Aircraft Fundamentals

Question 1

What control surface is used to change the pitch of the aircraft?

Answer 1

Elevators (movable part of the tailplane)

Question 2

What is the main purpose of the tailplane on an aircraft?

Answer 2

Pitch stability

Question 3

By what aerodynamic mechanism do control surfaces change the orientation of an aircraft/

Answer 3

Control is achieved by changing the lift on the relative surface to create a moment about the appropriate axis with respect to the centre of gravity

Question 4

What control surface controls yaw motion?

Answer 4

Rudder (Mounted on trailing edge of fin)

Question 5

How is roll achieved on an aircraft?

Answer 5

Rotation about longitudinal axis controlled by differential deflections of ailerons

Question 6

In what direction does the lift force act?

Answer 6

Right angle to direction of flight

Question 7

What are the 4 primary forces acting on an aircraft?

Answer 7

Lift, Weight, Thrust, Drag

Question 8

Define the angle of attack of an aerofoil

Answer 8

Angle between chord line and direction of airflow

Question 9

What distance on a aerofoil corresponds to the chord length?

Answer 9

Distance of the straight-line between the leading edge and trailing edge

Question 10

Define what is meant by a camber or the mean line of an airfoil?

Answer 10

Line that is always midway between the upper and lower surfaces of the wing

Question 11

In words, what is the equation for the aspect ratio of the wing?

Answer 11

Span divided by mean chord

Question 12

Does a short stubby wing have low or high aspect ratio?

Answer 12

Low

Question 13

What is sideslip?

Answer 13

Aircraft moving in a sideways direction as well as into the oncoming airflow

Question 14

Define the true airspeed of an aircraft?

Answer 14

Speed relative to the air

Question 15

Define the equivalent airspeed of an aircraft

Answer 15

airspeed at sea level that would give the same dynamic pressure as the true airspeed at the actual altitude the aircraft is flying

Question 16

What is free stream

Answer 16

The air far upstream of the aircraft which has not yet been disturbed by the aircraft

Question 17

What is the general equation for lift? Define the meaning of each term in the equation.

Answer 17

0.5rhoV^2SCl

Rho - Air density
V - True Airspeed
S - Wing surface area
Cl - Coefficient of lift

Question 18

What is bernoullis equation? Define each term

Answer 18

0.5Rhov^2 + p = po

Rho - Airdensity
V - True airspeed

p - static Pressure
po = total pressure

Question 19

Is the actual lift force produced by the difference in static pressure or dynamic pressure on a aerofoil?

Answer 19

Static Pressure

Question 20

For low angles of attack what is the relationship between lift coefficient and angle of attack for a general airfoil?

Answer 20

linear relationship

Question 21

How does camber of the airfoil affect the relationship between lift coefficient and angle of attack?

Answer 21

camber increases the coefficient of lift for a corresponding angle of attack.

Question 22

How is a stall reflected in the curve of lift coefficient versus angle of attack?

Answer 22

Sudden drop in Cl

Question 23

What is the physical mechanism that results in a boundary layer?

Answer 23

Air flowing past a surface tries to stick to it and speeds up as it gets further away from the surface.

Question 24

Briefly describe the behaviour of air flowing over a wing in a laminar boundary layer?

Answer 24

Air flows smoothly in a streamlined manner

Question 25

What is the equation of reynolds number? Define all the terms

Answer 25

rhovl/mu

rho - air density
v - true airspeed
l - a characteristic length
mu - dynamic viscosity of air

Question 26

Why is the reynolds number important?

Answer 26

Used to characterise and predict airflow. Predict transition from laminar to turbulent flow

Question 27

In terms of airflow over a wing, which type of airflow corresponds to stall?

Answer 27

turbulent

Question 28

How do flaps temporarily increase the lift on a wing?

Answer 28

Increases the camber on the wing which increases the coefficient of lift curve

Question 29

What is the general equation for drag? define meaning of each term

Answer 29

0.5rhov^2scd

rho - air density
v - true airspeed
s - wing surface area
cd - coefficient of drag

Question 30

what are the 3 types of parasitic drag?

Answer 30

Form drag
Skin friction drag
Interference drag

Question 31

What is the commonly used relationship between the drag coefficient and the lift coefficient also called the drag polar.

Answer 31

cd=a+bcl^2

Question 32

what is a shockwave?

Answer 32

abrupt changes in airspeed, temperature and pressure

Question 33

Define mach number

Answer 33

true airspeed/ speed of sound

Question 34

What values of mach number correspond to transonic flow and explain the meaning of transonic flow

Answer 34

0.7 < 𝑀 < 1.4 – transonic flow, compressibility becomes important, some locally supersonic airflow around the aircraft

Question 35

What is the purpose of swept wing?

Answer 35

reduce the effect of high speed flow