Modal Constraints On Helicopter Dynamic Force Determination

The effectiveness and accuracy of helicopter dynamic force determination technology can be limited by factors which are related to the number and significance of the, independent orthonormal modes participating in the helicopter response at the frequency of interest. When the number of dominant modes (rigid body plus elastic) is. less than the number of forces being determined, random errors in the measured acceleration mobilities can result in unacceptable loss of accuracy in the determined forces. This phenomenon is illustrated by numerical calculations based on a laboratory model. It is shown that a modal participation parameter is identifiable which can readily be used to assess the reliabiiity of the calculated forces.