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Map preparation, quick and sloppy | by Johan G
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Map preparation, quick and sloppy

Preparing for a short VFR flight from N'Djamena (ICAO code FTTJ) to an airstrip outside Dourbali and back using pjedvajs Pilatus PC-9M in FlightGear 2.4.0 (an open source flight simulator).


I have not done this in a while, but have some nice memories from doing similar things in the past. Specially when I manage to pass the checkpoints on time. :-)


This time I cheated though, having "Real wheather", which would have updated the weather on regular intervals using fresh weather data (METAR), turned off.



The cruise altitude is 1000 ft AGL (above ground level) and the cruise speed 180 KIAS (knots indicated air speed).


The steps taken when preparing the map was:

1. Plotting the track using the pen and the protractor,

2. jotting down the true track and back track along with magnetic track and backtrack calculated using readings from the closest isogonic line (showing the magnetic deviation along that line),

3. marking easily recognizable checkpoints along the track,

4. measuring the distances by "copying" them using the divider and measure them against the graduation along the meridians (to do it against the parallels would indicate longer distances towards the poles), and finally

5. calculate the time I should pass each of the checkpoints from the air speed and distances using the flight computer and jot them down beside the checkpoints.


Do notice the lack of minute marks. I missed them a lot while flying.


The mistakes I did was that I measured the distance to the last checkpoint to short and that I somehow forgot to do the TAS (true air speed) to KIAS calculation... But at the altitude (968ft airport elevation + 1000 ft AGL = 1968 ft) it doesn't do as much difference as it could have done at say 20,000ft.


The flight was done on a FlightGear multiplayer server that was connected to a server that was saving a track of the flight. The flight track can be viewed at the FlightGear Tracker web site.


The flight computer is a Jeppesen CR-3. I have in the past, a couple of years ago, been able to do the wind calculations, but this time I cheated and had zero wind. Why the CR and not an E6-B? The CR can be manipulated with one hand, except for when plotting the wind dot, and all the parts is fastened together.


The chart is ONC K-3 (Operational navigation chart, sheet K-3), or rather the part of it that could fit an A4 sized sheet of paper while being true to scale (1:1 million), about 160 by 100 nautical miles. The chart was downloaded from the Map Collection of the Perry-Castañeda Library at the University of Texas Libraries. After the map was printed on a colour laser printer I laminated the upper side to make it possible to use it with a "grease" pencil. The grease pencil can be erased using water.


The photograph has been edited in GIMP to do a slight colour correction and a not so slight curve adjustment making the most of the image a lot brighter and the chart more readable.

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Taken on February 13, 2012