Equivalence of flapping and feathering
The performance of the rotor blade depends upon its angle of incidence to the tip-path plane. A given blade incidence can be obtained with different combinations of flapping and feathering. Consider the two situations illustrated in Fig. 4.19: these are views from the left side with the helicopter in forward flight in the direction shown. In situation 1 the shaft axis coincides with the TPA; there is therefore no flapping but the necessary blade incidences are obtained from feathering according to Equation 4.8. Blade attitudes at the four quarter points of a rotation are as indicated in the diagram. In situation 2 the shaft axis coincides with the NFA.By definition this means that feathering is zero: the blade angles however are obtained from flapping according to Equation (4.4). It is seen that if the feathering and flapping coefficients B1 and a1 are equal, the blade attitudes to the tip-path plane are identical around the azimuth in the two situations. The blade perceives a change in nose-down feathering, via the swash-plate, as being equivalent to the same angle change in nose-up flapping.
The performance of the rotor blade depends upon its angle of incidence to the tip-path plane. A given blade incidence can be obtained with different combinations of flapping and feathering. Consider the two situations illustrated in Fig. 4.19: these are views from the left side with the helicopter in forward flight in the direction shown. In situation 1 the shaft axis coincides with the TPA; there is therefore no flapping but the necessary blade incidences are obtained from feathering according to Equation 4.8. Blade attitudes at the four quarter points of a rotation are as indicated in the diagram. In situation 2 the shaft axis coincides with the NFA.By definition this means that feathering is zero: the blade angles however are obtained from flapping according to Equation (4.4). It is seen that if the feathering and flapping coefficients B1 and a1 are equal, the blade attitudes to the tip-path plane are identical around the azimuth in the two situations. The blade perceives a change in nose-down feathering, via the swash-plate, as being equivalent to the same angle change in nose-up flapping.
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