C07 - Introduction to Drag

Question 1

Define Drag?

Answer 1

The force on an object that resists its motion.

Question 2

Drag requires ‘____’ to overcome it?

Answer 2

Energy.

Question 3

What is the Drag Formula?

Answer 3

D = Cd x ½ p V² x S.

Question 4

True or False. Surface Friction Drag is one of the most significant sources of Drag?

Answer 4

True.

Question 5

Define Boundary Layer?

Answer 5

A layer of stationary air immediately surrounding a moving object.

Question 6

True or False. Viscosity has a significant effect to the Boundary Layer?

Answer 6

True.

Question 7

A ‘____’ is produced between each layer in a Boundary Layer?

Answer 7

Sheer Force.

Question 8

Boundary Layer is the ‘____’ between the Aircraft and Air. When speed is ‘____’ of Airflow, you no longer have the Boundary Layer (2)?

Answer 8

• Friction.

- 90%.

Question 9

The Boundary Layer is defined as the area extending from the Aircraft’s surface out to the point where the speed of the Airflow is ‘____’ of the free-stream flow?

Answer 9

99%.

Question 10

What are the two types of Boundary Layers?

Answer 10

• Laminar.

- Turbulent.

Question 11

Describe three characteristics of a Laminar Boundary Layer?

Answer 11

• Thin.
• Slippery.
• Low Energy.

Question 12

Describe three characteristics of a Turbulent Boundary Layer?

Answer 12

• Thick.
• Draggy.
• High Energy.

Question 13

In a Laminar Boundary Layer all flow is approximately ‘____’ to the surface?

Answer 13

Parallel.

Question 14

In a Turbulent Boundary Layer all flow is ‘____’ and moves in ‘____’ (2)?

Answer 14

• Chaotic.

- Several Directions.

Question 15

Name the Velocity Gradient associated with Laminar and Turbulent Boundary Layer (2)?

Answer 15

• Laminar = Shallow Velocity Gradient.

- Turbulent = Steeper Velocity Gradient.

Question 16

Which Boundary Layer creates from Skin Friction?

Answer 16

Turbulent Boundary Layer.

Question 17

What are the measurements of a Laminar and Turbulent Boundary Layer (2)?

Answer 17

• Laminar = few millimetres thick.

- Turbulent = 2cm deep.

Question 18

Define Transition Point?

Answer 18

Where the Boundary Layer changes from Laminar to Turbulent.

Question 19

Define Adverse Pressure Gradient?

Answer 19

Occurs when the Static Pressure increases the direction of the airflow.

Question 20

What relationship does the Adverse Pressure Gradient share with Transition Point?

Answer 20

The Transition Point is never aft of the Maximum Thickness Point on a Wing.

Question 21

Define Separation Point?

Answer 21

The point at which the Boundary Layer separates from the Upper Surface of the Aerofoil.

Question 22

A deep, ‘____’ forms behind the Separation Point?

Answer 22

Turbulent Wake.

Question 23

Behind the Separation Point, what happens to the direction of Flow?

Answer 23

It reverses.