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? –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.

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.

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

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.

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:

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.

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.)

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 75 th meridian is is noon EST.

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.

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

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.

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

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

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.

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

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)

What are the coordinates of KHUF? How about KSIV