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THREE-DIMENSIONAL WINGS
Wings designed to operate at high speeds are generally thin and employ sweepback in order to increase the critical Mach number. In some instances the sweep is variable to accommodate operation at both low and high speeds. Many airplanes for which the primary mission involves supersonic flight employ delta planforms. Generally, the trend is to increase the sweepback with increasing Mach number until a point is reached where the delta planform becomes more advantageous from a structural as well as aerodynamic viewpoint.
Typical operational aircraft with differing planform shapes are illustrated in Figure 5.25. The Boeing 727 has a midchord sweep angle of approximately 27° with a cruise Mach number of around 0.84 at 6705 m (22,000 ft). The aspect ratio of its wing equals 7.2. The Vought A-7D has about the same midchord sweep angle with a maximum Mach number in level flight at 1525 m (5000 ft) of around 0.88. Its aspect ratio of 4.0 is much lower than that of the 727. The Grumman F-14A and Aerospatiale/BAC Concorde have supersonic capability and employ planforms of a low aspect ratio that are approximately delta shaped. The F-14A employs variable sweep, sometimes
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Figure 5.25 Typical modern high-speed airplanes, (a) Boeing 727-200 three-turbofan short/medium-range transport. (b) Vought A-7D tactical fighter version of the Corsair II for the USAF. (c) Grumman F-14A Tomcat carrier-based multimission fighter, (d) Aerospatial/BAC Concorde supersonic transport. (John W. R. Taylor, Jane’s All the World’s Aircraft, Pilot Press Ltd, 1977.Copyright© 1977Pilot Press Ltd.) |
referred to as a “swing wing.” Fully forward its aspect ratio equals approximately 7.6. When swung to the rear, the wing and horizontal tail combine to produce a delta wing having an aspect ratio of approximately 1.0. The maximum design Mach number of the F-14A, according to Reference 5.11, is 2.4. The Concorde’s planform shape is referred to as an ogee. It has an aspect ratio of 1.7 and is designed to cruise at a Mach number of 2.02 at 15,635 m (51,300 ft).
