Chapters on Atmosphere, Speed, Lift, Drag

Question 1

Amount of Aerodynamic Force created is closely linked to the?

Answer 1

Air mass flow over the object.
Greater near sea level.

Question 2

Air Density Decreases if?

Answer 2

Air Pressure Reduces.
Temperature Increases.
and
Humidity Increases.

Question 3

Air Density equals?

Answer 3

Rho, which = Pressure over Temperature

Question 4

Humidity facts?

Answer 4

Water vapour is lighter than completely dry air.
Air Density reduces when humidity increases.
Lower density reduces aircraft performance.

Question 5

Kinetic Energy

Answer 5

Ek = 1/2mv^2

Air has kinetic energy
- Exerts dynamic pressure on an aircraft

Question 6

Dynamic Pressure, q equation is?

Answer 6

q = 1/2 rho V squared 
Rho = density of air (or static pressure) 
V = True Air Speed

Question 7

Dynamic Pressure facts?

Answer 7

Increases if Air density increases.
Increases rapidly if the TAS increases (square law).
The Airspeed indicator is a Dynamic Pressure Gauge

Question 8

Total Pressure is?

Answer 8

Total Pressure = Static Pressure (rho) plus Dynamic Pressure (q)

Question 9

Calibrated Air Speed, CAS is equal to?

Answer 9

The IAS corrected for instrument error and predictable pressure errors.

Question 10

True Airspeed, TAS, is?

Answer 10

The actual speed of the aircraft through the air.

The IAS can exceed TAS when air Density is greater than 1.225kg per metre squared, such as when,
Close to the surface.
High pressure,
Cold day.

Question 11

Equation of Continuity key fact?

Answer 11

The Air mass flow entering a stream tube must remain the same at all points along it.

Question 12

Bernoulli’s Theorem key fact?

Answer 12

The sum of the static pressure plus the kinetic energy = Constant.

Question 13

Total Pressure = ?

Answer 13

Static Pressure plus Dynamic Pressure.

Question 14

Venturi Effect is?

Answer 14

When airflow lines converge together, speed increases. When airflow lines diverge, speed reduces.

Question 15

Total Pressure = ?

Answer 15

= Static Pressure plus Dynamic Pressure.
which,
= Static Pressure plus half rho V squared.

Question 16

4 Types of Aerofoil?

Answer 16

Symmetrical.
Positive Camber.
Negative Camber .
Bioconvex.

Question 17

Increasing the AoA on a Cambered Aerofoil leads to?

Answer 17

Centre of Pressure moves forward.
Stagnation points moves round and down on the underside.
Peak Suction Point Moves forward.
Drag increases, this is form drag.

Question 18

Effect of increasing AoA on Symmetrical Aerofoil are?

Answer 18

Centre of Pressure does not move.

Question 19

Stagnation Point is ?

Answer 19

The point at which the Dynamic Pressure = zero on the surface of the Aerofoil.

Question 20

Lift facts.

Answer 20

Lift is perpendicular to the relative airflow.
whereas,
Drag is parallel and in the same direction as the relative airflow.

Question 21

Aerodynamic Force Coefficient equation is?

Answer 21

Aerodynamic force = q times S times Cf.

Where q = dynamic Pressure of airflow, which is half rho V squared.
S = surface area of the Aerofoil.
Cf = Coefficient of Aerodynamic Force.

Question 22

Lift Equation is?

Answer 22

L = q times S times C L, ie. q S Cl .
where,

q = Dynamic Pressure of airflow (KE),
which equals half rho V squared ie. 1/2 rho V^2
S = Surface area of the Aerofoil.
C l = Coefficient of lift, a dimensionless number used to balance equation.

In level flight, lift force = weight force.

Question 23

Coefficient of Lift is?

Answer 23

The Natural lifting ability of an Aerofoil for a given airflow speed and Aerofoil surface area
It measures the ability of a wing to produce lift.

What impacts the coefficient of lift?

The angle of attack.
Thickness of the Aerofoil.
The Camber of the Aerofoil.

Question 24

Effect of Angle of Attack on a Symmetrical Wing?

Answer 24

As the pressure difference, which is perpendicular to the airflow, increases, so too must Coefficient of lift.

At 0 degrees, the C L = 0 and the Amount of lift = 0.

As the angle of attack increases so does the coefficient of lift .

The Coefficient of Pressure, CoP, is always 25% down the length of the wing in sub supersonic aircraft.

Question 25

The Effect of Aerofoil Thickness on Coefficient of Lift, C L?

Answer 25

As the thickness increases, the C L MAX increases.
The lifting ability is greater for a thicker aerofoil.

The Stalling angle of attack increases.

Thinner designs are better for high speed flights as there is less drag, but they have to perform a faster landing.

Question 26

The Effects of Camber?

Answer 26

A more cambered wing will have:
More lift for a given surface area.
A higher C L MAX.
Maybe a slightly increases Stalling Angle of Attack.

Question 27

Effect of Trailing Edge Flat on the Coefficient of Lift, C L?

Answer 27

A trailing edge flap increases the camber of the aerofoil for a given airspeed.

It Increases the Coefficient of Lift, C L.
But also increases the Coefficient of drag, C d.

The Lift to drag ratio decreases.

Means you can land slower.
The Stalling angle of attack, AoA, decreases.

Question 28

Lift in Level Flight?

Answer 28

The Lift force equal and opposite to the weight force.

Question 29

Coefficient of Lift, C l, and angle of attack, AoA, for Aerofoils. Facts.

Answer 29

High Speed Aerofoils are;
- Thin.
- Sharp.
- Less Cambered.
- Have a Lower Coefficient of Lift Max, C l MAX,
and a lower critical angle of attack, AoA.

Slow Speed Aerofoils are:

• Thicker.
• Have an Increased Camber.
• Have Rounder leading edges.
• Higher C l MAX
• Higher critical AoA.

Question 30

Load Factor equations.

Answer 30

For straight and level flight;
Load Factor = Lift over Weight.

In a turn:

Load Factor = 1 over cosine of the angle of bank, AoB.

Question 31

Stall Speed in a turn?

Answer 31

= Stalling speed at 1 g x times the square root of the Load Factor in a turn.

Question 32

2 Types of Profile Drag?

Answer 32

Form Drag.

Skin Friction Drag.

Neither are associated with the production of lift.

Question 33

Drag Equation is?

Answer 33

Drag = q times S times Cd ie. qSCd

As q = half rho V squared, ie. 1/2rhoV^2,

Drag = half rho V squared times S times C d, ie. 1/2 rho v^2 S Cd

D is proportional to,

the Indicate Air Speed squared

the Surface Area of the wing, S, and

the Coefficient of Drag, Cd.

Question 34

Coefficient of Drag =?

Answer 34

A measure of drag per unit area and unit dynamic pressure.

Question 35

Two Types of Boundary are?

Answer 35

Laminar Flow Boundary,

and

Turbulent Flow Boundary.

Question 36

The Laminar Boundary is?

Answer 36

1-2mm Deep.
Up until transition point.

CANT EXIST PAST THE POINT OF MAX THICKNESS.

Question 37

Turbulent Boundary is?

Answer 37

After the transition point.
1-2cm thick.

Flow moves in many directions.

Question 38

Adverse Pressure Gradient is?

Answer 38

Because air flows from high Pressure To Low Pressure.
Air from the underside of the wing where there is high pressure, wants to get on top of the wing where there is low static pressure.
It does this by coming up from under the trailing edge as there is an adverse pressure gradient, and working its way up to the separation point.

Question 39

Separation Point is?

Answer 39

The point at which the airflow separates from the aerofoil.

As angle of attack increases, the separation point, SP, moves forward.

As angle of attack decreases, the SP moves aft.

Question 40

Laminar boundary layer is?

Answer 40

1-2mm thick.

Prone to separation.

Question 41

Turbulent Boundary is?

Answer 41

Relatively deep, 1-2cm.
Flow is in many directions.