TWENTYFIFTH EUROPEAN ROTORCRAFT FORUM Paper n H9 PREDICTION OF THE OFF-AXIS RESPONSE TO CYCLIC PITCH USING A MANEUVERING FREE WAKE MODEL BY COLIN THEODORE

This paper presents a study on the effect of wake modeling on the prediction of the off-axis response to pilot inputs for a hingeless and an articulated rotor helicopter, including a comparison with flight test data. The free wake model can capture geometry changes due to maneuvering flight. The prediction of the response to pilot inputs improves only slightly; in particular, the off-axis response is still predicted in the wrong direction. The effects due to wake geometry have the correct direction, but they are weak. Key discrepancies between simulation and test develop after less than one half rotor revolution following the maneuver, when body rates are negligible and therefore the wake geometry has not changed appreciably. The mechanism causing these initial discrepancies remains unclear, and appears to be related to angular accelerations, rather than rates. If wake geometry is important, a relaxation type free wake might not be appropriate, and an unsteady free wake may be necessary.