GUY NORRIS / LOS ANGELES
Embraer's choice of General Electric's CF34 to power its 170 regional jet has been the latest success for a venerable family of small engines
Almost 30 years after the firstvariant of the General Electric CF34 series entered service as the military TF34, the latest member of this small, but highly successful turbofan family is poised to go into service on Embraer's 170 regional jet.
The CF34-8E secured its place on the Brazilian airliner in mid-1999 after a battle with the SPW14, a conceptual engine proposed jointly by Snecma and Pratt & Whitney Canada. "It was a tough challenge because, with a paper engine, you can make it speak to any requirement," says GE's small commercial engines general manager Charles Blankenship.
Despite the promises of its opponent, the CF34 had some major aces up its sleeve. Apart from highly competitive offerings on product support, life-cycle costs, thrust-to-weight ratio and price, the 14,200lb-thrust -8E variant offered to Embraer was based fundamentally on the existing -8C1. "We had a proven platform with the -8C1, which was then in the mid- to late stages of certification," says Blankenship. "The main thing was it was running and flying."
The other ace, or so it seemed at the time, was the engine's recent selection for the now-defunct Fairchild Dornier 728. "This meant we had started work for an underwing application, so on a couple of fronts we had some state of maturity," says Blankenship. "The 728 selection was also important to Embraer because it took a couple of months out of the development cycle." The Brazilian company's timetable was challenging, adds Blankenship. "They wanted it to fly in no time."
Double the thrust
Like the -8C1, the -8E incorporates the larger 1.17m (46.2in)-diameter wide chord fan that was introduced to virtually double the thrust capability of the -8 series over the baseline -3. The fan generates higher airflow and an increased pressure ratio, and is contained by a Kevlar reinforced ring. The 10-stage high-pressure (HP) compressor is based on that of the F414 military engine, and the machined-ring, bolted-dome combustor is derived from a mix of predecessors, including the F404, CF6 and the CF34 family itself. The first three stages of the HP compressor are blisks, which help to reduce weight and minimise inter-stage leakage, says GE.
Aft of the combustor, the two-stage HP turbine feeds into a four-stage low-pressure (LP) turbine with improved three-dimensional aerodynamics and low parts count. The -8E is also full-authority digital engine (FADEC) controlled, with automatic starting, hot-start prevention, automatic power reserve (APR) detection/activation, automatic in-flight ignition, and continuous self-test and built-in diagnostics.
To meet the slightly increased thrust needs of the Embraer 170, as well as the 728 and Bombardier's CRJ900, GE embarked on a series of "thrust bump" changes to the baseline -8C1. Launched in 1999, the resulting "-8 Growth" programme simultaneously embraced changes for all three new applications, and was the first such effort ever undertaken in commercial jet engine development. Key features included the introduction of compressor bore cooling through the use of a vortex spoiler, improved vane materials for greater temperature tolerance, and a new HP turbine rotor for enhanced durability. This last change included making the forward shaft integral with the stage one HP turbine disc, and was accompanied by structurally thickening the web material itself.
The design also included improved cooling air delivery to the turbine blades and helped meet collective -8 growth requirements for a 5% rise in APR thrust, up to a 10% increase in normal take-off thrust and a 14% boost in climb thrust over the -8C1.
With three applications looming, GE picked up the pace of the -8 growth programme. HP compressor rig tests began in October 2000, and assembly and instrumentation of the first complete test engine (minus definitive compressor and turbine changes) were completed the next month.
Propulsion tests
By January 2001, the first propulsion system was on test at GE's Lynn, Massachusetts, site, and ground tests had just begun at Peebles, Ohio, on the first engine due to be tested on GE's Boeing 747 flying testbed.
This engine finally took to the air in April 2001 bolted beneath the port wing of the 747 at Mojave, California. Tests of the engine with the full-up compressor and turbine modifications began in July 2001, with US Federal Aviation Administration certification achieved for the whole -8 growth programme in April, 2002.
Initial -8E flight test engines were shipped to Embraer in 2001 in preparation for the first flight of the 170 in February 2002. To pave the way for the integration of the engine and to keep pace with the Brazilian company's record-setting schedule, GE committed a full-time team to Embraer's San Jose dos Campos-based joint definition phase. "It was Embraer's plan to have all the suppliers in the same room, and to have everything in their digital mock-up language," says Blankenship. "We had to hit the ground running at their location with the people we needed. It was a challenge to keep up at first. We had a new aircraft, a substantially new engine and a new customer, all at once."
The -8E effort dovetailed with the wider-scale development of the -8 growth family, a certification process that would eventually include 19 major engine tests at Peebles, Lynn and at the Japanese test site of Ishikawajima Harima Heavy Industries (IHI), a revenue-sharing partner in the programme. Specific tests for the -8E were also conducted in conjunction with nacelle and reverser supplier MHD - a joint venture between Aermacchi and Hurel Hispano (formerly Hurel Dubois). Aermacchi is responsible for the inlet, fan cowl and several engine build-up units, while Hurel Hispano developed the aft fan cowl and neatly devised thrust reverser.
With most 170 flight tests completed, the GE-Embraer team is focused on developing the -8E-powered 175 regional jet, as well as the smooth service entry of the 170 in September. In support of the longer-term goals of Embraer, GE is also developing a performance improvement package (PIP) for the -8E to overcome specific fuel consumption (SFC) challenges discovered during test flights on the 170. "We're talking about picking up 0.3% here and another 0.2% there," says Blankenship, who plays down the shortfall. "It is not a major situation - we just need to tighten up the configuration."
Improvement option
Although no significant hardware or software changes are envisaged, the PIP will focus on improved cooling and tighter clearances. One SFC improvement option considered for the PIP, but rejected, was the replacement of the -8E's noise-reducing chevron nozzle with a more conventional conical exhaust. "However, it turns out the configuration needs the chevrons for noise reasons," says Blankenship.
GE is set to deliver the first 175 flight-test engines in the third quarter, and is developing the next CF34 variant, the -10E for the stretched Embraer 190. The -10E is rated at around 18,500lb thrust (82.5kN) and incorporates a 3D aerodynamically designed HP compressor, a low-emissions single annular combustor that cuts nitrous oxide emissions by up to 12% compared with a current unit, and a low parts count HP turbine.
The -10, also selected for the China Aviation Industry I ARJ21 regional jet, will also sport chevrons. Development work on the ARJ21 variant has begun.
Source: Flight International
