Michelin weighs options for 787 tire technology
Michelin still has to decide whether to offer its near-zero-growth tire technology to the Boeing 787 program. The U.S. airframer has already selected the French manufacturer as a 787 supplier, but the tire maker has yet to fully weigh the pros and the cons of employing the NZG material that is already available for the Airbus A380 and A340-500/600 airliners and Dassault Falcon 7X business jet.
The NZG technology (available with radial structures only) gives the tire more damage resistance. Its first application was on the Concorde, after investigators discovered that a tire burst triggered the July 2000 fatal crash when the tire hit a foreign object on the runway. When heated by contact with the ground, an NZG tire expands less than a usual radial tire–3 percent versus 8 percent–therefore, it is more resistant, just as a rubber band is difficult to cut unless it is stretched.
Safety is not the only attractive feature of the NZG tire. The new NZG material allows the manufacturer to make the tire thinner, thus it encounters less heat, less fatigue and, consequently, less wear. In some applications, however, NZG tires do not bring enough benefit to substantiate their higher price.
On the A380, one NZG tire bears more than 72,000 pounds at speeds up to 200 knots. Michelin, which competes with Bridgestone for A380 tire business, claims the NZG allows a total weight saving of 800 pounds while still achieving this high load resistance.
Low weight and high load resistance are two of the five design criteria for aircraft tires. The others are wear resistance (the number of landings a tire can perform before retread–typically 300 for a commercial airplane), endurance (how many times a tire typically can be retread–from two to seven) and speed capability.
Michelin offers both bias-ply (the most conventional) and radial (the most modern) technology to all four market segments: commercial, regional, military and general aviation. According to the company, radial technology is statistically safer. Michelin claims to have one third of the world market, including both original equipment and retrofit, and two thirds of the market for radial tires.
Asked why radial technology has not forced bias technology out of the market yet, François Corbin, Michelin’s director of the airplane product line, explained how deeply tire technology influences an aircraft’s design. It is not just a change of rims on the wheels. “The strains transmitted to the aircraft are different–during turns, for example and impact the entire landing gear’s design,” he said. Therefore, it would be too expensive to redesign aircraft originally fitted with bias tires.
Michelin now offers commercial operators pay-per-landing terms. “We sell a number of landings and take care of retreading the tires,” Corbin explained.
The company is vying for selection for the tire requirement on both the Russian RRJ and the Chinese ARJ regional jets.