(Image courtesy: Lockheed Martin Corporation)

Next-generation Honeywell turboshaft engine could power Sikorsky-Boeing’s Future Vertical Lift family

The latest version of Honeywell Aerospace’s seven-stage axial compressor T55 turboshaft engine is nearing the final phase of development. Designed with next-generation technology to increase reliability, power, and fuel economy, the Honeywell T55-L-71X will find a home onboard the medium-lift Sikorsky-Boeing SB-1 Defiant (stylized as “SB>1 DEFIANT”) compound helicopter demonstrator.

Although initial SB-1 Defiant test flights for the U.S. Army Future Vertical Lift (FVL) program were conducted using Honeywell T55-GA-714A engines that traditionally power the Boeing CH-47 Chinook, both the Chinook and Defiant are both slated to receive the upgraded engine.


Read more: Sikorsky-Boeing’s FVL contender takes flight


“This is a new era for the T55 engine,” says John Russo, senior product director, Military Turboshaft Engines, Honeywell Aerospace. “Our improvements come from new technology infused into the compressor section of the engine that will reduce maintenance costs, increase aircraft readiness and lower the fuel burn – all while increasing the aircraft’s useful load and flight range.”



Variants of the T55 engine, internally developed by the Lycoming Turbine Engine Division in the 1950s, have powering the U.S. Army’s Chinook helicopters for generations. More than 6,000 T55 engines have been produced and the engine has accumulated over 12 million operating hours.             

Now produced by Honeywell, the newest iteration in the series of engine modernizations positions the Army to take advantage of next-generation technologies while maintaining the support infrastructure it needs to move forward with its FVL platform. FVL will comprise a family of five military helicopters for the United States Armed Forces, all of which share common hardware such as sensors, avionics, and engines to reduce operational costs and increase readiness.



While the focus of the latest T55 variant is on fuel savings, reliability, and maintainability, the improvements also create a downstream result of greater horsepower. It is designed to be incorporated as a kit during overhaul for existing aircraft and as a “forward-fit” option for new aircraft.

“This commonality will leverage all the Army’s existing support structure, and also bring the engine up to the latest certification standards to set a long-term growth path for airframe weight increases and power demands,” Russo added. “We want to congratulate the Sikorsky-Boeing team on reaching its first flight milestone, and we look forward to powering many more flights.”



Sikorsky-Boeing SB-1 Defiant testing will continue as the U.S. Army weighs a decision on its FVL platform. The Defiant is challenged by Bell Helicopter’s V-280 Valor third-generation, v-tail tiltrotor design.

Phoenix-based Honeywell Aerospace is a division of Honeywell International Inc.


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William Kucinski is content editor at SAE International, Aerospace Products Group in Warrendale, Pa. Previously, he worked as a writer at the NASA Safety Center in Cleveland, Ohio and was responsible for writing the agency’s System Failure Case Studies. His interests include literally anything that has to do with space, past and present military aircraft, and propulsion technology.

Contact him regarding any article or collaboration ideas by e-mail at william.kucinski@sae.org.

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