AOPA Pilot Magazine - March 1958 - (Page 35)

all, ifs a scarce birddog that can point more than one way at a time, and this "one waff ia the heading. The second direction of interest ia "course." Course ia the direction you wish to travel over the ground. Let's emphasize again not to confuse such terms true course, magnetic course, and compass course. They simply indicate different ways of ineasurhg the same identical direction, your course or desired direction of travel. At this point we should note the difference between course and heading. Your airplane will move thr&ugh the air in the direction it 2. heading. However, da we all know, the air itself may be moving' in another d i m tioa. This causes it to drift or move across the ground in a direction different from ita heading. Therefore, in order to make good our desired course, we must anticipate this effect and select, a heading which i differs ent from our course. This difference i .called the "drift correction." s Sometimes we eaimot anticipate the effect of the 'wind exactly, and our aircraft will move acroas the ground in a direction different from the desired direction or course. This third basic direction, the one in which our aircraft actually passes over the ground, i called "track." s The difference between our track and our heading i the "drift" or actual s wind effect, whereas the difference between our course and our heading is the "drift correction" or anticipated wind e S d Last of all, the pilot m a y be intermated in specifying the direction of foists other than his destination such aa a radio station or landmark. For this purpose we define the term, '¥bearing. Baring is the direction of any one point from some other designated pint. In summary, let us consolidate the - do not coincide exactly. The most northerly direction of these lines of force is called "magnetic north." Since the comnags, i the absence n of errors, will point toward magnetic north, this becomes a useful reference direction for in-flight measuremeats. The relationship between magnetic north and true north is shown in ground. (3) TrackÑth direction i which fifiure (2) where both the meridians n an aircraft actually and the magnetic lines of force are illustrated. As can be seen here the passes over the ground. (41 BearingÑth direction of one direction of magnetic north varies point from some other from that of true north. This difference is called magnetic variation, or designated point. The T e next problem which a pilot aimply *%ariatimy' amount of h faces is that, in order t o measure this variation is dependent solely an? direction, he mast have another upon the location on the earth and known direction, or reference direction, with which he can cornthe first, W commoaly measure any die rection clockwise from our selected reference direction, from 0 t o 866", ' as shown m figure (1). Having discussed the four basic directions in which a pilot is iuterFIG. 1 ested, it now remains to select ap" propriate reference directions with which he can compare or measure the basic ones. There are four fun& mental reference directions which are useful for aerial navigation. OWSG the relationship of these four to one another is clearly understood it will be 'W simpfeat matter for you to interpret all bf the directioml terms such a8 magnetic course, true track, compass heading, e t cetera, without rdyiny on confusing memoir crutches or slogans for converting from one to the other. Tha first fundamental reference direction is "true north." True north la the direction of t h e earth's *or& note from the point where the iaeaaFIG. 2 urement is made. S n e the earth is ic anriroxfanately a sphere an infinite number of gmt circles, e&ch passing through both the north and Hie south polea, can be drawn about the earth. These circles are called meridians, and they appear as lines running north and south on the maps which represent the earth's surface, S c theae lines extend toward the ie n north pole or true north and since they appear at regular intervals on a saw, they provide the handiest reference direction for measuring any other desired direction on a map. However, once a pilot is airborne, he hae no means o directly deterf mining the direction of true north. H e must rely on a compass which tends t o align itself with the lines of force of the earth*? magnetic field. These lines of force closely apomximate the meridiane in most locations, but unfortunately the two four h a i r directions and their deftnitions aa f o l l m : (11 hadim-the direction in which the nose of an aircraft ifl actually pointing or heading. ( S ) Course-the direction in which you desire an aircraft to over the - MARCH, 1958

Table of Contents for the Digital Edition of AOPA Pilot Magazine - March 1958

AOPA Pilot Magazine - March 1958
Contents
Calendar
Legally Speaking
Editorial
What About Airspace Use, Mr. Pyle?
10,000 Seconds Under the Hood
Flying Weather One Month Ahead
AOPA Weathercast
AOPA 185579
Air-Age Teenagers Give City a Lift
Your Radio and You
Operation Cost Cut
Put Your Fabric to the Test
Are You "Compasss Punchy?
Yankee Duster in Latin America
South American Challenge
I Lived Through a Graveyard Spiral
Safety Corner and Accident Report
On the Airways
Travel
What's New?
Classified Department

AOPA Pilot Magazine - March 1958

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