return | |

Figure 2 depicts a plot of control column force as it relates to normal acceleration for a stable airplane. It does not represent the data for any specific airplane, but instead reflects the typical maneuvering stability characteristics of a conventional, unaugmented airplane. The left axis displays elevator column force values that increase in the up direction, while the bottom axis displays normal acceleration (g) values that increase in the right direction. The lower the slope, the less the maneuvering stability. The lower-left corner of the graph shows that a certain amount of force must be applied before the airplane starts to move from 1g flight. Called friction and breakout, this situation results from the need to overcome control column static friction and the feel system centering spring.
The plot makes it obvious that CG location and its effect on positive longitudinal static stability influence maneuvering stability. The maneuvering stability, or stick force per g, is higher at a forward CG, regardless of altitude. In other words, at any altitude, the stick force per g is higher when the CG is forward than when the CG is further aft. This has significant consequences for steep turning maneuvers. For example, to perform a level turn at 60 degrees of bank requires 2g in any airplane. While the plot shows that the airplane is still more stable at a forward CG than an aft CG, it also shows that altitude greatly affects the force required to pull the same 2g at any CG location. This plot graphically demonstrates that maneuvering at high-altitude requires less column force than it does at low altitude.
MANEUVERING STABILITY
A column force is required to maneuver longitudinally. For most airplanes, static stability attempts to maintain the airplane in 1
return to top | Boeing Home | Commercial |