F/A-18C to E Wing Morphing Study for the Abrupt-Wing-Stall Program

Abstract

Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. AbstractIn an effort to determine the impact of various wing parameters on the abrupt wing stall phenomenon encountered by the pre-production F/A-18E, various characteristics of the F/A-18C wing were modified to reflect the design changes incorporated into the F/A-18E wing.The parameters evaluated during this study included thickness, camber, twist, leading-edge radius, leading-edge flap-chord ratio and the addition of a leading-edge snag. The wing parameters were modified independently and then in combination to determine their impact on the abrupt stall.

Recommendations for CFD Procedures for Predicting Abrupt Wing Stall

“…The first candidate FOM consisted of the character of the lift coefficient vs. AoA curve, where a change in sign of the slope of the curve was apparent in the region where AWS was encountered in both windtunnel experiments 9 and flight tests for the F/A-18E. However, the change in sign of the lift-curve slope was found to be less of a reliable indictor of the onset of AWS when compared to the change in sign of the wing root bending moment coefficient 10 as illustrated in Figure 4 for the F/A-18C at 0.8 and 0.9 Mach. At 0.9 Mach the lift coefficient does not indicate a change in slope, while the C WB curve shows a zero slope at 11 degrees AoA.…”

Recommendations for Computational-Fluid-Dynamics Procedures for Predicting Abrupt Wing Stall

“…A composite FOM for indicating the onset of AWS has been developed, 10 which consists of the sectional lift coefficient and its derivative with respect to AoA plotted along the wing span. The quantification of the abruptness of lift loss is thought to be a measure of the sensitivity of the wing configuration to uncommanded roll.…”

“…This parameter has proven to be a reliable indicator of the onset of AWS for each of the aircraft configurations considered in this study and provides numerous insights into where the problem occurs, both in terms of AoA and location along the wingspan. 8,10,11 Figures 6 and 7, taken from Ref. 10, show plots of the sectional lift coefficient and its derivative with respect to AoA for two different aircraft configurations.…”

“…8,10,11 Figures 6 and 7, taken from Ref. 10, show plots of the sectional lift coefficient and its derivative with respect to AoA for two different aircraft configurations. Figure 6 gives the results for the baseline F/A-18C, and Fig.…”

Review and Recommended Experimental Procedures For Evaluation Of Abrupt Wing Stall Characteristics

“…A Blue Ribbon Panel determined that a poor understanding of the phenomena causing the problem existed, and made the recommendation to: "Initiate a national research effort to thoroughly and systematically 2 study the wing drop phenomena." The problem area addressed by the AWS Program [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] is the unexpected occurrence of highly undesirable lateral-directional motions at high-subsonic and transonic maneuvering conditions. One of the recommendations made by Chambers 2 was "to define and assess candidate figures of merit for the prediction of wing drop and wing rock from experimental methods.…”