Aircraft stability Flashcards
What is stability
Stability is the ability of an aircraft to return to its trimmed path after being disturbed without the aid of the pilot’s control.
What are the four forces acting on an aircraft
Thrust
Drag
Weight
Lift
The vertical axis proves what type of stability
Directional
The lateral axis provides what type of stability
Longitudinal
The longitudinal axis provides what type of stability
Lateral
What is directional stability
Provided by the Fin and Aft Keel surface.
A change in aircraft direction produces an
increase or decrease in Fin Lift due, to the
change in Angle of Attack. The Fins
effectiveness is governed by its surface area
and distance from the Centre of Gravity
(pendulum effect),
What is longitudinal stability
Provided by the Taiplane.
What are the four design features that provide lateral stability
Dihedral angle
Sweepback
Keel surface
High Wing Low Centre of Gravity
what is dihedral angle
Dihedral Angle is the angle between the wings and the aircraft’s Lateral Datum Line
If the wings go up or down
what is sweepback
During Sideslip the new Relative Airflow passing over
the Lower Wing produces greater Lift than the High
wing due to the shorter effective Chord and greater
effective Camber. It also presents a greater effective
span to the ainflow.
What is keel surface
During side slip the tail fin and rudder experience a force
exerted on them by the airflow This force, being above
the Centre of Gravity, tends to right the aircraft.
What is High wing/Low centre of gravity
(Sometimes known as Pendulum Stability)
As weight always acts vertically downwards, during a
sideslip the weight acting through the Centre of Gravity
tends to align the Centre of Lift. This creates a
correcting moment.
What is anhedral
Some aircraft with swept wings are too stable and need to
be destabilised. Anhedral is one method used to do this
i.e. to reduce Dutch roll, where lateral stability
overcomes directional stability.
What is Negative Dynamic Stability
Negative Dynamic Stability - aircraft is disturbed from its
trimmed path, oscillations increase further away from its
trimmed path.
What is Neutral Dynamic Stability
Neutral Dynamic Stability - aircraft is disturbed away from
its trimmed path, oscillations continue at the same rate as the
original disturbance around its trimmed path.