8.4

Question 1

What 2 types of stability are there?

Answer 1

Static stability

Dynamic stability

Question 2

What is positive static stability?

Answer 2

Tendency to return to the equilibrium.

Question 3

What is negative static stability?

Answer 3

Tendency to continue in displacement direction.

Question 4

Why is dynamic stability?

Answer 4

How the continuous motion of body varies over time.

Question 5

What is undamped oscillation?

Answer 5

No friction forces so something forever oscillating after initial displacement.

Question 6

What is negative dynamic stability?

Answer 6

Another force acting on the ball which is stronger than friction, such as wind.

Question 7

If a pivot point is above the centre of gravity, what is the static stability?

Answer 7

Positive.

Question 8

How does distance affect the stability between pivot point and centre of gravity?

Answer 8

Longer the distance, the greater the stability.

Question 9

What dynamic stability is usually required in aircraft design?

Answer 9

Positive dynamic stability.

Question 10

What are the three aircraft axes?

Answer 10

Longitudinal
Vertical
Lateral

Question 11

Why does lateral stability refer to?

Answer 11

Roll movement around longitudinal axis

Question 12

What does directional stability refer to?

Answer 12

Yaw movement around vertical axis.

Question 13

What does longitudinal stability refer to?

Answer 13

Pitch movement around the lateral axis.

Question 14

When does the aircraft have positive static stability?

Answer 14

When sum of all forces and all moments is equal to 0.

Question 15

What axis is a weathercock stability around?

Answer 15

Vertical axis.

Question 16

What does the directional stability depend on?

Answer 16

Fin of aircraft, also called vertical stabiliser.

And sweep back of wing.

Question 17

How does sweepback of a wing provide directional stability?

Answer 17

When aircraft deflected from original path, the forward going wing presents larger frontal area to airflow than other wing.

Question 18

Why is lateral stability mainly determined by?

Answer 18

Wing

More specifically angle of attack

Question 19

What do dihedral angles help to restore?

Answer 19

Level flight.

Question 20

What is a side-slip?

Answer 20

Aircraft glides to one side without changing flight direction.

Question 21

What does a side skip cause?

Answer 21

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)

Question 22

Where is the side slip angle?

Answer 22

Angle between the aircraft centreline and the side slip direction.

(Wing in side slip direction= more lift)

Question 23

What is a Dutch roll?

Answer 23

Lateral directional oscillation.

Question 24

Where does a Dutch roll tend to exist?

Answer 24

Where there is greater effect on the lateral stability than on the directional stability.

Question 25

What aircraft is the Dutch roll a problem on?

Answer 25

Aircraft with swept wings

Question 26

How is the problem of Dutch roll reduced?

Answer 26

Reducing sweep angle of wings and improving directional stability.

Question 27

What is used to improve directional stability on aircraft?

Answer 27

Yaw damping System.

Question 28

What nose rotation is there if a gust hits the upper front part of the aircraft?

Answer 28

Nose down rotation.

Question 29

When is positive longitudinal stability achieved?

Answer 29

When centre of gravity as a resultant of all aircraft weights is forward of the aerodynamic centre.

(Neutral point)