8.4 - Flight Stability and Dynamics Flashcards
What is static Stability?
The inherent ability of an object to return to its original status or condition of equilibrium (After disturbed from that position or condition) is called static equilibrium
What is dynamic stability?
While static stability deals with the tendency of a displaced body to return to equilibrium, dynamic stability deals with the resulting motion and time.
If an object is disturbed from equilivrium, the time history of the resulting motion defines the dynamic stability of the object.
Explain positive, negative and neutral dynamic stability
An object demonstrates positive dynamic stability if the amplitude of motion decreases with time.
If the amplitude of motion increases with time, the object is said to possess dynamic instability.
If the amplitude of motion or oscillation is not dampened, that does mean remains constant, then the objecct shows neutral dynamic stability.
Longitudinal stability/control about the …
lateral axis
Lateral stability/control about the …
longitudinal axis
Directional stability about the …
vertical (normal) axis
What effects longitudinal stability and how is it maintained on an aircraft?
Position of Centre of Gravity - must never be too far back or nose up tendency. Control: Aircraft loading
The pitching moment on the wings - Aircraft disturbed nose up will cause AOA to increase. Centre of Pressure (Cp) will move forward creating nose up tendency. Control: Aircraft design
The horizontal stabiliser - If nose up, AOA on horizontal stabiliser will alter. This is a restoring moment and will depend on: 1. Area of stabiliser and 2. Length of the fuselage (law of lever)
What is dihedral and how does it affect lateral stability?
'’Lateral stability about the longitudinal axis’’
The shape of the wing causes it to return to wings level flight after it has been disturbed.
It is considered laterally stable, if too much dihrdral angle is used, the plane may become so stable that intentional rolling is not even possible.
Used for less manoeuvrable planes
What methods are used to achieve lateral stability?
(Lateral stability about the longitudinal axis)
Dihedral Angle
Sweepback
(Keel Effect)
High Wings (Wings above Cg)
How does Anhedral affect lateral stability?
Anhedral wings will make the aircraft laterally unstable to improve manouvrability (fighters etc)
Explain Dutch roll
Occurs mostly on swept wing aircraft
due to Lateral stability and weak Directional stability
Aircraft turns, adverse yaw and then sideslips.
Correcting actions of wings and rudder cause it to keep in this cycle
Solved with rudder or Rudder Damper
Yaw and Roll
How is active directional stability carried out?
Active stability is to combat ‘dutch roll’
Excessive work would be put on pilot if they had to correct all instabilities.
Therefore an automatic damping system is used.
