New GE turboprop bristles with technology

At EAA AirVenture in Oshkosh, Wisconsin, in late July, GE was showing off a full-size mockup of the all-new engine entirely 3-D printed. The mockup shows how parts of the engine case can be made thinner in some areas where stress is lower and how internal channels can be manufactured in from the start, as opposed to more traditional manufacturing, which would grind away material after casting or milling.

The dramatic reduction in parts for the production engines means more strength, lighter weight, and fewer parts and vendors in the supply chain, which lowers costs, explained Paul Corkery, general manager of the project for GE. The result is better fuel efficiency and in theory a longer life for the engines. Corkery said that with some 1,100 hours and 900 starts on test engines they have now validated that the engine burns 15 percent less fuel than competitive engines and holds horsepower to a higher altitude. The engine will be rated at 1,300 shaft horsepower and have a 4,000-hour TBO right out of the box.

Engine manufacturing is not the only way GE is infusing new technology into the program. The engine also carries a dual-channel full authority digital engine control system, an unusual feature on turboprop engines. The change allows for truly single-lever management of the powerplant, down from four levers in traditional single-engine turboprops. Digital control of the engine allows it to run slower at idle, which eliminates the need for using beta on the propeller during taxi, which reduces noise. Digital control of the McCauley propeller and the fuel flow means the system can continuously fine-tune pitch for any phase of operation, including taxi.

The engine brings numerous features to the small turboprop market that are typically found only in much larger engines, such as variable geometry compressor stator vanes to improve performance, a 16:1 pressure ratio for improved efficiency, and single-crystal blades allowing for higher internal temperatures.

Pilots and maintenance personnel will care more about the engine’s ability to capture a river of data, which can be used to predict maintenance cycles. Typical engines capture only about eight to 12 data points, according to Corkery. The Catalyst engine will capture some 70 parameters every 8 milliseconds. Among the data collected are location and ambient conditions such as information about dust in the air and weather conditions. The data will be fed to the Denali’s Garmin G3000 cockpit for downloading on the ground, or it can be automatically uploaded once the weight-on-wheels switch is actuated. With that, GE can make a “digital twin” of the engine, comparing performance to other engines in the fleet, and help predict maintenance events. Over time, it will help the company target service bulletins to a particular engine as opposed to mandating them fleet-wide, for example.

Corkery says the company is on track to certify the engine in about 15 months, in sync with Textron’s plan for the Denali itself.

Martin Tuck, technical marketing specialist for Textron, said the airframe’s static test and fatigue articles are being tortured regularly with the goal of demonstrating 30,000 cycles by the time certification occurs. A prototype is scheduled to fly later this year, and two production aircraft will join the flight test program in early 2020.

When completed, the aircraft with its large cabin door is expected to carry four passengers up to 1,600 nautical miles with a maximum cruise speed of 285 knots. Full-fuel payload will be 1,100 pounds with up to 11 seats, including the option for an aft belted lavatory.