help with radials

[Ryan]

Im 10 lessons into my instrument and loving it. But I need a little help with radials. I understand how they work, my only confusion comes in when my instructor says to fly a certain radial and sometimes it seems I need to dial the heading he states to the top of the vor and other times I need to dial in the reciprical of the heading he states. I hope Im making myself clear on this confusion. I realize it has something to do with if your flying outbound on the radial or inbound.

Thanks for the help guys

Ryan

 

[Andy Neill]

Whether you put the desired radial at the top or the bottom has no effect on the needle being centered when you are on the radial. What does make a difference is whether the needle will be directional for the heading you are flying or not.

For instance, if you were to fly the 180 radial (south of the station) inbound on a course of 360 and put 180 at the top of the CDI, you would find that the needle would be non-directional. That is, if it indicated a deviation to the left, you would turn right to intercept the radial or if indicating to the right, you would turn left to intercept the radial.

On the other hand, if you put 360 at the top (and 180 at the bottom), you would find that the needle was directional. If indicating off to the right, you would turn right to intercept.

A phrase I used when learning about radial intercepts and tracking is to say "If I were to fly heading X, the needle will tell me what direction the desired course is from my position" In the xase of the example given above, I would say, "If I were to fly course 360 (as is necessary to track the 180 inbound), the needle will tell me what direction the 360 course is from my position." X is what you put at the top of the CDI to get directional information for the course you want to fly.

 

[Mr. Cole]

To avoid the reverse sensing Andy discussed, your OBS should be set to approximately the course you're flying. Radials are defined away from a station. So to use Andy's example, if you're south of the station flying on a heading of 360 towards the VOR, you are on the 180 radial on a heading of 360. However, as soon as you cross over the VOR, your heading is still 360, but you're flying From the VOR on the 360 radial. In short, whenever you're flying to a VOR, your heading is the reciprical of the radial you're on. When flying away from the VOR, your course and radial are the same.

Dave

 

[bigD]

This is the sort of thing a PC flight sim is great for. If you have access to one, and once you get your head around what you need to do, just practice flying radials to and from various VOR's. After awhile it just becomes second nature.

 

[midlifeflyer]

This is the sort of thing a PC flight sim is great for. If you have access to one, and once you get your head around what you need to do, just practice flying radials to and from various VOR's. After awhile it just becomes second nature.

...or try the excellent Java-based navigational trainers at http://roye.home.netcom.com/flighttraining/ and http://www.visi.com/~mim/nav/

 

[bigD]

Oooooh! Those are pretty cool. I never knew about them.

 

[midlifeflyer]

Oooooh! Those are pretty cool. I never knew about them.

What's kinda nice is that they can be downloaded and run locally.

 

[Tweetdrvr]

You have to remember that these exercises are to prepare you to fly and comply with ATC instructions.

Controllers will often tell you to fly heading xxx and track the ABC radial either inbound or outbound. This is what determines what you put in the top of the OBS or HSI course window, if you have one.

You have to be able to visualize your position in relation to the station so that you can question if required the validity of this intruction and more importantly that you can comply with the instruction and do it safely.

If you are southeast of the VOR, and the controller tells you to fly heading 310 to intercept the 090 radial and track it inbound, then you need 270 in the OBS, and you should have a "TO" indication, if not, then you have either an invalid/impossible set of instructions or you misheard/misunderstood the controller.

Fly Safe!

 

[Mr. Cole]

Good points Tweet. Use the indicator flags to determine whether the OBS setting is taking you to or from the desired place. Dialing 90 into the OBS would give a FROM indicator given that position relative to the VOR, because based on that position, flying 90 degrees takes you away from the VOR. However, since you are East of the station, ableit Southeast, 270 takes you in the direction of the station. In fact, the way that I tend to think of the TO/FROM flag and the OBS is that the heading on the OBS combined with the flag tells you whether that heading will take you away from or to the station. A radial and its recip are just the same line, but the names/numbers change as you pass through the VOR.

If the plane had been to the Southwest of the VOR in Tweet's example, 270 in the OBS would have given a FROM indication on the VOR instead of a TO indication, and flying a heading of 310 would lead to intercepting the 270 radial OUTBOUND. Only thing that changed is what side of the VOR you happen to be on with respect to that 90-270 line.

Dave

 

[KickSave]

Im 10 lessons into my instrument and loving it. But I need a little help with radials. I understand how they work, my only confusion comes in when my instructor says to fly a certain radial and sometimes it seems I need to dial the heading he states to the top of the vor and other times I need to dial in the reciprical of the heading he states. I hope Im making myself clear on this confusion. I realize it has something to do with if your flying outbound on the radial or inbound.

Thanks for the help guys

Ryan

It doesn't matter whether you are heading inbound or outbound, your heading should correspond with the radial you have tuned in, if you want to track that radial.

If you are south of the VOR station and want to head south (outbound, i.e 180 hdg), then the top of your OBS should have 180 tuned in. If you are south of the VOR and want to head north/inbound, you would tune in 360 in the OBS.

If you are east of the station and want to head west (inbound, i.e. 270 hdg), the top of your OBS should have a west setting (270 radial)

The confusion comes when you are ON a radial and flying TO a station, but you should still be tuned (top of the OBS) to the reciprical so that your heading matches. Your position might be ON the 090 radial, but you are flying heading 270 and tuned to the 270 on top of the OBS. The Heading you are on while tracking a radial should match the radial tuned at the top of the OBS, regardless of if you are flying inbound or outbound. Otherwise you will get reverse sensing and end up lost and confused.