Pratt & Whitney Canada PT6


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 while the PT6B/C are turboshaft variants for helicopters.

Development

In 1956, Pratt & Whitney Canada's 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. They completed the detailed design of an engine for Canadair's small jet trainer, the CL-41. It was a 3,000 lb-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. The early development of the PT-6, which first ran in December 1963, was beset with engineering problems, cost overruns and lack of sales. It was almost cancelled. 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.
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.
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.
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.
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.
In response to the General Electric GE93, in 2017 Pratt & Whitney Canada started testing core technology and systems for a proposed 2,000 hp engine to replace the most powerful versions of the PT6.
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.
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.

PW100

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

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. A similar general arrangement with a free-turbine power take-off at the exhaust end had been shown by Armstrong Siddeley Motors at the Farnborough Airshow in 1957.
An early design improvement, incorporated in the PT6A-20, was the pipe diffuser patented by Vrana, another of the original PT6 team. It replaced the vaned type diffuser used in centrifugal compressors. The pipe diffuser became standard design practice for P&WC. 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". 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. The starter has to accelerate only the gas generator, making the engine easy to start, particularly in cold weather. 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. 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. 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.

Operational history

By the 40th anniversary of its maiden flight in 2001, over 36,000 PT6As had been delivered, not including the other versions.
Up to October 2003, 31,606 delivered engines have flown more than 252 million hours.
Till November 2015, 51,000 have been produced.
The family logged 400 million flight hours from 1963 to 2016.
The PT6 family is known for its reliability with an in-flight shutdown rate of 1 per 333,333 hours up to October 2003,
1 per 127,560 hours in 2005 in Canada,
1 per hours from 1963 to 2016,
1 per 651,126 hours over 12 months in 2016.
Time between overhauls is between 3600 and 9000 hours and hot-section inspections between 1800 and 2000 hrs.
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.

Variants

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 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 PT6A family is a series of free-turbine turboprop engines providing 500 to 1,940 shp
variantequivalent
shaft
horsepower		shaft
horsepower		applications
PT6A-6525 eshp500 shp
PT6A-11AG528 eshp500 shpAir Tractor AT-400
Schweizer Ag-Cat G-164B Turbine
PT6A-15715 eshp680 shpAir Tractor AT-400
Air Tractor AT-501
Frakes Turbocat
Schweizer Ag-Cat G-164B Turbine
PT6A-20579 eshp550 shpde Havilland Canada DHC-6 Twin Otter Srs. 100-200
PT6A-21580 eshp550 shpBeechcraft King Air C90A/B/SE
Beechcraft Bonanza
Royal Turbine Duke
Evektor EV-55 Outback
PT6A-25, -25A580 eshp550 shpBeechcraft T-34C Turbo Mentor
PT6A-25C783 eshp750 shpEmbraer EMB 312 Tucano
Pilatus PC-7/PC-7 MKII Turbo Trainer
PZL-130 Orlik / TC-II Turbo-Orlik
PT6A-27715 eshp680 shpBeechcraft 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-28715 eshp680 shpEmbraer EMB 121 Xingu
PT6A-29778 eshp750 shp
PT6A-34783 eshp750 shpEmbraer EMB 110 Bandeirante/111
Embraer EMB 821 Carajá
Grumman Mallard
JetPROP DLX
PAC P-750 XSTOL
Quest Kodiak
Vazar Dash 3 Turbine Otter
Viking DHC-6 Twin Otter 400
PT6A-34AG783 eshp750 shpAir 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-35787 eshp750 shpBlue 35
JetPROP DLX
PT6A-36783 eshp750 shp
PT6A-38801 eshp750 shp
PT6A-110502 eshp475 shpSchweizer AG-Cat Turbine
Royal Turbine Duke
PT6A-112528 eshp500 shpCessna Conquest I
PT6A-114632 eshp600 shpCessna 208 Caravan
PT6A-114A725 eshp675 shpCessna 208 Caravan
PT6A-116736 eshp700 shp
PT6A-121647 eshp615 shp
PT6A-135787 eshp750 shpBeechcraft 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

variantequivalent
shaft
horsepower		shaft
horsepower		applications
PT6A-40749 eshp700 shp
PT6A-41903 eshp850 shpBeechcraft King Air 200/B200
Piper Cheyenne III/IIIA
PT6A-42903 eshp850 shpBeechcraft C-12 HuronF
Beechcraft King Air 200/B200
Blackhawk XP42 King Air 200
StandardAero King Air 200
Blackhawk XP42A C-208 Caravan Series
Piper Meridian
PT6A-451070 eshp1020 shp
PT6A-501022 eshp973 shpde Havilland Canada DHC-7 Dash 7
PT6A-52898 eshp850 shpBeechcraft King Air B200GT/250
Blackhawk XP52 King Air 200/B200
Enhanced Aero B200GTO
StandardAero King Air 200/B200
PT6A-60, -60A1113 eshp1050 shpBeechcraft Super King Air 300/350
PT6A-60AG1081 ehsp1020 shpAir Tractor AT-602
Ayres Thrush 550P/660
PT6A-61902 eshp850 shp
PT6A-62950shpKAI KT-1/KO-1
Pilatus PC-9 Turbo Trainer

variantequivalent
shaft
horsepower		shaft
horsepower		applications
PT6A-64747 eshp700 shpEADS Socata TBM 700
PT6A-65B, -65R1249 eshp1173 shpBeechcraft 1900/1900C
Polish Aviation Factory M28 Skytruck
PT6A-65AG, -65AR1298 eshp1220 shpAir Tractor AT-602
Air Tractor AT-802/802A/802AF/802F
Ayres Thrush 660/710P
PT6A-66, -66A, -66D905 eshp850 shpNational Aerospace Laboratories SARAS
Piaggio P.180 Avanti
Ibis Ae270 HP
EADS Socata TBM 850
PT6A-66B1010 eshp950 shpPiaggio P180 Avanti II
PT6A-67, -67A, -67B, -67P1272 eshp1200 shpBeechcraft Starship
Epic LT
IAI Heron TP
Pilatus PC-12
Pilatus PC-12NG
PT6A-67D1285 eshp1214 shpBeechcraft 1900D
PT6A-67AF, -67AG, -67R, -67T1294 eshp1220 shpAir Tractor AT-802/802A/802AF/802F
Ayres Thrush 710P
Basler Turbo BT-67
Shorts 360 / 360-300
PT6A-67F1796 eshp1700 shpAir Tractor AT-802/802A/802AF/802F
PT6A-681324 eshp1250 shpT-6A Texan II
Pilatus PC-21
Embraer EMB-314 Super Tucano
TAI Hürkuş

;T74-CP-700
;T74-CP-702
;T101
;PT6B-9
;PT6B-16:
;PT6C
;PT6D-114A
;Soloy Dual Pac:2x PT6D-114A engines driving a single propeller through a combining gearbox, capable of independent operation.
;PT6T
;ST6
;ST6B
;STN 6/76

Applications

The engine is used in over 100 different applications.

PT6A