Wing Group – Civil Aircraft
The wing is a thin, flat, hollow structure. The hollow space is used for fuel storage in sealed wet tanks or in separate tanks fitted in; it also houses control mechanisms – accounted for separately. As an option, the engines can be mounted on the wing. Wing-mounted nacelles are desirable for wing-load relief; however, for small turbofan aircraft, they may not be possible due to the lack of ground clearances (unless the engine is mounted over the wing or it is a high-wing aircraft – few are manufactured).
The drivers for the wing group mass are its planform reference area, Mt); aspect ratio, AR(t); quarter-chord wing sweep, A/(t); wing-taper ratio, A(t); mean-wing t/c ratio, (q); maximum permissible aircraft velocity, V(t); aircraft limit load, n(t); fuel carried, (q); and wing-mounted engines, (q). The aspect ratio and wing area give the wing span, b. Because the quarter-chord wing sweep, Л/, is expressed in the cosine of the angle, it is placed in the denominator, as is the case with the t/c ratio because the increase in the t/c ratio decreases the wing weight by having better stiffness.
A well-established general analytical wing-weight equation published by SAWE  is as follows (others are not included):
Mw — K( MdgNz)x1 Swx2 ARx3(t/c)x4(1 + Л)х5(^Лі/4)х6(В/С)Х7 Sc/8 (8.19)
where C — wing-root chord, B — width of box beam at wing root, SCS — wing – mounted control-surface reference area, and Mdg — MTOM.
The equation is modified for coursework. The term (MdgNZ)x1 in this book’s nomenclature is (MTOM x nult)0 48. The term (B/C)tx7 SCSx8 is replaced by the factor
1.5 and included in the factor K. The lift load is upward; therefore, mass carried by the wing (e. g., fuel and engines) would relieve the upward bending (like a bow), resulting in stress relief that saves wing weight. Fuel is a variable mass and when it is emptied, the wing does not get the benefit of weight relief; but if aircraft weight is reduced, the fixed mass of the engine offers relief. Rapid methods should be used to obtain engine mass for the first iteration.
Writing the modified equation in terms of this book’s notation, Equation 8.19 is replaced by Equation 8.20 in SI (the MTOM is estimated; see Chapter 6):
Mw — cw X kuc X ksl X ksp X kwl X kre x (MTOM X Hult)0’48 X SW78 X Ar
X (1 + k) X (1 WFuel_massjH_ 0)
where cw — 0.0215 and flaps are a standard fitment to the wing.
kuc — 1.002 for a wing-mounted undercarriage; otherwise, 1.0
ksl — 1.004 for the use of a slat
ksp = 1.001 for a spoiler
kwi = 1.002 for a winglet (a generalized approach for a standard size) kre = 1 for no engine, 0.98 for two engines, and 0.95 for four engines (generalized)
If nonmetal is used, then mass changes by the factor of usage. For example, x% mass is nonmetal that is y% lighter, the component mass would be as follows:
MWciviLnonmetal = Mwcivil — x/y x MWdvu + x x MWdva (8.21)
In a simpler form, if there is reduction in mass due to lighter material, then mass is reduced by that factor. If there is a 10% mass saving, then:
MWcivil_nonmetal — 0-9 x MWcivil_all metal