VOR and reverse sensing

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

"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.

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?

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/avia...or-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

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

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

"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.

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.

"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

"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.