GUY NORRIS / LOS ANGELES
General Electric's venerable T700/CT7 family is powering up for a 21st century renaissance, with variants being tested and new markets in its sights
Ask anyone in the military propulsion business and they will tell you that any engine with a 30-year history and around 12,000 units in the field is considered "mature", at best. All the more surprising, then, that General Electric's seasoned T700/CT7 family is in the throes of a major revamp with new, more-powerful variants in test and development, and substantial new market opportunities on the horizon.
"It is considered an important family for the company and we are constantly modernising it," says GE military turboshaft/ turboprop general manager Ed Birtwell. Fed with new technologies from the CT7-8 and US government/industry Joint Turbine Advanced Gas Generator (JTAGG) programmes, the engine is undergoing extensive regeneration. Leading the way are the T700-701D and CT7-8C/8E versions, while preparations are under way for the new centreline GP3000 - a planned 3,000shp (2,235kW) joint GE/Pratt & Whitney turboshaft aimed at the improved turbine engine programme (ITEP).
A development T700-701D is being stripped down and inspected at GE's Lynn, Massachussetts, plant after undergoing its official durability testing at the US Army's Redstone Arsenal site in Huntsville, Alabama. The tests, undertaken in a newly commissioned test cell at Redstone, are part of the formal military qualification for the engine, which is destined for the Sikorsky UH-60M Black Hawk modernisation programme. Under this effort, a mixed fleet of UH-60As, and more powerful UH-60L variants, will be inducted, modified and re-engined to produce a commonly configured fleet of around 1,217 UH-60Ms.
Hot-section changes
The existing T700-700s on the UH-60A and -701C engines on the UH-60L versions will be returned for upgrading to the 2,000shp-rated -701D by either GE or the US Army's Corpus Christi depot in Texas. The upgrade consists chiefly of changes to the hot section, with modifications to the power turbine third stage, stator nozzles and shroud as well as (in the case of the -701As) an all-new high-pressure (HP) turbine, digital electronic controls and anti-icing bleed valve. The basic -701D package also includes first- and second-stage blade material changes as well as upgrades to the combustor liner.
Flight testing of the first -701D powered UH-60M started on 17 September, two days ahead of schedule, at Sikorsky's West Palm Beach test centre in Florida, with a second test aircraft (a rebuilt UH-60L) due to follow shortly. During initial tests, the UH-60M reached speeds up to 120kt (220km/h) and successfully executed 45¡ turns. GE says the -701D provides 25% more shaft horsepower than the -700, and 5% more than the -701C. It will also be more durable and, as a result of the increased power, will enable the -60M to carry greater payloads with a reduced maintenance burden. Some indication of this is expected during the tests, which will later include two additional aircraft. These will involve a new-build HH-60M and a rebuilt UH-60A similar to the first test machine, both to start tests between January and April 2005. Low-rate initial production is targeted to start later in 2005, with full-rate production expected to climb to around 60 a year by 2007. This rate is expected to be sustained through to around 2023-25, by which time the follow-on future utility rotorcraft (FUR) is expected to be in service.
The FUR requirement, formerly dubbed the UH-60X, calls for a machine capable of lifting almost 4,100kg (9,030lb) over 135km (75nm), or roughly twice the payload/range of the current UH-60A. "To accomplish that we'll need around 3,000shp, as well as roughly a 25% improvement in sfc [specific fuel consumption] and yet still have the installed weight of the current T700," says Birtwell. "We're looking for a 60% improvement in power- to-weight ratio, so to get there means a new centreline engine that's a spin-off from the JTAGG," he adds. Key JTAGG technologies expected to find their way into the ITEP engine include enhanced durability, high-work turbine nozzles and rotors as well as an advanced axial-centrifugal compressor that was demonstrated during runs of the JTAGG 1 core.
Although the go-ahead on the planned teaming with P&W on the GP3000 awaits US government funding to be approved, Birtwell says: "That's the game plan for ITEP. There's talk of accelerating it now, but in the meantime we're continuing technical developments through our own research and development," he adds. The engine will also be required to meet a 20% reduction in overhaul and acquisition costs, part of which is linked to life-cycle fatigue extensions of up to 15,000 and 7,500 for cold and hot parts, respectively.
The engine will grow from the CT7-8C, which is in development for the Sikorsky H-92. "We're in the process of completing the design now, and we will be aiming to get the engine certificated in mid-2007," comments Birtwell. The -8C will have double the power of the baseline T700-700, thanks largely to successive improvements to the gas generator and power turbine over recent years. Rated at 3,000shp, the-8C represents a 25% power increase over the CT7-8 and will use improved hot section materials as well as a new three-stage power turbine, which will be tested for the first time in a completed engine during the first quarter of 2004.
Although growing H-92 payload/weight requirements helped drive the -8C development, additional impetus came from the need to challenge Rolls-Royce Turbomeca's RTM322, which has been aggressively targeted at several imminent helicopter programmes. These include a planned MH-60K/L Black Hawk upgrade for the US Army Special Operations Command, which will require additional power.
Search and rescue
The RTM322 is also being discussed with Sikorsky and the US Air Force for a combat search and rescue (CSAR) requirement, as is the -8C. The new platform is intended to supplement and eventually replace the current HH-60 Pave Hawk and UH-1 Huey fleet, although it is believed the new aircraft will allow the newer HH-60s to be flowed down to replace the Hueys initially.
Another contender for the CSAR role is the Lockheed Martin/AgustaWestland US101, which is also competing with the H-92 for the US Presidential VXX helicopter requirement. GE's victory in the engine selection for the VXX US101 bid, yet to be confirmed as Flight International closed for press, is expected to give it a major leg-up in the follow-on USAF CSAR competition. The final selection of the VXX, which will replace around 20 VH-60N and VH-3D Presidential helicopters, is targeted for early in the second quarter of 2004 with entry-into-service in 2008. Certification of the CT7-8E in the US101 is also expected in 2004.
Another, more certain, market is the T700-401/401C-powered re-engined US Marine Corps AH-1Z Cobra and UH-1Y Huey. The combined AH-12/UH-1Y flight test effort passed the 1,000 flight hours milestone in mid-2003, and appears to be on track for completion in late 2004. The Marines plan to upgrade 100 UH-1Ys from UH-1N standard, and will convert up to 180 AH-1Ws to AH-1Zs. Value of the overall contract to GE is estimated to be around $300 million. The -401C powering theUH-1Y produces up to 8% more power than the baseline -401 in the AH-1Z, and is being considered as the common powerplant for both helicopters.
With new business also continuing to come in with further sales of the T700-701C powered Boeing AH-64D Apache
Longbow attack helicopter to Kuwait and Japan, the "production of the engine continues to be very strong, with some good solid platforms getting their lives extended", says Birtwell. For an engine with roots tracing back to a first run in 1973, the family looks set for a remarkable renaissance that seems certain to see it in operation another 30 years from now.
Source: Flight International
