Help! Which side of the prop goes out?

[Douglas]

I am replacing the prop on my Carbon Cub S+, but both sides of the prop look nearly the same to me. I'm using the PKZ1019, P-51 BL, 9x6 prop. Which side faces in toward the engine? The only difference that I see is that one side is just a hole in the center, and the other side has an indented area around the hole for the prop shaft. My assumption is that it is indented side that face OUT and away from the engine and the indented area is there to sink in the nut. But I don't know.

 

[Aireal Anarchist]

side with numbers printed on it face forward

 

[mrjdstewart]

numbers always forward no matter where the prop is located.

 

[Douglas]

numbers always forward no matter where the prop is located.

This prop has no numbers on it, but I just realized that one side is concave so that obviously is the side that faces in toward the engine.

 

[BATTLEAXE]

other side has an indented area around the hole

That's the side that goes next to the motor if there are no numbers. Direct replacement props for certain models will be specific to that model so there usually is no need for the numbers.

However props made for random models will always have the numbers facing forward. In you case the indented area around the hole is the back of the prop, usually there to take a prop collar to help the prop fit multiple sizes of prop shafts. Most of the time there will be a plastic frame of around 4-8 prop collars of different inside diameters.

If there is no immediate wat to identify prop direction sometimes you can tell by the prop itself. The blade are usually designed just like a wing, the leading edge of the blade will be more rounded and the trailing edge will be sharp.