Article

Effects of Combinations of Aspect Ratio and Sweepback at High Subsonic Mach Numbers

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Abstract

Effect of aspect ratios of 2, 3, and 5 and sweepback angles of 0 Degrees, 30 Degrees, and 45 Degrees on the aerodynamic characteristics of a NACA 65-110 airfoil, with two-inch chord was investigated. Mach range was from 0.40 up to choking (0.870 - 0.960). Section characteristics were also determined. Sweepback and low aspect ratio each tend to delay and lessen compressibility effects. When in combination, effects of sweepback and low aspect ratio are cumulative but less than additive.

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... Kachel (2013) used taper ratio in distributing wing weight and confirmed its positive effect. Adler (1947) compared the effect of sweep on wings of constant aspect ratio at Mach 0.925, he found a significant drop in drag with increasing sweep angle, while the optimum lift he obtained was at 30 • of sweep. (Yen et al. 2011) assured that swept wings increase generated lift at a specific sweep angle, compared to non-swept wings. ...
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The aerodynamic performance of a 3-D NACA 6409 wing in ground effect was examined numerically with different wing configurations. The influence of changing twist angles, anhedral angles, taper ratios, and sweep angles on the aerodynamic performance was examined and compared with based model. Structured mesh domains were built, and RANS turbulence model Spalart-Allmaras was solved with a commercial solver. Base model numerical results show good agreement with available experimental data. The results show that wash-in twist has a positive effect on wing aerodynamic performance near ground proximity, as well as anhedral angles. Although swept wings have a negative effect on aerodynamic efficiencies compared with non-swept wings, an optimum swept twisted wing configuration was proposed to achieve higher aerodynamic efficiency, while applying wing sweep. Tapered wings produced a slight increase in aerodynamic efficiency in a narrow range of taper ratios. Speed variation has no drastic or abrupt effect on results.
Chapter
In this chapter we discuss the aerodynamics of swept wings in transonic flow. To demonstrate the merits of swept-back wings, simple sweep theory is presented. It is shown why a swept wing can experience local supersonic flow while still being in subcritical conditions, thereby postponing the onset of strong shock waves and drag divergence. It is also shown how the wave drag coefficient of a swept wing can be estimated based on the wave drag coefficient of an unswept wing. This method can be used to show the favorable effect of wing sweep on the wave drag coefficient over the transonic Mach number range. Apart from these advantages the chapter also presents the adverse effects of wing sweep. It is shown how the chordwise pressure distribution changes over the center section and tip section of a swept wing of finite span. It is explained what shape modifications (both in airfoil and in planform) can be applied to reduce the form drag of the center section of an aft-swept wing. In addition, viscous effects on swept wings are detailed. In particular, the transition mechanisms of attachment-line instabilities and crossflow vortices are explained. It is also shown why aft-swept wings are susceptible to tip stall and how a controlled form of stall can lead to a stable leading-edge vortex. Finally, the aeroelastic implications of (aft-)swept wings are detailed: a change in aerodynamic twist due to wing bending and a resulting reduction in control surface effectiveness. This chapter contains 7 examples and closes with 24 practice problems.
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