C07 - Introduction to Drag Flashcards
Define Drag?
The force on an object that resists its motion.
Drag requires ‘____’ to overcome it?
Energy.
What is the Drag Formula?
D = Cd x ½ p V² x S.
True or False. Surface Friction Drag is one of the most significant sources of Drag?
True.
Define Boundary Layer?
A layer of stationary air immediately surrounding a moving object.
True or False. Viscosity has a significant effect to the Boundary Layer?
True.
A ‘____’ is produced between each layer in a Boundary Layer?
Sheer Force.
Boundary Layer is the ‘____’ between the Aircraft and Air. When speed is ‘____’ of Airflow, you no longer have the Boundary Layer (2)?
- Friction.
- 90%.
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?
99%.
What are the two types of Boundary Layers?
- Laminar.
- Turbulent.
Describe three characteristics of a Laminar Boundary Layer?
- Thin.
- Slippery.
- Low Energy.
Describe three characteristics of a Turbulent Boundary Layer?
- Thick.
- Draggy.
- High Energy.
In a Laminar Boundary Layer all flow is approximately ‘____’ to the surface?
Parallel.
In a Turbulent Boundary Layer all flow is ‘____’ and moves in ‘____’ (2)?
- Chaotic.
- Several Directions.
Name the Velocity Gradient associated with Laminar and Turbulent Boundary Layer (2)?
- Laminar = Shallow Velocity Gradient.
- Turbulent = Steeper Velocity Gradient.
Which Boundary Layer creates from Skin Friction?
Turbulent Boundary Layer.
What are the measurements of a Laminar and Turbulent Boundary Layer (2)?
- Laminar = few millimetres thick.
- Turbulent = 2cm deep.
Define Transition Point?
Where the Boundary Layer changes from Laminar to Turbulent.
Define Adverse Pressure Gradient?
Occurs when the Static Pressure increases the direction of the airflow.
What relationship does the Adverse Pressure Gradient share with Transition Point?
The Transition Point is never aft of the Maximum Thickness Point on a Wing.
Define Separation Point?
The point at which the Boundary Layer separates from the Upper Surface of the Aerofoil.
A deep, ‘____’ forms behind the Separation Point?
Turbulent Wake.
Behind the Separation Point, what happens to the direction of Flow?
It reverses.
