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KM-2 magdec entry required?


TaygaMongun

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9 hours ago, TaygaMongun said:

Wondering if it's necessary to use the KM-2 at all. If you perform no corrections, it should display true north. Unless the KM-2 has an additional compensation function? 

The instruments read true north, (and the DISS-15 works off true north) but that information most often comes from a magnetic compass (AFAIK).

So you need to input the declination on the KM-2 to get true north.

If no declination is entered, the instruments should read magnetic north.


Edited by Northstar98
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51 minutes ago, TaygaMongun said:

Wondering if it's necessary to use the KM-2 at all. If you perform no corrections, it should display true north. Unless the KM-2 has an additional compensation function? 

 

29 minutes ago, Northstar98 said:

The instruments read true north, but that information comes from a magnetic compass (AFAIK).

So you need to input the declination on the KM-2 to get true north.

Northstar is correct. 

But you don't need to use it per se, you can just apply declination to whatever your HSI is showing.

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Unfortunately the use of the system hasn't been properly explained anywhere, including ED manuals. And it doesn't work correctly in Mi-8 either, so I'm not sure if ED will even do it right this time. 

I'm certainly no expert and I don't know how exactly it was used in Mi-24. But I've played a bit with Tupolev Tu-154 addon for MSFS which simulates a similar doppler navigation system. The heading gyros (Greben system in Mi-24) can operate in two modes. "MK" which uses information from magnetic sensor to orient the gyros to magnetic north, and "ГПК", when the gyro is disconnected from magnetic sensor and maintains the orientation in space. It's similar to "Free/Slaved" gyro switch in western aircraft, inluding DCS UH-1. The system in Mi-24 also allows you to input current latitude. This is important in ГПК mode, because it lets the system to cancel precession errors due to earth rotation in space, which are known and constant for a given latitutde. It leaves us only with small errors due to gyro system imprecision. In MK/slaved mode the gyro is constantly adjusted to magnetic north, so precision/precession errors are cancelled anyway. 

So why not simply leave it in MK and use magnetic heading? There are several reasons. One is that magnetic sensor does not like changes in acceleration, just like your whiskey compass and can give erratic corrections. Other is that magnetic navigation is not reliable in some parts of the world, including northern latitudes, places with large iron ore deposits below the surface, etc. Planning for a nuclear war that would cause a lot of magnetic interference may also have something to do with it. Last but not least, with proper data DISS system allows to fly a "great circle" path, which is the shortest path between two waypoints. 

For example in the Tu-154, the pilots would orient their gyros to magnetic north during startup, enter the magnetic declination at the startup location, which would in turn set the main navigation gyros to true north, but still keep some of the RMI instruments showing magnetic headings, to ease the terminal navigation around the airport. After that they will turn off the magnetic correction, and rely only on gyro stored headings. Enroute, using the DISS system and pre-computed route angles they would be able to fly a great-circle route between waypoints, without the need of expensive INS, and long before GPS became operational. 

If you want to read more about it, check the chapters about "НВУ Navigation" https://docplayer.net/89266328-Project-tupolev-tupolev-tu-154m-english-manual.html

 

In the Mi-24, another purpose of KM-2 panel may be that if you set the gyros to magnetic heading but the moving map is oriented to true north, then without correction the angles and your position won't match. But that's just my guess. I noticed some weird issues in DCS when I tried to navigate in the Mi-24 on longer flights.


Edited by some1
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1 hour ago, some1 said:

I noticed some weird issues in DCS when I tried to navigate in the Mi-24 on longer flights.

I'm guessing that's because of DCS' flat Earth maps which don't really represent true north accurately, nor does it allow you to fly great circle routes.

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Ok that's understood. I am used to navigating 'АК' mode in eastern aircraft, so i apply magdec to change it from 'МК' to 'АК', thence navigate with true north references. I am more familiar with the Tu-134A's NAS-1 than the Tu-154's NVU. 

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6 hours ago, some1 said:

But I've played a bit with Tupolev Tu-154 addon for MSFS

Project Tupolev?

6 hours ago, some1 said:

The heading gyros (Greben system in Mi-24) can operate in two modes.

3 modes

6 hours ago, some1 said:

It's similar to "Free/Slaved" gyro switch in western aircraft,

The naming convention is the same as in the PT, but the functions are different.

In the Mi-8/24, mode ГПК is "Slaved," MK is approximately "Raw" and 3K is "Free."

I don't know which (PT/Belsimtek)is correct, of if they are both correct.

6 hours ago, some1 said:

In the Mi-24, another purpose of KM-2 panel may be that if you set the gyros to magnetic heading but the moving map is oriented to true north, then without correction the angles and your position won't match. But that's just my guess.

My understanding is this will be the primary use of the system for users.

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35 minutes ago, randomTOTEN said:

3 modes

2 modes, really. In the Mi-8, the third position of the switch besides "MK" and "ГПК" is "AM" which is astro compass, and it's not functional in the aircraft. In the Mi-24, the third position is "3K", which means "SET HEADING", or maybe "SELECTED HEADING". Either way, I think this is the position used to adjust the gyros manually to a new heading, something that in the Mi-8 (and L-39 Albatros) is done from ГПК mode using a separate switch labelled "3K". I don't see such switch in the Mi-24 Greben panel or anywhere else, and this "3K" mode does nothing. But some way to adjust the gyros in ГПК mode has to be possible.... eventually. Now it's obviously WIP. 

49 minutes ago, randomTOTEN said:

The naming convention is the same as in the PT, but the functions are different.

In the Mi-8/24, mode ГПК is "Slaved," MK is approximately "Raw" and 3K is "Free."

Nope, I highly doubt that. These aren't the non-descriptive codes, but rather the shortcuts for a navigation device type, kind of like "ADF", or "ILS". MK is "magnetic compass" (магнитный компас). ГПК is "гирополукомпас' , which literally translates to "gyro-half-compass", but in English aviation nomenclature would be a Directional Gyro. Swapping these functions like you suggest would be hella confusing for Russian speakers. 

The DCS Mi-8 manual describes these positions just like I did. MK is "slaved", ГПК is "free" (sometimes called "DG"). I was wrong to say that it doesn't work in DCS Mi-8, it actually works fine in the sim, just slower than I expected. 

 

It's interesting to see the operational difference between Russian and Western systems. In most Western aircraft, the heading gyros are primarily used in "SLAVED" mode and the magnetic correction system would be disabled only at very high latitudes or in case of malfunction. While in the Russian aircraft from that era, it seems to be more common to fly without it for most of the time. 

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17 minutes ago, some1 said:

2 modes, really. In the Mi-8, the third position of the switch besides "MK" and "ГПК" is "AM" which is astro compass, and it's not functional in the aircraft. In the Mi-24, the third position is "3K", which means "SET HEADING", or maybe "SELECTED HEADING". Either way, I think this is the position used to adjust the gyros manually to a new heading, something that in the Mi-8 (and L-39 Albatros) is done from ГПК mode using a separate switch labelled "3K". I don't see such switch in the Mi-24 Greben panel or anywhere else, and this "3K" mode does nothing. But some way to adjust the gyros in ГПК mode has to be possible.... eventually. Now it's obviously WIP. 

Nope, I highly doubt that. These aren't the non-descriptive codes, but rather the shortcuts for a navigation device type, kind of like "ADF", or "ILS". MK is "magnetic compass" (магнитный компас). ГПК is "гирополукомпас' , which literally translates to "gyro-half-compass", but in English aviation nomenclature would be a Directional Gyro. Swapping these functions like you suggest would be hella confusing for Russian speakers. 

The DCS Mi-8 manual describes these positions just like I did. MK is "slaved", ГПК is "free" (sometimes called "DG"). I was wrong to say that it doesn't work in DCS Mi-8, it actually works fine in the sim, just slower than I expected. 

 

It's interesting to see the operational difference between Russian and Western systems. In most Western aircraft, the heading gyros are primarily used in "SLAVED" mode and the magnetic correction system would be disabled only at very high latitudes or in case of malfunction. While in the Russian aircraft from that era, it seems to be more common to fly without it for most of the time. 

In Mi-8 is it MK mode or Free/DG where by adjusting the HSI essentially allows you to correct for magnetic declination? Is that the labeled 3K switch in Mi-8? 

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A couple more info and images about the Greben-1 and KM-2. I'll check with calm after work.

 

https://kzref.org/issledovanie-harakteristik-malogabaritnoj-girovertikali-mgv-1.html?page=3

https://lektsia.com/1x9e6.html

 

 

96395_html_m7deff26e.jpg

 

The system check made at 1m16s of the video is working as the info bellow. Note the 315° that is also at the text label next to the button itself (контроль).

ПРОВЕРКА РАБОТОСПОСОБНОСТИ

Выключить выключатели «-27В», «36В 400Гц» на «КПАП-В». Через 10 минут после включения питания переключатель режима на ПУ-38 поставить в положение «МК». Нажать кнопку «контроль» на КМ-2. УППС и РМИ-2 должны отработать курс 315 image104.gif 10 градусов.

PERFORMANCE CHECK (Google Translate)

Turn off switches "-27V", "36V 400Hz" on "KAP-V". 10 minutes after turning on the power, set the mode switch on the PU-38 to the “MK” position. Press the "control" button on the KM-2. UPSS and RMI-2 must complete course 315 image104.gif10 degrees.

image.png

 

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Yep, it looks like now by default, with Petro setting magdec, the instruments are showing true headings instead of magnetic. Which aligns well with the moving map also showing true headings on the flightplan. So to navigate using DISS system we should now enter true headings into the computer.

Which is the opposite from Mi-8, which uses magnetic headings for display and for doppler navigation. 


Edited by some1

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4 hours ago, some1 said:

Yep, it looks like now by default, with Petro setting magdec, the instruments are showing true headings instead of magnetic. Which aligns well with the moving map also showing true headings on the flightplan. So to navigate using DISS system we should now enter true headings into the computer.

Which is the opposite from Mi-8, which uses magnetic headings for display and for doppler navigation. 

 

Isn’t possible to correct for magnetic deviation on Mi-8 however by using its GK like dial to move HSI correct amount kindve like a DG mode? But I guess that’s no where near as precise as this KM-2 system 

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Interesting, yeah pressing match in Mag mode seems to constantly need “Match” presses. But what I did was press Match in Mag mode, switch to gyro so it uses the gyro for all information based off that initial magnetic + declination alignment, and I didn’t need to align/match at all afterwards. Wonder if that’s intended 

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On 4/27/2022 at 10:53 AM, TaygaMongun said:

Wondering if it's necessary to use the KM-2 at all.

 

On 4/30/2022 at 5:13 PM, AeriaGloria said:

Wonder if that’s intended 

Hi! With some experience from Project Tupolev Tu-154B-2 and Felis Tu-154M modules, I can confirm it is standard procedure to use the 'Magnetic' mode to align the gyro when the aircraft is stationary during start-up. The alignment is done by pressing and holding the 'sync' button. After the alignment the selector should go back to the 'Gyro' mode in the center. It is not intended to use the 'Magnetic' mode to perform the whole flight.

However the precision of the gyro will still decline over time. So the gyro still needs alignment after some time and distances covered. From my Tu-154 experience I remember that the manual requires the crew to perform gyro alignment mid-air every time before leaving cruise stage and initiating decent towards the destination, when the magnetic reading is stable. It is a descent checklist item. So I guess for the Hind we can also perform regular alignment using the autopilot.

57c30c1b2e0df_Selection_29082016_020042.

This is the PU-11 unit (part of the TKS-P2 navigation system) panel on the Tu-154. It couples with the KM-5 compass and operates generally in the same way with the Greben-1 and KM-2 combination in DCS. The differences are that PU-11 has a latitude input dial combined in it while Greben-1 has this dial separated for the CPG seat in the Hind, and PU-11 governs two gyro systems (one for the Captain and one for the F/O) while Greben-1 governs only one.

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58 minutes ago, SqnLdr_chuishan said:

 

Hi! With some experience from Project Tupolev Tu-154B-2 and Felis Tu-154M modules, I can confirm it is standard procedure to use the 'Magnetic' mode to align the gyro when the aircraft is stationary during start-up. The alignment is done by pressing and holding the 'sync' button. After the alignment the selector should go back to the 'Gyro' mode in the center. It is not intended to use the 'Magnetic' mode to perform the whole flight.

However the precision of the gyro will still decline over time. So the gyro still needs alignment after some time and distances covered. From my Tu-154 experience I remember that the manual requires the crew to perform gyro alignment mid-air every time before leaving cruise stage and initiating decent towards the destination, when the magnetic reading is stable. It is a descent checklist item. So I guess for the Hind we can also perform regular alignment using the autopilot.

57c30c1b2e0df_Selection_29082016_020042.

This is the PU-11 unit (part of the TKS-P2 navigation system) panel on the Tu-154. It couples with the KM-5 compass and operates generally in the same way with the Greben-1 and KM-2 combination in DCS. The differences are that PU-11 has a latitude input dial combined in it while Greben-1 has this dial separated for the CPG seat in the Hind, and PU-11 governs two gyro systems (one for the Captain and one for the F/O) while Greben-1 governs only one.

Thank you for posting this. It illuminates quite a bit. I’m very surmised this wasn’t mentioned in the KM-2 video released.

It seems that going into MAG and aligning after only 30-45 minutes yields only a couple degree improvement in accuracy. But around 1 hour or more the difference becomes larger. And if you are navigating long distances all the more important to decrease times between syncing. 
 

What that Tu-154 procedure says makes sense, however, I’ve been meaning to test. In real life and In DCS, how much of the needing to re align periodicallly is due to time, due to travel distance, and how much is becuase of maneuvering causing gyro innacuracies. 
 

If it’s maneuvering, it would make sense why perhaps Mi-24 would need more frequent adjustment then an airliner like Tu-154 

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Thanks a lot!

Yesterday talking with a former KA-32 firefighter pilot (Ka-32 has a similar Greben-2 system) confirmed me that the Gyro is the standard flight position, with the Mag position used to enter the MagVar with the KM-2 and synchronize it with the pushbutton,

Only doubt now is the 3rd position of the Mag/Gyro/HDG and the tune/oper switch. 


Edited by Tarres
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On 5/3/2022 at 11:46 PM, Tarres said:

Thanks a lot!

Yesterday talking with a former KA-32 firefighter pilot (Ka-32 has a similar Greben-2 system) confirmed me that the Gyro is the standard flight position, with the Mag position used to enter the MagVar with the KM-2 and synchronize it with the pushbutton,

Only doubt now is the 3rd position of the Mag/Gyro/HDG and the tune/oper switch. 

 

Figured it out. In HDG/ZK, you can set course yourself just like with 3K switch on Mi-8. In HDG/ZK mode the HSI moves like gyro mode, except when you press Synch/match button, the RMI/HSI will move slowly clockwise, allowing you to stop it at a certain heading. Don’t know what use that would be except to set heading to runway heading on takeoff 

Testing tonight, and MAG/MK seems to drift nearly a degree a minute. While Gyro mode drifts about 2.5-5 degrees per hours it seems. Trying to figure out how much it’s drift is based on time, travel distance; and movement/turning 


Edited by AeriaGloria

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4 hours ago, Razorback said:

If you press match during the flight in order to keep the accuracy, the Greben selector stay on GYRO ?

If Greben in Gyro, pressing match/synch does nothing. 
 

Only has functions in MAG/MK and HDG/ZK modes. 

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  • 8 months later...

So, Begin of Jan 23 and it's maybe time to check if I am still using the correct way to use the KM-2 in order to have as much as precision when selecting a course with the Mi-24.

During startup : Greben on MAG position
At the end of startup : reset (3s) and the place the Greben knob on GYRO (screenshot)

The F-10 map display now the magnetic and the true course if you want to go from your position to another place on the map.
Since the magnetic declination is corrected by the Greben of the Mi-24P, I have to display the true heading on my HSI, Doppler and even course AP... Correct?

My second question : do you change the latitude on the KM-2 when you are flyning on Caucasus, Syria or other maps ?
For my point of view, if you are alone on the cockpit seta, Petrovitch will set the KM-2 on the correct position. Once Again, am I Correct ?

Stil no interest in pushing SYNCH during long flights as long as the Greben is on Gyro?
Even if I am landed and that I replace the Greben switch on MAG during a few seconds ?

Thxxx

KM-2.JPG


Edited by Razorback
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12 hours ago, Razorback said:

So, Begin of Jan 23 and it's maybe time to check if I am still using the correct way to use the KM-2 in order to have as much as precision when selecting a course with the Mi-24.

During startup : Greben on MAG position
At the end of startup : reset (3s) and the place the Greben knob on GYRO (screenshot)

The F-10 map display now the magnetic and the true course if you want to go from your position to another place on the map.
Since the magnetic declination is corrected by the Greben of the Mi-24P, I have to display the true heading on my HSI, Doppler and even course AP... Correct?

My second question : do you change the latitude on the KM-2 when you are flyning on Caucasus, Syria or other maps ?
For my point of view, if you are alone on the cockpit seta, Petrovitch will set the KM-2 on the correct position. Once Again, am I Correct ?

Stil no interest in pushing SYNCH during long flights as long as the Greben is on Gyro?
Even if I am landed and that I replace the Greben switch on MAG during a few seconds ?

Thxxx

KM-2.JPG

 

1. Best accuracy is always keeping it in MAG position, as that enables magnetic update. GYRO position is for flights in high latitudes or over magnetic anomalies. Gyro position will accumulate a few degrees of error every hour 

 

For example, real life manual tells you to always use MAG unless above 80 degrees latitude or large magnetic anomalies are known 

2. no, you are not moving many latitudes during a single flight 

Petro will always set KM-2 to proper declination so your HSI will always be in true heading 

Sync has no effect it seems unless in Gyro mode on which case it quickly aligns it I believe 


Edited by AeriaGloria
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