The Art of the Helicopter John Watkinson - Karatunov.net

Technical background 49
Fig. 2.30 The input waveform is multiplied by the target frequency and the result is averaged or integrated.
At (a) the target frequency is present and a large integral results. With another input frequency the integral is
zero as at (b). The correct frequency will also result in a zero integral shown at (c) if it is at 90 ◦ to the phase of
the search frequency. This is overcome by making two searches in quadrature.
For simplicity the traditional practice has been to redefine the transform so that the
numbers come out positive. This causes confusion for those who are familiar with
transforms but are studying helicopters for the first time.
2.15 Centrifugal and Coriolis forces
Most calculations in mechanics involve a stationary frame of reference. However, as
helicopters contain some major rotating parts, designers sometimes find it convenient
for analysis to use a rotating frame of reference turning at the same angular velocity
as the blade. The blade is then usefully more or less stationary with respect to the