SAWE Report - Cal Poly San Luis Obispo

5.6 Drag
The drag of the aircraft was divided into four parts: parasite drag, wave drag, induced drag, and
trim drag. The parasite drag was estimated using a component build method with form and
interference factors. The wave drag was calculated using the formula presented in Brandt &
Stiles. The wave drag efficiency factor was calculated from cross sectional area distributions
using the de Kármán integral and the theoretical wave drag of a perfect Sears-Haack body. The
cross sectional area distributions were measured at transonic and supersonic (Mach 1.6)
conditions. The transonic case was measured by passing vertical planes through a solid model of
the aircraft and measuring the intersecting area. The supersonic case was measured by passing
Mach cones through the model, measuring the intersecting area, and projecting that area onto the
vertical plane. For both cases, the engine capture area was subtracted from sections containing
the inlet, engine, and nozzle. The resulting area distributions shown in Figure 5.11 and Figure
5.12 match reasonably well with that of a perfect Sears-Haack body. Both distributions yield a
wave drag efficiency factor of approximately 2.14 (based on 80 ft 2 (7.4 m 2 ) max. area and 100 ft
(30.5 m) length).
90
80
70
Sears-Haack
Wing
Cross Sectional Area (ft 2 )
60
50
40
30
Fuselage
Vertical Tail
Horizontal Tail
20
10
0
0 200 400 600 800 1,000 1,200
Fuselage Station (inches aft datum)
Figure 5.11 - Transonic Area Distribution
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