Page 208 - Understanding Flight

CH07_Anderson 7/25/01 9:00 AM Page 195

Airplane Performance 195

Maneuvering speed

Turn radius Stall speed Structural limit

Absolute minimum

Speed
Fig. 7.13. Turn radius as a function of speed.

performance turn is made at a bank angle, and thus wing loading, just
slightly less than what would cause a stall.
For a given airplane, the faster one goes the higher the wing loading
that can be achieved before stalling in a turn and thus the tighter the
turn. This is illustrated by the curve marked absolute minimum in
Figure 7.13. The slower the stall speed, the more slowly the airplane
will be going to achieve the same load factor in a turn and the tighter
the turn. So the slower the stall speed the tighter the high-
performance turn.

Structural Strength Limit
The second characteristic that limits the turn performance is the struc-
tural strength of the airplane. This sets the limit to the load on the wing
and is marked structural limit in Figure 7.13. For airplanes in the “nor-
mal” category, which applies to most general-aviation airplanes, the
load limit is 3.8. We just saw that a maximum performance turn, at
double the straight-and-level stall speed, exceeds this limit. Thus, the
pilot must either reduce the bank angle at this speed or slow down.
If we combine the stall speed limit and the maximum load factor
limit, there is a specific condition where the airplane is at both limits.
The speed at which this occurs is the maneuvering speed. At this