VOR Radials

[Golden Rivet]

Quick question of flying VOR Radials.

If you are flying west for example, towards a VOR, you are flying a VOR radial of 90 Degrees TO.

As you fly over the top of the beacon and out the other side, are you still flying a 90 Degree radial or is this now classified as a 270 FROM radial.

Thanks

GR

[fireflybob]

A radial is always your magnetic bearing FROM the VOR.

What the CDI indicates is another matter and is dependent on position relative to the VOR and OBS selection.

[Onan the Clumsy]

Hard to add to what ffbob said really. Radials radiate.

You could rephrase your initial statement from...

"you are flying a VOR radial of 90 Degrees TO"

...into...

"you are flying along the 090 radial Towards the VOR"

and your last sentence from...

"or is this now classified as a 270 FROM radial"

...into...

"or is this now classified as the 270 radial"

[Tinstaafl]

At first in your example, you are on the 090 radial FROM the VOR and at that instant happen to be travelling towards it. You could be tracking in any direction and would still be on the 090 radial from the aid.

After crossing the aid you will be on the 270 radial from the aid.

The radial you're on is by definition described from the station ie they radiate FROM the aid.

Since the CDI will be centred if the OBS is selected to the radial you're on OR the one opposite the next problem is to determine which side of the VOR you're on.

If you're on the same side of the VOR as the radial then the FROM flag will show. If the other side of the beacon then the TO flag is shown.

Bear in mind a TO or FROM flag will show whether or not you're located on the OBS selected radial. Which one is displayed depends on whether you're in the same hemisphere as the OBS selected radial.

The TO or FROM flag & its display relative to the hemisphere stems from what would happen if you held the same heading as the radial. If you were on the 270 radial & also set 270 as a heading then you would track FROM the aid.

Ergo, if you were on the opposite side of the VOR - still with the 270 HDG then you must track TO the aid.

Don't forget that if you were on the opposite side of aid compared to the 270 radial then you would be on the 090 radial.

Hence '...track TO the VOR on the 090 radial...' or in a more abbreviated form '090 radial TO the VOR' then after passing overhead you would be '...tracking on the 270 radial FROM the aid.'

[Black_Dawn]

GR

any radio signal coming out of a VOR station is defined as a Radial.

Now an example:

let's consider you are tracking a course of 90° TO the XXX vor ( CDI centered, OBS 090°), maintaining a heading of 090° (no wind); now in this case you are on radial 270°. After passing the vor you'll have an indication FROM and now you are on radial 090° (OBS still set at 090°).

To recap the meaning of Radial: RADIAL is always a Course FROM the VOR station.
Whatever your heading,whenever you say you are on radial eg. 180 XXX VOR: you are telling the controller you are South of XXX VOR.

Hope this can help

B_D

[Golden Rivet]

Thanks for the answers chaps - I Think my confusion lay with the OBS selection.

So if you are approaching the VOR at say 240 Deg from the VOR and wanted to exit the VOR on the 60 Degree radial you would set the OBS to 60 deg.

[BOAC]

GR - at the risk of confusing you :eek: , if you set 060 on the OBS when you are south west of the beacon, and get onto that track (while you ARE STILL southwest of the VOR!) , you will be on the 240 radial FROM the VOR. You can then leave the OBS set on 060 and track right through the o/head (with consumate skill, of course!) and out the other side. You will then be on the 060 radial FROM the VOR.

There are articles here (http://www.deltabyte.com/wingtips/mtcfi07.htm) and here (http://www.navfltsm.addr.com/vor-nav.htm) which may help?

[Golden Rivet]

Thanks - great links.

[Onan the Clumsy]

So if you are approaching the VOR at say 240 Deg from the VOR and wanted to exit the VOR on the 60 Degree radial you would set the OBS to 60 deg.

You can centre the CDI with two OBS settings: The radial you're on and its reciprocal. Set the OBS to the one that's closest to what your compass says and you'll get the correct TO/FROM flag and needle sensing, no matter whether the VOR is in front of you or behind you.

[FlyingForFun]

Wow, there are some over-complex answers here! All correct, but over-complex nonetheless!

GR, it's actually quite simple. If you're tracking to/from a VOR, you set your OBS to be roughly equal to your heading. The equipment works everything else out for you, and displays the correct indication. That's it.




(What then happens is it compares your OBS setting to the radial you're on. If they're more than 180 degrees out, it displays a To flag, otherwise it displays a From flag.)

The only confusing part of using a VOR is if the OBS is not roughly the same as your heading. Because the VOR display has no idea what heading you're on, if you're on the 090 radial, with 090 set on the OBS, but tracking 270 (i.e. to the VOR), it will display a From flag, because it doesn't know that you're actually flying away from the beacon. The needle will also indicate in the wrong sense. But this can be avoided by following the simple rule: OBS is roughly equal to your heading.

(Of course, that only applies to tracking to/from a VOR. If you just want a position fix, you always find a From flag, regardless of your heading... but that's a different story, a different use for the same tools.)

Hope that helps!

FFF
------------------

[fireflybob]

More accurate to say that you set the OBS to your desired magnetic track (whether or not you are flying away from or towards the VOR). This assumes that you wish the deviation needle to work in the demand sense.

This way the deviation needle will work in the demand sense, ie needle left, turn left and vice versa.

It's really quite simple!

[Crossunder]

Hm. Didn't know people were still using OBIs... ;)

[Golden Rivet]

Not many people using VLF Hyperbolic Navigation these days, but the UK CAA still feels it necessary to put it into the Engineering sylabus ?

[DoctorA300]

Goldie,
Forget all this sparky stuff, i hear there are still some corroded
shear decks out there :} :} :} ;) :E

[Golden Rivet]

Alas, I'm on the line now so I'm not allowed to snag them.

Do have a sneeky peek through the outflow valve now and then !

Regards