"Dudley Henriques" wrote in message hlink.net...

you are absolutely right about one VOR radial ident NOT being a
positive"position" fix. True, having a directional bearing from a single VOR
is better than having nothing at all, but even if only a single VOR is
involved, it is ALWAYS recommended that a SECOND VOR be chosen, and a cross
check made before considering what you have as a "fix" When discussing a
position FIX, TWO is the magic number, NOT one! The second of the two can be
DME, an ADF bearing, or a second VOR positive radial ident, but when
discussing a position fix, ESPECIALLY on a student newsgroup, using a single
VOR radial as an example of a geographical fix is wrong in my opinion, and I
would urge all students NOT to begin thinking of a positive geographical fix
on these terms.....PERIOD!!!!

Dudley, I know you're aware of this, but since this is a student
newsgroup I think it should be mentioned that it *is* possible to
obtain a reasonable position estimate using a single VOR.

These days, I suppose a pilot is more likely to be in a cockpit
with 2 GPS and no VOR than to be in a cockpit with no GPS and 1 VOR,
but let's suppose that's the situation. Only 1 VOR station can
be received, for some reason.

Of course you're correct that a single VOR simply places you on a line.
So to determine position, we need additional information.

We all know (or can see, if we think about it) that the distance between
VOR radials varies with distance from the station by a function of 1 in
60. At 60 nm from the station, it's roughly 1 nm between radials,
30 nm it's roughly 0.5 nm between radials. IOW, we use the distance
between radials to estimate our distance from the station.

How to do so practically? We use time and our knowledge of our plane's
approximate groundspeed. One centers a radial, then turns the OBS to
deflect the needle 10 degrees, notes the time, and flies until the
needle centers. Note the time again.

Let's say one is flying a typical GA plane with a groundspeed of
about 2 nm/min. Let's say it took 3 minutes to fly 10 degrees.
We calculate our distance as 60 * (2 nm/min * 3 min)/10
or 36 nm from the VOR.

To boil it down:
*know your airplane's approx. speed in nm/min
*calculate 6 * speed in nm/min * time in min to fly 10 deg

Of course, for accuracy, one would need to correct for wind
either by estimating groundspeed, or by flying in both directions
and averaging the time.

I mention it because I was taught this technique as a student, but
many don't seem to be. As I said, Dudley, I'm sure you're aware
of it, and I don't mean to contradict what I see as your basic point
that a single VOR radial by itself does not, in fact, give position
but rather only 1/2 of the information needed to derive position.

The practical aspect of the above method is that awareness of
the distance between radials as a function of distance from the
station helps smooth VOR intercepts, something I need to remind
myself of as I use GPS far more often than VOR these days.

Best,
Sydney