Using VORs to determine exact location

[UnAnswerd]

I just started reading about radio navigation. And no, my flight instructor hasn't done anything with the VOR equipment in the airplane yet. It seems a little confusing. I believe however, that I know enough to be able to find my exact location on a sectional chart, even if I am totally lost. All I'm asking here, is if you guys could kindly inform me if I have made any mistakes in my methods. Here's the scenario...

The only sectional chart I have onboard the airplane is for NY state. After all, that's where I initially departed. I have little choice but to assume (and hope) for the moment that I am still in NY state...

There are many VOR stations dotted across the state, so I start by trying some of them out. I tune into the Glens Falls Vortac on 110.2, and turn up the volume. I hear a Morris-code identifier, and it corresponds to the dots and dashes on the chart. I found a station!!! I then start turning the OBS dial until the course deviation needle on the VOR indicator centers. It centers on the 130-degree radial, with a "TO" ambiguity indication. I now have some valuable information. Because I have a "TO" indication on the 130-degree radial, I know for a fact that I'm somewhere west-northwest of the station. Unfortunately, that's about all I know....

Just for the Hell off it, I continue turning the OBS knob until the deviation needle centers a second time. This time is centers on the 310-degree radial with a "from" ambiguity indication. This makes sense, because it is merely the reciprocal of what had been displayed before. I draw a line outward from the 310 vortac radial across my chart. I now know that I could be anywhere along this line. I could be only with a few nautical miles of the station. I could also be well over 100 nautical miles from the station and still be receiving a signal. Unfortunately, I do not have DME equipment, so I'm still pretty lost...

I want to eliminate confusion, and positively determine which way the aircraft is pointed. So while the needle is centered on the 310 radial, I turn the aircraft to a magnetic heading of 310-degrees. Now I at least know which way I'm flying along this line, and it is directly away from the station...

I tune into another station located nearby. I tune into the Watertown Vortac on 109.8, and identify it. I again rotate the OBS knob until the needle centers. It centers on the 107-degree radial with a "from" ambiguity indication. I again draw a line outward from this radial, and note that it intersects the previously drawn line. The point of intersection is directly over the Adirondack mountains. Perhaps this explains the wilderness terrain visible out my window. In any event, I have gone from being totally lost, to pinpointing my exact location, which is 44NM northeast of my departure point KUCA. True course back home is 225 degrees. Add 13 degrees of magnetic variation, and I'll swing the airplane to 238 degrees. Estimating a groundspeed of 110KTS, I should be in the vicinity of the airport in approximately 24 minuets according to my E6B flight computer........

If you've made it this far, I thank you. Please let me know how I did!!!

 

[Kream926]

deleted previous b/c i didnt read the whole thing


but ya you got the juust of it, adirondaks ay?
we had a cottage in old forge. i used to go to school in herkimer, you by any chance near there

 

[FN FAL]

Think of a vor as a light house with strobe light on top and a rotating beacon.

This is an analogy, so bear with me...

Lets say for argument that the beacon on the lighthouse rotates 360 degrees a minute. And lets say that the stobe light flashes when the beacon is pointing due north.

So think about it for a second...the strobe flashes and you see it, so you start your time and knowing that the rotating beacon was pointed north when the strobe flashed and that it rotates 360 degrees a minute, you see the rotating beacon 45 seconds later.

You would be west of the light house. To/From what's that? FROM the light house you'd be on the 270 "radial". A bearing "to" the light house would be 90 degrees.

 

[User546]

I'm going to preface this right off with it's midnight, and I dont have a New York sectional in front of me.

But the scenario you wrote out sounds like you have a good understanding of radio navigation. What you just described is called "triangulation". Except typically how I teach it, and was taught to me, is to tune in two VOR's, and then center up each one (helps to have two VOR's in the plane), with a FROM indication.

Then plot a line (invisible or drawn) on your map using a straight edge, and the VOR compass rose displayed, and draw that line outwards from the VOR station. Now repeat the same step for the other VOR station, and where those two lines intersect is exactly where your at.

From that point you can then plot you a way home as you described.

Also a little tip: When choosing VOR's to triangulate with, it always helps best if you pick VOR's that are more horizontal to each other. Or in easier visual terms, VOR's that are displayed across from each other (at any distance) rather then up and down on the map. If that's all you got then you can certainly use them, but you'll have much better luck finding your position with horizontally placed VOR's then the other.

If you got FS2004, I recommend you do some practice triangulation using the airplane and VOR's. Theres an endless amount of ways to do it using a sim, so have fun!

Good job though, keep up the good work!

 

[FracCapt]

If you've made it this far, I thank you. Please let me know how I did!!!

Looks to me like you have a pretty good understanding of VOR's and how they work. It all looks good to me.

 

[qmaster3]

Unanswerd,

http://www.vrotate.com/VOR/vor.html

Here's one. I posted another VOR simulation site on here some time ago, but can't find it. If you google around there are of good Websites.

Cheers,
q

 

[Dr Pokenhiemer]

What you have done is called a "Resection". You find two known points (VOR's), and draw a line from those two points--where they cross is exactly where you are.

 

[nosehair]

I then start turning the OBS dial until the course deviation needle on the VOR indicator centers. It centers on the 130-degree radial, with a "TO" ambiguity indication. I now have some valuable information. Because I have a "TO" indication on the 130-degree radial, I know for a fact that I'm somewhere west-northwest of the station. Unfortunately, that's about all I know....

Just for the Hell off it, I continue turning the OBS knob until the deviation needle centers a second time. This time is centers on the 310-degree radial with a "from" ambiguity indication. This makes sense, because it is merely the reciprocal of what had been displayed before. I draw a line outward from the 310 vortac radial across my chart. I now know that I could be anywhere along this line.

Wasted effort here - Remember, you are flying the plane while you're doing all this twisting & turning. When the needle centered with a "TO" indication with 130 at the top, you only need look at the bottom of the OBS to read the reciprocal radial.

It is considered best habit to always get a "FROM" indication so that you don't get confused by randomly centering with either a "TO" or a "FROM", and then having to figure which way you're looking at it, so that is the way to center, with a "FROM", but sometimes, in bad weather, bumpy air, etc, if the needle centers on "TO", you can just look at the bottom of the OBS and get the "FROM" radial.

 

[TurboS7]

Ancient process, used just after the last great war, using land based VHF omini directional frequencies, usually only able to determine location while moving to within 1/2 nautical mile.

 

[groundpointsix]

Also a little tip: When choosing VOR's to triangulate with, it always helps best if you pick VOR's that are more horizontal to each other. Or in easier visual terms, VOR's that are displayed across from each other (at any distance) rather then up and down on the map. If that's all you got then you can certainly use them, but you'll have much better luck finding your position with horizontally placed VOR's then the other.

Could you explain the reasoning behind this? I was never taught this as a primary student and if it truly is easier I'd like to teach it to my students this way. Maybe I'm just missing something in your explanation.

 

[User546]

Could you explain the reasoning behind this? I was never taught this as a primary student and if it truly is easier I'd like to teach it to my students this way. Maybe I'm just missing something in your explanation.

Sure I'll try to explain it better here. It wasn't very easy to put into words when I originally typed it.

Lets assume your looking at a sectional map.

You would primarily want to pick VOR's that were located (for illustrative purposes) "east-west" of each other. VOR's that are located "north-south" of each other makes it harder to triangulate your exact position.

For instance, say you have North VOR, and located 100 miles south of it is South VOR. Your lost somewhere in the between the two. It will be somewhat more difficult to pinpoint your exact location by centering up with a FROM indication. Where the lines intersect together could be very difficult to pinpoint an exact point.

And I'm not saying that it wont work, or that you can't use "north-south" located VOR's, but you'll have much better results with the "east-west" VOR setup.

Am I still talking greek?? If I had a sectional I could show you in a second what I mean!

 

[VNugget]

You're trying to say that if you're between the two VORs, you won't get a good position because the radials will be laying over each other and the "intersection" will be the whole line(s). But that will hold true for both North/South and East/West.

What you want is VORs positioned so the radidals intersect, ideally, at a 90 degree angle, so the intersection will be definite.

 

[qmaster3]

You're trying to say that if you're between the two VORs, you won't get a good position because the radials will be laying over each other and the "intersection" will be the whole line(s). But that will hold true fo both North/South and East/West.

What you want is VORs positioned so the radidals intersect, ideally, at a 90 degree angle, so the intersection will be definite.

YES in marine or aviation Navigation. Another benefit, the more perpendicular the Navaids are the longer you can use them to get your fix.

 

[A Squared]

Could you explain the reasoning behind this? I was never taught this as a primary student and if it truly is easier I'd like to teach it to my students this way. Maybe I'm just missing something in your explanation.

It doesn't make sense to you because... well, it doesn't make sense. There is nothing magical about VOR's which are east-west of each other as opposed to VOR's which are North-south of each other. It is just pure nonsense.

As far as the accuracy of the position you determine, the very best solution for your position will come from 2 VOR's whose radials cross your position at 90 degrees. For example; you're on the 180 radial of the ABC vor and the 270 radial of the XYZ vor. This, of course is merely the best case. You can determine your position perfectly adequately for the purpose of navigation by using radials which cross at much shallower angles. At the extreme end though, your position determination becomes ambiguous. Example: Say the XYZ and ABC vor's are exactly east-west of each other and you are right in the middle of them. You tune your VOR and find you are on the 090 radial of the ABC VOR. OK, now you tune to XYZ and find you are on the 270 radial of the XYZ Vor. But you still don't know where you are on those radials, because they are the same line, all you know is that you are on the line formed by the ABC 090 and XYZ 270. Without a crossing radial or a DME, or some other information, you don't know where you are on that line. This isn't because they are east west of each other. the same would hold true if they were north-south and you were on the 000 and 180 radials, or they were northeast-southwest of each other and you were on the 045 and 225 radials

 

[User546]

Gentleman, it's just a recommendation, it's not a "set in stone" rule!! Lets not over-analyze it too much!

And yes, you all have good rebuttals to the method.

 

[air_chompers]

Really off the topic, but does anyone know where I can get some jetpilot uniforms? (BA and Delta and mabey NWA)

 

[A Squared]

Gentleman, it's just a recommendation, it's not a "set in stone" rule!!

Ummm, it's not merely just "not set in stone", it's wrong, as in Incorrect. I hope that you will stop teaching students this. Only 2 things will come of teaching this.

1) you will confuse your students, because they will be unable to understand why this is true (because it isn't)

or.

2) They will realize that you are wrong and ignore this.

Of these, the second is the most desirable outcome. Personally, I would not want to be teaching at a level at which the best I could possibly hope for is that the student will realize I'm wrong and disregard my teachings.

 

[UnAnswerd]

If you got FS2004, I recommend you do some practice triangulation using the airplane and VOR's.

I have it, but didn't know you could do that. I will certainly try it.

Thanks for the information!

 

[UnAnswerd]

Wasted effort here - Remember, you are flying the plane while you're doing all this twisting & turning. When the needle centered with a "TO" indication with 130 at the top, you only need look at the bottom of the OBS to read the reciprocal radial.

It is considered best habit to always get a "FROM" indication so that you don't get confused by randomly centering with either a "TO" or a "FROM", and then having to figure which way you're looking at it, so that is the way to center, with a "FROM", but sometimes, in bad weather, bumpy air, etc, if the needle centers on "TO", you can just look at the bottom of the OBS and get the "FROM" radial.

I figured that, but as you said, centering a second time with a "FROM" indication seems to be the recommended procedure. I guess as long as you understand how to interpret the indications, you shouldn't get confused with a "TO" indication. Thanks bringing that up.

 

[User546]

I have to respectfully disagree with you A_Squared.

There is nothing wrong with how I teach it. It was taught to me, and it has always worked. Whether I'm not conveying my thoughts clearly enough or what, I'll stand behind it 100%. And I dont think I'm wrong in saying that so would the majority of other CFI's that have learned and teach it this way.