144,000/12 = 12,000 feet 2. Determine the ground coverage. Now that you know the altitude at which the mission must be flown to obtain a scale of 1/12,000, you can determine the amount of ground coverage on each frame. Again, this  information  can  be  determined  using  the  IFGA formula. Remember that the forward overlap required is 60 percent. The remaining 40 percent of the 9-inch negative is usable imagery for GGF. You must first find the size of the usable portion of the negative for GGF. This is accomplished as follows: 0.40 9 = 3.6 inches of useable image area for GGF ^I=^G   so G = I A F A F G =3.6 ^12,000=3,600  feet 12 The amount of side lap required is 40 percent. This leaves only 60 percent of the useable negative image area for GGS. You determine the usable portion of the negative for GGS as follows: 0.60 9 = 5.4 inches of usable image area for GGS G= 5.4 12,000 12 =5,400  feet 3.  Determine  the  total  number  of  frames required.  Next, you need to determine the total number of frames required to complete the mission. You know that the area to be mapped is 10 nautical miles east and west by 20 nautical miles north and south. Therefore, the strips will be flown north and south. The number of exposures per strip is determined by dividing the GGF into the length of the map. First convert nautical miles into feet (1 nmi = 6,080 ft) and multiply by 20 (length of area to be mapped). 6,080 20 = 121,600 feet Next, divide by the GGF as follows: 121,600/3600 = 33.77 or 34 frames per strip. Remember to add four more frames. This totals 38 frames for each strip. Now you must find the number of strips required. The area to be mapped is 10 nautical miles long. Calculate the number of strips as follows: 10 (nautical miles) 6,080 (feet per nautical mile) = 60,800 feet 60,800/5400 (GGS) = 11.25 or 12 flight strips Remember to add one strip, so a total of 13 flight strips  is  required. To determine the total frames required for the mapping  mission,  you  must  multiply  the  number  of frames required for GGF by the number of flight strips required as follows: 13 38 = 494 frames 4. Draw flight lines on the chart. Your next step is to draw the flight lines on the chart used to fly the mission. The scale of this chart is 1/50,000. To determine the distance between the plotted lines on the chart, you must convert the GGS into inches, and then multiply the GGS (in inches) by the scale of the chart as follows: 5,400 (feet) 12 = 64,800 (inches) 1/50,000 = 1.29  inches The distance between flight lines on the chart is 1.29 inches apart. A multi-finger divider should be used to draw these lines. 5. Determine the time interval between exposures. To determine the exposure interval, first convert the aircraft speed to feet per second. The true aircraft speed is operating at 140 knots, but there is a wind of 15 knots coming from the north. Since the aircraft will be flying in a north and south direction, the wind factor must be taken into consideration. At this time determine the corrected  airspeed  in  knots,  then  determine  the  airspeed in feet per second as follows: 1.  Corrected  airspeed. a. Aircraft flying toward the north Corrected airspeed (140 knots - 15 knots = 125 knots) b. Aircraft flying toward the south Corrected airspeed (140 knots + 15 knots = 155 knots) 2. To determine aircraft speed in feet per second, you  must  multiply  the  corrected  airspeed  by  the conversion factor of 1.7. a. Aircraft flying toward the north = 212.5 feet per second b. Aircraft flying toward the south = 263.5 feet per second To calculate the exposure interval, you must use the following  formula: T=^D_S 4-25