Honeywell’s turbine engine folks are poised for show and tell about something new from something old–the time-tested TFE731 turbofan family–and something a lot newer: advanced technology aimed at developing a state-of-the-art engine in the 10,000-pound-thrust class.
Ron Rich, director of advanced aerospace technology, recently previewed these developments for NBAA Convention News. He described the TFE731-50 as the latest in the TFE731-20/40/60 family of improvements on the original TFE731 turbofans. It will be a direct physical replacement for TFE731-5 installations in aircraft such as the Raytheon Hawker 800XP.
A closely related “low risk” derivative of the -60 engine, with existing fan design and fan diameter scaled to match the TFE731-5B inlet, the TFE731-50 will be operated at 4,750 pounds, the same as the -5B, but with much better temperature margins. The-50 is to be certified at up to 5,000 pounds of thrust.
The TFE731-50 uses the -5B’s core, Rich noted. “It is basically a TFE731-60, only a little bit smaller. The -50 uses a somewhat different fan module and gearbox, with a wide chord damperless fan blade whose diameter is 95 percent of the 731-60’s.” That fan blade, he said, will yield 7 percent greater efficiency than the TFE731-5B blade for improved temperature-specific fuel consumption (tsfc).
The TFE731-50, in development since 2004, is destined for the new Hawker 900XP, which will supersede the 800XP. All flight testing has been completed and FAA certification paperwork was in progress before the start of the show.
The TFE731-20/40/60 series’ first application was in 1995 for Dassault Falcon 20 retrofits, and the number of engines in service as of September 1 was 1,626 with a total of 3.5 million operating hours. The latest addition to the family offers enhanced climb performance with up to a 7-percent range improvement for ISA standard-day takeoffs when flat-rated to the TFE731-5BR’s thrust. However, after a “hot and high” takeoff the Dash 50 will provide up to 24 percent more range, Honeywell promises. It features a new N1 digital electronic engine control, in essence a single-channel FADEC with hydromechanical backup. Rich added that this newest TFE731 has shown potential for greater cruise airspeed with demonstrated higher cruise thrust than the -20/40 or -5B engines.
Bigger Engines Coming
His enthusiasm bubbled when he turned to Honeywell’s developing engine technology. He first discussed plans to evaluate a blend of existing and new technology for a family of engines ranging from 5,000 to 10,000 pounds of thrust. The Tech 7000 program is to be patterned on the certified HTF 7000 now flying on the Bombardier Challenger 300.
Rich said the initial effort will be concentrated on the 7,000-pound class to produce a core engine capable of being scaled both up and down. Paramount among Tech 7000 goals is lowered cost of ownership, to be achieved through better tsfc and thrust-to-weight ratio, with bonuses of lower emissions and noise.
He said the engine core that emerges from Tech 7000 will have “far more similarities than differences” compared to the production HTF 7000 but will incorporate “green technologies” for cleaner, quieter operation while boosting performance and economy. Honeywell will gain the latter, he predicted, by achieving higher pressures and temperatures for efficiency gains in the compressor and high-pressure turbine sections. The trick to that, he said, is in striking a balance between higher thermal and pressure values while preserving component reliability and service life.
A key to achieving these goal will be the use of improved materials. “We’ve already introduced Alloy 10, a powder metal disk alloy in the turbine disk,” Rich said. “It has demonstrated improved life under higher stress levels and temperatures.” He then produced a turbine blade, discolored by heat but showing minimal erosion, which Rich credited to an intricate pattern of advanced internal geometry and cooling techniques applied on an small scale. He also credited a new thermal barrier coating for blade cooling that is applicable across the Honeywell Engines product line.
Rich added that Tech 7000 development will seek to improve fan system efficiency for the capability to achieve higher turbine inlet and discharge temperatures with a high level of durability. He summarized the program as first “having a roadmap of where we’re going…then deciding how we’re going to do it and with what as we scale up to the 10K [10,000-pound-thrust] class.”
He said the HTF 7000 will be an advanced materials demonstrator to evaluate advances in combustion, cooling and temperatures, with reductions in noise and emissions through exhaust innovations. Rich said each candidate technology will be assigned a Technology Readiness Level measured on a scale of 1 to 9. That rating will be determined through demonstrations on an actual engine “and beating the be-jeebers out of it.” When a piece of new technology achieves a TRL 1 rating it will be ready to move on to full scale development, Rich added.