Flutter of Pairs of Aerodynamically Interfering Delta Wings

Abstract

To examine the effect on flutter of the aerodynamic interference between pairs of closely spaced delta wings, several structurally uncoupled 1/80 th-scale models were studied by experiment and analysis. Flutter test boundaries obtained in NASA Langley's 26-in. transonic blowdown wind tunnel were compared with subsonic analytical results generated using the doublet lattice method. Trends for several combinations of vertical and longitudinal wing separation were determined, showing flutter speed significantly affected in the closely spaced configurations. For some configurations, a flutter mechanism coupling flexible modes of both surfaces at a disinctive flutter frequency was predicted and observed. The flexibilities of both surfaces were concluded to be essential to the analysis. Nomenclatureb r = reference semi-chord of trailing wing c = mean aerodynamic chord of leading wing / = frequency, Hz g -damping h = biplanar (vertical) wing separation k = stiffness matrix / = streamwise (longitudinal) wing separation m = mass matrix M = Mach number