Air Navigation

[manxcat]

To kollsman
I agree with you…when somebody writes in a sarcastic vein–it’s often easy to misunderstand the meaning. Thanks for your clear-headed explanation.

Thanks again & Have a Nice Day,
–Joseph

[manxcat]

To kollsman,
I agree with you. When somebody writes in a sarcastic vein like LaPook did… it’s often easy to misunderstand the meaning. Thanks for your clear-headed explanation.

Thanks Again & Have a Nice Day,
–Josepht

[kollsmanUser]

Glad to help.

GL is a plain-spoken guy – I’ve interacted with him a few times and I have always come away wiser.

[kollsmanUser]

BTW, I forgot to reply to your comments about Bill Polhemus. Yes, he was a very skilled navigator. I recall he flew in the pit on B-58s and possibly B-52s.

I am a big fan of his Polhemus Celestial Computer for Air Navigation. I use one regularly, along with a current-epoch Pub249v1 for timed 3-body shots. I get very good accuracy using it.

I do not recall seeing his paper on the recreated flight – I’d be interested in seeing it but have no time to do so, so save your stamps! 😉

[manxcat]

To: kollsman,
I am envious of your personal communications with Gary LaPook, I tried to track him down on the Internet for a few weeks, some years ago, but had no luck. I got as far as the http://www.stratusproject.com/, which is a donation site for an Earhart Plane sonar search group. Gary LaPook is shown as being on staff at Stratus Project. I have a picture of LaPook standing in front of the Titanic’s graving dry dock, holding his bubble octant.
I was much luckier in tracking down Ann Pellegreno; and have exchanged Email with her a number of times. She must be in her 90s by now. She lost her long time husband when he crashed one of their private planes very near their home in Texas in recent decades. She has never volunteered information to me, rather, she has made some short answers to my direct questions. For example: when I mentioned to her what I had read about the Polhemous Computer, her one word answer was that it was “GENIUS”. And when I asked about takeoffs and landings on Howland Island, she answered that she thought that she would have probably been able to land on a runway at Howland (but she wouldn’t have “liked” it) Then, she added that taking off from Howland would’ve been dangerous, especially if there were a lot of birds roosting on the island—because the birds would’ve been taking-off at the same time the plane was. I was proud of the fact that I was able to inform her of a few interesting things that she didn’t know about Earhart’s World Flight.
Regarding the Polhemous Report: My offer will always open.
Thanks Again & Have a Nice Day,
—Joseph

[Steven Carleton]

The dancing bubble issue can be mostly mitigated on land by either hanging the sextant from a branch using a taut-line hitch, or by setting it atop a relatively level rock, ledge, or stump. I’ve gotten with a few miles using an A-10 or a Mark IX this way, even without an averager.

[RWJ76]

As long as you can see your bubble and the celestial body you’re good to go, day or night. I use a professional bubble attachment on my marine sextant to take sights from my back porch. I reduce my sights from a GPS position using a non-programmable trig. calculator as it gives me instant feedback on the accuracy of my sight (intercept should be 0.0 with no plotting required). For a single observation, I can count on my LOP being within 10 NM. If I take the average of 5 sights I can count on a sub 5NM accuracy. This degree of accuracy is usually acceptable in aircraft celestial navigation.

[manxcat]

To: RJW76
So, the aeronautical Almanac’s formulas are totally different than the maritime Almanac’s–do to the fact that you’re taking sightings at all hours of the day?

[manxcat]

To: Steven
I have a classic book on the subject of celestial navigation when on land and the author uses a sturdy surveyors tripod to steady the horizon bubble… but you would need a pack-mule to lug it into the mountains.

[kollsmanUser]

No, the Air Almanac and Nautical Alamanac are optimized for different things but they contain very much the same information. The Air Almanac is optimized to speed up the calculations required to reduce a sight – in particular, determining the GHA of the object that was sighted.

The NA lists GHA for objects on the hour. But what if the shot was taken at 14 minutes and 37 seconds after the hour? To compute the correct GHA, the navigator has to read an extra table to account for the minutes and seconds after the hour to then calculate the GHA.

What the AA does is list GHA for objects at 10 minute intervals. This means that the navigator has fewer calculations to do. On the other hand, to use the AA in this way, the navigator has to time the sight so that it falls on the selected time. (The AA does contain the same tables to convert time to GHA for use in a pinch, but why do it if you don’t have to?)

If you look at the NA and the AA on the same day and the top of each hour, you will see that the entries are the same.

So using the AA means that the air navigator does the precalculations ahead of time for a shot at a specific time rather than the nautical practice of taking the shot whenever and then reducing using the recorded time of the sight – notice that the order between shooting and reducing is reversed between the two methods.

As an example, in practice, I might plan to shoot fixes at 1 hour intervals, and let’s say it’s dark and I choose to do 3-star fixes. I would look at my plan and perhaps say that the time is 1430Z and I want to plan a shot for 1450Z. I would then look at the AA for the day and find 1450 and record GHA-Aries. At this point, I can then work out my assumed longitude at time 1450 and use that to compute LHA-Aries. LHA-Aries then becomes an input to Pub249V1 where I can pull out 3 candidate stars. After a bit of simple math, I can then set up my sextant. Say I am doing 2 minute shots (averager), I would start the first star at 1441Z, the second at 1445Z, and the last at 1449Z which result in shots centered at 1442Z (+8 minutes), 1446 (+4 minutes), and 1450 (+0 minutes) – these nice integer numbers make MOO and MOB calculations a snap.

The whole air navigation process is aimed at generating a fix very quickly so that many fixes can be done in the course of the flight. Aircraft move fast and running out of gas is catastrophic.

[manxcat]

To: kollsmanUser,
I had to look up a few Celnav videos to read your post, but I’ve basically got it! (very informative) An immediate question I have for aeronautical navigation is: What if your plan planned shots consistently can’t be obtained at the times you’ve assigned for them? (as due to weather et cetera)

[kollsmanUser]

If the shot can’t be done at the pre-planned time, what one would do depends on a few things.

Let’s say one of the star shots was delayed by 1 minute due to something simple like sextant or mount issues. If using MOO and MOB, the multiplier is the number of minutes before or after the fix time. So, let’s say we delayed the first shot by 1 minute – so instead of multiplying the MOO+MOB corrections by +8, we would multiply by +7. We are, in effect, advancing the LOP by slightly less than was originally planned.

Note that the multiplier changes to negative if the shot occurs *after* the fix time.

This works, of course, for non-integer minutes – say instead we delayed the first shot by 30 seconds: then the multiplier would be +7.5

This change to the multiplier can be handled very quickly once the Nav gets back to his station.

I’m not sure what duration you imply by “consistently can’t be obtained” – if the sky is obscured and you can’t climb above it, your dead reckoning skills will have to do. You can bet that the crew will be looking for stars out the windows and if one appears they will get the Nav on it quickly and then take a shot at the fleeting target. On something as unstable as an aircraft, the averager will get better results, but if all the Nav has is a fleeting view, he/she will be prepared to take a snapshot and record the time. He may not even know what star it was, but from the Veeder-Root counter (bearing), recorded altitude, and a 2102-D star finder more likely than not he will be able to figure it out. The reduction would then follow nautical practice.

[manxcat]

To: kollsmanUser,
Regarding your post’s last paragraph: I have read that there is a section in the Almanacs that gives coordinates for many celestial bodies that aren’t used for navigation purposes. So possibly, anything you can get a fix on can be used for your naviation–Joseph

[kollsmanUser]

Correct – there is a table of secondary stars with SHA and declination given. It is helpful if, say, you accidentally shoot Castor instead of Pollux.

[manxcat]

To: KollsmanUser
I try to encourage everybody posting on this site regarding aerial celestial navigation done the old fashioned, hard way, with a handheld bubble device… without computers and advanced technologies. This must really be a rapidly vanishing art… followed closely by the few sailors who perform professional level celestial with sextants at sea. So, keep up the good work KollsmanUser!

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