Nellis TACAN and ILS

[Frederf]

Desert Fox, localizer position is indeed only based on signal ratio. CDI shows position the same on the centerline and tracking center and on the centerline but rapidly moving laterally. If someone takes a photograph of a CDI centered and shows it to you, you can't tell if that airplane is stabilized on the center of the beam or if that airplane was just instantaneously centered but flying completely at right angles. But bank steering has to give different commands not just based on position but also position trend. Flying quickly across the center it doesn't give the same bank command as stable on the center. Just knowing position isn't sufficient.

 

I used to be confused about the ILS bank steering too. "How can it figure out the steering commands with just loc signal and not desired course?!" But someone instructed me that with the use of trend information it could (and does) work without knowing course. It makes sense that the system could have been designed to use course knob setting; that would have provided enough info to run everything but it wasn't.

[Zeagle]

Fred...I disagree. You always need to set the course on the HSI. However, you may be technically correct on the CDI. I don't work on them. I just used them in the air.

Edited April 9, 2021 by Zeagle

[Caldera]

Hey all,

 

Still missing the part about the "bank steer bar".  This refers to the LSB? 

 

Obviously this is not cross track error as I think this through a bit more.  That deals with the projected course line versus a fixed position, but still kind of sort of. 

 

Let me ask this then.  If the LSB only responds to bank, not direction, then why do I see the LSB line up in the very center of the ADI as I cross the center line of the localizer at a 90 degree angle with wings level?

 

Another question I have.  In the mission builder on the Nellis map there is a diagram representing the localizer at the end of runway 21L.  On the end of this diagram that is away from the runway it has the ILS frequency and another number that I had guessed was the heading of the localizer.  That number at Nellis is 22.  What or why is that?

 

Caldera

[Frederf]

The official name of the yellow vertical element on the ADI is bank steering bar. When bar is centered then current aircraft bank is equal to computed/commanded aircraft bank at least in the ILS context. The commanded bank is a computer calculation based on inputs of localizer position, trend rate, pre-v-post capture state, and has a attenuation factor (so it doesn't get too sensitive in close). DCS's implementation is simplistic in that it is a bank as a simpler function. In the real airplane you would see a command to counter bank before you reached the middle of the localizer beam. It would say "woah partner, you're flying across the beam too quickly for how far you are from the center beam, better bank the other way." The behavior of the DCS and real bar behavior is different. DCS behavior is workable but not exactly correct.

 

In the editor I see white text at N 36°23.3' W 114°51.9' as 109.10 MHz and 220°. That second number is the approach course of the localizer. Be aware that this 220° is the DCS ruler azimuth of the localizer which will not coincide with the magnetic course instruments in the A-10.

[Caldera]

Frederf,

 

OK  So that means that since number on the diagram is 220 (my bad) would indicate that the localizer center line and the runway are actually at 214?

 

This from Chucks Guide page 507.  Just what he calls them?

 

 

 

Caldera

Edited April 9, 2021 by Caldera

[Frederf]

Nevada typically has a variation of around 15 each degrees if I remember so more like 205. I would set up a sample flight right on that centerline to be sure before I trusted it in IMC though. It'll vary depending on year and even in diff parts of the map I think. Yeah, a little loose terminology is all.

[Ramsay]

10 hours ago, Caldera said:

So that means that since number on the diagram is 220 (my bad) would indicate that the localizer center line and the runway are actually at 214?

 

MagVar for the Nevada map is approx. 12° E, so the center line for Nellis RWY 21L is on approx. 208° Magnetic.

 

You can use the A-10C's CDU Position Page to read the MV for any particular date/location.

 

Edited April 9, 2021 by Ramsay
typo

[corvus5624]

13 hours ago, Zeagle said:

Fred...I disagree. You always need to set the course on the HSI. However, you may be technically correct on the CDI. I don't work on them. I just used them in the air.

 

Do you mean you have to set course in DCS (which is true), or do you mean it also works likes this in real-life? It is technically possible to provide steering direction towards the runway based on ILS alone (without setting the course). That does not mean that the A-10C does not require you to set the course, I don't know how it works in real-life.

[jaylw314]

12 hours ago, Caldera said:

Frederf,

 

OK  So that means that since number on the diagram is 220 (my bad) would indicate that the localizer center line and the runway are actually at 214?

 

This from Chucks Guide page 507.  Just what he calls them?

 

 

 

Caldera

 

 

Chuck's guide just calls them that, you could call it anything you want I suppose

 

The key is that the traditional "glideslope indicator" and "localizer deviation indicator" which show your position error are the arrow on the left and the CDI on the HSI. 

 

The yellow bars on the ADI are fancier electronic dojiggery stuff that is supposed to be a little more advanced and easier to follow than the traditional pointers.  They show some combination of your position error and your rate error.  So if you're left of centerline, but correcting to the right, the needle will start right of center.  There's a point at which the steering bar will be left of center.   That would cue you in that it's time to bank left to line up with the runway heading again.

 

Maybe an easier way to describe them is "what would the autopilot do?"  In fact, a lot of flight directors are just indicators for what the approach autopilot is doing or would do.

 

IRL, there are ILS approaches that allow you to fly to lower minimums if you have a flight director, so they are seen as being functionally superior to the traditional GS and CDI indicators

[Caldera]

Hey all,

 

Thanks for your input.

 

Caldera

[Caldera]

Ramsay,

 

How do you get to that page?

 

All I can find is:

 

 

This is CDU --> NAV --> OPTIONS

 

Caldera,

Edited April 13, 2021 by Caldera

[Tippis]

…or you go via the UFC: FUNC + HACK (POS), although that's more for if you're repeating the CDU on one of the MFDs.

Edited April 13, 2021 by Tippis

[Caldera]

Thanks,

 

Taking a closer look...

 

Caldera

[carbolicus]

I’ve recently got the A10C and am just getting into the basics of instrument flying.  Having commercial flying experience IRL I’ve noticed that the ILS, whilst functional enough, doesn’t seem to be quite realistic and I gather from this thread that it’s a DCS limitation that the course to the runway has - unrealistically - to be set in the HSI for the ILS to work.  (Whether or not this works if there is no TACAN near the airport I haven’t yet discovered.)

Whatever, here’s what I do to make the experience realistic enough to be satisfying:

First, use the ruler in the Mission Editor to measure the exact heading of the runway and convert it to magnetic.

Second, set up a man-portable TACAN beside the near end of the runway.  This will effectively provide the localiser information which DCS currently seems not to (at least, that’s how it seems to me as I see it so far!)

Now when you fly your ILS approach, if you dial in your TACAN frequency to the man-portable TACAN and set course to the exact runway magnetic heading, then the steering bars on the ADI will behave more or less exactly as the ILS deviation bars do on a conventional civilian-type VOR/ILS indicator.

To be super-realistic, stick a bit of tape over the DME information on the HSI (if only, VR makes you feel almost as if you could do this!) and use the altimeter (set to QFE of course!) to gauge your distance from the runway threshold. And do it at night, in a strong gusty crosswind, with a 300 foot cloud base, in an under-powered light twin with one engine out, and in the words of Kipling “you’ll be a man my son!”

[ASAP]

17 hours ago, carbolicus said:

I’ve recently got the A10C and am just getting into the basics of instrument flying.  Having commercial flying experience IRL I’ve noticed that the ILS, whilst functional enough, doesn’t seem to be quite realistic and I gather from this thread that it’s a DCS limitation that the course to the runway has - unrealistically - to be set in the HSI for the ILS to work.  (Whether or not this works if there is no TACAN near the airport I haven’t yet discovered.)

Whatever, here’s what I do to make the experience realistic enough to be satisfying:

First, use the ruler in the Mission Editor to measure the exact heading of the runway and convert it to magnetic.

Second, set up a man-portable TACAN beside the near end of the runway.  This will effectively provide the localiser information which DCS currently seems not to (at least, that’s how it seems to me as I see it so far!)

Now when you fly your ILS approach, if you dial in your TACAN frequency to the man-portable TACAN and set course to the exact runway magnetic heading, then the steering bars on the ADI will behave more or less exactly as the ILS deviation bars do on a conventional civilian-type VOR/ILS indicator.

To be super-realistic, stick a bit of tape over the DME information on the HSI (if only, VR makes you feel almost as if you could do this!) and use the altimeter (set to QFE of course!) to gauge your distance from the runway threshold. And do it at night, in a strong gusty crosswind, with a 300 foot cloud base, in an under-powered light twin with one engine out, and in the words of Kipling “you’ll be a man my son!”

Trolling right? I'm torn about which movie quote fits best here....

 

"Amazing, not one word of that was correct." -Luke Skwalker

or

"Nowhere in your incoherent rambeling mess, did you come even close to a correct answer. I award you no points, and may god have mercy on your soul."

-that guy from Billy Madison

 

If you're not trolling, there's a lot to unpack there. Suffice to say that the instruments work fine, they are correctly simulated, and whatever issue you are having is most likely user error, or a lack of knowledge about instrument procedures.

Also, looking back through the rest of this thread and holy cow people like to overcomplicate everything... Read the ILS approach plate and do what it says. stop trying to reinvent the approach. The approach says the inbound course is 209 (which you should spin into the HSI), and the DME is based off the TACAN of 12X. Which you should also read off the HSI...

Edited March 28 by ASAP

[carbolicus]

Hi ASAP - Definitely not a troll here, I am an ex-professional pilot honest!  However, not greatly experienced with DCS nor hi-fidelity aircraft!

It’s just that with all the aeroplanes I flew you selected the ILS frequency, and localiser and glideslope indications then appeared on the ILS display with no further action and there was certainly no need to dial in the runway heading on the VOR as well.

However, I never flew military aircraft (except for basic trainers Chipmunk, Bulldog and Slingsby) and so have no idea about how they handle ILS systems, and thanks for putting me right on the need to dial in the runway heading for the A10C.

And yes, I was wrong about the need to set up your own TACAN - just experimented and realised that with TACAN off and ILS selected, if you dial in the runway heading on the HSI you do indeed get localiser info. However, if there is no TACAN near the airport (as in some on the Caucasus map which I’ve been using), setting up a man-portable TACAN at the end of the runway does mean you can get DME.  This is useful, and in real life DMEs are often co-located with the ILS.

[ASAP]

1 hour ago, carbolicus said:

Hi ASAP - Definitely not a troll here

Sorry, I retract my snarky movie quotes then. I honestly couldn't tell because the last paragraph came across as super sarcastic and I couldn't tell if you were joking.

1 hour ago, carbolicus said:

 selected the ILS frequency, and localiser and glideslope indications then appeared on the ILS display with no further action and there was certainly no need to dial in the runway heading on the VOR as well.

The A-10's instruments are from the original A-10A, which was not actually built with an ILS because they never planned on it flying high enough to be able to use one, and if they really needed it they would just do a PAR approach.  In other words, the jet isn't smart enough to know what you want to do. There's a limited number of ILS frequencies available and they are used by lots of different airports so the jet has no way knowing what airport you want to land at and what runway you are trying to fly to. TECHNICALLY, it does not matter what you have spun in on the needle, you will get accurate indications showing you left or right of course no matter what. BUT if the needle is pointing in some random direction and not aligned with the runway it is much more difficult for the pilot to interpret, the procedure is to spin in the inbound course onto the HSI.

 

1 hour ago, carbolicus said:

And yes, I was wrong about the need to set up your own TACAN - just experimented and realised that with TACAN off and ILS selected,

Generally speaking, you would never turn your TACAN off when you turn the ILS on. Even if you are using the paired DME on the ILS, you'd have the paired tacan channel tuned and you are still using the TACAN DME.

1 hour ago, carbolicus said:

However, if there is no TACAN near the airport (as in some on the Caucasus map which I’ve been using), setting up a man-portable TACAN at the end of the runway does mean you can get DME.

 

In real life you have to fly a published approach which would show you exactly what to use. Just because the TACAN is not on the airfield doesn't mean you can't use it for an approach. There are plenty of approaches where a TACAN is located miles from the base and you still use a crossing radial or DME to identify the FAF. Or there's a paired DME with ILS you could use that. Or you can use GPS substitution for TACAN DME (DME only, not radial information). The real problem with a lot of the DCS instrument approaches is that there are not adequate published approaches to use.

Nellis on the other hand can be flown exactly the way it is meant to be flown in real life per the published Hi-ILS 21L. It is simulated perfectly fine.