GE Takes On PT6 Engine With Advanced Turboprop
AeroBD | The AERO news Company…Dubai, UAE, Nov. 27, 2015 : General Electric is launching a family of advanced turboprop (ATP) engines following its selection by Textron to power the company’s newly disclosed next-generation single-engine turboprop aircraft.
The $400 million GE development represents an all-out assault on Pratt & Whitney Canada’s half-century dominance of the business and general aviation turboprop market with the PT6, and builds on the bridgehead already established with the smaller H80 engine. GE, which won the new Textron application after beating out competition from P&WC and other engine makers, will develop the 1,300- to 2,000-shp family at its newly announced European-based Turboprop Center of Excellence.
Few details have been revealed yet about Textron’s single-engine turboprop. However, the aircraft is expected to seat less than 12, have a range of 1,500 nm and cruise at speeds higher than 280 knots.
“The new engine will allow airframers to design a new class of turboprop airplanes,” says Brad Mottier, vice president and general manager of GE Aviation Business and General Aviation and Integrated Systems. At its heart is a powerful compressor with nearly double the pressure ratio of comparable engines, linked to a full-authority integrated propulsion control system that will govern both engine and propeller pitch as an entire system. The engine will have 20% better fuel burn and produce 10% more power at altitude than comparable turboprops.
Configured for reverse flow to reduce overall engine size and weight, the turboprop will incorporate a CT7/T700-derived high-pressure (HP) compressor with four axial stages and a single centrifugal stage. Titanium is used throughout the compressor. “That’s unique,” says ATP general manager Gordon Follin. “It helps us get the weight down and allows us to put extra power and fuel efficiency in a package that’s about the same size as today,” he adds. GE is using the same iteration of three-dimensional aerodynamics design used in the GE9X for Boeing’s 777X airliner engine to design the shaping of airfoils and blades in the compressor, which results in “a pressure ratio of 16:1, compared to the 9 or 10:1 of what you have today,” adds Follin.
Air feeds from the compressor impeller into a reverse flow single-annular combustor, the design of which resembles that in the GE-Honda HF120 engine. The combustor liner will feature “advanced features and materials” says Mottier. “We are taking 2010s technology to a class of engines that is more used to 1960s and ’70s technology. We think it is extremely innovative for this class but without it being necessary to break boundaries.”
The power section includes a two-stage HP turbine and three-stage low-pressure (LP) turbine. The HP turbine will be made of single-crystal materials and, GE says, will be the first in this class of engines to be fully cooled. The LP turbine will also be counter-rotating, “. . . so we pick up some efficiency there,” adds Follin. “It will be a smaller-diameter-airflow engine but we are getting efficiency because we are getting extra power through the thermodynamics, not the airflow. We are using commercial engine technology which will allow us to run at higher temperatures with much better maintenance intervals than the products in this class today.”
Configured around two opposing shafts driven by the power turbine, Mottier says, the design “breaks new ground” in having a digital electronic control system that governs both the core gas turbine engine and the propeller. “The system handles the optimum conditions as well as the different failure mechanisms. It controls how hard you drive the core, the back pressure on the LP turbine and how hard you drive the prop.” Compared to the electronic engine control used in the H80, the new turboprop will be controlled by a full-authority system with more control logic. The system will provide dynamic control rather than relying on predetermined control schedules. “There are some smarts in there,” says Mottier.
“Because the propeller and engines have never been really controlled as an integrated system, we developed very sophisticated computer models of the propeller as it interacts with the engine, engine inlet, the wing and fuselage,” Mottier says.
The engine, which will run for the first time in early 2018, is designed to produce a “step function change in performance which is required for us to break into this segment, and to do it in a package that fits into the current PT6 envelope,” he says.
The ATP is the first product of the Center of Excellence that GE is establishing in Europe, where several government-sponsored export credit agencies (ECAs) can provide financing to support international sales. The move followed the expiration of the U.S. Export-Import (Ex-Im) Bank authorization earlier this summer, and despite subsequent congressional moves to reinstate Ex-Im, GE says the center was established amid continuing uncertainty and the need to support $11 billion in sales opportunities in the pipeline requiring credit financing.