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And another VOR question :). Arcs around VOR's (Read 808 times)
May 17th, 2004 at 6:20pm

GeneticA   Offline
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Hi all,

Here is another VOR question.

For some approaches I am required to track a VOR station's 10nm arc.

For this, I adjust the NAV2 radio to the VOR, then try to adjust myself such that the needle will point at a 90 degree angle to my heading and at the same time try to keep my distance to the VOR at 10nm.

This is, of course, not a comfortable way to track it, but it is what I can imagine to do.

Is there a better way? What is the proper way to track a circle around a VOR?

Thanks in advance.
 

I'm trying to land&&This aeroplane of ours gracefully&&But it seems just destined to crash&&(Björk - So Broken)
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Reply #1 - May 17th, 2004 at 7:56pm

Nexus   Offline
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Quote:
Hi all,

Here is another VOR question.

For some approaches I am required to track a VOR station's 10nm arc.

For this, I adjust the NAV2 radio to the VOR, then try to adjust myself such that the needle will point at a 90 degree angle to my heading and at the same time try to keep my distance to the VOR at 10nm.

This is, of course, not a comfortable way to track it, but it is what I can imagine to do.

Is there a better way? What is the proper way to track a circle around a VOR?

Thanks in advance.


Executing a DME ARC approach requires lots of practice. But it will help if you do some calculations before, so you have an overview of the procedure. But the way you described it is how pilots actually performs DME ARCs manually (in GA aircrafts)

I'm not sure if this will help you to FLY it better, but hopefully you'll be able to understand it better Smiley

What we want to find out is basicly:

A) How many degrees each mile travelled on the arc will cross (from the VOR reference)
B) The distance we're flying on the arc
C) Our Total AirSpeed (TAS), so we can calculate how long we will fly the arc.

And here's the answers:

A) Divide the radius of the arc by 60
So if the Radius was 12, each mile travelled on the arc would mean a 5 degree (60/12=5) deviation from the VOR

B) Now divide the answer above with the number of degrees to travel on the arc ie: 102 degrees/5=20.4nm)
So the distance we travel on the arc is 20.4 miles.

C) the TAS calculation. Add one half of the flightlevel to your IAS. Let's pretend you'll enter the arc at FL100 at 190KIAS = 190+50=240kts TAS or 4nm/min

Now by using the data above, we can determine the distance to travel, how fast we're flying and how long we'll stay on the arc

Distance to travel = 20.4nm
TAS = 4nm/min
Time on the arc= 20.4/4 = 5.1 minutes

Lead-in turn is marked on the approach chart, so I will leave that calculation out for now. Message might become even more dull than it already is... Roll Eyes
 
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Reply #2 - May 18th, 2004 at 4:22am

GeneticA   Offline
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Thanks for the answer.  Smiley

Quote:
But the way you described it is how pilots actually performs DME ARCs manually (in GA aircrafts)

Hmm, I think I was a pilot in my previous life  Grin  Tongue

Then, how it is done with bigger aircraft? (And what does "GA" stands for?)

(Well, not an airliner pilot  Grin)
 

I'm trying to land&&This aeroplane of ours gracefully&&But it seems just destined to crash&&(Björk - So Broken)
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Reply #3 - May 18th, 2004 at 8:59pm

Nexus   Offline
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Quote:
...Then, how it is done with bigger aircraft? (And what does "GA" stands for?)

(Well, not an airliner pilot  Grin)


In the Boeings (or whatever large airliner) this procedure is MUCH easier..obviously due to the advanced equipment found on these aircrafts. Whenever I have to fly a DME ARC, I simply go to the flight management computers FIX page, and type in the VOR station. I can now select to have a radius of choice displayed around it as a green dottet circle. makes a great visual reference when flying the arc manually.

If I was about to fly it by using autopilot I will type in place-bearing-distance waypoints like: JNC275/12

JNC is the VOR...275 is the bearing and 12 is the distance. If you create multiple waypoints like this and only change the bearing you'll end up with  a couple of waypoints on the arc so the autopilot can fly it Smiley

here's a picture of one of my flights:
...

 
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Reply #4 - May 19th, 2004 at 8:56am

GeneticA   Offline
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You have a different cockpit there. Shocked (PMDG I guess). I am 100% sure that this is impossible with the default aircraft.

Thanks for the help.
 

I'm trying to land&&This aeroplane of ours gracefully&&But it seems just destined to crash&&(Björk - So Broken)
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Reply #5 - May 19th, 2004 at 3:33pm

Dan   Offline
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GA = General Aviation
 
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Reply #6 - Aug 31st, 2004 at 11:20pm

Boss_BlueAngels   Offline
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Good-Lord that's a lot of calculations! lol  I just figure in 15 minutes for each approach, and i've been within +/- 4 minutes on all XC flights. lol

Just do it the way they train instrument pilots... tune 10, turn 10.  As you track toward the with Nav 1, set your Nav 2 up so you have the needle centered with a (well, it's easier to start this way... I ARC with a FROM now..) TO... now, if your initial turn onto the arc is to the right, look at the 90 degree heading on the right side of the OBS... so, if you're naving TO the station on the 180 degree radial, and you're going to arc up to the 090 radial (Inbound course 270), you would have NAV 1 centered on 360 with a TO, and Nav 2 set up with a 360 TO also... Since you're already going through the 180 radial, you will want to rotate the OBS on NAV 2 10 degrees to 250, so instead of turning to 090, you will turn to 080.  (And to determine your lead off, it's half your TAS divided by 10... so if you're approaching at 100 kts, you would lead off your turn onto the arc by 0.5 nm.) OK, now you make your right hand turn and you have 350 set on top of your OBS and the needle is off to the right.  As you keep heading 080 for your NO WIND heading, the needle will swing through the center of the VOR indicator, and when this happens you "tune 10, turn 10" and rotate the OBS to 340, and then turn left also to 070, etc untill you reach your inbound course of 270 and ARC inbound.

Now, there are two ways to do this... ARCing with a TO (like I described, MUCH less brain work... you arc to the left, you turn the OBS to the left, you turn inbound to your left, inbound course is to the left on the OBS, very simple)  but a lot of people like you to ARC with a FROM.  (I think it's stupid, but people say it's easier because you know what radial you're on... guess they are unable to read upside down. lol)  And with a FROM, everything is Bss Ackwards. lol  

So there you go, the "official" description of how to do it.  Now with the wind is when it gets real fun, but as long as you remember what your NO WIND heading should be, you should be just fine keeping it within .5.  ARC's are pretty fun, the last couple day's I've done several 16 DME arcs (real easy, gives you lots of time to setup stuff) and coming back home get to do a 7 DME arc which goes by REAL fast. lol  

Oh yeah and the way I always do things in real life is set up NAV 1 to what I'm doing now, and NAV 2 to what I will be doing later... EXCEPT for when I do an ARC... I ARC with Nav 2 and have NAV 1 set up for either inbound radial, or ILS or LOC.  
 

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