AIRSPEED VS. GROUND SPEED - Ground speed is how fast an airplane is traveling, relative to a fixed point on the ground. If there's a strong wind pushing an aircraft, that's reflected in the ground speed. Airspeed, in contrast, is how fast an airplane is really flying strictly under its own power, which is calculated by subtracting the wind speed from the ground speed. Airspeed doesn't just affect airplanes. It also affects our vehicles on the ground. A car's airspeed on the highway is what really determines its fuel efficiency, rather than ground speed or the speedometer reading.

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Airspeed Vs. Ground Speed

What's the Difference Between Airspeed and Ground Speed?

BY PATRICK J. KIGER

Back in February 2019, a Virgin Atlantic Boeing 787 jet flying over Pennsylvania in route from Los Angeles to London reached what might seem like an amazing speed of 801 miles per hour (1,289 kilometers per hour), according to CBS News.

But the speed record wasn't because that Virgin Atlantic aircraft itself was exceptionally fast.

Like a sprinter running with the wind at his back, the aircraft benefited from an exceptionally fast jet stream, a high-speed wind moving at 231 miles per hour (371.7 kilometers per hour). It was the fastest jet stream in more than 60 years.

As this explainer on the NASA website details, ground speed is how fast an airplane is traveling, relative to a fixed point on the ground.

Think of it this way: Ground speed is how fast an airplane's shadow would move across the land. If there's a strong wind pushing an aircraft, that's reflected in the ground speed.

Airspeed, in contrast, is how fast an airplane is really flying strictly under its own power, which is calculated by subtracting the wind speed from the ground speed. 

NASA explains:

On a perfectly still day, the airspeed is equal to the ground speed. But if the wind is blowing in the same direction that the aircraft is moving, the airspeed will be less than the ground speed.

Airspeed doesn't just affect airplanes. It also affects our vehicles on the ground.

As this study published in 2013 in the International Journal of Energy and Environmental Engineering describes, a car's airspeed on the highway is what really determines its fuel efficiency, rather than ground speed or the speedometer reading.

NOW THAT'S INTERESTING

As NASA points out, a kite has a ground speed of 0 miles per hour, because you're holding it on the end of a string. But since it moves in the air, it has an airspeed that's equal to the speed of the wind.

Patrick J. Kiger has written for HowStuffWorks since 2008 covering a wide array of topics, from history and politics to pop culture and technology. He worked as a newspaper reporter for the Pittsburgh Press, and the Orange County Register in California, where he covered one of the biggest serial murder cases in U.S. history, and also as a staff writer at Baltimore Magazine. As a freelancer, Patrick has written for print publications such as GQ, Mother Jones and the Los Angeles Times, and on the web for National Geographic Channel, Discovery News, Science Channel and Fast Company, among others. In recent years, he's become increasingly interested in how technological advances are altering urban life and the design of cities, and has written extensively on that subject for Urban Land magazine. In his spare time, Patrick is a longtime martial arts student and a fan of crime fiction, punk rock and classic Hollywood films.

https://science.howstuffworks.com/transport/flight/modern/airspeed-vs-groundspeed.htm