MGRS grid navigation with the Mi-8 Doppler

[TasDozer]

Hi folks,

I've not seen this written up in any manuals or tutorials for the Mi-8 specifically, so I thought I'd show how to navigate on the MGRS grid (or, any grid actually) with the Mi-8 Doppler system.

The video is what you get when you hit "Start Recording" in OBS and upload a single unedited take. So here's the essential steps:

1. Set COURSE ANGLE to the magnetic bearing of MGRS Grid North for your area. (Use F10 ruler and measure up the side of an MGRS square). For Tshinvali it's 345°M.
2. Set LATERAL DEVIATION KM and DISTANCE KM to the easting and northing of a landmark you'll overfly after takeoff. E.g. Tshinvali stadium is at MM1676, so I set EAST 016, FORWARD 076
3. Turn on the Doppler system as you overfly that landmark
4. Your EAST and FORWARD positions are now your MGRS coordinates and will keep updated as you fly
5. Use the Left/Right/Fwd/Aft buttons to correct your position as needed when you have an opportunity

The reason to use a landmark as your starting point rather than your takeoff point: you get no groundspeed below 50 km/hr, and I'm pretty sure it takes a few minutes for the doppler radar to warm up, so if you're starting up as fast as you can (and why wouldn't you) you're going to be off by several hundred metres.

Your Doppler radar will lose lock if your bank angle exceeds about 15°, pitch angle exceeds about ±10°, drift angle exceeds 45°, or groundspeed drops below 50 km/hr. It's not the end of the world - it will continue to feed the nav computer with the last groundspeed and drift angle it had (or 0 km/hr if anything under 50 km/hr - I'm not certain on that one), and this will make your position less accurate.

The English cockpit for the Mi-8 currently has labels on the DISS-15 Doppler nav computer which don't agree with the Russian cockpit or the translations in the manual but I think this is getting looked at:

• LATERAL DEVIATION KM is labelled DRIFT ANGLE KM
• DISTANCE KM is labelled FLIGHT PATH KM
• COURSE ANGLE is labelled MAP ANGLE

Disclaimer: so far I've only tested this as far as the distance between Tshinvali and the clearing 40km away where people with rifles make holes in my hydraulic system.

Edited March 18, 2023 by TasDozer

[Kang]

That's nice to know

[AeriaGloria]

On 3/18/2023 at 6:08 AM, TasDozer said:

Hi folks,

I've not seen this written up in any manuals or tutorials for the Mi-8 specifically, so I thought I'd show how to navigate on the MGRS grid (or, any grid actually) with the Mi-8 Doppler system.

The video is what you get when you hit "Start Recording" in OBS and upload a single unedited take. So here's the essential steps:

1. Set COURSE ANGLE to the magnetic bearing of MGRS Grid North for your area. (Use F10 ruler and measure up the side of an MGRS square). For Tshinvali it's 345°M.
2. Set LATERAL DEVIATION KM and DISTANCE KM to the easting and northing of a landmark you'll overfly after takeoff. E.g. Tshinvali stadium is at MM1676, so I set EAST 016, FORWARD 076
3. Turn on the Doppler system as you overfly that landmark
4. Your EAST and FORWARD positions are now your MGRS coordinates and will keep updated as you fly
5. Use the Left/Right/Fwd/Aft buttons to correct your position as needed when you have an opportunity

The reason to use a landmark as your starting point rather than your takeoff point: you get no groundspeed below 50 km/hr, and I'm pretty sure it takes a few minutes for the doppler radar to warm up, so if you're starting up as fast as you can (and why wouldn't you) you're going to be off by several hundred metres.

Your Doppler radar will lose lock if your bank angle exceeds about 15°, pitch angle exceeds about ±10°, drift angle exceeds 45°, or groundspeed drops below 50 km/hr. It's not the end of the world - it will continue to feed the nav computer with the last groundspeed and drift angle it had (or 0 km/hr if anything under 50 km/hr - I'm not certain on that one), and this will make your position less accurate.

The English cockpit for the Mi-8 currently has labels on the DISS-15 Doppler nav computer which don't agree with the Russian cockpit or the translations in the manual but I think this is getting looked at:

• LATERAL DEVIATION KM is labelled DRIFT ANGLE KM
• DISTANCE KM is labelled FLIGHT PATH KM
• COURSE ANGLE is labelled MAP ANGLE

Disclaimer: so far I've only tested this as far as the distance between Tshinvali and the clearing 40km away where people with rifles make holes in my hydraulic system.

 

This is very awesome thank you! 
 

Roll limits are actually +/-30 degrees, and +/-7 degrees for pitch. 
 

It wil take a few minutes to turn on, and if you lose generators from rotor droop that will also cause it to go out for a few minutes and restart.