15 replies to this topic

[J_S_W]

Credit goes to Charles Wood for this tutorial.  If you are the original author and would prefer to have your content removed, please contact Brad or Jon.

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hi everyone ,

The basic principle of operation of the VOR is very simple. the VOR facility transmits two signals at the same time. One signal is constant in all directions, while the other is rotated about the station. The airborne equipment receives both signals, looks (electronically) at the difference between the two signals, and interprets the result as a radial from the station.

With VOR, course information must be manually entered into the indicator. The VOR indicator below shows an aircraft heading toward, "TO," the station on the 345° radial. This aircraft is south of the station.





The VOR display has four elements:

1 )A Rotating Course Card, calibrated from 0 to 360°, which indicates the VOR bearing chosen as the reference to fly TO or FROM. Here, the 345° radial has been set into the display. This VOR gauge also digitally displays the VOR bearing, which simplifies setting the desired navigation track.
  
2)The Omni Bearing Selector, or OBS knob, used to manually rotate the course card.
  
3)The CDI, or Course Deviation Indicator. This needle swings left or right indicating the direction to turn to return to course. When the needle is to the left, turn left and when the needle is to the right, turn right, When centered, the aircraft is on course. Each dot in the arc under the needle represents a 2° deviation from the desired course. Here, the pilot is dead-on course.
  
4)The TO-FROM indicator. This arrow will point up, or towards the nose of the aircraft, when flying TO the VOR station. The arrow reverses direction, points downward, when flying away FROM the VOR station. A red flag replaces these TO-FROM arrows when the VOR is beyond reception range, has not been properly tuned in, or the VOR receiver is turned off. Similarly, the flag appears if the VOR station itself is inoperative, or down for maintenance. Here, the aircraft is flying TO the station.




To grasp the VOR system you must understanding that it is entirely based on radials away from the station.


  



the arrow on the 0° radial points away from the center of the compass rose. this radial points to the west of true north because of the west magnetic variation. North on a VOR is Magnetic North. So, if you overflew this VOR on the 0° radial, you would be flying away from the VOR.

Similarly, note the arrows by the 30°, 60°, 90° marks and the rest of the way around the compass rose. They all point away from the station. Radials are always away from the station.

There is only one line on the chart for each numbered radial for a particular VOR station. Whether you are flying it outbound or inbound, or crossing it, a radial is always in the same place.

The only possible complication lies in the reciprocity of the numbers. Whenever you are proceeding outbound, your magnetic course (and heading when there is no wind) will be the same number as the radial. Turn around and fly inbound you must mentally reverse the numbers and physically reverse the OBS setting so that your course is now the reciprocal of the radial. But the radial you are flying on hasn't changed.





This aircraft is north of the Omni station, flying on the 345° radial away FROM the station. The CDI shows the aircraft on course and the FROM flag is present, pointing down, toward the station behind.

Edited by Brad, 25 August 2003 - 08:27 PM.

[J_S_W]

This aircraft is south of the Omni station. Its magnetic course is 345°. Walk through the steps below to understand the VOR reading.



The aircraft isn't on the 345° radial because that radial extends from the Omni to the northwest as shown by the arrow.
  

The aircraft is actually on the reciprocal radial, the radial pointing towards the plane. That reciprocal radial is 165°, away from the station like all radials.
  

If the 165° radial were set into the VOR, the FROM flag would properly show, because the aircraft is away from the Omni on that radial.
  

Here is the important point. If the OBS is rotated until the needle centres and the FROM flag shows, it will always show the correct radial from the Omni that the aircraft is on regardless of the aircraft heading.
  

To eliminate the confusion of location relative to an Omni, the magnetic course of the aircraft and the radial setting on the VOR should be the same.
  

Presumably the aircraft is flying in the desired course direction, so its heading will be approximately the same as the VOR setting, i.e., the magnetic course. The heading may differ slightly from the VOR because of the correction needed to correct for wind drift.
  

Thus, with the OBS set to 345° the CDI needle shows the aircraft on course and the TO flag is showing, pointing up, toward the station ahead.
to know whether you are flying TO or FROM an Omni, the OBS setting must be approximately the same as the aircraft heading.





The above illustration shows the confusion that can result, yes, that the VOR indicator can actually provide wrong information if the OBS isn't set properly.

Same example as before. The aircraft is south of the BEACON, on the 165° radial. It is flying northwest. Observe the COMPASS. The aircraft is heading 345° as desired. But the OBS was improperly set to 165° and the VOR is falsely informing the pilot, with a nicely centred needle, that he/she is flying away FROM the BEACON. The aircraft, of course, is flying TOwards the BEACON.

the TO-FROM confusion disappears if the aircraft heading and the OBS setting are approximately the same which they weren't here. Pay attention to this and you will stay out of trouble.

This sort of error usually happens when the pilot rotates the OBS, watching only for a centred needle, not also paying attention that the setting should approximate the magnetic course, or aircraft heading.



Wandering off course?







This aircraft has drifted to the right of the desired course. To be "on course" the aircraft must be on the red line. Not paying attention to a crosswind, or simply letting the heading wander could do it. In any event, the VOR needle has swung to the left, indicating that the aircraft must move to the left to return to course. So a left turn is in order. a pilot always turns towards the needle to return to course, assuming that the OBS setting approximates the aircraft heading.

This aircraft is 4° off course. Each dot of the arc under the needle is a 2° deviation from the desired course. Don't confuse heading, the direction of the aircraft's nose, with course, the desired track along the ground. Only with no wind will heading and course be the same.

[alio]

Brad can you make this sticky as well. Oh and a good job J_S_W keep it up.

[buksie]

Brilliant man. A must for the newbees to fs.

[Byron]

Good job "Mr. Tutorial"   Very usefull

[blixel]

Great tutorial.  I might print this out for my own notes.  But...

It's nice to know how the "old school" instruments work, and probably a requirement for real pilots, but wow... that's some seriously archaic stuff.  Thank God for GPS.  Great information though.  I do a little bit of VOR flying in the flight sim every now and then just to change it up.

So let me see if I got this straight.

I want to fly West to East from Point A to Point B.  I study my flight maps and I see there is a VOR tower between the two points, slightly North.  I draw a line from the VOR tower to the airport at Point A and see that it's radial is 210 degrees.  Then I draw a line from the VOR tower to the airport at Point B and see that it's radial is 120 degrees.

So I take off from Point A, fly TO the VOR on the 210 degree radial which would give me a heading something like 030 degrees (210-180=30).  Once I pass over top of the VOR tower, I then change my heading to 120 degrees, fly away from the VOR tower on the 120 degree radial, and in theory I will intercept Point B.

Am I even close?

Edited by blixel, 25 August 2003 - 11:15 AM.

[Brad]

Looks like you nailed it blixel.

Now you know how those of us feel that started flying back before GPS was an option!  Hmmm, maybe I should post a Dead Reckoning tutorial.  That'll really get the juices flowing!

[DeathScytheHellEW]

This VOR is just confusing me ! I'll just stick to GPS/ILS flight ! Just those two are all I need to fly around in a plane . The ILS Tutorial taught me about ILS and it helped me alot so I guess this one is good too . Keep it up!

Edited by DeathScytheHellEW, 26 October 2003 - 01:33 PM.

[wildwobby]

ok whats the point of using GPS if it does everthing for you?

[turboproper]

I just have to say i'm an "old fashion" and i still prefer to  fly with the VOR over the GPS, there is something about the way our pilots used to Fly before the GPS that still amaze me. Even Saint Exupery had helpers on the ground lighting fires at night to show him the way... That's an extreme, i know, but the Vor is way more exiting because you have to make the whole navigation, the GPS makes everything for you.

Great job with the VOR Tutorial!!

Edited by turboproper, 21 December 2003 - 08:54 PM.

[pepe]

Sure GPS is a great modern stuff for flying doing nothing, like electric choppers do what cookers like the most while cooking, cutting that incredible one like the other onion slices. If real cookers still using sharp lovely knifes, real pilots will still using lovely VOR's. Because they love to fly and working with them over the fly IS AS REAL AS IT IS!!!  

[number6]

VOR? VOR?
don't talk to me about vor. i cant make head nor tale of what that Rod Machado is talking about. yer know the guy, him from flight sim that thinks im a crap pilot. oh, you wasnt ment to know that bit.
anyway. he talks a foreign language to me. i have to keep reading what he has written time and time again. thwn when i get into the cessna i forget all i have read. he keeps stopping the lessons cause i don't follow his instuctions.
          

[Chief Wiggum]

I have a doubt with VOR

I'm in a 360° course. I may set OBS to 360? And if I turn to 90°? I continue with the OBS in 360° or move it to 90°?

NAV/GPS switch should be set to NAV or GPS?

   VOR1 is ILD and VOR2 is VOR??    

Sorry for all these doubts, hope you don't get mad  

Edited by Chief Wiggum, 16 January 2004 - 01:59 PM.

[pilot17]

great tutorial for learning VOR!

great work!  

[Captain R]

number6, on Dec 30 2003, 02:26 PM, said:

VOR? VOR?
don't talk to me about vor. i cant make head nor tale of what that Rod Machado is talking about. yer know the guy, him from flight sim that thinks im a crap pilot. oh, you wasnt ment to know that bit.
anyway. he talks a foreign language to me. i have to keep reading what he has written time and time again. thwn when i get into the cessna i forget all i have read. he keeps stopping the lessons cause i don't follow his instuctions.
          

yup I know what you mean !!

[ozzys cat]

Nope, I couldn't work it out either. That Rod bloke had me going around in circles   But yesterday, half an hour with a 'real' instructor in a C152 and VOR makes perfect sense!!

I never realised that you could use it to get a fix if you are lost.....its so simple. As long as you have a rough idea of where you are (say within 50 miles) and have two VOR stations in range, you can use VOR to identify your position.

You will need a map showing the location of the VOR stations. Simply locate and tune to VOR station number 1. Now rotate the OBS until the line centres itself and read of the heading on the gauge (ie, 090) so that means you are on the 090 radial from that VOR station. Now draw that line on the map, the line should run on 090 radial east of the station.

Now re-tune to the 2nd VOR and repeat the above process. Again draw the line on the map and you should see that the two drawn lines cross each other......and that is your position!! Not as deadly accurate as GPS but good enough to give you a fix where you can see where you are from visual reference points. Just make sure you don't get your 'To' and 'from' flags mixed up and rember that the gauge will centre on not just 090 but also 270 so you need to be aware of which side of the VOR station you are, should be fairly obvious as your lines will go off in completely the wrong direction.

Hope that makes some sort of sense