Secretary of Defense James Mattis makes it clear in the latest National Defense Strategy and is echoed by both Deputy Secretary of Defense Patrick Shanahan and Army Chief of Staff Gen. Mark Milley: Readiness is our military’s number one priority.
The importance of readiness is nothing new for Army Aviation. Over 40 years ago, the Vietnam War taught the Army harsh lessons about what it takes to keep a helicopter fleet ready to fight. Those lessons led to numerous corrective actions with the goal of improving Army Aviation readiness, not the least of which being the development of a new turbine engine—General Electric’s T700.
GE’s T700 turbine engine offered significant performance and reliability improvements in a simple design that greatly reduced the required maintenance footprint and resulted in lower life-cycle costs. The engine’s continued success is largely due to its fully modular design, enabled by operating on a single-spool core. Combat operations around the world have proven that full modularity maximizes field maintainability, resulting in greater combat flexibility. Thus, full modularity has been a key contributor to Army Aviation readiness for more than 40 years.
History, and my personal experience as an Aviation Brigade Commander, can attest to the significance of full modularity in combat, particularly when fighting in an immature theater of operation where the logistical lines of communication are not fully developed. This was the case during the initial phase of Operation Iraqi Freedom in 2003—the Army depended on the T700’s modularity to maintain readiness. Most operations took place from assembly areas or forward operating bases located in the middle of the desert, requiring repetitive launch and recovery in extremely sandy conditions. The full modularity of the single-spool T700, and subsequent flexibility to remove, clean and repair critical portions of the engine without needing to send an entire engine to the rear, helped enable commanders to maintain a high combat operations tempo in a way that a less modular engine could not.
Full modularity is key to future Army Aviation readiness
The fact is, most turbine engines are modular. Modularity is the ability to quickly and easily disassemble an engine into major sub-assemblies or modules. Full modularity extends this modular concept to an engine’s hot section. It provides maintainers unparalleled access to interior components and enables performance restoration in even the most austere field conditions.
The Army is now seeking the next generation of helicopter power with its Improved Turbine Engine Program (ITEP). The program calls on industry to produce a new turbine engine that will provide 50 percent more power, 25 percent better fuel efficiency and reduced life-cycle costs over GE’s T700 engine. Two companies, GE and the Advanced Turbine Engine Company (ATEC, a JV between Pratt & Whitney and Honeywell), are competing for this contract award—GE with the T901 and ATEC with the T900.
With the T901, GE is combining its T700 experience with a deep technology stack, including more than $9 billion of investments over the past decade, to ensure Army Aviation’s continued readiness. The company assessed multiple engine configurations, including single- and dual-spool core designs, and ultimately confirmed that meeting ITEP performance and growth requirements has far more to do with engineering and technology than engine architecture. Therefore, it was the correct decision to stick with a proven single-spool core design for the T901 to maintain full modularity, increase reliability and decrease life-cycle costs.
The dual-spool core architecture has been around since the 1940s and can somewhat improve engine performance, especially when faced with overcoming compressor design and material technology challenges. Many engine manufacturers, including GE, use the design in larger engines for fixed-wing applications, but it has never been attempted in a helicopter engine.
This fact is no coincidence. Helicopters operate much closer to the ground than fixed-wing applications where sand and dust landings are often a reality. The resulting ingestion of dust and dirt will eventually degrade any engine’s performance, making field maintenance essential to maximizing time-on-wing and sustaining readiness in combat.
Furthermore, fitting the extra frames and bearings necessary to spin an additional shaft inside a small helicopter engine adds a large amount of relative weight and could ultimately lead to degraded reliability. The single-spool core design meets ITEP requirements with lower readiness risk to the warfighter.
Sikorsky HH-60U Black Hawk. Photo courtesy of Sikorsky
21st century technologies ready for military aviation
The technologies GE employed to achieve ITEP performance and growth requirements on a single-spool core are already flying. Chances are you’ve recently flown on a commercial airline powered by one of GE’s newest turbofan engines utilizing the same technologies being incorporated into the T901. GE estimates that by the time the T901 enters full rate production, these technologies will have 715 million combined commercial flight hours, easily proving their readiness for U.S. military applications.
While these advanced technologies are ready for today’s military applications, GE is still discovering the full potential of their benefits to engine design. For example, in 1976 the GE T700 engine was built with the latest technologies of the time and could produce 1,500 shaft horsepower (SHP). Since then, through engineering and technology advancements, the engine family has doubled its shaft horsepower capability. The T901 will benefit from similar continuous improvement and growth of its single-spool core architecture to give the Army a versatile engine that can easily integrate into today’s Apache and Black Hawk fleets, as well as meet growth requirements for Future Vertical Lift.
Speaking from experience, complexity is the enemy of readiness, and seems to be in direct conflict with our nation’s senior military leaders’ top priority. As the Army’s doctrine evolves, with Multi-Domain Operations requiring combat units to operate for extended periods with minimal logistics footprint, aviation commanders will require the flexibility that a fully-modular engine provides. And when it comes to ITEP, only the combat proven, fully-modular single-spool core design of GE’s T901 can meet the Army’s tough performance and growth objectives without sacrificing readiness.
Greg Gass is a retired U.S. Army Aviator with over 23 years of aviation experience.