Let's say we have four turboprop engines. Three are flat rated to 850HP and one is 867 HP. In no particular order they can maintain that power at ISA plus 37,28,49,24 degrees. Flat rating (a number less than an engine's thermodynamic maximum), as I understand it, is established to increase an engine's longevity while also preserving takeoff and climb horsepower in hot/high takeoff. That horsepower number can then be maintained to higher altitudes without overstressing the engine.
The engines are all from the same Pratt and Whitney - Canada PT6A family as some of you will have guessed. They are:
Dash 140 @ ISA +24C
Dash 66B @ ISA +28C
Dash 52 @ ISA +37C
Dash 66D @ ISA +49C
The 66D is kind of an outlier due to its mission but maybe useful for comparison.
My question is (finally, you are saying), that given the closeness of some of these specs why are there so many different ones doing more or less the same job? More importantly, what would the internal differences be to effect these numbers? I ask this because I can read specs but know nothing of the materials, blades, angles, etc. that make them.
The engines are all from the same Pratt and Whitney - Canada PT6A family as some of you will have guessed. They are:
Dash 140 @ ISA +24C
Dash 66B @ ISA +28C
Dash 52 @ ISA +37C
Dash 66D @ ISA +49C
The 66D is kind of an outlier due to its mission but maybe useful for comparison.
My question is (finally, you are saying), that given the closeness of some of these specs why are there so many different ones doing more or less the same job? More importantly, what would the internal differences be to effect these numbers? I ask this because I can read specs but know nothing of the materials, blades, angles, etc. that make them.