VOR question

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GauzeGuy

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GauzeGuy
I did my instrument written yesterday, didn't go that badly although not quite as well as I would have liked.

One thing that I was rather disturbed by is that my understanding of VOR navigation apparently isn't quite as good as I thought. I understand the basic principle of having the OBS match the heading whether TO or FROM to avoid reverse sensing. The questions that got me though involved finding the reciprocal (TO indication) then centering the CDI. Obviously, what got me is that I would add rather than subtract, or some variation on that.

Are there any good ways to remember when to do what? Or is this a case where it's just a confusing FAA test question that has little application in the "real world?"
 
Add 180 (or substract it makes no difference) or you can just read the obs setting on the mark at the bottom of the indicator rather than the top.

Of course I have an HSI, so it's less of a problem :)
 
Heading has nothing to do with this. All that matters is location and course selection.

The shortcut to this is if you are interested in knowing what radial you're on, twist for centered and TO, and the radial is at the top. If you want to fly a given radial OUTbound FROM a station, put the radial at the TOP of the CDI, and then fly that course. If you want to fly a given radial INbound TO a station, put the radial at the BOTTOM of the CDI and then fly the course at the TOP.
 
Go fly them more. I struggled a lot with VOR navigation until I flew them a lot post PPL. Take a local trip using only airways, it'll help a lot.
 
I don't think I'm explaining my concern very well. I know how to fly to and from a VOR and how to avoid reverse sensing.

The specific issue I ran across were with questions like "Which OBS selection on the No. 2 NAV would center the CDI and change the TO/FROM indication to a TO?" I can figure out the number of degrees the OBS would need to be changed, however I'm adding when I should be subtracting, etc.
 
GauzeGuy said:
I don't think I'm explaining my concern very well. I know how to fly to and from a VOR and how to avoid reverse sensing.

The specific issue I ran across were with questions like "Which OBS selection on the No. 2 NAV would center the CDI and change the TO/FROM indication to a TO?" I can figure out the number of degrees the OBS would need to be changed, however I'm adding when I should be subtracting, etc.
Click to expand...

Maybe this will help...

Adding degrees you turn right
Subtract is a left turn
 
GauzeGuy said:
I don't think I'm explaining my concern very well. I know how to fly to and from a VOR and how to avoid reverse sensing.

The specific issue I ran across were with questions like "Which OBS selection on the No. 2 NAV would center the CDI and change the TO/FROM indication to a TO?" I can figure out the number of degrees the OBS would need to be changed, however I'm adding when I should be subtracting, etc.
Click to expand...

Think in terms of absolute courses, rather than relative bearings, and it's a lot simpler.

E.g., you want a course of 230 deg TO. Turn the OBS so that 230 is at the top of the CDI. If you want a course of 230 deg FROM, use the bottom of the CDI instead. No addition nor subtraction there.
 
MAKG1 said:
Think in terms of absolute courses, rather than relative bearings, and it's a lot simpler.

E.g., you want a course of 230 deg TO. Turn the OBS so that 230 is at the top of the CDI. If you want a course of 230 deg FROM, use the bottom of the CDI instead. No addition nor subtraction there.
Click to expand...

Yes, that's what I would normally do. Again, to reiterate what I mentioned before, this was a specific Inst. Airplane Knowledge test question that I was trying to better understand. It is phrased in such a way where the importance of that relative bearing is important. Otherwise normally, yes I'd agree that one should set the OBS accordingly and fly towards it -- simple enough.

At this point, I think I'm just a bit too worried about test world and should just focus on the real world application of VOR nav since I'm through with the knowledge test.

Thanks to all for your help! :yes:
 
GauzeGuy said:
I don't think I'm explaining my concern very well. I know how to fly to and from a VOR and how to avoid reverse sensing.

The specific issue I ran across were with questions like "Which OBS selection on the No. 2 NAV would center the CDI and change the TO/FROM indication to a TO?" I can figure out the number of degrees the OBS would need to be changed, however I'm adding when I should be subtracting, etc.
Click to expand...
OK -- the figure shows you the needle somewhat off center, with a FROM indication. Let's say for argument the OBS is set to 330, with a FROM, and two dots of deflection to the left side of the CDI. That means you're two dots off the 330 radial (since radials are FROM) and two dots is four degrees, so you're on either the 326 or 334 radial. Clearly, you are getting this far. Now, which one is it?

The needle is pointing to the left side of the CDI, and if you look at the CDI as cardinal directions rather than left/right, you see the needle is on the west side of the center (where, in effect, you are). That means the 330 radial is 4 degrees west of you, so you are 4 degrees east of the 330 radial. The radial four degrees to the east side of 330 is 334, so you are on the 334 radial. Now, if you twist the CDI to put the radial you're on (334) at the BOTTOM of the CDI, you'll get centered and TO. So, look at the CDI and see what's directly oppoisite 154, and you'll see it's 154.

And this is a whole lot easier to explain with a real CDI in front of you as well as being able to apply better in practice.
 
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Are you studying for the IFR written, or trying to understand VOR in flight?
 
ja_user said:
Are you studying for the IFR written, or trying to understand VOR in flight?
Click to expand...

Took the written yesterday, passed it. Just making sure I understand what I got wrong out of the test.
 
Hopefully I'm understanding you correctly. You're looking for a quick reciprocal bearing/radial math trick right?

These are the ones I use:
The Trick Version 1:
Add 200, then subtract 20:
230 + 200 = 430
430 + 20 = 450
You might have noticed that a course of 450º does not make a whole lot of sense (unless you’re an engineer). Well, lets try again shall we?

The Trick Version 2:
Subtract 200, then add 20:
230 – 200 = 30
30 + 20 = 50


I might be wrong about what your concern is, but here are 2 great references for reciprocals, and VOR navigation tricks:

Reciprocals:
http://selair.selkirk.ca/Training/misc/math/reciprocals.html

VOR Nav:
http://m0a.com/31dayspc/day-28

Also, a great training app that I used, is called PilotsCafe Nav Trainer Basic. Available on App store and Android.
Link: http://www.pilotscafe.com/products/navtrainer.html
Awesome little free app that lets you move the CDI, OBS, VOR loc, and plane location around to practice.


I hope that helps, and I know how frustrating all the nav stuff can be, so congratulations on passing your written!!!
 
Ron Levy said:
OK -- the figure shows you the needle somewhat off center, with a FROM indication. Let's say for argument the OBS is set to 330, with a FROM, and two dots of deflection to the left side of the CDI. That means you're two dots off the 330 radial (since radials are FROM) and two dots is four degrees, so you're on either the 326 or 334 radial. Clearly, you are getting this far. Now, which one is it?

The needle is pointing to the left side of the CDI, and if you look at the CDI as cardinal directions rather than left/right, you see the needle is on the west side of the center (where, in effect, you are). That means the 330 radial is 4 degrees west of you, so you are 4 degrees east of the 330 radial. The radial four degrees to the east side of 330 is 334, so you are on the 334 radial. Now, if you twist the CDI to put the radial you're on (334) at the BOTTOM of the CDI, you'll get centered and TO. So, look at the CDI and see what's directly oppoisite 154, and you'll see it's 154.

And this is a whole lot easier to explain with a real CDI in front of you as well as being able to apply better in practice.
Click to expand...

Sir, you just taught me something new! Great! I never thought to use cardinal direction instead of left/right for more precise solutions to course location. Thanks
 
Archammer said:
Sir, you just taught me something new! Great! I never thought to use cardinal direction instead of left/right for more precise solutions to course location. Thanks
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That concept is even more important in flight than it is on the written. The CDI only tells you what heading to fly, not which way to turn. Then, the heading indicator ("DG") tells you which way to turn to get to that heading. We beat that issue to death on Day 3 of PIC's 10-day instrument course, and we do not advance to Day 4 in the syllabus until the trainee has that squarely understood and incorporated in their thinking for VOR orientation, interception, and tracking. However, once you understand and internalize that concept, it becomes far easier to accurately perform VOR orientation/interception/tracking, procedure turns, holding patterns, and instrument procedures.
 
Ron Levy said:
That concept is even more important in flight than it is on the written. The CDI only tells you what heading to fly, not which way to turn. Then, the heading indicator ("DG") tells you which way to turn to get to that heading. We beat that issue to death on Day 3 of PIC's 10-day instrument course, and we do not advance to Day 4 in the syllabus until the trainee has that squarely understood and incorporated in their thinking for VOR orientation, interception, and tracking. However, once you understand and internalize that concept, it becomes far easier to accurately perform VOR orientation/interception/tracking, procedure turns, holding patterns, and instrument procedures.
Click to expand...

Well you just made my task management much easier with that little gem! Thank you very much
 
Archammer said:
Well you just made my task management much easier with that little gem! Thank you very much
Click to expand...
I'll be in the Austin this weekend doing a finish-up with a pilot in Giddings. If you want to meet to talk about PIC training, let me know.
 
Ron Levy said:
I'll be in the Austin this weekend doing a finish-up with a pilot in Giddings. If you want to meet to talk about PIC training, let me know.
Click to expand...

Sounds good to me. I'll be at GTU on Saturday afternoon, and then down at 1T8 for the Spaghetti Fly in on Sunday. I'll PM you my phone number, give me a call if you get some free time, and we'll try and meet up!

Thanks.
 
I bought a $1 app on ipad that showed what the VOR displays relative to your plane location. Used it a few times just to try it out.
 
Ron Levy said:
The shortcut to this is if you are interested in knowing what radial you're on, twist for centered and TO, and the radial is at the top.
Click to expand...

Wait, what? Which radial you're on is always a FROM. I think you got the above twisted around - Twist for centered and FROM and the radial you're on is at the top, or twist for centered and TO and the radial you're on is at the bottom.

I know you know this, and your other messages in this thread are correct, but I think you got one too many twists and turns and FROMs and TOs typed too fast here. ;)
 
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