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CH07_Anderson 7/25/01 9:00 AM Page 193

Airplane Performance 193

wings and the passengers only 40 percent larger than in straight-and-
level flight. That is, the load factor is 1.4. The induced power and
induced drag will be increased to about twice their values in straight-
and-level flight. The pilot has two choices to compensate for the
increased induced power, increase the power available or decrease the
parasitic power to compensate. The former implies adding more
engine power, the latter reducing the speed and increasing the angle
of attack. For most general-aviation pilots a turn is entered at constant
power, the pilot adjusts the angle of attack with the elevator, and the
airplane loses speed.
In Table 7.1 we look at the performance of an airplane making a
180-degree turn, in a 45-degree bank, at three different speeds. For a
given bank the radius of the turn increases as the speed squared while
the time to make the turn increases as the speed. For all three speeds
in the table the forces felt by the passengers will be the same,
though the turns will be quite different. This is shown in The SR-71 takes 8 minutes to
Figure 7.12, which illustrates turns at three speeds for an complete a 180-degree turn at
airplane in a 45-degree bank for 20 seconds. The effect of cruise.
speed on turn performance is quite dramatic.

Table 7.1 Turn Performance for 45 Degree Bank at Three Different Speeds

Speed mi/h (km/h) 140 (224) 280 (450) 560 (900)

Radius of turn, mile (km) 0.25 (388) 1 (1.6) 3.9 (6.2)

Time to make 180 degrees 20 40 80

560 mi/h
280 mi/h

140 mi/h

Fig. 7.12. Turns with a 45-degree bank for 20 seconds
for three speeds.