Celestial Nav and Dead Reckoning Across the Ocean to a Tiny Atoll...

Hello,

I recently got curious about celestial navigation, and that led me to the very cool sextant guage that was created for FS9 (I think) and ported over to FSX by Kronzky. Since this forum is where I've found the majority of discussion about this guage and the techniques of navigating with it, I thought I'd post a summary of my first long flight using it (Ford Island NAS to Johnston Atoll, the sample flight suggested in the sextant documentation). I'm a RW pilot but haven't done any serious dead reckoning in a real long time, so that was fun in itself.

I used the vintage cockpit reworking of Jahn's C-47 (v3.12), and used compass, sextant and dead reckoning only. No radio aids (though there is an NDB charted on Johnston, don't know if it exists in FSX), and certainly no GPS or shift-Z for position or wind data. I used Google Earth to plot on, and a combination of skyvector and ASN's flight planner to put the the dead reckoning together. U.S. Naval Observatory for assumed position celestial data (Sun only, this was a daytime flight).

It's roughly 710nm to Johnston Atoll from Ford Island in Honolulu. Using the 10 to 1 rule of dead reckoning, we figure our maximum likely dead reckoning error at the end of the trip is 71 miles. It could theoretically be in either direction, so we intentionally offset our course so we know for sure which way to turn to find the atoll. We therefore offset our course to arrive 71 miles NNW of Johnston Atoll at 0230z, having already noted in the celestial data that the Line Of Position from the sun that passes through Johnston Atoll at that time is running 341-161 degrees. We therefore plan to arrive at that point 71 miles NNW of Johnston at the proper time to intercept that LOP, so we can turn SSE and keep taking sun shots if necessary to follow that LOP to the atoll.

The completed "chart" after the flight, done in Google Earth, showing the planned course offset to the north: (Click to enlarge for easier reading.)

Steps taken to complete the flight:

1. Departed Ford Island at 22:27z on 10/05/16 (date simply chosen because there wasn't much weather on route then).

2. Coast-out of Oahu a few minutes later.

3. Geez, we've been offshore less than an hour and it's already feeling very lonely out here...

4. First shot on the sun at 23:38z.

The LOP passes through our assumed position (as seen on the Google Earth map above). We don't know how far left or right of course we might be, but the speed line verifies we're the proper distance from Oahu as calculated by dead reckoning, so our planned ground speed is validating. Press on.

(Result of 1st sun shot, showing a zero nm distance to the sun deviation from our Assumed Position.)

5. Second sun shot at 00:38z, for another speed line:

Results of this one indicate we're 5nm further west than planned. Possibly a little better groundspeed than planned, or possibly slop in the sextant reading. I chose not to correct for it yet, and see how the next shot looks in an hour.

6. Third sun shot at 01:38, for another speed line:

This line indicated 0nm error from assumed position again, so I left the groundspeed and ETA to destination alone.

7. Took another sun shot at 02:08z, to verify position 30 minutes out from intercepting our LOP to the Atoll. Distance checked good, although we're starting to see some clouds. Wondering if I'm going to have to climb to get the most critical shot of all in 30 minutes, the one that tells us when to turn SSE onto the LOP.

8. Uh Oh... approaching LOP intercept, it's getting thicker:

9. LOP intercept! Only 45 seconds early, well within the margin of error of the sextant (or at least, me using it). Took a couple tries but I got lucky with a break in the clouds. Turned left to a magnetic heading of 149 degrees to run down the LOP. (And got busy enough that I forgot to get a pic of the 2nd biggest moment of the flight, lol.)

Continued below, attachment limit reached.

Great Post!! Takes me back a whole lot of years!! As of when GPS and LORAN weren't available. :cool::cool:

Michael

Sorry, since I'm new here I had to have the post approved by an admin before I could post a comment with the conclusion:

10. And THE biggest moment of the flight - Land Ho!

(Unfortunately I couldn't find any good scenery for this little atoll, so it's default.)

11. Took one more sun shot just to prove I (hopefully) understand what I'm doing - It shows us right on our LOP we were intending to run to the island (a positive distance deviation would have indicated we were right of the LOP, and a negative distance deviation would have indicated we were left of LOP.

12. Arrival, 4 minutes late. Lonely place.

So, for anyone more knowledgeable than me, what do ya think: do I understand this stuff correctly, or did I just get lucky? ;)

This really was a lot of fun. I'm thinking of continuing the pacific adventure - right now I'm leaning toward a 1400nm run down to Christmas Island, and I think I'll do it mostly at night with an arrival an hour after sunrise... that way I can take LOPs off multiple stars for most of the night and be able to fix my position more exactly. This is twice as long of a flight, after all...

And after that? Maybe down to the Marquesas islands, then west through French Polynesia / Tahiti, the Cooks, Fiji, American Somoa... lots to explore, and good scenery available for most of those places. (I'm sure I'll lose motivation long before finishing all that, but it's fun to think of possibilities).

Seriously, again I want to thank Dave Bitzer, Mark Beaumont, and Kris Ogonowski (Kronzky) for developing (and documenting) this guage. It's a small part of an overall simulation but it really opens up new challenges. Thanks guys!

Yes great post like Rupert said, so perhaps you'd like to copy it into the 'How do you keep FSX interesting' sticky thread so that it won't scroll away and get lost?..:)

THREAD- https://www.flightsim.com/vbfs/showthread.php?248567-How-do-you-keep-FSX-interesting&

Here are some 'navigation-type' posts from it that might interest you-

p2- Photoreal cross-country.

p5- Earhart's last flight.

p8- Dole air race, California to Hawaii

p25- Flight 19 final flight route.

p33-Sextant navigation.

p34- Kingsford Smith trans-Pacific flight.

p35- DME flying.

PS- here's the thread's full index-

https://www.flightsim.com/vbfs/showthread.php?248567-How-do-you-keep-FSX-interesting/page42