The Wave of the Future—Advanced Turboprop Project

Like many of the ACEE projects, the turboprop’s history started before ACEE was born.12 The project began in the early 1970s with the collab­oration of two engineers: Daniel Mikkelson. of NASA Lewis, and Carl Rohrbach of Hamilton Standard, the Nation’s last propeller manufacturer. Mikkelson. then a young aeronautical research engineer, went back to the old NACA wind tunnel reports, where he found a “glimmer of hope” that propellers could be redesigned to make propeller-powered aircraft fly faster and higher than did those of the mid – to late 1950s.13 Mikkelson and Rohrbach came up with the concept of sweeping the propeller blades to reduce noise and increase efficiency. At Lewis, Mikkelson sparked the interest of a small cadre of engineers, who solved key technological prob­lems essential for the creation of the turboprop, while at the same time attracting support for the project. The engineers also became political advocates, using their technical gains and increasing social acceptance to fight for continued funding. This involved winning Government, industry, and public acceptance for the new propeller technology. While initially the project involved only Hamilton Standard, the aircraft engine manufactur­ers—Pratt & Whitney. Allison, and General Electric —and the giants of the airframe industry— Boeing. Lockheed, and McDonnell-Douglas—jumped on the bandwagon as the turboprop appeared to become more and more technically and socially feasible. The turboprop project became a large, well-funded, “heterogeneous collection of human and material resources” that contemporary historians refer to as “big science.”14

At its height, it involved over 40 industrial contracts, 15 university grants, and contracts with all 4 NASA Research Centers: Lewis. Langley, Dryden, and Ames. The project nonetheless remained controversial through its life, because of technical and social challenges. Technically, studies by Boeing, McDonnell-Douglas, and Lockheed pointed to four [330] [331] [332]

John Klineberg, right. and Andy Stofan in 1983 with an Advanced Turboprop model. (NASA Glenn Research Center (NASA GRC].)

areas of concern: propeller efficiency at cruise speeds, both internal and external noise problems, installation aerodynamics, and maintenance costs.’5 Socially, the turboprop also presented daunting problems. Because of the “perception of turboprops as an old-fashioned, troublesome device with no passenger appeal ” the consensus was that, “the airlines and the manufacturers have little motivation to work on this engine type.”’6

The project had four technical stages: “concept development" from 1976 to 1978. “enabling technology” (1978 to 1980), “large scale integra – tion" (1981 to 1987), and finally “flight research” in 1987.” During each of [333] [334] [335]

ELEMENTS NEEDED FOR DEVELOPMENT OF ADVANCED
TURBOPROP AWCRAFT

Advanced Turboprop elements, including the propeller, nacelle, aerodynamics, and noise control. (NASA Glenn Research Center [NASA GRCJ.)

these stages, NASA’s engineers confronted and solved specific technical problems that were necessary if the Advanced Turboprop project were to meet the defined Government objectives concerning safety, efficiency, and environmental protection. Industry resistance and NASA Headquarters’ sensitivity to public opposition were among the key reasons that of the six projects within the ACEE program, only the Advanced Turboprop failed to receive funding in 1976. John Klineberg. Director of Lewis Research Center, recalled that it was delayed “because it was considered too high risk and too revolutionary to be accepted by the airlines."*4 Everyone, it seemed, associated the advanced turboprop technology with the possi­bility of inciting an aeronautical “revolution ” a paradigm shift, or. as a Forbes magazine headlined it in 1981, “The Next Step.” As surely as “jets drove propellers from the skies," the new “radical designs" could bring a new propeller age to the world.*9 Donald Nored proclaimed that they were the “wave of the future."[336] [337] [338]

Unfortunately, the airline industry was reluctant to return to the propel­ler. According to Nored, executives in the industry were “very conservative, and they had to be.” They were “against propellers” because they had “com­pletely switched over to jets.” Because of their commitment to the turbojet, they raised numerous objections to a new propeller, including noise, main­tenance, and the fear that the “blades would come apart.” Nored recalled each problem had to be “taken up one at a time and dealt with."[339] The revo­lutionary propeller-driven vision of the future frightened the aircraft indus­try with its large investment in turbofan technology. Aircraft structures and engines are improved in slow, conservative, incremental steps. To change the propulsion system of the Nation’s entire commercial fleet represented an investment of tremendous proportions. Even if the Government put sev­eral hundred million dollars into developing an advanced turboprop, the air­frame and aircraft engine industries would still need to invest several billion dollars more to commercialize it. Revolutionary change did not come easily to an established industry so vital to the Nation’s economy.

While fuel savings between 20 to 30 percent were one reason to take this risk, another important political factor favored its development. The Soviet Union had a “turboprop which could fly from Moscow to Havana.”[340] [341] The continuing Cold War prompted the United States to view any Soviet technical breakthrough as a potential threat to American security. During the energy crisis, the knowledge that Soviet turboprop transports had already achieved high propeller fuel efficiency at speeds approaching those of jet-powered planes seemed grave indeed and gave impetus to the NASA program. During the Government hearings, NASA representatives displayed several photos of Russian turboprop planes to win congressio­nal backing for the project:0 The Cold War helped to define the turbo­prop debate. No extensive speculation on the implications of Russian air

Single – and counter-rotation turboprops. (NASA Glenn Research Center [NASA GRC].)

superiority for American national security seemed necessary. The Soviet Union could not be allowed to maintain technical superiority in an area as vital as aircraft fuel efficiency.

The first step in developing a turboprop was to create a small-scale model. Technically, the entire future of the Advanced Turboprop project initially depended on proving whether a model propfan could achieve the predicted fuel-efficiency rates. If this model yielded success, then project advocates would be able to lobby for increased funding for a large research and development program. Thus, even during its earliest phase, the technical and social aspects of the project worked in tandem. Lewis project manag­ers awarded a small group of researchers at Lewis and Hamilton Standard a contract for the development of a 2-foot-diameter model propfan. called the SR-1. or single-rotating propfan. Single-rotating meant that the propfan had only one row of blades, as opposed to a counter-rotating design with two rows of blades, each moving in opposite directions. This model achieved high efficiency rates and provided technical data that the small group of engineers could use as ammunition in the fight to continue the program.

This success led to the formal establishment of the program in 1978 and the enabling technology phase. Technically, this phase dealt with four critical problems: modification of propeller aerodynamics, cabin and com­munity noise, installation aerodynamics, and drive systems. Propeller aerodynamic work included extensive investigations of blade sweep, twist, and thickness. In the late 1970s, for the first time, engineers used comput­ers to analyze the design of a propeller. The advantage of propellers in sav­ing fuel had to be balanced against a potential increase in noise pollution.[342] New computer-generated design codes not only contributed to improved propeller efficiency, but also to solving many of the problems associated with noise. The final two technical problems of the enabling phase dealt with installation aerodynamics and the drive system. Numerous installa­tion arrangements were possible for mounting the turboprop on the wing. Should the propeller operate by “pushing” or “pulling” the aircraft? How should the propeller, nacelle, and the wing be most effectively integrated to reduce drag and increase fuel efficiency? Wind tunnel tests reduced drag significantly by determining the most advantageous wing placement for the propeller. Engineers also examined various drive train problems, including the gearboxes.

After 2 years of work, the turboprop idea began to attract greater commercial and military interest and support. The Navy’s assistant com­mander for research and technology planned to incorporate it as a “viable candidate” for future long-range and long-endurance missions [343] [344] [345]

A Lockheed-California vice president lent his support to the project, saying it would result in performance improvement for military applica­tion and “provide important means for future energy conservation in air transportation.”4* In 1978. the vice president for engineering at United Airlines reported that, after the company’s management review on the ACEE turboprop project, it was “impressed with the progress made to date and the promise for the future.”4′ One year later, United Airlines president Percy A. Wood reiterated support for the program. Wood was “impressed” with the program and believed it was of “utmost impor­tance” for the Nation and would have a “major impact” on the future of air transportation.[346]

With the small-scale model testing complete and growing industry support, the project moved into its most labor – and cost-intensive phase — large-scale integration. The project still had serious uncertainties and prob­lems associated with transferring the designs from a small-scale model to a large-scale propfan. The Large-Scale Advanced Propfan (LAP) project initiated in 1980 would answer these scalability questions and provide a database for the development and production of full-size turbofans. As a first step, NASA had to establish the structural integrity of the advanced turboprop.[347] Project managers initially believed that in the development hierarchy, performance came first, then noise, and finally structure. As the project advanced, it became clear that structural integrity was the key technical problem.[348] Without the correct blade structure, the predicted fuel savings could never be achieved. NASA awarded Hamilton Standard the contract for the structural blade studies that were so crucial to the success of the program. In 1981. Hamilton Standard began to design a large-scale, single-rotating propfan. Five years later, construction was completed on a 9-foot-diameter design very close to the size of a commercial model, which was so large that no wind tunnel in the United States could accom­modate it. The turboprop managers decided to risk the possibility that the European aviation community might benefit from the technology NASA had so arduously perfected. They shipped the SR-7L to a wind tunnel in Modane. France, for testing. In early 1986, researchers subjected the model to speeds up to Mach 0.8 with simulated altitudes of 12,000 feet. The results confirmed the data obtained from the small-model propeller designs. The large-scale model was a success.

Another key concern was unrelated to technological capability. This was a social question concerning passengers: How receptive would they be to propeller-driven aircraft? Laminar flow control and supercritical airfoils could be integrated into an airframe design without the public realizing, for the most part, the technology was even there. Turboprops were different because the propeller was one of the more visible parts of the airplane and was regarded as being from the "old days” when noisy “puddle-jumpers” were flown at low altitudes in turbulence. If the public would not fly in a turboprop plane, all the efficiency savings would be lost flying empty planes across the country.

In response to this concern. NASA and United Airlines initiated an in-flight questionnaire to determine customer reaction to propellers. Both NASA and the industry were aware of the disastrous consequences for the future of the program if this study found the public opposed the return of propeller planes. As a result, the questionnaire deempha- sized the propeller as old technology and emphasized the turboprop as the continuation and advancement of flight technology. The first page of the survey consisted of a letter from United Airlines’ vice president of marketing to the passenger asking for cooperation in a “joint industry – government study concerning the application of new technology to future aircraft.”’1 This opening letter did not mention the new turboprops. The turboprop, inconspicuously renamed the “prop-fan” to give it a more posi­tive connotation, did not make its well-disguised appearance until page 4 of the survey, where the passenger was finally told that “‘prop-fan’ planes could fly as high, as safely, and almost as fast and smooth as jet aircraft.” This was a conscious rhetorical shift from the term "propeller” to “prop – fan” to disassociate it in people’s minds from the old piston engine technol­ogy of the pre-jet-propulsion era. Brian Rowe, a General Electric engineer involved in advanced propeller projects, explained this new labeling strat­egy. He said. "They’re not propellers. They’re fans. People felt that modern was fans, and old technology was propellers. So now we’ve got this modern propeller which we want to call a fan.”[349] [350] The questionnaire explained to the passenger that not only did the “‘prop-fans’… look more like fan blades than propellers,” they would also use 20 to 30 percent less fuel than jet aircraft did.

The questionnaire then displayed three sketches of planes—two were propeller driven, and the third had a turbofan. The passenger had to choose

SR-7L Advanced Turboprop on gulfstream jet in 1987. (NASA Glenn Research Center.)

which one he or she would “prefer to travel in.” Despite all the planes being portrayed in flight, the sketches depicted the propellers as simple circles (no blades present), while the individual blades of the turbofan were visible. These were all subtle and effective hints to the passenger that the “prop-fan” was nothing new and that they were already flying in planes powered by engines with fan blades.

Not surprisingly, the survey yielded favorable results for the turboprop. Of4,069 passengers surveyed, 50 percent said they “would fly prop-fan,” 38 percent had “no preference,” and only 12 percent preferred a jet.*-‘ If the air­lines could avoid fare increases because of the implementation of the turbo­prop. 87 percent of the respondents stated they would prefer to fly in the new turboprop. Relieved and buoyed by the results, NASA engineers liked to point out that most of the passengers did not even know what was currently on the wing of their aircraft.[351] [352] According to Mikkelson. all the passengers wanted to know was “how much were the drinks, and how much was the ticket."[353] Equally relieved was Robert Collins, vice president of engineering for United Airlines, who concluded that this “carefully constructed passen­ger survey. . . indicated that a prop-fan with equivalent passenger com­fort levels would not be negatively viewed, especially if it were recognized for its efficiency in reducing fuel consumption and holding fares down.”[354]

Success spawns imitators. While NASA continued to work with Allison, Pratt & Whitney, and I lamilton Standard to develop its advanced turboprop. General Electric (Pratt & Whitney’s main competitor) was quietly develop­ing an alternative propeller system—the unducted fan (UDF). In NASA’s design, the propeller rotated in one direction. This was called a single rota­tion tractor system and included a relatively complicated gearbox. Since one of the criticisms of the turboprop planes of the 1950s (the Electra. for example) was that their gearboxes required heavy maintenance. General Electric took a different approach to propeller design. Beginning in 1982, its engineers spent 5 years developing a gearless, counter-rotating pusher system. They mounted two propellers (or fans) on the rear of the plane that literally pushed it in flight, as opposed to the “pulling” of conventional pro­pellers. In 1983. the aircraft engine division of General Electric released the unducted fan design to NASA, shortly before flight tests were scheduled.

This took NASA completely by surprise. Suddenly, there were two turboprop projects competing for the same funds. Nored recalled: “They

The Dryden C-140 JetStar during testing of advanced propfan designs. Dryden conducted flight research in 1981-1982. The Lewis Research Center directed the technology’s development under the Advanced Turboprop program. Langley oversaw work on acoustics and noise reduction. The effort was intended to develop a high-speed, luel-efficient turboprop system. (January 1. 1981.) (NASA Dryden Flight Research Center [NASA DFRC|.) wanted us to drop everything and give them all our money, and we couldn’t do that.”” NASA Headquarters endorsed the “novel” unducted fan pro­posal and told Lewis to cooperate with General Electric on the unducted fan development and testing. Despite NASA’s initial reluctance to support two projects, the unducted fan proved highly successful. In 1985. ground tests demonstrated a fuel-conservation rate of 20 percent. Development of the unducted fan leapt ahead of NASA’s original geared design. One year later, on August 20, 1986. General Electric installed its unducted fan on the right wing of a Boeing 727. Thus, much to NASA engineers’ dismay, the first flight of an advanced turboprop system demonstrated the technical feasibility of the unducted fan system —a proprietary engine belonging to entirely General Electric, not a product of the joint NASA-industry team. Nevertheless, the competition between the two systems, and the willing­ness of private industry to invest development funds, helped build even greater momentum for acceptance of the turboprop concept. [355]

NASA engineers continued to perfect their single-rotating turboprop system through preliminary stationary flight-testing/* The first step was to take the Hamilton Standard SR-7A propfan and combine it with the Allison turboshaft engine and gearbox housed within a special tilt nacelle. NASA engineers conducted a static or stationary test at Rohr’s Brown Field in Chula Vista. CA. mounting the nacelle, gearbox, engine, and propeller on a small tower. The stationary test met all performance objectives after 50 hours of testing in May and June 1986. a success that cleared the way for an actual flight test of the turboprop system. In July 1986, engineers dis­mantled the static assembly and shipped the parts to Savannah, GA, for reassembly on a modified Gulfstream II with an eight-blade, single-rotation turboprop on its left wing.[356] [357] [358] The radical dreams of the NASA engineers for fuel-efficient propellers were finally close to becoming reality. The plane contained over 600 sensors to monitor everything from acoustics to vibration. Flight-testing —the final stage of advanced turboprop develop­ment—took place in 1987. when a modified Gulfstream II took flight in the Georgia skies. These flight tests proved that the predictions NASA made in the early 1970s of a 20- to 30-percent fuel savings were indeed correct.

On the heels of the successful tests of both the General Electric and the NASA-industry team designs came not only increasing support for propeller systems themselves, but also high visibility from media reports predicting the next propulsion revolution. The New York Times predicted the “Return of the propellers” while the Washington Times proclaimed, “Turboprops are back!’v, l> Further testing indicated that this propulsion technology was ready for commercial development. As late as 1989, the U. S. aviation industry was “considering the development of several new engines and aircraft that may incorporate advanced turboprop propulsion systems.”[359] But the economic realities of 1987 were far different from those predicted in the early 1970s. Though all the problems standing in the way of commercialization were resolved, the advanced turboprop never reached production, a casualty of the one contingency that NASA engineers never anticipated—fuel prices decreased. Once the energy crisis passed, the need for the advanced turboprop vanished. Oil cost S3.39 per barrel in 1970. It was $37.42 per barrel in 1980. By 1988. it had dropped to $14.87 per barrel, and ACEE programs such as Laminar Flow Control and the Advanced Turboprop lost their relevance.[360] [361] As the energy crisis sub­sided in the 1980s and fuel prices decreased, there was no longer a favor­able ratio of cost to implement turboprop technology versus savings in fuel efficiency. As John R. Facey, Advanced Turboprop Program Manager at NASA Headquarters, wrote, “An all new aircraft w ith advanced avion­ics, structures, and aerodynamics along with high-speed turboprops would be much more expensive than current turbofan-powered aircraft, and fuel savings would not be enough to offset the higher initial cost.”[362]

Yet managers of the Advanced Turboprop program, such as Keith Sievers, were convinced that the NASA-industry team had made a signifi­cant contribution to aviation that ought to receive recognition. Although NASA won several Collier trophies, which are regarded as the most pres­tigious award given annually for aerospace achievement for innovations related to the space program, it had produced no winners in aeronautics for almost 30 years. If the turboprop could win such an honor, it might justify the importance of this work. In hopes of winning the Collier Trophy, Sievers began mobilizing the aeronautical constituency that had participated in turboprop development. Although NASA Headquarters initially expressed some reluctance to press for the prize for a technology that was unlikely to be used, at least in the near future, the timing was perfect. There was little competition from NASA’s space endeavors, since staff members in the space directorate were still in the midst of recovering from the Challenger explosion. As a result, in 1987 the National Aeronautic Association awarded NASA Lewis and the NASA-industry Advanced Turboprop team the Collier Trophy at ceremonies in Washington, DC, for develop­ing a new fuel-efficient turboprop propulsion system/’4 The winning team

John Klineberg holding the Collier Trophy (May 13. 1988). (NASA Glenn Research Center (NASA GRCJ.)

included Hamilton Standard, General Electric, Lockheed, the Allison Gas Turbine Division of General Motors. Pratt & Whitney, McDonnell – Douglas, and Boeing —one of the larger and more diverse groups to be so honored in the history of the prize.

Some specific technologies that were designed for the turboprop proj­ect are in use today. These include noise reduction advances, gearboxes that use the turboprop design, and solutions to certain structural problems.

such as how to keep the blades stable.[363] [364] Today, the technology remains “on the shelf,” or “archived ” awaiting the time when fuel conservation again becomes a necessity. When interviewed in the mid-1990s, NASA engi­neers involved in the Advanced Turboprop Project remained confident that future economic conditions would make the turboprop attractive again. When fuel prices rise, the turboprop’s designs will be “on the shelf." ready to provide tremendous fuel-efficient savings. But NASA engineers did not build their careers around technologies that were ultimately neglected. Donald Nored sentimentally reflected on the project, waved goodbye to the future of turboprops, and said, “We almost made it. Almost made it.”f’6