Here's a page for you to explore the relative velocity between an
aircraft in flight, the ground, and the air through which the
airplane moves. In this animation, the white clouds move relative to
the ground at the wind speed, the airplane moves relative to the
ground at the ground speed, and the airplane moves relative to the
air at the airspeed. Airspeed is the important velocity for the
generation of lift and drag.
These two aircraft are going to take-off and both have to reach 120 mph of
airspeed to generate enough lift to take off. The top aircraft flies into a
20 mph wind; the bottom aircraft flies with a 20 mph tail wind. The
accelerations are the same, so they have identical ground speeds which
change as they move down the runway. About halfway down the runway, the
ground speed of both aircraft is 100 mph. At that location, the top aircraft
has an airspeed of 120 mph (Airspeed = Ground Speed - Wind Speed; 120 = 100 - (-20)),
while the lower aircraft has an airspeed of only 80 mph (80 = 100 - 20). So
the plane flying into the wind takes off first. The lower aircraft
does not have sufficient airspeed until its groud speed is 140 mph
(120 = 140 - 20). This occurs near the end of the runway just before the
trees!
More information about these velocities
is given on the Relative Velocity
Slide.
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