AIRCRAFT AND AUTOMOTIVE SYSTEMS (ME110)

Size: px

Start display at page:

Download "AIRCRAFT AND AUTOMOTIVE SYSTEMS (ME110)"

Leo Waters
5 years ago
Views:

1 s School of Environment and Technology Aircraft & Automotive Systems (ME110) Division of Engineering and Product Design Semester Two Examination, June, 2010 B.ENG. HONOURS DEGREE COURSE AIRCRAFT AND AUTOMOTIVE SYSTEMS (ME110) EXAMINERS: DR J J LEARY, DR D J MASON Instructions to Candidates: The time allowed is 2 hours Attempt any 4 questions only The total number of questions is 6 Each question carries 25 marks This is a CLOSED-BOOK examination Special Requirements: Answer sheet (Q2, Q6 and Figure 4.1) June 2010 Page 1 of 17

Question 1 (a) The "equal transit time theory", as shown in Figure Q1a below, states that the air over the upper surface of an aerofoil arrives at the trailing edge at the same time as the air

2 Question 1 (a) The "equal transit time theory", as shown in Figure Q1a below, 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, and this is the reason it flows faster over the top. Is this statement true? Give an explanation to justify your answer. Figure Q1a (b) In Figure Q1b below, the Venturi theory of lift is shown. Is this theory correct? Explain your answer and make reference to the accuracy of the four statements made in the diagram. Figure Q1b QUESTION 1 CONTINUES ON THE NEXT PAGE Page 2 of 17

Question 1 (continued) (c) (d) Draw three diagrams which clearly shows the relationships between camber, chord and thickness for an aerofoil with (i) zero camber, (ii) positive camber, (iii) negative

3 Question 1 (continued) (c) (d) Draw three diagrams which clearly shows the relationships between camber, chord and thickness for an aerofoil with (i) zero camber, (ii) positive camber, (iii) negative camber. (6 marks) In Figure Q1c below, a twin-engine aircraft is flying through the top of a cloud. Explain, with the aid of diagrams, how the observed vortices are caused. (4 marks) Figure Q1c QUESTION 1 CONTINUES ON THE NEXT PAGE Page 3 of 17

4 Question 1 (continued) (e) The Lift Equation is given by: where: C L is the lift coefficient ρ is the density of the fluid (1.225 kg/m³ for air at sea level, 1000 kg/m³ for fresh water) v is the free-stream velocity, 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 (planform) surface area of the lifting surface F L is the lift force produced Using the aerofoil data in Figure Q1d, estimate the size of an aerofoil which, when attached to the roof of a car of mass 750 kg, would cause the car to take off at 120 kph. Figure Q1d Page 4 of 17

5 Question 2 Answer the following questions (use the attached answer sheet). Each correct answer will be awarded 1 mark. An incorrect answer will be awarded a negative mark. 1 Which is a longitudinal primary control surface for an aircraft? a Flaps b Slats c Spoilers d Elevator 2 The function of the flaps is to: a Increase lift and increase stalling speed b Increase lift and decrease stalling speed c Decrease the drag at stalling speed d Decrease the drag and decrease takeoff speed 3 What is the camber of a cambered aerofoil section? a The straight line joining leading edge to trailing edge b The middle line between upper and lower surfaces c The length of the lower surface d The angle between the upper and lower surface at the trailing edge 4 When an aircraft is in steady level flight, what is the relationship between the lift, drag and thrust? a Lift=thrust, drag=weight b Lift=weight, drag=thrust c Drag=lift, lift=weight d Weight=drag, lift=thrust 5 What is the equation for the thrust of a gas turbine engine? a air mass flow rate through engine x (V jet exhaust - V aircraft ) b air mass flow rate through engine x (V aircraft ) 2 c fuel mass flow rate x (V jet exhaust ) 2 d fuel mass flow rate x (V jet exhaust - V aircraft ) 6 Which of the following is not a type of gas turbine engine a Straight through jet b Bypass fan engine c Free turbine engine d Ramjet engine 7 Which of the following is not a secondary control on an aircraft? a Lateral control wheel. b Flap deployment handle. c Throttles d Rudder pedals. 8 On a helicopter what is the function of the tail rotor? a To enable the helicopter to fly sideways. Page 5 of 17

6 b To stop the helicopter spinning whilst in flight. c To provide power for the helicopter hydraulic system. d To provide cooling for the engine. Aircraft & Automotive Systems (ME110) 9 What force acting on the main rotor blades keeps the blades level? a The main rotor thrust. b The weight of the rotor blades. c The aerodynamic drag acting on the blades. d The centrifugal forces acting on the blades. 10 In a helicopter at fixed rotor speed which control sets the rotor thrust? a The pedal b The cyclic c The throttle d The collective 11 What is the name given to the blade vertical cyclic motion as the blades rotate? a The lagging motion. b The blade dynamic response. c The flapping motion. d The blade bending motion. 12 What units are altitude usually displayed in, inside an aircraft cockpit? a Metres. b Miles. c Kilometres. d Feet. 13 What units are aircraft airspeed measured in? a MPH b Knots c Knots per hour. d Kilometres per hour. 14 What is the safe takeoff distance of an aircraft? a The distance to lift off. b The distance from lift off to 35 feet above ground level. c The sum of 'a' and 'b'. d 1.15 times the sum of 'a' and 'b'. 15 What is the aspect ratio of a wing? a the wing area divided by the wing chord b the wing area divided by the wing span c the wing span divided by the wing chord d the wing span divided by the wing area 16 What is the reference wing area? a The sum of the upper and lower wing surface areas. b The area used in calculations for the aerodynamic coefficients. c The area of the wing exposed to the airflow. d The planform area including the area inside the fuselage. Page 6 of 17

7 17 What is the fuselage reference line (FRL)? a A line connecting the front of the fuselage to the end of the fuselage. b A vertical line from the bottom of the fuselage to the ground. c A horizontal line from wing tip to wing tip passing through the centre of gravity. d A vertical line from the centre of gravity to the ground. 18 What is meant by 'stall' a When the aircraft is decelerating too fast. b When the aircraft loses lift. c When the aircraft loses all power on the engines. d When the aircraft is pulling too much 'g'. 19 In the standard I.C.A.O. atmosphere what is meant by the 'tropopause'? a An altitude where there is no air. b An altitude where the temperature is absolute zero. c An altitude above which the temperature is constant. d An altitude below which the temperature is constant. 20 What does the coefficient CD0 represent? a The Skin Friction drag coefficient. b The Induced drag coefficient. c The Profile Drag drag coefficient. d The Total drag coefficient. 21 Parasitic drag is caused by : a The downwash from the elevators b The wing tip vortices causing turbulence c The ground effect and resistance of the tyres d The resistance caused by moving a solid object through a fluid 22 When the lift is zero, the induced drag is a Equal to the parasitic drag b Zero c Greater than the parasitic drag d Negative 23 A nautical mile is : a 1 degree of circumference at the equator b 1 minute of circumference at the equator c 1 second of circumference at the equator d 1 radian of circumference at the equator 24 The pitch of an aircraft is the : a Length of the aircraft from nose to tail b The angle between the fuselage and the horizontal c Rotation about the longitudinal axis d Height of the nose above the centre of gravity 25 The wing loading is the : a Weight of the wing with fuel tanks filled Page 7 of 17

8 b The weight of the wing divided by the area of the wing c The weight of the aircraft divided by the wing area d The area of the wing multiplied by the acceleration due to gravity (25 marks) Page 8 of 17

9 Question 3 (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 shown in Figure Q3.1 below. Figure Q3.1 Derive an expression for each of the lift forces F1 and F2 required for steady horizontal flight in terms of a, b, c, W and L. (8 marks) (b) Given the following design information, calculate F1 and F2. W = 1000 N a = 2 m b = 0.5 m c = 5 m L = 8 m (3 marks) (c) Explain why F1 or F2 generate negative lift. (d) Given the following equations for lift and drag for an aerofoil, and the aerofoil data shown in the graphs in Figure Q3.2 (shown overleaf), and assuming an Page 9 of 17

10 angle of attack of 12 o, calculate the areas of each wing required in part (b) for steady level flight at 100 kph. where: C L is the lift coefficient and C D is the drag coefficient 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 (m 2 ) of the lifting surface Figure Q3.2 (8 marks) (e) Estimate the total drag force caused by the addition of the two wings. (4 marks) Page 10 of 17

11 Question 4 A pressure-volume diagram for a reciprocating internal combustion engine is shown in Figure 4.1 (a copy is attached for you to write on). (a) (i) Draw a sketch of a pressure-volume diagram for a 2-stroke engine. (ii) Draw a sketch of a pressure-volume diagram for a 4-stroke engine. (iii) Using Figure 4.1 identify whether the engine is operating on a 2-stroke, or 4-stroke cycle. (1 marks) (b) Using Figure 4.1 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. (c) 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 (1 marks) (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. (iii) When Figure 4.1 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? (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 pv n pv mrt constant Conservation of energy Q pdv mcv T Constants R = kj/kg K Page 11 of 17

12 Pressure [bar] Aircraft & Automotive Systems (ME110) c v = kj/kg K n = 1.35 Diesel fuel has a lower heating value of 43.0 MJ/kg and a higher heating value of 45.9 MJ/kg Volume [m 3 ] Figure 4.1 Figure 4.1 appears on a separate sheet at the end of the exam paper so that it can be detached and returned with the script. Page 12 of 17

13 Question 5 a) Describe the process of ignition in a diesel engine and how the rate of combustion is controlled. b) Describe the meaning of the term stoichiometric ratio for a hydrocarbon fuel. c) Explain with reasons what determines the upper and lower limits of air/fuel ratio for combustion in a diesel engine. How does this differ for a petrol engine? d) Construct a table to indicate relative differences between petrol and diesel fuel for volatility, density, calorific value, viscosity, cetane rating, and octane rating, in terms of qualitative differences. e) Describe one recent technical innovation for improving the efficiency, quietness or cleanliness of diesel engines. Page 13 of 17

14 Question 6 Answer the following questions (use the attached answer sheet). Each correct answer will be awarded 1 mark. An incorrect answer will be awarded a negative mark. 1 The diesel engine was invented by: a Otto Diesel b Carl Otto c Rudolf Diesel d Carl Diesel 2 Hydrocarbon fuels consist of: a Oxygen atoms, Hydrogen molecules b Carbon molecules, Hydrogen molecules c Hydrogen atoms, Carbon molecules d Carbon atoms, Hydrogen atoms 3 Viscosity is a measure of the resistance of a fluid to flow when a pressure is applied, and : a increases with increasing temperature up to the flashpoint b decreases with increasing temperature c is independent of temperature d reaches a minimum at the freezing point 4 In stationary air (at room temperature and atmospheric pressure) air molecules travel at an average speed of: a 0 m/s b 3 m/s c 30 m/s d 300 m/s 5 Compared to 1 kg of Diesel fuel, the same mass of petrol fuel is a heavier b more voluminous c lighter d less voluminous 6 Petrol is most similar in chemical composition to a Kerosene b Napthane c Petroleum d Gasoline 7 A single cylinder 4-stroke engine running at 3000 rpm completes each stroke in a 10 ms b 20 ms c 40 ms d 50 ms 8 Which valve starts to open at the top of the exhaust stroke? Page 14 of 17

15 a b c d Exhaust Inlet Exhaust + Inlet None 9 If the volume above a piston is 10 cc at TDC and 100 cc at BDC, the Compression ratio and most likely engine type are: a 11:1 and Diesel b 10:1 and Diesel c 11:1 and Petrol d 10:1 and Petrol 10 A spark plug is not needed in a diesel engine because: a The hot air causes the droplets to burn b The compression ignition causes a spark c The diesel fuel is ignited by the injector d The volatility of diesel causes a spark 11 Compared to diesel fuel, petrol fuel has : a Lower viscosity, higher density b Lower density, higher volatility, higher calorific value c Higher flashpoint temperature, lower volatility d Lower calorific value, lower volatility 12 According to Boyle's Law, if a large piston compresses air at atmospheric pressure from 100 litres to 0 litres, the pressure would increase by : a 0 bar b 99 bar c 100 bar d infinity 13 The primary function of the throttle (butterfly) valve in a petrol engine is to a Restrict the flow of inlet air b Restrict the flow of fuel c Restrict the exhaust flow d Restrict the spark timing 14 The stoichiometric ratio for the combustion of Methane (CH 4 ) in pure Oxygen (O 2 ) is a 1 b 2 c 3 d 4 15 The stoichiometric ratio for complete combustion in a real petrol engine is about: a 1 : 1 b 1.4 : 1 c 14 : 1 d 144 : 1 Page 15 of 17

16 16 A diesel engine uses the following equipment to pre-mix fuel with air before it is injected into the combustion chamber : a carburettor b heat plug c EGR system d none of the above 17 Which is the odd one out? a CH 4 b C 2 H 6 c C 2 H 4 d C 3 H 8 18 The mass of air in a classroom with dimensions 8 m x 5 m x 3 m is about : a 100 g b 150 g c 50 kg d 150 kg 19 If a hydrocarbon fuel burns with a leaner air/fuel ratio than stoichiometric, the following gases will be found amongst the products of combustion: a Oxygen (O 2 ) b Carbon monoxide (CO) c Carbon dioxide (CO 2 ) and carbon monoxide (CO) d Hydrogen gas (H 2 ) and carbon dioxide (CO 2 ) 20 If an engine produces a torque of 100 Nm at 3000 rpm, the power produced is closest to: a 300 kw b 100 kw c 30 kw d 10 kw 21 Which fuel has the highest calorific value (MJ/kg)? a Diesel b Petrol c Hydrogen d Ethanol 22 1 kwh of electrical energy is the same as: a 1 MJ b 1.8 kj c 3.6 MJ d 1 kj 23 1 kwh of electrical energy is equivalent to the energy content of the following quantity of petrol : a 0.1 litre b 1 litre c 0.01 litre d litre Page 16 of 17

17 24 1 kg of Carbon produces the following amount of CO 2 after combustion: a 3.63 kg b kg c 7.26 kg d kg 25 A petrol engine is only 30% efficient and 70% of the energy is wasted as heat because: a the engine needs 70% of the energy to run at idle b of limits set by laws of thermodynamics for heat engines c only diesel engines can be more efficient than the Carnot cycle d the hot reservoir is only 30% hotter than the cold reservoir (25 marks) Page 17 of 17

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

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