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8 Things You Never Knew About Supersonic Flight

Breaking the sound barrier doesn't just come with a loud bang. Check out these variables that affect an aircraft transitioning to supersonic flight...

1) Mcrit

This occurs when airflow passing over the aircraft first reaches the speed of sound. At Mcrit, air flowing over the wings can be traveling supersonic, while the aircraft itself is still traveling subsonic.

2) Temperature

On an ISA day at sea level, the speed of sound is approximately 661 knots. As temperature decreases, the speed of sound also decreases. That's because cold air is more dense, and sound can't travel through it as quickly.

USAF

3) Bank Angle and Gross Weight

As gross weight and bank angle increases, Mcrit decreases. If you are nearing this value, something as simple as banking your aircraft could cause you to reach Mcrit.

USAF

4) Normal Shock Waves

A normal shock wave is created from a build up of pressure waves on the airfoil. As air flows across a normal shock wave, it slows from supersonic to subsonic, and temperature and static pressure increase.

5) Bow Wave

This type of shock wave is again formed by the build up of pressure waves, but in the subsonic region in front of the airfoil. As air flows across this shock wave, it deflects upward into the direction of the airstream.

NASA

6) Turbine Engines and Supersonic Flight

Turbine engines are not designed to ingest supersonic airflow. Engines that travel in supersonic flight regimes are designed to slow down airflow in front of the engine. These designs include diverging engine inlets or engine spikes, like what's found on the SR-71. The engine ingests subsonic airflow, and then speeds it back up to supersonic speeds after the fuel/air mixture is burned and exhausted out the back of the engine.

7) Coffin Corner

As you increase in altitude, the true airspeed that you stall increases, and your maximum operating Mach limit decreases. In some aircraft, like the U-2, you can be only a few knots from stall and Mach overspeed at the same time.

8) Swept Wings

By sweeping the wings, you can increase the critical Mach number. This allows jets to fly faster without dealing with the high-drag effects of transonic flight. (Read more about it here.)


Corey Komarec

Corey is an Embraer 175 First Officer for a large regional airline. He graduated as an aviation major from the University of North Dakota, and he's been flying since he was 16. You can reach him at corey@boldmethod.com.

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