Since airplanes are not physically connected to the ground, the pilot must fly the airplane through the air to position it as desired with respect to the ground. Ground reference maneuvers are taught to help pilots understand the effects of wind by maneuvering the aircraft in patterns over the ground.
The airplane is flying through the air. So, if there is a 20 knot wind from the left, the airplane will drift right over the ground. If the pilot wanted to stop this drift, the airplane would have to be turned slightly left. If the wind were from behind the airplane, a tailwind, the airplane moves over the ground at a faster speed. Flying with a headwind means a slower speed over the ground.
The airplane can be flown at the same airspeed the whole time, but its direction of flight over the ground and speed over the ground are affected by the winds.
Airspeed is to be kept constant during all of these maneuvers, which are usually flown at about 1,000 feet above the ground.
Rectangular Course
One ground reference maneuver you will learn is the rectangular course. You will fly a rectangle, about one mile along each side, at an altitude of about 1,000 feet above the ground, using roads or a field as your rectangular pattern to fly around.
As you fly the four legs of the rectangle, you experience wind from ahead, behind, left, and right. If you the wind is coming from the left or right, you will have to point the airplane into the wind somewhat to stop the airplane from drifting over the field you are trying to fly around.
During the leg in which the wind is at your back, you will have to make a steep turn at the corner. This is because you are traveling faster over the ground than you are flying, and will have to turn more than 90 degrees to angle the airplane slightly into the wind for the next leg. On the upwind leg, the opposite is true. Only a shallow turn is required, since you are moving more slowly over the ground and will make less than a 90 degree turn to angle into the wind for the upcoming leg.
S-Turns
The pilot picks a road or other straight line and attempts to make left and right semicircle turns along that straight line. The goal is to make all the semicircles uniform in size over the ground. To accomplish this task, the pilot must constantly be aware of and correct for the wind.
S-Turns require the pilot to constantly change the airplane's bank angle. As the airplane turns upwind, it slows down over the ground. If the pilot is to draw an even semi-circle over the ground, a slower rate of turn must be used. When the airplane turns downwind, however, a steep bank angle must be used to quickly turn the airplane, which is now traveling at high speed over the ground.
Turns Around a Point
In this maneuver, the pilot chooses a point to try and fly a circle around over the ground. Again, the pilot must use shallower angles upwind, where the groundspeed is slow. Steep angle of bank must be used when downwind, where groundspeed is fast.