurements were within 0.05 percent, or five times as accurate as required according to Davis.

“In 1978 we designed the first platform weighing system. It was so unique it was patented. Since then we have sold 20,000 of them,” he said. “Calling our product just a scale is not doing the product justice, GEC’s product truly is a precision weighing device.”

Click here for on how to learn more about aircraft weighing!