21st Congress of International Council of the Aeronautical Sciences, Melbourne, Australia, 13-18 September, 1998
Paper ICAS-98-7.2.1

FROM THE HALE GNOPTER TO THE ORNITHOPTER- OR HOW TO TAKE ADVANTAGE OF AIRCRAFT FLEXIBILITY

Pendaries C.
ONERA, France

Keywords: hale gnopter, ornithopter, aircraft flexibility

In order to achieve their outstanding performances, the hale gnopters need a specific design: high aspect-ratio wings and low wing loading. These characteristics imply flexibility, low frequency modes and aeroelastic phenomena at low speed. Therefore, wing flexibility has to be taken into account at the early stage of conceptual aircraft design. The flight dynamics equations of a free flexible aircraft are presented in this paper. The new aspects of the modelization lies in the full coupling between rigid-body modes and flexible modes. The first results of this modelization revealed different kinds of instabilities: the classical flutter due to a coupling between flexible modes, and other instabilities due to the coupling between rigid modes and flexible modes, like the instability of the first bending mode, leading to a kind of flapping movement. The evolution of the rigid-body modes with the speed is also clearly affected by the presence of flexible modes. The propulsion by wing flapping without articulations at the wing-root is then studied to show that this propulsion mode could be an alternative to propellers.

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