GE Aviation is contemplating construction of a U.S.-based overhaul center for its H-series turboprops, according to Matt Gerus, GE Aviation senior marketing manager for turboprop engines. “As the fleet size grows we are seriously taking a look at putting an overhaul shop in the U.S.,” Gerus told AIN.
At present, engines needing overhaul are shipped to the Walter factory in the Czech Republic. Shipping takes seven to 10 days each way. GE bought Walter engines in 2008. Walter is best known for its M601 turboprop engine, with more than 1,500 produced since 1975. After it acquired Walter, GE took the core of that engine’s technology and combined it with advanced materials and design features such as a new compressor section with a two-axial blisk ahead of a centrifugal third stage. This improved engine became the basis for GE’s new H series of turboprops, and the H75 (750 shp) has been selected to power the Nextant G90XT, a remanufacture of the 90-series Beech King Air. Nextant expects to receive certification for that aircraft in the third quarter of this year.
“GE undersold how good this engine is,” said Jay Heublein, Nextant executive vice president of global sales and marketing. “Our performance data shows a 10- to 12-percent improvement in specific fuel consumption over the standard PT6 engines, which is just incredible.”
Protracted Inspection Intervals
TBO for the H75 will be 4,000 hours. However, not all overhauls are created equal, Gerus noted. Averaging around $200,000, the GE overhaul encompasses not just the turbine but the propeller governor and fuel control unit as well. “You are pulling the whole engine off; you don’t have to pull components off at weird intervals and send them back individually. When you get the engine back from us, all of the relevant accessories have been overhauled.” The H series requires no midlife hot-section inspection, uses a fuel slinger instead of fuel nozzles, and employs an axial stage compressor instead of reverse flow.
“On a PT6 you typically have a 200- to 400-hour fuel nozzle cleaning regime, which we completely avoid. There’s no maintenance to the fuel system at all,” Gerus said. “Because we don’t have clogging nozzles or hot spots in the combustion chamber, you get even thermal distribution and we can avoid the hot-section inspection.”
There are relatively minor inspections required on the H75, and GE is phasing them to coincide with required inspections on the G90XT at 100-, 300- and 900-hour intervals. The H75 comes with a 1,000-hour/24-month warranty, but Gerus said that GE is looking to extend it. GE also currently does not offer an hourly maintenance plan for the engine, but that could also change as the number of engines in the field grows, Gerus said.
“Turboprop annual utilization is typically low and the ownership cycle is six to seven years. The first two owners don’t need to worry about overhaul; it is the third owner who is going to bump into it. Convincing the first guy to pay for an hourly maintenance plan is tough. An aircraft on the program is worth more in the marketplace, but you need to convince the owner of that and create that value. Remember, the first owner is paying for something he may never use. The valuation services, banks and insurance companies also will play a role in generating greater acceptance among turboprop owners, and there are distinct benefits from being enrolled. It gives the owner piece of mind, knowing what maintenance costs are going to be.”
Program Update
GE is making progress on its other turboprop programs as well, according to Brad Mottier, vice president and general manager of business and general aviation and integrated systems.
GE is working with agricultural aircraft manufacturer Thrush to certify the H80 to run on diesel fuel, currently 30 to 40 percent less expensive than jet-A. Demand to burn diesel is coming mainly from operators in South America, and some Brazilian operators are already flying with it. A demonstration program was recently completed with the EASA. While those test results are pending, GE is working with the EASA and Brazil’s ANAC to certify diesel in the H series. “We think it’s going to be a big deal,” Mottier said, noting the Russians’ long experience with running the Walter M601, the progenitor of the H series, on diesel for ground power units. However, Mottier cautioned that regulatory barriers make approval of diesel for the H series in the U.S. unlikely in the near term.
Mottier noted the July first flight of the Let-410NG, a 19-seat twin turboprop powered by 850-shp H85s. He said GE worked with Let to develop new gearboxes that reduce the propeller speed to 1950 rpm from 2080 rpm. GE is also working with Ikhana on the Twin Otter H series modification that is under development. Meanwhile, work continues on the single-lever EEC power unit GE subsidiary Unison Industries is developing for the Nextant G90XT. The EEC is coupled with a backup mechanical fuel control unit and has automatic torque, speed and temp limits that prevent exceedances and thereby bring down the cost of engine overhauls.
Mottier said that GE is positioning itself to be the engine provider of choice for the next-generation regional turboprop and would take advantage of any related business aviation applications. Research on this front is continuing at the GE research center and wind tunnel in Oklahoma alongside Dowty’s concept of a new generation of propellers.
