PT6 | |
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A PT6A-20 on display at the Canada Aviation and Space Museum | |
Type | Turboprop / turboshaft |
National origin | Canada |
Manufacturer | Pratt & Whitney Canada |
Major applications | Beechcraft Super King Air de Havilland Canada DHC-6 Twin Otter Pilatus PC-12 Sikorsky S-76 |
Variants | Pratt & Whitney Canada PT6T |
The Pratt & Whitney Canada PT6 is one of the most popular turboprop aircraft engines in history,[1] and is produced by Pratt & Whitney Canada. The PT6 family is particularly well known for its extremely high reliability, with MTBO's on the order of 9000 hours in some models.[2] In US military use, they are designated as T74 or T101. The main variant, the PT6A, is available in a wide variety of models, covering the power range between 580 and 920 shaft horsepower in the original series, and up to 1,940 shp (1,450 kW) in the "large" lines. The PT6B and PT6C are turboshaft variants for helicopters.
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Development of the PT6 family started in the late 1950s, apparently as a modern replacement for the Pratt & Whitney Wasp radial engines they were producing at that time. It first flew on 30 May 1961, mounted on a Beech 18 aircraft at de Havilland Canada's Downsview, Ontario facility. Full-scale production started in 1963, entering service the next year. By its 40th anniversary in 2001 over 36,000 PT6As had been delivered, not including the other versions.[3] The engine is used in over 100 different applications.
The engine consists of two sections that can be easily separated for maintenance. In the gas-generator section air enters through a grill into the low-pressure three-stage axial compressor, then into a single-stage centrifugal compressor, through the annular reverse-flow combustion chamber, and finally through a single-stage turbine that powers the compressors at about 45,000 rpm. Some power is also taken from the compressor end of the shaft to power an accessories section, which also loads the engine when idle to keep it from racing out of control, because the fuel control unit can't prevent that. The hot gas from the gas generator section then flows into a separate power section of the engine, containing a single-stage turbine driving the power take-off system at about 30,000 rpm. For turboprop use, this powers a two-stage planetary output reduction gearbox, which turns the propeller at a speed of 1,900 to 2,200 rpm. The exhaust gas then escapes through two side mounted ducts in the power turbine housing, and is directed away from the engine in order to provide about 600 lbf (2,700 N) of jet thrust. The engine is arranged such that the power turbines are mounted inside the combustion chamber, reducing overall length.
In most aircraft installations the PT6 is mounted backwards in the nacelle, so that the intake side of the engine is facing the rear of the aircraft. This places the power section at the front of the nacelle, where it can drive the propeller directly without the need for a long shaft. Intake air is usually fed to the engine via an underside mounted duct, and the two exhaust outlets are directed rearward. This arrangement also aids maintenance by allowing the entire power section to be removed along with the propeller, exposing the gas-generator section.
Several other versions of the PT6 have appeared over time. The PT6A large added an additional power turbine stage and a deeper output reduction, producing almost twice the power output, between 1,090 and 1,920 shp (1,430 kW). The PT6B is a helicopter turboshaft model, featuring an offset reduction gearbox with a freewheeling clutch and power turbine governor, producing 1,000 hp (750 kW) at 4,500 rpm. The PT6C is a helicopter model, with a single side-mounted exhaust, producing 2,000 hp (1,500 kW) at 30,000 rpm, which is stepped down in a user-supplied gearbox. The PT6T Twin-Pac consists of two PT6 engines driving a common output reduction gearbox, producing almost 4,000 hp (3,000 kW) at 6,000 rpm. The ST6 is a version intended for stationary applications, originally developed for the UAC TurboTrain, and now widely used as auxiliary power units on large aircraft, as well as many other roles.[4]
When de Havilland Canada asked for a much larger engine, roughly twice the power of the PT6 Large, P&WC responded with a new design initially known as the PT7. During development this was renamed to become the Pratt & Whitney Canada PW100.
The PT6A is a free turbine providing 500 to 1,940 shaft horsepower (433 to 1,447 kW).
reduction gearing and output shaft, as the engine is intended for integration with a combining gearbox incorporating power turbine governors and a propeller output shaft.[8]
Name | PT6A-11AG | PT6A-50 | PT6A-68C | PT6B-36A | PT6B-37A | PT6C-67B | PT6C-67C | PT6C-67E | PT6T-6B |
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Diameter | 483 mm | 483 mm | 483 mm | 825 × 495 mm | 495 mm | 584 mm | 584 mm | 584 mm | 825 × 1105 mm |
Length | 1.58 m | 1.73 m | 1.83 m | 1.5 m | 1.63 m | 1.50 m | 1.50 m | 1.50 m | 1.67 m |
Dry weight | 193 kg | 169 kg | 172 kg | ||||||
Power | 550 kW (748 PS) | 705 kW (958 PS) | 1175 kW (1600 PS) | 732 kW (995 PS) | 747 kW (1015 PS) | 895 kW (1217 PS) | 1252 kW (1702 PS) | 1324 kW (1800 PS) | 1469 kW (2000 PS) |
Specific fuel consumption | 353 g/ekWh | 0.581 lbs/shph | 0.584 lbs/shph | 0,602 lbs/shph |
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