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AC 150/5300-4B Appendix 3 6/24/75 2. WIND ROSE. The wind rose is a scaled graphical presentation of wind data in terms of speed and direction. Figure 3 shows an example of a standard wind rose format. The radial lines of the diagram are posi- tioned so that areas between them are centered on the direction from which the winds are recorded. As winds have been reported for years from the 16 main points of the compass, diagrams having 16 divisions will be most useful. Beginning January 1, 1964, surface winds have been reported to 36 points rather than 16 points. The description contained in Figure 2 indicates how the 36 points report can be con- verted to 16-point data. a. The concentric circles represent limits between speed group sec- tors; i.e., 3, 12, 18, 24, 31, 38, and 39+ mph. Radii for these groups should be accurately scaled to the representative speeds. b. The segments enclosed by radial lines and concentric circles on the diagram represent speed -direction combinations. The data from the wind summary for each combination of speed and direction are trans- ferred to the appropriate area on the diagram as a percentage of the total observations recorded. c. After the percentage for speed -direction combination has been entered in the appropriate sector of the wind rose diagram, an apparent best orientation is determined by a preliminary observa- tion. The optimum orientation is that which covers the greatest percentage of winds in excess of 10.5 knots or 12 mph. d. This is determined graphically by using a strip of transparent material on which three parallel and equally spaced lines have been drawn. The middle line represents the runway centerline and the distance between the outside lines is, to scale, equal to the diameter of the 12-unit circle. It is placed over the wind rose so that its centerline passes through the center of the wind rose. e. Using the center of the wind rose as a pivot, the template is rotated until the sum of the percentages appearing between the outside lines becomes maximum. The percentage shown in each segment of the wind rose is assumed to be equally distributed over the area of the segment. When one of the outside lines on the template cuts through a segment, the fractional part of the percentage appearing in that segment within the outside lines is to be used in the summation of the percentages contributing to the wind coverage. Fractional areas are determined visually and tabulated to the nearest tenth of a percent. f. The total percentage of all the areas covered by the template represents the percentage of time that winds with a 90-degree crosswind component of 12 mph or less will occur.. Page 2 Par 2