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the grommet is 150 units as illustrated in A of Figure 4.34.
4.14.2.6. The ground vector is represented by one of the track lines, with its tail at the origin and its head
at the appropriate speed circle. If the track is 15o to the right of the TH, and the GS is 180 knots, use the
track line 15o to the right of the centerline and consider the intersection of this line with the 180 speed
circle as the head of the vector as illustrated in B of Figure 4.34.
4.14.2.7. The tail of the wind vector is at the grommet and its head is at the head of the ground vector as
shown in C of Figure 4.34.
4.14.2.8. Thus far, nothing has been said about the direction of the vectors. Since the true index is over
the centerline beyond the head of the air vector, this vector always points toward the index. Therefore,
TH is read on the compass rose opposite the true index.
4.14.2.9. Since track is TH with the drift angle applied, the value of track can be found on the scale of
the circular plate opposite the drift correction on the drift scale. The wind vector is drawn with its tail at
the grommet as shown in Figure 4.35. Since WD is the direction from which the wind blows, it is
indicated on the compass rose by the rearward extension of the wind vector. Therefore, the most
convenient way to draw the wind vector is to set WD under the true index and draw the vector down the
centerline from the grommet; the scale on the centerline can then be used to determine the length of the
vector.
4.14.2.10. Conversely, to read a wind already determined, place the head of the wind vector on the
centerline below the grommet and read WD below the true index.
4.14.3. Wind Triangle Problems. Depending on which of the six quantities of the wind triangle are
known and which are unknown, there are three principal types of problems to solve. They are to solve
for (1) the ground vector, (2) the wind vector, and (3) TH and GS. The following discussion gives the
steps for the computer solution for each type. Work each sample problem and notice that the same wind
triangle is shown on the computer that is shown on the chart, even though it is not completely drawn on
the computer.
4.14.3.1. To find ground vector when air vector and wind vector are known:
Given: TH 100o
TAS 210 knots
W/V 020o/25 knots
Find: Track and GS
AFPAM11-216 1 MARCH 2001 139
Figure 4.34. Plotting a Wind Triangle on Computer.
4.14.3.2. This type of problem arises when TH and TAS are known by reading the flight instruments and
when the WD and velocity are known from either the metro forecast or from calculations in flight.
4.14.3.3. Study Figure 4.36 and determine what has happened. By flying a TH of 100o at a TAS of 210
knots in a wind of 020o/25 knots, the aircraft has actually moved over the ground along a track of 107o at
a GS of 208 knots.
140 AFPAM11-216 1 MARCH 2001
Figure 4.35. Draw Wind Vector Down From Grommet.
Figure 4.36. Solving for Track and Groundspeed Using Chart.
4.14.3.4. Computer Solution: First, set the data:
4.14.3.4.1. Set WD (020o) under the true index.
AFPAM11-216 1 MARCH 2001 141
4.14.3.4.2. Draw the wind vector from the grommet down the centerline, making its length (25 units)
along the speed scale to conform with the windspeed (25 knots).
4.14.3.4.3. Set the TH (100o) under the true index by rotating the compass rose.
4.14.3.4.4. Slide the card up or down until the TAS (2l0 knots) is under the grommet. The graphic
solution is now displayed on the computer as illustrated in Figure 4.37. The ground vector lies along one
of the radiating track lines with its head at the head of the wind vector.
Figure 4.37. Solving for Track and Groundspeed Using Computer.
4.14.3.4.5. Read GS (208 knots) on the speed circle which passes through the head of the ground vector.
4.14.3.4.6. Read the drift angle (7o right) by counting the number of degrees from the centerline to the
ground vector; that is, to the head of the wind vector.
4.14.3.4.7. Determine track (107o) by applying the drift angle to the TH. If the track is right of the center
line, it is greater than the TH; so the drift angle must be added to the TH. An alternate method of
determining track on the computer is to read the drift angle at the head of the ground vector, then
transform this value to the drift scale on the same side of the true index and read the track on the
compass rose of the circular disk.
142 AFPAM11-216 1 MARCH 2001
4.14.3.5. To find wind vector when air vector and ground vector are known.
Given: TH 270o
Track 280o
TAS 230 knots
GS 215 knots
Find: wind vector
4.14.3.6. This type of problem arises when determination of TH and TAS can be done by reading the
flight instruments and finding track and GS either by measuring the direction and distance between two
　
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