HIGH -SPEED FLIGHT WEEK 9 TOPIC Speed Ranges ► ► SPEED OF SOUND ► is actually the speed of transmission of a small disturbance through a medium. ► the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. Under standard temperature conditions of 15 °C, the speed of sound at sea level is 661 knots or 761 mph. Mach Number The ratio of the true airspeed of the aircraft to the speed of sound in the same atmospheric conditions . REGIMES OF FLIGHT ► Subsonic► Movement of a vehicle through the atmosphere at a speed appreciably below that of sound waves ► Mach numbers below 0.75 TRANSONIC FLIGHT ► Refers to the condition of flight in which a range of velocities of airflow exist surrounding and flowing past an air vehicle or an airfoil that are concurrently below, at, and above the speed of sound in the range of Mach 0.75 to 1.2. A United States Navy F/A-18F Super Hornet in transonic flight U.S. Navy F/A-18 approaching the sound barrier. SUPERSONIC FLIGHT ► the speed of an object that exceeds the speed of sound (Mach 1) ► Mach numbers from 1.20 to 5.00 HYPERSONIC FLIGHT ► Hypersonic flight is flight through the atmosphere below about 90 km at speeds above Mach 5, a speed where dissociation of air begins to become significant and high heat loads exist. ► The X-24B in flight. CRITICAL MACH NUMBER ► the lowest Mach number at which the airflow over any part of the aircraft reaches the speed of sound. ► At the critical Mach number a disturbance referred to as a shock wave, takes place in the airflow over the wing. SHOCK WAVE In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium SONIC BOOM ► A sonic boom is the sound associated with the shock waves created whenever an object travels through the air faster than the speed of sound. Sonic booms generate enormous amounts of sound energy, sounding similar to an explosion or a thunderclap to the human ear.