azeem
Topic Author
Posts: 132
Joined: Mon Jul 03, 2000 8:17 pm

Radials

Wed Oct 04, 2000 3:00 pm

Hi there

Can anyone please provide information on radials. How to intercept them and how to set courses etc.

Thanks
 
Guest

RE: Radials

Wed Oct 04, 2000 5:13 pm

Well once you have the VOR tuned and identified turn the knob till the numbers around it has got to the radial you would like to fly on are at the top. BE VERY CAREFUL ABOUT IF YOU ARE GOING DIRECTLY TO OR FROM THE VOR!!! From that the the needle will normally swing one way (unless you are on your radial) From there fly towards your the needle at an angle of 30 degrees. I am not an instrument pilot so this might be a little bit rough, I am sure some one will correct me if I am wrong, and please feel free too. But lets say you are wanting to fly a heading of 360 TO and the needle is to the left you should fly try and intercept it with a heading of 270. Also when you start to see it move slowly roll out to a heading of 360. If it is not off by too much then less it fine! Also be warned when you are close to the VOR the needles goes all over the place do not chase it stick to your heading.
I think I have covered everything!
Iain
 
Guest

RE: Radials

Thu Oct 05, 2000 12:33 am

Azeem,

I found this one web site that simulates an airplane flying around with 2 VOR stations. You can position the airplane and the stations in various ways and observe how the needles behave. It is a great learning tool. Check it out:
http://www.visi.com/~mim/nav/

Best regards,
Nut
 
Buff
Posts: 1066
Joined: Fri Mar 16, 2007 1:29 pm

RE: Radials

Thu Oct 05, 2000 5:40 am

Nut: GREAT site for beginners. Well done! I was going to make a post on this last night for Azeem but was too tired.

If I could add to what you and Iainhol have posted, one of the biggest difficulties beginners have with VOR/ADF navigation is visualizing where they are relative to the transmitting station, be it a VOR or an NDB. When dealing with VOR's one is dealing with "Radials" which one also has the benefit of a visual tool, i.e. the VOR display. With the ADF which tracks NDB's with a needle pointer, the exercise is quite a bit more difficult, especially with an older fixed-card ADF (do they even have those things anymore?), or worse, a drum style DG!!

Back to Radials: One of our avionics experts could give a better technical explanation, but I'll give a layman's view here on what they are, how they're created and received and how to "track" one.

What: A Radial is an aviation term (in our context) that applies to signals radiated from a VOR (VHF Omnidirectional Range). There are 360 of them, for all intents and purposes. It's easiest to visualize them by pretending the VOR transmitter is the hub of a bicycle wheel, and the 360 radials are the spokes. As the spokes leave the hub, they tend to fan out; as they move inwards on the hub, they converge. Likewise with a VOR, as you get farther FROM the VOR station, the "radial" you are "on" gets wider and wider, hence less and less accurate. Conversely, as you fly TO the VOR, the radial gets tighter and, in effect more precise flying is required to stay "on" one. I've capitalized the FROM & TO above because they are two very important terms used in VOR navigation. Radials are named for the 360 "spokes" they represent - hence the radial going straight north (magnetic) from the VOR is called the 360 degree radial; the radial emanating north east is the 045 radial; the radial to the east - 090; the radial to the southwest - 235 radial; northwest - 315 radial and so on.

How: Each VOR station radiates a couple of signals in a slightly out of phase condition. One of these signals is an omnidirectional signal going out in all directions; the other is a uni-directional signal that is rotated in direction (somebody said) 30 times a second, moving from 000 degrees to 359 degrees 30 times a second. As the moving signal reaches 000 degrees, both signals overlap and are "in-phase"; as the uni-d signal continues to 090, the two signals are then 90 degrees out of phase; at 180, 180 degrees out of phase. Then as it continues to 270, the signal is only 90 degrees out of phase decreasing to 0 at OOO. They can only be out of phase at a maximum of 180 degrees. Any more or less makes them + or - out of phase. That's why at the 270 radial, it's only 90 degrees out. Make sense? The VOR receiver in the airplane translates this phase measurement into something you can see and interpret - the VOR needle and the TO/FROM indicator - the two of three things you need to navigate. The TO/FROM indicator lets you know the orientation of the "out-of-phase" or +/- condition mentioned above.

Using the information: First thing that needs to be done is to tune and identify the transmitting station. As it's a VHF signal, it's restricted to line of site. At 6,000' of altitude, you can expect about about 90 miles of reliable range. The identification is by either morse code (published on charts) or voice identification and almost always in a three-letter format. This identification can't be stressed enough as more than once you will mis-tune and end up using the wrong signal - a recipe for disaster.

Second is to determine where you are relative to the VOR. A "radial" is ALWAYS identified on a VOR receiver as a FROM indication with the needle centred. ALWAYS a FROM indication - remember that for as long as you're in aviation. Very, VERY important if you are just learning.

If you use the site that Nut links us to above, you can move the little airplane around and then spin the associated VOR needle until it centres and gives you a FROM indication. A picture is worth a million words. When you get that indication, then you can do the same thing with the other VOR needle and notice a different FROM indication with the needle centred. If you then plot these two radials on a map, they will intersect and that is where you are on the map.

That's the first step in navigating. Know where you are starting from. And that's the basics of learning the VOR.

I'm going to stop here and wait for a response from Azeem to see if this makes sense. If it doesn't, then saying anything else will cause more confusion!!

Let me know!

Best Regards,

Buff

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