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Episode 97: Airplane on a Conveyor Belt
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| Started By | Thread Subject | Replies | Last Post | |||
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| ctpmn | How Stuff Works - Airplane / Conveyor Belt (page: 1 2 3) | 53 | Jun 27 2008, 10:28 AM EDT by EnderGT | |||
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Thread started: Feb 7 2008, 2:31 AM EST
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The airplane myth was actually a very simple myth, and I’m really unsure as to why people would believe that wheel movement would stop the plane from taking off. What I must assume is that most people believe is that the wheels on a plane are actually powered; but that is untrue. The wheels on planes are simply a way to reduce friction between the plane and the runway, much like ball bearings, or even oil in an engine, though they do provide directional assistance to keep the plane from achieving a yaw like motion which planes routinely incur while in flight. The law of motion plays a large part in this myth as objects at rest tend to stay at rest, so even though the wheels were turning the plane was not moving in the direction of the treadmill very quickly, the part that it did move was caused by the friction from the wheels interacting with the landing gear. So when the plane used it engines to achieve take off it made its takeoff speed. Something that I did not see mentioned in the episode is that planes take off speed is really relative to the wind speed and not to groundspeed. That is why the plane could take off on a run way. If there was a 100 mile per hour head wind one a plane with a 90 mile per hour necessary take off speed the plane, if tied down, would literally be lifted off the ground and continually fly like a kite.
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Keyword tags:
Airplane
Conveyor Belt
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| cknox | Bernoulli Priciple | 7 | Jun 24 2008, 10:14 AM EDT by EnderGT | |||
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Thread started: Jun 20 2008, 3:04 PM EDT
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The Bernoulli Principle describes the relation of a fluid speed to its pressure. Air, being a fluid, experiences this same correlation and because such, the Bernoulli Principle has often been misrepresented as what causes the lifting affect on an airplane wing.
In reality, the Bernoulli Principle has negligible affect on an airplane's wing, generating lift or otherwise. I'll qualify this as being below mach speeds. The common explanations are: 1. Air has farther to travel across the top than across the bottom of the wing, so it goes faster, which generates lower pressure, relative to the bottom. The difference in pressures produces the force known as lift. 2. A cutaway of an airfoil is compared to the cutaway of a venturi. Because the Bernoulli Principle explains the lower pressure at the greatest restriction, say in a carburetor, that similar shapes mean the airfoil works the same way. Both explanations are flawed. Ex.1 - Air does not travel faster over the top of a wing. This misconception was probably someone thinking that two air molecules need to come back together at the tail end, but they don't. This is what generates the vortex behind the wing. Ex.2 - A pure stretch of the imagination. Similar in shape, but not environment. The venturi encircles the air flow, the airfoil does not. This changes how the air reacts to these different surfaces. Air above the wing actually has to compress to get out the way of the wing. The faster the wing speed, the greater the compression.
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Keyword tags:
aerodynamics
air speed
airplane
bernoulli
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