Past Paper Theory Questions

Question 1

True/False:
The phenomenon of wave drag occurs when the aeroplane is exposed to headwind gusts at regular intervals

Answer 1

False
Wave drag is caused by a sudden separation of flow on the upper surface of the aerofoil. This occurs when the local velocity becomes greater than Mach 1

Question 2

True/False
The generation of a rolling moment following a sideslip pertubation is known as the dihedral effect

Answer 2

True
When an aircraft experiences side-slip (to the right for example), the right wing will generate more lift than the left, and vice versa. This side-slip generates a rolling moment that acts away from the side-slip helping to restore the aircraft to a ‘neutral’ position

Question 3

True/False
The primary purpose of wing sweep is to reduce induced drag

Answer 3

False
The primary purpose of wing sweep is to shift the critical mach number closer to one and to delay the onset of wave drag

Question 4

True/False
The flight speed that minimises drag is larger than the flight speed which minimises power required

Answer 4

True
Look at the graph on: ‘Important Aeroplane Velocities’, slide 2

Question 5

True/False
In order to maximise the angular velocity in a level turn, an aeroplane needs to be flown close to the stall effect

Answer 5

True
Eq for ωmax uses nmax
Refer to ‘Turning Flight’, Slide 3

Question 6

True/False
Adverse yaw can be corrected by rudder deflection

Answer 6

True
The rudder as a control surface controls the yaw (the side to side motion) of the aircraft

Question 7

True/False
The minimum glide angle of an aeroplane is independent of the air density

Answer 7

True
The minimum glide angle, γ remains constant while the vsink increases as altitude decreases.
‘Straight and Unaccelerated Gliding’, Slide 2

Question 8

True/False
Minimum thrust required by a jet aeroplane at higher altitude is equal to the minimum thrust required at sea level

Answer 8

True
Thrust required is independent of altitude however thrust available decreases as altitude increases.
SLUF, slide 2

Question 9

True/False
The runway length for take-off is approximately proportional to the square of the aeroplane weight

Answer 9

True
Lift off and Landing Ground roll are both proportional to W^2 and inversely proportional to ρ
‘Take-off and Landing’, slide 4

Question 10

True/False
Propeller-driven aeroplanes can stay airborne for longer at higher altitudes

Answer 10

False
Power required increases as altitude increases and power available decreases

Question 11

True/False
The Oswald efficiency factor (e) depends on aeroplane geometry

Answer 11

True

Question 12

True/False
The phenomena of flutter, wing divergence and excessive pressure in the stagnation point impose a maximum flight speed

Answer 12

True
They are classed as structural limits, are represented as the vertical line on the right -hand side of the V-n diagram
See ‘V-n Diagram’, slides 2-3

Question 13

True/False
The horizontal tail of a classically configured aeroplane is needed to generate sufficient lift to balance the aeroplane weight

Answer 13

False
The lift force produced by the tail balances out the nose-up pitching moment produced by the lift from the wings

Question 14

True/False
Induced drag decreases as an aeroplane flies faster

Answer 14

True
Induced drag decreases while parasitic drag increases, thus the overall drag increases.
‘Thrust Required and Power Required’, slide 2

Question 15

True/False
Lift and drag forces are oriented, respectively, perpendicular and parallel to the zero-lift line of an aeroplane

Answer 15

False
In SLUF the lift and drag forces are oriented, respectively, perpendicular and parallel to the flight direction

Question 16

True/False
In order to trim an aeroplane after unsymmetric engine failure (assume sufficient thrust is still available) it needs to be flown at a negative side-slip angle

Answer 16

False
The angle being positive or negative depends on which engine has failed

Question 17

True/False
Wing sweepback decreases the dihedral effect

Answer 17

False

Question 18

True/False
Directional stability is independent from lateral and longitudinal motion

Answer 18

False
Directional stability is independent of longitudinal motion (pitch) but it is closely linked to lateral motion (roll).
For example during side-slip (adverse yaw) a roll moment is produced.

Question 19

True/False
Fuel consumption of jet-propelled airplanes per distance flown is minimal at the flight velocity associated with minimum drag

Answer 19

False
Fuel consumption would be minimised at the flight velocity associated with minimum power

Question 20

True/False
Longitudinal static stability requires that the centre of gravity of a classically configured aeroplane is located behind the neutral point

Answer 20

False
When the centre of gravity is behind the neutral point the aircraft is unstable. The centre of gravity needs to be ahead of the neutral point.
‘Neutral point and static margin’, slide 2

Question 21

True/False
Two airplanes cruise at the same altitude, they carry different payloads but are otherwise identical. In order to maximise range, the one with more payload needs to fly faster than the one with less payload

Answer 21

True
Unsure where there is evidence to support this 😢

Question 22

Consider the aerodynamic expressions
1. (CL^1/2)/CD |max
2. CL/CD |max
3. (CL^3/2)/CD |max

a) Which are relevant for gliding flight? Explain why.

b) Which are relevant for cruising flight of a propeller-driven airplane?
Explain why.

c) Which are relevant for cruising flight of a jet-propelled airplane?
Explain why.

d) Which is associated with the highest cruise velocity

Answer 22

a) 2 as it gives minimum glide angle and 3 as it gives minimum sink velocity

b) 2 as it gives max range and 3 as it gives max endurance

c) 1 as it gives max range and 2 as it gives max endurance

d) 1 gives fastest flight

Question 23

What is the advantage of high aspect ratio wings?

Answer 23

Low induced drag

Question 24

What is the primary motivation for wing sweep?

Answer 24

Higher drag divergence mach number

Question 25

Name 3 geometric features on an aeroplane which determine the amount of dihedral

Answer 25

1. High/low placement of wings on fuselage
2. Dihedral angle
3. Wing sweep
   ‘Lateral-directional coupling effects: Dihedral effect’, slide 1

Question 26

Name five factors which determine the ground roll length of an aeroplane for take-off

Answer 26

1. Air density
2. CLmax
3. Thrust available
4. Wing area
5. Ground roll friction
6. Airplane weight

‘Take-off and Landing’, slide 4

Question 27

Consider a v-n diagram of a typical aeroplane
a) Sketch the graph
b) Mark the manoeuvre point
c) Label each boundary section of the flight envelope with at least one limiting phenomenon

Answer 27

b) Manoeuvre point is where the stall curve meets the top line
c) Curved sections limited by stall
Top and bottom limited by the wing root bending moment
RH side limited by wing flutter, wing divergence, excessive pressure at stagnation point and heat due to friction

Question 28

Name three types of drag

Answer 28

1. Induced drag
2. Wave drag
3. Pressure drag
4. Skin friction drag

Question 29

Why do some aircraft have swept wings?

Answer 29

Wing sweep increases the the drag divergence flight speed → The airplane can fly faster without experiencing wave drag

Question 30

Why do golf balls have dimples rather than a smooth surface?

Answer 30

The rougher surface triggers turbulence in the boundary layer; for turbulent flow the wake region is narrower → less pressure drag

Question 31

Name three phenomena which limit the maximum flight velocity of an airplane

Answer 31

1. Wing divergence
2. Excessive pressure in stagnation point
3. Engine power
4. Heat due to friction
5. Wing flutter