Features Aircraft Innovations
50 Years in the Air

In 1963, the Beech Aircraft Company installed the very first production model of Pratt & Whitney Canada’s (P&WC) new PT6 gas turbine engine in its proof-of-concept Beech 87. Five years later, Bell Helicopter ordered the first P&WC turboshaft, the PT6T Twin-Pac, for a twin-engine version of its UH-1H.

P&WC employee A. Valdez works on a PT6T Twin-Pac. (Photo courtesy of P&WC)

In the 50 years since that Beech purchase, P&WC has developed and certificated 90 variations of its PT6 turboprop and turboshaft engines. They are used in more than 130 different applications in commercial, military, general aviation, business, helicopter, agricultural and utility aircraft.

With some 390 million hours of flight time logged, it’s no wonder that P&WC likes to say that the PT6 engine opened up the world.

To date, P&WC has manufactured 42,000 PT6A engines, the “A” designating turboprop engines for fixed-wing aircraft, and another 10,000 PT6B, PT6C and PT6T engines, the “B,” “C” and “T” designating turboshaft engines for helicopters.

The PT6T, the Twin-Pac, is the company’s biggest-selling PT6 turboshaft engine, with more than 6,900 delivered since the family entered service in the 1990s. The three variations of the Twin-Pac have accumulated more than 39 million flying hours in such applications as oil exploration, emergency medical service, maritime patrol and utility operations.

Fully half of P&WC’s annual engine assembly production is devoted to the PT6 engine: about 100,000 square feet of production area in the Lethbridge, Alta., Longueuil, Que. and Bridgeport, W.V. facilities is devoted to assembling mote than 1,000 PT6 engines a year, with a surge capacity capable of boosting that by several hundred more units a year.

Bell’s new 412EPI, introduced this March, uses an upgraded P&WC PT6T-9 Twin-Pac. (Photo courtesy of Bell Helicopter)

When P&WC decided in 1957 to build a turboprop engine for a target market then powered by piston engines, company engineers made a seminal decision: in a departure from other gas turbine engines of the time, P&WC would design the new gas turbine with an opposed shaft. In this design, the compression and power sections are placed end to end and are uncoupled; that is, the compression and power sections can turn at different speeds. In the conventional, non-opposed shaft design, the shaft for the power end is inside the compression shaft, requiring more complexity to, for instance, meet varying power requirements during flight.

This design feature is common to both the turboprop and turboshaft PT6 engines. The main difference between the two is the addition of a reduction gearbox for the turboprop. Helicopters usually already have their own main rotor and tail rotor gearboxes.

From this free turbine concept flow several key advantages of the PT6 engine: lighter components, since the engine does not have to turn the propeller or helicopter blades during startup; higher power-to-weight ratio; and a simpler, modular design, which, among other things, enables a wide choice of propeller speeds, easier maintenance and greater reliability.

As the decades flew by and flight hours climbed, the PT6 engine established an in-flight shutdown rate that was consistently only one third of today’s turbine industry standard of 10 events per millions hours.

Ease of maintenance translates into aircraft technicians in all corners of the world being able to complete all essential line maintenance tasks. “You can do most of the maintenance in the field, which was completely different from the other engines of that time,” explains Nick Kanellias, general manager of sales and marketing at P&WC. “The opposed shaft allows you to remove the power section on-wing. This allows easy access for turbine inspections and maintenance. This is a big advantage.”

The first PT6 engine had 500 shaft horsepower (SHP), but now P&WC offers PT6 engines ranging from 500 SHP to 2,000 SHP. P&WC has also increased the engine’s power-to-weight ratio by 40 per cent. Among the turboshaft engines the PT6B variations have 1,000 SHP, the PT6C variations deliver 1,200 to 2,000 SHP and the PT6T variations deliver 1,800 and 2,000 SHP.

Bell has been a long-time customer of P&WC. “The P&WC PT6 series is well known for its reliability and performance. In addition, P&WC’s customer support is world-class, mirroring Bell Helicopter’s commitment to providing industry-leading support throughout the entire life cycle of an aircraft,” notes Bell communications analyst Bridget Garcia.

In that 1968 turboshaft project, the Canadian Armed Forces asked Bell to develop a twin-engine version of the UH-1H, which it called the UH-1N, or Twin-Huey. P&WC and Bell jointly developed a combining gearbox that connected to the PT6 Twin-Pac on one side and the UH-1H transmission on the other. The commercial version of this aircraft became the Bell 212.

Bell has used several variations of the PT6T in its 412 airframe, beginning with the PT6T-3. Over time, different variants of the Bell 412 have utilized the PT6T-3B, the PT6T-3BE, and now, the PT6T-3D in the Bell 412EP and the PT6T-9 in the Bell 412EPI, which Bell introduced this year.

The Bell 412EPI uses upgraded PT6T-9 engines, which have 15 per cent more power. The SHP ranges from 2 x 1,021 for maximum continuous power to 1 x 1,280 for One Engine Inoperative (30 seconds).

The new Eurocopter EC175 uses a P&WC PT6C-67E engine that develops 1,775 SHP take-off power and 2,067 SHP maximum emergency power. (Photo courtesy of Eurocopter)

P&WC won the competition to supply its PT6C-67E for the new Eurocopter EC175, which should receive certification in the oil and gas mission configuration in early 2014. As of August, Eurocopter had taken 46 orders for the EC175.

Sikorsky has purchased approximately 200 PT6 engines for its S-58T and S-76B helicopters. The company cites several reasons for selecting P&WC, including engine size, power available, control system characteristics, mounting systems, structural integrity, reliability and maintainability.

Sikorsky’s public relations specialist, Frans Jurgens, explains why the firm chose the PT6 Twin-Pac for the S-58. “It proved to be an excellent engine for qualifying operation in falling and blowing snow. It also allowed us to qualify for engine icing certification by analysis rather than having to demonstrate in an icing tunnel.” Sikorsky used the PT6B-36A and PT6B-36B for the S-76B.

P&WC continues to refine its PT6 turboshaft engine. For example, the latest generation PT6 turboshaft, the PT6C-67E, has a dual channel full authority digital engine control system to reduce pilot workload. By improving the materials and design technologies for its PT6 engines over the past half-century, P&WC reports that it has been able to maintain an optimal balance of reliability, durability, mission performance, fuel consumption and greenhouse gas levels, and purchase, operating and maintenance costs.

The company’s commitment to continue delivering this quality in the next half-century is underscored by an observation by Richard Dussault, P&WC’s vice-president of marketing: “There is an interesting thing about the helicopter market,” he said. “The civilian market alone has 20,000 helicopters. A lot of them are 25 years old and more. Close to half of the thousand helicopters produced each year are replacement machines. It is an older fleet with good potential for replacement with modern, more capable machines.”