4/17/2023 0 Comments Airfoil shapeThe top surface of a wing contributes greatly to turning the fluid flow. Why is it not entirely correct? (HAND-OUT) (Newtonian) The Newtonian explanation provides a pretty intuitive picture of how the wing turns the air flowing past it, with a couple of exceptions: The top surface of the wing is left completely out of the picture. As the air particles strike the bottom surface of the wing, they impart some of their momentum to the wing, thus incrementally nudging the wing upward with every molecular impact. How Lift is Created (Newtonian) Each individual air particle bounces off the bottom surface of the wing and is deflected downward. If one pushes on the other, both move - one due to the action force and the other due to the reaction force. You can see a good example of this by watching two skaters at an ice rink. How Lift is Created (Newtonian) Newton’s 3 rd Law: For every action there is an equal, and opposite, reaction. This explanation also predicts that planes should not be able to fly upside down, although we know that many planes have this ability. However, many wings are symmetric (shaped identically on the top and bottom surfaces). For many types of wings, the top surface is longer than the bottom. In fact, these two air particles have no 'knowledge' of each other's presence at all, and there is no logical reason why these particles should end up at the rear of the wing at the same moment in time. Why is it not entirely correct? (HAND-OUT) (Bernoulli) There are several flaws in this theory, although this is a very common explanation found in high school textbooks and even encyclopedias: The assumption that the two air particles described above rejoin each other at the trailing edge of the wing is groundless. The Longer Path explanation deduces that this faster moving air develops a lower pressure on the top surface, while the slower moving air maintains a higher pressure on the bottom surface. How Lift is Created (Bernoulli) Bernoulli's equation, a fundamental of fluid dynamics, states that as the speed of a fluid flow increases, its pressure decreases. Since the particle traveling over the top goes a longer distance in the same amount of time, it must be traveling faster. How Lift is Created (Bernoulli) Let's assume that two nearby particles split up at the leading edge, and then come back together at the trailing edge of the wing. Air particles that approach the leading edge of the wing must travel either over or under the wing. How Lift is Created (Bernoulli) The Longer Path Explanation: holds that the top surface of a wing is more curved than the bottom surface. Newton – Focused his studies on the deflection of air or fluid on an object and its reaction. Who’s Theory on Lift Is Correct? Bernoulli – Focused his studies on the curvature of the wing, and the differing air pressure over the top and bottom of the wing. This explains why spacecraft don't have wings unless the spaceship spends at least some of its time in air. Ī Few Words About Fluid Consequently, neither lift nor drag can be created in space (where there is no fluid). Lift and Drag can exist only in the presence of a moving fluid ( object is stationary and the fluid is moving OR fluid is still and the object is moving through it ). Basic aerodynamic tests are sometimes performed underwater. Straight and Level Flight In order for an airplane to fly straight and level, the following relationships must be true: Thrust = Drag Lift = Weight Q1 - What would happen if Drag is greater than Thrust? Q2 - What would happen if Lift is greater than Weight?Ī Few Words About Fluid A principal concept in aerodynamics is the idea that air is a fluid (like all gases, air flows and behaves in a similar manner to water and other liquids). This decreases the pressure and causes lift. When you blow across an airfoil you are increasing the speed at which the air moves across the top of the airfoil. Tests the Effects To test the effects of pressure and airspeed, take a regular piece of notebook paper and hold it up like the girl at the left. Slower air on the underside of the wing creates more air pressure than the upper curved part of the wing (faster moving air)…creating lift. Forward driving force of a propeller attached to an engine, or the forward force produced by gases escaping rearward from a jet or rocket engine. Ĥ Forces of Flight (Continued) Thrust : Pushes the plane forward. Friction will continue to push against objects until it stops. Drag is the resisting force called friction. Gravity pulls everything near or on Earth towards the center of Earth. Ĥ Forces of Flight Gravity (Weight) : Pulls the plane down. Aerodynamics is the study of forces and the resulting motion of objects through the air. What is aerodynamics? The word comes from two Greek words: aerios = concerning the air. Presti Northport Middle School Technology
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