Chapter 7 - Drag

Question 1

Give the x2 types of drag in 2D

Answer 1

Form - Px differential

Skin friction - Viscosity of the air over the skin

Question 2

Give the formula for drag

Answer 2

D = 1/2PV^2 CD

Question 3

Give the formula for CD

Answer 3

CD = (D/IAS^2)
—————
S

Question 4

How is the boundary layer slowed

Answer 4

By Skin Friction

Question 5

Surface friction drag is

Answer 5

Molecules trapped to the surface of the a/c and carrying them forward. The molecules above also get trapped slightly because the air viscous

Question 6

How is the boundary layer defined

Answer 6

A layer of air that extends out 99% to the free stream flow

Question 7

A laminar boundary layer is

Answer 7

Thin, slippery and low energy

Question 8

A turbulent boundary layer is

Answer 8

Thick, Draggy and high energy

Question 9

What is the point when laminar turns to turbulent called

Answer 9

Transition point

Question 10

2 mm depth
prone to seperation
Little skin friction
Is which boundary layer

Answer 10

Liminar boundary

Question 11

Turbulent Boundary layer has which velocity gradient

Answer 11

Steep - because its thicker and mixing more

Question 12

Low Reynolds number means which force is dominant and applies where

Answer 12

Viscous force is dominant at LE / laminar boundary layer

Question 13

High Reynolds number means which force is dominant and applies where

Answer 13

inertial forces is dominant at the TE / turbulent boundary layer

Question 14

At what point can there be no more laminar flow

Answer 14

Max thickness

Question 15

Why does air try to come round the aerofoil

Answer 15

it always wants to travel from high to low

Question 16

At which point does the air leave the aerofoil and because of what

Answer 16

the separation point because of the adverse pressure gradient

Question 17

At which speed is the adverse pressure gradient greater

Answer 17

slow