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DETAILED STUDY 3.2: INVESTIGATIONS: AEROSPACE (FLIGHT) Students should demonstrate the knowledge and skills to: apply the concepts of forces, moments and equilibrium to balancing an aircraft; explain lift in terms of Bernoulli’s equation and the rate of change of momentum; explain drag; skin friction drag, pressure drag and principles of thrust; analyse aircraft performance including takeoff, climb, descent and cruise; use computer models to investigate phenomena associated with flight; Students are asked to identify a focused problem or research question and formulate a set of responses to a set of questions. AEROSPACE (FLIGHT): AN EMERGING AN INNOVATIVE INDUSTRY The history of sustained powered flight celebrates its one hundredth anniversary in 2003. It is indeed startling that that first sustained powered flight of Wilbur and Orville Wright on 17 December 1903 lasted 12 seconds and covered 36.6 m which is less than the wingspan of a Boeing 747 airplane (wingspan of 64.4 m). http://www.ueet.nasa.gov/StudentSite/historyofflight.html From those early days to today’s technologically sophisticated aircraft represents a huge quantum leap, and the story of the men and women involved in making the breakthroughs throughout the history of powered flight, and those making the breakthroughs today, is extremely interesting. www.edwards.af.mil/.../splash/ mar98/cover/spaceage.htm APPLYING THE CONCEPTS OF FORCES, MOMENTS AND EQUILIBRIUM TO BALANCING AN AIRCRAFT To look at forces, moments and equilibrium the following diagrams from the text Aeroplane General Knowledge and Aerodynamics are very useful. This useful book is used by Victorian students studying for their private and commercial pilot licences and is available from: http://www.aviationtheory.net.au/ The diagram below from Aeroplane General Knowledge and Aerodynamics (Chapter 2: Forces in Flight, p.11.) shows the equilibrium conditions required in the vertical direction for the plane to be stable both on the ground and in the air: on the ground the Weight Force down (acting though the geometric centre of mass of the aircraft) is balanced by the Reaction Force up, while in straight and level flight the Weight Force down is balanced by the Lift Force up. These concepts tie in neatly with Newton’s three laws of motion studied in Area of Study 1: Movement. The diagram below from Aeroplane General Knowledge and Aerodynamics (Chapter 2: Forces in Flight, p.11.) illustrates the equilibrium condition in the horizontal direction. In steady straight and level flight, the Drag Force (caused by air friction) needs to be balanced by the Thrust Force (provided by the engine). These two diagrams can be combined to give the diagram below (Aeroplane General Knowledge and Aerodynamics (Chapter 2: Forces in Flight, p.12.)). If the lift force is more than the weight force the plane goes up and if the weight force is more than the lift force the plane goes down. If the thrust force is more than the drag force then the plane speeds up (accelerates) and if the drag force is more than the thrust force the plane slows down (decelerates). Although the Lift Force may be the same magnitude as the Weight Force sometimes it may not be acting through the same point. Such a misalignment of forces causes an imbalance. This imbalance is called a turning moment (or torque) and needs to be balanced say by the tailplane wing or the trim creating a balancing force. Such a situation is shown in the diagram below (Aeroplane General Knowledge and Aerodynamics, Chapter 2: Forces in Flight, p. 12.). http://www.grc.nasa.gov/WWW/K-12/airplane/bga.html At the ‘howstuffworks’ website there is also a good explanation and useful diagrams of the four main forces acting on airplanes: http://travel.howstuffworks.com/airplane1.htm The Physics of Flight website run by the United States Air Force also contains useful information and diagrams covering these concept areas: http://www.usafa.af.mil/dfp/cockpit-phys/cp_pf0.htm The Dryden Flight Research Centre – Education website has a good Adobe PDF file titled ‘Flight Testing Newton’s Laws’ which can be downloaded for free and which covers many of the concepts studied: http://www.dfrc.nasa.gov/Education/OnlineEd/NewtonsLaws/index.html Unfortunately, it does not use SI units. A version of the document with the units converted to SI units is available from RMIT University (Contact Prof Lachlan Thompson (RMIT Aerospace) who has a number of aerodynamics resources available on CD, including the SI version of ‘Flight Testing Newton’s Laws’, for a nominal cost). EXPLAINING LIFT IN TERMS OF BERNOULLI’S EQUATION AND THE RATE OF CHANGE OF MOMENTUM Bernoulli Daniel Bernoulli (1700-1782), son of a family of famous Swiss mathematicians, contributed much to our understanding of hydrodynamics. He was the first to solve the differential equation now known as Bernoulli’s Equation. He held chairs in anatomy, botany and physics at Basle in Switzerland. Bernoulli’s Equation Static Pressure + Dynamic Pressure = Constant Total Pressure (C) and how it relates to flight is covered in Aeroplane General Knowledge and Aerodynamics (pp.15-17). The authors introduce air density. They explain, using a non-mathematical treatment, how lift is created by reaction forces generated via pressure differentials above and below the wing (which in turn are due to velocity differences in the respective airstreams). The Dryden Flight Research Centre – Education website downloadable Adobe PDF file titled ‘Flight Testing Newton’s Laws’ has a good section on developing lift using the rate of change of momentum (See page 3.4 of Developing Lift in the Adobe PDF file): http://www.dfrc.nasa.gov/Education/OnlineEd/NewtonsLaws/index.html At the ‘howstuffworks’ website there is a good discussion as well as some useful diagrams concerning popular explanations of lift, viz: ‘Two of the most popular explanations today are the Longer Path explanation (also known as the Bernoulli or equal transit time explanation) and the Newtonian explanation (also known as the momentum transfer or air deflection explanation). While many versions of these explanations are fundamentally flawed, they can still contribute to an intuitive understanding of how lift is created.’ http://travel.howstuffworks.com/airplane2.htm Halliday, Resnick and Walker provide a nice concise explanation (with a clear diagram) in terms of Newton’s third law (An Airplane Wing p.461, Fundamentals of Physics Extended with Modern Physics, 4th edn, John Wiley and Sons, 1993). A useful investigation of the Bernoulli Effect can be undertaken by using the air stream from a vacuum cleaner (in reverse mode) and placing a number of light balls (e.g. table tennis balls) and other light objects of various shapes in the air stream. Some interesting demonstrations of various aspects of the Bernoulli Effect can also be found at: http://onezine.s-one.net.sg/@School/Standrew/mech_bernoulli.htm The San Francisco Exploratorium has some interesting experiments on the Bernoulli Effect and also some interesting images (for example, the one below where the beach ball is being held at an angle in the airstream): http://www.exploratorium.edu/books/bernoulli/ The following resources are also useful for investigations in this area. Aviation and Space Science Projects, Dr Ben Millspaugh, TAB Books, 1992 contains a number of experimental investigations in aerodynamics including the Bernoulli Effect. NASA has a free airfoil simulator program: FoilSim II (80KB) which can be downloaded from: http://www.grc.nasa.gov/WWW/K-12/airplane/foil2.html With this free software from NASA you can investigate how an aircraft wing produces lift by changing the values of different factors that affect lift. FoilSim II computes the theoretical lift of a variety of airfoil shapes. The user can control the shape, size, and inclination of the airfoil and the atmospheric conditions in which the airfoil is flying. The program includes a stall model for the airfoil, a model of the Martian atmosphere, and the ability to specify a variety of fluids for lift comparisons. The program has graphical and numerical output, including an interactive probe which you can use to investigate the details of flow around an airfoil. EXPLAINING DRAG; SKIN FRICTION DRAG, PRESSURE DRAG AND PRINCIPLES OF THRUST Although the concepts of drag, skin friction drag, pressure drag and principles of thrust and how these relate to flight are covered in Aeroplane General Knowledge and Aerodynamics (pp.25-29, 33-34 and 39), the explanations and diagrams provided by this text might be too complex for some Unit 2 Physics students. LIST OF USEFUL ELECTRONIC RESOURCES/WEBSITES At the ‘howstuffworks’ website there are also good explanations and useful diagrams covering these concepts: http://travel.howstuffworks.com/airplane1.htm The Physics of Flight website run by the United States Air Force also contains useful information and diagrams covering these concept areas: http://www.usafa.af.mil/dfp/cockpit-phys/cp_pf0.htm The Dryden Flight Research Centre – Education website has a very useful Adobe PDF file titled “Flight Testing Newton’s Laws” (which can be downloaded for free) which also covers these concepts. http://www.dfrc.nasa.gov/Education/OnlineEd/NewtonsLaws/index.html NASA History of Flight http://www.ueet.nasa.gov/StudentSite/historyofflight.html NASA High speed research aircraft www.edwards.af.mil/.../splash/ mar98/cover/spaceage.htm Women in Aviation Educational, historical, and networking resources to empower women in all aspects of aviation http://www.women-in-aviation.com/ Aviation Theory Centre Has texts such as: Aeroplane General Knowledge and Aerodynamics http://www.aviationtheory.net.au/ Aerodynamics and Aircraft Design http://www.flyg.kth.se/education/msc/courses/4E1212/downloads/aerolinks.ht m Aerodynamics of Flight Langley research centre http://history.nasa.gov/SP-367/cover367.htm NASA Aerospace Activities and Lessons http://www.grc.nasa.gov/WWW/K-12/aeroact.htm Walter Fendt A Java applet on Levers which looks at Turning Moments and Torque http://www.walter-fendt.de/ph14e/lever.htm http://www.walter-fendt.de/ph11e/lever.htm NASA Beginner's Guide to Aerodynamics http://www.grc.nasa.gov/WWW/K-12/airplane/bga.html Howstuffworks Forces acting on airplanes http://travel.howstuffworks.com/airplane1.htm Howstuffworks Explanations of lift http://travel.howstuffworks.com/airplane2.htm Physics of Flight United States Air Force http://www.usafa.af.mil/dfp/cockpit-phys/cp_pf0.htm Dryden Flight Research Centre – Education “Flight Testing Newton’s Laws” http://www.dfrc.nasa.gov/Education/OnlineEd/NewtonsLaws/index.html Double Helix Club Plane designs http://www.publish.csiro.au/helix/cf/issues/th64b4.cfm Bernoulli Effect Interesting experiments re the Bernoulli Effect http://onezine.s-one.net.sg/@School/Standrew/mech_bernoulli.htm http://www.exploratorium.edu/books/bernoulli/ NASA Airplane simulator http://www.grc.nasa.gov/WWW/K-12/Enginesim/index.htm Microsoft’s Flight Simulator 2002 Commercial flight simulator http://www.microsoft.com/games/fs2002/ FlightGear Non-Commercial flight simulator http://www.flightgear.org/Docs/InstallGuide/getstartch1.html National Aerospace Training Trial Introductory Flights www.nationalaerospace.net Forces in Flight Flash Animation www.aviationnow.com/content/ncof/ncflearn.htm NASA sites: http://education.nasa.gov http://www.dfrc.nasa.gov/ NASA Dryden Flight Centre PDF document ‘Flight Testing Newton’s Laws’ available free online (an SI Units version is available from RMIT) at http://www.dfrc.nasa.gov/Education/OnlineEd/NewtonsLaws/index.html http://www.dfrc.nasa.gov/gallery