Page 177 - Understanding Flight

CH06_Anderson 7/25/01 8:59 AM Page 164

164 CHAPTER SIX

a b c d
Fig. 6.12. What the area rule means to fuselage design.

Fig.6.13. Two T-38 Talons with fuselage “waist.” (Photo courtesy of the U.S.Air Force.)

d has a waist to compensate for the wings, giving it the same cross-
sectional area as a. Fuselage b has higher wave drag due to the
absence of a waist. Fuselage c has the same wave drag as a and d but
at the cost of a small fuselage everywhere.
The area rule is used in the design of most modern fighter aircraft.
A notable airplane with an obvious use of the area rule is the T38
Talon, shown in Figure 6.13.
In the discussion above, a simplification was made. To illustrate the
area rule we used the cross-sectional area as seen from the front, that
is, the area of a slice perpendicular to the axis of the airplane. In
reality, the cross-sectional area must be held constant along a
Eight days after the end of WWI
slice whose angle is a function of the airplane’s design Mach
the world speed record was set
number. Illustrating this complicated result is beyond the
at 163.06 mi/h (262.36 km/h).
scope of this book.