Gold,
Check out this thread for a fast design.
http://www.rcuniverse.com/forum/m_70.../tm.htm#709204
Here is the airspeed calculation.
There are 63360 inches in a mile.
There are 60 minutes in ah hour.
Airspeed is calculated as follows.
Pitch / 63360 = miles per propeller revolution
RPM * 60 = revolutions per hour
miles per propeller revolution * revolutions per hour = miles per hour
OR
63360 / 60 = 1056
I wrote a calculator that figures out airspeed for you at
http://www.missionwings.com/airspeed.asp .
RPM * Pitch / 1056 = miles per hour