8.4 Flashcards
What 2 types of stability are there?
Static stability
Dynamic stability
What is positive static stability?
Tendency to return to the equilibrium.
What is negative static stability?
Tendency to continue in displacement direction.
Why is dynamic stability?
How the continuous motion of body varies over time.
What is undamped oscillation?
No friction forces so something forever oscillating after initial displacement.
What is negative dynamic stability?
Another force acting on the ball which is stronger than friction, such as wind.
If a pivot point is above the centre of gravity, what is the static stability?
Positive.
How does distance affect the stability between pivot point and centre of gravity?
Longer the distance, the greater the stability.
What dynamic stability is usually required in aircraft design?
Positive dynamic stability.
What are the three aircraft axes?
Longitudinal
Vertical
Lateral
Why does lateral stability refer to?
Roll movement around longitudinal axis
What does directional stability refer to?
Yaw movement around vertical axis.
What does longitudinal stability refer to?
Pitch movement around the lateral axis.
When does the aircraft have positive static stability?
When sum of all forces and all moments is equal to 0.
What axis is a weathercock stability around?
Vertical axis.
What does the directional stability depend on?
Fin of aircraft, also called vertical stabiliser.
And sweep back of wing.
How does sweepback of a wing provide directional stability?
When aircraft deflected from original path, the forward going wing presents larger frontal area to airflow than other wing.
Why is lateral stability mainly determined by?
Wing
More specifically angle of attack
What do dihedral angles help to restore?
Level flight.
What is a side-slip?
Aircraft glides to one side without changing flight direction.
What does a side skip cause?
A flow of air in the opposite direction to the relative wind
(Strikes down going wing at greater angle than up going wing)
(More lift on down going wing)
Where is the side slip angle?
Angle between the aircraft centreline and the side slip direction.
(Wing in side slip direction= more lift)
What is a Dutch roll?
Lateral directional oscillation.
Where does a Dutch roll tend to exist?
Where there is greater effect on the lateral stability than on the directional stability.
What aircraft is the Dutch roll a problem on?
Aircraft with swept wings
How is the problem of Dutch roll reduced?
Reducing sweep angle of wings and improving directional stability.
What is used to improve directional stability on aircraft?
Yaw damping System.
What nose rotation is there if a gust hits the upper front part of the aircraft?
Nose down rotation.
When is positive longitudinal stability achieved?
When centre of gravity as a resultant of all aircraft weights is forward of the aerodynamic centre.
(Neutral point)
