Planform Shape

A civil aircraft designer would seek the maximum possible aspect ratio that a struc­ture would allow. This minimizes induced drag (see Equation 3.13). The V-n dia­gram (see Section 5.7) determines the strength requirement in pitching maneuvers creating maximum stress from the bending moment at the wing root. Civil aircraft do not have high roll rates (unless it is a small aerobatic aircraft). Choice of material and aerofoil t/c ratio contributes to structural integrity. For civil aircraft, a trape­zoidal wing planform (with or without extensions; see Section 3.14) would be the dominant choice. The least expensive to manufacture is a rectangular planform, but there is no cost benefit for highly utilized commercial aircraft to offset drag reduc­tion (i. e., fuel-saving). Rectangular planforms are used in smaller club and sports aircraft with a low level of utilization.

Wing Reference Area

The wing reference area is obtained from the sizing of wing-loading W/S. At this stage, without knowing the aircraft weight, an initial estimate is derived from statis­tical values reflecting successful past designs. Subsequently, the wing will be sized to the requirement (see Chapter 1). Some iteration is required because component weights are revised at the stages of the study. In coursework activity, one iteration is sufficient.

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