Ian Sheppard/PARIS
Hispano-Suiza has carried out new extreme attitude tests on the BMW Rolls-Royce BR715 engine accessory/transfer gearbox assembly for the Boeing 717. The tests are designed to ensure that the aircraft can cope if it encounters an abrupt drop in air density.
Jean-Luc Doublet, vice-president of Hispano Suiza's aeronautical equipment division, says the tests were required by Boeing following cases of severe clear air turbulence such as that encountered by a United Airlines Boeing 747 between Tokyo and Honolulu on 28 December, 1997. On that occasion the aircraft experienced forces of -0.8g.
The tests are being carried out at the company's Colombes plant near Paris, and cover "no-load" followed by "load" tests. Doublet says the gearbox is inverted to ensure that in such an event the scavenge pumps remain effective and do not become "unprimed" or excessively hot owing to low oil levels, and that no oil becomes trapped.
The current test rig inverts a gearbox and its accessory equipment in 20s, says Doublet, although Boeing asked for a shorter time. "Boeing requested simulation of an air pocket after the Tokyo-Honolulu incident", he says, adding that the current requirement was only for -1g "gravity inversion".
"We turn it upside-down quickly, wait 50s until all the oil is opposite the scavenge and turn again to achieve a pressure peak in the oil tank," says Doublet. The worst case is far easier to test on a rig than in flight trials, he adds. The first two production gearboxes are to be delivered in August.
Meanwhile, the company is working to cut costs. Its Colombes plant has been tasked with reducing production lead-time for new designs to 20 weeks. This is being helped on the BR715 gearbox by the introduction of the ProEngineer parametric modeller computer program, an "expert system" to refine the design automatically. Each gear has around 24 parameters, says Doublet, who adds: "The new design makes it very easy to change gears 'under the wing'."
In addition, the time to surface treat a gear has been cut from three weeks to three days since the operation was moved to Snecma's Colombes plant in early 1997, while a new $0.8 million furnace will see treatment fall to 6h, saving 10% in the cost of each gear, believes Doublet. "Low price is a big challenge, especially if you want 30,000h reliability", he says.
Source: Flight International
