Stability

Question 1

Static stability describes the -

Answer 1

immediate, or initial, tendency of a body following a disturbance

Question 2

Dynamic stability describes a body’s -

Answer 2

reaction to its static stability and is a function of both time and displacement

Question 3

an aeroplane which is displaced from equilibrium and then returns to its original position, without overshooting its original point of equilibrium is -

Answer 3

both statically and dynamically stable

Question 4

If the aeroplane is displaced a greater distance the return to equilibrium will be delayed as it overshoots its original position by decreasing oscillations, this effect is called?

Answer 4

damped phugoid

Question 5

The effectiveness of the download of the tailplane depends upon:

1. The ___ of the tailplane
2. The distance between the tailplane’s _____ of _______ and the aeroplane’s ____ of _____
3. The _____ of the tailplane
4. The _____ ratio of the tailplane

Answer 5

1. The size of the tailplane
2. The distance between the tailplane’s centre of pressure and the aeroplane’s centre of gravity
3. The shape of the tailplane
4. The aspect ratio of the tailplane

Question 6

If the centre of gravity is located ahead of the centre of pressure, ensuring that a nose down moment is created by the two forces, this is referred to as -

Answer 6

positive static longitudinal stability

Question 7

If the centre of gravity is directly below the centre of pressure there would be no pitching moments about the centre of gravity, this is referred to as -

Answer 7

neutral static longitudinal stability

Question 8

Regarding CG:

The effectiveness of the tailplane is determined by -

Answer 8

The distance of the tailplane’s centre of pressure and aeroplane’s centre of gravity.

Question 9

If the centre of gravity is behind the centre of pressure not only is aeroplane unstable, possessing an undesirable nose up pitching tendency, but the effectiveness of the tailplane is reduced due to the shorter moment arm. This is referred to as?

Answer 9

Negative static longitudinal stability

Question 10

As the angle of attack is increased the centre of pressure moves forward. This in itself is an -

Answer 10

unstable movement because as it moves closer to the centre of gravity it reduces the nose down moment provided by lift and weight.

Question 11

The nose down tendency of a static longitudinal stable aircraft is counteracted by the -

Answer 11

the tailplane

Question 12

The tailplane is usually mounted at a smaller angle of incidence than that of the mainplane, an arrangement which is referred to as -

Answer 12

Longitudinal dihedral

Question 13

Longitudinal dihedral provides -

Answer 13

Dynamic Longitudinal stability

Question 14

Other than lateral dihedral:

Another design feature used to provide lateral stability places ____ area of the _______ and fin _____ the centre of gravity of the aeroplane. During sideslip the reaction of this surface area with the resultant airflow acts as a ________ force.

Answer 14

Another design feature used to provide lateral stability places large area of the fuselage and fin above the centre of gravity of the aeroplane. During sideslip the reaction of this surface area with the resultant airflow acts as a correcting force.

Question 15

To compensate for the too much lateral stability provided by the high fin and keel. The method is -

Answer 15

Anhedral of the wings

Question 16

Sweepback offers -

Answer 16

increase lateral stability

Question 17

inboard trailing edge flaps suffer from -

Answer 17

decrease lateral stability

Question 18

Dutch roll describes a condition in which -

Answer 18

lateral stability is greater that its directional stability

Question 19

Spiral instability(roll followed by yaw) describes a condition in which -

Answer 19

the directional stability of an aeroplane is greater than its lateral stability.

Question 20

Sensitivity for spiral dive will occur when:

Answer 20

The static directional stability is positive and the static lateral stability is relatively weak

Question 21

The tendency to Dutch Roll increases when:

Answer 21

when lateral stability is strong and directional stability is relatively weak

Question 22

The ‘short period mode’ is an:

Answer 22

Oscillation about the lateral axis