By 1980, airlines may be trading in some of their jet aircraft for some propeller-driven airplanes similar to the ones they used 30 years ago, a Lockheed Corp. official predicted yesterday.
"We believe propellers are about ready to make a big comeback," William E. Arndt, manager of the propulsion and acoustics department of Lockheed-Georgia Co., told listeners at a technology symposium yesterday.
Unlike the turboprops that vibrated noisily and relatively slowly across the country in the 1950s, however, the new aircraft will have advanced-technology propellers that will allow cruise speeds and levels of cabin comfort comparable with modern turbofan jet aircraft, he said. In addition, the new aircraft show promise of consuming between 15 and 20 percent less fuel than those with turbofan engines.
According to Arndt, Lockheed will propose designing and modifying an existing aircraft for full-scale flight research of the new type of propeller, called the "propfan," later this year or early next year at the request of the National Aeronautics and Space Admiistration. NASA currently plans to flight-test such a plane in 1986, he added. So far, testing has been limited generally to scale models in wind tunnels.
Lockheed has been considering a number of off-the-shelf engines and aircraft to convert for the test but currently is leaning toward Gulfstream American's Gulfstream II airplane and a Detroit-diesel Allison engine, arndt said.
The innovative kind of propeller, with potential for high efficiency at cruise speeds up to 550 miles an hour, first was proposed in 1975 by the Hamilton Standard Division of United Technologies Corp. In addition to the large fuel savings, studies showed that this type of propeller could help solve problems of exterior noise, cabin vibration and interior noise found with the older turboprops, Arndt said.
Hamilton Standard's proposal followed a NASA-sponsored study which indicated that the propeller offered more potential fuel savings than advanced turbofan jet engines if the propeller could be made to operate efficiently above a speed of 520 miles an hour. Propeller technology in the past hadn't advanced beyond a cruise speed of 415 miles an hour.
Renewed interest in the turboprop and its fuel-efficient characteristics was sparked by price increases of jet fuel from 12 cents a gallon in 1973 to a predicted $2 a gallon by 1985 and from less than 25 percent of the operating costs of the airlines at one time to two-thirds of their costs.
Some technical problems have to be resolved before the propfan actually can be introduced on a production aircraft, Arndt acknowledged. The unknowns include whether a large-scale propfan can be built light enough for flight and still be stiff enough to sustain the dynamic loads of high-speed flight, whether cabins can be made quiet enough without using heavy noise-reducing materials that would negate the performance gain of the propfan, and whether the propeller can be installed on an aircraft without excessive loss of aerodynamic efficiency.
But he was optimistic. "Curret planning indicates that propfan technology could be ready for use in aircraft by the late 1980s," he said.