http://www.mh-aerotools.de/airfoils/prpstati.htm

This article seems to suggest keeping the prop angle of below 10 deg to optimize static thrust; above 25 deg the prop begins to stall during static flight.

If the tip of the prop is 10 deg, then

Pitch / (Diameter * Pi) = Tan(10) = 0.176

Pitch = Diameter * 0.176 * Pi = 0.554 * Diameter

So if Diameter is 18", pitch should not exceed 10 if you want at least the tip to generate thrust efficiently.

But, come on, we want not only the tip, but also the entire prop to generate static thrust efficiently.

So, wanting the middle of prop blade to be efficnent,

Pitch / (Diameter/2 * Pi) = Tan(10) = 0.176

Also, we want the prop tip to function like helicopter blade, whose optimal angle is 5 deg:

Pitch / (Diameter * Pi) = Tan(5) = 0.275

These two equations lead to this roughly:

Pitch = 0.28 * Diameter

So 18" prop should have Pitch of 5 if we want the tips to act like helicopter and the middle to lift efficiently.

So, props like 18x6, 30x10, 14x4, 12.25x3.75 work great for static thrust, because little or none the prop stalls during static flight.

http://www.mh-aerotools.de/airfoils/propuls3.htm