A 12-year-old competition to define the most important military helicopter engine for perhaps the next half a century has entered an intense, final phase: by January 2019, the US Army plans to select the contractor for its Improved Turbine Engine Programme (ITEP). The ITEP contract will develop and test a new, 3,000shp (2,240kW)-class turboshaft engine as a drop-in replacement after 2025 for more than 1,300 Sikorsky UH-60 Black Hawks and more than 600 Boeing AH-64 Apaches in the army's inventory alone.

ITEP is also the army's favoured option to power the smallest versions of a proposed family of high-speed, Future Vertical Lift (FVL) systems, so the winning bidder for the engine contract is likely to control the market for medium-sized military rotorcraft propulsion for decades to come.

The competition for the prized contract formed quickly after the army launched the predecessor Advanced Affordable Turbine Engine (AATE) programme in 2006, which transitioned into ITEP four years later.

GE Aviation supplies the 2,000shp-class T700-701 engines for nearly all Apaches and Black Hawks today, so it jumped into the ITEP competition with the T901 (formerly GE3000) design, which features a similar, one-spool architecture for the gas generator module of the engine.

Meanwhile, Honeywell and Pratt & Whitney decided to team up as ATEC for the chance to seize GE's near-monopoly position on propulsion for medium-lift, military helicopters. The army's requirement for a 3,000shp engine bridges a gap in turboshaft power between the T700 and Honeywell's 4,800shp T55 engine, which is used to power the heavy-lift Boeing CH-47 Chinook.

But the nature of the army's requirements for ITEP pose some unique – and impressive – challenges for competing design teams. For the first time, the service is developing a new turboshaft engine as a "drop-in" replacement on existing aircraft, rather than for a clean-sheet new rotorcraft. That means the 3,000shp ITEP must be a drop-in replacement for the 2,000shp T700 on Black Hawk and Apache helicopters, with minimal changes required to the inlet, mount and exhaust. As a result, the army requires the ITEP engine to generate 50% more power within the same space and roughly same volume of airflow as used by the T700 today.

Moreover, the army also wants the ITEP engine to be cheaper to operate and easier to maintain than the T700. In addition to producing 50% more thrust, the service requires its engine to consume 25% less fuel in an uninstalled configuration.

Asking for 50% more thrust and 25% less fuel consumption with no increase in engine size or weight is a tall order, but the army has no other option. Even with recent upgrades, the existing Black Hawk and Apache fleets are running out of time.

Army aviation leaders have been explaining the depth of the problem for years. The empty weight of the UH-60 has increased by 35kg (78lb) a year on average, as the army has responded to new threats and missions by adding on an ever-increasing array of gadgets. A platoon of 40 soldiers once carried by four UH-60s now requires about twice the number of aircraft.

The army also is operating in a different environment from the one it anticipated when the UH-60 and AH-64 were designed in the mid-1970s. The original requirements for both aircraft called for the ability to hover at 2,000ft with the temperature at 35˚C (95˚F). By the early 2000s, it had increased the "hot/high" hovering requirement to 4,000ft, requiring GE to increase thrust from 1,700shp in the original -701 engine to 2,000shp in the T701D.

By fielding a 50% more powerful ITEP engine, the army plans to raise the hovering ceiling for the Black Hawk and Apache fleets on a hot day to 6,000ft, allowing both aircraft to operate on a greater percentage of hot days in Afghanistan. A UH-60 powered by a T700-701D engine can hover at 6,000ft, but only when carrying no more than five soldiers, according to army studies. The same aircraft powered by the ITEP engine should be able to lift 13 troops, with 65% more range.

The ITEP engine's improved fuel efficiency will help solve multiple problems. In addition to extending the range of a fully loaded UH-60 or AH-64, the army is relying on ITEP to dramatically cut fuel consumption. By carrying a larger payload much farther, the service reduces the amount of fuel consumed on each trip and the overall number of sorties.

Those reasons help explain why ITEP has jumped to the top of the priority list among army aviation acquisition programmes. Developing and fielding the new 3,000shp engine is more important right now than FVL – its concept that aims to replace all the army's helicopters over time with high-speed rotorcraft, such as the Bell V-280 Valor, Sikorsky S-97 Raider or Sikorsky/Boeing SB-1 Defiant.

As the ITEP programme transitions from a competition to a development effort, the question will be whether either bidder is up to the task. The two competitive rivals – GE and ATEC – are approaching the problem with different engine architectures.

GE designed the T700 in the mid-1970s with a single-spool gas generator – that is, a single turbine module drives a compressor to generate power. That single-spool approach has served the T700 and -701 engine family over a 40-year-period. The company's submitted T901 design for the ITEP contract features the same architecture.

"These are relatively small engines to begin with. They have to fit into the existing helicopters. There's not a lot of extra space," says Mike Sousa, a business development director for GE's advanced turboshaft programmes.

"If you've got the ability to make a compressor that will meet their requirements for the programme without the added complexity of going to two spools, that certainly seems like the right approach," he adds. "It's going to help you reach the weight objectives of the programme and the part count is going to be lower."

In some ways, the debate over a single- or dual-spool architecture for the ITEP engine echoes the rivalry in the market for commercial turbofan engines. GE and P&W both have relied on variations of a dual-spool engine architecture since the 1950s, while Rolls-Royce had moved to a three-spool design by the late 1960s. In that debate, R-R has argued that a three-spool approach creates opportunities to reduce part count by, for instance, using fewer stages in the high-pressure compressor.

"It's very possible if we were doing a single-spool that we might have an extra stage of compression, so there are some possible part-count offsets from the aerodynamic advantages of going to the two-spool," says Jerry Wheeler, vice-president of the ATEC joint venture.

Both bidding teams acknowledge the challenge of meeting the army's requirements. To generate 50% more thrust within the same dimensions and mass flow volume as the -701, the core of the ITEP engine needs to be significantly more efficient at generating power. Each individual component within the engine must be improved. Traditional metallic rolling element bearings, for example, will not be sufficient. GE and ATEC have designed their engines with hybrid bearings, fearing metallic races and ceramic rollers.

Both companies have produced engines with hybrid bearings outside the military turboshaft market, but it is considered a critical technology for the ITEP engine by the government. "Those bearings had run in our demonstrator engine testing, so they have been demonstrated in a relevant environment," says Wheeler.

Sousa agrees: "We have a whole bunch of data on that – both from other places within the business, as well as in turboshaft-specific demonstrators."

Other critical elements for a military turboshaft engine are the inlet particle separators. No civilian application of a turboshaft engine is meant to routinely operate in the kind of conditions that US Army helicopters face, especially in fine dust and sand particles found in the Middle East. Engine air particle separators have made huge strides in the past two decades, but the army wants to take the next step with that technology with the ITEP engine.

The challenge for the engine designer is coming up with the right method to screen out fine particles, while allowing the airflow to pass relatively undisturbed into the compressor of the engine. Meeting the army's "aggressive goals" for the particle separation device has been a key focus of development work on test rigs and demonstrators over the past decades. Both teams are convinced that the test data proves their technology is now ready to enter production.

"It was definitely one of the design challenges, but our inlet particle separator team did a fantastic job during the design process and we were able to prove it out through testing," Wheeler says.

In addition to Honeywell's experience with inlet particle separators on the T55 and T64 engines in military service, GE has dealt with the same issues with the -701 programme. "We have had a number of different technology programmes to demonstrate in the particle separator performance as well as pressure loss," Sousa says. "And the ways we do it today are fundamentally different from the ways we did it 30 years ago, when we were designing the T700. We certainly have much better modelling tools for particle separators that show us what happens to those particles."

Then, there is the core of the engine itself. The compressor for the ITEP must be able to ingest the airflow downstream of the particle separator, then convert the mass flow into a combustible gas with far greater efficiency than the -701 does today in order to meet the army's goals.

Both companies have the advantage of building on several decades of developments in 3D aerodynamic design of compressor aerofoils, the intricately shaped blades that guide the reluctant airflow to higher and higher pressures.

Packaged together, the new technologies will redefine the state of the art in the military turboshaft market, no matter which team wins the ITEP competition.

The engine is so powerful, in fact, that the army could be tempted to seek new improvements for the next iteration of the UH-60 fleet. In fact, Sikorsky has developed a roadmap of potential technology improvements for the Black Hawk that could be enabled by installing the ITEP engine. A chart showing each of the improvements was displayed in a presentation to several Latin American military chiefs during a 4 April press conference at the FIDAE air show in Santiago, Chile.

"We are just looking at designs that can improve the aerodynamics so you get more thrust at higher altitude," Chris Van Buiten, vice-president of Sikorsky Innovations, tells FlightGlobal. "It's our job just to be ready in case the customer is interested in not having that barrier."

"In fact, if you just drop an ITEP engine into a Black Hawk, you get a big change in capability with what's already there," Van Buiten says. "At the same time, we are maturing technology to bring that even further."

A good example, he says, is potentially funding an upgrade to the gearbox, which is currently limited to transmitting 3,400shp to the main rotor system. With two ITEP engines generating a total of 6,000shp, a more powerful gearbox would allow the UH-60 to hover with more people above 6,000ft.

Another upgrade candidate is the tail rotor. If the main rotor is provided with more lifting authority, an improved tail rotor design may be necessary to counter the higher torque. "If you think about putting in an ITEP engine, you could run out of tail rotor authority when you're at high altitude," Van Buiten says. "The Black Hawk has got a pretty exceptional tail rotor already, so it will capture a lot of it."

Source: FlightGlobal.com