When you harness a single powerplant to the nose of a brand-new airframe, that engine better be reliable. In this case the engine is GE Aviation’s new advanced turboprop (ATP) and the airframe is Textron Aviation’s new single-engine turboprop, or SETP.
The move marks GE’s most ambitious foray yet into the business and general aviation arena. “ATP has a number of unique features that have never been seen before in this market segment,” asserts Brad Mottier, vice president of GE Aviation’s Business and General Aviation and Integrated Systems business.
GE Aviation says those features result in:
• a 16:1 overall pressure ratio;
• 20 percent lower fuel burn compared to the competition;
• 10 percent more engine power at altitude;
• 850 to 1,650 shaft horsepower;
• 33 percent longer time between overhaul, compared to the competition;
• the highest power-to-weight ratio in its class.
The package may be new, but the constituent parts of that package are not. The ATP, says Mottier, “is taking technologies from different (GE) engines and architectures from other engines and putting them together in this new platform.” GE Aviation’s BGA engine chief contends, “We are doing this at very low risk.” That’s because the high-pressure ratio compressor, the stator vanes, and the cooled turbines have more than a billion flight hours on a multitude of GE commercial aircraft engines. The ATP’s aerodynamics borrow on more than 150 million hours of field use in commercial powerplants.
The engine’s modular architecture is based on the CT7 turboshaft, a family of engines that has managed to rack up more than 100 million flight hours — 5 million of them in hot and harsh environments. ATP gets its compressor from the CT7.
ATP is a reverse flow affair, one in which air enters the engine near the back of the powerplant and flows out via exhaust stacks on the side. In that respect it’s similar to GE Aviation’s H Series of turboprops.
All this serves to reduce the risk that can be associated with new powerplants, and cut those unexpected revelations that can wreak havoc on a program.
By the Numbers
That bodacious 16:1 overall pressure ratio is really efficient, “a step-change,” says Mottier. Cooled turbine blades and a multiple-stage low-pressure turbine contribute to the ratio. By way of reference, he says competitive engines have overall pressure ratios in the “9:1 to 10:1 range.”
Twenty percent less fuel burn and 10 percent more power at altitude are accomplished via computer-control of the engine, coupled with a prop that’s integrated into a propulsion control system. “That is a first,” contends Mottier. “It’s never been done in this [BGA] marketplace.”
Propulsion control optimizes prop speed, prop pitch and the powerplant itself in a given flight regime — takeoff, descent, and cruise. The way things are right now in this particular BGA niche, “you have a propeller control lever and a throttle.” The ATP is linked to a single lever, one that controls both the prop and the powerplant.
There’s a fundamental difference between overhaul intervals in the BGA market compared to the commercial airline arena. Business and general aviation aircraft fly fewer hours. At the same time, somewhat counterintuitively, the “engine overhaul cycle is much shorter.” A commercial powerplant will stay on wing 20,000 hours, perhaps more. By contrast, BGA engines stay put in the 3,500- to 5,000-hour range. Fewer flight hours, more frequent overhauls. Mottier says, “ATP’s time between overhauls will increase more than 30 percent, virtually a full third." With the ATP, Mottier says control logic prevents you from doing incremental damage to the engine, damage that mounts up and hurts long-term durability.
Czechmate
For the time being, ATP design and testing will be at GE Aviation’s existing facilities. By 2020 the engine maker plans to start manufacturing ATPs in the Czech Republic at the GE Turboprop Center of Excellence (CoE), which is now under construction.
Why the Czech Republic? GE Aviation has been there since 2008, when it acquired Walter Engines. In 2012 GE’s existing Czech facility began producing H Series turboprops, with power in the 750 to 850 shaft horsepower range.
GE Aviation leveraged the robust design elements of the Walter M601 engine, incorporating 3-D aerodynamic design techniques and advanced materials to create the H Series of turboprops. That’s important. Mottier says, “With the new [Czech-based CoE] the ATP will join the H Series as the first engines designed, tested, and manufactured outside the United States, incorporating the best of our proven technologies into our newest family of turboprops powering next-gen aircraft, like Textron’s SETP.”
When people ask Mottier, ‘How are things going in Europe?’ the exec answers that there are some 12,000 GE Aviation employees there now, about 2,000 of them engineers. “Over the last decade,” says Mottier, “we’ve established centers for manufacturing and engineering in Europe that perform some of the design work for engines that are manufactured here in the United States.” GE manufactures parts in Europe that are then assembled here in the U.S. As far as the advanced turboprop effort is concerned, engineering project management and systems engineering group will be European-based. He says they’ll “use European resources to the maximum extent possible. This is a global [author’s emphasis added] engine.”
Heretofore GE Aviation has been building out its H80, a small horsepower turboprop that competes with the PT6 in the smaller power range precincts, from 750 to 850 horsepower. But the company wanted something with substantially more punch, a powerplant in the 1,300 to 1,650 horsepower range.
Textron's Request for Proposal
Mottier says Textron told GE Aviation the airframer would issue a request for proposal and see what other parties could come up with. The upshot: if such an engine would be produced at the right price it would be significant and Textron could develop a new, clean-sheet airframe, one built around the new powerplant’s capabilities.
That was in December 2014, and the race was on. The field was narrowed to a trio of competitors and GE Aviation ended up on top. Mottier describes what lies ahead now for him and his team a “once-in-a-career opportunity,” an opportunity potentially worth US$40 billion in revenue over the next 25 years. No less than GE Chairman and CEO Jeff Immelt highlighted ATP’s possibilities in the company’s most recent annual report.
According to Textron Aviation spokeswoman Lindsay Adrian, GE advanced turboprop will be the only engine the new SETP uses. “We’re designing the aircraft to be powered,” solely by the ATP. “Our single-engine turboprop will combine the best of both clean-sheet aircraft and new engine design,” says Adrian. “Selecting GE as our engine partner reflects the best fit for the mission.”
Textron is moving methodically, with consummate caution, in releasing details about SETP — declining just now to announce the name, maintenance advances, projected in-service date, or where the aircraft will be built. What is known is that it will have a range in excess of 1,500 nautical miles and a speed greater than 280 knots. Adrian says the single-engine craft will sport “best-in-class operating costs.”
