An airfoil is the cross-section shape of a wing. The figure below is the airfoil of subsonic aircrafts. subsonic airfoils usually have rounded leading edges, the function of this kind of design can decrease flow separation in a wide range of angle of attack.
On the contrast, Supersonic airfoils usually have thin section and sharp leading and trailing edges, with the sharp of angled planes which is called double wedge airfoils or opposed arcs which is called biconvex airfoils. These two types are the most common airfoils in supersonic airfoils. Sharp edges can prevent the formation of bow shock when the supersonic flow past airfoils. However, sharp edge will also increase the airfoils’ sensitiveness to changes in…show more content… K < KIC is a necessary condition of achieving a safe design. Therefore, material’s fracture toughness must satisfy this requirement.
Since the requirements are so strict, a combination of titanium alloys, aluminum alloys and polymer matrix composites is better choice for aircraft structure. Titanium alloys have a excellent corrosion-resistance, thermal stability and strength; Aluminum alloys are light but strong; while polymer matrix composites have great lightness, stiffness and heat resistance. Aluminum alloy is the basic structural material of Concorde, which is the initial designs of the SST aircraft. Now almost all the supersonic aircrafts are military aircraft. They are mainly made of lightweight carbon-fiber reinforced polymer composite materials to achieve high fatigue strength, specific strength, reasonably high creep strength and corrosion-resistance.