An Efficient Propeller Design

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  • Topic: Airfoil, Propeller, Lift
  • Pages : 9 (2968 words )
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  • Published : April 6, 2012
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Efficient Propeller Design|

AbstractHow does a helicopter generate enough lift to fly? How does a speedboat get moving fast enough to pull someone on water skis? Here's a project on designing propellers to do the job. ObjectiveThe goal of this project is to investigate how changes in chord length affect the efficiency of propellers.IntroductionA propeller, like an airplane wing, is an airfoil: a curved surface that can generate lift when air moves over it. When air moves over the surface of a moving propeller on an airplane, the air pressure in front of the propeller is reduced, and the air pressure behind the propeller is increased. The pressure imbalance tends to push the airplane forward. We say that the propeller is generating thrust.The same principle applies to helicopter propellers, only now the propeller rotates around the vertical axis. The pressure on top of the propeller is reduced, and the pressure underneath is increased, generating lift.The illustration below (Figure 1) defines some terms that are used to describe the shape of a propeller. The radius (r) of the propeller is the distance from the center to the tip. The chord length (c) is the straight-line width of the propeller at a given distance along the radius. Depending on the design of the propeller, the chord length may be constant along the entire radius, or it may vary along the radius of the propeller. Another variable is the twist angle (β) of the propeller, which may also vary along the radius of the propeller. | Figure 1. Illustration of terms used to describe propellers. The radius, r, of the propeller, is the distance from the center to the tip, along the center line. The chord length, c, is the straight-line width of the propeller at a given distance along the radius. The twist angle, β, is the local angle of the blade at a given distance along the radius (Hepperle, 2006).| In this project you will investigate how changing the chord length affects the efficiency of the propeller. You will keep the other design features (radius and twist angle) constant, changing only the chord length of the propeller. To measure the efficiency of the propeller, you'll connect the propeller to the shaft of a small DC motor. You will use the breeze from a household fan to make the propeller turn, which will cause the shaft of the motor to spin. In this configuration, the motor will act like a generator. You'll monitor the voltage produced by the motor to determine the efficiency of the propeller.Terms, Concepts, and Questions to Start Background ResearchTo do this project, you should do research that enables you to understand the following terms and concepts: * propeller terms: * chord, * radius, * pitch, * rotational speed (measured in revolutions per minute or RPMs); * airfoil, * forces on an airplane in flight: * thrust, * drag, * lift, * weight. Questions * How do you think increasing the chord length will affect the efficiency of the propeller? Bibliography * Wikipedia is a good place to start for basic information on propellers: Wikipedia contributors, 2006. "Propeller," Wikipedia, The Free Encyclopedia [accessed November 21, 2006] * You'll definitely want to check out the Propellers section (among others) of NASA's Beginner's Guide to Aeronautics. This site is packed with useful information on the science of flight: NASA, 2006. "Beginner's Guide to Aeronautics," NASA Glenn Research Center [accessed November 22, 2006] * For more advanced students, these webpages on aerodynamics of model aircraft by Martin Hepperle will be useful. There is even a Java program that you can use to test your design ideas on the computer before building them: * Hepperle, M., 2005. "Propulsion by Propellers," Aerodynamics for Model Aircraft [accessed November 21, 2006]...
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