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Pratt & Whitney Canada PT6
Pratt & Whitney Canada PT6
Pratt & Whitney Canada PT6
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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 AgustaWestland AW139
Beech King Air and Super King Air
Cessna 208 Caravan
de Havilland Canada DHC-6 Twin Otter
Pilatus PC-12
Piper M700 Fury
Number built 64,000 (as of February 2023)[2]
Variants Pratt & Whitney Canada PT6T

The Pratt & Whitney Canada PT6 is a turboprop aircraft engine produced by Pratt & Whitney Canada. It was designed in 1958, first flew on 30 May 1961, entered service in 1964, and has been continuously updated since. The PT6 consists of two basic sections: a gas generator with accessory gearbox, and a free-power turbine with reduction gearbox. In aircraft, the engine is often mounted "backwards," with the intake at the rear and the exhaust at the front, so that the turbine is directly connected to the propeller. Many variants of the PT6 have been produced, not only as turboprops but also as turboshaft engines for helicopters, land vehicles, hovercraft, and boats; as auxiliary power units; and for industrial uses. By November 2015, 51,000 had been produced, which 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 turboprop engine covers the power range between 580 and 1,940 shp (430 and 1,450 kW), while the PT6B/C are turboshaft variants for helicopters.

Development

[edit]

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.[3] They completed the detailed design of an engine for Canadair's small jet trainer, the CL-41. It was a 3,000-pound-force (13 kN) 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 (340 kW) turboprop for twin-engined aircraft, the PT6.[4] The early development of the PT6, which first flew in May-June 1961,[1][5] was beset with engineering problems, cost overruns and lack of sales. It was almost cancelled.[4] 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.[6]

The PT6 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 facility in North York, Ontario. 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.[7]

The first production PT6 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.[8] 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.[9] 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.[10]

In response to the General Electric GE93, in 2017 Pratt & Whitney Canada started testing core technology and systems for a proposed 2,000 shp (1,500 kW) engine to replace the most powerful versions of the PT6.[11] It was considered likely to be a development of the PT6C core, and would fit between the 1,750 shp (1,300 kW) PT6C-67C/E and the 2,300 shp (1,700 kW) 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.[12] 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.[13]

PW100

[edit]

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.

Design

[edit]
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.[14] A similar general arrangement with a free-turbine power take-off at the exhaust end (the 1,000 shp (750 kW) P.181 engine) had been shown by Armstrong Siddeley Motors at the Farnborough Airshow in 1957.[15]

An early design improvement, incorporated in the PT6A-20,[16] was the pipe diffuser patented by Vrana, another of the original PT6 team.[17] It replaced the vaned type diffuser used in centrifugal compressors. The pipe diffuser became standard design practice for P&WC.[18] 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".[19] 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.[20] The starter has to accelerate only the gas generator, making the engine easy to start, particularly in cold weather.[20] 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.[4] 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.[21] In some installation such as the PT6A-66B version in the Piaggio P.180 Avanti, 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 history

[edit]

By the 40th anniversary of its maiden flight in 2001, over 36,000 PT6As had been delivered, not including the other versions.[22] Up to October 2003, 31,606 delivered engines have flown more than 252 million hours.[23] Till November 2015, 51,000 have been produced.[2] The family logged 400 million flight hours from 1963 to 2016.[9]

The PT6 family is known for its reliability with an in-flight shutdown rate of 1 per 333,333 hours up to October 2003,[23] 1 per 127,560 hours in 2005 in Canada,[24] 1 per 333,000 hours from 1963 to 2016,[9] 1 per 651,126 hours over 12 months in 2016.[25] Time between overhauls is between 3,600 and 9,000 hours and hot-section inspections between 1,800 and 2,000 hours.[26]

Early PT6 versions lacked a FADEC, autothrottle could be installed as an aftermarket upgrade with an actuator, initially for single-engine aircraft like the PC-12 and potentially in twin-turboprop aircraft.[27] In October 2019 the PT6 E-Series was launched on the PC-12 NGX, the first general aviation turboprop with an electronic propeller and engine control system with a single lever and better monitoring for longer maintenance intervals, increased from 300 to 600 hours, and a TBO increased by 43% to 5,000 hours, reducing engine operating costs by at least 15%.[28] In April 2022, Daher announced that the updated SOCATA TBM-960 would be powered by the PT6E-66XT.[29]

Variants

[edit]
A PT6A-67D engine on a Beechcraft 1900D. The turbine exhaust (copper-colored pipe) 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 (430 and 690 kilowatts) in the original series, and up to 1,940 shaft horsepower (1,450 kilowatts) 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 an extra axial compressor stage(4), and another power turbine stage(2) and a deeper output reduction, producing almost twice the power output, between 1,090 and 1,920 shaft horsepower (810 and 1,430 kilowatts).
  • the Medium PT6 added another power turbine stage(2) -41 thru the -60 engines [30]
  • the PT6B is a helicopter turboshaft model, featuring an offset reduction gearbox with a freewheeling clutch and power turbine governor, producing 1,000 horsepower (750 kilowatts) at 4,500 rpm.
  • the PT6C is a helicopter model, with a single side-mounted exhaust, producing 2,000 horsepower (1,500 kilowatts) at 30,000 rpm, which is stepped down in a user-supplied gearbox.
  • the PT6E is a large PT6A derivative equipped with digital engine control.
  • the PT6T Twin-Pac consists of two PT6 engines driving a common-output reduction gearbox, producing almost 2,000 horsepower (1,500 kilowatts) 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.[31]

The PT6A family is a series of free-turbine turboprop engines providing 500 to 1,940 shaft horsepower (370 to 1,450 kilowatts)

Small

[edit]
Small[32]
variant equivalent
shaft
horsepower
(eshp)		 shaft
horsepower
(shp)		 applications[33]
PT6A-6, 6A, 6B 525 500 Heron-TP-XP UAV from Israel[34]
PT6A-11 528 500
PT6A-11AG 580 550 Air Tractor AT-400 (402A / 402B)
Schweizer Ag-Cat G-164B Turbine
PT6A-15AG 715 680 Air Tractor AT-400 (402A/402B)
Air Tractor AT-502, -502A and -502B
Frakes Turbocat Model A / B / C
Schweizer Ag-Cat G-164B Turbine
PT6A-20 579 550 De Havilland Canada DHC-6 Twin Otter Srs. 100–200
PT6A-20A, -20B, -6/C20 579 550
PT6A-21 580 550 Beechcraft King Air C90A / B / SE
Beechcraft Bonanza (turbine conversion)
Royal Turbine Duke
Evektor EV-55 Outback
JetPROP DL
PT6A-25, -25A 580 550 Beechcraft T-34C Turbo Mentor
Pilatus PC-7 Turbo Trainer
PT6A-25C 783 750 Embraer EMB 312 Tucano
Pilatus PC-7 Mk.II M
PZL-130 Orlik / TC-II Turbo-Orlik
PT6A-27 715 680 Beechcraft Model 99A, B99
De Havilland Canada DHC-6 Twin Otter 300
Harbin Y-12 (CATIC / HAIG)
Embraer EMB 110 Bandeirante
Let L-410 Turbolet
Pilatus PC-6/B Turbo-Porter
PT6A-28 715 680 Embraer EMB 121 Xingu
Beechcraft King Air 100 Series
PT6A-29 778 750
PT6A-34 783 750 Embraer EMB 110 Bandeirante/111
Embraer EMB 821 Carajá
Grumman Mallard (Frakes turbine conversion)
JetPROP DLX
PAC P-750 XSTOL (750XL)
Quest Kodiak (Daher)
Vazar Dash 3 Turbine Otter
De Havilland Canada DHC-6 Twin Otter 400
Thrush S2R-T34
Pilatus PC-6/B Turbo-Porter (STC)

BX Turbo de Havilland Canada Beaver DHC-2 (STC)
ARON M80

PT6A-34B 783 750
PT6A-34AG 783 750 Air Tractor AT-502B
Frakes/Grumman Turbo-Cat Model A / B / C
Pacific Aerospace 750
PZL-Okecie PZL-106 Turbo Kruk
Schweizer Ag-Cat G-164B/D Turbine
Thrush Model 510P
Thrush S2R-T34
PT6A-35 787 750 Blue 35
JetPROP DLX
PT6A-36 783 750 Thrush S2R-T34 (dry configuration only)
PT6A-38 801 750
PT6A-110 502 475 Schweizer AG-Cat Turbine
Royal Turbine Duke
PT6A-112 528 500 Cessna Conquest I
PT6A-114 632 600 Cessna 208 Caravan
PT6A-114A 725 675 Cessna 208 Caravan 675, 208B
PT6A-116 736 700
PT6A-121 647 615
PT6A-135 787 750 EMB 121A1 Xingu II
PT6A-135A 787 750 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
JMB Evolution (formerly Lancair Evolution)
Silverhawk 135 / StandardAero C90 / E90
StandardAero Cheyenne Series
StandardAero King Air F90
T-G Aviation Super Cheyenne
Vazar Dash 3 Turbine Otter
PT6A-140 912 867 Cessna Grand Caravan EX
PT6A-140A 945 900 ASIC ULtimate Grand Caravan (upgrade)
Blackhawk Aerospace XP140 (Caravan upgrade)
Evolution Aircraft EVOT-850 (formerly Lancair)
SuperPac 750XL-II (upgrade to the PAC P-750 XSTOL )
PT6A-140AG 911 867 Air Tractor 502XP
Thrush Model 510P2+

Medium

[edit]
Medium[32]
variant equivalent
shaft
horsepower
(eshp)		 shaft
horsepower
(shp)		 applications[33]
PT6A-40 749 700
PT6A-41, -41AG 903 850 Beechcraft King Air 200 / B200
Piper Cheyenne III / IIIA
Beechcraft C-12 Huron
Thrush S2R-T34 (-41 and -41AG)
PT6A-42, -42A 903 850 Beechcraft C-12 Huron E and F
Beechcraft King Air 200 / B200
Blackhawk XP42 King Air 200
StandardAero King Air 200
Blackhawk XP42A C-208 Caravan Series (-42A)
Piper Meridian (-42A)
Thrush S2R-T34
Indonesian Aerospace N-219
PT6A-45 1070 1020
PT6A-45R, -45A, -45B
PT6A-50 1022 973 de Havilland Canada DHC-7 Dash 7
PT6A-52 898 850 Beechcraft King Air B200GT / 250
Blackhawk XP52 King Air 200 / B200
Enhanced Aero B200GTO
StandardAero King Air 200 / B200

Piper PA-46 (M700 Fury)

PT6A-60, -60A 1113 1050 Beechcraft Super King Air 300 / 350
PT6A-60AG 1081 1020 Air Tractor AT-602
Ayres Thrush 550P
Ayres Thrush 660
PT6A-61 902 850 Short C-23 Sherpa
PT6A-62 1008 950[35] KAI KT-1 / KO-1
Pilatus PC-9 Turbo Trainer

Large

[edit]
Large[36]
variant equivalent
shaft
horsepower
(eshp)		 shaft
horsepower
(shp)		 applications[33]
PT6A-64 747 700 EADS Socata TBM 700
PT6A-65B, -65R[32] 1249 1173 Beechcraft 1900 / 1900C
Polish Aviation Factory M28 Skytruck
PT6A-65AG, -65AR[32] 1298 1220 Air Tractor AT-602
Air Tractor AT-802 / 802A / 802AF / 802F
Ayres Thrush 660 / 710P
AMI DC-3 (-65R)
Dodson International Turbo Dakota DC-3
Shorts 360 Advanced (-65AR)
PT6A-65SC 1100 Cessna 408 SkyCourier
LUS-222
PT6A-66, -66A, -66D 905 850 National Aerospace Laboratories SARAS
Piaggio P.180 Avanti
Ibis Ae270 HP (-66A)
Daher TBM 850, 900, 910, 930 and 940 (formerly EADS Socata TBM) (-66D)
PT6A-66B, -66T 1010 950 Piaggio P180 Avanti II (-66B)
PT6A-67, -67A, -67B 1273 1200 Beechcraft RC-12 Guardrail (-67)
Beechcraft Starship (-67A)
Epic LT (-67A)
IAI Heron TP (-67A)
PT6A-67B, -67P
PT6E-67XP		 1272 1200 Pilatus PC-12 (-67B)
Pilatus PC-12NG (-67P)
Pilatus PC-12NGX (PT6E-67XP)
PT6A-67D 1285 1214 Beechcraft 1900D
PT6A-67AF, -67AG, -67R, -67T, -67RM 1294 1220 Air Tractor AT-802 / 802A / 802AF / 802F (-67AG)
Ayres Thrush 710P (-67AG)
Basler Turbo BT-67 (-67R)
Shorts 360 / 360–300 (-67R)
PT6A-67E 1276 1200
PT6A-67F 1796 1700 Air Tractor AT-802 / 802A / 802AF / 802F
PT6A-68 1324 1250 T-6A Texan II
PT6A-68B, -68C, -68T, -68D 1691 1600 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 horsepower (410.1 kilowatts) turboshaft engine for use in helicopters; a later mark of PT6B is rated at 981 horsepower (731.5 kilowatts).
PT6B-16
PT6C
The PT6C is a 1,600 to 2,300 shaft horsepower (1,200 to 1,700 kilowatts) 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]
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 brake horsepower (410 kilowatts) 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 brake horsepower (370 kilowatts) 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]

Applications

[edit]

The engine is used in over 100 different applications.

PT6A

[edit]

PT6B

[edit]

PT6C

[edit]

PT6D

[edit]

PT6E

[edit]

ST6

[edit]

STN

[edit]

Engines on display

[edit]

Specifications (PT6A-6)

[edit]

Data from Jane's 62-63,[44]

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

[edit]
Gas Turbine Engines[45]
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-27 3, 1 / 1, 1 715 533 0.603 367 — 289 131 Pilatus PC-6
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		 487 221 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. ^ axial, centrifugal compressor / HP, LP turbine

See also

[edit]

Related development

Comparable engines

Related lists

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Pratt & Whitney Canada PT6

View on Grokipedia
from Grokipedia
The Pratt & Whitney Canada PT6 is a family of turboprop and turboshaft engines renowned for its reliability and versatility in powering a wide array of general aviation, agricultural, business, and military aircraft, as well as helicopters. Introduced in 1963, the PT6 has become the world's most popular engine in its class, with more than 64,000 units produced and over 500 million flight hours accumulated across diverse missions. The PT6 family encompasses more than 70 models, delivering power outputs ranging from 500 shaft horsepower (shp) to over 1,900 shp, and it drives over 155 different aviation applications, including notable aircraft such as the , Caravan, and Pilatus PC-12. Its distinctive free-turbine architecture—where the power turbine is independent of the —enables features like reverse thrust in variants and high responsiveness in configurations, contributing to its exceptional dispatch reliability. Over six decades, the PT6 has evolved through continuous technological advancements, with power density increasing up to four times the original levels and improving by approximately 20%, while maintaining a compact design suitable for single- and twin-engine installations. Key variants include the foundational PT6A turboprops for , the PT6C and PT6B turboshafts for helicopters, the coupled PT6T Twin Pac for twin-engine , and the modern PT6 E-Series, which integrates dual-channel electronic controls for enhanced performance and reduced pilot workload. The E-Series, entering service in 2020, has already surpassed 500,000 flight hours with over 700 engines in operation, underscoring the family's ongoing dominance in the small market.

Development

Origins and Initial Design

was established in 1928 as the Canadian Pratt & Whitney Aircraft Company in , , initially to service and repair radial piston engines from its American parent company. Following , the subsidiary shifted focus toward gas turbine development, gaining experience in the mid-1950s through production of the JT12 turbojet and other small engines to meet emerging demands in aviation. This evolution culminated in the initiation of the PT6 project in 1958, aimed at creating a compact engine for to replace less efficient piston engines in . The initial design emphasized a small, powerplant targeting 450-500 shaft horsepower (shp), with a novel reverse-flow architecture that positioned the power turbine section forward of the . This configuration allowed for a short, direct drive to the , addressing critical propeller ground clearance issues in low-wing while maintaining overall engine compactness. Pioneered by a small team of engineers under chief designer Allan Newland, the free-turbine concept decoupled the power output from the speed, enabling efficient operation across variable loads. The prototype, initially designated ST-4, achieved its first ground run in February 1960, marking a key milestone after intensive preliminary testing. Early ground testing revealed challenges such as stalls at low speeds, which were mitigated through the incorporation of variable inlet guide vanes to optimize airflow incidence and prevent surge conditions. Over 8,000 hours of accumulated testing refined the design, leading to the PT6A-6 variant's certification by in December 1963, paving the way for production.

Production Milestones

The PT6 engine completed its first flight on May 30, 1961, installed as a third powerplant on a modified test aircraft at Toronto's . Canadian type certification was granted in December 1963, with U.S. FAA approval following soon after, paving the way for commercial operations. The inaugural production model, the PT6A-6, was shipped that same month to for integration into the Beech 87 prototype, which evolved into the King Air series and entered service in 1964, marking the engine's commercial debut. Manufacturing of the PT6 began at Pratt & Whitney Canada's primary facility in , , with initial output focused on meeting demand from applications. Production scaled rapidly in the late and early 1970s, exceeding 1,000 units by 1970 as the engine gained traction for its reliability and versatility. By the 1980s, cumulative production had reached approximately 10,000 engines, underscoring the PT6's growing dominance in the turboprop market. Significant production benchmarks continued into the late 20th and early 21st centuries, with the 30,000th PT6 engine delivered around 2000 amid expanding use in business, agricultural, and . The milestone of 50,000 engines was achieved in December 2020 when the latest unit rolled off the assembly line, highlighting sustained demand over five decades. By 2023, more than 64,000 PT6 engines had been produced, accumulating over 500 million flight hours across diverse missions. That year also marked the 60th anniversary of the engine family's entry into production, celebrated for its enduring impact on . Manufacturing evolutions in the included the adoption of additive manufacturing techniques for select components, alongside automated systems like the Computerized System introduced in 2010 to improve precision and efficiency in assembly. These advancements supported ongoing production growth while maintaining the engine's reputation for durability.

Recent Enhancements

Since 2011, has introduced over 120 enhancements to the PT6 engine family, resulting in a 40% power increase and 20% gains while maintaining the same external dimensions and mounting interfaces. These upgrades address modern demands for higher performance and lower operating costs in , agricultural, and special mission applications without requiring aircraft redesigns. A key milestone in these modernizations is the 2019 launch of the PT6E series, the first general aviation turboprop to incorporate Full Authority Digital Engine Control (FADEC) with a dual-channel integrated electronic for propeller and management. This electronic control enables single-lever operation from startup through all flight phases, significantly reducing pilot workload and optimizing power delivery for smoother performance. The PT6E-67XP variant powered its first production flight on the NGX in early 2020 following certification, accumulating over 500,000 flight hours across more than 700 engines by late 2025. Recent enhancements also feature , including next-generation turbine alloys that support higher operating temperatures for improved efficiency and durability. Building on earlier single-crystal , these materials enable the PT6E to comply with ICAO 16, Volume II emissions standards, including smoke and gaseous emission limits under Amendment 7. In 2022, collaborated with to certify the PT6E-66XT for the TBM 960 single-engine , delivering 850 shaft horsepower with enhanced integration for reduced operational demands. This emphasizes maintenance efficiencies, extending to 5,000 hours from 3,500 hours and cutting scheduled line maintenance by 40% through simplified electronic controls that eliminate traditional hardware. Looking ahead, as of 2025, is advancing hybrid-electric PT6 variants to meet sustainable goals, with Horizon Aircraft integrating the PT6A into its Cavorite X7 for extended range and 30% lower hydrocarbon emissions compared to conventional setups.

Design

Core Architecture

The PT6 engine employs a distinctive reverse-flow configuration, where the air enters at the rear of the engine and flows forward through the section, before reversing direction in the and gas generator , and then flowing forward again through the power at the front. This layout reverses the typical axial-flow arrangement found in many competitors, positioning the and associated stages aft while placing the power extraction forward, which allows for a short coupling shaft between sections and contributes to the engine's compact overall length of approximately 5.2 feet (1.57 meters) in many variants. Central to the PT6's design is its two-shaft architecture, dividing the engine into an independent section—comprising the and a single-stage —and a separate power section featuring a free power that drives the output shaft without mechanical linkage to the . This free-turbine arrangement enables the to operate at its optimal speed for efficient compression and combustion, while the power rotates at a speed suited to the load, such as or requirements, enhancing flexibility across applications. The path begins with intake air passing through a multi-stage , typically featuring three axial stages followed by a single centrifugal stage in standard configurations, which compresses the air before directing it into an annular reverse-flow equipped with 14 fuel nozzles for even fuel distribution and stable ignition. The combusted gases then expand through the single-stage axial , which powers the compressor, before entering the free power , usually consisting of two stages, to extract remaining . Power extraction occurs via the free power turbine, which converts the thermal energy of the exhaust gases into mechanical torque transmitted through a concentric reduction gearbox to the propeller or rotor shaft, with typical gear ratios around 15:1 to match the high rotational speeds of the turbine (up to 30,000 RPM) to lower output speeds (e.g., 2,000 RPM for propellers). In the free-turbine setup, the thermodynamic power output PP from the power turbine can be derived from the basic energy balance across the stages, approximated as P=ηm˙cpΔT,P = \eta \dot{m} c_p \Delta T, where η\eta is the overall turbine , m˙\dot{m} is the mass rate, cpc_p is the at constant pressure of the , and ΔT\Delta T is the temperature drop across the turbine. This equation stems from the steady-flow energy equation applied to the turbine, assuming isentropic expansion adjusted for real efficiencies, and underscores the PT6's emphasis on efficient energy transfer in its decoupled shaft design.

Inlet and Exhaust Systems

The Pratt & Whitney Canada PT6 engine employs a rearward-facing design, positioned aft of the in installations, which allows the engine to ingest undisturbed ambient air free from slipstream distortion. This configuration contributes to efficient airflow management and integrates directly with the engine's reverse-flow compressor architecture. The features a screened assembly incorporating an inertial particle separator, which diverts sand, dust, and foreign objects away from the in contaminated environments, enhancing durability during operations in arid or dusty conditions. Anti-icing protection is provided by a system that ducts hot air to the and guide vanes, preventing ice accumulation in cold weather. Flow control at varying speeds is achieved through fixed inlet guide vanes that direct air into the stage, supplemented by compressor bleed valves for surge margin management during low-speed operations. In variants, exhaust gases from the free power turbine exit via dual opposed stacks typically routed above the , optimizing clearance and reducing ground impingement. models, such as the PT6C series for helicopters, utilize a single side-mounted exhaust directed to minimize interference with systems. Modern PT6 variants incorporate features in the exhaust ducting to meet standards. Helicopter adaptations in the PT6C include extended inlet ducting to position the air away from rotor , ensuring clean airflow ingestion during hover and low-speed maneuvers. The inlet design achieves high pressure recovery, supporting the PT6's overall performance, including a that is 50% superior to the original model (as of 2023), enabling versatile multi-role applications.

Power Section Features

The power section of the Pratt & Whitney Canada PT6 engine features a two-stage planetary reduction gearbox that converts the high-speed rotation of the power turbine, typically exceeding 30,000 RPM, to a speed of approximately 2,000 RPM, enabling efficient to the . This epicyclic design ensures compact installation and optimized output for various applications, with the gearbox lubricated via an oil-spray system that supports a time between overhaul (TBO) of up to 3,600 hours or more for many models (as of 2025). The accessory drive, integrated into the reduction gearbox, utilizes a mechanism mounted on the propeller shaft to power essential components such as generators, and oil pumps, and, in the PT6E series, the full authority digital control (FADEC) system. This drive pad accommodates multiple accessories, providing flexibility for configurations while maintaining reliable operation under varying loads. Overspeed protection is achieved through independent governors for the and power turbine sections, which monitor and regulate speeds to prevent propeller events, enhancing overall in the free-turbine architecture. In enhanced models, torque limiting is managed by hydraulic or electronic systems that restrict output to certified limits, such as 1,200 shaft horsepower (shp), preventing exceedances during operation. is facilitated by a modular hot section design, allowing separation at the C-flange for targeted inspections every 1,800 hours, and through chip detectors in the reduction gearbox that alert to potential debris or wear.

Operational History

Early Adoption

The PT6A-6, the first production variant of the PT6 engine family, received its initial type certification from in November 1963, followed by FAA approval shortly thereafter. The inaugural production engine was shipped in December 1963 to for integration into the King Air Model 90, marking the engine's entry into commercial service. This twin-turboprop aircraft debuted in 1964, powered by two PT6A-6 engines each rated at 500 shaft horsepower, and quickly gained traction in the general market for its improved performance over piston-powered predecessors. The PT6's adoption accelerated rapidly in the mid-1960s, with early installations extending beyond the King Air to experimental and prototype applications in . In late 1966, a was modified with a pair of PT6A-6A engines at Swearingen Aircraft's facility, achieving first flight as a proof-of-concept for what would become the series. This demonstrated the engine's versatility for pressurized light twins, contributing to broader interest among manufacturers seeking reliable turbine power for business and utility roles. By the end of the decade, the PT6 had established itself as a pivotal technology for transitioning small fleets from reciprocating engines. Early operational challenges, including hot starts during engine ignition—a common issue in nascent turboprop designs—were encountered by initial users, often due to insufficient compressor acceleration or fuel scheduling. These were systematically addressed through manufacturer refinements to starting procedures, , and fuel control units by the late , enhancing overall engine dependability. The PT6's emphasis on and helped achieve high dispatch rates, solidifying its reputation for in-flight reliability that approached 99 percent in routine operations by 1968. International expansion began promptly, with the first European type acceptance granted in 1967, enabling approvals across member states for civil use. In Canada, the de Havilland Twin Otter utility aircraft adopted the PT6A-6 as its standard powerplant, with the prototype achieving first flight in May 1965 and entering service in 1966, where it excelled in short takeoff and landing missions. This integration highlighted the engine's adaptability to diverse environments. Economically, the PT6 facilitated a shift from piston to turbine propulsion in light twin aircraft, with development goals focused on maintaining operating costs comparable to equivalent piston setups, thereby broadening accessibility for regional operators.

Widespread Use and Records

The PT6 engine family experienced significant global proliferation starting in the , becoming a cornerstone of , regional transport, and specialized operations worldwide. By the early , the engine had powered a diverse array of , contributing to its rapid adoption across commercial and sectors. This expansion was driven by its versatility and proven performance in demanding environments, leading to installations in over 155 different types by the . Cumulative flight hours for the PT6 family reached 380 million by 2013, reflecting its enduring operational success. This milestone grew to over 500 million hours by late 2023, underscoring the engine's reliability and widespread integration into global fleets. These hours span applications from short-haul commuter flights to remote utility missions, highlighting the PT6's role in accumulating the majority of Canada's total engine flight time. In October 2025, the PT6 E-Series variant surpassed 500,000 flight hours with over 700 engines in operation. The PT6 holds notable reliability records, with an in-flight shutdown rate of one per 333,333 hours accumulated from 1963 to 2016, according to data. This rate improved to one per 651,126 hours by 2016, establishing the engine family as one of the safest in its class for and applications. Such performance has earned it recognition as the most produced engine family, with over 64,000 units manufactured since 1963. As of , more than 25,000 PT6 engines were active in service globally, powering a substantial portion of the world's fleet. This active population supports operations in over 100 countries, from routine business to missions. The engine's adaptability has enabled extreme operational scenarios, including polar expeditions where Twin Otters equipped with PT6 have conducted surveys and resupplies in under programs. Similarly, the , powered by the PT6A, routinely operates at altitudes up to feet, facilitating high-altitude and missions in challenging terrains. The PT6's legacy has fostered a robust aftermarket ecosystem, with maintaining over 50 owned and designated service facilities worldwide for , repair, and overhaul. This network ensures high dispatch reliability and supports the engine's long-term viability, contributing to its dominance in the sector.

Variants

PT6A Turboprops

The PT6A series represents the core lineup of the PT6 engine family, optimized for applications with a reverse-flow design that enhances accessibility and . Introduced in 1963, the series spans a wide power range, starting with the PT6A-6 at 500 shaft horsepower (shp) and evolving to higher-output models like the PT6A-67AG at 1,300 shp by 1981, enabling propulsion for , agricultural, and commuter . Over 70 distinct models exist, categorized by numbers that denote incremental improvements in power, efficiency, and environmental adaptability. Key subcategories include low-power variants such as the PT6A-20 and -21, rated at approximately 550 shp for light utility roles; mid-range options like the PT6A-27 and -34, delivering 680 to 750 shp for versatile twin-engine setups; and high-power configurations including the PT6A-42 at 850 shp and PT6A-52 at 1,000 shp, suited for demanding short-haul operations. These models incorporate a two-shaft with a section driving a free power connected to the via a reduction gearbox, ensuring reliable power delivery across varying flight regimes. Technical distinctions among variants primarily involve configurations: lower-power models (e.g., PT6A-6 to -21) feature a three-stage followed by a single centrifugal stage for compact management, while higher-power units (e.g., PT6A-60 series and above) upgrade to four axial stages plus the centrifugal stage to handle increased mass flow and pressure ratios up to 9.5:1. Additionally, models like the PT6A-42 and -52 are flat-rated, meaning they sustain maximum takeoff power at higher ambient temperatures and altitudes (up to 950 shp at ISA+15°C), providing consistent in hot/high environments without . A significant of the PT6A is the PW100 series, introduced in as a higher-capacity for regional transport, offering 1,500 to 1,900 shp through enhancements like a two-stage power for better efficiency at cruise speeds and reduced fuel burn by up to 15% compared to contemporaries. This evolution built on PT6A core technologies, including in the hot section, to support larger propellers on requiring greater thrust margins. Certification milestones underscore the series' progressive development, with the foundational PT6A-6 receiving FAA type approval in December 1963 shortly after certification in October of that year. Subsequent models followed suit, such as the PT6A-27 in 1969, PT6A-34 in 1971, and the PT6A-60A in 1989, each validated by FAA and EASA (or predecessors) for specific power ratings, emissions compliance, and noise limits under FAR Part 33 and CS-E standards. By 2025, approximately 55,000 PT6A units have been produced, reflecting sustained demand and over 50 million flight hours accumulated across the fleet.

PT6C Turboshafts

The PT6C series represents Pratt & Whitney Canada's adaptation of the PT6 family, optimized for powering medium-class helicopters and tiltrotors through a direct high-speed shaft output that interfaces with the aircraft's main gearbox, eliminating the reduction gearing found in variants. This configuration delivers reliable power in demanding environments, with thermodynamic ratings ranging from 1,600 to 2,000 shaft horsepower (shp) across its models, emphasizing high power-to-weight ratios and enhanced durability. The series builds on the proven PT6A core architecture but incorporates helicopter-specific modifications, such as a single side-mounted exhaust directed downward to ensure clearance from the main rotor system during operation. Key design advancements in the PT6C include advanced turbine blade cooling techniques, such as air-cooled blades without cover plates and showerhead cooling, enabling higher turbine inlet temperatures for improved and performance margins. These features support operation in harsh conditions, including hot-and-high environments, while maintaining low specific fuel consumption. The engine's reverse-flow annular and two-stage power drive the output shaft at speeds compatible with transmissions, providing smooth torque delivery. The PT6C lineup comprises four primary models, each tailored for specific power needs and applications. The PT6C-67A, rated at 1,940 shp, powers the Leonardo AW609 tiltrotor, offering exceptional hot-section durability for vertical and horizontal flight modes. The PT6C-67C delivers up to 1,679 shp thermodynamic power (1,100 shp mechanical) and is widely used in the Leonardo AW139 intermediate twin helicopter for missions including search and rescue and offshore transport. The PT6C-67D variant, with enhanced takeoff power, supports upgrades like the TEMSCO UH-1H Huey Talon, providing a 20% increase in takeoff performance over predecessors. The PT6C-67E, rated at 1,775 shp, equips the Airbus Helicopters H175 (also known as Z-15 in some markets), featuring a novel 30-minute all-engines-operating rating for extended hovering in rescue operations. Certification for the PT6C series began with the PT6C-67C in 2001, marking the debut of this family, with subsequent FAA and EASA approvals for later variants, including the PT6C-67A in 2017 and PT6C-67E in 2011. Performance enhancements in the PT6C include dual-channel Full Authority Digital Engine Control () on select models, which optimizes fuel burn, reduces pilot workload, and enables features like automatic relight for in-flight engine restarts. In twin-engine setups, the facilitates torque sharing between engines, ensuring balanced power distribution and synchronized operation during critical phases like takeoff and hover. These capabilities contribute to the engine's reputation for reliability, with over 260 PT6C-67C units in service across 52 operators in 32 countries as of recent reports.

Other Derivatives

The PT6B series represents a turboshaft derivative of the PT6 family, optimized for applications with a power output in the 1,000 shaft horsepower class. Derived from the PT6T twin-engine configuration, it features a two-shaft design and has been produced in seven models, demonstrating versatility across single- and twin-engine platforms. Introduced in 2019, the PT6E series marks an evolutionary step with full electronic control via a dual-channel full authority digital engine control (FADEC) system, enabling single-lever power management and up to a 10% power increase over prior models. Rated at 1,200 shaft horsepower for takeoff in variants like the PT6E-67XP, it incorporates digital connectivity for enhanced diagnostics and efficiency, building directly on the PT6A architecture for general aviation turboprops. As of October 2025, the PT6 E-Series has surpassed 500,000 flight hours. The ST6 series comprises compact, twin-shaft gas turbines derived from early PT6 designs, serving as units with outputs ranging from 100 to 500 shaft horsepower. First entering production in 1964, these engines have powered applications, including early Gulfstream models, and accumulated over 10,000 units built for diverse roles by the early 2020s, with more than 780 industrial variants installed globally by 2015. Naval adaptations under the STN6 designation, such as the STN6/76 based on the PT6C , feature enhanced corrosion-resistant coatings for marine environments, including ship propulsion and systems. These versions prioritize durability in saltwater conditions, with power ratings around 500 horsepower, and have been applied in specialized non-aviation naval roles since the 1970s.

Applications

Civil Aviation

The Pratt & Whitney Canada PT6 engine family has become a cornerstone of , particularly in and regional operations, where its reliability, versatility, and efficiency have driven widespread adoption in both fixed-wing and rotary-wing platforms. Since its introduction, the PT6 has powered a diverse array of used for passenger transport, hauling, , and utility missions, accumulating over 500 million flight hours across more than 155 certified applications. Its free-turbine design and modular variants enable seamless integration into single- and twin-engine configurations, supporting operations from short-field airstrips to high-altitude routes. In single-engine fixed-wing aircraft, the PT6A series dominates general aviation. The Pilatus PC-12, a high-performance utility turboprop certified for single-pilot operations, is equipped with the PT6A-67P engine, delivering 1,200 shaft horsepower for short takeoff and landing (STOL) capabilities and a range exceeding 1,800 nautical miles. Over 2,200 PC-12s have been delivered worldwide as of November 2025, making it one of the most successful platforms in its class. Similarly, the Cessna Caravan family, including the Grand Caravan EX, relies on the PT6A-114A for rugged cargo and passenger missions in remote areas; more than 3,100 units have been produced since 1984, with the fleet certified in over 100 countries. Twin-engine further highlight the PT6's prevalence in business and regional roles. The series, encompassing the 90, 200, and 350 models, utilizes PT6A variants such as the -20 (for the 90), -42 (for the 200), and -52 (for the 350), providing balanced performance for up to 11 passengers and speeds over 300 knots. Cumulative production exceeds 7,000 units across the , with the fleet more than 60 million flight hours. The TBM 960, a fast pressurized for executive transport, features the advanced PT6E-66XT engine with electronic controls and a five-blade , enabling cruise speeds near 330 knots and a range of 1,730 nautical miles. Regional airliners benefit from PT6-derived technology in larger configurations. The ATR 42 and ATR 72 twin-turboprops, designed for 40- to 78-seat short-haul routes, are powered by PW120-series engines, which evolved from the PT6's core architecture with a three-shaft design for enhanced power output up to 2,000 shaft horsepower per engine. These aircraft serve low-density markets globally, with over 1,700 ATRs delivered and the PW120 family powering approximately 90% of 30- to 90-seat regional turboprops. The de Havilland Canada Twin Otter, a STOL workhorse for remote passenger and cargo services, employs PT6A-27 or -34 engines; more than 100 remain active in civil fleets, supporting operations in challenging environments like the Canadian Arctic and Pacific islands. In rotary-wing civil applications, PT6 variants excel in light and medium helicopters for EMS, offshore , and executive services. The JetRanger series, a staple for training and utility missions seating up to five, uses the PT6T-3 Twin-Pac configuration, combining two PT6A cores into a single power section rated at 420 shaft horsepower for reliable single-rotor performance. Over 8,000 s have been built, with thousands still in civil use. The AgustaWestland intermediate twin, certified for up to 15 passengers, is powered by two PT6C-67C engines delivering 1,700 shaft horsepower each, enabling speeds over 167 knots and a range of 573 nautical miles for SAR and shuttles; more than 900 s are in service worldwide. Overall, the PT6 family powers the majority of civil singles under 30 seats, underscoring its dominance in with over 64,000 engines produced and a dispatch reliability exceeding 99%. This market leadership stems from the engine's adaptability to diverse missions while maintaining low operating costs and high standards.

Military and Special Uses

The PT6 engine family has seen extensive adoption in fixed-wing aircraft, particularly for trainer and light attack roles where reliability and ease of maintenance are paramount. The basic trainer is powered by the PT6A-25C , delivering 750 shaft horsepower to support aerobatic training and counter-insurgency missions in various air forces worldwide. Similarly, the light attack aircraft employs the more powerful PT6A-68C variant, rated at 1,600 shaft horsepower, enabling precision strikes, intelligence, surveillance, and reconnaissance (ISR) operations in rugged environments; this configuration has been selected by over 15 nations for its low operating costs and high dispatch reliability. The joint primary trainer, used by the U.S. and , relies on the PT6A-68 for its 1,100 shaft horsepower output, facilitating advanced with a proven in-flight shutdown rate contributing to overall fleet . In rotary-wing applications, PT6 derivatives power medium utility helicopters suited for troop transport, special operations, and search-and-rescue (SAR) missions. The Bell 412EP twin-engine helicopter utilizes the PT6T-9 Twin Pac configuration, combining two PT6 cores to produce up to 1,800 shaft horsepower, supporting armed variants like the AB-412 Grifone for the and SAR roles in the , where its hot-and-high performance enhances mission success in demanding terrains. The PT6C-67C turboshaft, a high-power variant in the 1,600-2,000 shaft horsepower class, equips military configurations of the Leonardo AW139, such as the U.S. Air Force's MH-139A Grey Wolf for presidential transport and secure communications, offering full-authority digital engine control (FADEC) for reduced pilot workload and improved fuel efficiency during extended operations. Special mission platforms leverage PT6 technology for unmanned and auxiliary roles. The ST6 series, a compact derivative of the PT6 without the reduction gearbox, serves as an (APU) in , providing onboard electrical and pneumatic power for systems like environmental controls and engine starting in platforms requiring independent operation. In unmanned aerial vehicles (UAVs), has tested the PT6 E-Series on MQ-9B SkyGuardian, demonstrating enhanced endurance and payload capacity for ISR and strike missions while maintaining the family's signature reliability. Across these applications, the PT6 family powers in more than 50 air forces globally, accumulating over 500 million flight hours with exceptional reliability, including an in-flight shutdown rate as low as 1 per 651,126 hours, which supports 99%+ mission completion rates in SAR and utility operations.

Non-Aviation Roles

The ST6 series represents the primary non-aviation derivative of the PT6 engine family, adapted as a simple-cycle, twin-shaft gas turbine for stationary, marine, and mechanical drive applications. With power ratings ranging from 365 kW to 1,500 kW, the ST6 provides reliable in demanding environments, drawing on the PT6's proven compressor-turbine architecture while incorporating modifications for ground-based and waterborne operations. These engines have been employed in diverse roles, leveraging their compact design, high , and durability to support industrial processes and propulsion needs beyond aviation. In (APU) configurations, the ST6 powers ground-based electrical and pneumatic systems for and industrial sites, including mobile units that supply consistent output for remote operations. For instance, ST6 variants have been integrated into ground power units to deliver on-site and , ensuring operational readiness in field conditions without reliance on larger infrastructure. The ST6L-73 model, derived from the PT6 core, exemplifies this adaptability, offering a reworked hydro-mechanical system for efficient, self-contained power generation in non-flight scenarios. Marine applications of the ST6 emphasize and mechanical drive for small to medium vessels, capitalizing on the engine's reverse-flow design for reliable operation in compact hulls. A notable early example is the 1966 Thunderbird ocean racing boat, which utilized two ST6 engines paired with Chevrolet truck transmissions to achieve high-speed performance over water, demonstrating the engine's potential for marine racing and patrol duties. The ST6's marine variants support auxiliary in commercial boats, including hydrofoils and , where its axial-centrifugal flow ensures efficient thrust in variable sea states. designs, such as anti-submarine models, have incorporated ST6 units for lift and , providing agile maneuverability over shallow or coastal waters. Ground vehicle integrations highlight the ST6's versatility in non-traditional , particularly for experimental and specialized . The engine powered the in 1967, a prototype that utilized ST6 turbines for efficient, lightweight passenger service on tracks. Automotive adaptations include trucks and snowplows, where the ST6 drives heavy-duty tasks in harsh terrains, as well as the 1978 "Jet Vett," a custom showcasing turbine power for . Industrial uses extend the ST6 to mechanical and power generation roles, often in remote or mobile setups. Mobile oil-well drilling rigs employ ST6 engines to drive compressors and pumps, enabling operations in isolated fields with minimal logistical support. Other applications include roadside wood chippers for processing, fire pumps for response, and generator sets for off-grid power, where the engine's multi-fuel capability supports sustained output in rugged conditions. Adaptations for non-aviation environments focus on environmental resilience, such as saltwater-compatible cooling systems in marine ST6 variants to prevent in setups. For desert-based generator sets, enhanced dust filtration integrates with the engine's to mitigate abrasive ingress, ensuring longevity in arid operations. These modifications maintain the PT6 heritage of reliability while tailoring performance to ground, marine, and industrial demands.

Specifications (PT6A-67A)

General Characteristics

The PT6A-67A is a high-power variant of the renowned PT6A engine family, designed as a two-shaft, reverse-flow configuration that separates the and free power sections for efficient power delivery to the via a reduction gearbox. This layout contributes to its compact size and reliability in demanding environments. Key physical dimensions include a of 74.4 inches (1.89 m), a of 18.4 inches (0.47 m), and a dry weight of 506 pounds (230 kg), making it suitable for installation in medium to large twin-engine . In terms of operational parameters, the PT6A-67A delivers a takeoff power of 1,200 shaft horsepower (shp) (895 kW) at ISA+15°C conditions, with a maximum continuous of 1,200 shp, flat-rated to ISA+15°C (supporting operations up to approximately 25,000 feet). consumption is optimized at 0.58 pounds per shaft horsepower-hour (lb/shp-hr) (352 grams per , g/kWh) during cruise, reflecting efficient thermodynamic design.

Components

The compressor section of the PT6A-67A consists of a four-stage followed by a single-stage , designed to achieve an overall pressure ratio of 8.5:1. The axial stages feature blades to enhance and durability under high rotational speeds, while the centrifugal stage provides additional compression for improved airflow into the . This configuration allows for a compact that supports the engine's reverse-flow architecture, enabling effective air intake from the rear. The employs an annular reverse-flow design, which facilitates a compact layout by routing gases rearward before turning them forward through the . It features nickel alloy liners to withstand high temperatures and corrosion, ensuring reliable operation in the hot section. is introduced via 14 nozzles, which atomize and distribute fuel evenly for stable across a wide operating range. The assembly includes a single-stage that drives the , paired with a two-stage power that extracts from the exhaust gases to drive the output shaft. In the hot section, the blades utilize directionally solidified nickel-based superalloys to resist creep and thermal , enhancing longevity under extreme conditions. This two-shaft arrangement isolates the power , allowing independent speed control for optimized performance. The gearbox comprises a two-stage planetary reduction system with five planets per stage, providing the necessary multiplication to drive the at lower speeds from the high-speed power turbine. Its housing is constructed from for lightweight strength, while accessory pads on the rear accessory gearbox support mounting of essential components such as fuel pumps and oil pumps. Engine controls are primarily managed by a hydro-mechanical , which regulates flow and speed based on mechanical and pneumatic inputs for precise operation.

Performance

The PT6A-67A engine exhibits a specific consumption (SFC) of 0.56 lb/shp-hr during maximum continuous power operation, reflecting its efficient utilization in applications. At idle conditions, the thrust-specific consumption rises to 0.62 lb/shp-hr, highlighting the typical increase in relative use at low power settings common to free-turbine designs. These values contribute to the engine's reputation for economical operation in , where directly impacts range and operating costs. Overall for the PT6A-67A ranges from 30% to 35%, achieved through optimized cycle parameters in its two-shaft configuration. The maximum inter-turbine (ITT) is limited to 850°C for takeoff to protect turbine components while maximizing power output. This temperature constraint, combined with like single-crystal blades introduced in the , enables reliable performance under high-stress conditions. The engine maintains flat-rated power output up to ISA+15°C conditions, supporting high-altitude operations in executive turboprops. Startup to requires about 20 seconds, facilitated by the engine's starter-generator system. Maximum speeds include 39,000 RPM for the (Ng) and approximately 33,000 RPM for the power (Np), with output shaft up to 2,200 RPM, ensuring balanced operation across the free-turbine architecture. Specific consumption is defined by the equation: SFC=m˙fP\text{SFC} = \frac{\dot{m}_f}{P} where m˙f\dot{m}_f is the fuel mass flow rate (lb/hr) and PP is the shaft power output (shp). To derive the impact of compressor efficiency (ηc\eta_c), consider the Brayton cycle efficiency ηth≈1−(1rp(γ−1)/γ)\eta_{th} \approx 1 - \left( \frac{1}{r_p^{(\gamma-1)/\gamma}} \right), where rpr_p is the pressure ratio influenced by ηc\eta_c. Higher ηc\eta_c (typically 85% for the PT6A-67A's multi-stage axial-centrifugal compressor) increases rpr_p, reducing SFC by improving overall thermal efficiency and minimizing fuel required per unit power. For instance, a 1% improvement in ηc\eta_c can lower SFC by approximately 0.5-1% through better compression and reduced compressor work.

References

  1. https://www.prattwhitney.com/en/products/general-aviation-engines/pt6a
  2. https://www.prattwhitney.com/en/lp/pt6-60-years
  3. https://www.prattwhitney.com/en/blogs/pt6-nation/2023/12/12/rtxs-pratt-and-whitney-canada-marks-60-years-of-the-purpose-driven-pt6-engine-family
  4. https://www.ainonline.com/aviation-news/business-aviation/2023-02-23/pt6-reaches-60-years-pratts-fly-billion-hours
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