Aerofoils: How Wings Work - Assignment Example

Aerofoils - How Wings Work Tasks Introduction In order to have a flight that is steady an aircraft enough upward force need to be provided for the aircraft that is able to counter its weight. Unlike he laws that act in spacecraft and ballistic missiles, air is responsible for supplying the force that is required by the aircraft. The responses to questions that have been given in the following section explain how an aircraft is able to fly in the air. 1. Explain what are the common misconceptions about lift?   There is a misconception of generation of lift as long as there is a difference in speed between the air that is immediately surrounding the aerofoil and that in the general atmosphere (Piercy, 1955). However, this is not always the case since there can be situation where we have air streams that are next to each other having difference in their speed yet there will be no pressure difference in the air streams. Change in the direction of the air is seen be responsible for lift creation as this change in direction of the air result to pressure difference between the general atmosphere and the air that is close to the aerofoil. Having a difference in pressure between the upper side and the general atmosphere alone will not result to a lift. It is necessary that the pressure at the lower side of the aerofoil should have a higher value of pressure that will bring about the necessary pressure difference that can result to lift creation (Mercury, 2013). 2. Explain how an aerofoil really generates Lift? A lift is generated in an airfoil owing to its shape, where the upper side of the aerofoil is much curved when compared to the lower side. This shape brings about a low pressure in the upper side while the lower side will have a high pressure and this difference in pressure brings about the 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?) By the front part being rounded in shape result to a rapid change in speed and also the direction of the air and this in turn results to the pressure being reduced. On the other have by the lower side being flatter the change in pressure will not be substantial as that in the upper side (NASA). This difference in pressure results to the aircraft being lifted. The design of the wing is also such that it is tapered at the rear so as to reduce the level of turbulence in the rear side that if present would likely lead to the aerofoil and the aircraft as whole being destroyed 4. What other shapes will generate lift?  (will a house brick generate lift? a saucer? a football? Draw some shapes) 5. What causes Drag and what are the different types of Drag? Drag is generally brought about by the aircraft encountering air resistance by the air during flight. Parasitic drag is as a result of the motion of the plane in the air with its forms being drag and skin friction. Form drag is also known as pressure drag depends on the shape or size of the object that is moving in the air where there is large drag when a body has large exposed cross section while the body with a thin exposed section will have a lower drag (Houghton, 2006). There is purposeful creation of induced drag in order for the required lift to be created. When the aircraft is moving at a very low speed the induced drag is supposed to be very high since and this is realized by increasing the angle of attack. With an increase in the speed of the aircraft the angle of attack is reduced thus resulting to reduction in induced drag. 6. What is a boundary layer?   Ideally the that is immediate to the aircraft aerofoil is supposed to have zero velocity as a result of the air viscosity with the air speed increasing as you move away from the aerofoil to a point where the velocity changes to a free stream value ( Technical Notes National Advisory Committee for Aeronautics, 1939).The boundary layer is that layer between the wall of the aerofoil and that point where the free stream velocity is achieved. 7. What are wingtip vortices and what causes them? A wingtip is circular pattern that results from rotating air that is left behind in the processing of generating a lift in an aerofoil. When there is generation of wingtip vortices at other points apart from the wingtips, then these will be referred to as lift-induced vortices. 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 =  With  being the density, v represents velocity of fluid (air) with respect to the aerofoil, A represents the reference area  is the lift and  is drag coefficient. The coefficients depend on inclination of object, viscosity and compressibility of fluid (air), and size and shape of object (aerofoil for this case). 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 By use of the XFLR5 software the graphs were plotted for CL against Alpha and CD against Alpha as can be seen in files design, design2 designgraph 10. From the plots in section nine, what angle gives zero lift? What angle gives maximum lift? There is maximum lift at angle 100 for a Reynolds number of 300000 while zero lift will occur when the angle of attack is 40  If it flies upside down, what is the maximum lift, and at what angle? 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 is as shown below. Conclusions From the discussed questions the principle of functioning of aerofoils to bring about lift has been clarified. In the aerofoil design process consideration of the shape that will bring about a desirable lift at what is considered as reasonable speed is an important aspect. Having a thick aerofoil may give the lift which is desired by the designer at relatively lower speed of air but this may result to creation of drag that is unreasonably high. It has been seen that in order for the desired lift to be attained at lower speed the angle of attack is to be increased. 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