Page 266 - Aircraft Stuctures for Engineering Student

8.4 Symmetric manoeuvre loads 247

Again the method of successive approximation is found to be most convenient for
the solution of Eqs (8.12), (8.13) and (8.14). There is, however, a difference to the pro-
cedure described for the steady level flight case. The engine thrust T is no longer
directly related to the drag D as the latter changes during the manoeuvre. Generally,
the thrust is regarded as remaining constant and equal to the value appropriate to
conditions before the manoeuvre began.

Example 8.3
The curves C,, a and CM,CG for a light aircraft are shown in Fig. 8.10(a). The aircraft
weight is 8000 N, its wing area 14.5 m2 and its mean chord 1.35 m. Determine the lift,
drag, tail load and forward inertia force for a symmetric manoeuvre corresponding to
n = 4.5 and a speed of 60 m/s. Assume that engine-off conditions apply and that the
air density is 1.223 kg/m2. Figure 8.10(b) shows the relevant aircraft dimensions.

As a first approximation we neglect the tail load P. Therefore, from Eq. (8.12), since
T = 0, we have
LznW (i>

0.20 20

0.15 15

0. IO 10

0.05 5

0 0

(b)
Fig. 8.10 (a) C,, cy, CMgG - C, curves for Example 8.3; (b) geometry of Example 8.3.