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The checkpoints selected should be prominent features common to the area of the flight. Choose checkpoints that can be readily identified by other features such as roads, rivers, railroad tracks, lakes, and power lines. If possible, select features that make useful boundaries or brackets on each side of the course, such as highways, rivers, railroads, and mountains. A pilot can keep from drifting too far off course by referring to and not crossing the selected brackets. Never place complete reliance on any single checkpoint. Choose ample checkpoints. If one is missed, look for the next one while maintaining the heading. When determining position from checkpoints, remember that the scale of a sectional chart is 1 inch = 8 SM or 6.86 NM. For example, if a checkpoint selected was approximately one-half inch from the course line on the chart, it is 4 SM or 3.43 NM from the course on the ground. In the more congested areas, some of the smaller features are not included on the chart. If confused, hold the heading. If a turn is made away from the heading, it is easy to become lost.
Roads shown on the chart are primarily the well-traveled roads or those most apparent when viewed from the air. New roads and structures are constantly being built, and may not be shown on the chart until the next chart is issued. Some structures, such as antennas may be difficult to see. Sometimes TV antennas are grouped together in an area near a town. They are supported by almost invisible guy wires. Never approach an area of antennas less than 500 feet above the tallest one. Most of the taller structures are marked with strobe lights to make them more visible to a pilot. However, some weather conditions or background lighting may make them difficult to see. Aeronautical charts display the best information available at the time of printing, but a pilot should be cautious for new structures or changes that have occurred since the chart was printed.Dead Reckoning
Dead reckoning is navigation solely by means of computations based on time, airspeed, distance, and direction. The products derived from these variables, when adjusted by wind speed and velocity, are heading and GS. The predicted heading takes the aircraft along the intended path and the GS establishes the time to arrive at each checkpoint and the destination. Except for flights over water, dead reckoning is usually used with pilotage for cross-country flying. The heading and GS as calculated is constantly monitored and corrected by pilotage as observed from checkpoints.
The Wind Triangle or Vector Analysis
If there is no wind, the aircraft’s ground track is the same as the heading and the GS is the same as the true airspeed. This condition rarely exists. A wind triangle, the pilot’s version of vector analysis, is the basis of dead reckoning.
The wind triangle is a graphic explanation of the effect of wind upon flight. GS, heading, and time for any flight can be determined by using the wind triangle. It can be applied to the simplest kind of cross-country flight as well as the most complicated instrument flight. The experienced pilot becomes so familiar with the fundamental principles that estimates can be made which are adequate for visual flight without actually drawing the diagrams. The beginning student, however, needs
15-13
INSTR
UCTIONS FOR USE1. Place hole over intersection of true course and true north line.2. Without changing position rotate plotter until edge is over true course line.3. From hole follow true north line to curved scale with arrow pointing in direction of flight.4. Read true course in degrees, on proper scale, over true north line. read scales counter-clockwise.SECTIONAL CHART SIDE - 1:500,000NAVIGATIONAL FLIGHT PLOTTER0 180 270 90 10 190 280 100 20200 290 110 30 210 330 150 340 160 350 170 300 120 310 130 320 140 330 150 340 160 350 170 190 10 200 20 210 30 220 40 230 50 240 60 250 70 260 80 NAUTICAL 5 MILES101520253035404550556065707580 NAUTICAL 85 MILES0 STATUTE 5 MILES1015202530354045505560657075809585100 90 DEGREESModeClrOn/OffDistVolWtWx÷:789xSto456−Rcl123+Bksp0.+/-=CMPTSD Alt: As Wind Wt. Bal Timer Conv: Dist Vol Wt WxAPlotterBMechanical Flight ComputerCElectronic Flight Computer
Figure 15-18. A plotter (A), the computational and wind side of a mechanical flight computer (B), and an electronic flight computer (C).
to develop skill in constructing these diagrams as an aid to the complete understanding of wind effect. Either consciously or unconsciously, every good pilot thinks of the flight in terms of wind triangle.
If flight is to be made on a course to the east, with a wind blowing from the northeast, the aircraft must be headed somewhat to the north of east to counteract drift. This can be represented by a diagram as shown in Figure 15-19. Each line represents direction and speed. The long blue and white hashed line shows the direction the aircraft is heading, and its length represents the distance the airspeed for 1 hour. The short blue arrow at the right shows the wind direction, and its length represents the wind velocity for 1 hour. The solid yellow line shows the direction of the track or the path of the aircraft as measured over the earth, and its length represents the distance traveled in 1 hour, or the GS.
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Pilot's Handbook of Aeronautical Knowledge航空知识手册3(23)
