Coursework Example: Civil Bizjet Aircraft
The discussion on subsonic aircraft continues linearly from previous chapters.
9.18.1 Geometric and Performance Data
The geometric and performance parameters discussed herein were used in previous chapters. Figure 9.13 illustrates the dissected anatomy of the coursework baseline aircraft.
Aircraft cruise performance for the basic drag polar is computed as follows:
• cruise altitude = 40,000 ft
• LRC Mach = 0.65 (630 ft/s)
• ambient pressure = 391.68 lb/ft2
• ambient temperature = 390 K
• ambient density = 0.00058 sl/ft3
• ambient viscosity = 2.96909847 x 107lbs/ft2
• Re/ft = 1.2415272 x 106 (use the incompressible zero Mach line, as explained in Section 9.7.1)
• CL at LRC (Mach 0.65) = 0.5
• Cl at HSC (Mach 0.7) = 0.43
Fuselage (see Figure 9.13)
• fuselage length, Lf = 15.24 m (50 ft)
• average diameter at the constant crosssection barrel, Df = 1.75 m (5.74 ft)
. Lf IDf = 8.71
• fuselage upsweep angle = 10 deg
• fuselage closure angle = 10 deg
Wing (see Figure 9.13)
• planform reference area, SW = 30 m[17] [18] [19] (323 ft2)
• span = 15 m (49.2 ft)
• aspect ratio = 7.5
• wing MAC = 2.132 m (7 ft)
• root chord at centerline = 2.86 m (9.38 ft)
• tip chord = 1.143 m (3.75 ft)
• quarterchord wing sweep = 14 deg
• aerofoil: NACA 65410 with 10% tic ratio for design CL = 0.4
Empennage (see Figure 9.13)
• Vtail: SF = 4.4 m2 (47.34 ft2)
• span = m (ft)
• MAC = (7 ft)
• Htail: Sh = 6.063 m2 (65.3 ft2)
• span = 5 m (ft)
• MAC = (4.2 ft)
Nacelle (see Figure 9.13)
• nacelle length = 2.62 m (8.6 ft)
• nacelle diameter = 1.074 m (3.52 ft)
• nacelle fineness ratio = 2.62I1.074 = 2.44
9.18.2 Computation of Wetted Areas, Re, and Basic CF
An aircraft is first dissected into isolated components, as shown in Figure 9.15. The Re, wetted area, and basic 2D flatplate CF_baSiC of each component are worked out herein.
Fuselage
The fuselage is conveniently sectioned into three parts:
• total wetted area, Awf = 110 + 340 + 170 + 50 = 670 ft2
• fuselage Re = 50 x 1.2415272 x 106 = 6.2 x 107
• from Figure 9.19b (fully turbulent) at LRC, the incompressible basic CFf =
0. 0022
Wing
• wing exposed reference area = 323 – 50 (area buried in the fuselage) = 273 ft2
• MAC = 2.132 m (7 ft), AR = 7.5
• For t/c = 10% of the wing wetted area, Aww = 2.024 x 273 = 552.3 ft2
• root chord, CR = 2.86 m (9.38 ft)
• tip chord, CT =1.143 m (3.75 ft)
• wing Re = 7 x 1.2415272 x 106 = 8.7 x 106
• from Figure 9.19b at LRC, the incompressible basic CFw = 0.003
Empennage (same procedure as for the wing)
• Vtail
• reference area, SV = 4.4 m2 (47.34 ft2)
• exposed reference area = 47.34 – 7.34 (area buried in the fuselage) = 40 ft2
• for t/c = 10% the Vtail wetted area, AwVT = 2.024 x 40 = 81 ft2
• taper ratio = 0.6
• MAC = 2.132 m (7 ft)
• Vtail
• Re = 7 x 1.2415272 x 106 = 8.7 x 106
• from Figure 9.19b (fully turbulent) at LRC, the incompressible basic
CF_Vtail = 0.003
• Htail
• reference area, SH = 6.063 m2 (65.3 ft2); it is a Ttail and it is fully exposed
• for t/c = 10%, the Htail wetted area, AwHT = 2.024 x 65.3 = 132.2 ft2
• taper ratio = 0.5
• MAC = 1.28 m (4.22 ft)
• Htail Re = 4.22 x 1.2415272 x 106 = 5.24 x 106
From Figure 9.19b (fully turbulent) at LRC, the incompressible basic CF_Htail = 0.003185.
Nacelle
• length = 2.62 m (8.6 ft)
• maximum diameter = 1.074 m (3.52 ft)
• fineness ratio = 2.45
• nacelle Re = 8.6 x 1.2415272 x 106 = 1.07 x 107
• twonacelle wetted area, Awn = 2 x 3.14 x 3.1(Dave) x 8.6 – 2 x 5 (two pylon cutouts) = 158 ft2
• from Figure 9.19b (fully turbulent) at LRC, the incompressible basic CFnac =
0. 0029
Pylon
• each pylon exposed reference area = 14 ft2
• length = 2.28 m (7.5 ft)
Table 9.9. Summary of Bizjet component Reynolds number and 2D basic skin friction (CFbasic) Reference Characteristic

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

(d) aftend crosssectional 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%
• wingfuselagebelly fairing, if any (higher value if it houses undercarriage):
5%
• ECS (see Section 9.8) gives 0.06 ft2: 3.6%
• Total ACFf increment: 41.8%
Table 9.10 gives the Bizjet fuselage ACFf components.
Add the canopy drag for twoabreast seating f = 0.1 ft2 (see Section 9.8.1). Therefore, the equivalent flatplate area, f, becomes = CFf x AwF + canopy drag.
ff = 1.416 x 0.0022 x 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
ACFw = CFw x 1.4 x (aerofoil t/c ratio)
= 0.003 x 1.4 x 0.1 = 0.00042(14% ofbasic Cfw) [20]
Item 
ACFw 
% Of CFwbasic 
Supervelocity 
0.0004200 
14 
Pressure 
0.0000175 
0.58 
Interference (wingbody) 
0.0000430 
1.43 
Flaps gap 
5 

Excrescence (others) 
5 

Total ACfw 
26 
Table 9.11. Bizjet wing ACFw correction (3D and other shape effects) 
• Interference
= 9.382 x 0.6 x [{0.75 x (0.1)3 – 0.0003}/552.3]
= 87.985 x 0.6 x (0.00075 – 0.0003)/552.3 = 0.02375/552.3 = 0.000043 (1.43% of basic CFv,)
• Other effects. For excrescence (nonmanufacturing; e. g., controlsurface gaps):
flap gaps: 5% others: 5%
total ACFw increment: 25%
Table 9.11 gives the Bizjet wing ACFw components.
Therefore, the equivalent flatplate area, f, becomes = CFw x Aww.
ff = 1.26 x 0.003 x 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. [21]
Table 9.12. Bizjet nacelle ACFn correction (3D and other shape effects)

Nacelle
• fineness ratio = 2.45
• nacelle Re = 1.07 x 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):
ACFn = CFn x 0.025 x (length/diameter) x R02 = 0.025 x 0.003 x 2.45 x (1.07 x 107)02 = 0.000184 x 0.0393 = 0.0000072(0.25% ofbasic CFf)
• Other increments are shown in Table 9.4 for one nacelle. For two nacelles (shown in wetted area):
fn = 1.8325 x 0.0029 x 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. [22]
Table 9.13. Bizjetparasite drag buildup summary and CDpmin estimation

Leave a reply