I've found that drawing props isn't as hard as it seems. With a little bit of practice, it's acutally quite easy.
Firstly, draw the central "shaft". (not the propeller shaft that runs inside the ship and connects to the engines, I am reffering to the part that the blades are attatched to)
Next, draw one of the blades. Look at other propellers to get a feel for how they should be shaped. Most props have 3 or 4 blades, some times more.
Lastly, add a little bit of shading if you wish. This shows the shape and pitch of the blades aswell as making larger ones look less flat. You can look at other props to show how this is done.
Here are some examples I have drawn for some of my ships, both RL and AU:
Note: In terms of shading, I probably am one of the most extreme, so be sure to look at other's to get a really good feel on the concept.
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"If people never did silly things nothing intelligent would ever get done." ~Ludwig Wittgenstein