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:
9 = 3.6 inches of useable image area for GGF
I=G so G =
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:
9 = 5.4 inches of usable image area for GGS
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).
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:
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:
12 = 64,800 (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
b. Aircraft flying toward the south
Corrected airspeed (140 knots + 15 knots = 155
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
b. Aircraft flying toward the south = 263.5 feet
To calculate the exposure interval, you must use the