L12 - Aircraft Dynamic Lateral and Directional Stability

Question 1

What are the three dynamic modes associated with lateral and directional stability?

Answer 1

Roll subsidence
Dutch Roll
Spiral

Question 2

What is roll subsidence?

Answer 2

normal roll to counter disturbance.

Question 3

What is dutch roll?

Answer 3

A circular oscillation consisting of yaw coupled with roll and sideslip

Question 4

What is the typical period for dutch roll?

Answer 4

3 to 15 seconds

Question 5

What causes dutch roll?

Answer 5

Turbulence, swept wings, pilot interaction, control system

Question 6

What is the spiral mode?

Answer 6

As it sounds, non oscillatory motion where aircraft enters spiral that tightens.

Question 7

What is the time period of spiral mode?

Answer 7

Slow, can be around 100 seconds, depends on size of aircraft.

Question 8

What can reduce the risk of spiral mode?

Answer 8

Dihedral and dorsal fin.

Question 9

Which roots are associated with each mode?

Answer 9

Small negative magnitude - Spiral Mode
Largeer negative magnitude - Roll subsidence
Imaginary values - Dutch roll

Question 10

What are the 8 different dynamic modes?

Answer 10

2 Phugoid
2 short oscillations
1 roll mode
1 spiral mode
2 dutch roll mode