To minimize repeating work that is similar in nature, the chosen aerofoil section for worked-out examples is kept the same for both civil and military aircraft designs. For a relatively low cruise Mach number of 0.65 at the LRC and 0.74 at the HSC, the NACA 65–410 is chosen for both designs. It is not exactly a supercritical aerofoil but serves the learning process because it is a known aerofoil successfully applied to many aircraft (Appendix C gives the details of NACA 65–410 aerofoil).

6.5.2 Wing Design

When the aerofoil section has been selected, the next task is to obtain the following information, which would be iterated to the final size through various design phases, as shown in Chart 2.1. Initially, all geometric details are taken from past experience (i.e., the statistical data of the aircraft class), followed by formal sizing, fine-tuned through CFD analyses and wind-tunnel testing, and finally substantiated through flight-testing (modifications are made, if required).

1.Determine the wing planform shape and its reference area. It should maximize the aspect ratio and optimize the taper ratio. In addition, the wing ensures adequate fuel volume. At this stage, it is considered that the wing structural layout can accommodate fuel capacity and movable control and lifting surfaces.

2.Determine the wing sweep, which is dependent on maximum cruise speed (see Section 3.16).

3.Determine the wing twist; a typical statistical value is 1 to 2 deg, mostly as washout (see Section 3.14).

4.Determine the wing dihedral/anhedral angle; initially, this is from the statistical data (see Section 3.14).

5.Determine high-lift devices and control areas. At first, the type is selected to satisfy the requirements at low cost. The values of its aerodynamic properties initially are taken from statistical data (see Section 3.10).

Section 6.3.2 discusses general considerations for wing design. Given here are suggestions to establish these parameters (see also Section 3.16).

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.