The in-development geared turbofan (GTF) has been attracting most of the headlines at engine manufacturer Pratt & Whitney lately, and it does indeed promise to make a large leap in powerplant efficiency and environmental friendliness when it enters airline service in 2013. The GTF achieves its gains in large part from the integral gearbox that allows both the fan up front and the core farther downstream to turn at their optimum speeds–slower in the case of the larger-than-usual fan and faster for the compressor and power turbine.
The configuration is not especially well suited to propelling a business jet (it falls short on high-altitude thrust), but business aviation will reap some of the benefits of the program: the PW810 destined to power the Cessna Citation Columbus has the same core (including P&W’s Talon combustor technology for low oxides of nitrogen) as the PW1000G GTF chosen by Bombardier and Mitsubishi to power, respectively, their C Series and MRJ airliners. Pratt & Whitney uses the same program name, PurePower, for both engines.
Compared with existing engines of similar thrust, the PurePower engine in its airliner GTF guise will reduce fuel burn by between 12 and 15 percent and noise and NOx emissions by more than 50 percent, P&W says. The PurePower PW810 for the Columbus, P&WC’s first foray into the large business jet segment, will be “seven to ten percent better than the state of the art,” Pratt & Whitney Canada president John Saabas told AIN. “Big jumps in business-jet efficiency will not be had by another squeeze of the existing lemon.”
The PW810 will, however, make decent gains in noise control, coming in 15 to 20 dB below Stage 4 limits. These improvements are attained by advanced fan shock-wave management and by sound attenuation panels that reduce more than one frequency, according to Saabas. The PW810 will also maximize the Columbus’s climb performance, which is important both for reducing external noise in the airport environment and for cutting fuel burn by propelling the airplane to fuel-efficient altitudes more quickly.
With its PW600 series, P&WC is the default engine for very light jets now in service, powering the Eclipse 500, Cessna Citation Mustang and Embraer Phenom 100. “We used the PW600 as a catalyst to change the ‘three Ps’ here–production, preparedness and process. The PW610 has pioneered processes for both the PW210 [the turboshaft chosen for the Sikor-sky S-76D] and the PW810.”
Some 9,000 operators fly 45,000 P&WC engines in 193 countries, and “we track every AOG globally, with parts depots in Amsterdam and Singapore, Muskegon and Montreal, and we’re fixing field problems,” said Saabas. “Support accounts for half of Pratt & Whitney Canada’s business.”
The Bigger Picture
Pratt & Whitney this spring held a media event at its Hartford, Conn. headquarters and provided an overview of, among other things, its milestones and advances in environmental cleanliness. Some samples:
• EcoPower engine wash will be available for the GE CF34 later this year. The detergent- and pollution-free process uses between 30 and 60 gallons of atomized water to clean an engine’s innards and improve efficiency by 1.2 percent. Cleaning effluent is collected, filtered and the water reused. The service is available at 18 locations serving 66 airports. “If every airline EcoWashed, one billion pounds of fuel and 3.2 billion pounds of CO2 emissions would be saved annually.” –Anupam Bhargava, P&W EcoWash general manager
• Aviation accounts for just 2 percent of CO2 emissions, and jetliners are now achieving 68 passenger mpg. The A380 and 787, however, will take passenger mpg to the mid-70s; the GTF should add between 12 and 15 passenger mpg to the airplanes it powers, compared with current-technology alternatives.
• Compared with the JT9D that powered the first Boeing 747, the PW4060 is 70 percent more fuel efficient and produces half the CO2 and 90 percent fewer hydrocarbon emissions.
• The GP7000 for the A380 has a bypass ratio of 9.5, the highest yet for a conventional turbofan. The GTF for Bombardier’s C Series will have a bypass ratio of 12.5 yet will be lighter than the equivalent engines it replaces–good for annual fuel savings of $1.5 million per aircraft at $2.50 a gallon. Compared with a 737-800, a GTF-powered aircraft will be 77 percent quieter on takeoff. P&W has spent $1 billion so far on the GTF program, and the engine has logged 12 flights aboard P&W’s 747 flying testbed and 27 flights aboard an Airbus-owned A340 flying testbed.
• The GTF’s fan speed will be less than 3000 rpm, and its tip speed will be one-third slower than that of a CFM56-5B.
• P&W has certified five new engines per year for the past decade.
• “We could see continued drops in business jet deliveries next year, beyond just this year. This is different from what we’ve ever seen before. It’s a crisis of confidence, and we don’t know whether the recovery will be V-shaped, U-shaped or bathtub-shaped.” –David Hess, Pratt & Whitney president
• “It’s a tough business case for field retrofits of the GTF. Residual values of older airplanes do not square with the value of the GTF engine.” –Todd Kallman, president of commercial engines
• “Biofuels hold promise but ASTM qualification issues must be addressed. Feedstocks must not deprive the food chain.” –Paul Adams, v-p of engineering
• A PW4090 sucks in one ton of air per second on takeoff. The PW4000 series burns about one quart of oil in 20 hours, versus between a half and one quart per hour for the JT8D.
• Only about 20 percent of compressor air is burned in the combustor; the remaining 80 percent cools the structure. Up to 8 percent of compressor air is used to cool the nozzle guide vanes, which accelerate the combustor outflow from Mach 0.1 to Mach 0.8.
• Some bearings now are handling 18,000 rpm versus just 6000 rpm on earlier turbine engines.