User Guide

TO, FROM, and the VOR INDICATOR
Let’s look at a typical VOR indicator (dis-
cussed in more detail in the Radio Flyer chap-
ter). You’ll notice an outer ring with degree
markings, an adjusting knob at the lower
left, and a needle with a center “target” and
five dots on each side.
Turning the knob rotates the ring to set
the indicator for the desired bearing or radial. If
the needle is centered, you’re exactly on that radial. You’ll notice,
however, that if you keep turning the knob, the needle will center
at two points, 180 degrees apart. One is the radial from the station,
the other is the bearing to the station. How do you know which is
which? By checking the indicator’s TO and FROM flags, which
appear as a white arrowhead pointing up or down, respectively.
POSITION FINDING AND TRACKING:
You can use the VOR two ways: simply to locate your position
(often in conjunction with Distance Measuring Equipment, or DME),
or to follow an exact course directly to or from the station: tracking.
Let’s try the simplest one first. Assume you’re flying some-
where in the vicinity of Podunk and want to find out where you
are. Tune in the Podunk VOR by selecting its frequency on the nav
receiver (see “Radio Flyer”) and look at the VOR indicator. The
needle will most likely be deflected fully to one side or the other.
Turn the knob (called the Omni Bearing Selector, or OBS) until the
needle centers. Now look at the TO/FROM flag. If it shows TO,
continue turning the OBS; the needle will first deflect, then center
once again, this time with the FROM flag in view.
The number at
the top of the indicator, with the needle centered and the FROM
flag in view, is the radial on which you’re currently located.
In this
illustration, we’ve once
again used the example
of the 315 degree radial
from Podunk, so you
know you’re somewhere
to the northwest of the
station.
As we continue to discuss aircraft radionavigation, that term,
as well as its companion, bearing‚ will come up frequently, usu-
ally associated with a specific degree value (for example, “the
315-degree radial from Podunk VOR”). It’s important to remem-
ber this simple fact: a radial
always refers to the direction
from the station to the air-
craft; a bearing always
refers to the direction
from the aircraft to the
station. Thus, we can
also say that for every radi-
al, there’s a corresponding
bearing 180 degrees away.
WHAT ABOUT HEADING?
Let’s go back to our bicycle wheel analogy for a moment.
Imagine that each spoke has, engraved in the metal every few
inches, its radial value in degrees, starting with 0 at the north. Let’s
also imagine a literate ant, crawling along and among the spokes.
He can read which spoke he’s on at any given moment - but he
doesn’t have any way of knowing, other than running his head
into either the hub or the rim, which way he’s going on the spoke.
VOR is rather similar: it allows you to directly determine
your location, but provides absolutely no information about
which way you’re pointed (your heading). In this respect, it’s like
GPS, but exactly the opposite of the ADF (Automatic Direction
Finder, which we’ll cover shortly), which can tell you your head-
ing, but has no direct information on your location.
Thus, the VOR might indicate that you are, indeed, on the
315 radial from Podunk - but you’ll have to refer to your magnet-
ic or gyro compass to determine which way you’re pointed (and,
at least in the short term, which way you’re going). VOR stations
are aligned to magnetic north, so when you look at them refer-
enced on a sectional chart they may be rotated so that their 0 radi-
al is rotated towards the Earth’s magnetic pole. Keep this in mind
during flight, since true north does not equal magnetic north in
most cases!
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Flight Instruction
125
Flight Instruction