Introduction To Drag Flashcards
1
Q
What are the 2 types of drag
A
- Form drag
- Skin friction drag
2
Q
Why do we get form drag?
A
Due to pressure gradient, opposite to the direction of flight
3
Q
How to we minimise form drag?
A
- Reducing frontal area
- Changing the shape of the object
4
Q
Why do we get skin friction drag?
A
- Due to shearing forces between layers of air molecules within the boundary layer
5
Q
What happens to speed of air molecules above the surface?
A
- As you go up, speed increases
- Eventually, there is a layer that moves at 99% of the free stream airspeed
6
Q
What are the types of boundary layers?
A
- Laminar boundary layer
- Turbulent boundary layer
7
Q
Properties of laminar boundary layer
A
- Shallow velocity gradient (slow increase)
- Thin layer
- Low energy; low drag
- Prone to separation (stall) due to low energy
8
Q
Properties of turbulent boundary layer
A
- Steep velocity gradient
- Thick layer
- High energy; high drag
- Resistant to separation (stall)
9
Q
Where are we likely to find a laminar boundary layer?
A
- Forwards of the max thickness due to adverse pressure gradient
- Requires smooth, clean surface
10
Q
Where are we likely to find a turbulent boundary layer?
A
- Rough or dirty surface
11
Q
How do we reduce skin friction drag?
A
- Keeping a smooth, clean, polished surface
- Occasionally repainting the A/C
