Get the Facts: Why Single-Spool is Superior for ITEP

By Tony Mathis, CEO and President of GE Aviation’s Military Systems business

The U.S. Army continues to make progress toward Milestone B and is nearing a decision on which engine to select for the Improved Turbine Engine Program (ITEP), its endeavor to re-engine Boeing AH-64 Apaches and Sikorsky UH-60 Black Hawks. GE is offering our new T901 turboshaft helicopter engine, which incorporates fully modular architecture and a single-spool core design. All of these are proven attributes from four decades of experience. There is a reason why we chose a single-spool core design for our T901 engine, which is currently used on all U.S. military helicopters and combat aircraft. Engines with a single-spool core are lighter weight, less complex, more reliable, easier to repair in the field, and less expensive to maintain than engines with a dual-spool core. Using a dual-spool core to achieve the Army’s ITEP performance requirements creates a much more complex engine that is harder to fix and more expensive to maintain over the course of its lifetime.

Above: Engines with a single-spool core are lighter weight, less complex, more reliable, easier to repair in the field, and less expensive to maintain than engines with a dual-spool core. Top: GE’s single-spool core T700 engine has powered all U.S. Army Black Hawk and Apache helicopters for the past four decades.

Tony Mathis is CEO and President of GE Aviation’s Military Systems business.

“Spool” is shorthand for the combination of a compressor connected to a turbine by a shaft. In a single-spool, the high-pressure turbine drives the entire compressor. With a dual-spool, in addition to the high-pressure turbine which drives a high-pressure compressor, an intermediate turbine is added to drive a low-pressure compressor. In both a single and dual-spool, a power turbine delivers power to the helicopter through an additional shaft at the center of the engine. That means a dual-spool core has three concentric shafts in a small engine, which drives daunting mechanical complexity and challenges. To meet the Army’s ITEP requirements — 50 percent more power and 25 percent better fuel efficiency — the engine needs better compression (a higher pressure ratio) in an architecture that is the same size as the current T700 engine. GE Aviation’s top engineers evaluated single and dual-spool engine designs to meet this challenge and determined that the required performance can be met with GE’s 3D aerodynamic technologies without adding additional spools. Additional spools only add more mechanical complexity and drive up risk. GE’s T901 engine meets the Army’s performance requirements by tapping into GE’s impressive stack of proven commercial technologies, including additive manufacturing, ceramic matrix composite (CMC) components, sand tolerant technologies, advanced cooling technologies and industry leading prognostic and diagnostic tools. We’ve invested $9 billion in maturing these technologies over the past decade to drive down risk, and these technologies currently fly in commercial aircraft, safely transporting passengers all over the world every day. GE’s single-spool core T700 engine has powered all U.S. Army Black Hawk and Apache helicopters for the past four decades. In addition, it is used to power multiple aircraft types for the U.S. Navy, U.S. Marine Corps, U.S. Air Force, U.S. Coast Guard, and other government agencies. Fifty countries also rely on the T700 engine to power their military and civil fleets. The T700 engine has racked up more than 100 million flight hours of experience and is globally adopted as a benchmark in rotorcraft propulsion excellence. Through continuous upgrades and technology advancements, GE has doubled the power of derivative engines in the T700 family over its lifetime and reduced its cost by 50 percent. What people love most about the T700 is its simplicity, its ease of maintenance, and the ability to fix it in the field, and that’s driven by modularity and the simplicity of the design. Soldiers can fix it in the field, in the desert, wherever they are. It’s modular. You just pull the module instead of shipping the whole engine back. You put a new module on, you put it back in the helicopter, and get back to the fight. As a result, GE carried over the benefits of a single-spool core architecture, ensuring the T901 engine is ready to continue delivering combat readiness to the Warfighter in the decades to come. The full modularity of the T901’s single-spool core provides the Army with unmatched shadow-of-the-aircraft maintainability. Combat units can swap out modular parts of the engine in the field and travel with fewer full-sized spare engines, simplifying logistical footprints and supply lines. A dual-spool engine is less modular, thereby less maintainable in the field, and requires units to travel with more full-sized spare engines. The fully modular single-spool design also offers superior growth potential at a lower cost through incremental improvements to engine modules, a significant advantage to meet the Army’s requirements. In conclusion, GE Aviation is always committed to delivering the best technology in support of the Army and the Warfighter. That is why we’re proud to offer the T901 engine. It offers the aerospace industry’s most advanced, proven technologies, and its single-spool core design makes it lighter, less complex, more reliable, easier to repair in the field and less expensive to maintain. Learn more about how GE’s T901 engine delivers superior readiness to the Warfighter here, or visit GET901.com.