In the mid-1960s,Piper, noting the success of Beech’s King Air, decided to explore the possibility of producing its own twin turboprop. The manufacturer hired legendary aircraft designer Ed Swearingen to retrofit a Piper PA–31P pressurized Navajo with 550-shaft-horsepower Pratt & Whitney Canada PT6A-20 turboprops. After a successful first flight in April 1967 and further tests indicated that the Pratt powerplant and Piper airframe were a good match, the PA–31T Cheyenne was launched.
The Cheyenne was a simple and reliable entry-level turboprop that was more affordable and faster than the King Air 90. However, the Cheyenne’s smaller cabin could only accommodate two pilots and four passengers—plus a fifth passenger if the belted potty seat were used. Baggage space was limited, but the airplane could operate from relatively short runways and be flown by a single pilot.
The initial production model of the Cheyenne was powered by two 620-shaft-horsepower Pratt & Whitney Canada PT6A-28 turboprops and included 30-gallon wingtip fuel tanks. Dual King Gold Crown avionics were standard. The Cheyenne first flew in October 1969 and was certificated in May 1972. Cheyenne deliveries began in 1974.
When Piper introduced the lower-powered and less expensive Cheyenne I in 1978, the manufacturer renamed its original twin turboprop the Cheyenne II. Essentially the only difference between the original Cheyenne and the Cheyenne II were some cabin configuration changes. The stretched PA–31T2 Cheyenne IIXL, which had a two-foot-longer fuselage than the original Cheyenne, entered production in 1981. The IIXL has an extra cabin window on the left side, a nearly 500-pound higher max takeoff weight, and is powered by more powerful 750-shaft-horsepower PT6A-135s. Besides offering more interior room, the IIXL’s longer fuselage eliminated the need for the stability augmentation system.
Over the years, many enhancements for the Cheyenne II have been developed, with the most notable being Blackhawk Modifications, Inc.’s XP engine upgrade, which involves replacing the Cheyenne’s original engines with new 750-shaft-horsepower PT6A-135A turboprop engines. The simple bolt-on upgrade enables operators to cruise approximately 20 knots faster.
The PT6A-135A engine was also the cornerstone of the Super Cheyenne conversion, which was offered by T-G Aviation of Hamilton, Ontario, Canada. Some Cheyenne operators have also boosted the speed of their airplanes by fitting them with cowl/ram air and exhaust stack aftermarket kits.
In addition, numerous panel upgrades have been developed for the Cheyenne II, including installation of lighter, more capable new-generation avionics from Aspen, Cobham (Chelton and S-TEC), and Garmin.
Piper built a total of 526 original Cheyennes and Cheyenne IIs, and 228 remain on the FAA registry, according to Vref. Prices range from $310,000 for a 1974 model to $520,000 for a 1983 model. Of the 81 Cheyenne IIXLs produced, 46 remain on the FAA registry. Prices range from $620,000 for a 1981 model to $680,000 for a 1984 model.
Engines | Two Pratt & Whitney PT6A-28s, rated at 620 shp Seats | Seats: Up to 8 (including two pilots) Max takeoff weight | 9,000 lb Max cruise speed | 277 kt Takeoff distance (over 50 ft obstacle) | 1,980 ft Range | 1,195 nm Wingspan | 42 ft, 8 in Length | 34 ft, 8 in Height | 12 ft, 9 in
Engines | Two Pratt & Whitney PT6A-135s, rated at 750 shp Seats | Seats: Up to 8 (including two pilots) Max takeoff weight | 9,474 lb Max cruise speed | 273 kt Takeoff distance | 2,042 ft Range | 1,060 nm Wingspan | 42 ft, 8 in Length | 36 ft, 8 in Height | 12 ft, 9 in
The PT6A-140AG engine sets the benchmark for performance and fuel efficiency for the agricultural segment, delivering 15 percent more power and five percent better specific fuel consumption (SFC) than other engines in its class.
The Cessna Caravan always needed more power, and competition to provide it was established with the supplemental type certificate (STC) awarded in 2013 to Blackhawk Modifications to install the 850-shpPratt & Whitney Canada PT6-42A in the short-fuselage 208A model as the XP42A.
It’s a missionary and a mercenary. A soldier and a spy. A record-setter and an also-ran. After 60 years of continuous production, the Pilatus PC–6 Porter, a legendary Swiss turboprop that has played more supporting roles than Kevin Bacon, will cease production in 2019.
The Douglas DC-3 Doesn’t Know the Meaning of the Word “Quit”
The same year the German airship Hindenburg crossed the Atlantic, the still-flying-today Douglas DC-3 was introduced to the world. The DC-3 is widely viewed as one of the most significant transport aircraft in history, due to its massive and long-lasting impact on the airline industry, and aerospace engineering. I got the chance to interview Ric Hallquist, the retired Chief DC-3 Pilot for Missionary Flights International who flew and worked on the beefy twin engine transport plane for over 30 years.
The Pratt & Whitney PT6 engine has been in use since 1961 and has since logged more than 380 million flight hours, the equivalent of about 250,000 round-trips to the moon. The most advanced PT6A engine family includes three power levels, “Small”, “Medium”, and “Large” that all have the advantage of turbine cooling, aerodynamic design, and advanced technologies in materials. Keeping these engines running efficiently and safely wouldn’t be possible without a periodic Hot Section Inspection.
The question of how a radial engine can be compared to a turbine engine is a question that has been asked many times over. Individuals in the Agricultural world are still asking themselves this question every year on a purely economic basis. However, the question can also be asked from a historic basis as well. In looking at the Pratt & Whitney family of Radial Engines and the PT6A family of engines, it is clear that the two are closely related.
A Bit of Background on Pratt & Whitney’s Engine Marvels: The PT6A, R-1340, & The R-985
A legendary engine deserves a story as extraordinary as it is, and such is the case with the early history of Pratt & Whitney’s PT6. This story begins decades before the turbulent history of the PT6 when radial engines were still the dominant engine for airplane use. The gas turbine engine of the PT6 revolutionized the industry, but not before the static, air-cooled radial engines had a few decades in the limelight.
Of all the radial engines, Pratt & Whitney’s R-985 was always a favorite since its inception in 1932. Simply sit back and watch a smile cross an aviation enthusiast’s face upon observing the sputter of the round radial engine as it starts up, and it is clear that these engines were something special.
However, the transition into the era of the PT6 was not an easy one. In fact, it was something of a miracle.
The Rise of the PT6
While the advancements of gas turbine engines were known to the aviation industry in the early 1950s, the expenses of the manufacturing, maintenance and repairing processes were problematic. However, that did not deter Pratt & Whitney Canada (PWC) while they forged ahead with their plans of designing a powerful gas turbine engine. They hired a team of specialists and proceeded with attempts to develop a 450 hp engine that had growth potential up to 500 hp. Their goal was to keep operating costs at a similar level as the previous radial engines, and their first foray into gas turbine engines was designed to fit small and lightweight airplane models.
However, they still needed to decide on a gas turbine technology, but eventually settled on a free turbine configuration that was more expensive, but had crucial advantages such as less starting power requirements, simplified controls for fuel and the ability for fixed-wing aircrafts to purchase off the shelf propellers rather than custom ones. Once the team decided to move in this direction, they still were not ready to get to work since they had to travel to Pratt & Whitney’s headquarters to convince the chief engineer that their plan was the right one. Upon securing his approval, the jubilant team started working on the ambitious project.
Unfortunately, their work was a blight on company balance sheets. The new design attempts led to a sort of development nightmare, but the chief engineer that approved the project still had faith in the vision. As a result, he sent a team of six experts spearheaded by a highly skilled engineer named Bruce Torell. The goal was to get the project back on track, and history reveals that this historic engine would have likely failed without his aid.
Progress was quickly made thanks to Torell’s engine expertise, but then the team faced obstacles from PWC itself. Despite aggressive attempts to terminate the project, work continued and was finally ready for flight testing in 1961. A search began for a suitable twin engine airplane to test with the PT6, and the team chose Beechcraft C-45 “Expeditor”. This Beechcraft Model 18 was equipped with two R-985s, meaning that the traditional radial engines played a huge role in the development and rise of the PT6. While further tweaks to the engine were made, the future of airplane engines was clear. Gas turbine technology was here to stay, it was just a matter of whether the PT6 was the engine that would dominate the airplane industry. It did, thanks to Beechcraft, the same company that used P&W’s radial R-985 engines of decades past. With that agreement, the PT6 finally saw mainstream success that produced its dominant run as one of the great engines of history and in fact was the first engine ever put on a King Air.
Growing global markets and ever-increasing customer bases have led to thousands of start ups, emerging growth companies, and the success of established companies. However, each company within this broad, three-tier classification can benefit from the use of a supply chain provider. As a company approaches the point of becoming an established company, the use of a supply chain provider becomes more prominent, and most established companies have an existing partnership with one of the major shipping providers. However, even some established companies continue to operate and handle all supply chain processes in-house, which represents an extreme risk for the company. If the in-house processes fail, the company tumbles and fails as well. Rather than waiting for your company to titter on the edge of complete failure, take a look at how supply chain services will improve your telecommunications abilities, networking needs, customer service departments, and storage of data within the cloud.
I’ve been privileged to know both the PT6A and the 9-cylinder Pratt engines. Both engines operate on a different technique for deriving horsepower from the combustion process, but at heart they are still both internal combustion engines that share the same engineering DNA.
One of the most complex parts of the R-1340/R-985 engine, which has remained relatively unchanged since December 24, 1925 when the very first R-1340 roared to life, is the supercharger or blower section. The blower section, which also serves as the anchor-point when installing the engine, is attached to the rear power case. The circular case receives the fuel/air mixture from the impeller assembly through diffuser channels then delivers the fuel/air mixture to the cylinders via the intake pipes. The blower is driven directly by the crankshaft through a spring loaded gear coupling located at the aft section of the crankshaft assembly. This ingenious design helps protect the blower gearing from sudden acceleration or deceleration. The spring loaded gear drives the floating gear. The impeller assembly, being indirectly driven by the crankshaft, turns ten or even twelve times crankshaft speed.
In like manner the PT6A Impeller is located in the gas generator housing which is the anchor point when installing the engine. The centrifugal impeller delivers air through diffuser tubes to the combustion chamber. The hot gases flow through a series of turbines which produce horsepower to the propeller shaft.
The impeller is only one area of similar design and function. The reduction gearing in both the PT6A & R-1340G engines are remarkably similar as well as many other features. It is not difficult to see a common engineering theory. Many pilots and mechanics love the history and engineering that goes along with engines and aircraft. Certainly looking and comparing two of the legacy engines from Pratt & Whitney is enjoyable information for many in the aviation community. I have always found it entertaining that as the PT6A engine took its first breath of life, there were R-985 engines on each side! The photo (left) is of the first flight of the PT6A, being test flown on a Beech 18 (May 1961).
In closing, I am a mechanic that holds to the history of aviation. Learning about the past can certainly give insight to the present while possibly holding a glimpse into the future. Drawing a comparison between these two engines certainly does that.
– Rob Seeman, Covington Aircraft Operations Manager
It’s the remarkable story of a remarkable engine. With more than 51,000 engines delivered to power some 130 different applications, the PT6 engine can tell quite a story of creativity and transformation. While we had a lot to choose from, we’ve put together a list of milestones for the engine as we mark its golden anniversary.
1957 – P&WC assembled a team of 12 talented young engineers after studies showed a market opportunity for 500 shp (shaft horsepower) class turboprop engines in the aircraft market then powered by piston engines. P&WC saw an opportunity to channel some of the profits from its piston engine spare parts business towards the development of gas turbine engines smaller than those made by its U.S. parent.
1963 – It’s what our celebration is all about. In December 1963, P&WC shipped the first PT6 production engine, the PT6A-6, to Beech Aircraft Company for its Beech 87, which later became the King Air. The PT6A-6 was a highly innovative gas turbine that represented a significant advance in technology from the traditional piston-driven engines used to power small aircraft. Gas turbines have a higher power to weight ratio than piston engines.
The first PT6 production engine. P&WC Archives (Records and Information Management).
1967 – Piper’s PA-31 Navajo took its first flight powered by PT6A-20s. Piper had enjoyed enormous success building light aircraft since the 1930s, but it took P&WC years of effort to get Piper to adopt turbine engines and move away from their traditional reliance on piston-driven engines.
1968 – P&WC’s ST6L73 engine (a derivative of the PT6A without the gearbox second stage) entered into service as an auxiliary power unit (APU) for the Lockheed L1011 airliner.
1968 – Bell Helicopter placed its initial order for P&WC’s first turboshaft, the PT6T Twin-Pac® engine
1970 – P&WC’s PT6T Twin Pac® entered into service. It is two engines coupled in a single package to power medium-sized, twin-engine helicopters.
1970 – The United States Military ordered 294 Bell 212s under the designation UH-1N equipped with PT6T Twin-Pac® turboshaft engines. Delivery also began in 1970.
1973 – The second-stage power turbine was introduced on the PT6A-41. This was a step change in engine power and efficiency.
1979 – An Air Tractor agricultural aircraft is powered by a PT6A engine and flies to the National Agricultural Aviation Association convention in Las Vegas – the first time such a combination was displayed in public.