Stability Control Chapter 6 Lecture 12 Stability Control

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

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.