Yeah, here is the fun part....

Each prop is shown as length and pitch. For example you have a 8x4 prop. That means its 8" long, and has a pitch of 4

Ideally the prop is supposed to move 4" forward for each revolution at its ideal speed. So...

13,986 x 4 = 55,994 inches per minute or 4,662 ft per min
4662 foot/minute = 52.9772727 mile/hour
Assuming its spinning at the correct speed, and there isnt any drag (like an airplane being attached to it)