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Light twin at 10,000 ft and 180 kt: DATCOM component drag build-up, polar, trim drag at 25 % MAC and Korn drag divergence

Tool	Aircraft Drag Build-Up and Trim Drag
Source	U.S. Air Force (1978). USAF Stability and Control DATCOM. Air Force Flight Dynamics Laboratory, Wright-Patterson Air Force Base, OH, Sections 4.1.5.1, 4.2.3.1, 4.3.3.1 and 4.5.3.1 (equations 4.1.5.1-a, 4.2.3.1-a and -b, figures 4.1.5.1-27, 4.1.5.1-28b, 4.3.3.1-37 and the four sample problems); Rubesin, M. W., Maydew, R. C., and Varga, S. A. (1951). NACA Technical Note 2305, eq. (10a); Loftin, L. K., Jr. (1980). NASA Reference Publication 1060, eq. (3.25).
Level	Undergraduate

Problem

An illustrative light twin (W 6,500 lb, S 180 ft^2, span 38 ft, chords 5.8 / 3.67 ft, natural sheet-metal surface k 0.16 mil) flies at 10,000 ft and 180 kt TAS. Build up its zero-lift drag from the wing (S_exp 154 ft^2, MAC 4.85 ft, t/c 0.15 at 0.40 c, unswept), horizontal tail (36 ft^2, 3.0 ft, t/c 0.10, 5 deg), vertical tail (22 ft^2, 3.6 ft, t/c 0.10, 25 deg), fuselage (32 x 4.5 ft) and two nacelles (6 x 2.6 ft, 98 ft^2 wetted, Q 1.3) with the Prandtl-Schlichting law, the NACA TN 2305 Mach factor and the DATCOM form factors, add cooling 0.0015, antennas 0.0010 and a 5 percent excrescence allowance, then find the polar with e 0.80, the drag, the trim drag with the c.g. at 25 percent MAC (C_mac -0.05, fuselage C_m,alpha 0.12/rad, tail 40 ft^2 at 17 ft, AR 4.5, e_t 0.8, eta_t 0.9) and the Korn drag-divergence Mach number (kappa_A 0.87).

Inputs to Enter

W 6,500 lb, S 180 ft^2, h 10,000 ft, V 180 kt, b 38 ft, c_r 5.8 ft, c_t 3.67 ft; surface natural sheet metal (k 0.16 mil), Prandtl-Schlichting, TN 2305 factor, Loftin fuselage wetted area, wing-body factor off
Components: Wing S_exp 154 ft^2 l 4.85 ft t/c 0.15 x_t 0.40 sweep 0 Q 1.0; Horizontal tail 36 ft^2, 3.0 ft, 0.10, 0.30, 5 deg, Q 1.05; Vertical tail 22 ft^2, 3.6 ft, 0.10, 0.30, 25 deg, Q 1.05; Fuselage l 32 ft d 4.5 ft; Nacelles (2) S_wet 98.0 ft^2 l 6.0 ft d 2.6 ft Q 1.3; x_tr 0 everywhere
Miscellaneous: cooling air 0.0015, antennas / lights / gaps 0.0010, landing gear (retracted) 0; excrescences 5 percent; e 0.80 entered
Trim: MAC 4.85 ft, h_ac 0.25, h_cg 0.25, C_mac -0.05, C_m,alpha,f 0.12, C_m0,f 0, a_w 4.9, S_t 40 ft^2, l_t 17 ft, AR_t 4.5, e_t 0.8, a_t 3.6, eta_t 0.9, d(eps)/d(alpha) 0.4; drag rise kappa_A 0.87

Open the Aircraft Drag Build-Up and Trim Drag tool (loaded with this example)

Answers

M 0.282, q 81.02 lb/ft^2; wing S_wet 319.6 ft^2 (2 S_exp (1 + 0.25 t/c)), Re 7.32e6, C_F 0.00314, FF 1.231 (L 1.2), R_LS 1.087, dC_D0 0.00745; fuselage S_wet 388.8 ft^2 (pi d^2 (l/d - 1)), Re 4.83e7, C_F 0.00234, FF 1.185 (f 7.11), 0.00600; tails 0.00179 and 0.00105; nacelles 0.00247 (FF 1 + 0.35/f = 1.152)
C_D0 = 0.01876 + 0.00250 + 0.00094 = 0.02220; f = C_D0 S = 3.995 ft^2; S_wet 925 ft^2; C_F,eq = 0.00432
Lifting line e_LL 0.9732 (printed; e 0.80 applied), K = 1/(pi 0.80 x 8.022) = 0.04960; C_L* = 0.6690, (L/D)max = 15.07, V_md = 146.9 kt, V_mp = 111.6 kt
C_L = 0.4457, C_Di = 0.009854, C_D = 0.03205, parasite 323.7 lb + induced 143.7 lb = 467.4 lb, L/D 13.91
Trim at h 0.25: C_Lw 0.4568, C_Lt -0.05537 (download 161 lb, 2.5 percent of the lift), C_D,trim = 0.000496 + 0.000054 = 0.000550 (8.0 lb, 1.7 percent), L/D trimmed 13.67; neutral point 0.5115, static margin 0.261
Korn M_dd = 0.87 - 0.15 - 0.4457/10 = 0.6754, Lock M_cr = 0.5677, no wave drag at M 0.282; total C_D 0.03260, D 475.4 lb

Notes

The tool's default inputs are this airplane; press Submit. The airplane is illustrative (stated on the page); the method is checked by test_drag_build_up.php (867 checks) against the four DATCOM sample problems (0.00834, 0.0875 / 0.0122, 0.0152, 0.0130 / 0.0129 / 0.0131 from the printed chart readings), the NASA CR-151971 A-4F / RA-5C build-up and an independent numpy / scipy script (References/Drag-Build-Up/checks/).