As Pratt & Whitney’s new engine starts to operate it is interesting to review its long gestation. The start of the GTF goes far back to an engine few recall, named the “SuperFan”. This engine was sold to Airbus for the first A340. It is rare to find an image of the original SuperFan engine. One of the original program’s members shared this drawing with us.
Early and critical work done by Howard Stryker and the IAE team on the SuperFan in the mid-80’s should not be forgotten.
In the early 1980s Pratt & Whitney and Rolls-Royce entered into a joint venture, named International Aero Engines (IAE). The goal of this JV was to develop an all new, mid-size, turbofan aero-engine. The JV included Pratt & Whitney, Rolls-Royce, a consortium of Japanese companies, Fiat of Italy and MTU of Germany. The headquarters of the new company was located in Pratt’s backyard, East Hartford, CT. The Engineering Department was located in Derby, England, home of Rolls-Royce.
The new engine was named the V2500 Turbofan, and offered 24,000lbs. to 30,000 lbs. of thrust. It was to feature both improved fuel consumption and low noise, using the best technologies of both principals. Rolls was responsible for the “cold section” and Pratt the “hot section”. It’s initial target airplane was the forthcoming Airbus A320.
The Pratt & Whitney portion of the team, located at Derby, consisted of fifteen engineers with various specialties, including design and performance. Once the Pratt engineering team was formed and operating, they frequently traveled to Airbus.
On one of these visits Howard Stryker, IAE’s Chief of Performance, was approached by a senior Airbus executive and asked whether, in the future, it would be feasible to improve the fuel consumption of turbofan engines by a large amount— say, up to 15%?
The reasoning behind the question was that Airbus’ design studies for a long range, four engine airplane (to become the A340), indicated that the wing’s fuel storage volume would be marginal for long range operation. That would put a premium on engine fuel burn efficiency. Stryker contacted the Pratt & Whitney Advanced Design Group in East Hartford for their experience and ideas.
Engine fuel efficiency is a high priority item in all aero engine designs. It is affected not only by component efficiencies, but by engine overall pressure ratio, maximum operating temperature, and bypass ratio.
Pratt had been doing studies for other airplane programs and had looked at the possibility of using a reduction gear between the fan and low turbine in order to permit use of a larger diameter fan and thus a higher bypass ratio. Pratt was asked to look at the feasibility of adopting such a system to the V2500 core engine.
After a few weeks of conceptual studies, Pratt and IAE decided that the results indicated that a more detailed study should be undertaken. As a result, the IAE V2500 “SuperFan” Project Team was formed. It was located offsite in Glastonbury CT, near IAE’s home in East Hartford. A team of twenty design and analytical engineers was led by Stryker as Project Manager.
The team spent several months of preliminary design of the SuperFan, including performance, weight, installation concepts and coordination with both Airbus and Boeing. After several months of study, it was concluded that, from an engineering standpoint, the SuperFan should be made an active IAE Program.
Ongoing discussions with the OEMs resulted in a Memorandum of Understanding for installation on the A340 in December 1986, The A340 was configured with the IAE SuperFan as the launch engine and offered to launch customer Lufthansa and others, like Royal Jordanian.
There was a problem, however, the active IAE SuperFan Program directly competed with other engine programs at both Pratt & Whitney and Rolls-Royce. In Pratt’s case it would be with the all-new PW4000. Moreover, the V2500 turbofan development program was experiencing problems and required redesign of the initial configuration. The cold section had problems with titanium on titanium and required significant redesign. This was the first variable HPC stator design for Rolls-Royce and the use of titanium rub strips in the HPC resulted in compressor failures during the development program. Rolls-Royce introduced a new lower pressure ratio HPC that coupled with a revised LPC became build of material.
As a result, at a joint meeting of Pratt and Rolls, it was decided not to fund IAE’s SuperFan Program. This decision was ill-timed because Airbus had already committed to the SuperFan and had been successfully pitching the A340 to customers. Bear in mind, Airbus had modified the A340 design for the SuperFan. In 1986, Airbus offered the SuperFan as primary engine. First deliveries were slated for 1992 while McDonnell Douglas and CFM cast doubt on the SuperFan. Airbus had a lot of its pride riding on this engine. Airbus had secured orders for 15+15 from Lufthansa and 20 from Northwest Airlines for their A340.
In 1987 the SuperFan was indefinitely delayed. P&W and Rolls-Royce contended that the SuperFan was no more than an engineering study and that they never committed to develop this engine. Airbus, understandably, was annoyed in extremis by this. The memory of this decision remains fresh with senior people at Airbus. Airbus scrambled to find a replacement and turned to GE for an engine for the A340, and the CFM56 was selected. Airbus then had to add 2.6 meters to the A340 wingspan to ensure more fuel capacity.
The Glastonbury SuperFan Engineering team was disbanded. Team members returned to their respective companies. One would think the awful story ends there.
But limited studies of the concept continued at Pratt. The reduction gear, in particular, was a key element in the concept and a development team was formed for design and rig testing. This team, of necessity, remained small. Their work was hidden in physical and budget terms from the top management at Pratt. The work performed is remarkable when looks back at the way it was undertaken. By 1992 a full scale demonstrator engine was assembled using a PW2000 core and a fan specially built by Hamilton Standard exploiting the benefits of this gear technology. The engine was run at the outdoor test stand at Pratt’s West Palm Beach facility. A large group of interested airline representatives were invited to see and hear the engine in early1992. Howard Stryker received the Aviation Week 1992 Laurels Award for the event. Sixteen years later, in 2008, P&W tested a full scale demonstrator engine using a PW6000 core. Over a twenty-year span, P&W invested over one billion dollars in the geared engine concept. When one looks back, it was the persistence and commitment of these engineers who successfully brought this game changing gear technology to life.
But in order to win support from Airbus for consideration of the new GTF engine on the proposed A320neo, Pratt had to go through a number of twists. Airbus wanted the engine to be offered under the IAE brand. After several unsuccessful attempts to win consensus of the IAE partners, Pratt had to fix that issue decisively. So Pratt bought the share of IAE owned by Rolls-Royce, and brought the IAE program fully under the Pratt brand. Pratt had missed an opportunity on the 737 Classic and it was not about to lose an opportunity of that magnitude again. It was going to win the Airbus selection, recover its reputation and deliver a ground breaking engine. The test GTF engine sent to Airbus for evaluation was flown on an A340-600 test bed. That engine was equipped with an extra oil pump to ensure the gear was well lubricated . P&W expected Airbus was going to test their engine aggressively. As it runs out, the additional pump was never activated as the engine coped with all Airbus’ tests.
Now decades later, what was conceived as the IAE SuperFan, is now called the Pratt & Whitney Geared Turbo Fan engine (GTF) and is going into commercial service on the Airbus A320neo. Ironically the launch customer was again Lufthansa.