converting airspeed (in knots) to feet is 1.7 (kts   1.7 = ft/sec). For example, when the airspeed is 125 knots, the ground speed, in feet, is 212.5 feet per second (125 1.7 = 212.5). Head winds and tail winds must also be considered. When head winds are present, you should subtract the head wind from the airspeed. Tail winds should be added to the airspeed. For example, when the aircraft is flying north at 125 knots and the wind is blowing from the north at 10 mph, then the corrected airspeed is 115 knots (125 - 10= 115). When the air craft is flying south, then the corrected airspeed is 135 knots (125 + 10 = 135). The corrected airspeed must be used to find the ground speed, in feet. For  the  time  interval  between  exposures,  the following formula should be used: T=^D S Where T = Time in seconds D = Ground-gained forward S = Ground speed in feet per second NOTE: When the interval between exposures can be accomplished in full seconds only, the tenths of a second should be dropped. By doing so, slightly more than  the  required  60-percent  forward  overlap  is provided. This can be advantageous. SCALE OF THE FINISHED MOSAIC MAP The scale of the finished mosaic map is determined by using the following formula: F S= 12A Where S= Scale F = Lens focal length A  =  Altitude The answer derived by using this formula gives a representative fraction (RF) in like-units. Notice that you must convert the altitude to inches, since the lens focal length is normally in inches. For example, you used a 10-inch focal-length lens for a mapping mission flown at 5,000 feet. You can determine the scale of the finished  mosaic  as  follows: S= 10 12 5,000 1 S=_6,000 The scale of the finished mosaic is 1/6,000 (1:6,000). To reinforce the mission planning procedures, you can use the following example: You  are  assigned  to  assist  in  the  mission calculations required for a recon mapping mission. You are   briefed   on   the   mission   and   the   following information  is  provided: Area to be mapped is 10 nautical miles east and west by 20 nautical miles north and south. Forward overlap required is 60 percent. Side lap required is 40 percent. Lens focal length is 12 inches. Negative size is 9 9 inches. True airspeed of aircraft is 140 knots. The wind is from the north at 15 knots. The scale of the chart used to plan and fly the mission is 1/50,000 (1:50,000). The required scale is 1/12,000 (1: 12,000). A graphic scale representing 3,000 feet is required on the printed mosaic map. 1. Determine the altitude. The first step in this problem is to determine the altitude at which the aircraft must fly to obtain the required scale of 1/12,000. The IFGA formula used to determine the altitude is as follows: ^I=^G  orA=^FG F A I Since G (ground coverage) is not known, you must substitute the required scale (1/12,000) for it. At a required scale of 1/12,000, each unit of I (on the film plane) records 12,000 units of G. Since A is measured in feet, you must divide your answer by 12 to get the units in feet. A=^{12 12,000}=^144,000 =144,000 1 1 Divide by 12 to get altitude units in feet 4-24