Glideslope and Localizer Needle Units (2AAC-2AB0-2AB4-2AB8)

[TobiBS]

Hi guys out there,

I am currenty writing a simple C++-Tool for logging purposes, it creates some datafiles that can be analyzed, reviewed and plotted. Therefore I had a look how to analyze the glideslope deviation. It seems that the mentioned Offsets are perfect for this, I already collected data succesfully, but I have no clue, what unit it is.

Neither in the documentaion, nor in FSInterrogate I found more than the value range which is actually from -127 to 127. Do you have any idea, whether it is in degrees or how it must be transformed to have degrees as result?

Thanks for your help in advance.

[Thomas Richter]

Hi

This values just display how far you are out of Center (value = 0), as long the GS is captured.

You need to read the GS available Offset as well to know that value zero means it is in Center or just that GS is not captured, then the value is of course zero too.

-------------------

Best Regards

Thomas Richter

Info@technical-service-richter.de

www.technical-service-richter.de

thomas@projectmagenta.com

support@projectmagenta.com

[TobiBS]

Hi

This values just display how far you are out of Center (value = 0), as long the GS is captured.

You need to read the GS available Offset as well to know that value zero means it is in Center or just that GS is not captured, then the value is of course zero too.

That is what I thought, but it didn't answered my question. I'd like to know in what unit it is measured. Does e.g. -2 corresponds to 2 degrees below the glideslope (or out of the localizer) or do I have to do any conversions, maybe it is that easy, but I can not find documenttion on that.

Nevertheless thank you for your post, maybe you can help me further.

[hsors]

Hi

I'm affraid you will not find any documentation about that

Typically, full ILS localizer deflection is 5° (2.5° each side). So, as far as FS modelizes things as it should, you will have a localizer scale of 128 = 2.5°

However I suspect this scaling will depend on the localizer beam width which is a known ILS FS parameter (distinct for each ILS).

The glide slope signals also consists of 2 overlapping beams (90 and 150 Hz). Since the thickness of the overlap is 0.7° above and below the defined ILS glideslope, I suppose the GS needle shows full deflection at top/bottom of the overlap area. This would result in a glide slope scale of 128 = 0.7°. Some tests (using aircaft & GS coordinates/elevations and trigonometry) could confirm that or not ;-)

Hervé

[TobiBS]

Hi

I'm affraid you will not find any documentation about that

Typically, full ILS localizer deflection is 5° (2.5° each side). So, as far as FS modelizes things as it should, you will have a localizer scale of 128 = 2.5°

However I suspect this scaling will depend on the localizer beam width which is a known ILS FS parameter (distinct for each ILS).

The glide slope signals also consists of 2 overlapping beams (90 and 150 Hz). Since the thickness of the overlap is 0.7° above and below the defined ILS glideslope, I suppose the GS needle shows full deflection at top/bottom of the overlap area. This would result in a glide slope scale of 128 = 0.7°. Some tests (using aircaft & GS coordinates/elevations and trigonometry) could confirm that or not ;-)

Hervé

OK, I experimented a bit and came to the conclusion that the glideslope value only changes to +/- 119. And with slewing I tried to find a coincidence between the indicators and the values. As you mentioned there is a good corelation for 2.5 degrees as a maximum value. I will include it like that and have it in mind, if something goes wrong.

But I found no reason, why Glideslope is only from -119 to +119. Maybe I need to accept it and forget about that fact.

Thanks for your help, it is always a pleasure to have such nice help in the flightsim forums.

[hsors]

Hi Thomas,

I think there is no fault about that.

The [NAV CSI] variable (localizer deviation) mapped by Peter at offset 0x2AAC full range is -127 to + 127 while the [NAV GSI] at 0x2AB0 is -119 to +119 ; this is described in the MS SDK. Don't ask me why ± 119 ;-)

There is also in FSX a [NAV GLIDE SLOPE ERROR] variable (degrees) but to my knowledge, Pete didn't map it (yet).

You could also try the byte variables at offset 0xC48 (localizer) ans 0xC49 (GS) whose ranges are ± 127

Regards

Hervé

[TobiBS]

Hi Thomas,

I think there is no fault about that.

The [NAV CSI] variable (localizer deviation) mapped by Peter at offset 0x2AAC full range is -127 to + 127 while the [NAV GSI] at 0x2AB0 is -119 to +119 ; this is described in the MS SDK. Don't ask me why ± 119 ;-)

There is also in FSX a [NAV GLIDE SLOPE ERROR] variable (degrees) but to my knowledge, Pete didn't map it (yet).

You could also try the byte variables at offset 0xC48 (localizer) ans 0xC49 (GS) whose ranges are ± 127

Regards

Hervé

Ok, I thought it could be a mistake, because I only read the documentation of FSUIPC and there it says +/-127. I will have a look for the 0xC48 and 0xC49 and crosscheck, if the results will be the same.

By the way, it is Tobias, not Thomas. :-)