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Aviation History
1991
1991 - 2640.PDF
Do.328 DESCRIBED Vying for power the Dornier Do.328, company narrowed For th, down the final choice of engines to the General Electric CT7-9D, Garrett TPE-341- 21 and the Pratt & Whitney PW119, says Gunter Rieck, devel opment project manager for the aircraft. Pratt & Whitney emerged the winner after a detailed evalua tion. Rieck says: "We ran through an analysis of all the different aspects of the engines, looking at criteria such as the performance and weight of the engine, installation, complexity of the mounting sys tem, inlet configuration and for eign object separation, and fuel and electrical systems". The company also examined the engine performance offered by the manufacturer and then calculated the resulting aircraft performance of each engine configuration. Beside evaluating the engine it self, Rieck says Dornier also paid attention to the backup services. "We examined product support, reliability, customer sup port, spares and ground support equipment, along with warranty and guarantee criteria," he says. Dornier also went to the operators to evaluate the market standing of the engines. "We wanted to try and determine the level of acceptability in the market. We got responses from different operators. Obvi ously this is not so easy to do, but we felt it was important, and it had a major effect on our decision," says the company. Dornier also considered engine price, and whether it would have to contribute to development costs. The result of the six-month evaluation proved to be less than completely decisive. "The Pratt & Whitney and Garrett engines were very close together," says Rieck, who adds: " On the technical side, the Garrett came out better. For instance, it had full- authority digital engine control. Overall, the pluses and minuses balanced out between the two engines, and the Pratt & Whitney engine was already developed." Despite the tortuous evaluation process that led to Dormer choosing the PW119, the period since has not been glitch-free. "When we selected Pratt & Whitney," says Rieck, "we agreed that the engine should be able to incorporate 10% growth in power without changing the hardware. At the end of last year we asked Pratt & Whitney about this; a customer was inter ested in hot-and-high performance and also payload growth." Garrett was a close contender, but Pratt & Whitney won the contract The outcome of this enquiry was that the engine, as originally selected, did not have the forecast improved power margin. "Pratt & Whitney investigated this and found that the PW119 doesn't have the growth poten tial. Instead they came up with a version called the PW119A, which offered a 10% improvement in thermodynamic perform ance, particularly at cruise speeds at 25,000ft [7,600m]." The potential power increase between the PW119 and the PW119A is from 855kW to 940kW, and possibly more. The major change is the adaption of the PW124 compressor for the PW119A, with an over all engine weight increase of 4kg. Approach noise is reduced, however, claims Rieck. Pratt & Whitney is paying for developing the variant. Initially, Rieck says, the engines will be installed at the PW119 power level, but increased power will be available if Dornier wants to exploit it. The first PW119A engines will be completed by January next year, and Rieck says that all the test aircraft will be fitted with these by the time performance tests are carried out. A similar evaluation process was carried out for the choice of pro peller, with Dowty, Hamilton Standard and Hartzell the three main contenders. Rieck says: "We wanted the propeller to be as light as possible and, because of noise requirements, we were sure to select a six-bladed propeller". Hartzell was extremely close to Dornier's requirements, with a large gap in terms of meeting criteria between the Hartzell corn-weight posite-blade propeller and those offered by the competition. "We had to consider Hartzell's lack of experience in dual-acting propellers," says Rieck, however. Despite this, Dornier opted for Hartzell. The Do.328's dual-acting propeller sys tem utilises a piston in the propeller hub, capable of adjusting pitch to maintain constant engine rpm and also to feather the blade when required. This is lighter than a single-acting propel ler, which uses flyweights and springs to control rpm by adjusting pitch. Noise levels are also reduced by propeller synchro- phasing. • Payload/range comparison Dornier 328 immxtw. © Reed Business Publishing Group 400 600 800 1000 1200 1400 1600 1800 2000 Range (nm) 34 FLIGHT INTERNATIONAL 9 - 15 October, 1991
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