RE: prop measurement
The pitch of a prop is defined as the distance the plane will travel forward in one prop revolution if the prop was in something like jello. On a 12X4 prop that is 4 inches. On a 12X4 prop let us put a dot at 3 inches and at 5 inches from the prop center. The angle of the prop at 3" is greater that the angle of the prop at 5", but both points move forward 4 inches when that dot makes a full circle. Determining the angle at that point is either a sine, cosine or a tangent function. At age 73 I'm too old to go any further.