ThePC-12 is the world’s best selling pressurized single-engine turboprop, with almost a two-to-one margin over its closest competitor. Strong points include having a cabin that’s larger than that of a King Air B200, a flat cabin floor and a 4.3 ft.- high by 4.4 ft.-wide aft cargo door, along with comparatively slow takeoff and landing speeds, excellent short-field performance and easy handling characteristics.
Of the more than 1,200 that have been delivered, nearly two-thirds are powered by Pratt & Whitney Canada’s PT6A-67B engine, which is rated at 1,200 shp for takeoff up to ISA+27.9C and 1,000 shp for climb and cruise up to ISA+22C. These aircraft were built from 1995 to early 2008. Assuming standard day temperatures, they can climb directly to FL 300 at maximum takeoff weight and typically cruise at 242-262 KTAS, depending upon aircraft weight.
But the -67B’s flat rating margins aren’t overly generous. Cruise speed decreases, as a result, about one knot for every degree OAT deviates above standard. Legacy PC-12s, thus, suffer a reputation similar to older Hawker Siddeley jets: Built for comfort, not for speed.
Pilatus remedied that shortcoming in 2008 with the introduction of PC-12NG, short for “next-generation.” These aircraft are fitted with the more powerful PT6A-67P engine, which produces 12-15% more thermodynamic horsepower and does so for more of the mission. The engine has higher temperature tolerant, single-crystal high-pressure turbine blades and an improved compressor with a higher pressure ratio, among other performance enhancements. The engine safely can operate 50C to 60C hotter than the -67B. Incorporating such improvements, the -67P can develop 1,200 shp up to ISA+35C shp for takeoff up, 1,200 shp for climb up to ISA+29C and 1,000 shp for cruise up to ISA+41C.
The -67P’s extra power enables the PC-12NG to climb from sea level to FL 300 about 21% quicker than the original aircraft and cruise 11-13 kt. faster. Typical cruise speeds are 255- 273 KTAS. That’s respectable for an aircraft with more interior volume than a King Air B200, 1,500+ nm of range and single-engine operating economics.
But the NG’s speed increase wasn’t enough for Chris Finnoff, past president of Pilatus Business Aircraft and now head of Finnoff Aviation Products. About the time that Pilatus began work on the PC-12NG, he launched his own -67P upgrade program for older PC-12 aircraft with the goal of claiming the title as producer of the world’s fastest PC-12.
The key to the additional speed was some clever negotiations with Pratt & Whitney Canada. Finnoff believed the -67P provided a surplus of climb power for PC-12NG, but it was loafing in cruise above 20,000 ft. So, he convinced PWC to develop an alternative operating envelope that would trade as much as 9% climb power for as much as 6.6% more horsepower in high altitude cruise at ISA+30C.
The extra cruise thrust boosts maximum cruise speed by 3-4 kt. at standard day temperatures and as much as 7-10 kt. on warm days, according to the Finnoff Aviation AFM supplement.
These data were verified by flight tests conducted by Arthur C. Barth in manufacturer’s s.n. 273 ([MSN 273) at Flight Test Associates in Mojave, Calif., before it ceased operations. They are based on an aircraft with average paint and drag polars, intermediate CG, and factory spec rigging of control surfaces, external doors and landing gear.
-Article from Aviation Week