Pratt & Whitney Canada PT6 

PT6
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
Number built	51,000[2]
Variants	Pratt & Whitney Canada PT6T

The Pratt & Whitney Canada PT6, produced by Pratt & Whitney Canada, is one of the most popular turbopropaircraft engines in history.[3] The PT6 family is known for its reliability with an in-flight shutdowns rate between 1 per 127,560 hours[4] and 1 per 333,333 hours.[5] Time between overhauls are between 3600 and 9000 hours and hot section inspections between 1800 and 2000 hrs.[6]

In US military use, they are designated as T74 or T101. The main variant, thePT6A, is available in a wide variety of models, covering the power range between 580 and 920 shaft horsepowerin the original series, and up to 1,940 shp (1,450 kW) in the "large" lines. The PT6B and PT6C are turboshaftvariants for helicopters.

Design and development

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 Waspradial 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 theNational Research Council in Ottawaand 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][7] It first flew on 30 May 1961, mounted on a Beech 18aircraft at de Havilland Canada'sDownsview, 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.[8] 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.[9] The igniter starts only the gas generator, making the engine easy to start, particularly in cold weather.[9] The engine consists of two sections that can be easily separated for maintenance.[9] 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-flowcombustion chamber, and finally through a single-stage 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-offsystem 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.[10]

Several other versions of the PT6 have appeared over time. The PT6A largeadded 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 helicopterturboshaft 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.[11]

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 ratioover 50,[12][13][14] although propeller airflow is slower than for turbofans.[15][16]

Variants

PT6A

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)

T74

United States military designation for the PT6A-20/27, used in theBeechcraft 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

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

PT6C

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

PT6D

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.[20]

Soloy Dual Pac

2x PT6D-114A engines driving a single propeller through a combining gearbox, capable of independent operation.

PT6T

PT6T

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

ST6

ST6

The ST6 is a variant of the PT6 that was originally developed as a powerplant for the UAC TurboTrainpower cars, but later developed as a stationary power generator andauxiliary 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.[21]

STN

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 500and later in Formula One races, in 1971.[22][23]

Applications

PT6A

PT6B

• AgustaWestland AW119 Koala
• Changhe Z-8F
• Avicopter AC313
• Lockheed XH-51
• Sikorsky S-76B
• Westland Lynx 606

PT6C

• AgustaWestland AW139
• Bell/Agusta BA609
• UH-1 Global Eagle upgrade
• Eurocopter EC175/Avicopter Z-15

PT6D

• Soloy Pathfinder 21

ST6

• UAC TurboTrain
• STP-Paxton Turbocar Indy racer

STN

• Lotus 56 USAC and Formula 1 racing car

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

• Maximum power output: 578 hp (431 kW) equivalent power at 2,200 output rpm for take-off
• Overall pressure ratio: 6.3:1
• Air mass flow: 5.3 lb (2 kg)/second
• Specific fuel consumption: 0.67 lb/hp/hr (0.408 kg/kW/hr)
• Power-to-weight ratio: 2.14 hp/lb (3.52 kW/kg)

Engines on display

A PT6 at the Frontiers of Flight Museum

Cutaway of a PT6 engine, McGill University

• There is a PT6 cutaway on display at the New England Air Museum,Bradley International Airport, Windsor Locks, Connecticut.[24]

Specifications (PT6A-6)

Data from Jane's 62-63,[25] helicopter annual 2009[26]