lines radiate, and the figures along the center line indicate the number of units distance of each circle from the center. Figures at various points of the face show the number of degrees between the center line and radiating lines.

c. The following rules are important:

(1) When the heading is given, the center line is used as the heading, and the wind vector is plotted from the center of the disk down the line.

(2) If the course is given it is used as the center line, and the wind vector is plotted from above to the center of the disk.

(3) Drift is always measured from heading to the course.

d. It should be noted that, having determined the drift angle to be right, the heading is found by subtracting the right drift angle from the course. If the drift angle is left, it is added to the course

to give the heading.

Example 1:

Given: Wind force and direction 30 knots from 315°.
Heading (true) 165°.

Air speed (true) 180 knots.

Find: Track.

Ground speed.

Solution by E-6B computer: (1) When using the E-6B computer to solve problems in which heading is given, the center line of the chart is used to represent the heading line. Hence, air speeds will be measured along this center line. The track (course) line will be one of the radiating lines to the right or left of the center line, and ground speed will be indicated along this radiating line. The drift, being measured from heading to track (course), will be read from the center line to the right or left to the track (course) line. In this type of problem the wind must be plotted from the center of the plotting disk straight down the center line of the chart. The tail of the wind arrow is at the center of the disk.

(2) Turn compass rose to read 315°, the direction from which the wind is blowing, at "true index." Plot wind arrow from center of plotting disk straight down center line of chart 30 units according to scale of center line. Set heading (165°), at true index and slide chart to read air speed (180 knots) at center mark of transparent disk. At end of wind arrow, read from radiating track (course) lines and speed circles of chart the drift (4° left) and ground speed (206 knots). Opposite 4° left on drift and variation scale read track (161° true).

(3) In solving vector triangles on the E-6B computer, it infre

quently occurs that the end of one of the vectors falls off the transparent disk, thus preventing solution unless 2-hour vector lengths are used instead of hourly lengths. When this occurs, the proper procedure is to divide the lengths of all known vectors by two before setting up on the computer. All vectors resulting from the solution will be read at one-half their true values. Throughout this procedure,

FIGURE 145.-Drawing wind vector-E-6B computer.

angles must not be reduced to one-half value. If any vector falls off the plotting disk when reduced to half-hour lengths, the problem may be worked by reducing all vectors to quarter-hour lengths.

e. Exercises. Find ground speed and track in each case.

(1) Heading=310°, air speed=170 knots, wind speed 40 knots, wind direction=185°.

(2) Heading=6°, air speed=285 m. p. h., wind speed=44 m. p. h., wind direction=127°. GS=310, T=359° Answer. (3) Heading=273°, air speed=126 knots, wind speed=33 knots, wind direction=147°.

(4) Heading=355°, air speed=320 m. p. h., wind speed=51 m. p.h., wind direction=292°. GS=300, T=4° Answer.

(5) Heading=96°, air speed=137 knots, wind speed=28 knots, wind direction=81°.

(6) Heading=4°, air speed=185 mph., wind speed=47 mph., wind direction=148°.

FIGURE 146.-Solution for course and ground speed-E-6B computer.

Given: Wind force and direction, 40 knots from 90°.
Course to be made good, 215°.

Air speed (true), 160 knots.

Find: Heading (true).

Ground speed.

Solution by E-6B computer: (1) When using the E-6B computer to solve problems in which course to be made good or track is given, the simplest procedure is to use the center line as the course (track) line. Ground speed will then be measured along the center line. The heading line will be one of the radiating lines to the right or left of the center line, and air speed will be indicated along the radiating line. The drift, being measured from heading to track, will be read from the radiating heading line to the right or left to the course (track) line which will be the center line of the chart. In the solving problems in which

the center line represents course (track), the wind must be plotted to the disk center from a point on the chart center line vertically above it. The head of the arrow is at the center of the disk.

(2) Set compass rose to direction from which wind is blowing (90° true) and plot wind to center from a point 40 units above it. Set course (215° true) opposite true index, and move chart until tail of wind arrow falls on true air speed (160 knots) as indicated on concentric circles. Read ground speed (180 knots) at center of disk. Read

drift (12° R.) at tail of wind arrow. Since the drift is 12° R., a true heading of 215°— 12° or 203° must be flown to make good the given

course.

g. Exercises. Find heading and ground speed in each case.

(1) Course=35°, air speed=187 knots, wind speed=42 knots, wind direction=73°.

(2) Course=312°, air speed=210 mph., wind speed=31 mph., wind direction=358°.

GS=187, H=318° Answer. (3) Course=63°, air speed=173 knots, wind speed=28 knots, wind direction=340°.

(4) Course=154°, air speed=245 mph., wind speed=53 mph., wind direction=12°.

(5) Course=237, air speed=310 mph., wind speed=47 mph., wind direction=149°.

(6) Course=3°, air speed=135 knots, wind speed=27 knots, wind direction=42°. GS=113, H=10° Answer.

Example 3:

Given: Wind force and direction; 20 knots from 260°.

FIGURE 148.-Solution for heading and ground speed-E-6B computer

Course to be made good, 340° true.

Scheduled ground speed, 150 knots.

Find: Heading.

Solution by E-6B computer. Set compass rose (fig. 149) to direction from which wind is blowing (260° true) and plot wind to disk center from point 20 units above it, marking head of wind arrow at center of disk. Set course to be made good (340°) opposite true index. Move chart until ground speed (150 knots) is under center of disk. At tail of wind arrow read air speed that must be maintained (154 knots) and drift (7° R.). The drift correction to be applied to course