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Tacan Offset in F-18


airea

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Hello guys, I am sure this was discussed before but I was not able to find via the search function (or more correctly, I found hundreds of treads and I dont know which includes what amount of info on this issue). This is quite a newbee question probably: I acquire the Tacan frequency on the HSI and measure the exact course of the runway from F10 screen. I set up my HSI with the measured course line and navigate for landing. But everytime, I end up a few miles to the left or right to the runway. I believe F-18 operates with true compass headings with no need to correct for the declination. I know that Tacan stations are generally a few hundred feet away from the landing strip but the offsett I encounter is generally 2-3 miles.

 

Thanks for the help...

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Good question. Was wondering about this as well.

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Be default, the F/A-18C uses magnetic headings, not true. Try again but correct for Variation this time, see if it gives a better outcome.

 

It will be much more helpful to include a specific example if you still have problems, because it's hard to generalize this stuff (where is the runway, where is the TACAN, what course was chosen, which direction is the error?).

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Despite magnetic heading versus true, wouldn't TACAN focus on bearing from the transmitter itself? Ultimately, we're interested in the bearing information transmitted by a radio antenna, not the earth itself.

 

And, in the scheme of things and beyond the scope of the game, the magnetic compass is going to become an increasingly useless instrument in the coming future. The various world navies, who have a vested interest in magnetic compass accuracy, have been tracking a pole shift for the better part of a century and all indications is that it's rapidly increasing to the point a steady magnetic pole might not last the century and, honestly, even within in my lifetime (I'm 41) hasn't been steady.

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Ultimately, we're interested in the bearing information transmitted by a radio antenna, not the earth itself.
True, but if he's using the earth to measure the desired radial, he's going to introduce an error.

And, in the scheme of things and beyond the scope of the game, the magnetic compass is going to become an increasingly useless instrument in the coming future. The various world navies, who have a vested interest in magnetic compass accuracy, have been tracking a pole shift for the better part of a century and all indications is that it's rapidly increasing to the point a steady magnetic pole might not last the century and, honestly, even within in my lifetime (I'm 41) hasn't been steady.

Any source for this? Magnetic poles are constantly moving. You can even measure the drift of continents with shifts of the earth's magnetic field.

https://en.wikipedia.org/wiki/Paleomagnetism

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True, but if he's using the earth to measure the desired radial, he's going to introduce an error.

 

Any source for this? Magnetic poles are constantly moving. You can even measure the drift of continents with shifts of the earth's magnetic field.

https://en.wikipedia.org/wiki/Paleomagnetism

 

Look up a map of the drift of the North Pole over the course of time it's been tracked. In the last 50 years it's moved dramatically from solidly in Canada to very close to the actual pole. There's been a growing anomaly in the South Pacific for at least a century tracked by both geologists and astronomers (in the latter case, it's due to a weakening of the Van Allen belts). But besides that, you'd have to pick through tons of random geology news articles that talk about signs, though an actual total reversal might be a while off, but there's evidence in the past it's happened within a human lifetime and could cause enough weakening in the next century to cause a navigation problem.

 

https://arstechnica.com/science/2014/10/the-north-pole-moved-to-the-north-pole-in-a-single-human-lifetime/

 

https://www.forbes.com/sites/trevornace/2019/02/05/earths-magnetic-north-pole-has-officially-moved/#52d129fc6862

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I should have clarified,

 

I was looking for sources for the claim "the magnetic compass is going to become an increasingly useless instrument in the coming future."

 

Interesting enough this is either the current situation, or was recently the situation regarding large magnetic anomalies in Russian territory. The Tu-154 (at least as simulated) is heavily reliant on gyrocompass navigation, and the system is replicated in the Mi-8, Ka-50(somewhat), and L-39 in DCS.

 

But still, having a direction sensing instrument that requires no source of power to function is incredibly useful, and I'm highly skeptical that any navy would characterize the humble device as "increasingly useless." Tracking and publishing the movement and position of magentic north has been going on for a very long time, and I don't see it becoming any less important in the foreseeable future.


Edited by randomTOTEN
I don't know why this forum has such a problem with formatting posts.
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For the near future there's merely a need to keep magnetic offset charts up to date. In the longer term all bets are off.

 

I like to read and write science fiction, so there's plenty of times where my brain is thinking 100 years in the future. One of my stories, set in 2116, makes a passing reference to the "canals of New York" to give you an idea. (Turns out, Kim Stanley Robinson had the same idea in his novel 2140.)

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It would not surprise me in the least to learn that 100 years from now every airplane, and every ship still has a magnetic compass in prominent display and good working order...

I see that as a "fighter jets don't need guns, they use missiles" kinda move. :music_whistling:

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I think in 100 years satellite-based radio navigation, advanced INS with accuracy that can't even be predicted today and digital compasses updated dynamically from a database of known offsets will be standard navigation even for civilians.

 

Let's face it, 100 years ago cloth-covered biplanes navigating by the seat of the pants were top of the line fighters. Twenty years later we had radar, radio navigation, all-metal monoplanes and the very earliest jets were on the drawing board. Twenty years after that supersonic fighters with radar targeting, nuclear air-to-air rockets and transcontinental bombers were normal. Let's not get into the advances in 1980 and 2000.

 

Trying to figure out technology in 2120? Ask a question, shake a Magic Eight-Ball and see what comes up, because that as good of an answer as the smartest research engineer will have today.

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Be default, the F/A-18C uses magnetic headings, not true. Try again but correct for Variation this time, see if it gives a better outcome.

 

It will be much more helpful to include a specific example if you still have problems, because it's hard to generalize this stuff (where is the runway, where is the TACAN, what course was chosen, which direction is the error?).

 

I have very recently started DCS:F-18 and now only going with the training missions or free flight in instant action section. In both Nevada and BlackSea maps, I had this issue in Nellis or Batumi landings. For example, in Batumi, when landing to 13 runway, I set my course setting to 126 and acquire the tacan freq of Batumi with distance info etc. But when I keep flying along the course line, I end up 1-2 miles to the left of the runway.

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The distance to Tacan station is around 10-12 miles when I acquire the Tacan signal. I follow the course line on the HSI and around 3-4 miles, I realize that the sunway is to the right by few miles. Interestingly, the course heading for Batumi is entered az 119 in the VFR landing tutorial, but the actual measurement on the runway itself shows as 126 degrees.

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119 degrees is the correct heading to fly - the kneeboard shows the runway in magnetic. F10 and the Mission Editor work in True North, hence the difference.

 

What is kneeboard? You mean the F-18 itself using magnetic heading? I measure the runway heading from F10 map with the scale on the map.

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The kneeboard is a clip-board that you would use to hold paper documents such as aircraft checklists, navigation charts, and airport information. It includes a strap and the pilot secures it to their thigh, thus it's a board at their knee = kneeboard.

There is a 2D version in DCS that is pulled up by holding down the "K" key on your keyboard, and can be toggled with RSHFT (Right Shift Key) + K. Pages are changed with the "[" and "]" keys.

 

 

The F/A-18C can display both Magnetic and True Heading. By default it uses magnetic, and this is the appropriate setting for the combat areas available. Yes you must correct for the differences in magnetic and true north when doing stuff like this.

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I mean the kneeboard using Right Shift + K.

 

 

F10 uses True North. So you will have to subtract the magnetic deviation (6-7 degrees) from the F10 measurement to give you the actual heading in the jet.

 

It depends from the map you are using

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Hello guys, I am sure this was discussed before but I was not able to find via the search function (or more correctly, I found hundreds of treads and I dont know which includes what amount of info on this issue). This is quite a newbee question probably: I acquire the Tacan frequency on the HSI and measure the exact course of the runway from F10 screen. I set up my HSI with the measured course line and navigate for landing. But everytime, I end up a few miles to the left or right to the runway. I believe F-18 operates with true compass headings with no need to correct for the declination. I know that Tacan stations are generally a few hundred feet away from the landing strip but the offsett I encounter is generally 2-3 miles.

 

Thanks for the help...

 

 

Another option is to switch the Hornet to True North

 

 

HSI > Data (upper right) > A/C(upper left) > MAG HDG (center right)

 

 

This will put a T in the HUD heading tape and I think switch all compass direction indicators to True North (except the backup compass). I haven't tried this personally for your exact case because I tend to fly visually once I get close enough to an airport TACAN (obviously this is only a good strategy in VFR conditions), but it may save you a little trouble.

 

 

You can use the same format to switch to DMS way point entry as well with LAT LON DCML button in the lower right.

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