Thanks Randie, that was a very useful link. I have to try it out and see how it looks.
I was just playing around with one of my RC aircraft, spinning the prop at different speed to have look. It seems to be a constant blur around the whole circle, on a photo it seems that the shutter speed of the camera has a great affect on how it looks.
The best way seems to be trial and error :)
I'll post some pics when I get it done (will take some time to get to that stage of building)
Michael