Operating instructions
BB_Sextant4.CAB

This is an on-screen charting gauge for finding your latitude/longitude from a sequence of two or preferably three sextant shots.

It is assumed the user is very familiar with the BB_Sextant gauge, and has the new 'BB_Sextant4.CAB' installed in their aircraft. If not, the accompanying Installation file should be read and followed first.

This gauge uses a BB_sextant gauge that has a different filename than the original. It is identical in operation with the original, but it has some added "hooks" so the gauge can share information with its new companion chart gauge. Although you cannot use the original BB_sextant.CAB, you can (and should) use the "_Sextant Manual" for the original sextant gauge. It can be found in the "Flight Simulator 9\Aircraft" folder.

1.Since this is only a "chart" manual, please use your normal procedure for preflight planning. Look at the picture below

The large red square depicts the new "chart" area. The small red circle surrounds and identifies the very small green circle that you will use to "locate" the fix on the chart. The Blue boundary is a "hot button" that will toggle an enlarged view of the chart, for more accurate adjustments.

Select the date, time, latitude, and longitude for the first position fix, and determine the elevations and azimuths to the three stars to be used to make the fix.

2. From pre-flight planning, or determination while in flight, when the time to make the fix approaches, enter the assumed latitude and longitude for the fix on the sextant workpad. For optimum results, the order in which the three stars is shot is important. First, the course line, next the check line, and finally, on the fix time, the speed line. This minimizes the error due to non-simultaneous shots. Said another way, the course line shot is of a star nearest the 3 or 9 o'clock direction (out the right or left cockpit window). The speed line is of a star near 12 o'clock, (or 6, if you have an astrodome). The check line is of a star near midway between the speed and course line directions. Usually you can start 5 minutes before hand and get the three one minute shots in. If you are running late, do the speed line on time, and the others later, but recognize that your position will be a few minutes "stale".

3. Look at the picture below

I have circled in red the "Distance N. miles" area, and the "star-1" area is circled in green. At the end of each shot, the distance in miles will show in the red circled area, and by clicking on the "star-1" area circled in green, the Blue line of position will appear on the chart in the proper place. Likewise for stars 2 (green line) and 3 (red line). Clicking the "star" area transfers the distance value to the chart, so it only works properly when the sextant is displaying that distance. (e.g. before it is reset for the following star shot) At 5 minutes before the fix time, enter the azimuth and elevation of star-1 (the course line star) and start the shot. When the first one minute sextant shot is complete, with the miles to advance/retard the "line of position" (LOP) showing in the sextant notebook window under the "DISTANCE N. MILES" label, click on the "star-1" hot-button at the top of the "chart" gauge, and the LOP will be drawn on screen. It will be at an angle normal to the direction to the star azimuth, and it will be offset from the assumed position (the center of the chart) by the distance circled in red. (Negative distances are "away" from the star). Change the azimuth and elevation for the second star. Take the second sextant shot, and again, when the miles data shows under the "DISTANCE N. MILES" label, click on the "star-2" hot-button on the "chart" gauge, and that star's LOP will be drawn on screen. Likewise shoot the third star and click "star-3". The center of the resulting cocked hat will be the measured aircraft position. If the size of the cocked hat is larger than the green circle, you have probably made a mistake somewhere.
There are green arrow hot buttons near the left and bottom edges of the chart that will move the green circle up/down or left/right. Move the green circle from the center position left to the position as shown on the picture below.

The display will now show the fix latitude/longitude ( 47° 25' and -122° -2') instead of the assumed position, which is still showing on the Sextant notepad. It is important to set the latitude first, since the longitude scale depends on the latitude. Note the "NM" in the bottom left that is circled in red. This hot button toggles the display at the top of the chart, also marked in red. The display gives the distance from the center of the chart (the assumed position) to the green circle (the fix), and the true (not magnetic) direction from the assumed position to the green circle.

4. The plot is now finished, and after the sextant user records the fix position (latitude and longitude), the chart can be cleared and readied for the next set of shots by toggling "NM", the three "star" hot-buttons, and using the green arrows.

5. Although not elegant, the chart may also be used to plot a course to the fix, as follows:

a. Set the assumed position on the sextant worksheet (It may already be set there).
b. Move the green circle to the current fix position. Clicking on the NM letters in the bottom left corner makes visable now at the top of the chart the true reverse course and distance from the fix to the assumed position. (If it isn't appropriate to fly to that assumed position (e.g. if the course change would be more than 20°), crank in the next assumed position along the route into the sextant notepad, and fly toward it, using the reverse course and distance now showing at the top of the chart.

6. To prepare for the next fix, set the next assumed latitude and longitude in the sextant, and "zeroize" the position of the green circle.

Acknowledgements:

This chart gauge is the result of hard work by many DC-3 Airways people. Guy Goddard and Mark Hilliard for providing the inspiration and motivation to do this addon gauge, Jim Daigneau for technical advice, expertise, problem solving and support, Norman Hancock for the beautiful graphic, and Jim Daigneau, Allan Greene, Norman Hancock, and Charles Wood for Beta Testing or documentation editing.

Thank you for your interest in this gauge. For a detailed worked example flight, see the accompanying file Sextant Chart Example. Send comments/suggestions to bitzer7@comcast.net or MABeaumont@aol.com

Dave Bitzer
Mark Beaumont
March 2008