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of 090o the aircraft is aided by a tailwind and travels farther in 1 hour than it would without a wind; thus,
its GS is increased by the wind. On the heading of 270o, the headwind cuts down on the GS and also
cuts down the distance traveled. On the headings of 000o and 180o, the GS is unchanged.
Figure 4.24. In 1 Hour, Aircraft Drifts Downwind an Amount Equal to Windspeed.
130 AFPAM11-216 1 MARCH 2001
Figure 4.25. Effects of Wind on Aircraft Flying in Opposite Directions.
4.12. Drift Correction Compensates for Wind. In Figure 4.26, suppose the navigator wants to fly from
point A to point B, on a TC of 000o, when the wind is 270o/20 knots. If the navigator flew a TH of 000o,
the aircraft would not end up at point B but at some point downwind from B.
4.12.1. By heading the aircraft upwind to maintain the TC, drift will be compensated for. The angle
BAC is called the drift correction angle or, more simply, the drift correction. Drift correction is the
correction which is applied to a TC to find the TH.
AFPAM11-216 1 MARCH 2001 131
Figure 4.26. Aircraft Heads Upwind To Correct for Drift.
4.12.2. Figure 4.27 shows the drift correction necessary in a 270o/20 knots wind if the aircraft is to make
good a TC of 000o, 090o, 180o or 270o. When drift is right, correct to the left, and the sign of the
correction is minus. When the drift is left, correct to the right, and the sign of the correction is plus.
4.13. Vectors and Vector Diagrams. In aerial navigation, there are many problems to solve involving
speeds and directions. These speeds and directions fit together in pairs: one speed with one direction.
4.13.1. By using vector solution methods, unknown quantities can be found. For example, TH, TAS, and
W/V may be known, and track and GS unknown. To solve such problems, the relationships of these
quantities must be understood.
4.13.2. The vector can be represented on paper by a straight line. The direction of this line would be its
angle measured clockwise from true north (TN), while the magnitude or speed is the length of the line
compared to some arbitrary scale. An arrowhead is drawn on the line representing a vector to avoid any
misunderstanding of its direction. This line drawn on paper to represent a vector is known as a vector
diagram, or often it is referred to simply as a vector as shown in Figure 4.28. Future references to the
word vector will mean its graphic representation.
132 AFPAM11-216 1 MARCH 2001
Figure 4.27. Maintaining Course in Wind.
4.13.3. Two or more vectors can be added together simply by placing the tail of each succeeding vector
at the head of the previous vector. These vectors added together are known as component vectors.
4.13.4. The sum of the component vectors can be determined by connecting, with a straight line, the tail
of one vector to the head of the other. This sum is known as the resultant vector. By its construction, the
resultant vector forms a closed figure as shown in Figure 4.29. Notice the resultant is the same,
regardless of the order, as long as the tail of one vector is connected to the head of another.
4.13.5. The points to remember about vectors are as follows:
4.13.5.1. A vector possesses both direction and magnitude. In aerial navigation, these are referred to as
direction and speed.
4.13.5.2. When the components are represented tail to head in any order, a line connecting the tail of the
first and the head of the last represents the resultant.
4.13.5.3. All component vectors must be drawn to the same scale.
AFPAM11-216 1 MARCH 2001 133
Figure 4.28. A Vector Has Both Magnitude and Direction.
Figure 4.29. Resultant Vector Is Sum of Component Vectors.
4.14. Wind Triangle and Its Solution:
4.14.1. Vector Diagrams and Wind Triangles. A vector illustration showing the effect of the wind on
the flight of an aircraft is called a wind triangle. Draw a line to show the direction and speed of the
aircraft through airmass (TH and TAS); this vector is called the air vector. Using the same scale, connect
the tail of the wind vector to the head of the air vector. Draw a line to show the direction and speed of
the wind (W/V); this is the wind vector. A line connecting the tail of the air vector with the head of the
wind vector is the resultant of these two component vectors; it shows the direction and speed of the
aircraft over the earth (track and GS). It is called the ground vector.
4.14.1.1. To distinguish one from another, it is necessary to mark each vector. Accomplish this by
placing one arrowhead at midpoint on the air vector pointing in the direction of TH. The ground vector
134 AFPAM11-216 1 MARCH 2001
has two arrowheads at midpoint in the direction of track. The wind vector is labeled with three
arrowheads in the direction the wind is blowing. The completed wind triangle is shown in Figure 4.30.
　
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