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The Pratt & Whitney Canada PT6 is a turboprop aircraft engine produced by Pratt & Whitney Canada. Its design was started in 1958, it first ran in February 1960, first flew on 30 May 1961, entered service in 1964 and has been continuously updated since. It consists of two basic sections: a gas generator with accessory gearbox and a free power turbine with reduction gearbox, and is often seemingly mounted backwards in an aircraft in so far as the intake is at the rear and the exhaust at the front. Many variants of the PT6 have been produced, not only as turboprops but also for helicopters, land vehicles, hovercraft, boats, as auxiliary power units and for industrial uses. By November 2015, 51,000 had been produced, had logged 400 million flight hours from 1963 to 2016. It is known for its reliability with an in-flight shutdown rate of 1 per 651,126 hours in 2016. The PT6A covers the power range between 580 and 1,940 shp (430 and 1,450 kW) while the PT6B/C are turboshaft variants for helicopters.

PT6
P&W PT6 (cropped).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 AgustaWestland AW139
Beech King Air and Super King Air
Cessna 208 Caravan
de Havilland Canada DHC-6 Twin Otter
Pilatus PC-12
Number built 51,000 (as of November 2015)[2]
Unit cost 750 hp -135A: $560,000[3]
1,050 hp PT6A-60A: $955,000
1,100 hp PT6A-68: $855,000[4]
Variants Pratt & Whitney Canada PT6T

DevelopmentEdit

In 1956, Pratt & Whitney Canada's (PWC) president, Ronald Riley, ordered engineering manager Dick Guthrie to hire a team of gas turbine specialists to design a small gas turbine engine. Demand for the Wasp radial engine was still strong and its production was profitable but the aim was to become Canada's prime engine company by focusing on a small gas turbine engine. Riley gave Guthrie a modest budget of C$100,000. Guthrie recruited twelve engineers with experience gained at various places including the National Research Council in Ottawa, Orenda Engines in Ontario, Bristol Aero Engines and Blackburn Aircraft.[5] They completed the detailed design of an engine for Canadair's small jet trainer, the CL-41. It was a 3,000lb thrust turbojet but the design was taken over by P&WA who developed it into the Pratt & Whitney JT12. The team had to wait for market assessments to define their next engine, a 450 shaft horsepower turboprop for twin-engined aircraft, the PT6.[6] The early development of the PT-6, which first ran in December 1963,[1][7] was beset with engineering problems, cost overruns and lack of sales. It was almost cancelled.[8] The team lacked the ability to deal with the technical difficulties, i.e. how to develop the engine, because, as one of the team Elvie Smith recalled, they came from research and design backgrounds. They learned how to run a development program, such as testing around the clock rather than on one shift, from a PWA team which directed the development for several months.[9]

The PT-6 first flew on 30 May 1961, mounted as a third engine in the nose of a Beech 18 aircraft which had been converted by de Havilland at its Downsview, Ontario facility. Full-scale production started in 1963, with service entry the following year. The Beech 18 continued as a PT6 and propeller flying test-bed until it was replaced with a Beech King Air in 1980. The King Air test-engine or propeller replaced one of the standard ones. In 1974 the Beech 18 had been unable to fly fast enough and high enough to test the PT6A-50 for the de Havilland Canada Dash 7 so a Vickers Viscount was modified as a PT6 test-bed with a Dash-7 installation in the nose.[10]

The first production PT-6 model, the PT6A-6, was certificated in December 1963. The first application was the Beech Queen Air, enticing the U.S. Army to buy a fleet of the U-21 Ute variant. This helped launch the King Air with Beechcraft selling about 7,000 by 2012.[11] From 1963 to 2016 power-to-weight ratio was improved by 50%, brake specific fuel consumption by 20% and overall pressure ratio reached 14:1.[12] Its development continues and while today its basic configuration is the same as in 1964, updates have included a cooled first-stage turbine vane, additional compressor and turbine stages and single-crystal turbine blades in the early 1990s. Its pressure ratio is 13:1 in the AgustaWestland AW609 tiltrotor, the highest that can be used without cooled turbine blades.[13]

In response to the General Electric GE93, in 2017 Pratt & Whitney Canada started testing core technology and systems for a proposed 2,000hp engine to replace the most powerful versions of the PT6.[14] It was considered likely to be a development of the PT6C core, and would fit between the 1,750 shp PT6C-67C/E and the 2,300 shp PW100 family. It was expected to be ready to launch by the end of 2017 for an initial helicopter platform with a 10-15% reduction in brake specific fuel consumption.[15] This 2,000 hp engine would target a possible new market such as a Super PC-12, a more powerful TBM, or a bigger King Air.[16]

PW100Edit

When de Havilland Canada asked for a much larger engine for the DHC-8, roughly twice the power of the Large PT6, Pratt & Whitney Canada responded with a new design initially known as the PT7, later renamed Pratt & Whitney Canada PW100.

DesignEdit

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

The rate at which parts deteriorate in a gas turbine is unbalanced insofar as the hottest parts need replacing or repairing more often than the cooler-running parts. If the hotter parts can be removed without disturbing the rest of the engine, for example without removing the complete engine from the aircraft, maintenance costs are reduced. It was achieved with the PT6 by having the hottest parts, the gas generator turbine and combustor, at the propeller end. They are removed without disturbing the rest of the engine with its connections to the aircraft. This arrangement was patented by designer Newland, one of the original PT6 team.[17] A similar general arrangement with a free-turbine power take-off at the exhaust end ( the 1,000 shp P.181 engine) had been shown by Armstrong Siddeley Motors at the Farnborough Airshow in 1957.[18]

An early design improvement, incorporated in the PT6A-20,[19] was the pipe diffuser patented by Vrana, another of the original PT6 team.[20] It replaced the vaned type of diffuser used in centrifugal compressors. The pipe diffuser became standard design practice for P&WC.[21] Another design change improved the part-speed functioning of the compressor. It is common to bleed air from a compressor to make it work properly at low engine speeds. The PT6 has a bleed arrangement which reuses the bleed air by returning it in a tangential direction at the entry to the compressor, an idea patented by Schaum et al. and titled "Turbine Engine With Induced Pre-Swirl At Compressor Inlet".[22] It acts like a variable vane and is known as a "Jet-Flap".

All versions of the engine consist of two sections that can be easily separated for maintenance: a gas generator supplies hot pressurized gas to a free power turbine.[23] The starter has to accelerate only the gas generator, making the engine easy to start, particularly in cold weather.[23] Air enters the gas-generator 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 a folded annular combustion chamber, and finally through a single-stage turbine that powers the compressors at about 45,000 rpm. Hot gas from the gas generator flows into the power turbine, which turns at about 30,000 rpm. It has one stage on the small engines and two stages on the medium and large ones. 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 turbines are concentric with the combustion chamber, reducing overall length.

In most aircraft installations the PT6 is mounted so that the intake end of the engine is towards the rear of the aircraft, leading to it being known by many as the "back-to-front" engine.[24] 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 aids maintenance by allowing the entire power section to be removed along with the propeller, exposing the gas-generator section. To facilitate rough-field operations, foreign objects are diverted from the compressor intake by inertial separators in the inlet.[25] In some installation such as the PT6A-66B version in the Piaggio Avanti P180, the engine is reversed, with the propeller acting as a "pusher", the accessory gearbox facing the front of the aircraft.

 
From left to right: propeller mount, reduction gear, exhaust, 2-stage free power turbine, 1-stage gas generator turbine surrounded by the combustor, 1 centrifugal then 4 axial compressor stages, intake, and accessories

Operational historyEdit

By the 40th anniversary of its maiden flight in 2001, over 36,000 PT6As had been delivered, not including the other versions.[26] Up to October 2003, 31,606 delivered engines have flown more than 252 million hours.[27] Till November 2015, 51,000 have been produced.[2] The family logged 400 million flight hours from 1963 to 2016.[12]

The PT6 family is known for its reliability with an in-flight shutdown rate of 1 per 333,333 hours up to October 2003,[27] 1 per 127,560 hours in 2005 in Canada,[28] 1 per 333000 hours from 1963 to 2016,[12] 1 per 651,126 hours over 12 months in 2016.[29]Time between overhauls is between 3600 and 9000 hours and hot-section inspections between 1800 and 2000 hrs.[30]

While lacking a FADEC, autothrottle can be installed as an aftermarket upgrade with an actuator, initially in single-engine aircraft like a PC-12 and possibly in twin-turboprop aircraft.[31]

VariantsEdit

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

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. In US military use, they are designated as T74 or T101.

Several other versions of the PT6 have appeared over time :

  • the Large PT6 added another 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.[32]

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

Small[33]
variant equivalent
shaft
horsepower
shaft
horsepower
applications[34]
PT6A-6 525 eshp 500 shp
PT6A-11AG 528 eshp 500 shp Air Tractor AT-400
Schweizer Ag-Cat G-164B Turbine
PT6A-15AG 715 eshp 680 shp Air Tractor AT-400
Air Tractor AT-501
Frakes Turbocat
Schweizer Ag-Cat G-164B Turbine
PT6A-20 579 eshp 550 shp de Havilland Canada DHC-6 Twin Otter Srs. 100-200
PT6A-21 580 eshp 550 shp Beechcraft King Air C90A/B/SE
Beechcraft Bonanza (turbine conversion)
Royal Turbine Duke
Evektor EV-55 Outback
PT6A-25, -25A 580 eshp 550 shp
PT6A-25C 783 eshp 750 shp Embraer EMB 312 Tucano
Pilatus PC-7/PC-7 MKII Turbo Trainer
PZL-130 Orlik / TC-II Turbo-Orlik
PT6A-27 715 eshp 680 shp Beechcraft Model 99A, B99
de Havilland Canada DHC-6 Twin Otter 300
Harbin Y-12
Embraer EMB 110 Bandeirante
Let L-410 Turbolet
Pilatus PC-6/B Turbo-Porter
PT6A-28 715 eshp 680 shp Embraer EMB 121 Xingu
PT6A-29 778 eshp 750 shp
PT6A-34 783 eshp 750 shp Embraer EMB 110 Bandeirante/111
Embraer EMB 821 Carajá
Grumman Mallard (turbine conversion)
JetPROP DLX
PAC P-750 XSTOL
Quest Kodiak
Vazar Dash 3 Turbine Otter
Viking DHC-6 Twin Otter 400
PT6A-34AG 783 eshp 750 shp Air Tractor AT-502B
Frakes/Grumman Turbo-Cat Model A/B/C
Pacific Aerospace 750XL
PZL-Okecie PZL-106 Turbo Kruk
Schweizer Ag-Cat G-164B/D Turbine
Thrush Model 510P
PT6A-35 787 eshp 750 shp Blue 35
JetPROP DLX
PT6A-36 783 eshp 750 shp
PT6A-38 801 eshp 750 shp
PT6A-110 502 eshp 475 shp Schweizer AG-Cat Turbine
Royal Turbine Duke
PT6A-112 528 eshp 500 shp Cessna Conquest I
PT6A-114 632 eshp 600 shp Cessna 208 Caravan
PT6A-114A 725 eshp 675 shp Cessna 208 Caravan
PT6A-116 736 eshp 700 shp
PT6A-121 647 eshp 615 shp
PT6A-135 787 eshp 750 shp Beechcraft King Air F90-1/C90GT/C90GTi/C90GTx
Blackhawk XP135A Cheyenne Series
Blackhawk XP135A Conquest I
Blackhawk XP135A King Air 90 Series
Cessna Conquest I
Lancair Evolution
Silverhawk 135/StandardAero C90/E90
StandardAero Cheyenne Series
StandardAero King Air F90
T-G Aviation Super Cheyenne
Vazar Dash 3 Turbine Otter
Medium[33]
variant equivalent
shaft
horsepower
shaft
horsepower
applications[34]
PT6A-40 749 eshp 700 shp
PT6A-41 903 eshp 850 shp Beechcraft King Air 200/B200
Piper Cheyenne III/IIIA
PT6A-42 903 eshp 850 shp Beechcraft C-12 HuronF
Beechcraft King Air 200/B200
Blackhawk XP42 King Air 200
StandardAero King Air 200
Blackhawk XP42A C-208 Caravan Series (-42A)
Piper Meridian
PT6A-45 1070 eshp 1020 shp
PT6A-50 1022 eshp 973 shp de Havilland Canada DHC-7 Dash 7
PT6A-52 898 eshp 850 shp Beechcraft King Air B200GT/250
Blackhawk XP52 King Air 200/B200
Enhanced Aero B200GTO
StandardAero King Air 200/B200
PT6A-60, -60A 1113 eshp 1050 shp Beechcraft Super King Air 300/350
PT6A-60AG 1081 ehsp 1020 shp Air Tractor AT-602
Ayres Thrush 550P/660
PT6A-61 902 eshp 850 shp
PT6A-62 950shp[35] KAI KT-1/KO-1
Pilatus PC-9 Turbo Trainer
Large[36]
variant equivalent
shaft
horsepower
shaft
horsepower
applications[34]
PT6A-64 747 eshp 700 shp EADS Socata TBM 700
PT6A-65B, -65R[33] 1249 eshp 1173 shp Beechcraft 1900/1900C
Polish Aviation Factory M28 Skytruck
PT6A-65AG, -65AR[33] 1298 eshp 1220 shp Air Tractor AT-602
Air Tractor AT-802/802A/802AF/802F
Ayres Thrush 660/710P
PT6A-66, -66A, -66D 905 eshp 850 shp National Aerospace Laboratories SARAS
Piaggio P.180 Avanti
Ibis Ae270 HP (-66A)
EADS Socata TBM 850
PT6A-66B 1010 eshp 950 shp Piaggio P180 Avanti II
PT6A-67, -67A, -67B, -67P 1272 eshp 1200 shp Beechcraft Starship
Epic LT
IAI Heron TP
Pilatus PC-12 (-67B)
Pilatus PC-12NG (-67P)
PT6A-67D 1285 eshp 1214 shp Beechcraft 1900D
PT6A-67AF, -67AG, -67R, -67T 1294 eshp 1220 shp Air Tractor AT-802/802A/802AF/802F (-67AG)
Ayres Thrush 710P (-67AG)
Basler Turbo BT-67 (-67R)
Shorts 360 / 360-300 (-67R)
PT6A-67F 1796 eshp 1700 shp Air Tractor AT-802/802A/802AF/802F
PT6A-68 1324 eshp 1250 shp T-6A Texan II
Pilatus PC-21 (-68B)
Embraer EMB-314 Super Tucano (-68C)
TAI Hürkuş (-68T)
T74-CP-700
(PT6A-20) United States military designation for the PT6A-20/27, used in the Beechcraft U-21 Ute.
T74-CP-702
(PT6A-29)
T101
United States military designation for the T101-CP-100 / PT6A-45R, used in the Shorts 330 and Shorts C-23 Sherpa.
PT6B-9
The PT6B-9 is a 550 hp (410.1 kW) turboshaft engine for use in helicopters. A later mark of PT6B is rated at 981 hp (731.5 kW).
PT6B-16
PT6C
The PT6C is a 1600 to 2300 horsepower (1190 to 1720 kW) engine for helicopters and tiltrotors.
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.[37]
PT6G
Gas producer for the Dornier Do132 helicopter.
Soloy Dual Pac
2x PT6D-114A engines driving a single propeller through a combining gearbox, capable of independent operation.
PT6T
Twin PT6 power units combining outputs through a gearbox for use in helicopters.
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.[38]
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.[39][40]

ApplicationsEdit

The engine is used in over 100 different applications.

PT6AEdit

PT6BEdit

PT6CEdit

PT6DEdit

PT6GEdit

ST6Edit

STNEdit

Engines on displayEdit

Specifications (PT6A-6)Edit

Data from Jane's 62-63,[43]

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

Gas Turbine Engines[44]
model stages[a] power SFC /h OPR dia. leng. weight applications
hp kW lb/hp g/kW lb kg
PT6A-21 3, 1 / 1, 1 550 410 0.63 380 19 in
48 cm
62 in
1.6 m
327 148 Beech Bonanza, King Air C90A/B/SE
PT6A-25 3, 1 / 1, 1 550 410 0.63 380 353 160 Beech T-34C
PT6A-25C 3, 1 / 1, 1 750 560 0.595 362 338 153 Embraer Tucano, Pilatus PC-7, PZL-130 Orlik
PT6A-114/A 3, 1 / 1, 1 600–675 447–503 0.64 390 350 160 Cessna 208 Caravan
PT6A-135A 3, 1 / 1, 1 750 560 0.585 356 7 338 153 Cessna Conquest, Piper Cheyenne, Beech King Air F90
PT6A-42 3, 1 / 1, 2 850 630 0.601 366 8 66.9 in
1.70 m
403 183 Beech King Air 200/B200, C-12 Huron
PT6A-60A 4, 1 / 1, 2 1,050 780 0.548 333 8.5 72.5 in
1.84 m
475 215 Beech Super King Air 300/350
PT6A-64 4, 1 / 1, 2 700 520 0.703 428 8.5 70 in
1.8 m
456 207 Socata TBM 700
PT6A-66 4, 1 / 1, 2 850 630 0.62 380 9.5 456 207 Piaggio P.180 Avanti
PT6A-65B 4, 1 / 1, 2 1,100 820 0.536 326 74 in
1.9 m
481 218 Ayres Turbo-Thrush, PZL M28 Skytruck, Beech 1900/C
PT6A-67B 4, 1 / 1, 2 1,200 890 0.546 332 10.8 530 240 Pilatus PC-12
PT6A-67D 4, 1 / 1, 2 1,271 948 0.546 332 10.8 515 234 Beech 1900D
PT6A-68 4, 1 / 1, 2 1,250 930 0.54 330 72.2 in
1.83 m
572 259 Beech T-6 Texan II
PT6A-68B 4, 1 / 1, 2 1,600 1,200 0.54 330 575 261 Pilatus PC-21
PT6B-37A 3, 1 / 1, 1 900 670 0.584 355 19.5 in
50 cm
64.4 in
1.64 m
385 175 Agusta A119 Koala
PT6C-67A 4, 1 / 1, 1 1,940 1,450 0.47 290 22.5 in
57 cm
59.3 in
1.51 m
Bell/Agusta BA609
PT6C-67C 4, 1 / 1, 2 1,100 820 0.49 300 Agusta A 139
PT6T-3B/BF 2 × 3, 1 / 1, 1 1,800 1,300 0.6 360 43.5 in
110 cm
65.8 in
1.67 m
668 303 Bell 412/SP/HP/EP
PT6T-3D/DF 2 × 3, 1 / 1, 1 1,800 1,300 0.595 362 692–681 314–309 Bell 412/SP/HP/EP
PT6T-6 2 × 3, 1 / 1, 1 1,875 1,398 0.591 359 660 300 Bell 212, 412/SP/HP/EP, Sikorsky S-58T
PT6T-68 2 × 3, 1 / 1, 1 1,970 1,470 0.591 359 665 302 Bell 412HP
  1. ^ compressor / HP, LP turbine

See alsoEdit

Related development

Comparable engines

Related lists

ReferencesEdit

  1. ^ a b "PT6 engine - The Legend". PT6 Nation. Pratt & Whitney Canada. Archived from the original on 19 February 2013.
  2. ^ a b "GE, Textron team up to make new turboprop engine, aircraft". Reuters. 16 November 2015.
  3. ^ Dick Karl (22 September 2010). "The Price for Power". Flying magazine.
  4. ^ "Pratt & Whitney Canada PT6A". Aeroweb. 17 May 2012.
  5. ^ Power - The Pratt & Whitney Canada Story, Kenneth H. Sullivan & Larry Milberry, CANAV Books 1989, ISBN 0-921022-01-8, p. 116
  6. ^ https://www.flightglobal.com/pdfarchive/view/1990/1990%20-%200238.html?search=pt6%20phenomenon
  7. ^ "Pratt's 'dirty dozen'". Aviation Week and Space Technology: 42–43.
  8. ^ https://www.flightglobal.com/pdfarchive/view/1990/1990%20-%200238.html?search=pt6%20phenomenon
  9. ^ Power - The Pratt & Whitney Canada Story, Kenneth H. Sullivan & Larry Milberry, CANAV Books 1989, ISBN 0-921022-01-8, p. 132
  10. ^ Power - The Pratt & Whitney Canada Story, Kenneth H. Sullivan & Larry Milberry, CANAV Books 1989, ISBN 0-921022-01-8, p. 290
  11. ^ Business Aviation Now (30 October 2012). "The Little Engine That Could ... and Did". Aviation Week Network.
  12. ^ a b c "A Discussion with Pratt & Whitney Canada President John Saabas". AirInsight. 9 June 2016.
  13. ^ "GE Aviation unveils strategy for dethroning PT6". Flight Global. 25 July 2016.
  14. ^ Stephen Trimble (22 May 2017). "Core technology tests set to begin for PT6 replacement". Flight Global.
  15. ^ Paul Jackson (23 May 2017). "PT6 – Engine of Change?". ShowNews. Aviation Week Network.
  16. ^ Guy Norris (12 October 2017). "PWC Opens Up On New PT6 Growth Engine". Aviation Week & Space Technology.
  17. ^ https://patents.google.com/patent/US3152443A/en
  18. ^ https://www.flightglobal.com/pdfarchive/view/1958/1958%20-%200224.html?search=february%20armstrong%20siddeley%20motors
  19. ^ https://www.flightglobal.com/FlightPDFArchive/1990/1990%20-%200242.PDF
  20. ^ https://patents.google.com/patent/US3333762A/en
  21. ^ http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleID=2174104
  22. ^ https://patents.google.com/patent/US4222703A/en
  23. ^ a b "An Engine Ahead of Its Time". PT6 Nation. Pratt & Whitney Canada.
  24. ^ https://www.flightglobal.com/pdfarchive/view/1990/1990%20-%200238.html?search=pt6%20phenomenon
  25. ^ Thomas A. Horne (December 2013). "The PT6 at". AOPA Pilot: T-7.
  26. ^ "Pratt & Whitney Canada's PT6 Turboprop Marks 40 Years of In-flight Success" (Press release). Pratt & Whitney Canada. 18 June 2001. Archived from the original on 5 October 2013.
  27. ^ a b "FLIGHT TEST: Pilatus PC-12 - Power of one". flightglobal. 21 September 2004.
  28. ^ "Evaluation-Single-Engine Turbine Airplanes Transporting Passengers in IFR Flight or Night VFR". Transport Canada. 16 January 2012.
  29. ^ Mike Gerzanics (6 June 2016). "Flight test : Upgraded Pilatus PC-12 powers ahead". flightglobal.
  30. ^ "PT6A engine TBO and HSI scheduling". Pratt & Whitney Canada.
  31. ^ John Croft (12 July 2017). "Autothrottle Feature Provides Hands-Free Turboprop Power". Aviation Week & Space Technology.
  32. ^ "Pratt & Whitney PT6A-42 Turboprop". Turbokart.com.
  33. ^ a b c d "Pratt & Whitney Canada PT6 Series Type Certificate" (PDF). Federal Aviation Administration. 21 June 2007.
  34. ^ a b c "PT6A". Pratt & Whitney Canada.
  35. ^ "Pratt and Whitney Canada PT6A-41 series engines Type Certificate" (PDF). EASA. 31 August 2007.
  36. ^ "PT6A -64/-66/-67/-68 Series Type Certificate" (PDF). Federal Aviation Administration. Retrieved 28 November 2009.
  37. ^ "PT6 Type Certificate Data Sheet Information". Federal Aviation Administration.
  38. ^ Bill Kilpatrick (August 1967). "The Big Engine That Almost Did". Popular Mechanics. Hearst Magazines: 69–71. ISSN 0032-4558. Retrieved 26 June 2011.
  39. ^ "Lotus, Pratt & Whitney 56B". Research Racing. Grand Prix Racing Online.
  40. ^ "Lotus 56B Pratt & Whitney". F1 Technical.
  41. ^ "DHC-2T Turbo Beaver" (Press release). Viking Air. 24 October 2018.
  42. ^ "Pratt & Whitney Canada PT6 Cutaway". New England Air Museum.
  43. ^ Taylor, John W.R. FRHistS. ARAeS (1962). Jane's All the World's Aircraft 1962-63. London: Sampson, Low, Marston & Co Ltd.
  44. ^ "Gas Turbine Engines" (PDF). Aviation Week. 28 January 2008. pp. 137–138.

External linksEdit