Dead reckoning / celestial nav - 1200nm of open Pacific

[speedy70]

The tutorial on the sextant is fine but the sextant used in aviation is a bubble sextant which is different to the one in the video, which is a marine one.

The reason being that the sextant has to be level to take a sight and therefore on an aircraft it has a type of spirit level to check that it is level.Hence the name "bubble" sextant.

I sold my sextant when GPS came in and it is now hanging on a pub wall where some of people say" whats that",others don't care.

Cheers Chris

[Hobart Escin]

Now, how this actual gauge works? I'm speculating here, but this is my guess: after you enter your assumed position and azimuth (compass direction) of the shot, the gauge calculates the difference in miles between the LOP (at 90 degree to the azimuth) you're ACTUALLY on from the LOP your assumed position is on. It calculates the difference in miles, rounded to the nearest 5. It forces you to attempt to line up a dancing sun or star in a dancing bubble - just like in reality. The worse your shot is (averaged over 1 minute) the more it factors error into that distance, and it displays that distance as a result at the end.

In reality, error can enter this process in many stages, several of which you don't actually have to perform using the gauge (averaging and interpolation using tables, for instance). The gauge simulates that by forcing you to round your assumed position to the nearest 5 minutes of lat/lon. The final result achieves a real-world level of (in)accuracy. It's all pretty brilliant, I think!

BTW, the gauge doesn't actually know anything about the position of any heavenly body. You can take a shot at any azimuth, at any time of day, and it'll return a result. It also doesn't care what expected elevation you enter (but you're still smart to enter one because the comparison of expected to measured elevation helps you understand the results).

So for practice purposes, you don't need to worry about looking up the almanac. You can shoot any azimuth you wish. When trying to simulate a real flight, I personally look up the almanac and only use what would really be available in the sky.
http://aa.usno.navy.mil/data/docs/celnavtable.php

Just for fun, I use the free AutoStar X utility that gives you an accurate (and much prettier) night sky in the sim. It's fun when you can actually identify the star you're "shooting" .

P3D - I don't know. I thought I saw somewhere that someone tried it and it worked. Worth a shot!

Stearman, you've got me hooked on trying this now, lol. I will give it a shot in P3D and see what happens. This is just too much fun to pass up, and I'm not entirely convinced a sextant isn't ultimately easier to use than some of these newer GPS units. Hey, for one thing we don't have to worry about RNP approaches.

Excellent explanation of the entire process though, and what a way to relive history and add a finishing touch of realism to Constellation simulation. No FMC, no GPS, no IRS, and only yourself to rely on over the vast, open ocean. I feel like singing The High and Mighty about right now. Wait! PHNL to KSFO, just like John Wayne and Robert Stack (except in a Lockheed bird this time)??? Hello, fun times ahead. Thanks again for your awesome post and very detailed explanations!

[youtube]http://www.youtube.com/watch?v=DJb5rizD6ao[/youtube]

[AviatorMoser]

Thanks for the clarification! Probably gonna try this on a Lisbon - Santa Maria training flight.

[BendyFlyer]

Stearman[/quote]So this was a great time. I sometimes feel silly for putting in the time I do with flight sim, probably especially because I fly for a living... but you know, it's stuff like this that makes me feel foolish for that. I don't think there's any reason to feel silly for gaining a greater respect for and understanding of our history by attempting to experience it to the best of our abilities. And I'm continually blown away by just how GOOD all this is! The whole FSX world, the physics that mean dead reckoning actually WORKS, and of course the extras like the sextant guage and the beautiful Connie. This... is pretty good stuff!

If anyone made it all the way through that novel, thanks for reading .[/quote]

I could not agree more, I spent a lot of my life with an aeroplane strapped to my backside but your are spot on about flight simulation, especially where its at now. I have spent my dotage exploring aviation history and thanks to sim being able get an idea what it was like to fly and operate aeroplanes that are long gone or now museum pieces which includes a lot of the early turbine equipment that was being retired before I was given the chance to fly for a living. I had thought the sextant gauge would not work in FSX but now it does there is going to be a lot of long distance flights done because GPS makes you mentally lazy and takes away your involvement and learning of the craft and art of navigation.

Thanks for a really good story and rundown on this now neglected navigation technique and in a superb simulator model to do it with. I guess the navigator just got fired.

[Stearmandriver]

Glad to see I'm not the only one who enjoys this stuff; there was more response than I expected, both here and at SOH. I think maybe I WILL try to make a little video tutorial, since there doesn't seem to be anything out there dealing with this gauge (or bubble sextants in aircraft in general). It'd be fun to see more people trying this kind of thing, maybe even a multiplayer event of some sort.

Those of you that have threatened to give this a try, don't forget to share your stories with us!

[TreeTops]

I would encourage you to make a tutorial. We have some great aircraft for flying many hours over water. The South Pacific is a great playground for the Connie and Stratocruiser. Having something like this would be awesome.
12 months ago when I did a tour of the South Pacific in the Guppy, starting at Brisbane working out to Tahiti, I was tempted to carry on to Pitcairn Island and then South America. The thought of an 8 hour flight and not finding a runway was a little too worrying for me. Having something like this program would make these sort of flights possible.
Logging engine conditions and fluid levels every half hour plus figuring out where the plane is in between makes for a busy flight.
Trev

[Cool]

Very very interesting
I will give it a try ASAP
Many thanks for sharing this "new way" of navigation
Pascal

[Paul K]

Hello all,

Since you seem to like classic airplanes here, I thought you might enjoy hearing about a recent flight I completed in the Connie.

Absolutely, Stearmandriver; what a great opening post. Informative, entertaining and very well illustrated with screenshots. I've really enjoyed reading your experiences and advice. I started learning the bubble sextant gauge in FS9 with Plane Design's Avro Lancastrian but it was always over land, where I could double check by looking out of the cockpit window. I never had the gumption to attempt a long over-water stretch as you have done.

I don't know about you, but I've always favoured 'old school' navigation over GPS, and I think there's quite a number of us of the same mind. Of course, it depends on the aircraft you're flying at the time - you're not going to reach for the chart, dividers and drift sliderule while in the PMDG 737NGX. With something like the Constellation, Stratocruiser or B-17 however, I think it becomes as important a part of the immersion as Accusim itself. I've started planning a 'themed' round-the-world trip for later in the year, and maybe with the combination of radio nav aids, Wothan's weather ship guage, and the Bitzer & Beaumont bubble sextant, I can eschew GPS altogether.

Once again - great thread. Thank you.