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Navigation Basics

Navigation Basics. AST 241 From Van Sickle’s Modern Airmanship chapter 11 6 th ed. Charts & Mapping. What is your definition of a map? Can any map accurately depict the surface of the earth? Why? Is the earth perfectly round? Why or Why Not?. Mapping. What is a great Circle?

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Navigation Basics

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  1. Navigation Basics AST 241 From Van Sickle’s Modern Airmanship chapter 11 6th ed.

  2. Charts & Mapping • What is your definition of a map? • Can any map accurately depict the surface of the earth? • Why? • Is the earth perfectly round? Why or Why Not?

  3. Mapping • What is a great Circle? • A sphere cut by a plane through the center gives the largest circle that can be drawn on that sphere. • In global navigation, the shortest distance between two points on the earth’s surface is a great circle route. • Any other circle is a small circle.

  4. Mapping • If we begin at the center of a sphere and divide it equally into 360 parts, each part becomes one degree. • Degrees are then divided into 60 parts: • Called minutes which are divided into 60 parts: • Called seconds. Thereafter they become decimals or fractions of seconds.

  5. Mapping • Determining position in the earth’s surface requires reference points: • On a sphere circles work best- we begin at the equator.

  6. Latitude/Longitude • Latitude ranges from 0 degrees at the equator to 90 degrees at the poles • What type of circle would the equator be? • It is a great circle, all other circles of latitude are small circles parallel to it and are thus “parallels” of latitude.

  7. Lat./long. • ½ of a great circle passing through the poles is called a “meridian” of longitude or simple “meridian.” • All meridians intersect at rt.angles to parallels. • In order for meridians to be useful as a reference point we need to establish a reference meridian which is:

  8. Lat./long. • The prime meridian located in: • Greenwich, England • In the western world, longitude is measured east or west of the prime meridian 0 – 180 degrees ending at the international date line in the pacific ocean • We now have intersections from which we can locate any point on earth.

  9. Lat./long. • The numbers of these intersecting lines are the “coordinates” of the earth. • There are many different types of coordinates but in aviation we use divisions of degrees as described earlier. • For example the coordinates for El Paso TX are 31Degrees 47 minutes North, 106 degrees 27 minutes West (Always give Lat. Followed by Long.)

  10. Time • We all know that it takes the earth roughly 24 hours to make one 360 degree rotation on its axis. • Thus if we divide 360 degrees by 24 we get 15 degrees. These divisions are where we get our time zones from- roughly • When the sun is directly overhead of the 75th meridian is is noon EST.

  11. Time • Since it is difficult to keep track of time in aviation we use the time over the prime meridian as a reference- UTC (GMT) or “zulu time.” • Thus we have conversion factors to convert our local times to UTC times ie. From EST to UTC add 5 hours.

  12. Map projections • Why are maps categorized according to projections? • The two most common projections are the: • Lambert Conformal Conic- (secantally cut projection- differs from a tangential conic) • Mercator

  13. Map projections • Refer to Fig. 11 (in Modern Airmanship) • As mentioned earlier all flat maps produce distortions- it is the job of the map maker to minimize these distortions with respect to the users most urgent needs.

  14. Measuring distance • Using grid coordinates- 1 minute of a latitude or longitude line is 1 Nautical Mile or 6080 feet: • (1.15 N.M.)

  15. Measuring Direction • Direction is expressed in degrees clockwise from the North Pole (true north). • The difference between true and magnetic north is: • Variation

  16. Map Scale • Map Scale- The ratio of the length of distance on a map to the true distance on the surface of the earth. For example aeronautical sectional charts the scale is 1:500,000 where one unit of the chart is equal to 500,000 units on the surface of the earth.

  17. Great Circle vs. Rhumb line • What is a great circle? • A rhumb line is a straight line drawn on a mercator map and cuts each meridian at the same angle. • On most aeronautical charts a straight line drawn closely approximates a great circle course

  18. Rhumb line ctn. • For example the in a true great circle route and a straight course drawn on a sectional chart would be about 10 miles on a NY to San Francisco trip. • Conversely, the difference in distance between a rhumb line course and a great circle course between NY and Paris is about 145 NM. Which is longer? (see fig. 11-4)

  19. What are the coordinates of KHUF? How about KSIV

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