1960 turboprop engine family by Pratt & Whitney Canada
How does the Pratt & Whitney Canada PT6 differ from other turboprop engines? - Aviation Stack Exchange
Inside the Pratt & Whitney Canada PT6 turboprop engine
Turboprop Engine Opinions
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Split Shaft
Several turboprop engines, including the PT6 turboprop engine, use an epicyclic gearbox only, many other turboprop engines use a multishaft gearbox. The latter usually results in the propeller axis being offset from the turbine axis.
In common with some other engines, the PT6 turbine is also reversed. This facilitates the split-shaft arrangement where the engine and propeller are driven by separate (but in-line) shafts, each connected to their own turbine wheel.
PT6
Image: P&W
Image:12Charlie
A contrasting and common design
Image:12Charlie
The difference is quite simple , with the Pratt and Whitney design there is no direct mechanical link between the turbine compressor and hot section to the propeller gearbox reduction drive . With the Allison design were you to turn the propeller by hand all the turbine parts will move all the way back to the inlet compressor . There is a direct mechanical link all the way through