These two wing designs are shown in Figure 7.Īerodynamic HeatingOne of the problems with airplanes and high-speed flight is the heat that builds up on the airplane’s surface because of air friction. The bow wave in front of the wing leading edge of view F would be attached to the leading edge, if the wing was a double wedge or biconvex design. The airfoil shown in Figure 6 is not properly designed to handle supersonic airflow. If the wing has a sharp leading edge, the shock wave will attach itself to the sharp edge. View F - The forward velocity of the airfoil is greater than Mach 1, and a new shock wave has formed just forward of the leading edge of the wing.Some airflow separation is still occurring. View E - The velocity has increased to the point that both shock waves on the wing, top and bottom, have moved to the back of the wing and attached to the trailing edge.Behind the normal shock waves, the velocity of the air is subsonic and the static pressure has increased. A normal shock wave is now forming on the bottom of the wing as well. View D - The velocity has continued to increase beyond the critical Mach number, and the normal shock wave has moved far enough aft that serious airflow separation is occurring.Some airflow separation starts to occur behind the shock wave. View C - The velocity has surpassed the critical Mach number, and a normal shock wave has formed on the top of the wing.View B - The velocity has reached the critical Mach number, where the airflow over the top of the wing is reaching Mach 1 velocity. ![]() View A - The Mach number is fairly low, and the entire wing is experiencing subsonic airflow.The scenario for the six views is as follows: View B is the wing of an airplane in supersonic flight, with the sound pressure waves piling up toward the wing leading edge. Figure 3A shows a wing in slow speed flight, with many disturbances on the wing generating sound pressure waves that are radiating outward. If the shock waves reach the ground, and cross the path of a person, they will be heard as a sonic boom. This piling up of sound energy is called a shock wave. At this point the sound energy starts to pile up, initially on the top of the wing, and eventually attaching itself to the wing leading and trailing edges. When the speed of the airplane reaches the speed of sound, however, the pressure waves, or sound energy, cannot get away from the airplane. For a slow-moving airplane, the pressure waves travel out ahead of the airplane, traveling at the speed of sound. Shock WavesSound coming from an airplane is the result of the air being disturbed as the airplane moves through it, and the resulting pressure waves that radiate out from the source of the disturbance. If an airplane flies faster than Mach 5, it is said to be in hypersonic flight. Supersonic speed is from Mach 1.20 to 5.0. At this speed, the shock wave which formed on top of the wing during transonic flight has moved all the way aft and has attached itself to the wing trailing edge. When an airplane is flying at supersonic speed, the entire airplane is experiencing supersonic airflow. Transonic speed is typically between Mach 0.80 and 1.20. The speed at which the shock wave forms is known as the critical Mach number. ![]() The shock wave also causes the center of lift to shift aft, causing the nose to pitch down. ![]() Stability problems can be encountered during transonic flight, because the shock wave can cause the airflow to separate from the wing. The shock wave forms 90 degrees to the airflow and is known as a normal shock wave. Over the top of the wing, probably about halfway back, the velocity of the air will reach Mach 1 and a shock wave will form. When an airplane is flying at transonic speed, part of the airplane is experiencing subsonic airflow and part is experiencing supersonic airflow.
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