Construction Highlights to Expedite the Creation of Lift - Assignment Example

Design features to facilitate the production of lift   Mechanics of lift production Lift is achieved when air flows under and over the wings of an aircraft. The upper side of the wing is longer compared to the under surface. The air must move within the same time along both sides. Therefore air on top flows faster than air at the wing bottom. This brings about air pressure difference between the two surfaces. The air that flows faster decreases the air pressure around the wing. It is this lowered pressure that causes the lift McCormick & Barnes (1979). This is known as the Bernoulli Effect. The upward pressure raising the plane is bigger than that that pushing the plane down. As a result a lift is then created as illustrated in the figure below. Figure 1, the creation of lift; Bertin, & Smith (2001).  Incase the plane is banking the lift will take place in a sideways direction. If the plane is inverted it will be pulled down by lift. The amount of lift created depends on the angle the wing meets the air. If this angle of attack is steep them more lift is achieved and vice versa. In the creation of lift the force created should be sufficient to overcome the force of gravity for the plane to rise Chanute (1997).  By use of both the continuity equation and the Bernoulli equation, it is possible to illustrate how air creates a lift when it flows over an air foil. Air flows over an air foil that is stationary such as the wing of an aircraft. A head of that wing the air moves with uniform speed. In order to move past the airfoil the air has to separate in two with one part flowing under while the other flows on top. Figure 2, Separation of air on a airfoil; Bertin, & Smith (2001).  The airfoil has asymmetrical shape meaning it has a bigger surface area on the upper side than the bottom. When air moves over the airfoil the upper surface displaces it more than the bottom surface. Based on the continuity law the loss of area of flow or displacement should cause increased velocity. For example there is an airfoil within a pipe that has flowing water. In a narrow part in the pipe the water flows faster. The big area on the upper side of the airfoil makes the pipe narrower compared to what the bottom surface can do. The flow of water on the top is faster than on the bottom. The velocity of flow is increased partly by the surface of the bottom airfoil but less than the upper foil flow. According to the Bernoulli equation increased velocity causes a reduction in pressure Bertin, Smith (2001). The air that moves over an airfoil has its pressure decreasing. The loss of pressure on the upper surface is bigger than that at the under surface. What results is a net force of pressure in a positive or upward directio Design features to facilitate the production of 3-lift The wings of an aircraft are specifically designed with features that make the aircraft to get lifted in the air. These design features may include a cross section of the leading edge that has a rounded shape. The trailing edge has a cross section that is sharp. It also has leading edge devices like extensions, slots and slats. Trailing edge parts such as the flaperons which have ailerons and flaps combined and the flaps. Close to the tips of the wings there are the ailerons which are used in rolling the aircraft anticlockwise or clockwise about the long axis. On the upper surfaces there are spoilers that disrupt the lift providing more traction when an aircraft lands but is still in motion. Vortex generators are made to prevent the separation of flow in transonic flow Smith (1992). The wing fences are useful in maintaining the attachment of the flow on the wing by hindering the separation of boundary layer from spreading. The winglets are put in place to prevent wingtip vortices from decreasing lift by increasing drag. There is the dihedral or a wing angle that is positive to the horizontal. This provides stability in the roll direction. Folding wings are good for allowing more storage in confined space in the hangar deck within the carrier of the air craft. The variable seep wings do allow outstretched wings in low speed flight Montgomery (2000). Lift augmentation Increasing the amount of lift can be done through a number of ways. The wing angle or plane attitude can be changed. The leading edge is tilted up to increase the distance of the upper flow of air which then increases its speed hence low pressure and increased lift. When the lift is increased the aero plane can rise. The lift that an airfoil can produce is dependent on the speed with which the wing is moving in the air. By use of some high lift devices it is possible to make the air flowing across the wing to move faster. This increases the vacuum that brings down the airstream on the wing. This produces more lift. The air is forced through some smaller slot or space ahead of the wing’s upper surface. On a plane there is a mechanical on the leading edge of its airfoil Norman (1992). The flap can be lowered so that the lift increases. The slat may also move forward when the plane lands. They increase camber hence the lift. When the forward speed of a wing is increased there is a lift change. When the speed is doubled the lift is four times. Lift augmentation devices, their benefits, and disadvantages There are a number of devices on aircrafts that can be useful in increasing the lift. The design of the aero plane wing allows it to make cruise speed creating the lift by use of forward speed alone. If the airplane is to fly slowly the lift has to be increased somehow. By raising the angle of attack what can possibly be done is limited. Aerodynamicists have come up with other means of raising the quantity of lift created. These are known as lift augmented devices and pilots use them often in most of their flights. There exist many devices for use on the wings of an aircraft for increasing lift. They are called trailing and leading edge flaps. There are other techniques that are useful for increasing the angle of attack include wing fences, vortex generators and discontinuous leading edges. Slat and slots This is a small device that looks like a wing and it is found ahead of the wing leading edge. It makes the air flow between the wing (slot and the slat) at a very high angle of attack. Currently the slats that can be retracted automatically are the ones in use because the fixed ones drag a lot at high speeds. The slats give energy to the air when the AOA is high. This gives the air flow some kinetic energy which delays separation making the stall speed to reduce and have a higher AOA in comparison to wings that have no slats. CL also goes higher Montgomery (2000). Figure 3, Slats and slots; Wegener & Peter (1991) Leading edge flaps Regional jets and air liners have leading edge flaps to increase wing camber, raise the angle of attack making the center of pressure to move forward. This can be accomplished through two ways Smith (1992). One can take the leading edge forward on the tracks to create a slat that has a slot. Otherwise one can use a kreuger flap that extends from under the leading edge. Figure 4; Leading edge flaps: Wegener & Peter (1991) Vortex generators These devices help to give energy to the flow of air so that air separation in high angle of attack occurs much later compared to when they are not there. In comparison to slats these devices have an advantage that they almost have no drag penalty when the speeds are high. When in operation, a small vortex is developed in the flow of air above the wing and it gives energy to the boundary layer which makes it to increase its resistance to separation. The wing has an advantage of flying at a high angle of attack, has a better aileron control and the pilot has a better feel. Figure 5; Vortex generators; Wegener & Peter (1991) The pilot can be sure that the vortex generators will cause a higher lift, better control when the flight is increased, shorter distances for take off and landing, tighter turns and gentler stall if necessary. Wing fences Wing fences and the discontinuous leading edge help to prevent the stall from moving above the wing to the ailerons and the tip when they put a vortex above the wing. This brings about an improved aileron control when the angle of attack is high even into stalls. Military aircraft and jets may have these devices Wegener & Peter (1991). Accidents/Incidents that have occurred due to loss of lift   Description of the accidents 1. McDonnell Douglas DC-10 On 3rd march 1974 a Turkish Airlines Flight 981 known as McDonnell Douglas DC-10 fell inside a forest in the north eastern part of Paris in France. The plane was destined for London but it was reported to crash within a short time of take off from the Orly airport. The plane had 346 people on board and none of them survived the crash. This was considered as the deadliest aeroplane crash to be seen until 1977 when the Tenerife disaster occurred. 2. Yakovlev Yak-42 The plane Yakovlev Yak-42 belonging to YAK service had taken off from Yaroslavl in Russia on a passenger flight destined for Minsk in Belarus. The plane had 8 crew members and 37 passengers on board. The aero plane crashed immediately after it had taken off just I kilometer away from the airport. Of all the 45 people on the plane only one person escaped with bad injuries while the remaining 44 were killed in the crash Montgomery (2000). 3. Flight 447 Air France jet 228 people on an Air France jet died after plunging in to the Atlantic Ocean when the jet stalled. Flight 447 had its pilot taking a rest when it malfunctioned en route to Paris from Rio De Jeneiro. The air bus had climbed 38,000 feet before it began to roll from left to the right. Marc Dubois the captain had taken a break 4 hours in the flight at the time the co pilot reported that there was heavy turbulence. He announced this to the passengers and the crew so that passengers could fasten their seat belts. Factors leading to the accidents 1. McDonnell Douglas DC-10 The cause of the accident was later found out to be a series of happenings inside the plane leading to a crash. The cargo door was reported to have detached causing an explosive decompression making the floor above to collapse. The collapsing door severed the cables helping in the controls. This denied the pilots control of the elevators the engine number 2 and the rudder. As a result the plane went into a steep dive before crashing. 2. Yakovlev Yak-42 The crash of the Yakovlev Yak-42 was found out to be a problem within the plane that could not allow it to gain more lift. After lift off, the plane could not climb further. This impacted an antenna out of the perimeter of the airport. The aircraft managed a height of just a few meters before it rolled left impacting the ground. The plane rested after a distance of I kilometer from the place it was taking off although it was broken into pieces. The fuselage was inside the Volga River while the tail was at the bank. It was reported that the weather was very good when the accident took place. There were only few clouds, with good visibility and low winds. 3. Flight 447 Air France jet The crash was believed to have resulted from a stall or lack of lift. Pilots acted against the norms by increasing instead of lowering the nose as a response to the alert that the airbus was almost losing lift. The angle of attack was high and the captain was not yet back to the controls 1 minute after the emergency and he left it to his assistants. The co pilot was trying to fly over the storm but the plane rolled sea wards. The crew could not tell the speed of the plane. It was later discovered that the speed sensors could have iced up. References Montgomery, J., 2000 exec. ed. Aerospace: The Journey of Flight. Maxwell Air Force Base, Ala.: Civil Air Patrol. Smith, H. 1992 “Skip.” The Illustrated Guide to Aerodynamics. 2nd edition. Blue Ridge Summit, Pa.: Tab Books Inc. Wegener, Peter P. 1991 What Makes Airplanes Fly? New York: Springer-Verlag. Norman F. Smith 1992 "Bernoulli and Newton in Fluid Mechanics" The Physics Teacher November 1972 Volume 10, Issue 8, pp. 451 McCormick, Barnes W., (1979), Aerodynamics, Aeronautics, and Flight Mechanics, Chapter 3, John Wiley & Sons, Inc., New York Chanute, O. (1997). Progress in Flying Machines. Dover Publications. Bertin, J. J.; Smith, M. L. (2001). Aerodynamics for Engineers (4th ed.). Prentice Hall. http://www.youtube.com/watch?v=oeEnJiUITeg&NR=1 http://www.luizmonteiro.com/Learning_Pitot_Sim.aspx http://www.experimentalaircraft.info/articles/aircraft-pressure-instruments-1.php  http://www.velozia.com/pitot-static-test http://www.skybrary.aero/index.php/Unreliable_Airspeed_Indications Read More

Vortex generators are made to prevent the separation of flow in transonic flow Smith (1992). The wing fences are useful in maintaining the attachment of the flow on the wing by hindering the separation of boundary layer from spreading. The winglets are put in place to prevent wingtip vortices from decreasing lift by increasing drag. There is the dihedral or a wing angle that is positive to the horizontal. This provides stability in the roll direction. Folding wings are good for allowing more storage in confined space in the hangar deck within the carrier of the air craft.

The variable seep wings do allow outstretched wings in low speed flight Montgomery (2000). Lift augmentation Increasing the amount of lift can be done through a number of ways. The wing angle or plane attitude can be changed. The leading edge is tilted up to increase the distance of the upper flow of air which then increases its speed hence low pressure and increased lift. When the lift is increased the aero plane can rise. The lift that an airfoil can produce is dependent on the speed with which the wing is moving in the air.

By use of some high lift devices it is possible to make the air flowing across the wing to move faster. This increases the vacuum that brings down the airstream on the wing. This produces more lift. The air is forced through some smaller slot or space ahead of the wing’s upper surface. On a plane there is a mechanical on the leading edge of its airfoil Norman (1992). The flap can be lowered so that the lift increases. The slat may also move forward when the plane lands. They increase camber hence the lift.

When the forward speed of a wing is increased there is a lift change. When the speed is doubled the lift is four times. Lift augmentation devices, their benefits, and disadvantages There are a number of devices on aircrafts that can be useful in increasing the lift. The design of the aero plane wing allows it to make cruise speed creating the lift by use of forward speed alone. If the airplane is to fly slowly the lift has to be increased somehow. By raising the angle of attack what can possibly be done is limited.

Aerodynamicists have come up with other means of raising the quantity of lift created. These are known as lift augmented devices and pilots use them often in most of their flights. There exist many devices for use on the wings of an aircraft for increasing lift. They are called trailing and leading edge flaps. There are other techniques that are useful for increasing the angle of attack include wing fences, vortex generators and discontinuous leading edges. Slat and slots This is a small device that looks like a wing and it is found ahead of the wing leading edge.

It makes the air flow between the wing (slot and the slat) at a very high angle of attack. Currently the slats that can be retracted automatically are the ones in use because the fixed ones drag a lot at high speeds. The slats give energy to the air when the AOA is high. This gives the air flow some kinetic energy which delays separation making the stall speed to reduce and have a higher AOA in comparison to wings that have no slats. CL also goes higher Montgomery (2000). Figure 3, Slats and slots; Wegener & Peter (1991) Leading edge flaps Regional jets and air liners have leading edge flaps to increase wing camber, raise the angle of attack making the center of pressure to move forward.

This can be accomplished through two ways Smith (1992). One can take the leading edge forward on the tracks to create a slat that has a slot. Otherwise one can use a kreuger flap that extends from under the leading edge. Figure 4; Leading edge flaps: Wegener & Peter (1991) Vortex generators These devices help to give energy to the flow of air so that air separation in high angle of attack occurs much later compared to when they are not there. In comparison to slats these devices have an advantage that they almost have no drag penalty when the speeds are high.

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