Pratt & Whitney Canada PT6

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"PT6" redirects here. For other uses, see PT6 (disambiguation).
P&W PT6.jpg
A PT6A-20 on display at the Canada Aviation and Space Museum
Type Turboprop / turboshaft
National origin Canada
Manufacturer Pratt & Whitney Canada
First run 1960[1]
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,[2] and is produced by Pratt & Whitney Canada. The PT6 family is particularly well known for its extremely high reliability, with MTBOs on the order of 9000 hours in some models.[3] 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.

Design and development[edit]

In 1956, PWC's President, Ronald Riley, foreseeing the need for engines with much higher power to weight ratios, ordered engineering manager Dick Guthrie to establish a development group to create a turboprop engine designed to replace piston engines. Demand for the Pratt & Whitney Wasp radial engine was still strong and its production line's output was robust and profitable. Riley gave Guthrie a modest budget of C$100,000. Guthrie recruited young engineers from the National Research Council in Ottawa and from Orenda Engines in Ontario. In 1958, the group began development of a turboprop engine intended to deliver 450 shaft horsepower. The first engine was powered up and run successfully in February 1960.[1][4] 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 the 40th anniversary of its maiden flight in 2001, over 36,000 PT6As had been delivered, not including the other versions.[5] The engine is used in over 100 different applications.

Design innovations included keeping the power turbine and propeller shaft sections independent, connecting them with a fluid coupling analogous to an automotive torque converter.[6] The igniter starts only the gas generator, making the engine easy to start, particularly in cold weather.[6] The engine consists of two sections that can be easily separated for maintenance.[6] In the gas-generator section air enters through an inlet screen into the low-pressure axial compressor. This has three stages on small and medium versions of the engine and four stages on large versions. The air then flows into a single-stage centrifugal compressor, through the annular reverse-flow combustion chamber, and finally through a single-stage compressor turbine that powers the compressors at about 45,000 rpm. The hot gas from the gas generator section then flows into a separate power section of the engine, containing a single-stage power 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. The engine is arranged such that the power turbines are mounted inside the combustion chamber, reducing overall length.

Epicyclic reduction gears on Pratt & Whitney Canada PT6 gas turbine engine.

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. It also allows rough-field operations with foreign objects slung outside and around the compressor intake by inertial separators in the inlet.[7]

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 2,000 hp (1,500 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.[8]

When de Havilland Canada asked for a much larger engine, roughly twice the power of the PT6 Large, Pratt & Whitney Canada responded with a new design initially known as the PT7. During development this was renamed to become the Pratt & Whitney Canada PW100. Turboprops such as the PT6 and PW100 may have a bypass ratio over 50,[9][10][11] although propeller airflow is slower than for turbofans.[12][13]



A PT6A-67D engine on a Beechcraft 1900D. The size of the turbine exhaust is prominent.

The PT6A family is a series of free turbine turboprop engine providing 500 to 1,940 shp (433 to 1,447 kW).

525 equivalent shaft horsepower (eshp) and 500 shaft horsepower (shp)[14]
528 eshp and 500 shp[14]
optimised for agricultural aircraft
715 eshp and 680 shp[14]
579 eshp and 550 shp[14]
580 eshp and 550 shp[14]
580 eshp and 550 shp (-25, -25A)
783 eshp and 750 shp (-25C)[14]
715 eshp and 680 shp[14]
715 eshp and 680 shp[14]
778 eshp and 750 shp[14]
783 eshp and 750 shp[14]
787 eshp and 750 shp[14]
783 eshp and 750 shp[14]
801 eshp and 750 shp[14]
749 eshp and 700 shp[14]
903 eshp and 850 shp[14]
903 eshp and 850 shp[14]
1070 eshp and 1020 shp[14]
1022 eshp and 973 shp[14]
898 eshp and 850 shp[14]
1113 eshp and 1050 shp (-60, -60A)
1081 ehsp and 1020 shp (-60AG)[14]
902 eshp and 850 shp[14]
1218 eshp and 950 shp[15]
747 eshp and 700 shp[16]
1249 eshp and 1173 shp (-65B, -65R)
1298 eshp and 1220 shp (-65AG, -65AR)[14]
905 eshp and 850 shp (-66, -66A, -66D)
1010 eshp and 950 shp (-66B)[16]
1272 eshp and 1200 shp (-67, -67A, -67B, -67P)
1285 eshp and 1214 shp (-67D)
1294 eshp and 1220 shp (-67AF, -67AG, -67R, -67T)
1796 eshp and 1700 shp (-67F)[16]
1324 eshp and 1250 shp[16]
502 eshp and 475 shp[14]
528 eshp and 500 shp[14]
632 eshp and 600 shp (-114)
725 eshp and 675 shp (-114A)[14]
736 eshp and 700 shp[14]
647 eshp and 615 shp[14]
787 eshp and 750 shp[14]
United States military designation for the PT6A-20/27, used in the Beechcraft U-21 Ute.
United States military designation for the T101-CP-100 / PT6A-45R, used in the Shorts 330 and Shorts C-23 Sherpa.


The PT6B-9 is a 550 hp (410.1 kW) turbo-shaft engine for use in helicopters. A later mark of PT6B is rated at 981 hp (731.5 kW).


The PT6C is a 1600 to 2300 horsepower (1190 to 1720 kW) engine for helicopters and tiltrotors.


The PT6D-114A is based on the PT6A-114A. The main difference is the deletion of the second stage reduction gearing and output shaft, because the engine is intended for integration with a combining gearbox incorporating power turbine governors and a propeller output shaft.[17]
Soloy Dual Pac
2x PT6D-114A engines driving a single propeller through a combining gearbox, capable of independent operation.


Twin PT6 power units combining outputs through a gearbox for use in helicopters.


The ST6 is a variant of the PT6 that was originally developed as a powerplant for the UAC TurboTrain power cars, but later developed as a stationary power generator and auxiliary power unit.
The ST6B-62 was a 550 bhp (410 kW) version of the PT6 developed for use in the STP-Paxton Turbocar, raced in the 1967 Indianapolis 500.[18]


STN 6/76
The STN 6/76 was a 500 bhp (370 kW) version of the PT6 developed for use in the Lotus 56, raced in the 1968 Indianapolis 500 and later in Formula One races, in 1971.[19][20]








Engines on display[edit]

Cutaway of a PT6 engine, McGill University

Specifications (PT6A-6)[edit]

Data from ,[22][23]

General characteristics

  • Type: Turboprop
  • Length: 62 in (1,575 mm)
  • Diameter: 19 in (483 mm)
  • Dry weight: 270 lb (122.47 kg)


  • Compressor: 3-stage axial + 1-stage centrifugal flow compressor
  • Combustors: Annular reverse-flow with 14 Simplex burners
  • Turbine: 1-stage gas generator power turbine + 1-stage free power turbine
  • Fuel type: Aviation kerosene to MIL-F-5624E / JP-4 / JP-5
  • Oil system: Split system with gear type pressure and scavenge pumps, with pressure to gearbox boosted by a second pump.


Name PT6A-11AG PT6A-50 PT6A-68C PT6B-36A PT6B-37A PT6C-67A PT6C-67B PT6C-67C PT6C-67D PT6C-67E PT6T-3B PT6T-6B
Width 483 mm 483 mm 483 mm 495 mm 495 mm 525 mm 584 mm 571 mm 571 mm 584 mm 1105 mm 1105 mm
Height 483 mm 483 mm 483 mm 495 mm 894 mm 525 mm 584 mm 571 mm 571 mm 584 mm 825 mm 825 mm
Length 1.58 m 1.73 m 1.83 m 1.5 m 1.63 m 1.67 m 1.50 m 1.50 m 1.50 m 1.52 m 1.67 m 1.67 m
Dry weight 193 kg 384 lb (174 kg) 385 lb (175 kg) 418 lb (190 kg) 446.7 lb (202.6 kg) 415 lb (188 kg) 446 lb (202 kg) 660 lb (300 kg) 673 lb (305 kg)
Maximum takeoff power 740 hp (550 kW) 945 hp (705 kW) 1,576 hp (1,175 kW) 981 shp (732 kW) 1,002 shp (747 kW) 1,940 shp (1,450 kW) 1,200 shp (890 kW) 1,679 shp (1,252 kW) 1,692 shp (1,262 kW) 1,775 shp (1,324 kW) 1,800 shp (1,300 kW) 1,970 shp (1,470 kW)
Maximum continuous power 887 shp (661 kW) 872 shp (650 kW) 1,675 shp (1,249 kW) 1,531 shp (1,142 kW) 1,585 shp (1,182 kW) 1,600 shp (1,200 kW) 1,745 shp (1,301 kW)
Specific fuel consumption 353 g/ekWh 0.581 lbs/shph 0.593 lbs/shph 0.507 lbs/shph 0.507 lbs/shph 0.602 lbs/shph 0.600 lbs/shph 0.591 lbs/shph

See also[edit]

Related development
Comparable engines
Related lists


  1. ^ a b "PT6 engine - The Legend". PT6 Nation. Pratt & Whitney Canada. Archived from the original on 2013-02-19. 
  2. ^ "United Technologies History". Archived from the original on 2007-10-17. 
  3. ^ "PT6A Model Specifications". [dead link]
  4. ^ "Pratt's 'dirty dozen'". Aviation Week and Space Technology: 42–43. 
  5. ^ "Pratt & Whitney Canada's PT6 Turboprop Marks 40 Years of in-Flight Success". Pratt & Whitney Canada. CCN Newswire. 2001-06-18. 
  6. ^ a b c "An Engine Ahead of Its Time". PT6 Nation. Pratt & Whitney Canada. 
  7. ^ Thomas A. Horne (December 2013). "The PT6 at". AOPA Pilot: T-7. 
  8. ^ "Pratt & Whitney PT6A-42 Turboprop". 
  9. ^ Ilan Kroo and Juan Alonso. "Aircraft Design: Synthesis and Analysis, Propulsion Systems: Basic Concepts Archive" Stanford University School of Engineering, Department of Aeronautics and Astronautics. Quote: "When the bypass ratio is increased to 10-20 for very efficient low speed performance, the weight and wetted area of the fan shroud (inlet) become large, and at some point it makes sense to eliminate it altogether. The fan then becomes a propeller and the engine is called a turboprop. Turboprop engines provide efficient power from low speeds up to as high as M=0.8 with bypass ratios of 50-100."
  10. ^ Prof. Z. S. Spakovszky. "11.5 Trends in thermal and propulsive efficiency Archive" MIT turbines, 2002. Thermodynamics and Propulsion
  11. ^ Nag, P.K. "Basic And Applied Thermodynamics" p550. Published by Tata McGraw-Hill Education. Quote: "If the cowl is removed from the fan the result is a turboprop engine. Turbofan and turboprop engines differ mainly in their bypass ratio 5 or 6 for turbofans and as high as 100 for turboprop."
  12. ^ "Turboprop Engine" Glenn Research Center (NASA)
  13. ^ Philip Walsh, Paul Fletcher. "Gas Turbine Performance", page 36. John Wiley & Sons, 15 April 2008. Quote: "It has better fuel consumption than a turbojet or turbofan, due to a high propulsive efficiency.., achieving thrust by a high mass flow of air from the propeller at low jet velocity. Above 0.6 Mach number the turboprop in turn becomes uncompetitive, due mainly to higher weight and frontal area."
  14. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab "Pratt & Whitney Canada PT6 Series Type Certificate" (PDF). Federal Aviation Administration. 2007-06-21. Retrieved 2009-11-28. 
  15. ^ "PT6A-62 data". Retrieved 2007-12-29. [dead link]
  16. ^ a b c d "PT6A -64/-66/-67/-68 Series Type Certificate" (PDF). Federal Aviation Administration. Retrieved 2009-11-28. 
  17. ^ "PT6 Type Certificate Data Sheet Information". Federal Aviation Administration. 
  18. ^ Bill Kilpatrick (August 1967). "The Big Engine That Almost Did". Popular Mechanics (Hearst Magazines): 69–71. ISSN 0032-4558. Retrieved 2011-06-26. 
  19. ^ "LOTUS PRATT & WHITNEY 56B". Research Racing. Grand Prix Racing Online. 
  20. ^ "Lotus 56B Pratt & Whitney". F1 Technical. 
  21. ^ "Pratt & Whitney Canada PT6 Cutaway". New England Air Museum. 
  22. ^ Taylor, John W.R. FRHistS. ARAeS (1962). Jane's All the World's Aircraft 1962-63. London: Sampson, Low, Marston & Co Ltd. 
  23. ^ Helicopter Annua 2009. 2009. 

External links[edit]