t/c = 10%

two-pylon wetted area Awp = 2 × 2.024 × 14 = 56.7 ft2

pylon Re = 7.5 × 1.2415272 × 106 = 9.3 × 106

from Figure 9.19b (fully turbulent) at LRC, the incompressible basic CFpylon = 0.00295

Table 9.9 gives the summary of Bizjet components Re and 2D CF basic.

9.18.3 Computation of 3D and Other Effects to Estimate Component CDpmin

A component-by-component example of estimating CDpmin is provided in this section. The corrected CF for each component at LRC (i.e., Mach 0.6) is computed in the previous section.

Fuselage

The basic CFf = 0.0022.

3D effects (Equations 9.9, 9.10, and 9.11)

Wrapping

CFf = CFf × 0.025 × (length/diameter) × Re−0.2

=0.0022 × 0.025 × (8.71) × (6.2 × 107)−0.2

=0.00048 × 0.0276 = 0.0000132 (0.6% of basic CFf )

Supervelocity

CFf = CFf × (diameter/length)1.5 = 0.0022 × (1/8.71)1.5

= 0.0022 × (0.1148)1.5 = 0.0000856 (3.9% of basic CFf )

Pressure

CFf = CFf × 7 × (diameter/length)3 = 0.0022 × 7 × (0.1148)3

=0.0154 × 0.00151 = 0.0000233 (1.06% of basic CFf )

Other effects on fuselage (see Section 9.8.1)

body pressurization – fuselage surface waviness: 5%

nonoptimum fuselage shape

(a)nose fineness – for 1.5 ≤ Fc f ≤ 1.75: 6%

(b)fuselage closure – above Mach 0.6, less than 10 deg: 0%

(c)upsweep closure – 10-deg upsweep: 8%

Table 9.10. Bizjet fuselage CFf correction (3D and other shape effects)

(d)aft-end cross-sectional shape – circular: 6

cabin pressurization leakage (if unknown, use higher value): 5%

excrescence (nonmanufacturing types; e.g., windows)

(a)windows and doors (higher values for larger aircraft): 2%

(b)miscellaneous: 1%

wing–fuselage-belly fairing, if any (higher value if it houses undercarriage): 5%

ECS (see Section 9.8) gives 0.06 ft2: 3.6%

Total CFf increment: 41.8%

Table 9.10 gives the Bizjet fuselage CFf components.

Add the canopy drag for two-abreast seating f = 0.1 ft2 (see Section 9.8.1). Therefore, the equivalent flat-plate area, f, becomes = CFf × Aw F + canopy drag.

f f = 1.416 × 0.0022 × 670 + 0.1 = 2.087 + 0.1 = 2.187 ft2

Surface roughness (to be added later): 3%

Wing

The basic CFW = 0.003.

3D effects (Equations 9.14, 9.15, and 9.16)

Supervelocity

CFw = CFw × 1.4 × (aerofoil t/c ratio)

= 0.003 × 1.4 × 0.1 = 0.00042 (14% of basic CFw )

Pressure

CFw = CFw × 60 × (aerofoil t/c ratio)4 × 6 0.125

AR

=(0.003 × 60) × (0.1)4 × (6/7.5)0.125

=0.18 × 0.0001 × 0.973 = 0.0000175 (0.58% of basic CFw )

=9.382 × 0.6 × [{0.75 × (0.1)3 − 0.0003}/552.3]

=87.985 × 0.6 × (0.00075 − 0.0003)/552.3

=0.02375/552.3 = 0.000043 (1.43% of basic CFw )

Other effects. For excrescence (nonmanufacturing; e.g., control-surface gaps):

flap gaps: 5% others: 5%

total CFw increment: 25%

Table 9.11 gives the Bizjet wing CFw components.

Therefore, the equivalent flat-plate area, f, becomes = CFw × Aww .

ff = 1.26 × 0.003 × 552.3 = 2.09 ft2

surface roughness (to be added later): 3%

Empennage

Because the procedure is the same as for the wing, it is not repeated. The same percentage increment as the wing is used for the coursework exercise. In the industry, engineers must compute systematically as shown for the wing.

V-tail

wetted area, AwVT = 81 ft2

basic CF H−tail = 0.003

It is a T-tail configuration with interference from the T-tail (add 1.2%).

fVT = 1.262 × 0.003 × 81 = 0.307 ft2

H-tail

wetted area, Aw HT = 132.2 ft2

basic CF V−tail = 0.0032

fHT = 1.25 × 0.0032 × 132.2 = 0.529 ft2

surface roughness (to be added later): 3%

Nacelle

fineness ratio = 2.45

nacelle Re = 1.07 × 107

wetted area of two nacelles, Awn = 158 ft2

basic CFnac = 0.0029

3D effects (Equations 9.14, 9.15, and 9.16)

Wrapping (Equation 9.9):

CFn = CFn × 0.025 × (length/diameter) × Re−0.2

=0.025 × 0.003 × 2.45 × (1.07 × 107)−0.2

=0.000184 × 0.0393 = 0.0000072 (0.25% of basic CFf )

Other increments are shown in Table 9.4 for one nacelle. For two nacelles (shown in wetted area):

fn = 1.8325 × 0.0029 × 158 = 0.84 ft2

surface roughness (to be added later): 3%

Pylon

Because the pylon has the same procedure as the wing, it is not repeated. The same percentage increment as for the wing is used in the coursework exercise. There is interference on both sides of the pylon.

each pylon exposed reference area = 14 ft2

length = 2.28 m (7.5 ft)

t/c = 10%

two-pylon wetted area Awp = 56.7 ft2

pylon Re = 7.5 × 1.2415272 × 106 = 9.3 × 106

basic CFpylon = 0.00295

for two pylons (shown in wetted area):

fpy = 1.26 × 0.00295 × 56.7 = 0.21 ft2

surface roughness (to be added later): 3%