Computation of 3D and Other Effects to Estimate Component Copmin A component-by-component example follows

Fuselage

From the previous section, at Mach 0.6, the basic CFf = 0.0021. [23]

Table 9.18. Vigilante fuselage ACFf correction (3-D and other shape effects)

Item

ACFf

% Of CFfbasic

Wrapping

0.000015

0.6

Supervelocity

0.000100

3.3

Pressure

0.0000274

0.8

Intake (little spillage)

2.0

Total ACFf

0.001050

6.7

The total ACFf increment is provided in Table 9.11. Table 9.18 lists the compo­nents of the Vigilante fuselage ACFf.

Therefore, in terms of the equivalent flat-plate area, f, it becomes = CFf x AwF:

f = 1.067 x 0.0021 x 1,474 = 3.3 ft2

Add the canopy drag, C^ = 0.08 (approximated from Figure 9.4).

Therefore, canopy = 0.08 x 4.5 = 0.4 ft2; ff = 3.3 + 0.36 = 3.66 ft2

Wing

From the previous section, at Mach 0.06, the basic CF = 0.00257.

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

• Supervelocity:

ACFw = CFw x 1.4 x (aerofoil t/c ratio)

= 0.00257 x 1.4 x 0.05 = 0.00018 (7% ofbasic Cfw)

Table 9.18 gives the components of the Vigilante fuselage ACFf. • Pressure:

/ 6 0.125

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

= 0.00257 x 60 x (0.05)4 x (6/3.73)0125 = 0.1542 x 0.00000625 x 1.06 = 0.00000102(0.04 % ofbasic Cfw )

• Interference: AFw for a thin high wing, use 3% of CFw • Other effects:

Excrescence (nonmanufacturing; e. g., control surface gaps):

• flap and slat gaps: 2%

• others (increased later): 0%

• total ACFw increment: 12.04%

Table 9.19 lists the components of the Vigilante wing ACFw.

Therefore, in terms of the equivalent flat-plate area, f, it becomes =

CFw x A w

f w = 1.12 x 0.00257 x 1,144.08 = 3.3 ft2

Table 9.19. Vigilante wing ACpw correction (3-D and other shape effects)

Item

ACFw

% Of CFwbasic

Supervelocity

0.0003850

7.00

Pressure

0.0000136

0.04

Interference (wing-body)

0.0000328

3.00

Flap/Slat Gap

2.00

Total ACfw

12.04

Empennage

Because it is the same procedure as for the wing, it is not repeated. The same per­centage increment as for 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 = 235.33 ft2

• basic Cf_V-tail = 0.00277

• fVT = 1.12 x 0.00277 x 235.33 = 0.73 ft2

• H-tail:

• wetted area, AwHT = 388.72 ft2

• basic Cf_H-tail = 0.002705

• fHT = 1.12 x 0.002705 x 388.72 = 1.18 ft2

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