VOR and reverse sensing

[Koopas Ly]

Hi all,

What is meant by reverse sensing?

Say I am southeast of the VOR station, and want to head straight to
that station in a northwest direction, at a heading of 300. I tune
and identify, and currently track the 300 radial (300 on the OBS),
with a "TO" indication, and the needle centered. If I wander to the
right of my course, the needle will swing to the left, so I'll turn a
few degrees to the left and rejoin the 300 radial.

First, am I tracking the 300 inbound radial or the 300 outbound
radial? What is the proper terminology?

Second, what if, instead of heading 300, I was heading 120. In other
words, what if I was heading in the exact reciprocal direction with
the OBS still at 300 and a "TO" indication? I assert that the needle
would still be centered; however, how would someone know that he's
indeed headed TOWARDS the station and not away from it?

Thanks!
Alex

[Hilton]

Koopas wrote:
> Hi all,
>
> What is meant by reverse sensing?
>
> Say I am southeast of the VOR station, and want to head straight to
> that station in a northwest direction, at a heading of 300. I tune
> and identify, and currently track the 300 radial (300 on the OBS),
> with a "TO" indication, and the needle centered. If I wander to the
> right of my course, the needle will swing to the left, so I'll turn a
> few degrees to the left and rejoin the 300 radial.
>
> First, am I tracking the 300 inbound radial or the 300 outbound
> radial? What is the proper terminology?

You are tracking the 120 degree radial inbound. You don't have inbound or
outbound radials. You have radials, and you can be inbound or outbound on
one of them. You are on the 120 radial, not the 300 radial.


> Second, what if, instead of heading 300, I was heading 120. In other
> words, what if I was heading in the exact reciprocal direction with
> the OBS still at 300 and a "TO" indication? I assert that the needle
> would still be centered; however, how would someone know that he's
> indeed headed TOWARDS the station and not away from it?

Because you'd have reverse sensing! :) Seriously, VORs have no idea which
way you're headed. Once you remember that, then things become easier. Now,
you are on the 120 radial headed AWAY from the VOR with 300 dialed in on the
OBS and you have a TO flag - because as far as the VOR receiver is
concerned, a 300 degree course would take you TO the VOR (remember, it
doesn't know which way you're going). Now, if you deviate to the right, the
needle will move to the RIGHT (reverse) because it thinks you're flying TO
the VOR and have deviated to the LEFT. That is reverse sensing. I don't
like the name cause it somehow implies the VOR is doing something
different - it isn't. It should be called "The pilot screwed up and dialed
in the wrong radial".

Hilton

[Thomas Lembessis]

(Koopas Ly) wrote in message >...
> Hi all,
>
> What is meant by reverse sensing?
>
> Say I am southeast of the VOR station, and want to head straight to
> that station in a northwest direction, at a heading of 300. I tune
> and identify, and currently track the 300 radial (300 on the OBS),
> with a "TO" indication, and the needle centered. If I wander to the
> right of my course, the needle will swing to the left, so I'll turn a
> few degrees to the left and rejoin the 300 radial.
>
>

If you're Southeast of the station, and are flying toward the station,
it is the 120 degree radial you are flying, not the 300. The 300
radial only exists northwest of the VOR; the 120 exists southeast of
the VOR.

First, am I tracking the 300 inbound radial or the 300 outbound
> radial? What is the proper terminology?
>

You are tracking the 120 degree radial; there is no
inbound/outbound distinction. VOR is a position instrument. The fact
that you are tracking the 120, with your OBS set at 300 is what
produces the "TO" flag on your omni head display.

> Second, what if, instead of heading 300, I was heading 120. In other
> words, what if I was heading in the exact reciprocal direction with
> the OBS still at 300 and a "TO" indication? I assert that the needle
> would still be centered; however, how would someone know that he's
> indeed headed TOWARDS the station and not away from it?
>

If your OBS is set at 300, and you have a "TO" indication, and your
heading is 120, you are flying AWAY from the station.
This would be where the "Reverse sensing" you describe would take
place.
To track the radial, you would fly away from the needle.

> Thanks!
> Alex

Hope this Helps

Thomas Lembessis

ATP, F/E (B-727)

[Tim Bengtson]

Koopas Ly wrote:

> What is meant by reverse sensing?

Here's a site that may just change your life:

http://www.campbells.org/Airplanes/VOR/vor.html

Tim

[Ron Natalie]

"Greg Burkhart" > wrote in message news:wh%_a.147370$o%2.63624@sccrnsc02...

> You're correct. If you're SE of the VOR, a 300 TO will give you the correct
> deflection if you're flying towards the VOR. If you do a 180° turn,

The easier way to think about it is to ignore "to/from" all together. If your
heading is the rougly the same as the OBS setting, then the left right indictions
of the needle will be normal. If you're heading is roughly the opposite of the
OBS setting then it's going to read backwards.

[Robert Perkins]

On 14 Aug 2003 23:18:27 -0700, (Koopas Ly)
wrote:

>First, am I tracking the 300 inbound radial or the 300 outbound
>radial? What is the proper terminology?

This assumes that you've positioned the OBS so that 300 is at the top
of the circle.

If the VOR says "TO" with the OBS set to 300 at the top, you're
positioned along the 120 radial, that is, you're southeast of the VOR
transmitter. Flying a heading of 300 will bring you TO the station,
flying 120 will fly you FROM the station. Notice here that the TOP of
the needle points to 300, and the BOTTOM points to 120.

If the VOR says "FROM" with the OBS set to 300 at the top, you're
positioned on the 300 radial, northwest of the transmitter. Flying a
heading of 120 will bring you TO the station, flying 300 will take you
FROM the station.

http://www.campbells.org/Airplanes/VOR/vor.html is what I read to make
sense of it all, after missing the questions on every FAA written
test. (thanks for posting it again, Tim; I had lost the link). After
going over that document I don't have problems using the VOR receivers
anymore at all.

Rob

[Jon Kraus]

Read this and then get back to us. It helped me tremendously. Good Luck.

http://www.campbells.org/Airplanes/VOR/vor.html

Jon Kraus
PP-ASEL
Student-IA


Koopas Ly wrote:

> Hi all,
>
> What is meant by reverse sensing?
>
> Say I am southeast of the VOR station, and want to head straight to
> that station in a northwest direction, at a heading of 300. I tune
> and identify, and currently track the 300 radial (300 on the OBS),
> with a "TO" indication, and the needle centered. If I wander to the
> right of my course, the needle will swing to the left, so I'll turn a
> few degrees to the left and rejoin the 300 radial.
>
> First, am I tracking the 300 inbound radial or the 300 outbound
> radial? What is the proper terminology?
>
> Second, what if, instead of heading 300, I was heading 120. In other
> words, what if I was heading in the exact reciprocal direction with
> the OBS still at 300 and a "TO" indication? I assert that the needle
> would still be centered; however, how would someone know that he's
> indeed headed TOWARDS the station and not away from it?
>
> Thanks!
> Alex

[Mike Rapoport]

"Koopas Ly" > wrote in message
om...
> Hi all,
>
> What is meant by reverse sensing?
>
> Say I am southeast of the VOR station, and want to head straight to
> that station in a northwest direction, at a heading of 300. I tune
> and identify, and currently track the 300 radial (300 on the OBS),
> with a "TO" indication, and the needle centered. If I wander to the
> right of my course, the needle will swing to the left, so I'll turn a
> few degrees to the left and rejoin the 300 radial.


> First, am I tracking the 300 inbound radial or the 300 outbound
> radial? What is the proper terminology?
>

If you are SE of the VOR then you are not on the 300 radial. Think of
radials as "radiating" out from the VOR. In your case you are on the 120
radial inbound


> Second, what if, instead of heading 300, I was heading 120. In other
> words, what if I was heading in the exact reciprocal direction with
> the OBS still at 300 and a "TO" indication? I assert that the needle
> would still be centered; however, how would someone know that he's
> indeed headed TOWARDS the station and not away from it?


If the needle was centered and you turn left and the needle goes left then
you would know that you are headed away from the VOR.

> Thanks!
> Alex

[Corky Scott]

On Fri, 15 Aug 2003 16:50:25 GMT, Jeffrey Voight
> wrote:

>Here's a tip somebody told me, and it's worked for me:
>
>When you see 'TO' think 'THROUGH'. That is, the 300 radial points all
>the way 'THROUGH' the VOR. So, if you are on the 300 radial, CDI says
>'TO (THROUGH)', you will fly 'THROUGH' the VOR station on a heading of 300.
>
>When you see 'FROM' think, where is that signal coming 'FROM'? That is,
>if I spin the dial on the CDI and it centers on 120 and FROM, that
>signal is coming 'FROM' the VOR on a heading of 120.
>
>The other thing he told me was that the only time I should see 'TO' is
>when I'm trying to get 'TO' the VOR. The only time I should see 'FROM'
>is when I'm trying to verify where I am (location fix). So, unless
>you're headed for the VOR itself, you should see a FROM indication (and,
>you should be drawing a line FROM the VOR on your map to fix your
>location). If you want to fly TO the VOR (and subsequently beyond it),
>you want to see TO on the CDI. Of course, once you've crossed the top
>of the milk bottle, you won't be flying TO the VOR anymore. You'll now
>just be verifying your position as you fly away FROM the station.
>Perhaps you want to turn after you cross the VOR. You'll still want to
>see FROM because no matter which way you turn, you'll still be flying
>away FROM the VOR (unless, of course, you're turning back TO the VOR for
>holding or just looking to get hit by other aircraft flying TO the VOR).
>
>Jeff...

I like this explanation Jeff. I've looked at the Joe Campbell website
describing his method of interpreting VOR's and I have more trouble
with that than with the normally taught method of interpreting the
VOR.

It's a nice mnenomic: to, through.

My instructor gave me another one the other day regarding when winds
are true or magnetic. Devilishly difficult to remember for me
ordinarily until he said "if it's written, it's true". Therefore when
you hear it spoken, it's the other one, magnetic.

For me, the "if it's written it's true" mnemonic works great because
all my life I've heard people tell me that they've seen it written so
it must be true. Doesn't matter that extremely often the written word
is NOT true, the fact that I've heard it so often made it an instant
memory prod for me.

Corky Scott

[Ross Oliver]

I think the main thing that confuses people about VORs is
differentiating between location and course guidance. So let's
remove the couse guidance aspect for a moment:

Imagine you are in a helicopter in a stationary hover pointed
at 360 magnetic. You tune in a VOR and set the OBS to 360. The needle
deflects full left. What does this mean? It means that the imaginary
line starting a the VOR and radiating out (hence "radial") toward the
magentic north pole is located somewhere to your left. Now you do a
180-degree pedal turn so your helicopter is pointed at 180 degrees.
What will happen to the CDI needle? Nothing, because you are stationary.
It will still be deflected full left. However, because you have turned
180 degrees, the radial is now actually to your right. THAT is reverse
sensing.

Another way to think of it is the CDI needle tells you which
direction you need to turn the OBS in order to center the needle.

So now you push the cyclic forward and start your helicopter moving.
You now want to use your CDI for course guidance. If your current
heading is within +/- 90 degrees of your OBS setting, the CDI needle
will be a "command instrument", i.e. it will tell you which direction
to turn in order to intercept the selected radial. If your current
heading is MORE than +/- 90 degrees from your current OBS setting,
then you must turn in the opposite direction of the needle to intercept.

So what about the TO/FROM flag? Your OBS is still set to 360. Now
draw a line perpendicular to 360 passing through the VOR. The TO/FROM
flag can tell you on which side of this perpendicular line you are
located. Like the OBS setting, the TO/FROM flag is NOT related to
what direction your aircraft is pointed. If the flag is indicating
FROM, then you are on the same side of the perpendicular line as the
360 radial. An indication of TO means you are on the opposite side
of the line.


Happy landings,
Ross Oliver

[flyer]

The concept that changed my way of thinking about VORs was that of the
"Poor man's HSI" published in IFR Refresher. Basically, superimpose
an imaginary airplane centered on the VOR dial with the nose pointed
at the OBS bearing that corresponds to your current heading. The
needle of the CDI now represents the location of the selected radial
with respect to the airplane flying that heading. It is easy to do
intercepts this way. Think of an OBS set at 090 degrees and you have
a right needle and a TO flag, for example. How would you intercept?
Put an imaginary airplane in the center of the dial with the nose
pointed at 120, for instance. That would intercept because the
airplane is flying toward the right deflected needle. This works out
best graphically with a VOR indicator that uses has a lateral
displacement needle rather than one that pivots from the top or
bottom, but both work. Would the intercept be TO or FROM the station?
If the TO indicator is showing at the top you would be intercepting
TO the station since your airplane is pointing toward the top of the
dial. If you put the imaginary airplane at a heading 210 you would
also intercept but heading is taking you away from the station. If
you put the imaginary airplane at a heading of 070 you would clearly
be flying away from the selected radial and would not intercept.
Tim Bengtson > wrote in message >...
> Koopas Ly wrote:
>
> > What is meant by reverse sensing?
>
> Here's a site that may just change your life:
>
> http://www.campbells.org/Airplanes/VOR/vor.html
>
> Tim

[Ron Natalie]

"Jeffrey Voight" > wrote in message ...

> When you see 'TO' think 'THROUGH'. That is, the 300 radial points all
> the way 'THROUGH' the VOR. So, if you are on the 300 radial, CDI says
> 'TO (THROUGH)', you will fly 'THROUGH' the VOR station on a heading of 300.

The "radial" does not go through the VOR. The OBS doesn't require you to be on the
radial you have it set to however. Once you fly to the VOR on a given radial the
TO/FROM indictaor will flip as you start flying out the reciprocal radial.

> When you see 'FROM' think, where is that signal coming 'FROM'? That is,
> if I spin the dial on the CDI and it centers on 120 and FROM, that
> signal is coming 'FROM' the VOR on a heading of 120.

Better, why don't you use this for TO as well? The operative word here
is that is where the signal is with respect to the VOR station NOT the
aircraft.

>
> The other thing he told me was that the only time I should see 'TO' is
> when I'm trying to get 'TO' the VOR. The only time I should see 'FROM'
> is when I'm trying to verify where I am (location fix).

Nonsense. You want the FROM indication when you are headed away from
the VOR, otherwise you will have reverse sensing.

The general rule is that you want to set the OBS to approxiately the same direction
you want to be headed. If you want to fly inbound on the 220 degree radial, you need
to set the reciprocal (40 degree) on the VOR because that is the direction you want
to be headed.

You need to crack the books a bit more.

[Dan Moos]

Some one please give me an "Amen!" if they feel as I do

Most of the VOR terminology mentioned in this thread is correct, but that
doesn't make it useful for a beginner.

Yes, if I'm SE of the station with a heading of 300, an OBS setting of 300,
and a TO indication, I am indeed on the 120 degree radial. This is the
"technically correct" way to describe the situation, and when our friend
starts doing IFR stuff, it is also the more intuitive in respect to doing
holds.

But he isn't doing holds, he's navigating, and is probably a student pilot
who is just getting into cross-country stuff. It is FAR more intuitive for
him to think in terms of being on an imaginary extension of the 300 degree
radial. And that too is overcomplicating it. What is wrong with percieving
radials as going through a station instead of as spokes on a wheel? When I
was learning thats how I did it, and all VOR tasks seemed simpler that way,
ESPECIALLY reverse sensing, which is easy to explain if you draw a radial on
paper that extends through the station.

Now I'm learning IFR stuff. Even though the way I thought of VORs wasn't the
official way, it was the way that gave me a thorough understanding of how to
use them for all tasks. This understanding made it easier to transition to
the more accepted way of describing radials, which admittedly makes more
sense for some IFR tasks, like holds fort instance.

Can I get an Amen?

[Andrew Sarangan]

Here is an article I wrote, similar to the one cited below, on how to
avoid reverse sensing altogether.

http://131.238.38.204/~sarangan/aviation/articles/vor-article.pdf



Jon Kraus > wrote in message >...
> Read this and then get back to us. It helped me tremendously. Good Luck.
>
> http://www.campbells.org/Airplanes/VOR/vor.html
>
> Jon Kraus
> PP-ASEL
> Student-IA
>
>
> Koopas Ly wrote:
>
> > Hi all,
> >
> > What is meant by reverse sensing?
> >
> > Say I am southeast of the VOR station, and want to head straight to
> > that station in a northwest direction, at a heading of 300. I tune
> > and identify, and currently track the 300 radial (300 on the OBS),
> > with a "TO" indication, and the needle centered. If I wander to the
> > right of my course, the needle will swing to the left, so I'll turn a
> > few degrees to the left and rejoin the 300 radial.
> >
> > First, am I tracking the 300 inbound radial or the 300 outbound
> > radial? What is the proper terminology?
> >
> > Second, what if, instead of heading 300, I was heading 120. In other
> > words, what if I was heading in the exact reciprocal direction with
> > the OBS still at 300 and a "TO" indication? I assert that the needle
> > would still be centered; however, how would someone know that he's
> > indeed headed TOWARDS the station and not away from it?
> >
> > Thanks!
> > Alex

[Robert Perkins]

On Fri, 15 Aug 2003 16:49:26 -0400, "Ron Natalie" >
wrote:

>> The other thing he told me was that the only time I should see 'TO' is
>> when I'm trying to get 'TO' the VOR. The only time I should see 'FROM'
>> is when I'm trying to verify where I am (location fix).
>
>Nonsense. You want the FROM indication when you are headed away from
>the VOR, otherwise you will have reverse sensing.

Not if you use the VOR as an instrument to help you with magnetic
headings, relying on the compass or DH for that data, rather than as a
command instrument.

Rob

[Robert Perkins]

On Sat, 16 Aug 2003 01:04:26 GMT, "Dan Moos" >
wrote:

>Some one please give me an "Amen!" if they feel as I do
>
>Most of the VOR terminology mentioned in this thread is correct, but that
>doesn't make it useful for a beginner.

You can't have one from me.

Learn and use a VOR the way it was designed: as an instrument which
tells you your *position*, *not* your course line, and you'll never
have a problem with reverse sensing.

>What is wrong with percieving
>radials as going through a station instead of as spokes on a wheel?

If you do it that way, you're not perceiving radials, you're
perceiving lines. If you want to follow an arrow to your course, use
an ADF. VOR's are better for position detection.

Rob

[Dan Moos]

"Robert Perkins" > wrote in message
...
> On Sat, 16 Aug 2003 01:04:26 GMT, "Dan Moos" >
> wrote:
>
> >Some one please give me an "Amen!" if they feel as I do
> >
> >Most of the VOR terminology mentioned in this thread is correct, but that
> >doesn't make it useful for a beginner.
>
> You can't have one from me.
>
> Learn and use a VOR the way it was designed: as an instrument which
> tells you your *position*, *not* your course line, and you'll never
> have a problem with reverse sensing.
>

Yes, and no. First of all, my method doesn't disagree with what you say.
Nothing I wrote suggests that I know which way the plane is pointing by
looking at a snapshot of the CDI needle. Because it doesn't.

BUT, if I have 300 degrees dialed in to the OBS and keep the needle centered
for a few minutes or more, I think the VOR is great for giving you a course
line. Thats why it is the primary instrument for IFR navigation. Of course,
you need to use other instruments to establish yourself on that course line,
and until you do, it is true that the VOR only gives you your position. And
as far as describing your position to someonelse (ATC maybe), your method
is much more proper. That is why when ATC says "Hold southeast of HUH on the
120 degree radial", it makes sense.

>> If you do it that way, you're not perceiving radials, you're
> perceiving lines.

Precisely. Most people understand lines, whereas radials require some
simplification. Really the only difference in doing it my way is that I
don't have to deal with reciprical values. I get the same results as your
method. I have NEVER misinterpreted a VOR reading, and personally think it
is the way of describing radials that is is taght in most places that is
responsible for confusing people about a simple instrument.

If you want to follow an arrow to your course, use
> an ADF. VOR's are better for position detection.
>

My method works equally on ADF. I just think of an ADF as a VOR that
requires me to read my compass or DG to get what I need. You CAN follows
"radials" on an ADF this way, and my imaginary line through the NDB method
is especialy usefull here because there is enough calculation going on in
your head to follow a specific course line with the ADF that you don't need
weird reciprical course values to muddle things up.

Actually, I think a VOR is a FAR superior course following instrument then
an ADF. Look at it this way. I'm enroute IFR to the IAF. Lets first suggest
that the IAF in this case is an NDB. I'm enroute, and I lose my directional
gyro. lets also say that turbulence isa makeing the mag compass unreadable.
At this point I have no concrete idea What my course line is. What is the
wind doing? Who knows, because to use the ADF for COURSE information, I need
to also know my actual heading. No DG or compass, and the wind could
eventually make my track WAY of line. And if I'm aproaching the IAF, I'll be
maybe 1000 feet or less above pattern altitude when I get there, not good if
I have no real idea from which direction I'm approaching the station.

Do the same exercise whith the VOR. No problem, because the VOR is giving
you constant COURSE information. If the wind screws with you, you will see
it.

Here lies the main problem. If you truly believe that the VOR gives you no
course line info, then your way of thinking has caused you to not really
understand the instrument.

[Casey Wilson]

> >
> > Learn and use a VOR the way it was designed: as an instrument which
> > tells you your *position*, *not* your course line, and you'll never
> > have a problem with reverse sensing.

No, with one exception, it does not tell you your position. That single
exception is when you overfly the antenna. Then, you may presume the antenna
is some altitude dependent radius from the nadir. Otherwise, the only thing
the VOR will tell you is BEARING from the station.

[Dan Luke]

"Casey Wilson" wrote:
> > > Learn and use a VOR the way it was designed: as an instrument
which
> > > tells you your *position*, *not* your course line, and you'll
never
> > > have a problem with reverse sensing.
>
> No, with one exception, it does not tell you your position.
That single
> exception is when you overfly the antenna.

No. One may use a VOR receiver and CDI to compute one's position by
flying perpendicular to a radial, timing the observed deflection, and
applying a simple formula.
--
Dan
C172RG at BFM

[Casey Wilson]

"Dan Luke" > wrote in message
...
> "Casey Wilson" wrote:
> > > > Learn and use a VOR the way it was designed: as an instrument
> which
> > > > tells you your *position*, *not* your course line, and you'll
> never
> > > > have a problem with reverse sensing.
> >
> > No, with one exception, it does not tell you your position.
> That single
> > exception is when you overfly the antenna.
>
> No. One may use a VOR receiver and CDI to compute one's position by
> flying perpendicular to a radial, timing the observed deflection, and
> applying a simple formula.

In which case the VOR did NOT give you your position. The calculation
required additional instruments: A timer and some device (compass or DG) to
fly perpendicular to a radial, not to mention the use of the ASI, and so
forth. I say again, the VOR did NOT give you your position. By the way,
flying perpendicular to one radial is NOT perpendicular to the next, so the
calculation is flawed.

[Dan Luke]

"Casey Wilson" wrote:
> In which case the VOR did NOT give you your position. The
calculation
> required additional instruments: A timer and some device (compass
or DG) to
> fly perpendicular to a radial, not to mention the use of the ASI,
and so
> forth.

Silly hair splitting. You also said the VOR will give you bearing from
the station: how will it do that without the use of other equipment?
--
Dan
C172RG at BFM

[Peter Duniho]

"Casey Wilson" > wrote in message
...
> No, with one exception, it does not tell you your position. That
single
> exception is when you overfly the antenna. Then, you may presume the
antenna
> is some altitude dependent radius from the nadir. Otherwise, the only
thing
> the VOR will tell you is BEARING from the station.

How is that not "position"? Granted, it's not a very accurate description
of one's position, but it certainly describes one's position to an extent.

Given that the word "position" is simply being used to contrast with
heading, course, and other related terms, your objection seems pretty silly
to me.

Pete

[Casey Wilson]

"Peter Duniho" > wrote in message
...
> "Casey Wilson" > wrote in message
> ...
> > No, with one exception, it does not tell you your position. That
> single
> > exception is when you overfly the antenna. Then, you may presume the
> antenna
> > is some altitude dependent radius from the nadir. Otherwise, the only
> thing
> > the VOR will tell you is BEARING from the station.
>
> How is that not "position"? Granted, it's not a very accurate description
> of one's position, but it certainly describes one's position to an extent.
>
> Given that the word "position" is simply being used to contrast with
> heading, course, and other related terms, your objection seems pretty
silly
> to me.

Who is being silly? You are relating apples and oranges. Bearing is
related to heading and course, position is related to geographical
coordinates. A single VOR won't tell you squat about geographical
coordinates.
Given that the "standard service volume" (AIM 1-1-8) is at least 40
nautical miles, the definition is not a trivial thing. I have tuned into VOR
stations as much as 85 miles away. So, where am I on that line from the
station.
Let's consider that the acceptable angular error [ FAR 91.171(b)(3) ]
can be plus/minus 6 degrees. I don't have my calculator, but I think the
formula is cosine of the angle times the distance... I'm only guessing, but
I think that at the forty mile limit, the aircraft could be as much as five
to seven miles on either side of the displayed bearing angle. Hmm, let's
see: base times height divided by two [40 miles times 5 miles then divide by
2] gives 100 square miles. Wait, that was only the half-angle -- multiply
by two to cover the other side and we are up to 200 square miles of area
over which the airplane could be flying.
I like using the VOR, I like having two of them in the panel. Hell, I
even like the ADF -- got one of those too. When I triangulate any two of
those, I have a rough idea of my 'position.'

[Peter Duniho]

"Casey Wilson" > wrote in message
...
> Who is being silly? You are relating apples and oranges. Bearing is
> related to heading and course, position is related to geographical
> coordinates. A single VOR won't tell you squat about geographical
> coordinates.

I have no idea what you're talking about.

Bearing relative to the VOR station is all about your position relative to
the station. Knowing your bearing relative to the station greatly narrows
down your geographical coordinates. You can get a lot more accurate using a
second VOR or DME, but that doesn't change the fact that even a single VOR
is telling you a lot about your geographical coordinates.

While on the other hand, the bearing relative to the VOR has NOTHING to do
with heading or course. Nothing at all. It boggles my mind that you would
say it does. The mistaken impression that it does have something to do with
heading or course is where lots of people (the original poster included) get
confused. You're just making matters worse by saying that it does.

> Given that the "standard service volume" (AIM 1-1-8) is at least 40
> nautical miles, the definition is not a trivial thing. I have tuned into
VOR
> stations as much as 85 miles away. So, where am I on that line from the
> station.

Just knowing you're on that line is useful GEOGRAPHICAL POSITION
information.

> [...] and we are up to 200 square miles of area
> over which the airplane could be flying.

All you're doing is bickering about just how accurate the GEOGRAPHICAL
POSITION information is. A single VOR isn't very accurate at all. Two VORs
are more accurate. A VOR with DME is even more accurate. Two VORs with DME
each are even more accurate. And a GPS receiver is even more accurate. So
what? They all still give you geographical positions.

> I like using the VOR, I like having two of them in the panel. Hell, I
> even like the ADF -- got one of those too. When I triangulate any two of
> those, I have a rough idea of my 'position.'

No triangulation is needed to get a rough idea of your position.
Triangulation reduces the "roughness" of your position estimate, but a
single VOR receiver alone gives you a rough idea of your position. (An ADF,
of course, does no such thing...it MUST be referenced to another instrument
to provide ANY positional information at all).

Pete

[Steve House]

Student here, following debate with interest but I don't understand the
issue at disagreement. Considering "bearing" as distinct from "relative
bearing", is not the bearing the clockwise angular direction with respect
to the meridian over its origin of a line drawn from one point to another?
And since the 0 radial of the VOR station is aligned to the magnetic
meridian, each VOR radial indicates directly the magnetic bearing from the
VOR station to an object that lies somewhere along it. To get one's bearing
from the VOR station, than, can you not just rotate the OBS until the needle
is centred? If the "from" flag is up then the OBS ring reads out directly
the magnetic bearing to the aircraft as viewed from the VOR station, and if
the "to" flag is up, the OBS is showing the reciprocal. So don't you know
you're somewhere along that line? Of course, neither indication gives the
actual aircraft position without using some other additional means to
establish distance from the station - DME, triangulation on another station,
etc. Same principle with a movable card ADF set to or slaved to one's
compass heading, except that its needle is always indicating the bearing to
whatever station that's tuned so one needs to convert that reading into the
radial bearing from the station of interest to the plane (I know that the
conversion assumes the magnetic variation at the plane's position is not
different from that at the station's position, if you want to get precise).

"Dan Luke" > wrote in message
...
> > "Casey Wilson" wrote:
> > In which case the VOR did NOT give you your position. The
> calculation
> > required additional instruments: A timer and some device (compass
> or DG) to
> > fly perpendicular to a radial, not to mention the use of the ASI,
> and so
> > forth.
>
> Silly hair splitting. You also said the VOR will give you bearing from
> the station: how will it do that without the use of other equipment?


> --
> Dan
> C172RG at BFM
>
>

[Casey Wilson]

"Steve House" > wrote in message
...
> Student here, following debate with interest but I don't understand the
> issue at disagreement. Considering "bearing" as distinct from "relative
> bearing", is not the bearing the clockwise angular direction with respect
> to the meridian over its origin of a line drawn from one point to another?
> And since the 0 radial of the VOR station is aligned to the magnetic
> meridian, each VOR radial indicates directly the magnetic bearing from the
> VOR station to an object that lies somewhere along it. To get one's
bearing
> from the VOR station, than, can you not just rotate the OBS until the
needle
> is centred? If the "from" flag is up then the OBS ring reads out directly
> the magnetic bearing to the aircraft as viewed from the VOR station, and
if
> the "to" flag is up, the OBS is showing the reciprocal. So don't you know
> you're somewhere along that line?

Yes. That was my point exactly. Only, somewhere along that line could
be anywhere within about a 200 square mile area when you factor in the
inherent accuracy of the single VOR.

>Of course, neither indication gives the
> actual aircraft position without using some other additional means to
> establish distance from the station - DME, triangulation on another
station,
> etc.

Yes. That was my point exactly.

[karl gruber]

"Peter Duniho"
*** I have no idea what you're talking about*****

In an unusual turn of events, the newsgroup idiot has spoken with some
knowledge. Peter has no clue since his head has been up his ass for so long
it's stuck there.

Knowing the radial one is on is only half the position formula. Position is
a vector quantity. Knowing your radial is a scalar quantity and distance is
needed to provide the vector quantity, position.

*****No triangulation is needed to get a rough idea of your position.
Triangulation reduces the "roughness" of your position estimate, but a
single VOR receiver alone gives you a rough idea of your position. (An
ADF,*****

Were you asleep in basic algebra, Peter? As you certainly were in private
pilot ground school. Peter, you are so easy to pigeon hole. Too bad aviation
has become such an easy place for fat ass know it alls to flop.

http://www.sasked.gov.sk.ca/docs/physics/u1b3phy.html


Karl

[Ron Natalie]

"Jeffrey Voight" > wrote in message ...

> Using your rule, I wouldn't be able to take a position fix without
> turning the plane.

I didn't say that, I was refering to flying the VOR. I was specifically countering
your statement that you only use the FROM flag when you are trying to hunt
the radial.

> You need to get less emotional about mnenomics

I'm not emotional, I'm just trying to avoid getting prosepective students all
messed up with your bizarre incorrect information.

[Ron Natalie]

"Robert Perkins" > wrote in message ...

>
> Not if you use the VOR as an instrument to help you with magnetic
> headings, relying on the compass or DH for that data, rather than as a
> command instrument.
>
You're going to sit there spinning the needle all the time to figure out what
radial you are on. Then you're going to look at the compass to figure out
if you are left or right of the course and turn that way, and then continually
recenter the needle to see what change that made?

No sane person flies the VOR that way. The needle isn't the command instrument,
but it tells you which side of the course you are, you then apply a currention to
the heading (turn towards the needle) and fly it using your primary heading
reference.

[Robert Perkins]

On Mon, 18 Aug 2003 10:06:10 -0400, "Ron Natalie" >
wrote:

>
>"Robert Perkins" > wrote in message ...
>
>>
>> Not if you use the VOR as an instrument to help you with magnetic
>> headings, relying on the compass or DH for that data, rather than as a
>> command instrument.
>>
>You're going to sit there spinning the needle all the time to figure out what
>radial you are on.

No, you're going to spin the needle once until you've centered it and
the thing says "FROM". Then you know what radial you're on, and you
can use the needle to choose headings to intercept the radial.

Regarding position, it's true that one VOR won't tell you your exact
position. But if you combine pilotage from a chart with the relative
position data ("southeast of the station", "west of the station",
whatever.), you will have your position.

And in ANY case, what prevents the one-VOR-equipped pilot from flying
a standard-rate turn and tuning first one VOR for a fix, and then a
second for another fix, thus establishing his position very
accurately?

Gawrsh, maybe I really ought to go get that instrument rating... ;-)

> Then you're going to look at the compass to figure out
>if you are left or right of the course and turn that way, and then continually
>recenter the needle to see what change that made?

No! That's madness. I'm not going to recenter the needle at all; I'm
going to fly a heading for two minutes and take a second reading from
the VOR, and not ever use the needle to steer the airplane unless I'm
flying right to the station.

Rob

[David Megginson]

Robert Perkins > writes:

> Regarding position, it's true that one VOR won't tell you your exact
> position. But if you combine pilotage from a chart with the relative
> position data ("southeast of the station", "west of the station",
> whatever.), you will have your position.

You get an approximate position fix from a single VOR transmitter by
flying perpendicular to the radial and timing how long it takes you to
get to a different radial (say, 10 degrees off). It's not all that
practical or accurate in real-life, of course, but it does sort-of
work.

Apologies in advance if I've missed the point of the thread and
duplicated a previous posting.


All the best,


David

--
David Megginson, , http://www.megginson.com/

[Dudley Henriques]

"gross_arrow" > wrote in message
om...


if the vor system is properly explained
> to begin with, it is not all that hard to grasp. learning anything
> "wrong" would, imho, only lead to subsequent confusion and necessitate
> eventual re-learning the correct way.

It's for this EXACT reason that I posted about what Duniho was saying, and
it has nothing to do with the simple 101 fact that a VOR bearing has nothing
to do with aircraft heading. Any pre cross country student should know this.
The problem with what he was saying is that he was STRESSING beyond what was
normal under the circumstances of the discussion, that a single VOR bearing
from a single VOR is sufficient enough to be of great value in estimating a
geographical fix ,which it absolutely is not. Every student from day one
should be taught that a single VOR bearing is just step one in obtaining a
"fix". If a single VOR is all that's available in the aircraft, then a
second VOR should be
selected to establish the cross reference necessary
to establish a "fix". The point I'm making here is a simple one. In teaching
navigation to students, it's my opinion that it's just not appropriate for
ANYONE to stress the importance of a single VOR bearing as sufficient in any
way whatsoever in establishing a fix.
This is a student group; not rec.aviation.pilots. People are learning to fly
over here. There's a right way and a wrong way to approach the issues that
are discussed on this particular group. I have no problem with Duniho per
se'. I don't post to him at all if it's possible to avoid it. If I see
something from ANYONE that peaks my interest as a flight instructor, I
usually post a response. It's not meant to be personal, although in Duniho's
individual case, I'll admit freely that I just don't have any use for the
man. There is much in what he says at times that is both true and useful.
This occasion wasn't one of those times; in my professional opinion anyway.
Dudley Henriques
International Fighter Pilots Fellowship
Commercial Pilot/CFI
Retired

[Snowbird]

"Dudley Henriques" > wrote in message . 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

[Dudley Henriques]

"Snowbird" > wrote in message
om...
> "Dudley Henriques" > wrote in message
. 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


What you are saying here is completely accurate. However, if you read back
through Duniho's posts on this thread, there is not ONE instance where he
even comes close to mentioning what you and I, and I assume Duniho knows as
well, is the correct procedure for establishing a reasonable distance check
from a single VOR using the procedure you have outlined. His entire context
deals directly with the premise that a single VOR bearing used alone is
valuable POSITIONAL information. This is not true at all. He does mention
that additional information is "helpful", but he is STRESSING the point that
a single bearing alone is valuable positional information.
The reason I entered a reply was because he was "correcting" someone who had
correctly stated that a single bearing from a VOR was only that....a single
bearing, and NOT a position fix, which is absolutely correct. In fact,
Duniho's opening statement was
"How is this not a position fix?"
As I said, this is a student group. Pilots who post here should be keenly
aware of that. In aviation training, we work fairly hard to get student
pilots to understand that TWO sources are required for position fixes, not
ONE! That second source can indeed be a second VOR bearing, an ADF bearing,
a DME readout, or indeed, a distance check on a single radial as you have
mentioned. If Duniho or anyone else for that matter wants to post here that
a single VOR bearing is valuable positional information, they should include
the need for that second source as PARAMOUNT to obtaining a position fix,
and not simply mention a second source as being desirable, but not
necessary, as did Duniho in his explanations on this thread.
That's my opinion, and as a professional flight instructor, I'll go with
that.
Dudley Henriques
International Fighter Pilots Fellowship
Commercial Pilot/CFI
Retired

[Casey Wilson]

>
> 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.

No offense intended, but you might have missed a crucial point in
earlier posts in this thread. There was a contention that position could be
derived from a single VOR simply by knowing which radial the airplane was on
at a given moment.

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

Which is exactly my original 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.

Thanks, Sydney

[Don Tuite]

On 20 Aug 2003 04:33:13 -0700, (Snowbird)
wrote:

> . . . 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.

1) I think you mean that you offset the OBS by ten degrees from what
it reads when the needle is centered. (The needle itself not being
conspicuously calibrated in degrees.)

2) Don't you then need to fly a course at right angles to the bearing
TO/FROM the station, in the direction that will intercept the new OBS
setting? For example, if your track coincided with the bearing TO the
station, the needle would only center when you were (nearly) over the
station. Your distance from the station would then be (essentially)
zero, regardless of flight time. (There's an even more trivial case
if you fly outbound on the radial -- you eventually fly off the
chart.)

I'm not an instructor, but my inclination would be to tell a student
to save this cute stuff for when he/she's bored on a long
cross-country. If you really need to know where you are, don't screw
around. Use multiple VOR stations and triangulate.

Don

[journeyman]

On 20 Aug 2003 04:33:13 -0700, Snowbird > wrote:

[snip]
>
>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.

[double-snip]

>I mention it because I was taught this technique as a student, but
>many don't seem to be.

FWIW, this technique is the subject of a couple of questions in the
IFR written test question bank. It's an interesting academic exercise,
but I can't see much practical use for it, especially IFR.


Morris

[Don Tuite]

On Thu, 21 Aug 2003 02:19:32 -0000,
(journeyman) wrote:


>FWIW, this technique is the subject of a couple of questions in the
>IFR written test question bank. It's an interesting academic exercise,
>but I can't see much practical use for it, especially IFR.

I believe it's a variation on a technique in *American Practical
Navigator* (Bowditch) for determining how far a sailing vessel is off
a lee-shore headland. It was probably known to Odysseus.

Don

[Snowbird]

"Casey Wilson" > wrote in message >...
> >
> > 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.
>
> No offense intended, but you might have missed a crucial point in
> earlier posts in this thread. There was a contention that position could be
> derived from a single VOR simply by knowing which radial the airplane was on
> at a given moment.

No offense taken, and I didn't miss that point at all.

I thought I said so, but, it was probably too well hidden by too
many other words :)

My intention was only to explain an additional technique.

Perhaps a clearer way to make my point would have been to say,
while I agree two of *something* is needed, a 2nd VOR or ADF is
not needed; a 2nd radial from the same VOR, and a method of determining
the distance between them, may substitute.

Cheers,
Sydney

[Snowbird]

Don Tuite > wrote in message >...

On Thu, 21 Aug 2003 02:19:32 -0000,
> (journeyman) wrote:
> >FWIW, this technique is the subject of a couple of questions in the
> >IFR written test question bank. It's an interesting academic exercise,
> >but I can't see much practical use for it, especially IFR.

Morris, as I think I mentioned, for the technique itself I concur.

The IFR written questions, though, are just geared towards seeing
if the pilot is aware of the relationship between distance from
the VOR vs. distance between radials.

I do think there's some practical use for that awareness. For
one thing, it allows one to understand what the error may be on
a VOR approach where the VOR is 20-30 nm off the field (there
are a number of those around here). For another, it is helpful
in understanding how to intercept a radial smoothly at varying
distances from the station, something at which I could improve.

> I believe it's a variation on a technique in *American Practical
> Navigator* (Bowditch) for determining how far a sailing vessel is off
> a lee-shore headland. It was probably known to Odysseus.

Interesting, Don. I suppose it's off-topic, but could you explain?
The reference to Odysseus implies that it's very low technology.

It may have been known to Odysseus, but my impression is, it's
not known to many of today's pilots :). We just had our #2 OBS
repaired, and our avionics repairman opined that 9 out of 10
pilots couldn't find our airport from a nearby VOR with 2 working
NAVS, 2 working OBS, 2 hands, and a flashlight. He might have a point.

Thanks,
Sydney

[journeyman]

On 21 Aug 2003 17:08:56 -0700, Snowbird > wrote:

>The IFR written questions, though, are just geared towards seeing
>if the pilot is aware of the relationship between distance from
>the VOR vs. distance between radials.

Makes sense.

>I do think there's some practical use for that awareness. For
>one thing, it allows one to understand what the error may be on
>a VOR approach where the VOR is 20-30 nm off the field (there
>are a number of those around here). For another, it is helpful
>in understanding how to intercept a radial smoothly at varying
>distances from the station, something at which I could improve.

Interesting. That's not what I'd consider practical knowledge. It's
more theoretical background, a frame of reference to understand the
behavior. But I can see your viewpoint.


Morris