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Aviation History
1991
1991 - 3240.PDF
SAAB 2000 DESCRIBED the engine case: this is driven off the high-pressure spool, at spool speed, via straight-cut bevel gears and a shaft. Normal rotational speed-for the high-pressure spool is 14,428rpm: the low-pressure spool ro tates at 15,378rpm at take-off rating, and at 13,280rpm in climb or cruise. Aircraft accessories are driven off the back of the propeller reduction gearbox. Interestingly, this accessory gearcase is self-contained, even having its own independent oil supply. The main engine oil tank is a Saab-specific item, a massive fabrication hung to the side of the power section. The GMA 2100 power section weighs some 435kg: with the gearbox, but dry, it weighs 702kg. For the Saab 2000, the GMA 2100 is flat-rated at 3,097kW (4,152shp), which power output it can maintain at ambient temperatures of up to 37°C. The variant for the IPTN N250 will be lower-rated, at 2,610kW, retaining that rating at up to 44°C. As the development engines have been run at nearly 4,500kW, there is obvious uprating potential for both these existing customers. The power unit's nacelle is built by an Allison-led team, which is responsible for the control system and systems integration: the structure and cowls are built and assembled by Westland Aerospace, with Lord Mounts responsible for vibration and noise limitation, Hispano-Suiza for systems design and manufacture, AiResearch for the air-turbine starter and Lucas for the alter nating-current generator. SLOW-TURNING PROPELLER Saab has selected a Dowty six-bladed 3.81m propeller for the 2000. As part of Saab's drive to reduce noise and vibration, the propeller turns at the unusually low speed of 950rpm in the cruise, compared with l,250rpm for the Saab 340's propellers. The goal for interior noise is an average 76dBA. Saab says that the biggest contributor to interior noise is blade-pass frequency, which in this case is 95Hz. To reduce the effect of the propellers on cabin noise, the blade-tip-to-cabin-wall clearance is double that of the 340. Other major contributors to airborne noise are propeller slipstream, including its excitation of the tail. Saab has done much computer analysis of the fuselage structure under such excita tions, tracing the pressure waves and their effect. It has found that not only does the propeller pressure field rotate with the propeller as expected, but the resulting pulses move up and down the length of the cabin, leading to considerable cyclic distor tion. It has found that the effect is much reduced if the pressure waves from the two propellers are in line: the propellers' con trols will ensure that the blades are in phase at all times. Some 150 pairs of visco-elastic cylindrical vibration dampers are attached to the structure. 14 SAAB 2000 DESCRIBED Taking 2000 to market It is a measure of the relationship between Saab and Crossair, launch customer of both the 340 and 2000, that Crossair's charismatic president, Moritz Suter, was able to demand a window in the toilet of the new aircraft. "We live in such a beautiful area, with all those mountains", he says, "that we can't afford that our passen gers miss one second of that view". Suter was one of the first to convince Saab that a 50-seat high-speed commuter was needed. "For him, the market was obvious," says Christer Skogsborg, general manager of Saab aircraft, "and he pushed us very hard; but we wanted a worldwide requirement, and particularly we wanted to get the USA involved. We had heavy finan cial commitments, and our workload was very high, so we had to delay the pro gramme until it was better for us." ORDER BOOST In early 1989, shortly after the (non-fatal) landing accident to one of its prototype JAS39 fighters had knocked Saab's confi dence, American Airlines put options on 50 2000s, along with a firm order for 50 Saab 340s. This, coupled with Suter's firm order for 25 of the 50-seaters and the same number of options, gave Saab the boost it needed to go ahead with the 2000. Saab has sold just 46 2000s so far, with options on 146, the principal launch cus tomer besides Crossair being Northwest Airlines' subsidiary Northwest Airlink, with ten firm orders. The orderbook is clearly not overflowing — but Ahlborg remains bullish, and hints that significant orders are just around the corner. Ahlborg thinks the 2000 should pick up "at least a third" of the 1,200-aircraft market for 50-seaters, and that some of the orders will be big, saying: "No question about it. We're already seeing regionals tied to the major airlines in Europe, even if, like Crossair, they are operating independently." The majors, Ahlborg contends, "... want to standardise their equipment in order to provide as seamless a service between air craft as possible". The 340, from which the Saab 2000 is derived, has captured more than 60% of the European market for 30- to 40-seaters, and 35% of the world market, according to Saab. "The 340 changed our culture completely," says 2000 programme manager Oster, "from one that was geared mainly to military aircraft, to one that was properly balanced Skogsborg (inset) "...wanted to get the USA involved:" Skywest took 20 options FLIGHT INTERNATIONAL 11 - 17 December, 1991
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