GE Aviation’s T901 Engine

GE Aviation’s T901 turboshaft, one of two development engines competing for the US Army’s Improved Turbine Engine Program (ITEP) requirement for a 3,000shpclass replacement for the GE T700s powering the Army’s Sikorsky H-60 and Boeing AH-64 fleets, has the same number of modules as the T700 and is dimensionally identical. However, in other respects the T901 differs greatly from its predecessor, according to Ron Hutter, executive director of the T901 program for GE.

While GE doesn’t confirm the numbers of compressor and highpressure turbine (HPT) stages in the T901 (the T700 has five axial and one centrifugal compressor stages and two HPT stages), Hutter told AIR International that in addition to being a single-spool design like the T700, the more powerful T901 also has four modules and is as highly modular as its predecessor.

“We wanted to leverage all of the value that we have in the current T700 architecture, so [the T901 has] the same level of modularity and the same definition of modularity”, said Hutter. “The key to the modular concept [is that] … when you’re at the battlefield and you’re in austere conditions and your whole supply chain is limited, you really want to be able to do as much maintenance on the battlefield as possible – and that’s what we’ve been able to accomplish with the T700.”

Continued Hutter: “That was always the goal for the T901 – so you can do that maintenance in the field, you can do it in the shadow of the aircraft. The single spool allows for that level of modularity. The key there is, when you do field maintenance, you don’t want to expose any of the bearings to contamination, so we have sealed sumps as part of this single-spool architecture. We’ve demonstrated this very successfully with the T700 over the last, almost, 40 years.”

Because an ITEP programme requirement for the T901 and the Pratt & Whitney-Honeywell ATEC T900 (which are competing to win the Army’s T700 replacement contract) is that the engine has to be compatible with the existing helicopters and will have to serve as a drop-in replacement for the T700, both engines have to have the same dimensions as the T700. However, to meet the US Army’s ITEP requirements, they also have to be 50% more powerful than the T700, off er 25% lower specific fuel consumption and provide reduced life-cycle parts and maintenance costs.

An expanded view of the T901 engine.
GE Aviation
AH-64D Apaches from 1st Attack Reconnaissance Battalion, 82nd Combat Aviation Brigade, descends onto the forward rearming and refuelling point during an aerial gunnery exercise, at Fort A.P. Hill, Virginia.
Cpl Randis Monroe/US Army
UH-60 Blackhawks from the 101st Combat Aviation Brigade rehearse an air assault demonstration to celebrate the 75th Anniversary of the 101st Airborne Division (Air Assault) at Fort Campbell, Kentucky.
Sgt Marcus Floyd/ US Army

The drop-in requirement means the eventual ITEP production engine has “got to have the same mount locations”, the same inlet and exhaust dimensions and the same interfaces as the T700. The winner of the production contract – for some 6,000 installed engines on 3,000 helicopters, plus spares – will have to ensure that “as many things as possible on the helicopter are kept exactly the same” as with the T700, said Hutter.

As a result, in the T901 as in the T700, “We have a power-turbine module, we have a hot-section module, we have a cold-section module and an accessory module”, Hutter confirmed. Because the T901 is a single-spool design, all of its high-pressure turbine stages and its axial and centrifugal compressor stages are on the same spool. Some of the T901’s compressor stages and all of its HPT stages – plus the combustor – are in its hot-section module, but the coldsection module “is essentially the compressor”, said Hutter.

“We also have the same [T700- like] design methodology there in terms of the configuration of the compressor”, he said. “We’ll have a split case so that you can down-case the compressor in the field and do … maintenance on the compressor blades if needed. You can blend out [foreign object debris] damage on blades individually. If there are some bent tips on some of the compressor blades, you can clip off some damage there and put it back together and keep running in the field.”

The T901’s power-turbine module contains one or more freewheeling low-pressure turbine stages. These drive the accessory gearbox poweroutput gear shaft that provides power to the helicopter’s main-rotor and tail-rotor systems.

All this modularity means that theoretically “you can remove the power turbine and get to the hot section that way, but in practice it’s not done”, said Hutter. Typically, in the field, maintenance crews will remove an ITEP engine from a helicopter hangared overnight, replace or repair any module requiring work, put the module back in the engine and re-install the engine in the helicopter, performing all the work right next to the aircraft.

“You can take the power turbine off and then that gives you access to the hot-section module and you can remove the hot-section module from the back”, explained Hutter. “It all comes out through the back of the engine.” As with the T700, “The mounts for the [T901] engine are on the cold-section module”, said Mike Sousa Jr, director of business development for GE Aviation’s advanced turboshaft programmes. “So if you remove the cold-section module, there would be nothing to hold the hot-section module in place.”

The T901 has a “significant number” of additively manufactured parts, according to Hutter. One particular additively manufactured part in the T901 replaces a component that in the T700 is made from 51 piece-parts. Unlike the T700, the T901 also uses an unspecified number of ceramic matrix composite parts in its hot section, to provide “lighter weight, higher temperature capability, less cooling air required – [providing] benefits for performance”, said Hutter.

Additionally, using advanced, computerized diagnostic and prognostic tools that include predictive data analytics, “One of the things we’ll be able to do on this new engine is … real-time data counting, so you’ll be able to where the parts’ lives are on the engine as it runs real-time”, said Hutter. “That’ll all be stored on the engine [as] part of the HMS [health and monitoring] system. That’s kind of taking it to the next level.”

“The system on the T901 has an engine health monitoring system that is part of the engine rather than being part of the helicopter HMS, because the T901 engine is designed to go into the existing Blackhawk and Apache with minimal changes to any other aircraft systems”, explained Sousa. “We really think that’s going to reduce pilot and maintainer workload.” Chris Kjelgaard

An infographic on the AH-64 Apache powered by the proposed GE T901 engines.
GE Aviation
An infographic on the UH-60 Blackhawk powered by the proposed GE T901 engines.
GE Aviation