Kestrel Aircraft has selected Honeywell’s TPE331-14GR to power its all-composite single-engine turboprop. The Brunswick, Maine-based company was founded by Alan Klapmeier, co-founder of Cirrus Aircraft, to bring the former Farnborough Aircraft F1 Kestrel turboprop to market.
The F1 prototype, which Kestrel now owns, is powered by a Pratt & Whitney Canada PT6-67A flat-rated to 1,000 shp. It first flew on July 29, 2006. The TPE331-14GR is rated at 1,759 thermodynamic horsepower but will be flat-rated to 1,000 shp, according to Kestrel, “to allow for better high-altitude, high-temperature performance.”
The TPE331-14GR is a single-shaft engine with dual centrifugal compressors, cooled turbine blades and aluminum structure. The TPE331 series engines are direct drive, meaning that the engine shaft is connected to the gearbox, which drives the propeller.
The PT6 is a split-shaft engine, with a free turbine. One shaft has its own power turbine driving the gearbox and propeller; the other shaft, along with the compressor stages and its turbine, moves the power turbine.
Both engines have their advantages, but some pilots like the TPE331 direct-drive’s responsiveness to throttle input. Honeywell has shipped 436 TPE331-14GRs, which have logged more than 5.7 million hours in the Jetstream 41, Piper Cheyenne 400 and other aircraft. The -14GR has a 9,000-hour TBO in commercial use, but that will likely be lower for a business aircraft that doesn’t fly as much.
In the research done for its annual business aviation market forecast, Honeywell has developed an algorithm to determine the potential of a new aircraft model, according to Mike Bevans, Honeywell director of technical sales. The algorithm considers cabin volume, speed at maximum range, takeoff field length and other factors, and the results correlate closely with comparative market share, he explained, and help identify potential markets for new aircraft.
“We look at this [algorithm] and it helps us decide where to place bets,” Bevans said. “Engine bets are big, and this is one we went after hard. We’re delighted that Kestrel picked us.” He added that Honeywell will certify a version of the -14GR for the Kestrel, with external changes to fit the aerodynamic shape, including relocation of accessories.
The path to the TPE331 may have been paved somewhat by Comp Air’s Model 12, which has flown and thus demonstrated high-speed, long-range capability with a large-volume cabin in a composite, low-wing design. Comp Air is still trying to bring the Model 12 to market. “The Comp Airs are pretty sporty airplanes,” Bevans said.
“Making sure we had the right supplier to further progress on the design was pivotal,” Klapmeier said. “Honeywell’s commitment to the success of the Kestrel program makes them a real team member.”