SCHOOL OF COMPUTING, ENGINEERING AND MATHEMATICS SEMESTER 2 EXAMINATIONS 2013/2014 ME110. Aircraft and Automotive Systems

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1 s SCHOOL OF COMPUTING, ENGINEERING AND MATHEMATICS SEMESTER 2 EXAMINATIONS 2013/2014 ME110 Aircraft and Automotive Systems Time allowed: TWO hours Answer TWO questions from THREE in Section A and TWO questions from THREE in Section B Items permitted: Any approved calculator Items supplied: Graph paper Marks for whole and part questions are indicated in brackets [ ] ME110/2013/2014 Page 1 of 10 Printing date: 20/10/2014

2 Section A Attempt TWO questions in this section Question 1 The Equal Transit Time Theory is often associated with wings and the development of lift forces. Provide a description of the theory, using a sketch to aid your explanation. Describe whether or not the theory is valid, stating your reasons. [6 marks] (b) (i) Describe how lift forces acting on a wing might be defined according to Newtonian force relationships. Provide a sketch to aid your explanation. [4 marks] (ii) Describe how lift forces acting on a wing might be defined according to Bernoulli s Principle. Provide a sketch to aid your explanation. [4 marks] (c) With the aid of a sketch, describe how wingtip vortices are developed. [6 marks] (d) Describe the two principal categories of drag force that aircraft are subjected to during flight, sketch their typical characteristics with respect to flight velocity. [5 marks] ME110/2013/2014 Page 2 of 10 Printing date: 20/10/2014

3 Question 2 Calculate the Reynolds number at a location x = 0.3 m along the chord length of an aircraft wing at each of the following velocities; u = 20, 40, 60, 80 and 100 knots. Assume International Standard Atmosphere (ISA) conditions for pressure and temperature. Take: R = 287 J/kg K; μ = 18 x 10-6 kg/m s; 1 knot = mph; 1 mph = 1.61 km/h. Re x = ρux μ [9 marks] (b) Calculate the thickness of the boundary layer, δ, at a location x = 0.3 m along the chord length of an aircraft wing at each of the following velocities; u = 20, 40, 60, 80 and 100 knots. You may consider the flow over the wing as a flat plate case. Present your answers in mm. Re Transition = δ Laminar = x 4.91 Re x 0.5 δ Turbulent = x Re x 0.2 [10 marks] (c) Sketch an aerofoil section and label five important geometric features. [3 marks] (c) Sketch and label five types of control surfaces found on a typical aircraft. [3 marks] ME110/2013/2014 Page 3 of 10 Printing date: 20/10/2014

4 Question 3 (b) (c) (d) Define the plotted lines and axis as numbered (1) to (7) in the graph shown in Figure Q3. [6 marks] An aerodynamic load of 1956 N is required from a front wing on a racing car in order to allow it to drive around a corner at 180 mph. Referring to the graph below, determine the wing area required if the lift to drag ratio is to be optimised. Assume International Standard Atmosphere (ISA) conditions for pressure and temperature. Take: R = 287 J/kgK; 1 mph = 1.61 km/h. C L = F Lift 1 2 ρu2 A [8 marks] If the wing design for part (b) is limited to a width of 1.8 m and a chord length of 0.4 m by regulation, sketch and describe a wing design that would satisfy this case. Sketch and label a typical plot for tyre slip angle with respect to friction coefficient for a road car tyre and also for a racing car tyre. Describe the reasons for any differences between the tyre characteristics. [5 marks] [6 marks] (4) (2) (3) C D (7) (1) (5) (6) Figure Q3 ME110/2013/2014 Page 4 of 10 Printing date: 20/10/2014

5 Section B Attempt TWO questions in this section Question 4 A pressure-volume diagram for a reciprocating internal combustion engine is shown in Figure Q4 (at the end of the paper). Using Figure Q4.1 mark where the following events start and end: (i) Induction of air into the engine (ii) Compression of the air (iii) Combustion of the air-fuel mixture (iv) Work is produced by the engine (v) The products of combustion are removed from the engine. (b) At the start of the compression stroke: V = 0.54 litre, p = 100 kpa, T = 300 K At the end of the compression stroke: V = 0.04 litre (i) Find the compression ratio of the engine (ii) Calculate the pressure and temperature of the air at the end of the compression stoke, assuming that the air behaves as an ideal gas. [4 Marks] Question 4 continues over the page. ME110/2013/2014 Page 5 of 10 Printing date: 20/10/2014

6 (iii) When Figure Q4 was recorded the engine was running at a speed of 1500 rev/min and consumed fuel at the rate of 0.75 kg/h. What was the air to fuel ratio? [4 Marks] (iv) Assuming that there is no change in volume during the combustion process, compute the temperature at the end of the combustion process. Useful equations For an ideal gas During compression Conservation of energy Constants R = kj/kg K c v = kj/kg K n = 1.35 pv mrt n pv constant Q pdv mcv T Take the calorific value of Diesel fuel to be 42.5 MJ/kg [5 Marks] ME110/2013/2014 Page 6 of 10 Printing date: 20/10/2014

7 Question 5 Describe how ignition is caused in a petrol engine and name the operating cycle used. [5 marks] (b) Describe how ignition is caused in a Diesel engine and name the operating cycle used. [5 marks] (c) Describe the motion of a piston in a reciprocating engine running at a constant crankshaft speed; when does the piston reach its maximum and minimum linear velocity? [3 marks] (d) Describe how a petrol fuel injector works in a traditional petrol engine [5 marks] (e) Explain the purpose of a throttle in a traditional petrol engine. [4 marks] (f) Describe three types of reciprocating engine piston-cylinder configurations. [3 marks] ME110/2013/2014 Page 7 of 10 Printing date: 20/10/2014

Question 6 The Mercedes C-class sportcoupe, shown in Figure Q6.1 was sold in two versions: 1. The C180 K with a 1.8 litre supercharged spark ignition gasoline engine.

8 Question 6 The Mercedes C-class sportcoupe, shown in Figure Q6.1 was sold in two versions: 1. The C180 K with a 1.8 litre supercharged spark ignition gasoline engine. Maximum power output = 104 kw Based upon the standard fuel efficiency test a vehicle with this engine would consume 6.1 litres of gasoline over a 100 km journey. 2. The C220 CDI with a 2.0 litre turbocharged Diesel engine. Maximum power output = 109 kw Based upon the standard fuel efficiency test a vehicle with this engine would consume 5.7 litres of Diesel over a 100 km journey. Figure Q6.1 Calculate average fuel energy consumed per kilometre in the standard fuel efficiency test for each vehicle and hence determine which version of the vehicle had the most fuel efficient engine. [11 marks] Fuel Density [kg/m 3 ] Calorific Value [MJ/kg] Gasoline Diesel Table Q6 Fuel properties Question 6 continues over the page. ME110/2013/2014 Page 8 of 10 Printing date: 20/10/2014

5 litre Density of fuel = 775 kg/m 3 Calorific value of fuel = 42.7 MJ/kg Figure Q6.2 (i) Calculate the energy stored in the battery pack of the Tesla and the energy density of the pack.

9 (b) The Tesla Roadster, Figure Q6.2a is an electric vehicle based upon the chassis of a Lotus Elise, Figure Q6.2b. Mass of vehicle = 1238 kg Mass of battery pack = 450 kg Capacity of battery pack = 53 kwh (b) Mass of vehicle = 903 kg Volume of fuel tank = 43.5 litre Density of fuel = 775 kg/m 3 Calorific value of fuel = 42.7 MJ/kg Figure Q6.2 (i) Calculate the energy stored in the battery pack of the Tesla and the energy density of the pack. (ii) Calculate the energy stored in the fuel tank of the Lotus and the energy density of the tank. (iii) When the Lotus is driven at an average speed of 20 m/s the drag force on the vehicle is 400 N. If the average fuel conversion efficiency is 13% then calculate the distance travelled by the vehicle. [5 Marks] (iv) When the Tesla is driven at an average speed of 20 m/s the drag force on the vehicle is 420 N. If the electric motor has an efficiency of 90% then determine whether the Tesla will have a greater range than the Lotus. [5 Marks] ME110/2013/2014 Page 9 of 10 Printing date: 20/10/2014

10 Pressure [bar] Student Number Volume [m 3 ] Figure Q4 ME110/2013/2014 Page 10 of 10 Printing date: 20/10/2014

SCHOOL OF COMPUTING, ENGINEERING AND MATHEMATICS SEMESTER 2 EXAMINATIONS 2014/2015 ME110. Aircraft and Automotive Systems

s SCHOOL OF COMPUTING, ENGINEERING AND MATHEMATICS SEMESTER EXAMINATIONS 014/015 ME110 Aircraft and Automotive Systems Time allowed: ONE hour THIRTY minutes Answer TWO questions from THREE Items permitted: