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 (1251.7 = 212.5).Head winds and tail winds must also be considered.When head winds are present, you should subtract thehead wind from the airspeed. Tail winds should beadded to the airspeed. For example, when the aircraftis flying north at 125 knots and the wind is blowing fromthe north at 10 mph, then the corrected airspeed is 115knots (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 theground speed, in feet.For the time interval between exposures, thefollowing formula should be used:T=^{D}SWhereT = Time in secondsD = Ground-gained forwardS = Ground speed in feet per secondNOTE: When the interval between exposures canbe accomplished in full seconds only, the tenths of asecond should be dropped. By doing so, slightly morethan the required 60-percent forward overlap isprovided. This can be advantageous.SCALE OF THE FINISHEDMOSAIC MAPThe scale of the finished mosaic map is determinedby using the following formula:FS=12AWhereS= ScaleF = Lens focal lengthA = AltitudeThe answer derived by using this formula gives arepresentative fraction (RF) in like-units. Notice thatyou must convert the altitude to inches, since the lensfocal length is normally in inches. For example, youused a 10-inch focal-length lens for a mapping missionflown at 5,000 feet. You can determine the scale of thefinished mosaic as follows:S=1012 5,0001S=_{6,000}The scale of the finished mosaic is 1/6,000 (1:6,000).To reinforce the mission planning procedures, youcan use the following example:You are assigned to assist in the missioncalculations required for a recon mapping mission. Youare briefed on the mission and the followinginformation is provided:Area to be mapped is 10 nautical miles east and westby 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 themission 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 requiredon the printed mosaic map.1. Determine the altitude. The first step in thisproblem is to determine the altitude at which the aircraftmust fly to obtain the required scale of 1/12,000. TheIFGA formula used to determine the altitude is asfollows:^{I}=^{G} orA=^{FG}FAISince G (ground coverage) is not known, you mustsubstitute the required scale (1/12,000) for it. At arequired scale of 1/12,000, each unit of I (on the filmplane) records 12,000 units of G. Since A is measuredin feet, you must divide your answer by 12 to get theunits in feet.A=^{12 }^{12,000}=^{144,000}=144,00011Divide by 12 to get altitude units in feet4-24

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