Nomencl atureThe aerodynamic efficiency of aircraft can be improved appreciably by the use of wings with supercritica1 airfoils and/or by the addition ofThe tests covered a Mach number range from about 0.6 to 0.95 and were conducted in three phases. First, static aerodynamic data were measured at near scaled airplane cruise conditions to verify that the flutter model was aerodynamic_ ally representative of the airplane supercritical wing (SCW) both with and without winglet. wingtip mounted wing1ets. 1 -4 Information on the flutter aspects of these configurations is limited, but the results of available studies S -11 have s~own that the use of either a supercritica1 airfoil or wing1et can reduce appreciably the flutter speed of a wing. Further, these studies indicate that the flutter characteristics of supercritical wings and, in some instances of wings with winglets, may not be predicted accurately by conventional analytical methods. Because supercritica1 wings and wings with winglets are in use or being considered for use on high-speed executive jet transports, the present study was undertaken to provide guidance for the flutter design of such aircraft and to enlarge the flutter data base on supercritica1 wings and winglets.The specific objectives of the present study were (1) to determine experimentally the effect of a wing1et on the transonic flutter characteristics of a realistic supercritica1 wing, (2) to correlate these experimental results with analyses, (3) to explore for angle-of-attack induced flutter, and (4) to examine effects of elastic deformations on some aerodynamic characteristics of this supercritical wing. The model us~d in this study was a 1/6.5-size, dynamically and elastically scaled semispan version of a supercritical wing proposed for an executive jet transport. This airplane had a cruise Mach number of 0.82 and its wing was designed to carry a winglet for increased aerodynamic performance. To separate the mass effect from the aerodynamic effect of the winglet, the model was tested with three interchangeable wingtips: a normal tip, a tip with a winglet. and a normally shaped tip that was mass ballasted to simulate the winglet mass and pitch inertial properties. The model was tested cantilever-mounted on a five-component aerodynamic force balance attached to the sidewall of the Langley Transonic Dynamics Tunnel as shown in Figure 1. The model was equipped with orifices at the 0.30 semispan station to measure the chordwise static pressure distribution.Pretest flutter analyses were made for each wingtip confi~uration using doublet lattice unsteady aerodynamics which included wing/wing1et interference effects. 12 Wing static pressure distributions at two tunnel test conditions were calculated using a Jameson full potential aerodynamic code (FL022) for use as part of the model aerodynamic verification. 13 This code cannot model fuselage effects.
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
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