The Boeing 757-200 Research Paper Example | Topics and Well Written Essays - 1750 words

The Boeing 757-200 - Research Paper Example Changes included wing design and engines. Aim This essay will discuss the unique aerodynamic characteristics of the Boeing 757-200. Boeing 757-200 The Boeing 757-200 entered operational service in 1983 and featured numerous design enhancements in the areas of propulsion, aerodynamics, avionics and materials, aimed at meeting its medium haul clients requirements of increased fuel efficiency, decreased noise and increased operational performance (Boeing). The aircraft was available in passenger and freighter configurations, with a maximum takeoff weight of 255,000 pounds (lbs) providing increased payload or range (Boeing). To achieve these enhancements, modified or new design features included; Wing design, Engines, Improved light weight materials, and Modified flight station instrumentation. Wing Design The 757-200’s wing is swept at 250, has a longer span, higher upper surface camber and lower under surface camber, combined with sharper leading edges (Boeing). Relating these f eatures to the lift equation: Lift= CL x (? p V2) x wing area (s), where CL is the coefficient of lift and p (rho) is density, (Dole and Lewis, 2000), as the wing area has increased, this, along with the increase in camber (increasing CL), means that lift is improved. Additionally, as wingspan increases, wingtips are farther apart which reduces the impact of trailing vortices on the wing and decreases induced drag (aerospaceweb). The 757-200 wing shape is a supercritical airfoil (Figure 1) (aerospaceweb). This is commonly used on aircraft that cruise at transonic (less than Mach 1 (Dole and Lewis, 2000)) speeds and is designed to reduce drag through delaying the speed at which the compressibility effect becomes significant (Aerospaceweb). Compressibility effect is the increase in density at an aerofoil due to forward motion (FAA, 2001). Figure 1: Boeing 757 wing airfoil section The differences in pressure distribution over the supercritical airfoil can be seen in comparing between t he conventional and supercritical sections, as seen at Figures 2 and 3 (aerospaceweb). Figure 2: Pressure distribution over a conventional airfoil Figure 3: Pressure distribution over a supercritical airfoil Figure 4 (aerospaceweb) shows the coefficient of lift versus angle of attak for the 757-200 wing section. Figure 2: Boeing 757 wing airfoil section lift coefficient The aerodynamic benefits of a supercritical airfoil is related to critical Mach number. Accelerated airflow over an upper airfoil section due to wing camber can reach Mach 1 where the aircraft Mach number (speed) is lower. The speed at which the flow over the wing surface reaches Mach 1 is called the critical Mach number (FAA, 2001). As speed increases above the critical Mach number, areas of supersonic flow are created over the airfoil surfaces. This is accompanied by a shock wave which varies pressure and density. An adverse pressure gradient is created by slowed airflow, inducing higher pressure, which may result in a rapid separation of the airflow from the surface of the airfoil. This separation creates an area of turbulent wake resulting in rapid increases in drag. The Mach number at which this begins to occur is known as the drag divergence Mach number (FAA, 2001). The benefits of a super critical airfoil in combination with swept wings are that the critical Mach number is close to one thereby delaying and reducing the large increase in drag due to wave drag (aerospaceweb). In addition to the above, modified wing sweep enables the optimal combination between required cruising speed, CL and drag divergence (FAA, 2001), whilst the sharper leading edge reduces parasitic drag (Applied Aerodynamics, 2007). It is considered the sharper leadi