VOR and reverse sensing

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

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

(Koopas Ly) wrote in message . com...
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)

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

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

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

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

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

"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

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