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# Why airplanes fly aerodynamics

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• This is a great in-depth analysis of how airplanes work. Great content!

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• There are 4 forces that act on a plane in flight. Lift, Thrust, Weight and Drag.
• Weight is a force that is always directed toward the center of the earth. The magnitude of the weight depends on the mass of all the airplane parts, plus the amount of fuel, plus any payload on board (people, baggage, freight, etc.). The weight is distributed throughout the airplane. But we can often think of it as collected and acting through a single point called the center of gravity. In flight, the airplane rotates about the center of gravity. Flying encompasses two major problems; overcoming the weight of an object by some opposing force, and controlling the object in flight. Both of these problems are related to the object&apos;s weight and the location of the center of gravity. During a flight, an airplane&apos;s weight constantly changes as the aircraft consumes fuel. The distribution of the weight and the center of gravity also changes. So the pilot must constantly adjust the controls to keep the airplane balanced, or trimmed.
• Air resists aircraft motion because it is sticky. Directly proportional to velocity and air density. Newton’s 1 st law, air will stay at rest unless acted on by a force, which is the plane moving through it. Thus the plan must give up some of it’s energy to push the air out of the way. As the airplane moves through the air, there is another aerodynamic force present. The air resists the motion of the aircraft and the resistance force is called drag . Drag is directed along and opposed to the flight direction. Like lift, there are many factors that affect the magnitude of the drag force including the shape of the aircraft, the &amp;quot;stickiness&amp;quot; of the air, and the velocity of the aircraft. Like lift, we collect all of the individual components&apos; drags and combine them into a single aircraft drag magnitude. And like lift, drag acts through the aircraft center of pressure.
• A propulsion system provides thrust. Our 1 st example of Newton’s 3 rd law. All propulsion systems use action/reaction to propel the plane forward. To overcome drag, airplanes use a propulsion system to generate a force called thrust. The direction of the thrust force depends on how the engines are attached to the aircraft. In the figure shown above, two turbine engines are located under the wings, parallel to the body, with thrust acting along the body centerline. On some aircraft, such as the Harrier, the thrust direction can be varied to help the airplane take off in a very short distance. The magnitude of the thrust depends on many factors associated with the propulsion system including the type of engine , the number of engines, and the throttle setting . For jet engines, it is often confusing to remember that aircraft thrust is a reaction to the hot gas rushing out of the nozzle. The hot gas goes out the back, but the thrust pushes towards the front. Action &lt;--&gt; reaction is explained by Newton&apos;s Third Law of Motion.
• To overcome the weight force, airplanes generate an opposing force called lift . Lift is generated by the motion of the airplane through the air and is an aerodynamic force. Lift is directed perpendicular to the flight direction. The magnitude of the lift depends on several factors including the shape, size, and velocity of the wing &amp; aircraft. We’ll explore lift in greater detail shortly and understand how Newton’s 3 rd Law applies. &amp;quot; Aero &amp;quot; stands for the air, and &amp;quot; dynamic &amp;quot; denotes motion. The magnitude of the lift depends on several factors including the shape , size , and velocity of the aircraft. As with weight, each part of the aircraft contributes to the aircraft lift force. Most of the lift is generated by the wings. Aircraft lift acts through a single point called the center of pressure . The center of pressure is defined just like the center of gravity, but using the pressure distribution around the body instead of the weight distribution. The distribution of lift around the aircraft is important for solving the control problem. Aerodynamic surfaces are used to control the aircraft in roll , pitch , and yaw .
• We’ve covered the basics, let’s get a better understanding of lift. Lift comes from turning air downward, called the “downwash”. The picture illustrates down wash and wing vortices.
• You need a fluid (air acts like a fluid) and motion. You need air and you need the wing to be moving through the air (or air to be moving over the wing). ***So, if the lift off speed of a small aircraft is 50 kts, will it try to fly in a strong wind? You bet it will – that’s why we always tie airplanes down! Laws/principals proposed by Bernoulli &amp; Newton are used to explain lift. (although neither of them proposed the theories for that reason)
• Illustration from Plane Math: http://www.planemath.com/ (See Internet Resources) Kite or How to send your wife to Home Depot to get a 4’ x 8’ sheet of plywood on a windy day.
• You can clearly see the downwash affect as the air is accelerated downwards. Newton’s 2 nd law, F=MA. There must be a force generated. Air has mass and the wing accelerates it. Then Newton’s 3 rd law comes into play. If we create a force one way, there must be an equal and opposite one … Lift. Let’s explore it further. For a body immersed in a moving fluid, the fluid remains in contact with the surface of the body. If the body is shaped, moved, or inclined in such a way as to produce a net deflection or turning of the flow, the local velocity is changed in magnitude, direction, or both. Changing the velocity creates a net force on the body. It is very important to note that the turning of the fluid occurs because the molecules of the fluid stay in contact with the solid body since the molecules are free to move. Any part of the solid body can deflect a flow.
• You can clearly see the downwash affect as the air is accelerated downwards. Newton’s 2 nd law, F=MA. There must be a force generated. Air has mass and the wing accelerates it. Then Newton’s 3 rd law comes into play. If we create a force one way, there must be an equal and opposite one … Lift. Let’s explore it further. For a body immersed in a moving fluid, the fluid remains in contact with the surface of the body. If the body is shaped, moved, or inclined in such a way as to produce a net deflection or turning of the flow, the local velocity is changed in magnitude, direction, or both. Changing the velocity creates a net force on the body. It is very important to note that the turning of the fluid occurs because the molecules of the fluid stay in contact with the solid body since the molecules are free to move. Any part of the solid body can deflect a flow.
• Understanding a Venturi tube is essential to understanding lift. As velocity in the constriction increases, pressure must decrease.
• Venturi tubes describe what happens over a wing. A wing acts like half a venturi tube.
• We’ve covered how Newton’s Laws of Motion are used to explain lift. Let’s talk now about how Bernoulli’s Principle helps. When moving air encounters an obstacle--a person, a tree, a wing--its path narrows as it flows around the object. Even so, the amount of air moving past any section of the path must be the same, because mass can be neither created nor destroyed. The air must speed up where the path narrows, in order to have the same mass flowing through it. So air speeds up where its path narrows and slows down where it widens.
• We’ve covered how Newton’s Laws of Motion are used to explain lift. Let’s talk now about how Bernoulli’s Principle helps. The air above a wing tends to move faster than the air below it. According to Bernoulli&apos;s Principle, slower air has higher pressure than faster air. That means that the air pressure pushing up on the bottom of the wing is greater than the pressure pushing down, so the wing goes up.
• A wing is shaped and tilted so the air moving over it moves faster than the air moving under it. Bernoulli’s Principle says that as air speeds up, its pressure goes down. The faster-moving air above exerts less pressure on the wing than the slower-moving air below. The result is an upward push on the wing--lift! Illustration from “How Things Fly” (See Internet Resources)
• Here we observe the resulting pressures from turned or redirected flow.
• Bernoulli’s Principal explains how pressure variation around a wing results in a net aerodynamic force. Air moving more quickly over the top of the wing creates lower pressure above. For more detail, visit the Glenn Research Center site: http://www.grc.nasa.gov/www/k-12/airplane/right2.html
• The pressure fields can be described as a set of forces acting along the entire surface of the wing top and bottom. Just as the pressure varied with AOA, so do the forces.
• Combine all of the individual forces to get the Net Force.
• As the AOA varies, so does the lift generated.
• As the AOA varies, so does the lift generated.
• ### Why airplanes fly aerodynamics

1. 1. Presentation on Aerodynamics of Plane Presented by: Arindam Sarkar 5 th semester. Roll no. 106 Mechanical Engineering PRIYADARSHINI COLLEGE OF ENGINEERING
2. 2. Why Airplanes Fly Aerodynamics Institute of Computational Fluid Dynamics
3. 3. Aerodynamics? <ul><li>Aero – means Air </li></ul><ul><li>Dynamics – means Motion </li></ul><ul><li>Aerodynamics – the study of air in motion </li></ul><ul><li>Important Point: Air is “ Viscous ” </li></ul><ul><li>Uh, that means it’s Sticky </li></ul>
4. 4. Airplane Parts Fuselage (Body) Wing Horizontal Stabilizer Vertical Stabilizer Empennage (Tail) Engine
5. 5. 4 Forces of Flight
6. 6. Weight Center of Gravity (CG)
7. 7. Drag Newton’s 1 st Law Applies
8. 8. Thrust Newton’s 3 rd Law Applies
9. 9. Lift Newton’s 3 rd Law Applies Weight Lift Thrust Drag
10. 10. Think About It It’s “Tug-a-War” <ul><li>The motion of the airplane through the air depends on the relative strength and direction of the forces we’ve discussed. </li></ul><ul><li>If the 4 forces are balanced , the aircraft cruises at constant velocity and altitude. </li></ul><ul><li>If the forces are unbalanced , the aircraft accelerates in the direction of the largest force. </li></ul>
11. 12. More on Lift … Lift in Depth
12. 13. What’s it take to create lift? Air and motion. How do we explain lift? Newton’s Laws of Motion and Bernoulli’s Principal are used to explain lift.
13. 14. Newton’s Third Law states that for every action there is an equal and opposite reaction.
14. 15. Stream Lines
15. 16. Streak Lines 10 ° AOA Newton’s 2 nd and 3 rd Laws Apply Note: Downwash Air Accelerated Down AOA: Angle Of Attack - the angle that the wing meets the oncoming air.
16. 17. Streak Lines 0 ° AOA
17. 18. Streak Lines -12 ° AOA
18. 19. Streak Lines 10 ° AOA Newton’s 2 nd and 3 rd Laws Apply Note: Downwash Air Accelerated Down AOA: Angle Of Attack - the angle that the wing meets the oncoming air.
19. 21. Venturi Tube <ul><li>Bernouli’s first practical use of his theorem </li></ul><ul><li>Where are venturi tubes used today? </li></ul>
20. 22. What is a wing? <ul><li>A wing is really just half a venturi tube. </li></ul>
21. 23. A fluid (and air acts like a fluid) speeds up as it moves through a constricted space Bernoulli’s Principle states that, as air speeds up, its pressure goes down.
22. 24. Bernoulli's Principle: slower moving air below the wing creates greater pressure and pushes up.
23. 25. Bernoulli’s Principle: Air moving over the wing moves faster than the air below. Faster-moving air above exerts less pressure on the wing than the slower-moving air below. The result is an upward push on the wing--lift!
24. 26. Pressure Field Result of the accelerated flow on top and decelerated flow on bottom.
25. 27. Bernoulli’s Principal: pressure variation around the wing results in a net aerodynamic pushing up.
26. 28. http://www.grc/nasa.gov/WWW/Wright/airplane/shape.html
27. 29. Velocity Vectors
28. 30. Forces on the Airfoil Forces act along the entire surface.
29. 31. Net Force Combining all the forces. Which way does the lifting force actually work?
30. 32. Lift Relates to AOA Zero Lift at Zero AOA
31. 33. That’s Why Airplanes Fly.
32. 34. References <ul><li>“ The Beginner’s Guide to Aeronautics”, NASA http://www.grc.nasa.gov/WWW/K-12/airplane/ </li></ul><ul><li>“ IRROTATIONAL PLANE FLOWS OF AN INVISCID FLUID”; Colombini, Marco; UNIVERSITY OF GENOA http://www.diam.unige.it/~irro/ </li></ul><ul><li>Institute of Computational Fluid Dynamics http://www.icfd.co.jp/index-e.htm </li></ul><ul><li>See How It Flies ; Denker, John S. http://www.av8n.com/how/#mytoc </li></ul><ul><li>“ Bumblebees finally cleared for takeoff”; Wang, Z. Jane; Cornell http://www.news.cornell.edu/releases/March00/APS_Wang.hrs.html </li></ul><ul><li>DNS of Separated Flow around NACA0012 Airfoil; Shih, et al. (1992, 1995); University of Texas http://www.uta.edu/faculty/hshan/research/gallery.shtml </li></ul>
33. 35. Thank you
34. 36. Lift Relates to AOA Zero Lift at Zero AOA