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Navigational Elements Know the four elements of navigation. 1. State how the Earths size and shape affect navigation. 2. State how to determine position. 3. State how to determine direction. 4. State how to determine distance. 5. State how to determine time.

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Overview 1. Earths Size and Shape 2. Position 3. Direction 4. Distance 5. Time

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Earths Size and Shape For most navigational purposes, the Earth is assumed to be a perfect sphere. Measured at the equator, the Earth is approximately 7, miles in diameter, and the diameter through the poles is approximately 7,901 miles.

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Earths Size and Shape Great Circles and Small Circles Defined as a circle on the surface of a sphere whose center and radius are those of the sphere itself. It is the largest circle that can be drawn on the sphere. The single most important aspect of great circles for navigators is that the arc, or piece of the circle, is the shortest distance between two points on a sphere. Circles on the surface of the sphere other than great circles are defined as small circles.

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Earths Size and Shape Great Circles and Small Circles

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Position Lines of reference are necessary in order to locate specific points on the Earth. These lines are known as parallels of latitude and meridians of longitude. The numbers representing a position in terms of latitude and longitude are known as coordinates of that position.

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Position Latitude The equator is a great circle midway between the poles, and its plane is perpendicular to a line connecting the poles.

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Position Latitude The location of the latitude is determined by figuring the angle at the center of the Earth between the latitude and the equator.

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Position Longitude Indicates east-west location. There is no natural starting point for numbering longitude. When the English-speaking people began to make charts, they chose the meridian through their principle observatory in Greenwich, England, as the zero degree line.

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Position Longitude The Greenwich Meridian is sometimes called the first or prime meridian, although it is actually the zero meridian. Longitude is counted east and west from this meridian through 180 o. The Greenwich Meridian is the 0 o longitude on one side of the Earth; and, after crossing the poles, it becomes the 180 th meridian. These designations define the Eastern and Western Hemispheres.

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Position Finding the Place If a globe has the circles of latitude and longitude drawn upon it and if the latitude and longitude of a place has been determined, a given point can be located on the globe in its proper position.

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Position Finding the Place Latitude is expressed as either north or south of the equator in degrees up to 90, and longitude is expressed as either east or west and is expressed in degrees up to 180. A degree ( o ) of arc may be subdivided into smaller units by dividing each degree into 60 minutes () of arc. Each minute may be further subdivided into 60 seconds () of arc. Smaller areas can be located by going beyond degrees and minutes and using seconds.

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Direction Direction is the position of one point in space, relative to another, without reference to the distance between them. The points of a compass are not adequate for modern navigation. It has been replaced, for the most part, by a numerical system.

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Direction

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Since determination of direction is one of the most important parts of the navigators work, the various terms involved should be clearly understood. Course – Intended direction of travel Heading – where the airplane if pointed Track – The actual direction that was traveled

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Direction? Course –In Red Track Heading –Aircraft Heading changes

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Heading – Track - Course Note the winds

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Direction A line that makes the same angle with each meridian is called a rhumb line. Flying this sort of path results in a greater distance traveled, but it is easier to steer. Between two points on the Earth, the great circle is shorter than the rhumb line, but the difference is negligible for short distances (except in high latitudes).

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Distance Measured by the length of a line joining two points. In navigation, the most common unit of measuring distance is the nautical mile. The nautical mile is about 6,076 feet. Equal to 1 minute of arc on a meridian, which is 1 minute of latitude. To convert nautical miles to statute miles, the nautical mile figure can be multiplied by the factor To convert statute miles to nautical miles, multiply the statute miles by 0.87.

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Distance Speed is closely related to the concept of distance, which determines the rate of change of position. Speed is usually expressed in miles per hour, either statute or nautical. If the measure of distance is nautical miles, it is customary to speak in terms of knots.

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Time The Earth makes a complete rotation of 360 o during a 24 hour day. Zone Time Before the establishment of zone time in 1883, every city and town had its own time. Each time zone is 15 o of longitude (1 hour of angular measure) in width, and the first zone centers on the prime meridian. The United States has four standard time zones (in the contiguous states).

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Time Greenwich Mean Time The use of Greenwich Mean Time (GMT) avoids the necessity of considering time zones. GMT is the time of day at any given moment at Greenwich, England.

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Around the world in 24 zones! 24 Time Zones A through Z Zulu time last I and O not used

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World View 24 Zones

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Summary 1. Earths Size and Shape 2. Position 3. Direction 4. Distance 5.Time 6.Website for further information: pilots_handbook/chapter_14.htm

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