Will the propeller make a comeback?
Among big air carriers in this age of jets and supersonic transport, the plucky old propeller plane has become as passe as the barnstormer's silk scarf. Now, however, a research thrust is under way that may usher in a new era of propeller-driven airliners in the 1990s. The drive to resurrect the propeller is being pushed by the punishing price of fuel. In the pre-oil-embargo days of the early 1970s fuel made up 25 percent of the direct operating cost of an aircraft. Today it makes up close to 50 percent.
Airlines have been busily looking for ways to stretch a gallon of petrol. The search has included use of more tough plastic composites to shed weight, development of fuel-stingy jet engines, and research into innovative wing and fuselage designs.
All of these hold promise in shaving costs - and some already have. But many aviation experts believe the single biggest boost in efficiency between now and the end of the century will come from new space-age propeller systems.
In recent testimony before a House subcommittee, Roger Schaufele, vice-president of engineering for Douglas Aircraft Company, called advanced propeller work the ''most promising'' of the near-term fuel-conservation ideas.
There's some deja vu in all of this. The history of aviation up to the advent of the jet in the 1950s revolved around the propeller. It still is a member in good standing in the aviation community. Besides all the small planes, many big commercial transports still are pulled through the skies on propeller power.
But the new generation of propfans are much different from the old. For one thing, they don't carry the standard three or four blades of conventional craft. Most configurations being sketched have eight to ten thin, curved blades that give the system the look of a pinwheel. The fans are driven by tur-bines similar to those in today's jets.
The result, at least in the lab, is a fast but highly efficient plane, compared with conventional turboprops. Wind tunnel tests have shown that they can cut fuel consumption by as much as 30 percent over today's jet engines - and approach the same speeds (500 mph).
''Industry is just clamoring for this technology,'' contends William Strack, a propeller expert with the National Aeronautics and Space Administration's (NASA) Lewis Research Center in Cleveland.
Engineers long suspected that speedy, efficient prop planes could be built. But until recently they lacked the materials and computing power to move their schemes beyond the idea shop. A number of US engine and aircraft manufacturers have been developing advanced propeller technologies since the late 1970s. Research, too, is going in the USSR, France, Japan, and Britain.
The airworthiness of the ideas will soon be tested. NASA-Lewis is sponsoring a ground and flight test program for advanced propfans. It will award a contract to a US firm within the next few months. Large manufacturers, including McDonnell Douglas and Lockheed-Georgia, are vying for the project. Snags remain, though. Among them:
* Ensuring the strength of the blades. Other than tests with small models, no one knows how the thin fans will hold up at high speeds.
* Avoiding too much noise and vibration in the cabin. Can a prop-fan be built to rival the relative quiet and smoothness of the jet?
* Checking to see that the airflow behind the propeller doesn't upset the aerodynamics of the wing.
* Devising a relatively maintenance-free engine and gearbox.
The researchers will look into these and other areas during the 48-month program. The first full-scale airborne tests of a propfan system are expected in two to three years. A commercial version isn't expected until 1992, at the earliest.
If propfans ever are produced - and manufacturers are now putting the bulk of their money into advanced versions of the well-proven jet engine - they will probably be fitted on short- to medium-range airliners (100- to 150-passenger). This is where the technology would yield the most benefits. ''Nobody really knows whether the idea is going to go,'' says William Arndt, advanced turboprop manager for Lockheed-Georgia. ''But until we stub our toe, we've got to look into it.''