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established positions of the aircraft or by determining the drift angle and GS by reference to the ground.
Refer to Figure 4.38 for a graphic solution.
Figure 4.38. Solving for Wind Using Chart.
4.14.4. Computer Solution (Figure 4.39). First, set in the data:
4.14.4.1. Set the TH (270o) under the true index.
4.14.4.2. Set the TAS (230 knots) under the grommet.
4.14.4.3. Find the drift angle (10o right) by comparing the TH (270o) with the track (280o). If the track is
greater than the TH, drift is right; if it is less, drift is left. Find the appropriate track line on the computer
(10o right of centerline).
4.14.4.4. Find the speed circle (215 knots) corresponding to the GS circle. The wind triangle is now
constructed. The mark made is the head of the wind vector and the head of the ground vector.
4.14.4.5. Rotate the compass rose until the head of the wind vector is on the centerline below the
grommet. Read the WD (207o) under the true index.
4.14.4.6. Read the windspeed (42 knots) on the speed scale between the grommet and the head of the
wind vector.
AFPAM11-216 1 MARCH 2001 143
Figure 4.39. Solving for Wind Using Computer.
4.14.4.7. To find true heading (TH) and groundspeed (GS) when true course (TC), true airspeed (TAS)
and wind vector are known:
Given: TC 230o
TAS 220 knots
W/V 270o/50 knots
Find: TH and GS
4.14.4.8. This type of problem arises before a flight or during a flight, when you need to determine a TH
to fly and a GS with which to compute an estimated time of arrival (ETA).
4.14.5. Chart Solution (Figure 4.40). First, construct the triangle.
4.14.5.1. Draw the wind vector in any convenient scale in the direction toward which the wind is
blowing (090o) and to the length representing the windspeed (50 knots) (from any origin).
4.14.5.2. Draw a line in the direction of the TC (230o) and of indefinite length, since the GS is not
known (from same origin).
4.14.5.3. Open the dividers an amount equal to TAS (220 knots); then, from the head of the wind arrow,
swing an arc with a radius of 220 NM to intersect the TC line (using the same scale as in step 1).
144 AFPAM11-216 1 MARCH 2001
4.14.5.4. Draw a line from the point of intersection of the arc and the TC line to the head of the wind
arrow.
Figure 4.40. Solving for True Heading and Groundspeed Using Chart.
4.14.5.5. To determine the TH (238o), measure the direction of the air vector.
4.14.5.6. To determine the GS (179 knots), measure the length of the ground vector, using the same
scale as before.
4.14.6. Computer Solution. There are two methods to solve for TH and GS. They are the slip-and-slide
method and the juggle method. Both will be discussed; however, the slip-and-slide method is normally
preferred.
4.14.6.1. Slip-and-Slide Method (Figure 4.41):
4.14.6.1.1. Set WD (270o) under the true index.
4.14.6.1.2. Draw the wind vector down the center from the grommet, making its length along the speed
scale correspond to the windspeed (50 knots).
4.14.6.1.3. Set the TC (230o) under the true index.
4.14.6.1.4. Set end of wind vector on the TAS (220 knots) by moving the slide.
AFPAM11-216 1 MARCH 2001 145
Figure 4.41. Solving for TH & GS Using Slip-and-Slide Method.
4.14.6.1.5. Read drift left or right (8o left).
4.14.6.1.6. Apply drift correction mathematically to TC and set this computed TH under the true index
(238o).
4.14.6.1.7. Move the slide up until the grommet is on TAS (220 knots). The wind triangle is now set up
correctly.
4.14.6.1.8. Read GS at the end of the wind vector (l79 knots).
4.14.6.2. The Juggle Method (Figure 4.42):
4.14.6.2.1. Set WD (270o) under the true index.
4.14.6.2.2. Draw the wind vector down the center from the grommet, making its length along the speed
scale correspond to the windspeed (50 knots).
4.14.6.2.3. Set the TAS (220 knots) under the grommet.
146 AFPAM11-216 1 MARCH 2001
Figure 4.42. Solving for TH & GS Using the Juggle Method.
4.14.6.2.4. Set the TC (230o) under the true index (Figure 4.42). The wind triangle is set up incorrectly,
for TC rather than TH is set under the true index. However, since the TH is not known, the TC is used as
a first approximation of the TH. This will give a first approximation of the drift angle, which can be
applied to the TC to get a more accurate idea of the TH.
4.14.6.2.5. Determine the drift angle (10o left) on the approximate heading (230o) to obtain a second
approximation of the TH (240o). If the drift angle is right, the drift correction is minus; if it is left, the
drift correction is plus.
4.14.6.2.6. Set the second approximate heading (240o) under the true index. Read the drift angle for this
heading (8o left). To correct the wind triangle, the drift angle which is read at the head of the wind vector
　
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