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;
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 features to the lift equation:
Lift= CL x (½ 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).
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