Test Flights Start for Titanium-Blade Engine

Aircraft engine leader Pratt & Whitney recently started flight tests of its PurePowerPW1200G engine family with the PW1217G engine for the Mitsubishi Regional Jet (MRJ) aircraft. Like other engines in the PurePower Geared Turbofan engine program, the PW1217G's fan blades incorporate titanium, not composites.

The PW1217G engine flew on a stub wing that was specially designed for the Pratt & Whitney Boeing 747SP flying test bed at the company's Mirabel Aerospace Centre in Quebec. This initial PW1200G flight test program is designed to validate the engine's performance, operability, and in-flight starting. Certification testing is scheduled to begin by the end of the second quarter.

More than 1,000 hours of full engine testing have been collected for the PW1200G, with more than 2,000 endurance cycles. Some of those test hours have included sea-level data, which will now be complemented by the altitude testing data. For the entire PurePower Geared Turbofan engine program, which also includes the PW1524G engine for the Bombardier Cseries aircraft, Pratt & Whitney has completed more than 2,400 hours and 7,600 cycles of full engine testing. Four PurePower engines are in test and nine engines are in the build cycle.

The PurePower engine family shares common cores that consist of an ultra-efficient high-pressure compressor, a low-emissions combustor, and a high-pressure turbine module. The engine's gear system lets the engine fan operate at a different speed than the speed of the low-pressure compressor and turbine.

For the PurePower Geared Turbofan engine's fan blades, Pratt & Whitney worked with its sister company, Hamilton Sundstrand, to design, build, and test three different types of blades: traditional titanium, molded composite, and hybrid metallic. The hybrid metallic configuration is a lightweight, high-strength, proprietary metallic construction with a titanium leading edge.

The team found that, at smaller fan diameters, which are characteristic of the single-aisle aircraft thrust class, the composite blade has to be very thick to pass the bird strike test. That's because, even with 3D fiber woven reinforcement, composites are inherently weak through the dimension of their thickness. Also, the bird danger does not scale with a fan's diameter.

Metallic materials provide better impact resistance for this smaller size engine class. This also allows them to be thinner, which improves aerodynamic performance. The thinner hybrid metallic fan blade weighs the same as the thicker composite fan blade, but also has higher performance. Based on feedback from operators, Pratt & Whitney designed the blade to eliminate the need for lubricating the fan blade root between shop visits, reducing maintenance.

The PurePower Geared Turbofan engine's fan blade design has been fully validated for fan blade out (FBO), bird strike, and post bird strike run-on capability, as well as icing testing, acoustic performance, and aerodynamic performance.

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