Pratt & Whitney Canada PT6

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PT6
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 100,000 Canadian dollars. 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.

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.[7]

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.

Variants[edit]

PT6A[edit]

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).

Small
PT6A-6
525 equivalent shaft horsepower (eshp) and 500 shaft horsepower (shp)[8]
PT6A-11
528 eshp and 500 shp[8]
PT6A-15AG
optimised for agricultural aircraft
715 eshp and 680 shp[8]
PT6A-20
579 eshp and 550 shp[8]
PT6A-21
580 eshp and 550 shp[8]
PT6A-25
580 eshp and 550 shp (-25, -25A)
783 eshp and 750 shp (-25C)[8]
PT6A-27
715 eshp and 680 shp[8]
PT6A-28
715 eshp and 680 shp[8]
PT6A-29
778 eshp and 750 shp[8]
PT6A-34
783 eshp and 750 shp[8]
PT6A-35
787 eshp and 750 shp[8]
PT6A-36
783 eshp and 750 shp[8]
PT6A-38
801 eshp and 750 shp[8]
-
Medium
PT6A-40
749 eshp and 700 shp[8]
PT6A-41
903 eshp and 850 shp[8]
PT6A-42
903 eshp and 850 shp[8]
PT6A-45
1070 eshp and 1020 shp[8]
PT6A-50
1022 eshp and 973 shp[8]
PT6A-52
898 eshp and 850 shp[8]
PT6A-60
1113 eshp and 1050 shp (-60, -60A)
1081 ehsp and 1020 shp (-60AG)[8]
PT6A-61
902 eshp and 850 shp[8]
PT6A-62
1218 eshp and 950 shp[9]
-
Large
PT6A-64
747 eshp and 700 shp[10]
PT6A-65
1249 eshp and 1173 shp (-65B, -65R)
1298 eshp and 1220 shp (-65AG, -65AR)[8]
PT6A-66
905 eshp and 850 shp (-66, -66A, -66D)
1010 eshp and 950 shp (-66B)[10]
PT6A-67
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)[10]
PT6A-68
1324 eshp and 1250 shp[10]
-
Small
PT6A-110
502 eshp and 475 shp[8]
PT6A-112
528 eshp and 500 shp[8]
PT6A-114
632 eshp and 600 shp (-114)
725 eshp and 675 shp (-114A)[8]
PT6A-116
736 eshp and 700 shp[8]
PT6A-121
647 eshp and 615 shp[8]
PT6A-135
787 eshp and 750 shp[8]
-
T74
United States military designation for the PT6A-20/27, used in the Beechcraft U-21 Ute.
T101
United States military designation for the T101-CP-100 / PT6A-45R, used in the Shorts 330 and Shorts C-23 Sherpa.

PT6B[edit]

PT6B-9
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).

PT6C[edit]

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

PT6D[edit]

PT6D-114A
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.[11]
Soloy Dual Pac
2x PT6D-114A engines driving a single propeller through a combining gearbox, capable of independent operation.

PT6T[edit]

PT6T
Twin PT6 power units combining outputs through a gearbox for use in helicopters.

ST6[edit]

ST6
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.
ST6B
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.[12]

STN[edit]

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.[13][14]

Applications[edit]

PT6A[edit]

PT6B[edit]

PT6C[edit]

PT6D[edit]

ST6[edit]

Engines on display[edit]

Specifications (PT6A-6)[edit]

Data from [16]

General characteristics

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

Components

  • 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.

Performance

Name PT6A-11AG PT6A-50 PT6A-68C PT6B-36A PT6B-37A PT6C-67B PT6C-67C PT6C-67E PT6T-6B
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

See also[edit]

Related development
Comparable engines
Related lists

References[edit]

  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. ^ "Pratt & Whitney PT6A-42 Turboprop". Turbokart.com. 
  8. ^ 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". Federal Aviation Administration. 2007-06-21. Retrieved 2009-11-28. 
  9. ^ "PT6A-62 data". Retrieved 2007-12-29. [dead link]
  10. ^ a b c d "PT6A -64/-66/-67/-68 Series Type Certificate". Federal Aviation Administration. Retrieved 2009-11-28. 
  11. ^ "PT6 Type Certificate Data Sheet Information". Federal Aviation Administration. 
  12. ^ Bill Kilpatrick (August 1967). "The Big Engine That Almost Did". Popular Mechanics (Hearst Magazines): 69–71. ISSN 0032-4558. Retrieved 2011-06-26. 
  13. ^ "LOTUS PRATT & WHITNEY 56B". Research Racing. Grand Prix Racing Online. 
  14. ^ "Lotus 56B Pratt & Whitney". F1 Technical. 
  15. ^ "Pratt & Whitney Canada PT6 Cutaway". New England Air Museum. 
  16. ^ Taylor, John W.R. FRHistS. ARAeS (1962). Jane's All the World's Aircraft 1962-63. London: Sampson, Low, Marston & Co Ltd. 

External links[edit]