Nellis TACAN and ILS

[Caldera]

Hey Guys,

 

I have attached my training mission.

 

I am attempting to learn ILS landings at Nellis.  A few things are happening that are weird and I do not understand.

 

First, just make to sure that I have it correct.  If the Localizer Steering Bar (LSB) is left then steer left.  If the Glide Slope Steering Bar (GSSB) is low then decrease altitude.  Always chase the bar.

 

What I notice is that the LSB never lines up with the runway.  I can chase the LSB to Timbuktu and back.  The GSSB and the Glide Slope Deviation Indicator (GSDI) are working just fine.  Both will put me right on the end of the runway only if I ignore the LSB.

 

Also the Course Deviation Indicator (CDI) of the TACAN never aligns with the runway.  It also has me headed to Timbuktu.

 

I have mapped the ILS Volume to the keyboard (I can not see the knob move). I can increase volume all day long but I get no sound at any time.  I get no Morse Code, no Outer Beacon, no Inner Beacon.  Nothing...

 

Would some one mind running this mission for me and letting me know if I am just all wet?

 

Thanks in advance,

Caldera

TRN-MSN5 Nellis.miz

Edited April 7, 2021 by Caldera

[randomTOTEN]

I see a little bug, otherwise sadly I think a case of being "all wet."

 

Yes, turn and pitch to follow the steering bars. I used your mission and they brought my very nicely to the runway.

I don't know what you're talking about with CDI for TACAN and runway alignment. It appears to be functioning correctly in your mission.

I couldn't get the identification of either station as well. In the A-10C II they changed the defaults on the audio panel so that everything is muted. In addition, it seems there is a bug where the ident audio doesn't actually play unless you adjust the volume, regardless of the fact it's already at full volume when you select it.

 

Hope it helps. yeah i know it can be confusing.

[Caldera]

rT,

 

Thanks for your review. 

 

Sorry for the bad photo.

 

Well, I don't get it then... 

 

The runway is at 210 and I am flying very close to 210.  The runway I am pretty much lined up on is 21L.  The LSB indicates that I need to change my course to the left.  If this was a VFR landing then I would obviously need to adjust my course the the right.  The more I chase the LSB left the worse the IFR solution gets. 

 

The TACAN is out to lunch...

 

Waypoint 1 exists at the end of the Localizer dead center between the two beams as displayed on the mission creator map.  I put it there for training purposes.  Waypoint 0 also the steerpoint, is at the center of runway 21L.

 

Caldera

[randomTOTEN]

1 hour ago, Caldera said:

The runway is at 210 and I am flying very close to 210.  The runway I am pretty much lined up on is 21L

Your course is set to 000

[jaylw314]

I can't see If you have your NMSP on ILS?

 

While I don't know if this is the cause of your problem, be aware the steering bars on the ADI are a "flight director", not guidance bars.  Left/right tells you to ROLL left and right, it's not just a course deviation indicator.  Likewise up/down tells you to pitch up/down.  It essentially tells you what to do with the stick, and it will adjust it to get you back on the proper course/glidepath.  Think of it as the kindergarten version of the CDI (which is on the HSI) and the GS indicator (the arrow at the left of the ADI).

 

I noticed on your HSI the course arrow is turned the wrong way, but the CDI is to the right of the arrow as it should be.

 

[dporter22]

As was said above, your course is set to 000 so that's the course the CDI is tracking.  You have to set your course to the published ILS course, in this case, 209 inbound for RWY 21L.

Edited April 7, 2021 by dporter22

[Zeagle]

what dporter22 said

 

Edited April 7, 2021 by Zeagle

[Caldera]

Hey Guys,

 

I got it to work and I made a few landings in the fog.

 

Still a bit baffling to me how the dang thing works.  Maybe I am too used to the fish finder in my boat that uses cross track error. 

 

The LSB will not work correctly unless I set the course to 210.  Why would any setting on an aircraft have any effect of the detected direction of Localizer signal?  The ground TACAN is a radial transmission at 1 degree intervals correct?  But the Localizer transmits to a fixed direction with left and right components.

 

MMSP?

 

Caldera

[Frederf]

Navigation mode select panel, NMSP, "nim-sip".

 

In the real A-10 the bank steering needle is not based on the course knob. In DCS it is. it's a limitation of the implementation.

 

TACAN is good to about 1/4 degree but it's analog so it doesn't have a resolution in the digital sense.

[Zeagle]

The localizer is simply a VOR but with a little better accuracy.  Tricks are used to make it not broadcast around a complete circle. Your HSI uses the signal from the localizer to show the difference between the radial you are on and the radial dialed in. It's that simple. So the dialed in radial is required. 

 

The GPS in your fishfinder works differently.

Edited April 8, 2021 by Zeagle

[corvus5624]

Are you talking about the ILS localizer?

 

As far as I know the localizer uses two beams. One beam is pointed a bit to the left of the centerline of the runway, the other a bit to the right. Both transmit at different frequencies (offset from the carrier frequency). By measuring the relative signal strength you can figure out where you are in relation to the runway centerline.

 

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

 

A VOR works by transmitting an omni directional signal and a directional beam that rotates. By measuring the phase between the two signals you can figure out on which radial you are.

 

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

 

So for TACAN navigation (which is basically VOR + DME) you have to set the course (i.e. desired radial you want to be on), but for ILS you would not need to set the course in order to the steering bars to work properly.

 

I don't think I ever had to set the course in the HSI in order for the ILS to work.

 

 

[corvus5624]

4 hours ago, Frederf said:

Navigation mode select panel, NMSP, "nim-sip".

 

In the real A-10 the bank steering needle is not based on the course knob. In DCS it is. it's a limitation of the implementation.

 

TACAN is good to about 1/4 degree but it's analog so it doesn't have a resolution in the digital sense.

So, I checked the ILS at Kobuleti. Approached runway 7, ILS tuned to 111.50 MHz, ILS selected at the NMSP. I can confirm that you need to set the course for the flight director to work. Didn't know that you had to do that in DCS. Guess I never noticed because I typically approach the airfield using TACAN (for which I do set the course).

 

Using the course knob is rather imprecise, for example for Kobuleti you have to set it to 64o (70o minus 6o magnetic variation). It is kind of hard to set it exactly to the runway direction. Well, it is manageable I guess, but it would be nice if it would work properly.

[randomTOTEN]

12 hours ago, Caldera said:

Why would any setting on an aircraft have any effect of the detected direction of Localizer signal?

Because it's a flight director, not a course deviation indicator.

 

Look at the image you posted. Even though the HSI needle is facing the opposite direction, it's showing the correct indication. You are left of the localizer beam for 21L.  If you turned the aircraft to 000 at that same position you would show being left of the localizer, exactly as the signals you are receiving indicate. You are left of the localizer for imaginary runway 36.

 

So ignore what's outside, look only at the HSI indication. It shows you flying away from the localizer, and it's off your left wing (to your right if you were pointed 000). To get on that localizer you need to make a left turn of 210 degrees. That is why the Steering bar is deflected left.

 

Of course, as you make that turn you get further away from the real localizer beam, not closer as the Steering Bar is attempting to accomplish. It will soon break. This is because of the course error.

 

I suspect the flight director system receives heading deviation, and course deviation, and processes both to output a steering command.

 

7 hours ago, Frederf said:

In the real A-10 the bank steering needle is not based on the course knob. In DCS it is. it's a limitation of the implementation.

I suspect this statement is not correct, but I don't know enough about the system to exactly say for certain. If it did not use course information it would just be another variant of localizer deviation needle.

 

Quote

It is kind of hard to set it exactly to the runway direction. Well, it is manageable I guess, but it would be nice if it would work properly.

Huh? There's a numerical output on the top right of the HSI..... You can precisely set the value easy.

Edited April 8, 2021 by randomTOTEN

[Leg2ion]

3 hours ago, corvus5624 said:

Using the course knob is rather imprecise, for example for Kobuleti you have to set it to 64o (70o minus 6o magnetic variation).

Where did you get your magvar from? Currently operating out of Kobuleti and havn't had any problems with setting 70^o and lining up. 

 

12 hours ago, Caldera said:

Still a bit baffling to me how the dang thing works.  Maybe I am too used to the fish finder in my boat that uses cross track error. 

Try either only using TACAN or ILS separately to see what each does independent of the other. As far as I know TACAN gives you a range and bearing to aim for, whereas ILS should (if it is working) give you a beam to drive down.

 

So for instance you can go point to point between TACANs, and it doesn't matter from what angle/height you approach the transmitters, whereas for ILS you need to be within range and pointed roughly in the right direction to get a steer.

 

Try setting up a simple NAVEX flight using TACAN transmitters to navigate between. You can just fly 'point to point' between them, or, as you tune into each transmitter also set a course/heading of the runway it is linked to, then you can manoeuvre so you approach the TACAN on the desired course/heading - overflying the TACAN parallel (or close) to the runway heading. 

 

Once in the 'ballpark' I tend to knock out TACAN, rely solely on ILS and set both course/heading  to the runway approach. Technically heading could change dependent on wind etc to maintain correct course.

[corvus5624]

24 minutes ago, randomTOTEN said:

Huh? There's a numerical output on the top right of the HSI..... You can precisely set the value easy.

 

 

I know, but in my opinion this is not precise   The precision with which I can set this is about 0.5o, or about lateral displacement 50 ft per nautical mile distance. Like I said, it is not a big deal. Butt if you use ILS, the steering bars should steer you to the center of the localizer beams. Apparently it does not do that, but it steers you to the course you set. If you enter the correct runway heading, it works well enough for me, but still it shouldn't be necessary.

[corvus5624]

8 minutes ago, Leg2ion said:

Where did you get your magvar from? Currently operating out of Kobuleti and havn't had any problems with setting 70^o and lining up. 

I think from the PHAK (Pilots Handbook of Aeronautical Knowledge). Baltic Dragons campaign 'The Enemy Within' also mentions this as the course to use for Kobuleti, from the frag order:

 

 

Here you see that the approach course to use for runway 07 is 064o. Using 70o will get you to the runway, but not aligned perfectly. Did you ever notice that you are not aligned perfectly if you set the course to 70o? Perhaps the difference is too small to notice if you fly in visual meteorological conditions?

[=4c=Nikola]

30 minutes ago, Leg2ion said:

Where did you get your magvar from? Currently operating out of Kobuleti and havn't had any problems with setting 70^o and lining up. 

 

If you fly raw data ILS, you will not see any difference between 070 and 064 degrees set on HSI. It will align you nicely.

 

If you follow Flight Director, setting HSI to 070 will offset your approach. (I've never seen this behavior IRL in multiple aircraft, but I have no idea about A-10, maybe it's correct, but I doubt).

[corvus5624]

12 minutes ago, =4c=Nikola said:

 

If you fly raw data ILS, you will not see any difference between 070 and 064 degrees set on HSI. It will align you nicely.

 

If you follow Flight Director, setting HSI to 070 will offset your approach. (I've never seen this behavior IRL in multiple aircraft, but I have no idea about A-10, maybe it's correct, but I doubt).

Do you know how to fly on ILS only in the DCS A-10CII, or on raw ILS data as you put it? I can't get it to work without setting the course in the HSI.

[=4c=Nikola]

5 minutes ago, corvus5624 said:

Do you know how to fly on ILS only in the DCS A-10CII, or on raw ILS data as you put it? I can't get it to work without setting the course in the HSI.

 

Setting course should not have any effect. 

 

You should just:

1. Set ILS power to ON (left outer knob at ILS panel)

2. Set correct ILS frequency

3. Turn ILS switch ON (bellow HSI panel)

4. Make sure the runway you're landing on is active by ATC (not sure whether this affects ILS)

[corvus5624]

I am actually following these steps. I know ILS works, because I get a glidescope. So I see two steering bars. Setting course should not have an effect indeed, but it seems it does have an effect in the sim. Bug?

[=4c=Nikola]

Just now, corvus5624 said:

I am actually following these steps. I know ILS works, because I get a glidescope. So I see two steering bars. Setting course should not have an effect indeed, but it seems it does have an effect in the sim. Bug?

 

I do not know what do you mean by "steering bars". If you consider "steering bars" two yellow lines on ADI (aka Flight Director), you are right. I believe that's not correct behavior in game.

 

By raw data I mean flying without flight director. 

[randomTOTEN]

Course should absolutely have an effect on the steering bars. The system isn't magic. It doesn't know what direction the localizer is pointing, thus could not calculate an intercept command without using the course info.

 

In Desert Fox's 2nd picture. The steering bar is trying to get him to turn right so he doesn't get off course (it thinks he is about to deviate to the left from on the beam).

Edited April 8, 2021 by randomTOTEN

[Frederf]

This is a well-hashed issue.

7 hours ago, Zeagle said:

The localizer is simply a VOR. Your HSI uses the signal from the localizer to show the difference between the radial you are on and the radial dialed in. It's that simple. So the dialed in radial is required.

 

VOR and LOC are similar in that they know position based on difference information. But in case of VOR the difference is in the time domain between the reference and sweep signals while in LOC the difference is in intensity of the left/right lobe signals. The airplane counts the seconds between receiving reference (north) signal and receiving sweep signal. E.g. if the sweep signal comes 55% of the cycle time after reference signal then position is 55% around the compass rose. Localizer receiver gets simultaneously both signals from 90 and 150 Hz modulated transmitters and compares their intensity. If signals are equal intensity then position is on middle axis. Fundamentally the systems work quite differently.

 

Both in game and in reality the CDI (which is the displaced needle in the center of the HSI) moves according to localizer signal intensity imbalance regardless of CRS knob setting. This is easily verified in DCS by flying the localizer centerline and wildly changing the CRS knob without any change in CDI deflection.

 

The bank steering bar on the ADI is where DCS and reality diverge. In DCS the director is comparing the localizer position against the CRS knob setting to develop a difference value. It then uses this difference value to command bank left/right and by how much. Obviously changing the CRS knob changes the difference value for any given localizer position. In real A-10 this is not how the system works. In real A-10 the data which drives the bank director is localizer position and also localizer position time rate of change.

 

4 minutes ago, randomTOTEN said:

Course should absolutely have an effect on the steering bars. The system isn't magic.

The magic is that the system knows both the localizer position and the localizer position trend over time. Knowing both position and position trend it's possible (and indeed how the real system works) to develop bank director commands without knowing course.

[randomTOTEN]

Just now, Frederf said:

The magic is that the system knows both the localizer position and the localizer position trend over time. Knowing both position and position trend it's possible (and indeed how the real system works) to develop bank director commands without knowing course.

That is a more modern way for the system to work, sure. But I know many of us have experience with systems that do actually rely on course info, so the current function is not a surprise.

[jaylw314]

36 minutes ago, randomTOTEN said:

That is a more modern way for the system to work, sure. But I know many of us have experience with systems that do actually rely on course info, so the current function is not a surprise.

At least according the flight manual, there's no reference to the ADI bank steering needle and the HSI CDItaking input from the course selector in ILS mode, just the localizer position.  The source I have is not terribly definitive, though.

 

Interestingly, it mentions the ADI bars can be used in FM ADF mode.  The banks steering needle shows direction and the pitch steering needle shows signal strength as it rises.  I'm guessing this is not modelled, anybody know?