For those with plenty of disposable income you could always buy blurs from a company like this http://www.propblur.com/172nd-scale.html. I myself haven't used them but they look sweet. My problem is the cost. 
Here's all the parts you need:
A sturdy plastic cap from an aerosol spray can
A nail
An Exacto Compass cutter
A Drill
Building the tool:
First I took the cap and preformed a little surgery. I left about a 1/4 inch lip to help keep the cap stiff to reduce flexing when applying pressure with the sand paper.
Next I drilled a hole in the center of the cap large enough to pass the nail through.
And now you're ready to make a prop blur. Here's how its done.
To make the blur itself I use Evergreen clear plastic. In the past I've used the clear lids that tend to come with Chinese take out food or something similar. With the Evergreen it costs about $5 for two sheets which will allow you to make up to a dozen or so blurs per sheet depending on the size of the blur you want.
The key tool in my opinion is the Exacto Compass. I found mine at a local craft store for under $10.
Using the kit supplied prop as a guide I measure from the center of the prop hub to the edge of the blade tip.
I then cut out a disk using the compass
Next using a pin vice I'll enlarge the center hole on the blur to accommodate the nail from the tool you just built. Keep in mind you may need different size nails for different size props.
Take the nail and pass it through the plastic disk you cut out. Then pass that through the aersole cap like pictured below
Then place the entire shaft of the nail into the jaws of the drill. Butt the jaws against the bottom of the cup and tighten
Next turn on the drill. While holding the drill drag sand paper across the disk. I've found through trial and error that its better to use a lighter grade sandpaper This allows you to still see through the blur to the aircraft. You can see the differences yourself below and decide for yourself which would work for you.
Course Paper finish
Finer Paper finish
I will try adding yellow tips and maybe some blade shadows later on but for now...
Thanks for looking
