Aircraft & Automotive Systems (ME110)
School of Environment and Technology
Division of Engineering and Product Design
Semester Two Examinations, May-June 2009
B.ENG. HONOURS DEGREE COURSE
AIRCRAFT & AUTOMOTIVE SYSTEMS (ME110)
EXAMINER: Dr. J.J. Leary
Instructions to Candidates:
 Time allowed: TWO hours
 Answer FOUR questions only
 The total number of questions is SIX
 Each question carries 25 marks
 This is a Closed-Book examination
Special requirements:
 None
May-June 2009
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Aircraft & Automotive Systems (ME110)
Question 1
(a) Describe Bernoulli's Theorem.
(4)
(b) Explain how a wing generates lift according to Bernoulli’s Theorem.
(4)
(c) The "equal transit time theory" states that the air over the upper surface of an
aerofoil arrives at the trailing edge at the same time as the air flowing under the lower
surface. Is this statement true? Give an explanation to justify your answer.
(4)
(d) For each of the wing sections (A)-(G) in Figure Q1.1, state whether the lift is zero,
positive, or negative.
(4)
Figure Q1.1
(e) Explain clearly from first principles why a wing section is typically shaped like an
aerofoil, as in Figure Q1.1(F) above, and the factors that determine the optimum
shape.
(4)
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Aircraft & Automotive Systems (ME110)
(f) Explain clearly, with the aid of diagrams, how the trailing vortices made visible by
the cloud in Figure Q1.2 (e.g. identified by A) are formed, i.e. what is their nature and
what is the cause of the swirls?
Figure Q1.2
(5)
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Aircraft & Automotive Systems (ME110)
Question 2
(a) An aircraft is being designed of length L with two thin wings generating lift forces
of F1 and F2. The weight of the aircraft is W (Newtons) and the distance of the
centre of gravity from the front of the aircraft is a. The other dimensions are given in
Figure Q2.1 below where L = a + b + c + d.
Figure Q2.1
Derive an expression for each of the lift forces F1 and F2 required for steady
horizontal flight in terms of a, b, c, d, W and L.
(8)
(b) Given the following design information:
W = 1000 N
a=1m
b = 0.5 m
c=5m
L=7m
calculate F1 and F2.
(3)
(c) Explain why F1 or F2 generate negative lift.
(2)
(d) Given the following equations for lift and drag for an aerofoil, and the aerofoil
data shown in the graphs in Figure Q2.2 (shown overleaf), and assuming an angle of
attack of 12o, calculate the areas of each wing required in part (b) for steady level
flight at 100 kph.
where:
CL is the lift coefficient and CD is the drag coefficient
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Aircraft & Automotive Systems (ME110)
ρ is the density of the fluid (1.225 kg/m³ for air at sea level)
v is the free-stream velocity (m/s), that is the speed of the lifting surface relative
to the atmosphere far enough away to be unaffected by the surface
A is the projected surface area (m2) of the lifting surface
Figure Q2.2
(8)
(e) Estimate the total drag force caused by the addition of the two wings.
(4)
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Aircraft & Automotive Systems (ME110)
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Aircraft & Automotive Systems (ME110)
Question 3
Answer the following questions about helicopters:
(a) Name the four primary controls.
(4)
(b) What is the function of the tail rotor?
(2)
(c) What is the function of the collective control?
(2)
(d) Which control drives the tail rotor?
(2)
(e) What force, applied to the main rotor, keeps the blades level?
(2)
(f) Describe two types of take-off available to helicopters.
(2)
(g) What is the ‘flapping’ motion of a rotor blade?
(4)
(h) With the aid of a diagram, explain how a helicopter accelerates from a
stationary hover position to moving forwards at a constant speed. Explain in
detail how the different controls and rotors achieve this.
(7)
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Aircraft & Automotive Systems (ME110)
Question 4
(a) In the P-V diagram for a petrol engine, describe which pressure is being
measured and which volume is being measured. (2)
(b) When air is being compressed, explain why the volume can never become zero.
(2)
(c) Table 4.1 (printed on the next page) shows a set of piston positions (1-8) and a
set of P-V diagrams (A-H). Correctly identify which goes with which, and give
your answer in the form of a paired list (i.e. number - letter). (8)
(d) Explain the following formula relating P and V and the heat energy Q released by
combustion during a time interval:
P2V2  P1V1  Q1
(3)
(e) Show how a P-V diagram can be created using the above formula in a
spreadsheet in the following format and show what you would enter into the first
three rows (i.e. rows 2, 3 and 4):
(5)
(f) Show how you would modify the above spreadsheet to compute the total work
done per cycle W, which is the total area enclosed by the P-V curve, using the
following formula:
(5)
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Aircraft & Automotive Systems (ME110)
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Aircraft & Automotive Systems (ME110)
Question 5
(a) Describe how ignition is caused in a petrol engine. (4)
(b) Describe how ignition is caused in a diesel engine. (4)
(c) Describe the differences between petrol and diesel fuels in terms of volatility,
density, calorific value, viscosity and cetane/octane rating. (4)
(d) For the Octane hydrocarbon molecule shown below:
calculate the stoichiometric molecule ratio for complete combustion in:
(i) Oxygen (O2) (4)
(ii) Air (21% O2, 79% N2) (4)
(e) Explain what is meant by "common rail" direct injection. This is used in the latest
type of diesel engine, using electronic control of fuel injection and higher pressures,
but explain how it is better than what was used before? (5)
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Aircraft & Automotive Systems (ME110)
Question 6
(a) Calculate how many MJ are equivalent to 1 kWh.
(5)
(b) Using the data below, calculate the unit cost of energy in p/MJ for each of the
following fuels and rate them in order of cost (in p/MJ) from cheapest to most
expensive:
(i) diesel
(3)
(ii) petrol
(3)
(iii) natural gas
(3)
(iv) coal
(3)
(v) electricity
(3)
Data
Diesel:
Calorific value = 45,800 KJ/kg
Cost = 94 p/litre
Density = 0.845 kg/litre
Petrol:
Calorific value = 46.9 MJ/kg
Cost = 90 p/litre
Density = 720 g/litre
Natural Gas:
Density = 717 g/m3
Boiling point = 111.55 K
Cost = 60 p/therm
1 therm = 105.506 MJ
Coal:
Cost = £209 / tonne
1 tonne = 1000 kg
Energy density = 32.5 MJ/kg
Electricity:
Cost = 9p / kWh
Energy density = not applicable
(c) An electric vehicle is powered by four batteries. Each battery is 24 V and has a
rating of 45 Ah. The batteries power electric motors which drive the car forwards.
Assuming that the car is travelling at a constant speed of 30 m/s, that the total friction
on the car is 50 N and that the efficiency of conversion is 90%, calculate the
maximum theoretical distance the car could travel before the batteries are exhausted.
(5)
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