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 airplane’s 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 Rotation Stability 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 wing’s aerodynamic center, the less stable the airplane becomes
Figure 6-8 p. 166

13. Please take out a sheet of paper Include today’s date & your name
Quiz on Chapter 6
Please take out a sheet of paper
Include today’s date & your name

14. Quiz on Chapter 6
List the three major axes of airplane and define the rotation about these three axis.