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(a) Simple delta |
(b) Cropped delta |
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(c) Notched delta |
(d) Double delta |
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[255]....or swept wings since they have some of the geometric characteristics of both. Typical wing-planform shapes of fighter aircraft are illustrated in chapter 11.
[257] ....appendix C. The near-zero sweep angle with accompanying high aspect ratio would be appropriate for landing, takeoff, and climb; whereas the intermediate sweep could be used for normal cruise at subsonic speeds. Flight at high-subsonic and supersonic speeds would call for the wing to be swept fully back.
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(a) No wing translation. |
(b) With wing translation. |
(c) No wing translation. |
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...various components that make up the complete area distribution. At the bottom of the figure is the variation of drag coefficient with Mach number for the original configuration and for the aircraft with modifications made in accordance with the transonic area rule. The modified aircraft easily passed through Mach 1.0 and entered the supersonic speed regime. The way in which the appearance of the F-102 aircraft was altered by application of the area rule is illustrated in figure 10.19. At the upper left is the experimental Convair XF-92A delta-wing research aircraft. At the upper right is the prototype F-102 delta-wing fighter that was unable to penetrate the supersonic speed range. Incorporating area-rule principles, the F-102A is shown at the lower left with its obvious fuselage indentation. The definitive form of the Convair delta-wing fighter, the F-106, is shown at the lower right and clearly displays the application of the area-rule concept. The reason for the appellation "wasp waist" or "Coke bottle" for aircraft designed according to area-rule concepts is obvious from figure 10.19.
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....of transonic and supersonic aircraft design. It clearly differentiates these aircraft from their subsonic ancestors.
....stability, control, and handling problems at high angles of attack in the stalled flight condition; such problems can occur at both high and low speeds. An early NACA flight study of the handling characteristics of an aircraft with swept wings was carried out in 1947 with a modified Bell P-63 propeller-driven fighter. This aircraft, fitted with wings of 35 sweepback, was redesignated the L-39 and is shown in figure 10.20. Note the wool tufts that are attached to the wing surfaces to indicate areas of unsteady or stalled flow. Extensive wind-tunnel studies of the high-angle-of-attack behavior of swept wings and of aircraft configurations equipped with such win s were also made in the years following World War II.
....taper ratio. The relative amount of aerodynamic load at each spanwise station is expressed by the span loading parameter GC/GLC, which is the product of the local section lift coefficient at a particular spanwise station and the wing chord at that position, divided by the product of the wing lift coefficient and the mean aerodynamic chord. The curves in figure 10.21(a) indicate that an increase in sweepback angle from 20 to 60 results in a large increase in the value of the loading parameter near the tip relative to that at the root for wings of aspect ratio 4.0 and taper ratio 0.4. Reducing the taper ratio from 0.6 to 0.25 on wings of aspect ratio 4.0 and 40 of sweepback causes a corresponding increase in the relative amount of load carried near the wingtip, as shown by figure 10.21(b). Variations in the aspect ratio for a given sweepback angle and taper ratio also have an important influence on the shape of the span loading curve.
....wing that results from the sweepback causes the boundary layer on the outboard sections of the wing to thicken, as compared with an unswept wing. The thicker boundary layer near the tip of the wing causes the maximum lift capability of these sections to be reduced, as compared with the two-dimensional value. The fences seen on the upper surface of many swept wings are intended to limit the spanwise boundary-layer flow and thus increase the maximum lift capability of the outboard sections; at the same time, the boundary layer builds up inboard of the fences and reduces the maximum lift coefficent of that part of the wing. Both these effects of the fence reduce the tendency toward pitch-up.
....approaches a restricted angle-of-attack range. The vibration is intended to alert the pilot to an approaching stall and to make him take corrective action to reduce the angle of attack. A stick pusher causes the control column to be pushed forward mechanically with a considerable force, perhaps 100 pounds, as the critical angle-of-attack range is approached. Sometimes the devices are employed together, in which case, the stick shaker is first activated, and if the pilot ignores the warning and permits the aircraft to continue pitching to a higher angle of attack, the stick pusher comes into action. Both the stick pusher and the stick shaker are activated by signals from instruments that sense parameters such as angle of attack, rate of change of angle of attack, attitude and its rate of change, or some combination of these parameters.