RE: Bernard Hunt EZB Pitch Specifications

Jim,

A plane that advances or goes forward 22.5" for each revolution of the prop is said to have a prop with a 22.5" advance ratio (AR).  If an EZB prop is built on a 22.5" helical pitch block, has an advance ratio of 22.5" (the as built helical pitch and the AR often do not come out to be the same), and is set at a pitch of 26" at a 5" radius, the prop blade will have an angle of attack (AoA) of 4 degrees along its whole length. How does one get the 4 degrees?  The angle of a blade set at 22.5" pitch is 35.6 degrees at a 5" radius.  The angle if the blade is set at 26" pitch at a 5" radius is 39.6 degrees.  The difference of 4 degrees is the AoA of the blade.

An EZB is often a much lighter and slower plane compared to an F1L.  The as flown AR's may not be the same so a good EZB prop design may not work well for an F1L.  As a point of comparison, my current F1L flies with an advance ratio of about 23" (this is by design and I built the prop on a 23" helical block).  I set my blades with an AoA of 7.5 to 8.5 degrees (or a 30" to 31" pitch at a 5" radius).  The prop has a 15" diameter.  This AoA (or pitch) is similar to many other F1L's, while the AR of my F1L is more than usual.  Stan Chliton's Spirit F1L has an AR of just over 20" and a pitch of 26.5" (I do not know the exact radius but somewhere between 4.5" and 5") for his 15" prop.  This gives an AoA of about 7-7.5 degrees.  The same AR, AoA, and pitch are found on Laurie Barr's CargoLifter F1L (14.7" prop diameter.  Both of these planes are among the best F1L's and one cannot go very wrong copying their design parameters.

Leo