Saturday, October 26, 2013

DCS Mi-8MTV2 Magnificent 8 - Basic Doppler Navigation - Flight Plan and Departure

I am about to cross the Caucasus Mountains with my Mi-8 and the fun started way before I strapped my virtual self into the cockpit.

As you may know, the Mi-8MTV2 has no fancy avionics, glass cockpit or GPS. Navigation is accomplished via a doppler system which is fed with data by the co-pilot/navigator. In the only two references that I have about the use of the doppler system, this gadget is fed on-flight so planning becomes a necessity. Manual, pen, paper and a calculator ready ... I never felt so flight-sim-nerd as tonight!

The idea of this mountain crossing was for the "Second Georgian War" series. But I had so much fun flying this mission that I will just write it as an independent entry. The purpose is to flight across the Caucasus from the Beslan airport to the outskirts of Tskhinvali, where a team of Russian peacekeepers is waiting a delivery of communications equipment.

Off course you can fly the Mi-8 using visual flying rules and crossing the Caucasus range is a mighty fun ride for that. But I wondered how such a flight would feel if the weather conditions were bad. So the first task at hand is to learn to use the doppler navigation system.

"Vibora", a very well known fellow from the Spanish online flying community "Alas Rojas" has created a great guide to the use of the Mi-8's doppler navigation system. Please follow this link (downloads a MS Word document, in english). That, and some trigonometry elbow grease was all I needed to use the Mi-8's main navigation gadget. Gracias!

The flight plan and the four steerpoints. Tskhinvali is a few kilometers south of the edge of this map.
The custom-made mission I made for this flight has no map updates for the player's position (i.e. F10 map shows nothing but just the map), to enforce the use of either visual or instrument flying rules as much as possible.

The flight plan has four steerpoints and three legs. The steerpoints' positions are designed to accomplish mainly two things: (i) crossing the Russia-South Ossetia border and not the Russia-Georgia border (note the red borderlines in the above map) and (ii) crossing the Caucausus Mountains at a relatively low barometric altitude, avoiding the highest points of the mountains.

During the mission/flight planning, I used the in-game ruler tool to take note of the following:

  1. Distances and bearings of all the steerpoints, relative to our point of origin. Bearing angles were substracted eight degrees, to obtain a true magnetic bearing (the in-game navigation chart is not aligned with the true magnetic north). 
  2. Distances and bearings of each steerpoint, relative to the previous steerpoint. Again, bearing angles were substracted eight degrees. 

The values obtained in the (1) point above allowed me to obtain the coordinates of each steerpoint, relative to the point of origin (at the Beslan airport). For example, the coordinates of steerpoint 3 are 82.5 Km south and 19.05 Km west relative to our point of origin.

The bearings obtained in (2) will be useful during in-flight navigation. From the map above, after passing steerpoint 2, I should change my course to 147 degrees to reach waypoint 3. In this flight the distances to travel in each leg were obtained just to get an idea. In other instances, these leg travel distances can be fed into the doppler system. But I will not do that today.

Let's jump into the cockpit for the next part. The operation mode selector for the doppler system is right behind the co-pilot/navigator seat (?!).

Yeah, that box with the lights. In your neck. Let's not ask why the hell was placed there. 
In the picture above, the selector switch is shown in one of the test positions. To operate the doppler system, move the selector switch to the last (rightmost) position.

The doppler system's panel is located in the co-pilot/navigator dashboard. A picture is shown below.

As you know, we still don't have an official flight manual for the DCS Mi-8. So what I am going to write about the use of the doppler system is likely incomplete. I can only hope is not downright incorrect.

The most basic way to describe the doppler navigation system of the Mi-8 is as a car's trip meter, with the difference being that it measures distances in 2 axis (x and y). The navigator sets a track or bearing and that becomes the y axis. Then he turns the on switch and the current aircraft position becomes the zero of the navigation system. After flying for a while, the navigator can read the "y" position in the second row of the doppler system's display (labeled "distance along the bearing axis" in the picture above) and the "x" position (labeled "cross track position" in the picture above) in the first row.

In the picture above, the navigation system has a bearing set to 0 degrees, so the y axis is the north-south magnetic axis and the x axis is the east-west magnetic axis. In this case, the aircraft has travelled 12 Km in the north direction and 33 Km in the west direction. Also of note in the picture above are the drift angle indicator (it indicates the difference between the magnetic heading of the aircraft and the actual direction of movement of the aircraft) and the ground speed indicator. Both o them are at zero in this picture because the aircraft has just been landed.

There are many ways to skin a cat and the navigation methods are likely many. In the real life Mi-17 manual included in the simulation, there two navigation methods listed.

One is the leg-based method, in which the co-pilot sets a bearing in the doppler system equal to the bearing of the next waypoint. He then monitors the movement of the aircraft in order to make sure that the cross-track distance is minimal and that the aircraft travels the chart-based calculated distance along that track. At the very instant that the aircraft passes a waypoint, the navigator sets the bearing of the new navigation leg and resets the doppler system by a quick on-off in the panel. It's a nice method, but the caveat I noticed is that there is a need to pass each waypoint with a bearing corresponding to the bearing of the next leg. I kind of accumulate no less than a kilometer of cross track trying to make a sharp turn and I don't like that. The other thing is that the quick on-off switch needs to be performed right on top of the waypoint, preferably with the aid of a visual reference. If you remember, the flight plan for this mission is a dry run for an almost zero visibility flight in which no such visual reference would be possible.

The other method is listed in the manual as great circle navigation. In this method, the navigator sets a bearing of 0 degrees and by doing so the "y" readings correspond to the north-south direction and the "x" readings (cross track) correspond to the east-west direction. During the flight planning, the navigator obtains the "x" and "y" coordinates of each waypoint and then navigates to such coordinates using the doppler's readouts. The bearings of each leg are a great help to do so, that's why I calculated them. The calculations for a great circle navigation are performed with spherical trigonometry but I am a slacker and did all my calculations in 2D.

Enough words for today. Let's take off from Beslan.

Departing from Beslan airport. After a short hovering check, we depart on a inconspicuous route towards our navigation's "point of origin" (a road bend near the airport). The doppler navigation system is still off.

Our navigation's point of origin is that road bend in the background below. Once we overfly it, we start the doppler system. Note how the bearing in the doppler system is set to 0 degrees and how all the counters are set to 0 Km.

 The first leg is supposed to be followed at a course of 210 degrees. The compass is the third instrument, starting from the left.
The first leg will take us out of this plain area and into the Caucasus Mountains.
This is how the doppler system panel looks like during our first leg. Note the heading selection (third row of the panel), still set at 0 degrees, despite our current heading of  210 degrees.
In the second part, the rest of the flight and the landing on the other side of the mountains.



RangerX3X said...

You are a brave soul choosing the Caucasus Mountains as part of your first flight with a unique navigation system. I would have flew a box around the airfield and called it a day!!

JC said...

Yeah, it was quite a ride! :)
How are you doing there?