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Recip Turbo – Propeller efficiency?

Asked by: 988 views , ,
Aerodynamics, Aircraft Systems, Flight Instructor

A C206 normally aspirated vs a turbo, both have 3 bladed props, 80"props that have an adjustable pitch from 12º to 27º.  

At 14,000 feet, the 206 normally aspirated will have a lower prop pitch angle compared to a turbo 206 at 14,000?  Obviously, the turbo can hold sea level to about 22,000, whereas the non-aspirated at 14,000 lost most of its power. What are the blade angles on this comparison?

I'm trying to understand how the same propeller can convert 285HP to useful torque at 14,000 compared to a normally aspirated producing 150hp. Is it all about pitch angles varying to "absorb" the extra torque?

Thanks

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1 Answers



  1. Russ Roslewski on May 13, 2023

    Pretty much, yes. The effect of the higher horsepower is to be able to turn the propeller at the same rpm but with a larger blade angle, thereby causing the airplane to go faster.

    Worded another way, greater blade angles are harder to turn fast, so they need more horsepower to do so. But being able to turn the propeller fast with a greater blade angle also allows you to go faster.

    Sometimes it’s easier to picture boat propellers. Imagine a boat propeller with a 1 degree blade pitch. It would be really easy to spin really fast, but you wouldn’t move very quickly through the water. Instead make it a 45 degree blade pitch, and it’s much harder to turn, but if you have the power to, you could go pretty fast. Also similar to the gears on a bicycle.

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