Page 209 - Understanding Flight

CH07_Anderson 7/25/01 9:01 AM Page 196

196 CHAPTER SEVEN

speed the wing will stall just before it exceeds the rated structural
limits. So in the normal category the tightest turn possible would be
made at 1.95 (the square root of 3.8) times the stall speed of the
airplane and at a bank angle of about 73.5 degrees. It would be an
uncomfortable turn with such a high g force.

The maneuvering speed of an airplane is the maximum speed
for an airplane to use during a maneuver or in turbulent air. As
discussed above, at this speed the wing will stall at just the
maximum rated load factor, and thus not exceed it. Since the
maximum load factor at stall is proportional to the speed
squared, the maneuvering speed of an airplane is just the stall
speed times the square root of the maximum load factor.
We know that the stall speed of an airplane increases with
load.Therefore, so does the maneuvering speed.Thus a more
heavily loaded airplane can safely fly faster in a storm than if it
were lightly loaded. It is important to note that the
maneuvering speed is an indicated airspeed.Thus the true
airspeed at the maneuvering speed increases with altitude.

Propulsive Power Limit
Now let us look at the importance of the propulsive power that is
available. As the airplane goes into a steep bank, the load on the wing
increases and the induced power and induced drag increase as the
load squared. So an airplane in a 4g turn experiences an increase in
induced power of 16 times. Thus the available propulsive
The radar return on the B-2
power may not be sufficient for the theoretical tightest turn.
Bomber and F-117 Stealth Fighter
When this condition is reached, the maximum performance
are roughly the same as an
turn is no longer at the maneuvering speed.
eagle.
Power available for both jet and propeller / piston engines
decreases with altitude and the induced power for straight-
and-level flight increases. There is also an increase in stall speed with
altitude. At some point, an airplane that is trying to achieve a
maximum performance turn becomes power-limited. Rather than turn
at the maneuvering speed, the minimum-radius turn will occur at a
somewhat lower speed. This will result in a load factor less than the