New Technologies Enable the Legend

There’s no doubt that the mighty PT6 engine has come a long way in 50 years. PT6 innovation continues to lead the industry because with each new version, the P&W team injects new technologies to keep the engine fresh and formidably competitive.

“It’s not by accident that today’s PT6 engine is up to four times more powerful than the original engine from 1963,” says Raymond Pelletier, PT6 Project Engineering Manager, who has worked on the engine program for many years. “The engine also has a 40 percent better power-to-weight ratio and up to 20 percent better specific fuel consumption (SFC) than the original.

That level of performance, along with many other improvements, is the result of introducing new technologies to the engine. It’s a legacy of accomplishment that has allowed the engine to lead, never follow. It’s why some 51,000 PT6 engines have been produced and found their way into more than 130 different aircraft applications.

PT6 Innovation

The following is a list of just a few of the major technology introductions and improvements made over the years.

• In 1973, a two-stage power turbine was added to the PT6A-41 to increase the engine’s power and fuel efficiency.
• In 1984, the PT6B-36 was equipped with an electronic engine control (EEC): a full authority digital engine control (FADEC) with a mechanical backup. The EEC reduces pilot workload by automatically monitoring engine power and preventing exceedances.
• In 1984, first-stage integral bladed rotor (IBR) technology was introduced on the PT6A-65 model, which resulted in fewer parts in the engine and better efficiency.
• Single-crystal blade technology was first introduced on the PT6A-67A in 1993. This resulted in increased temperature capability. This allowed the engine to operate at higher gas-path temperatures and providing more power for the same-size engine. 
• During the late 1980s and early 1990s, several aircraft manufacturers selected PT6A models for entry into the single engine turbine market.  Development was launched on the Piper Meridian, the SOCATA TBM and the Pilatus PC-12 among others. Together with the various aircraft manufacturers, P&WC launched Single Engine Reliability Teams (SERTs) to take the reliability of both the engine and the aircraft to a new level.  The SERTs were launched at the same time as process control changes were taking place in the aerospace industry.  This trend saw the adoption of new design standards, such as the use of best practices, and manufacturing improvements, as seen with standards such ISO 9000.  For example, P&WC was able to “mistake proof” certain maintenance actions through changes in the design of the engine.
• The mid 1990s to the early 2000s witnessed wide acceptance of this new generation of single turbine engine aircraft.  Production levels of the PT6 remained strong even as industry observers were predicting that the emergence of Very Light Jets (VLJs) would dampen demand for turboprops.  P&WC worked diligently on the continued improvement of the PT6.  Engine thermal power was increased through advances in materials, static component durability was improved through lessons learned from P&WC’s turbofan and turboshaft product lines, and specific fuel consumption (SFC) was improved through enhancements to the engine’s aerodynamics.
• Between 2005 and 2009, the PT6A-67P, the PT6A-66D and the PT6A-66B derivative engine models were all created to respond to the continued demand from turboprop aircraft manufacturers for more power, allowing them to increase aircraft speed and remain competitive with VLJs. 
• In 2010, the Computerized Visual Inspection System (CVIS), an automated inspection tool that verifies the integrity of the external assembly of new engines, was introduced to the manufacturing process for PT6 engines. This was a major step forward in quality assurance for the PT6 engine.
• By 2012, the manufacturing environment for the PT6 engine had become fully computerized. Parts are now designed digitally, producing a physical model that can be used from the casting process right through to inspecting the final machined part, a big step for PT6 innovation.
• New manufacturing processes – such as the precision drilling of the combustor liner, high-speed machining and adaptive machining – are continuously applied to the PT6 engine; they have greatly reduced the engine manufacturing lead-times and increased repeatability.
• Through the incorporation of advanced aerodynamics, a more efficient compressor and the latest generation of hot section materials, P&WC introduced the PT6A-140 engine in 2012, the first variant of next-generation products that produces 1,075 shp (shaft horsepower) thermal for significantly improved climb, cruise and take-off performance in hot and high operation.

“We have been able to grow the engine’s power capability primarily by taking advantage of advances in materials that permit operation at higher temperatures and advances in aerodynamic modelling capability that increase the flow through the engine,” says Pelletier. “It’s significant that the power of the engine has grown from 500 shp to 2,000 shp, yet there has not been a corresponding increase in engine size. In fact, if you look at the engine diameter, it has stayed the same.”

Operators of the PT6 engine can also find improvements in the engine’s inherent design. Very few tools are required to maintain the engine. Through the fuel nozzle ports, for example, technicians can access the internal components of the hot section using a simple boroscope.

“We have made exceptional progress over the years making what has always been a great engine even greater,” says Pelletier. “And we have some of the best engineers in the business working to ensure that this continues in the future.”