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Mini turbofan GE Honda HF120
By Patrick Hoevler
It was back in the 1940s that General Electric developed the first American jet engine to be built in large unit numbers, the J31. Over 50 years later, the company is returning to this thrust class. However, the new candidate is 20 percent more powerful, producing 9.11kN of thrust, and less than half the weight, to say nothing of the operating costs. Of course the new engine will not be powering a fighter aircraft, as the Bell P-59 was in its day, but the new very light jets (VLJ) of business aviation.
The HF120 is being built by the joint venture company GE Honda, which was founded in 2004 and is based in Cincinnati. The Japanese car manufacturer has already been working on similar powerplants for over 20 years. Its most recent prototype, the HF118, completed over 4,000 hours of testing. In an interview with FLUG REVUE, Shawn O'Day, marketing and sales manager at GE Honda, said, “GE was looking for growth opportunities, and business aviation offers big opportunities here. In 2003 GE met with Honda and was very impressed by their capabilities. The HF118 represents five generations of designing on their own. Now we are building the sixth generation with the HF120.” Programme manager Mark Wagner adds, “Honda has the lead on the engine design work, whereas GE is primarily responsible for systems integration and certification.”
The engine possesses a fan with swept wide-chord blades and a two-stage low-pressure compressor, both of which have are blisk designs. To save weight, the outlet guide vanes are constructed out of composite materials. Honda's Formula One (turbocharger) experience is one of the elements flowing into the design of the radial high-pressure compressor with its titanium impeller. “The impeller is the heart of the engine and particularly well suited to small engines. It is something that GE probably would not have come up with on its own,” says Wagner.
To save space, the engineers chose a reverse-flow configuration combustor which has laser drilled holes in it for cooling. GE for its part has, amongst other things, contributed its experience from the GEnx programme to the HF120 turbines. The material used for the discs contains powder metal, whereas the high-pressure turbine blades are constructed from a single-crystal alloy. The high- and low-pressure shafts rotate in opposite directions in order to better match aerodynamics in the turbines. The engine is controlled by a dual-channel FADEC. Compared with the less powerful HF118, the new architecture incorporates one extra stage in both the low-pressure compressor and the low-pressure turbine. To further enhance efficiency, the engineers systematically designed every component using 3D computational fluid dynamics. According to Wagner, one significant difference compared with larger engines is that the owner/operator of a VLJ wants to go straight to cruise altitude rather than doing step climbs as commercial aircraft do. “This means that the engine must cope with an elevated temperature for a longer fraction of the flight cycle.”
Shortly before this issue of FLUG REVUE comes out, a core engine was scheduled to be tested in Tokyo. The first full engine test of the HF120 is planned for the second quarter of this year. This will also take place in the Japanese capital city, in order to utilise Honda's fast prototyping capabilities, as Wagner explains. The certification tests will then probably commence in 2008 in Lynn, Massachusetts, chosen because of its geographical proximity to the FAA. Final assembly is likely to be at a GE facility. Production rates and times are also currently at the planning stage. “We definitely want to minimise the scope of assembly to stay competitive,” says Wagner. Competitor Pratt & Whitney Canada allows eight hours' final assembly time for its PW600. Certification of the HF120 is scheduled for April 2009, followed by entering into service with the HondaJet and Spectrum Freedom in the first half of 2010.
Customer interest is centred around costs. Here, GE Honda is marketing its sole product to date as a robust and simple design which, thanks to new blade materials and barrier coatings, should offer a time between overhauls of 5,000 hours. “Most comparable engines have to go into the workshop after 1,750 hours,” O'Day points out. GE Honda is currently conducting discussions aimed at setting up an appropriately tailored support network.
The company is hoping to sell a minimum of 200 engines per year. It does not want to stop at the HF120 either. “Our present agreement with Honda allows us to develop other engines in the thrust range of 4.44 to 15.55kN,” says Wagner. “But we are also increasingly looking beyond that limit.”
From FLUG REVUE 3/2007
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