Airspeed, Groundspeed, and The Difference Between Them

Posted on October 4, 2019 Michael Rodriguez Aviation

Earlier in 2019, a jet stream of 231 mph swirled high above New York City. Record-breaking speeds like that had not been seen since 1957, when the previous record of 223 mph was set. Aided by this powerful jet stream, a Virgin Atlantic flight reached 801 mph, a possible record for the Boeing 787 Dreamliner. Unfortunately, Boeing Company does not track the speed of their planes, so there’s no way to know for sure if it was a record. That said, the 787’s average cruising speed is 561 mph, a figure that seems meager in comparison.

It’s important to note that 801 mph was not the airspeed of the plane, but rather the groundspeed. While the two go hand-in-hand, there is a difference between airspeed and groundspeed. Groundspeed is how fast an airplane travels when all velocity is accounted for, meaning plane speed plus wind speed. More simply, groundspeed an airplane's speed relative to a fixed point on the ground. If you were watching a plane’s shadow, the shadow would be moving at the plane’s ground speed.

Airspeed is the speed an aircraft is flying under its own power without help from other factors like wind and jet streams. To calculate the airspeed, simply subtract the wind speed from the groundspeed. So while the Virgin Atlantic flight, manufactured by Airbus Industries was gliding along at a groundspeed of 801 mph, its airspeed was 570 mph, right around typical cruising speed. In NASA’s study of relative velocity, they state that on a perfectly still day, airspeed will be equal to groundspeed. But if the wind is blowing in the same direction that the aircraft is moving, the airspeed will be less than the groundspeed.

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