Lift And Drag Coefficients Of Planes Engineering Essay

Lift And Drag Coefficients Of Planes Engineering EssayThe term peregrine in prevalent language typically refers to liquids, but in the realm of physics, fluid describes both gases, liquids or plasmas that conform to the underframe of its container.Fluid mechanics is the work of gases and liquids at equalizer and in motion. It is divided into fluid statics, the hire of the behavior of stationary fluids, and fluid dynamics, the study of the behavior of moving, or black marketing, fluids. Fluid dynamics is further divided into hydrodynamics, or the study of water hunt down, and aerodynamics, the study of communicate move.Real-life applications of fluid mechanics included a variety of machines, ranging from the water-wheel to the snapplane. Many of the applications are according to several principles such as Pascals ruler, Bernoullis Principle, Archimedess Principle and etc.As example, Bernoullis principle, which stated that the greater the velocity of take to the woods in a fluid, the greater the dynamic pressure and the less the static pressure. In some some other words, slower-moving fluid exerts greater pressure than faster-moving fluid. The discovery of this principle ultimately made possible the development of the airplane. Therefore, among the most famous applications of Bernoullis principle is its use in aerodynamics.In addition, the study of fluids provides an understanding of a number of everyday phenomena, such as why an open window and door together create a draught in a room.Wind TunnelSuppose one is in a room where the heat is on too high, and there is no dash to adjust the thermostat. Outside, however, the air is cold, and thus, by opening a window, one can presumably cool down the room. But if one opens the window without opening the former door of the room, there will only be little temperature change. But if the door is opened, a nice cool breeze will blow finished the room. Why?This is because, with the door closed, the room con stitutes an area of relatively high pressure compared to the pressure of the air outside the window. Because air is a fluid, it will tend to flow into the room, but at one time the pressure inside reaches a certain point, it will prevent additional air from entering. The tendency of fluids is to move from high-pressure to low-pressure areas, not the other way around. As soon as the door is opened, the relatively high-pressure air of the room flows into the relatively low-pressure area of the hallway. As a result, the air pressure in the room is push downd, and the air from outside can at a time enter. Soon a wind will begin to blow through the room.The above scenario of wind flow rate through a room describes a rudimentary wind delve. A wind tunnel is a chamber built for the purpose of examining the characteristics of airflow in contact with solid preys, such as aircraft and automobiles.Theory of Operation of a Wind TunnelWind tunnels were first proposed as a means of studyi ng vehicles (primarilyairplanes) in free flight. The wind tunnel was envisioned as a means of reversing the usual paradigm instead of the affectation standing still and the aircraft moving at revivify through it, the same effect would be obtained if the aircraft stood still and the air moved at speed past(a) it. In that way a stationary observer could study the aircraft in action, and could measure the aerodynamic forces being imposed on the aircraft.Later, wind tunnel study came into its own the effects of wind on manmade structures or objects needed to be studied, when buildings became tall enough to present large surfaces to the wind, and the resulting forces had to be resisted by the buildings internal structure. tranquil later, wind-tunnel testing was applied toautomobiles, not so much to determine aerodynamic forces per second but more to determine ways to reduce the power needful to move the vehicle on roadways at a given speed.In the wind tunnel the air is moving relativ e to the roadway, while the roadway is stationary relative to the test vehicle. Some automotive-test wind tunnels have incorporated moving belts under the test vehicle in an effort to approximate the actual condition. Its represents a safe and judicious use of the properties of fluid mechanics. Its purpose is to test the interaction of airflow and solids in relative motion in other words, either the aircraft has to be moving against the airflow, as it does in flight, or the airflow can be moving against a stationary aircraft. The first of these choices, of course, poses a number of dangers on the other hand, there is little danger in exposing a stationary craft to winds at speeds simulating that of the aircraft in flight.Wind tunnelWind tunnels are used for the study of aerodynamics (the dynamics of fluids).So there is a wide range of applications and fluid mechanic theory can be applied in the device. airframe flow analysis (aviation, open improvements etc), aircraft engines (jets ) performance tests and improvements, car industry reduction of clang, better air penetration, reduction of losses and fuel consumption (thats why all cars now look the same the square off is not a question of taste, but the result of laws of physics) any improvement against and to reduce air friction i.e. the shape of a speed cycling helmet, the shape of the profiles used on a bike are designed in a wind tunnel. to measure the flow and shape of waves on a surface of water, in response to winds (very large swimming pools) Entertainment as well, in mounting the tunnel on a vertical axis and blowing from bottom to top. Not to simulate anti-gravity as said above, but to allow safely the experience of free-falling parachutes.The Bernoulli principle is applied to measure experimentally the air speed flowing in the wind tunnel. In this case, the construction of Pitot tube is made to utilize the Bernoulli principle for the task of measuring the air speed in the wind tunnel. Pitot tube i s generally an instrument to measure the fluid flow velocity and in this case to measure the speed of air flowing to assist further aerodynamic calculations which require this piece of information and the adjustment of the wind speed to achieve desired value.Schematic of a Pitot tubeBernoullis compare statesStagnation pressure = static pressure + dynamic pressureThis can also be written as,Solving that for velocity we getWhere,V is air velocitypt is stagnation or total pressureps is static pressureh= fluid heightand is air densityTo reduce the error produced, the placing of this device is properly aligned with the flow to avoid misalignment.As a wing moves through the air, the wing is inclined to the flight direction at some angle. The angle between thechord line and the flight direction is called theangle of set onand has a large effect on the turn backgenerated by a wing. When an airplane takes off, the pilot applies as muchthrustas possible to make the airplane roll along the runway. But just earlier draw nearing off, the pilotrotatesthe aircraft. The nose of the airplane rises, change magnitude the angle of attackand producing theincreased liftneeded for takeoff.The magnitude of the liftgeneratedby an object depends on theshapeof the object and how it moves through the air. For thinairfoils,the lift is directly proportional to the angle of attack for small angles (within +/- 10 degrees). For higher angles, however, the dependence is quite involved. As an object moves through the air, air moleculesstickto the surface. This creates a layer of air near the surface called a bourne layerthat, in effect, changes the shape of the object. Theflow numberreacts to the edge of the boundary layer just as it would to the physical surface of the object. To make things more confusing, the boundary layer may lift off or separate from the body and create an effective shape much different from the physical shape. The separation of the boundary layer explains why airc raft wings will absolutely lose lift at high angles to the flow. This condition is called awing stall.On the slide directn above, the flow conditions for deuce airfoils are shown on the left. The shape of the two foils is the same. The lower foil is inclined at ten degrees to the incoming flow, while the upper foil is inclined at twenty degrees. On the upper foil, the boundary layer has separated and the wing is stalled. Predicting thestall point(the angle at which the wing stalls) is very difficult mathematically. Engineers usually entrust onwind tunneltests to determine the stall point. But the test must be done very carefully, matching all the importantsimilarity parametersof the actual flight hardware.The darn at the right of the figure shows how the lift varies with angle of attack for a typical thin airfoil. At low angles, the lift is nearly linear. Notice on this plot that at slide fastener angle a small amount of lift is generated because of the airfoil shape. If the ai rfoil had been symmetric, the lift would be zero at zero angle of attack. At the right of the curve, the lift changes rather abruptly and the curve stops. In reality, you can set the airfoil at any angle you want. However, once the wing stalls, the flow becomes highly unsteady, and the value of the lift can change rapidly with time. Because it is so hard to measure such flow conditions, engineers usually carry the plot blank beyond wing stall.Since the amount of lift generated at zero angle and the location of the stall point must usually be determined experimentally, aerodynamicists include the effects of inclination in thelift coefficient.For some simple examples, the lift coefficient can be determined mathematically. For thin airfoils at subsonic speed, and small angle of attack, the lift coefficientClis given byCl = 2whereis 3.1415, andais the angle of attack expressed in radiansradians = 180 degreesAerodynamicists rely on wind tunnel testing and very sophisticated computer ana lysis to determine the lift coefficient.Lift coefficientThelift coefficient(or) is adimensionlesscoefficient that colligates theliftgenerated by an aerodynamic body such as awingor completeaircraft, thedynamic pressureof the fluid flow around the body, and a quote area associated with the body. It is also used to refer to the aerodynamic lift characteristics of a2Dairfoilsection, whereby the reference area is taken as the airfoilchord.It may also be described as the ratio of lift pressure todynamic pressure.Aircraft Lift CoefficientLift coefficient may be used to relate the totalliftgenerated by an aircraft to the total area of the wing of the aircraft. In this application it is called theaircraftorplanform lift coefficientThe lift coefficientis equal towhereis thelift force,is fluiddensity,is uncoiled airspeed,isdynamic pressure, andisplanformarea.The lift coefficient is adimensionless number.The aircraft lift coefficient can be approximated using, for example, theLifting-line th eoryor measured in awind tunneltest of a complete aircraft configuration.Section Lift CoefficientLift coefficient may also be used as a characteristic of a particular shape (or cross-section) of anairfoil. In this application it is called thesection lift coefficientIt is common to show, for a particular airfoil section, the relationship between section lift coefficient andangle of attack.It is also useful to show the relationship between section lift coefficients and sop up coefficient.The section lift coefficient is based on the concept of an infinite wing of non-varying cross-section, the lift of which is bereft of any three-dimensional effects in other words the lift on a 2D section. It is not relevant to define the section lift coefficient in terms of total lift and total area because they are infinitely large. Rather, the lift is defined per unit span of the wingIn such a situation, the above formula becomeswhereis thechordlength of the airfoil.The section lift coefficient for a given angle of attack can be approximated using, for example, theThin Airfoil Theory,or determined from wind tunnel tests on a finite-length test piece, with endplates designed to ameliorate the 3D effects associated with thetrailing vortexwake structure. bank line that the lift equation does not include terms forangle of attack that is because the mathematical relationship betweenlift andangle of attackvaries greatly between airfoils and is, therefore, not constant. (In contrast, there is a straight-line relationship between lift and dynamic pressure and between lift and area.) The relationship between the lift coefficient and angle of attack is complex and can only be determined by experimentation or complex analysis. See the accompanying graph. The graph for section lift coefficient vs. angle of attack follows the same general shape for allairfoils, but the particular numbers will vary. The graph shows an almost linear increase in lift coefficient with increasingangle of attac k, up to a maximum point, after which the lift coefficient reduces. The angle at which maximum lift coefficient occurs is thestallangle of the airfoil.The lift coefficient is adimensionless number.Note that in the graph here, there is still a small but positive lift coefficient with angles of attack less than zero. This is true of any airfoil with argot(asymmetrical airfoils). On a cambered airfoil at zero angle of attack the pressures on the upper surface are lower than on the lower surface.A typical curve showing section lift coefficient versus angle of attack for a cambered airfoilDrag CoefficientInfluid dynamics, thedrag coefficient(commonly denoted asor) is adimensionless quantitythat is used to quantify thedragor resistance of an object in a fluid environment such as air or water. It is used in thedrag equation, where a lower drag coefficient indicates the object will have lessaerodynamicorhydrodynamicdrag. The drag coefficient is always associated with a particular surface ar ea.The drag coefficient of any object comprises the effects of the two basic contributors tofluid dynamicdragskin frictionandform drag. The drag coefficient of liftingairfoilorhydrofoilalso includes the effects of liftinduced drag.The drag coefficient of a complete structure such as an aircraft also includes the effects ofinterference drag.DefinitionThe drag coefficientis defined aswhereis thedrag force, which is by definition the force component in the direction of the flow velocity,is themass densityof the fluid,is thespeedof the object relative to the fluid, andis the referencearea.The reference area depends on what type of drag coefficient is being measured. For automobiles and many other objects, the reference area is the frontal area of the vehicle (i.e., the cross-sectional area when viewed from ahead). For example, for a sphere(note this is not the surface area =).Forairfoils, the reference area is theplanformarea. Since this tends to be a rather large area compared to the projected frontal area, the resulting drag coefficients tend to be low much lower than for a car with the same drag, frontal area and at the same speed.Airshipsand somebodies of revolutionuse the volumetric drag coefficient, in which the reference area is thesquareof thecube rootof the airship volume. Submerged streamlined bodies use the wetted surface area.Two objects having the same reference area moving at the same speed through a fluid will experience a drag force proportional to their respective drag coefficients. Coefficients for unstreamlined objects can be 1 or more, for streamlined objects much less.