ACFT - Drag

Question 1

What is Drag? (1)

Answer 1

Air resistance experienced by the aircraft as it moves relative to the air
(Opposes Thrust)

Question 2

“The lower the Drag, the less the _____ required to balance it” (1)

Answer 2

Thrust

Question 3

What are the 2 main types of Drag? (2)

Answer 3

1. Induced Drag
2. Parasite Drag

Question 4

What is Induced Drag? (3)

Answer 4

1. Unavoidable by-product of lift and increases as the angle of attack increases (biproduct of lift)
2. Manifested as vortices at the trailing edge of the wing and especially at the wingtips
3. Created when a wing generates lift

Question 5

What is Parasite Drag? (1)

Answer 5

A type of aerodynamic drag that acts on any object when the object is moving through a fluid

Question 6

What are the 2 types of Parasite Drag? (2)

Answer 6

1. Profile Drag
2. Interference Drag

Question 7

What are the 2 types of Profile Drag? (2)

Answer 7

1. Skin friction
2. Form drag

Question 8

What is Skin friction drag? (5)

Answer 8

1. The surface area of the aircraft
2. Whether the boundary layer airflow near the surface is laminar or turbulent
3. Roughness on a surface (including ice) will increase skin friction
4. An increase in airspeed increases skin friction drag
5. An increase in aerofoil thickness increases skin friction drag from the wing

Question 9

What is Form drag? (2)

Answer 9

1. Results when the airflow separates from the surface of the aerofoil
2. The turbulent wake formed, increases drag

Question 10

What is Interference drag? (1)

Answer 10

Occurs when a substantial change of airflow direction occurs over an airframe

Question 11

How is Interference drag created? (1)

Answer 11

• In the landing configuration, with gear and flaps deployed, more skin friction, form drag and interference drag is generated
• Disturbed airflow interacts with the vortices and disperse them to an extent, meaning induced drag is reduced (slightly)

Question 12

When is Induced drag at its highest? (1)

Answer 12

When an aircraft is flying slowly, at a heavy weight and in a ‘clean’ configuration, such as in the early stages of climb

Question 13

Why is Induced drag important? (5)

Answer 13

• Extremely hazardous to aircraft
• Vortices drift with the prevailing wind and are more persistent in calm conditions
• The cause of a significant number of fatalities
• Vortices have been beyond the following aircraft’s ability to counter them
• Pilot reaction have caused A/C break-up

Question 14

How can induced drag be reduced? (2)

Answer 14

• Aspect ratio wing - Narrow wing is less affected and therefore more efficient
• Winglets or Sharklets (Wingtips)