propellers

There are many different ways. Some us PE props, some use plastic discs. It boils down to what you like on your models.

Dynamic propellers or prop blur are some of the PE brands. Clear discs are usually hand made.

BK

BK is correct. I use the disk method and paint the blur on it.

Here is a link to a tutorial.

http://gregers.fr.yuku.com/topic/11537/Prop-blur-tutorial-Picture-heavy#.WAbti-ArLIU

Gents Thank you very much for the information 

Mac

If you have a decent graphics/photo program on your computer, it may have a rotation blur function.  Scan one of the kit props with a scanner.  Take the image and use the rotation blur function on it- adjust until it is pleasing.  Then print out on a viewgraph/transparency sheet.  Cut out the circle and you have a spinning prop.

I replied to a post similar to this a few years ago.  I'll give you the abbreviated version on how I did it. I painted the props (yellow tips in my case), then scanned them into PhotoShop. Using the "radial blur" (spin) function in the "Filter" drop-down menu you can create the spinning prop effect. Once I got the effect I wanted I printed the images on adhesive clear label stock and then mounted them on clear plastic cut to the proper size. As I said at the time, it's more art than science.  I tried making decals, but the plastic label stock produced better results. Check the December, 2014 Online Reader Gallery (B-17G "Tailwind") for an image of the model.