How do VORs / LOCs work?

[ioan_jones]

I've only done some gliding so far, and since we generally use maps/GPS could someone please explain how VORs or Localisers work? Someone told me they are similar to NDBs, is that true?

Anyway, thanks a lot

[tom775257]

Hi,
what plane do you fly?? I'm still learning in K-21's.
A VOR is a VHF omni-range....it is a radio navigation 'station' that, to put it simply, allows you to track inbound or outbound to the station on a particular bearing ...so, for example, you could track inbound on a 35 degree radial etc. you would set the frequency of the VOR into the nav radio, then set the radial you want to track with the Omni bearing setting (OBS). You would then fly towards that radial and intercept it. Look on aeronautical charts for something that looks like a compass rose, usually it is a VOR.
The localiser provide pilots with course guidance to the runway centerline during approach in the horizontal plane (usually combined with the glideslope that provides vertical information to maintain usually a 3 degree glide slope from the horizon)
An NDB is just a fixed point, you couldn't designate to track towards it on a specific bearing, you can just head towards it.
tom.


[This message has been edited by tom775257 (edited 28 March 2001).]

[ioan_jones]

thanks a lot, think I've got it now....

I'm still learning to fly gliders, mostly K-13s, but the weather's been so bad and along with this FMD I havn't been able to fly much recently. Still, that what comes with living in the wettest country this side of Brazil in the wet season....

[Luftwaffle]

How does a VOR work?

It sends out two VHF signals. One signal is the same phase in all directions. The other signal varies in phase through the 360 degrees of the compass. Thus if you're due north of the station you receive the two signals in phase, and you are said to be on the 000 radial. If you're due south of the station, you receive them 180 degrees out of phase, and you are said to be on the 180 radial.

What do you use a VOR for?

Finding your position, following an airway (designated path between two of them), holding (waiting in place without interfering with other traffic) or flying an approach (descending towards a runway you can't see yet).

How do you use a VOR?

You set the VOR receiver in your aircraft to the frequency of the VOR station you are interested in, and then to a particular radial. An indicator on the instrument shows you which side of that radial you are on, and whether you would be going TO or FROM the station if you flew in the direction of that radial. (There are different sorts of VOR receivers, so I'm being slightly vague with regards to the "indicator".)

For example, lets say you select the 090 radial and the indicator points to the left and a FROM flag shows. That means you are southeast of the VOR. (If you flew due east you would be going away from the station, and you'd have to steer to the left to be on the 090 radial).

To find what radial you are on, turn the bearing selector slowly until the indicator centres -- shows neither a left nor right deflection -- with a FROM flag. Whatever bearing is selected is the radial you are crossing at that moment.

If you select a particular radial and then steer so as to keep the indicator in the centre, you are flying along that radial, from or to the station.

VOR vs. NDB

For a given position of your aircraft, the indications on your VOR will be the same regardless of which direction your aircraft is pointing. The needle on your ADF (NDB receiver) simply points to the NDB station, so the needle will swing around as you turn the aircraft around. That's the main difference from a pilot's point of view.

Tom775257 hasn't met this yet, but you *can* track towards or away from an NDB on a specified bearing. It just takes a bit of math, or an RMI (more expensive NDB receiver) instead of an ADF.

Also, an ADF can be used to pick up AM radio stations, while a VOR receiver can only receive entertainment radio if there happens to be a strong local station at the extreme top end of the commercial FM band.

A localizer is the same technology as the VOR, only it sends out a beam in a narrow range of directions from the threshold of a runway. Aircraft intercept the beam, and then using the same left-right indicator, follow it towards the runway. I don't think a localizer would be much use in glider navigation.

[tom775257]

Thanks Luftwaffle,

As per my profile, still learning!
you mentioned the RMI, I have heard this in reference to flying a DME arc, I heard it in passing and can't remember the context, is that relevant to traking to an NDB on a specific heading??
Thanks for the interesting post.
Best regards,
tom.

ioan_jones:
Darn the foot and mouth..my local gliding club is closed.
Yeah, I have been in a K-13 also, I prefer the K-21's...
I think I might take this opportunity of no gliding to try a big surge forwards in learning for PPL, however I need to sort my finances first (I am but a poor uni student.)
best regards.

[Luftwaffle]

A DME (it stands for Distance Measuring Equipment) is yet another navigational aid. It's represented charts by a square, and is often co-located with a VOR. The DME tranceiver on the aircraft sends out a signal. The DME on the ground receives this signal and sends back another one. The transceiver analyses the time difference to calculate your distance to the station.

A DME arc is simply an approach that requires the pilot to fly a course that is a consistent distance from a DME station. If the DME is co-located with a VOR or NDB, then the pilot can use the RMI as a guide to help stay on the arc.

This doesn't have much to do with tracking to or from a station, as obviously you're going around the station.

[Edited to answer the actual question.]

[This message has been edited by Luftwaffle (edited 30 March 2001).]