To: Grey Area
That is what Mr. Prouty said in an engineering text. Now let’s look at real life. On the Sikorsky heads (other than the S-76) the pitch horn leads the blade by 45-degrees. The maximum deflection of the swash plate is 45-degrees ahead of the commanded direction. That is, if the pilot pushes forward cyclic the swashplate will deflect downward 45-degrees ahead of the longitudinal axis. That means that when a blade is disposed over the right side and in alignment with the lateral axis the blade will have the greatest amount of pitch removed from it. The blade on the opposite side assuming a 4-blade system has the greatest amount of pitch added to it. With precession the blades will move downward over the nose and up over the tail. Now in my book 45 + 45 = 90. Other helicopters (Aerospatial) have a similar phase lag (angle) of 90-degrees but the numbers are 60 + 30 = 90. Now from an aerodynamic point of view the blades may not respond in 90-degrees and this is allowed in the certification documents, which state that the blades should move in the same sense as cyclic input. However they allow a deviation of several degrees as a result of coupling. This deviation can be compensated for by cyclic input. Maybe this is what Mr. Prouty was alluding to in his book. The only helicopter that I know of that has an offset hinge (cone hinge) that does not have a phase angle of 90-degrees is the Robinson. That is if you accept that pitch flap coupling will effect the 72-degree phase angle and make it respond like a 90-degree phase angle.