Course: Physics The Physics of Flight Notes for learners Level: National 4 and 5 April 2013 This advice and guidance has been produced for teachers and other staff who provide learning, teaching and support as learners work towards qualifications. These materials have been designed to assist teachers and others with the delivery of programmes of learning within the new qualifications framework. These support materials, which are neither prescriptive nor exhaustive, provide suggestions on approaches to teaching and learning which will promote development of the necessary knowledge, understanding and skills. Staff are encouraged to draw on these materials, and existing materials, to develop their own programmes of learning which are appropriate to the needs of learners within their own context. Staff should also refer to the course and unit specifications and support notes which have been issued by the Scottish Qualifications Authority. http://www.sqa.org.uk Acknowledgements © Crown copyright 2013. You may re-use this information (excluding logos) free of charge in any format or medium, under the terms of the Open Government Licence. To view this licence, visit http://www.nationalarchives.gov.uk/doc/open-government-licence/ or e-mail: psi@nationalarchives.gsi.gov.uk. Where we have identified any third party copyright information you will need to obtain permission from the copyright holders concerned. Any enquiries regarding this document/publication should be sent to us at enquiries@educationscotland.gov.uk. This document is also available from our website at www.educationscotland.gov.uk. 2 PHYSICS (NAT 4/5) © Crown copyright 2013 Contents Introduction and aims 4 The dynamics of flight 5 Lift vs weight 7 Generating lift (Newton’s third law) 9 Flight control surfaces 14 Investigation: Building a model glider 18 Investigation: Weight distribution 21 Investigation: Angle of attack 24 Investigation: Additional lift 28 Investigation: The banked turn 30 The ‘loop-the-loop’ challenge 35 The jet engine 37 Navigation 42 PHYSICS (NAT 4/5) © Crown copyright 2013 3 INTRODUCTION AND AIMS Introduction and aims The aviation industry is a huge worldwide industry that employs thousands of people in many fields, from pilots who fly planes to aeronautical engineers who design them. This investigation will enable you to learn about the importance of forces and Newton’s laws of motion in allowing planes to fly in a controlled manner. 4 PHYSICS (NAT 4/5) © Crown copyright 2013 THE DYNAMICS OF FLIGHT The dynamics of flight When a plane is flying through the air, there are four main forces acting on it. These are as follows: Weight: This force acts downwards, due to gravity, pulling the plane down to the ground. Any object in the air will have this force acting on it. Lift: This force acts upwards, and is generated by the wings of the plane. It acts against gravity to lift the plane into the air and keep it there. Drag: This force acts against the forward motion of the plane, just like air resistance acts on us when we ride a bike. It slows the plane down. Thrust: This force is produced by the engines of the plane to propel the plane forward. It acts against drag to make the plane go faster. Aircraft image courtesy of NASA: http://www.grc.nasa.gov/WWW/k-12/airplane/forces.html PHYSICS (NAT 4/5) © Crown copyright 2013 5 THE DYNAMICS OF FLIGHT Exercise: The balancing act 1. Explain in your own words the effect of the four different forces that act on a plane in flight. 2. Consider a plane that is flying at a constant speed. What can be said about the relative size of the thrust and drag forces? 3. Consider a plane that is flying at a constant height (altitude). What can be said about the relative size of the weight and lift forces? 4. Which of Newton’s three laws of motion did you apply to answer questions 2 and 3? 6 PHYSICS (NAT 4/5) © Crown copyright 2013 LIFT VS WEIGHT Lift vs weight In order for a plane to get into the air, it needs an upward force to lift it into the air. This force is called lift and it is generated by the wings of the plane. Newton’s first law of motion Isaac Newton changed our understanding of the universe with his three laws of motion. They can be used to describe how a plane stays in the air. Newton’s first law of motion states that: An object will remain at rest or move with a constant speed unless an unbalanced force acts upon it. In other words, an object will remain still until you apply a force, such as a push, to it. Object on a table Consider a vase sitting on a tabletop. According to Newton’s first law, there is no unbalanced force acting because the vase is not moving. However, there are forces that are acting on the vase: weight: this force is caused by gravity and it acts to pull the vase down to the ground reaction: this force is produced by the table and it acts to push the vase upwards. For the vase on the table both of these forces are said to be balanced – they are equal to each other. If the forces are equal, then the overall (resultant or unbalanced) force is zero. The vase will not move. Image of vase: Ilovebutter/Flickr Creative Commons PHYSICS (NAT 4/5) © Crown copyright 2013 7 LIFT VS WEIGHT Lift Cruising at a constant height A plane cruising at a constant height is very similar to the vase sitting on the table. The height does not change, so the forces acting up and down must be balanced. The two forces acting up and down on a plane are weight and lift, shown opposite. Weight Exercise: Find the weight and lift Shown below are the masses of some popular aircraft. 1. Use the following formula to calculate the weight of each aircraft: weight = mass × 9.8 W = mg 2. For each aircraft, calculate the lift produced by the wings to maintain a constant altitude. Boeing 747-400 Mass = 178,756 kg Airbus A380-800 Mass = 276,800 kg Boeing 757-200 Mass = 57,840 kg Airbus A330-300 Mass = 124,500 kg You may wish to visit the following website to see images of some of these planes: www.airliners.net 8 PHYSICS (NAT 4/5) © Crown copyright 2013 GENERATING LIFT (NEWTON’S THIRD LAW Generating lift (Newton’s third law) In order for a plane to stay in the air, the downward force of weight must be balanced by the upward force of lift. The lift is provided by the wings of the aircraft. Remember, according to Newton’s first law, for the plane to remain at a constant altitude then the downward and upward forces must be balanced. Newton’s third law of motion Newton’s third law of motion states: For every action, there will be an equal and opposite reaction. In other words, if you apply a force to an object in one direction, then the object will apply a force to you in the opposite direction. Imagine pushing the sharp end of a pin with your thumb. You apply a force to the pin (called an action force). The pin applies an equal and opposite force (called a reaction force) which pushes the pin into your thumb. You will also feel a small amount of pain! This is why you feel a force when you push on objects – the object is pushing back on you with the same force but in an opposite direction. PHYSICS (NAT 4/5) © Crown copyright 2013 9 GENERATING LIFT (NEWTON’S THIRD LAW Newton’s third law also applies when you go swimming. You push the water backwards with your hand (action force) so the water pushes you forwards (reaction force). In the same way, if you fire a paintball gun, the action force shoots the paintball forwards. The gun recoils into your shoulder as a result of the reaction force. Action force Reaction force Swimmer pushes water in backward direction. Water exerts a force on the swimmer. Image: Jim Bahn/Flickr Creative Commons 10 PHYSICS (NAT 4/5) © Crown copyright 2013 GENERATING LIFT (NEWTON’S THIRD LAW Exercise: Which way? For each of the objects below, draw a diagram to show the direction of the action and reaction forces. Air forced back Air forced back Air forced down Air forced down PHYSICS (NAT 4/5) © Crown copyright 2013 11 GENERATING LIFT (NEWTON’S THIRD LAW Generating lift with a wing An aeroplane wing generates lift by forcing air downwards (action force). This results in the wing being pushed upwards (reaction force) – the force of lift. Air must flow across the wing so in order to produce lift, so the aircraft must be moving through the air. This theory is based on Newton’s third law of motion that every action has an equal and opposite reaction. Lift Downward force on the air Image: Theresa Knott/Wikimedia Commons http://en.wikipedia.org/wiki/File:Angle_of_attack.svg 12 PHYSICS (NAT 4/5) © Crown copyright 2013 GENERATING LIFT (NEWTON’S THIRD LAW Exercise: Generating lift Consider the structure of a wing, shown in the diagram below. What factors do you think will affect the amount of lift that the wing will generate? Discuss in small groups and write a short report on what factors you believe will affect the amount of lift generated by a wing. Image: Pearson Scott Foresman/Wikimedia Foundation http://en.wikipedia.org/wiki/File:Alieron_A-44_(PSF).png PHYSICS (NAT 4/5) © Crown copyright 2013 13 FLIGHT CONTROL SURFACES Flight control surfaces To manage flight direction, aircraft use control surfaces. A plane can move about three axes as shown in the diagram below, changing the roll, pitch and yaw. Image courtesy of NASA http://commons.wikimedia.org/wiki/File:Roll_Pitch_Yaw.JPG A plane uses four basic control surfaces to control the flight – elevation, rudder, ailerons and flaps. These four surfaces are explained below. You will investigate their effects in detail later using a model glider. 14 PHYSICS (NAT 4/5) © Crown copyright 2013 FLIGHT CONTROL SURFACES Elevator – controlling the pitch An elevator is a control surface that makes the front of the plane (the nose) pitch up and down. Elevators are usually found at the back of the plane, on a part called the horizontal stabiliser. When the elevator points downwards, it causes the nose to point downwards. When the elevator points upwards (pitch up), it causes the nose to point upwards (pitch down). Image courtesy of R/C Airplane World: http://www.rc-airplane-world.com/how-airplanes-fly.html PHYSICS (NAT 4/5) © Crown copyright 2013 15 FLIGHT CONTROL SURFACES Rudder – controlling the yaw The rudder of the plane is used to move the nose to the left or the right (yaw). The rudder is located on the back edge of the vertical stabiliser or fin. The air flowing over the rudder pushes harder on one side than the other, which forces the nose of the plane to yaw either to the left or the right. When the rudder turns to the left the plane will yaw to the left. When the rudder turns to the right, the plane will yaw to the right. Image courtesy of R/C Airplane World: http://www.rc-airplane-world.com/how-airplanes-fly.html 16 PHYSICS (NAT 4/5) © Crown copyright 2013 FLIGHT CONTROL SURFACES Ailerons – controlling the roll Ailerons work in pairs to control the plane's roll. Each aileron moves at the same time but in opposite directions. When the left aileron moves up, the right aileron moves down and vice versa. This causes a decrease in lift on the wingtip with the upward-moving aileron and an increase in lift on the wingtip with the downward-moving aileron. These opposite changes in lift cause the plane to roll either to the left or the right. Flaps – increasing drag and generating extra lift Flaps are located on the back edge of each wing, usually between the fuselage and the ailerons. They extend downwards (and often outwards) from the wing. One purpose of the flaps is to generate more lift at slower speeds. They also generate more drag, which slows the plane down. You will notice that flaps are usually deployed on take-off to help the plane get airborne and while landing to help slow the plane down. You can see these control surfaces if you look at modern aircraft – the next time you fly, look out for them on the plane you fly in. Images courtesy of R/C Airplane World: http://www.rc-airplane-world.com/how-airplanes-fly.html PHYSICS (NAT 4/5) © Crown copyright 2013 17 INVESTIGATION: BUILDING A MODEL GLIDER Investigation: Building a model glider The Wright brothers1 (Wilbur and Oliver) built model gliders to learn and understand the importance of weight and balance in aircraft. If the weight is not positioned properly, the plane will not fly. For example, too much weight at the front (nose) will cause the plane to dive towards the ground. Small weights can be used with a model glider to change its weight distribution. Test flights can then be carried out to determine the effects of this on the glider’s flight. Wilbur and Orville also learned that the design of a plane was very important. Experimenting with models of different designs showed that planes fly best when the wings, fuselage and tail are designed and balanced to interact with each other. The Wright Flyer was the first plane to complete a controlled takeoff and landing. It was produced as a result of many experiments conducted by the Wright brothers. Gliders are still used in aviation design today. At NASA, model aircraft are used to test ideas in aviation, developing new concepts and trialling new designs. Some models fly in the air using remote control, while others are tested in wind tunnels. The goals of NASA research are to make planes fly more safely, perform better and become more efficient. In this investigation, you are going to construct a model glider to investigate the effects of weight distribution and control surfaces on the flight of a plane.2 The gliders will be made from polystyrene with paper clips or bulldog clips used to control the weight. 1 See photos of the Wright Brothers: http://faculty.etsu.edu/gardnerr/wrightbrothers/huffaker.htm 2 Glider based on NASA Right Flight Glider, http://www.nasa.gov/audience/foreducators/topnav/materials/listbytype/Right_Flight.html 18 PHYSICS (NAT 4/5) © Crown copyright 2013 INVESTIGATION: BUILDING A MODEL GLIDER Follow the instructions below to construct your model glider. You will need: two styrofoam trays glider template sellotape scissors sharp knife emery board. 1. Use scissors to cut the outer edges off the glider template so that it will fit on the inside of the tray. 2. Stick the template down onto the styrofoam tray using sellotape. 3. Using a sharp knife, carefully cut around the outline of the glider. This can also be done using a pin or a sharp pencil to make lots of close together holes along the outline of the glider. PHYSICS (NAT 4/5) © Crown copyright 2013 19 INVESTIGATION: BUILDING A MODEL GLIDER 4. After cutting around the template, turn the tray over and use the knife to complete the cutting where necessary. Then carefully push the components out of the tray. 5. Using a piece of sandpaper or an emery board, carefully remove the rough edges from around the wings, fuselage and horizontal stabiliser. 6. Gently push the wings through the hole in the fuselage. Ensure the wings are equal lengths on both sides of the fuselage. Repeat with the horizontal stabiliser. 7. Your glider is now ready to fly. 20 PHYSICS (NAT 4/5) © Crown copyright 2013 INVESTIGATION: WEIGHT DISTRIBUTION Investigation: Weight distribution In order for the model glider to fly properly, it is necessary for its weight to be correctly balanced. The initial test flights are going to investigate the distribution of the weight of the glider to optimise its flight. This will require several test flights, each with different amounts and positions of weights. Paper clips or blu-tac can be used to add weight to the glider. The distribution of weight can be changed by changing the position of the clips/blu-tac. What factor or factors of the flight of the glider will you use to compare how good each flight was? ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ Flight 1 – No additional weight Firstly, try to fly the glider with no additional weights added. Describe the flight of the glider. Use the terms roll, pitch and yaw (see the section on flight ‘control surfaces’ for more detail). You may use a diagram to help your description. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ PHYSICS (NAT 4/5) © Crown copyright 2013 21 INVESTIGATION: WEIGHT DISTRIBUTION Flight 2 – Adding weight to the nose Add a paper clip or blu-tac to the nose of the plane (as shown in the photograph). Now try flying the plane again. Describe the flight of the glider, again using the terms roll, pitch and yaw. In your description include the following: Was this flight improved over flight 1? What effect did the addition of the weight have? (Hint: Think about how the pitch of the plane has changed between flight 2 and flight 1.) ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ Flight 3 – Additional weight Add a second paper clip or more blu-tac to the front of your glider (as shown in the photograph). Repeat your test flight and watch carefully the flight path of the glider. Describe the flight path using the terms roll, pitch and yaw. In your description consider the following: Has the additional weight improved the flight? Is the glider flying ‘level’ yet? (Think about the pitch of the glider.) How could you improve the glider further? ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ 22 PHYSICS (NAT 4/5) © Crown copyright 2013 INVESTIGATION: WEIGHT DISTRIBUTION Finding the optimum weight distribution Carry out an investigation to find the optimum weight distribution for your glider. Use the space below to record the results of your investigation. The glider diagrams can be used to note the positions of the weights. Flight 4 _________________________________________ _________________________________________ _________________________________________ _________________________________________ Flight 5 _________________________________________ _________________________________________ _________________________________________ _________________________________________ Flight 6 _________________________________________ _________________________________________ _________________________________________ _________________________________________ Optimum weight distribution On the diagram opposite sketch the position of the weight or weights used for optimum weight distribution. PHYSICS (NAT 4/5) © Crown copyright 2013 23 INVESTIGATION: ANGLE OF ATTACK Investigation: Angle of attack In order to generate lift, the wing of the glider must force air downwards. By Newton’s third law this will result in an equal and opposite force upwards, which is called lift. The amount of lift provided by the wing depends on its angle of attack. Angle of attack Image: Pearson Scott Foresman/Wikimedia Foundation http://commons.wikimedia.org/wiki/File:Angle_of_attack_(PSF).png The angle of attack (pitch) of the glider can be changed by using the elevators on the horizontal stabiliser (at the rear of the glider). The elevators can move upwards or downwards and change the lift generated at the back of the glider. Image courtesy of NASA: http://www.grc.nasa.gov/WWW/k-12/airplane/elv.html 24 PHYSICS (NAT 4/5) © Crown copyright 2013 INVESTIGATION: ANGLE OF ATTACK When the elevator tilts upwards, it reduces the lift at the back of the plane. This causes the nose to rise which increases the angle of attack. When the elevator tilts downwards, it increases the lift at the back of the plane. This causes the nose to lower which reduces the angle of attack. Angle of attack Carry out an investigation into the effects of the elevators on the angle of attack of the glider. Use the space below to record the results of your investigation. Remember to describe the flight path of the glider using the terms pitch, roll and yaw. Flight 1 – Elevators level _________________________________ _________________________________ _________________________________ _________________________________ Flight 2 – Elevators raised _________________________________ _________________________________ _________________________________ _________________________________ Flight 3 – Elevators lowered _________________________________ _________________________________ _________________________________ _________________________________ PHYSICS (NAT 4/5) © Crown copyright 2013 25 INVESTIGATION: ANGLE OF ATTACK When a plane is taking off and gaining altitude, what position should the elevators be set to? Explain your answer. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ Extra: Stalled wings We have seen in the above investigation that if you increase the angle of attack, you can increase the lift generated by the wings. However, there is a certain angle of attack that you must never go above – this is known as the critical angle of attack. Above this angle, the wing will ‘stall’. This means that the wing no longer produces lift and when this happens the glider or plane will fall out of the sky. To produce lift, there must be smooth flow of air over the wings, as shown in the diagram below.3 This is known as ‘clean airflow’. The wing forces the air downwards. By Newton’s third law, the wing is forced upwards with an equal but opposite force, which is the lift. 3 GrahamUK/Wikimedia Common: http://en.wikipedia.org/wiki/File:Deep_Stall.png 26 PHYSICS (NAT 4/5) © Crown copyright 2013 INVESTIGATION: ANGLE OF ATTACK If the angle of attack it too great, the airflow over the wing breaks up and becomes turbulent. This is known as ‘dirty airflow’. As air is no longer being forced cleanly downwards, there is no resultant upward force. In other words, there is no lift. Carry out an investigation into the effects of changing the angle of attack on the flight of your glider. Use the elevators to change the angle of attack. What happens to the flight path of the glider when the wings stall? Use the space below to record the results of your investigation. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ PHYSICS (NAT 4/5) © Crown copyright 2013 27 INVESTIGATION: ADDITIONAL LIFT Investigation: Additional lift The majority of the lift is produced by the plane’s wings.4 Changes to the shape and size of the wing will affect the lift. One of the main ways of changing the shape of the wing is to use flaps. These are on the back of the wing (closest to fuselage on your glider). They extend outwards and downwards from the wing and increase lift at slow speeds. To deploy the flaps on your glider, start at one side and carefully bend them downwards. If the flap snaps, sticky tape can be used to reattach it. The effects of the flaps Carry out an investigation into the effects of deploying the flaps on your glider. Use the space below to record the results of your investigation. Remember to describe the flight path of your glider using the terms roll, pitch and yaw. Extra: Try launching the glider at different speeds and investigate the effects of the flaps at both low and high speeds. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ _____________________________________________________________ 4 Image: NASA at http://virtualskies.arc.nasa.gov/aeronautics/3.html 28 PHYSICS (NAT 4/5) © Crown copyright 2013 INVESTIGATION: ADDITIONAL LIFT Planes usually deploy the flaps when they are taking off. Why do you think this is so? ______________________________________________________________ ______________________________________________________________ When flying at high speed, planes usually have the flaps retracted (not deployed). Why would planes not fly with the flaps deployed all the time? ______________________________________________________________ ______________________________________________________________ Extra: The effects of wing area Carry out an investigation into the effect of changing the wing area on the lift of your glider. You will need to make an additional wing, with a larger area, using a new piece of styrofoam. Use the space below to record the results of your investigation. Ensure you keep the launch speed constant. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ _ PHYSICS (NAT 4/5) © Crown copyright 2013 29 INVESTIGATION: THE BANKED TURN Investigation: The banked turn When an aircraft wants to turn to the left or right, it flies a banked turn,5 which is controlled by both the ailerons and the rudder. This is a more advanced application of the changes of lift to the wings. Ailerons are used to make the aircraft roll. This is also known as making the aircraft ‘bank’. They work using the same principles as flaps to change the lift of a wing. The ailerons on your glider can be deployed in the same way as the flaps – gently bend the aileron either up or down starting at one of the edges. 5 Image: NASA at http://www.grc.nasa.gov/WWW/k-12/airplane/turns.html 30 PHYSICS (NAT 4/5) © Crown copyright 2013 INVESTIGATION: THE BANKED TURN To increase the lift on one of the wings the aileron should be pointed downwards. Then to reduce the lift on the other wing the aileron should be pointed upwards. Image courtesy of NASA: http://www.grc.nasa.gov/WWW/k-12/airplane/alr.html PHYSICS (NAT 4/5) © Crown copyright 2013 31 INVESTIGATION: THE BANKED TURN The effects of the ailerons Carry out an investigation into the effects of the ailerons on the flight of your glider. Use the space below to record the results of your investigation. Remember to describe the flight path of your glider using the terms roll, pitch and yaw. Include in your description the relevant Newton’s laws to describe the effects of the flight in terms of the weight and lift generated by the wing. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ 32 PHYSICS (NAT 4/5) © Crown copyright 2013 INVESTIGATION: THE BANKED TURN To complete a banked turn, the aircraft must also yaw in the direction of the turn. The rudder is used to make the plane to yaw to the left or right. When the ailerons and rudder are used together, the glider can be made to fly a banked turn. The moving air pushes with more force on one side of the rudder than the other, which causes the nose of the plane to yaw to the left or right. You can adjust the rudder on your glider by gently pushing it to one side or the other, starting at the top and working downwards. Making a banked turn Adjust the rudder and the ailerons such that the glider will fly a banked turn. You can choose in which direction you wish your glider to fly. Once you have achieved the banked turn, describe how you set the control surfaces of the glider and draw a diagram of the flight path. _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ PHYSICS (NAT 4/5) © Crown copyright 2013 33 INVESTIGATION: THE BANKED TURN The rudder and Newton’s third law We have seen from the investigation above that moving the rudder will cause the glider to yaw to the left or right. Explain, using Newton’s third law of motion, the action of the rudder on the flight of the glider. You may wish to consider the following: When the side of the rudder is in the air stream, it will experience a force pushing it on one direction. Newton’s third law states that for every action force, there is an equal and opposite reaction force. A diagram may also help your description. Can you explain how changing the position of the rudder will change the amount by which the glider will yaw in a given direction? _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ 34 PHYSICS (NAT 4/5) © Crown copyright 2013 THE ‘LOOP-THE-LOOP’ CHALLENGE The ‘loop-the-loop’ challenge So far you have optimised the weight distribution of your glider and investigated the effects of the ailerons and the flaps on the flight path. This challenge involves changing the control surfaces to achieve a ‘loop-the-loop’ with your glider.6 6 Davynin/Flickr Creative Commons PHYSICS (NAT 4/5) © Crown copyright 2013 35 THE ‘LOOP-THE-LOOP’ CHALLENGE Loop-the-loop Adjust the flight control surfaces on your glider to achieve a loop-the-loop. Think about the following: The lift required – which control surfaces generate additional lift? The position of the ailerons – the plane is flying straight. Launch speed and angle. Once you have achieved the loop-the-loop, describe in the space below what changes you made to the control surfaces. Explain why these changes resulted in a loop-the-loop. You can use a diagram to help with your explanation. _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ 36 PHYSICS (NAT 4/5) © Crown copyright 2013 THE JET ENGINE The jet engine A large number of aircraft are powered by the jet engine. Some aircraft have two, others have four and a small proportion of heavy aircraft have six. The jet engine has made long-distance flight a reliable and quick experience – flying from London to New York typically takes just 7–8 hours, and in the days of Concorde took as little as 5 hours as the plane flew at twice the speed of sound. Without doubt, the jet engine revolutionised air travel and as such revolutionised global travel and had a big impact on the world’s economy. An afterburner glows on an F-15 Eagle engine following a repair during an engine test run November 10, 2010, at the Florida Air National Guard base in Jacksonville International Airport, Fla. Shelly Gill/Wikimedia Commons. http://en.wikipedia.org/wiki/File:F100_F-15_engine.JPG PHYSICS (NAT 4/5) © Crown copyright 2013 37 THE JET ENGINE How a jet engine works The diagram below7 shows how a jet engine sucks in cold air from the fan blades at the front and ejects it out of the exhaust. Air is forced to flow in one direction through the engine. The core of the engine is where the combustion takes place – fuel is injected into the hot air and burns. This turns the turbines and the front fan to suck in more air. Explain, using the Newton’s second and third laws, how a jet engine works to propel an aircraft forward. In your explanation, consider how the engine can produce different amounts of thrust (forward force). ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ 7 K.Ainsqatsi/Wikimedia Commons: http://en.wikipedia.org/wiki/File:Turbofan_operation_lbp.svg 38 PHYSICS (NAT 4/5) © Crown copyright 2013 THE JET ENGINE Fan blades8 Conduct an experiment to investigate the effect of fan blades on the movement of air. You should consider the shape of the blade and investigate how changing the speed of rotation of the fan blades affects the movement of air. Describe the experiment that you carried out in the space below, recording your results and the conclusions you can draw from them. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ 8 Image of blades from Olivier Cleynan/Wikimedia Commons: http://en.wikipedia.org/wiki/File:Outer_nozzle_of_GEnx-2B_turbofan_engine.jpg PHYSICS (NAT 4/5) © Crown copyright 2013 39 THE JET ENGINE Reverse thrust When an aircraft lands, it can use the thrust from its engines to help slow it down on the runway. However, the engine’s fan direction cannot be reversed so there must be another method to force the air forwards. One design to force air forwards (known as reverse thrust) is shown in the photograph below.9 Explain, using Newton’s third law, why the above design can be used to help slow a plane down on the runway. Consider in your explanation the direction the air is forced in by the doors. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ 9 Bryan from Las Vegas/Wikimedia Commons: http://en.wikipedia.org/wiki/File:Boeing_737200_thrust_reverser.jpg 40 PHYSICS (NAT 4/5) © Crown copyright 2013 THE JET ENGINE Applying Newton’s second law We have seen that a jet engine produces thrust by forcing air through it in one direction. The thrust of an engine is measured in kilo Newtons (kN). As most planes have either two or four engines, the total thrust can be found by multiplying the single engine thrust by the number of engines. This allows the acceleration of the plane to be predicted using Newton’s second law: F ma Assuming there are no frictional forces acting, calculate the initial acceleration of each of the following aircraft. You will need to research the engine thrust and maximum take-off weights for each aircraft. The internet can be used for this task. (a) Boeing 787 Dreamliner (b) Boeing 777-200 (c) Boeing 747 (d) Airbus A330-300 (e) Airbus A340-600 (d) Airbus A380-800 PHYSICS (NAT 4/5) © Crown copyright 2013 41 NAVIGATION Navigation Air traffic control are responsible for giving directions to all aircraft both when they are in flight and when they are on the ground. They ensure that aircraft do not come too close to each other and are given the correct flight path to their destination. Vectors are key to navigation for aircraft. When air traffic control issue a pilot with a direction, they issue it as a vector. Sometimes a pilot will request a vector to a specific airport. Vectors are essential as they give both a magnitude (size of velocity or distance) and a direction. Both pieces of information are vital to the pilot. 42 PHYSICS (NAT 4/5) © Crown copyright 2013 NAVIGATION Vectoring aircraft You are in charge of issuing aircraft with a vector from Edinburgh Airport to different airports around Europe. You must issue the pilot with a displacement vector to their destination as the crow flies (single straight line between starting point and destination). Use the map below to help you.10 Do the same for these other flight paths: (a) Glasgow to London Heathrow: _________________________ (b) Glasgow to Paris Charles de Gaulle: _________________________ (c) Glasgow to Berlin Schonelfeld: _________________________ (d) Glasgow to Milan Malpensa: _________________________ 10 Blank_map_of_Europe_(polar_stereographic_projection)_cropped.svg/Wikimedia Commons: http://en.wikipedia.org/wiki/File:Europe_polar_stereographic_Caucasus_Urals_boundary.svg PHYSICS (NAT 4/5) © Crown copyright 2013 43 NAVIGATION Real-time air traffic control The following website allows you to watch commercial aircraft in real time: www.flightradar24.com Clicking on any of the aircraft will give information about it, its starting point and its destination. It will also tell you its speed and heading (its velocity vector), its altitude and whether or it is descending or ascending. Investigate aircraft that are flying near your school. Where are they flying to, and where have they flown from? On a clear day, can you spot the aircraft in the sky? 44 PHYSICS (NAT 4/5) © Crown copyright 2013