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TChapman500

VOR Navigation Issues

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Here's the situation.

 

1) I create a flight plan to go from the Dallas-Ft Worth airport to the Denver International Airport for FL350 with IFR.

2) I use the VORs that are used in FS98 instead of having them auto-assigned by FSX.

3) I use the headings listed in the flight plan and tune the radios to the correct VOR frequencies, navigating by what the results are.

4) The headings listed in the flight plans take me almost 10 degrees off course (according to the GPS) to the left or right seemingly in random order..

5) ATC does not like what I'm doing and they take me off of my intended course.

 

What happened?! How is it that I end up off course by 10 degrees when using the VORs to navigate when the flight plan tells me to fly those headings. EG: On one leg of the flight, the flight plan says to fly a heading of 317 towards the VOR. As it turns out, it's 309 that puts me on course. 309 is not a heading that is listed anywhere in the flight plan. There is a 310 on the final leg of the flight to get me lined up with the runway, but the headings listed are:

 

NUM - VOR ID - FREQ - HEADING IN/OUT

1) SPS - 112.7 - 305/317

2) LAA - 116.9 - 317/303

3) HGO - 112.1 - 303/310

4) FQF - 116.3 - 310/333

 

These headings do not give me the course that the GPS gives me. In fact, it seems that if I were to go strictly by these headings, I would have to make a large turn to one direction, then the other, just to center the HSI. Is there a better way to get the headings required so that the outbound portion of a leg from a VOR puts me directly in line with the inbound portion of the next VOR? What FSX gave me does not line up the VORs correctly.

 

According to the FS98 help for the flight, the headings are as followed:

 

Num - VOR ID - HDG IN/OUT

1) SPS - 320/313

2) LAA - 308/298

3) HGO - 298/300 (just before FQF)

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If you fly inbound to a VOR and this VOR is also a GPS waypoint you will be right on the spot.

 

But remember - the further away you are from the VOR the bigger the error (in miles) may be for 1 degree plus or minus. The flight plan only gives you the next whole number. Let's say the GPS path is actually at 278.3092 degrees and the plan says 278 degrees!

 

This could be approx. 11 miles at a 80 miles distance.

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Magnetic declination or variation, http://en.wikipedia.org/wiki/Magnetic_declination , and cross wind correction can both contribute to what you are seeing. I don't know which plane you are flying but, in most cases, you can press and momentarily hold the "d" key to adjust your HSI for magnetic variation. If you are flying a G1000 or some of the Garmin GPS's, you can see the cross wing indicator on the screen. ti's explanation and either or both of these can give you the kinds of errors you are seeing.


Joe Brown

gold_mustang1500.jpg

 

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Its a tricky subject, the VORs are aligned to magnetic north, are you using magnetic north? The HSI should be aligned to magnetic north though, It could just be that its all out of date and out of sync, i.e. the VORs are pointing to what was magnetic north 7 years ago but your using a flight planning software with todays variation. I have never noticed it as a problem in the sim with the VORs though.

 

There is often a difference between the runway headings and what modern plates will show.

 

What are you flying? a modern 737 actually automatically uses a combination of INS (and I think GPS) for positioning and only cross references with the VORs to chek for inertial drif, so use the FMC for navigation.

 

If you are flying a GA type such as a Baron then you probably would be daisy chaining VORs together into a route, then your a bit stuffed.

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Boeing 737-800. I compensated for wind direction. I'm talking about the course heading, not aircraft heading for the VORs.

 

Outbound on SPS, the HSI told me I was on course while the GPS told me I was 10nm to the right of my course.

Inbound on LAA, the HSI told me I was on course (once I had turned almost perpendicular to the course to intercept and back to the course heading) while the GPS told me I was 20nm to the left of my course..

For the rest of the flight, I was only slightly off course according to the GPS, while the HSI told me that I was on course.

 

In other words, even though the HSI told me I was on course, when I switched to the inbound VOR frequency, I had to turn almost perpendicular to the course to intercept it every time just so that the HSI told me that I was back on course. The GPS however, said that I was off course almost the entire flight.

 

Is there any way to save the course that the plane took so that I can show you what is going on?

 

[EDIT]

I'm using the headings that the default FSX flight planner has told me to use.

[/EDIT]

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Too late for that, However, to give you a picture of what happened, the map shows that I'm slowly drifting off course when I'm outbound, when I switch to the next inbound VOR, it shows me cutting across the course, then slowly drifting towards it. It appears to be about a 5-degree difference between the course of the map, and the course of the HSI. For the first leg of the trip, which was the longest, I drifted ~10nm to the right of the course, then shot across it to ~22nm to the left of the course, then drifted back onto the course, landing on course it right at the VOR. For the rest of the flight, the same thing happened, but the distances were much shorter and I didn't drift towards or away from the course as much.

 

I'll send you the flight plan I used. Navigating by VOR without ATC. ATC will go by the course on the map, not the VORs. You must use the VORs to get the full extent of my problem. The ILS I used at the destination airport is 110.15, HDG 350. Descend to 7,500 before reaching the FQF VOR. Start descent outbound on HGO VOR or just before (CAUTION: Requires 2,000 fpm+ descent rate). Make sure the flight plan is loaded so that you can see where the aircraft went relative to the course displayed on the map. Cruise altitude is 35,000 feet. Again, do not use ATC. Use only the VOR radios and HSI to the frequencies and headings listed below, and look at the results.

 

SPS - 112.70 - In 305 - Out 317

LAA - 116.90 - In 317 - Out 303

HGO - 112.10 - In 303 - Out 310

FQF - 116.30 - In 310 - Out (Tune ILS 110.15 - HDG 350)

 

KDFW_to_KDEN_FL350.zip

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I will try and take a look after work but I am going to be quite busy trying to modify my setup to try out DX10 mode again.

 

Hopefully someone else will pop by with the solution shortly!

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Guest

I'm using the headings that the default FSX flight planner has told me to use.

 

Maybe you shouldn't do that but simply tune into the VOR and fly directly to it...? So tune in, turn until the CDI is centered and TO is activated and then keep the CDI centered (which may require a slightly different heading if there is wind). Seems to me that would solve the problem (although I still am not entirely sure what's going wrong where :wink: )

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Like I said, I compensated for wind. The aircraft heading does deviate a couple of degrees from the course heading when there is a wind, but the course heading itself deviates by about 5 degrees to the right of the course that's on the map.

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2) I use the VORs that are used in FS98 instead of having them auto-assigned by FSX.

 

???


Gerry Howard

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Are you using the default FSX VORs and, if not, which VORs are you actually using?


Gerry Howard

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Again, don't use the flightplans headings but use the CDI to get to the VOR. Headings created by planners aren't the actual radials you need to fly to get to a VOR. Some time ago I tried to figure out radials that would lead my to an airport (using triangulation) using Plan-G but the headings the planner gave me never were the actual radials I had to fly. It just doesn't work like that, apparently. It all has to do with magnetic north and how the deviation changes when you move around.

 

When you navigate using VOR you have to actually USE them and not rely on headings calculated in a planner. Use the VOR the way it is intended and not only as some kind of landmark to fly towards using calculated heading without actually using the radials of the VOR! It doesn't send out signals for nothing! :wink: It's a waste if you don't use the information the VOR is presenting you!

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