I have to agree with some of the above posters, and the devs.
I spent last Saturday at the annual Planes of Fame airshow, which is mostly composed of warbirds, and this game seems to have done the props perfectly. (Note: I don't have the game yet, waiting for US release (yes I know about JustFlight)) When viewed head on, the props are invisible to barely-visible, and viewed from the side they're solid black ellipses, just like in all the screenshots and videos I've seen here.
And yes, there were plenty of examples for me to work off of. (Ignore the F-15)