Stability & Control Chapter 6 Lecture 12

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

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.

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

Airplane Axes Pitch-movement about the lateral axis Roll- movement about the longitudinal axis Yaw-movement about the vertical axis

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

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

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

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

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

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

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

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

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