Wing, Empennage, Pylons, and Winglets

The wing, empennage, pylon, and winglets are treated as lifting surfaces and use identical methodology to estimate their minimum parasite drag. It is similar to the fuselage methodology except that it does not have the wrapping effect. Here, the

Table 9.2. Typical CDn associated with sharp windshield type canopies

2-abreast-seating aircraft 0.1 sq. ft.

4-abreast-seating aircraft 0.2 sq. ft.

6-abreast-seating aircraft 0.3 sq. ft.

Adjust the values for the following variations: Kinked windshield (less sharp)

Smoothed (single-curvature) windshield Smoothed (double-curvature) windshield
interference drag with the joining body (e. g., for the wing, it is the fuselage) is taken into account bacause it is not included in the fuselage ff.

The methodology for the wing (denoted by the subscript w) is discussed in this section. The Re Rew is calculated first using the wing MAC as the characteristic length. Next, the exposed wing area is computed by subtracting the portion buried in the fuselage and then the wetted area, AWw, using the к factors for the t/c as in Section 9.7.2. Using the Rew, the basic CFwBASIC is obtained from the graph in Figure 9.19b for the flight Mach number. The incremental parasite drag formulae are as follows:

1. 3D effects [1].

(a) Supervelocity:

ACFw = CFw x K1 x (aerofoil t/c ratio)ave (9.15)

where K1 = 1.2 to 1.5 for the supercritical aerofoil and K1 = 1.6 to 2 for the conventional aerofoil

(b) Pressure:

/ 6 0.125

ACFw = CFw x 60 x (aerofoil t/c ratio)4ve x (9.16)

where the aspect ratio, AR > 2 (modified from [1]). The last term of this expression includes the effect of nonelliptical lift distribution.

2. Interference.

where K2 = 0.6 for high – and low-wing designs and CB is the root chord at the fuselage intersection. For the midwing, K2 = 1.2. This is valid for a t/c ratio up to 0.07. For a t/c ratio below 0.07, use the interference drag:

ACFw = 3to5% of CFw

The same relationships apply for the V-tail and H-tail. For pylon interference, use 10 to 12%. Interference drag is not included in the fuselage drag; rather, it is accounted for in the wing drag. (Pylon interference is both at aircraft side and with the nacelle.)

3. Other effects. (9.19)

Excrescence (i. e., nonmanufacturing such as control-surface gaps): Flap gaps: 4 to 5%

Slat gaps: 4 to 5%

Others: 4 to 5%

4. Surface roughness (to be added later).

The flat-plate equivalent of the wing-drag contribution is as follows (the subscripts are self-explanatory):

fw = (Cf w + ACFfwsupervel + ACFw_press + ACf w -inter + ACFw_other + ACFw-rough) x Awwi

which can be converted to CDpmin in terms of the aircraft wing area; that is:

[‘Cnpmin]w — fw/Sw (9.21)

(Note: Omit the term ACFwrough in Equation 9.20 if it is accounted for after comput­ing fs for all components, as shown in Equation 9.27).

The same procedure is used to compute the parasite drag of the empennage, pylons, and so forth, which are considered to be wing-like lifting surfaces.

fliftingsurface — [(CF + ^CFsupervel + ACF_press + ACf – inter + A-CF^other + ACF-rough), X Awlift^sur

CDpminliftingsurface — fliftingsurface/ Sw

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