High Speed Flight – Part 2

Source: en.wikipedia.org

High Speed Aerodynamics – Shockwave

In our previous article, we discussed the basics of high speed flight, understood the concept of Mach Number and how it differs with change in altitude and temperature. Well no matter how much we love flying at high speed, is it really that beneficial in the long run? Keep reading to find out more!

Before diving deeper into the concept, let us know how mach number is distinguished on the basis of relative speed of the boundary layer to the surface of the aircraft:

  • SUBSONIC: LESS THAN 0.75 MACH
  • TRANSSONIC: 0.75 MACH – 1.2 MACH
  • SUPERSONIC: 1.2 MACH – 1.4 MACH
  • HYPERSONIC: 1.4 MACH – 5 MACH

What is a Shockwave?

As an airplane reaches the speed of sound and catches up to its own pressure waves, the air ahead of it receives no warning of the plane’s approach. The airplane plows through the air, creating a shock wave. As air flows through the shock wave, its pressure, density, and temperature all increases sharply and abruptly.

When an aircraft approaches the speed of sound, the airflow over the wing reaches supersonic speed before the airplane itself does, and a shock wave forms on the wing. The airflow behind the shock wave breaks up into a turbulent wake, increasing drag.

When the airplane exceeds the speed of sound, a shock wave forms just ahead of the wing’s leading edge.

Source: www.aviationchief.com

Effects of Shockwave formation: At speeds higher than Mach 1, shockwave is formed on the upper surface of the aerofoil which leads to boundary layer separation aft of the shockwave causing loss of lift, leading to stall known as “Shock Stall”

Conclusion: Just to delay the event of shock-stall, changes in the structure of the wing are made, by making them “Sweepback”.

Source: www.flightliteracy.com

Fun Fact: The first airplanes to approach the speed of sound encountered unexpected conditions: sharply increased drag, violent shaking of the airplane, and loss of lift and control. Airplanes that approached this threshold often broke apart, as though there existed a “sound barrier” – an unbreakable speed limit. The sound barrier proved to be a myth in 1947, when the Bell X-1 flew faster than the speed of sound. With powerful engines and a design that minimises drag, airplanes now routinely fly faster than the speed of sound.

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