Stability

1
Stability Control

• Chapter 6
• Lecture 12

2
Stability Control

• Trim- balance, means that no net moment exists
  that tends to move the airplane out of this
  condition.
• We think of trim as being a trim tab on a
  stabilizer
• Trim in the aerodynamic sense means a lack of
  pitching moment achieved by pilot muscle or trim
  tab

3
Stability

• Stability refers to the airplanes tendency to
  return to the trimmed condition after a
  disturbance.
• Stability was studied by Cayley, Chanute,
  Lilienthal, Langley, the Wright Brothers.
• Wright brothers devised the canard configuration.

4
The Meaning of Stability

• Stability in general
• Figure 6-2
• Stable ball tends to return to equilibrium
  position in the bottom of saucer
• Unstable ball rolls away if displaced from
  equilibrium on inverted saucer
• Pilots experience instability in air masses in
  the form of turbulence

5
Airplane Axes

• Pitch-movement about the lateral axis
• Roll- movement about the longitudinal axis
• Yaw-movement about the vertical axis

6
Axis of RotationStability about the three axis

• Longitudinal Stability is stability in pitch
• Lateral Stability is stability in roll
• Directional Stability is stability in yaw
• Figure 6-3 p. 160

7
Longitudinal Stability

• The initial tendency for the airplane to restore
  itself to equilibrium after a pitch disturbance
  is static longitudinal stability.
• Equilibrium for an airplane is referred to as the
  trim condition.
• Figure 6-4 p. 161

8
Degrees of Stability

• Different airplanes vary in their degrees of
  stability
• Transport Aircraft vs. Training Aircraft (DSU)
• Figure 6-5 p. 162

9
Dynamic Stability

• Oscillation is movement from one side of the
  equilibrium point to the other
• The airplane will display an oscillatory motion
  after a disturbance
• How the airplane behaves over a period of time
  after the disturbance is the dynamic stability

10
Figure 6-6 p. 164

• Pitch angle vs. time for a dynamically stable
  airplane a, a dynamically unstable airplane
  b, and a neutrally stable airplane c
• Long Period- time to damp to half amplitude/ low
  period frequency
• Short Period-high frequency oscillation that
  occur after the long period

11
Center of Gravity Effects

• The center of gravity CG is the center of mass
  of the overall airplane
• The point were all of the weight can be
  considered to be concentrated
• Figure 6-7 p. 165

12
Center of Gravity

• Aft CG vs. Forward CG
• The farther aft the CG is located from the wings
  aerodynamic center, the less stable the airplane
  becomes
• Figure 6-8 p. 166

13
Quiz on Chapter 6

• Please take out a sheet of paper
• Include todays date your name

14
Quiz on Chapter 6

• List the three major axes of airplane and define
  the rotation about these three axis.