How do you appraise the popular PT6A engine, and how can they enhance the performance of an older turboprop aircraft? Jeremy Cox offers background information on the world’s most-popular turboprop
Turboprop engines trace their roots back to the Hungarian Jendrassik CS-1 which first ran in 1938 but never flew on an aircraft. It would be another seven years before the world’s first turboprop-powered aircraft – a Gloster Meteor F-1 – flew with a Rolls-Royce RB-50 Trent attached in September 1945.
The Vickers Viscount (1948) became the world’s first production turboprop aircraft, powered by the RR RB-53 Dart. Meanwhile, the world’s oldest ‘still flying’ turboprop aircraft is a 1953 Fairey Gannet powered by an Armstrong Siddeley Double Mamba ASMD 1 engine (two engines bolted to the same gearbox) driving two separate props concentrically mounted on the same thrust line.
It was in 1956 that the Canadian Pratt & Whitney Aircraft Company (later renamed Pratt & Whitney Canada (PWC)) proactively initiated the design and build of a new engine which would eventually become the world’s best-selling aircraft turboprop powerplant. The design mandate for the PT6A was to create a compact, lightweight, modular engine that could produce 500shp, and be serviced as much as possible ‘on-wing’ without removal.
The PWC team collaborated on a double-shaft, reverse flow, free-turbine design which produced more power than a fixed shaft engine, was quieter and virtually eliminated foreign object damage (FOD).
The initial target market for the PT6 engine was the piston-powered DHC-2 de Havilland Beaver. The power-to-weight ratio of a turbine engine versus a piston engine (the PT6 (325lbs) was less than half the dry weight of the current Wasp radial (653lbs), while producing 50hp more).
The first PT6 to take to the skies (1961) was mounted on an experimental Assault Support Helicopter. Later that same year, a Beech 18 was chosen as the first fixed-wing testbed aircraft. The nose section of its fuselage was modified to accommodate the new engine and Hamilton Standard Propeller and the rest, as they say, is history…
Today’s PT6A Series Engine
The modern PT6A Series Engine, starting from the output shaft (propeller mount) and working backwards to the rear of the engine, has the following modules and features:
- Drive Section Module: Epicyclic speed reduction gearbox enables a compact installation and output speed optimized for optimal power and low propeller noise;
- Power Section Module: Reverse-flow combustor optimized to provide low emissions, high stability and easy starting; single-stage compressor turbine which in many models has cooled vanes to maintain high durability; independent “free” power turbine with shrouded blades (forward-facing output for fast hot section refurbishment);
- Compressor Section Module: Multi-stage axial and single-stage centrifugal compressor that features reverse flow, radial inlet with screen for FOD protection;
- Accessory Section Module
Today, Pratt & Whitney Canada classifies the PT6A in three groups, as follows:
- Small engines: 500-999shp
- Medium engines: 1,000-1,400shp
- Large engines: 1,401-1,900shp
While we exclude specifics on military, helicopter or agricultural applications of the PT6A Series engine (our focus is exclusively fixed-wing Business Aviation applications), Business Aviation applications closely equal the other sectors mentioned approximately 50/50.
Specifically, in Business Aviation over 20,000 PT6A series engines have been installed in 54 different makes/models of business aircraft with the Beech King Air series the most prolific platform (10,774+ engines and counting), followed by the Cessna Caravan series (2,573+). The out-of-production Piper Cheyenne comes in third with 1,954 engines.
The ‘Top Three’ most prolific PT6A Models are as follows:
- PT6A-60A (as installed on the King Air 300 Series): 2,892+ engines
- PT6A-21 (as installed on the King Air C90 Series, excluding the GT models): 2,506+ engines
- PT6A-114A (as installed on the 208 Caravan Series, excluding the EX model): 2,149+ engines
Read the valuation of these top 3 most prolific PT6A engines at Avbuyer.com