Transcript Stability & Control - Delta State University

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.