Aerofoils: How Wings Work - Coursework Example

Aerofoils - How Wings Work Tasks Introduction Having a steady flight requires the availing of enough upward force on the wings of the aircraft such that its weight is countered. Laws that govern the movement of spacecrafts as well as ballistic missiles are not the same as those that govern the flying of aircrafts which as the name suggests its movement solely depends with the interaction with the air. The aircraft’s wing the component of the aeroplane that is responsible of creating lift and eliminating means that flying is not possible. In the manufacturing of aeroplane wing the shape of the wing which is described by its cross section (which is referred to as the aerofoil) is dependent on the type of aircraft. The designing of the aerofoil has a major objective of ensuring there is maximum lift is generated while lowering the amount of drag generated. In designing the aerofoils there is a keen interest in ensuring that airflow at the upper side is higher while at the lower side the speed is lower. In aerofoils Bernoulli’s principle comes into play at the stage where the wings are being tested in wind tunnels. According to Bernoulli’s principle there is reduction in pressure of a fluid as its speed increases and vice versa. The principle is explored in coming of with aerofoil design where the air flowing on the upper side that is more curved is much faster while in the lower side where there is less curving movement of air is at much less speed and thus resulting to generation of upward force. 1. Explain what are the common misconceptions about lift?   The common misconception about a lift being generated is that the only important thing is to have the speed of the air that is surrounding the aerofoil being different from that of the general surrounding air (the general atmosphere (Piercy, 1955). This is not real true since there may be streams of air on both side of the wind having relatively higher speed that the general atmosphere but this may not be accompanied by any pressure difference in the air. It is important that we have change in direction of the flow of air in the immediate surroundings of the wind because it is due to this change in direction that that pressure difference is developed between the immediate surrounding and that in the general atmosphere. Having difference in pressure between the air in the immediate surroundings of the wind and the general atmosphere will not guarantee generation of a lift. The pressure at the lower side of the wing is supposed to be relatively higher than that on the upper side so as to generate a lift as a result of the difference in pressure (Mercury, 2013). 2. Explain how an aerofoil really generates Lift? When the wing of the aircraft moves through the air is cut into two portions. In order for there to be continuity of the air that is split it is important that the air at the lower side and that at upper side should arrive at the tip at the same time. With the upper side being more curved it will mean that the air will need to travel faster in this upper side than the lower side. The higher speed of air in the upper side would result to having lower pressure on that surface while the lower side would have higher pressure and thus the difference in pressure would result into having a lift. 3. Why is an aerofoil shaped as it is?  (i.e rounded and not pointed at the front, why is it thicker in the middle, tapered at the rear, flatter underneath, with a camber making it curve on top?) The front part of the aerofoil is rounded so as to ensure that the change in speed is rapid as well as the change in direction of the air with the consequence being reduction in pressure while minimizing level of turbulence. With the lower side having a flatter shape there will be a smaller level of change in pressure in comparison to the change in the upper side of aerofoil (NASA). It is as a result of this difference in pressure that there is the generation of lift. The tapered shape at the rear is important in ensuring the air from the upper side and that from the lower side reunite smoothly with minimal level of turbulence. Turbulence is likely to result into destruction of aerofoil and the entire aircraft. 4. What other shapes will generate lift?  (will a house brick generate lift? a saucer? a football? Draw some shapes) A house will generate a lift since air inside the house is stationary while on the surface air is moving and this would result to pressure difference which into would generate lift. A source shape will also result in a lift if the curved part is made to face up. 5. What causes Drag and what are the different types of Drag? Drag is a consequence of the aircraft meeting air resistance in the process of flying. Parasitic drag may be form drag or skin friction. Form drag is also referred to as pressure drag is generated by virtue of the shape as well as the size of the object moving through air with high level of drag being experienced where the cross-section that is exposed to air is large while a body which has a thin section under direct exposure to the air in which it is moving will experience a smaller level of drag (Houghton, 2006). Induced drag is created intentionally as it contributes to generation of lift or rather it is proportional to the lift that is being generated. An aircraft moving at a very low speed will need to have a high level of induced drag since this is dictated by the fact that in order to have sufficient lift to keep the aircraft in the air there will be need to have a larger angle of attack which is associated with increased drag level. As the speed of the aircraft increases there is increase in the lift generated and in order to maintain the required level of lift the angle of attack is reduced which also result to a reduction in induced drag. 6. What is a boundary layer?   The air that immediately surrounds the aerofoil is assumed to have zero speed as a consequence of the air being viscous and as the distance from the aerofoil increases there will be an increase in the air speed up to a point where the speed will match that of the free stream speed. The layer from the wall of the aerofoil to the point where free stream speed start is what is referred to as the boundary layer. 7. What are wingtip vortices and what causes them? This referred to a pattern which takes a circular shape that is brought about by rotating air which that is left behind as lift is being generated by the aerofoil. Lift-induced vortices are the name given to Wingtip vortices that are generated at other points other than the wingtips. 8. What are the common formulas for Lift& Drag? (i.e CL, CD). What do they depend on? Give an example use of the equations. Lift (L) =  Drag =  Where  is air density, v is the speed of air relative to aerofoil, A gives the reference area,  represents the lift while  represents drag coefficient. The coefficients are dependent on body inclination, viscosity and compressibility of air (or any fluid under consideration), and size and shape of object. 9. Using the XFLR5 software package generate plots of CL and CD versus angle for any commonly used NACA 4 series aerofoil. You need to plot two graphs Using XFLR5 software there was plotting of graphs for CL against Alpha and CD against Alpha as can be observed in files aerofoil1, aerofoil2 aerofoil3 10. From the plots in section nine, what angle gives zero lift? What angle gives maximum lift? The maximum lift is achieved at angle 100 for a Reynolds number of 300000 while zero lift is seen to occur at angle of attack of 40  If aerofoil is made to fly upside down, the angle would be 10 with an angle of attack of Alpha =10 Reynolds of 300000 lift at alpha 4 11. Include a drawing of the aerofoil you have chosen in section nine The shape of the aerofoil appears as below. Conclusions From the issues which have been addressed as the answers to question were given the principles behind lift in aircrafts has been addressed. In the design of aircraft aerofoil the shape that will make the desirable lift to be achieved at a speed of air craft that is considered as being reasonable is the most important aspect. Thick aerofoils are likely to give the desired lift at a low aircraft speed but this would be accompanied by creating drag which is unreasonably high. For one to attain the required lift at a smaller angle of attack the aircraft need to move at a higher speed. The effect of changing the angle of attack is clearly visualized by using the XFLR5 software References Anderson, John D. (2004), Introduction to Flight (5th ed.), McGraw-Hill, pp. 352–361, §5.19, ISBN 0-07-282569-3 Clancy, L.J. (1975), Aerodynamics, Pitman Publishing Limited, London ISBN 0-273-01120-0 American flyers (2013). Different types of flaps, Houghton, E.L. and Carpenter, P.W.-2006- Fifth Edition Aerodynamics for Engineering Students Piercy N.A.V.-1955-Aerodynamics. Mercury (2013). Pressure at aerofoil NASA [Online] - Date seen: 10/11/14 Technical Notes National Advisory Committee for Aeronautics- 1939 Wegener, Peter P.-1991-What Makes Airplanes Fly: Pg.112 Read More

Explain how an aerofoil really generates Lift? When the wing of the aircraft moves through the air is cut into two portions. In order for there to be continuity of the air that is split it is important that the air at the lower side and that at upper side should arrive at the tip at the same time. With the upper side being more curved it will mean that the air will need to travel faster in this upper side than the lower side. The higher speed of air in the upper side would result to having lower pressure on that surface while the lower side would have higher pressure and thus the difference in pressure would result into having a lift. 3. Why is an aerofoil shaped as it is?  (i.e rounded and not pointed at the front, why is it thicker in the middle, tapered at the rear, flatter underneath, with a camber making it curve on top?) The front part of the aerofoil is rounded so as to ensure that the change in speed is rapid as well as the change in direction of the air with the consequence being reduction in pressure while minimizing level of turbulence.

With the lower side having a flatter shape there will be a smaller level of change in pressure in comparison to the change in the upper side of aerofoil (NASA). It is as a result of this difference in pressure that there is the generation of lift. The tapered shape at the rear is important in ensuring the air from the upper side and that from the lower side reunite smoothly with minimal level of turbulence. Turbulence is likely to result into destruction of aerofoil and the entire aircraft. 4.

What other shapes will generate lift?  (will a house brick generate lift? a saucer? a football? Draw some shapes) A house will generate a lift since air inside the house is stationary while on the surface air is moving and this would result to pressure difference which into would generate lift. A source shape will also result in a lift if the curved part is made to face up. 5. What causes Drag and what are the different types of Drag? Drag is a consequence of the aircraft meeting air resistance in the process of flying.

Parasitic drag may be form drag or skin friction. Form drag is also referred to as pressure drag is generated by virtue of the shape as well as the size of the object moving through air with high level of drag being experienced where the cross-section that is exposed to air is large while a body which has a thin section under direct exposure to the air in which it is moving will experience a smaller level of drag (Houghton, 2006). Induced drag is created intentionally as it contributes to generation of lift or rather it is proportional to the lift that is being generated.

An aircraft moving at a very low speed will need to have a high level of induced drag since this is dictated by the fact that in order to have sufficient lift to keep the aircraft in the air there will be need to have a larger angle of attack which is associated with increased drag level. As the speed of the aircraft increases there is increase in the lift generated and in order to maintain the required level of lift the angle of attack is reduced which also result to a reduction in induced drag. 6. What is a boundary layer?

  The air that immediately surrounds the aerofoil is assumed to have zero speed as a consequence of the air being viscous and as the distance from the aerofoil increases there will be an increase in the air speed up to a point where the speed will match that of the free stream speed. The layer from the wall of the aerofoil to the point where free stream speed start is what is referred to as the boundary layer. 7. What are wingtip vortices and what causes them? This referred to a pattern which takes a circular shape that is brought about by rotating air which that is left behind as lift is being generated by the aerofoil.

Lift-induced vortices are the name given to Wingtip vortices that are generated at other points other than the wingtips. 8. What are the common formulas for Lift& Drag? (i.e CL, CD).

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