New Small Turbine from Honeywell Engines & Systems

Honeywell Engines & Systems provided Show News with details of its new small turbine engine demonstrator program which could result in a new turbofan family to replace the venerable TFE731 line.

The technology demonstration is focused on a common gas generator that would support both Honeywell's proposed MPC 531 auxiliary power unit (APU) for a new generation of ultra-large widebody jetliners, and a turbofan series in the 3,000- to 6,000-pounds-thrust range. Because the market for the jumbojets is relatively small, Honeywell could not build a sound business case for the program without a dual use for the new engine core (in the past both the TPE331 turboprop and TFE731 were spun off cores originally designed for use as APUs).

To lead the airframers and verify technology and design points, Honeywell is "proceeding much like we did with the AS900, where we prefaced full-scale development with a technology demonstration program that ran for 18 months and explored the technologies we wanted use in the engine," reports the company's business development director, commercial propulsion, Victor Valente.

Once the concept has been proved in the demo program, Honeywell will be in a position to move to full-scale development -- if there are any takers for the engine. "We will be ready when they are," Valente promised. Between 30 and 40 engineers are currently working on the demonstration project. Honeywell plans to run a complete gas generator before year's end, complemented by separate component rig testing in early 2001 of the compressor, combustor, and turbines.

Honeywell's target is to reduce cost of ownership by 20% to 30% below that of current engines by keeping the design simple and using proven, conventional materials and technologies. According to Valente, the gas generator will combine axial and centrifugal stages in the compressor. The engine will employ an effusion-cooled combustor (as on the AS900 and advanced TFE731s) to assist in controlling the temperature profile into the turbines and retaining low emission levels. Conventional axial turbines will do the work in the engine, a single high-pressure stage in the core and either one or two low-pressure stages on the fan spool, depending on the thrust variant.

Honeywell is also evaluating both direct-drive and geared fan configurations. Based on its experience with the geared-fan TFE731 series, the company still contends that gearing "is the most technically sound solution to cover a fairly wide thrust range...leading you to a minimum number of stages in the engine," Valente said.

When it comes to engine performance, Valente was somewhat evasive, saying it was too early in the program to broach the subject and that performance had to be balanced with airframe manufacturers' design parameters.

Maintenance-wise, Honeywell aims "to make it accessible and easily maintainable, so that operators can decide the level of maintenance they want to do themselves and how much they want to send out," Valente said. A new small turbofan thus could see both fixed-interval and progressive-maintenance schemes, depending on operator preference. Initial intervals of 3,000 and 6,000 hours respectively for hot section inspection and TBO (matching those of the AS900) "would be a good starting point," Valente suggested.

"By running the gas generator and component rigs and satisfying the targets we've set for ourselves," Valente continued, "we will then be able to move quickly into full-scale development, which should be a fairly compact program, matching an aircraft developer's timeframe. We'd be looking at a 36-month certification program after that point, which we know from the AS900 program is an achievable timescale."

Honeywell's thrust window of between 3,000 and 6,000 pounds blankets the range of its existing TFE731 line. The company clearly intends to protect its hard-won TFE731 markets, forged when the engine had few rivals in its thrust class. "The priority now is 3,000 pounds and above," Valente said.