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46-47            ARMY AIR FORCES

(2) Draw the wind velocity vector from 230°. making it 1.5 cm long.
(3) Draw a line of indefinite length in the direction 308°, indicating the desired course.
(4) Draw the air speed heading vector by placing one end of a ruler on the head of the wind vector and mark where a vector 11 cm long will touch the course line.
(5) The segment of the course line cut off by the head of the air speed heading vector represents the ground speed.
(6) The angle between the air speed heading vector and the north line measured clockwise determines the heading.
d. Exercises.-(1) Course to be flown is 270°. Air speed of the airplane is 120 mph, and wind is 40 mph from 45°. Find the required heading and the ground speed.
(2) Wind is 30 mph from 180°. Desired course is 45°, and air speed of the airplane is 140 mph. What should be the heading and what will be the ground speed?
H=54°, GS=160 Answer.
(3) Air speed of the airplane is 125 mph. What will be the required heading to fly a course 135° if wind is blowing 25 mph from 225°? What will be the ground speed?
(4) Course to be flown is 225°, and wind is 30 mph from 90°. If air speed of the airplane is 160 mph, find the required heading and the ground speed.
H=217°, GS=180 Answer.
(5) Wind is 45 mph from 10°, and air speed of the airplane is 165 mph. If the course to be flown is 150°, what will be the required heading and what will be the ground speed?

47. Type III. - If the air speed, heading, ground speed, and track (angle of actual course flown) are known, the wind velocity can be found. These cases arise when the first two factors are obtained from instrument reading and the last two are computed by timing the flight between two landmarks on a map.
a. Plot both the air speed heading vector and the ground speed track vector from the given data.
b. Draw a vector with tail at the arrow end of the air vector and arrow at the arrow end of the ground vector. This is the wind vector.
c. By drawing a north line through the tail of the wind vector, one can measure the azimuth of the wind vector, that is, get the wind direction. The length represents the wind speed.
d. Note that the sum of the wind vector and the air vector is the ground vector; that is, Vw+Va=Vg.
e. Example: An airplane's air seed is 155 mph and its heading is 240°. By computation from a chart, it is found that the ground

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