Air Navigation

[JDavHouston]

“As you probably know, the nautical almanacs stop publishing the lunar tables back in the 1910’s”

I didn’t know that, as I’d only looked at the air almanacs. I’m planning in the near future to get checked out in a Seneca and start flying with friends from the Houston area over to Miama/Tampa/Key West (all celestial, is the idea, with them flying and me in the back seat navigating to see how I do!)

“In this book, the author states that the natural horizon, whenever it is visible, is much preferred to the bubble horizon; and apparently, even the maritime sextant using the two pots of reflective liquid placed on the ground–are preferred to the bubble-octant / sextant’s horizon which is the least preferred method for land navigation.”

Having messed with it, I can explain that one now.

As one looks down into the instrument, one has to ‘judge’ when the center of the bubble and the star are properly aligned, and even small motions of the hand send it all over the place. In a plane, this is the best one can hope to get, but it is easily the worst way to try to do it! Any other method of a horizon will easily be superior.

[manxcat]

To: JDavHuston From manxcat,
Regarding ‘Air Almanacs– Don’t they have computerized versions of air and maritime almanacs that are good for decades if not hundreds of years? Forever???
Regarding your explanation for bubbles not being the best alternative: You’ve explained all this to me once before–but it didn’t stick with me the first time around! I got the information in my previous post from the interesting book I mentioned; however, I didn’t mention another part of that same book, which seems to back-up your comment–‘You should have a tripod or other very stable support for all your navigational instruments’.

—Joseph

[mcaminos]

Hi Joseph, there are a couple of software to do sight reductions that have the nautical almanac until 2050 or even 2100. If you want the current copies of both the nautical and air almanacs, go to http://www.thenauticalalmanac.com and download them from there.

[manxcat]

To: Mcaminos From manxcat
Thanks for the heads up… I thought these long range tables were available.

[JDavHouston]

I’m sure y’all will be amused to know, I managed to get the bubble sextant calibrated. It took a lot of finagling and messing with lasers and spending a good chunk of time squinting at Polaris with a camera tripod from the 60s, but I managed to get it done~

[JDavHouston]

Tested out the calibration. Got a position within three miles of my actual location.

Now to try the thing in the air!

[manxcat]

To JDavHuston from manxcat,
Good Job… right-on!
–Joseph

[JDavHouston]

Thanks!

[kollsmanUser]

Hi – I’m coming to this discussion late so sorry for any rehashing of old data.

I regularly use a Kollsman periscopic sextant mounted to a tripod using a custom 3D printed base. I normally use the Polhemus computer to figure MOB (with MOO of 0 since I’m not in a fancy flying machine) to do the running fix or normal nautical reduction methods using Pub229. For fun, I do use the 2-minute averager and I do precomputed timed sights.

With the greater accuracy of Pub229 reductions, my 3-star fixes usually give a very small position triangle with a fix error in the 0.5-1nm range.

I like that I can take a shot on anything I can see at any time of day I am able to get out. I live in a forest so my sight lines are frequently obscured by trees, but I can see enough sky to get stars spread out enough to get good fixes.

[manxcat]

To: Kollsman…
I’ve posted to this board a few times. My interest in bubble sextants / octants is related to the failed Amelia Earhart flight of 1937. I’ve done research to better understand the problems encountered in that flight.
I have read that the routine of celestial navigation at sea is to obtain a fix, on at least four celestial bodies at the brake of dawn. Then again at around brunch, then at high noon, and lastly near sunset. My question is how this routine differs with an instrument containing an artificial horizon? Are you able to obtain usable fixes at all hours of the night? A bubble sextant / or octant is very limited in the range of body altitudes that you can obtain?

[kollsmanUser]

Manx – a few responses to your questions.

I believe it has already been mentioned in the thread, but Gary LaPook’s excellent website (https://sites.google.com/site/fredienoonan/home) has quite a lot of information on Noonan’s navigation.

It is fairly common in nautical practice to take a 3-star fix at morning and evening twilight. Stars/planets would be chosen at, ideally, 120deg apart in bearing to give a set of Lines of Position. On a boat or ship, running fix methods are then used to advance the LOPs to obtain a fix Between the twilights, it is usually only single body shots on the Sun, tho occasionally Moon shots can be mixed in. Sun shots can be taken at any time it is visible – a noon shot is often taken to determine local noon.

A nautical sextant needs a well-defined horizon to measure from which implies there must be enough light to see it. An aviation bubble sextant uses the bubble to level the instrument so sights can be taken at any time of day on any object the operator can see. If I remember correctly, the A-7 octant Noonan was likely using has a 2x optic – in clear air, even relatively dim stars can still be seen. In daytime, the bubble is easy to see – in the dark, the bubble needs some sort of illumination. In the early aviation instruments, the illumination was by something quite simple: Radium paint or a battery pack wired to a small rheostat controlling the brightness of a lightbulb – later, when access to aircraft electricity was easy to come by, light bulbs were driven by the aircraft electrical system via cable.

Why does an aviation sextant only have a 2x optic? Partly because an airplane can be a wobbly thing to take shots from – having the wider field of view helps find the body and then keep it in view. Remember, in a periscopic sextant, the only view the navigator has of the outside world is the view thru the instrument – tho the Veeder/Root counter and good preparation helps a great deal.

The air navigator has a couple of challenges taking the shot – the first is, as mentioned, the aircraft is not still. There’s plenty of things moving an aircraft around – vibration from the engines, Dutch roll, people moving about.

The second challenge is that the navigator has to move from window to window while holding a heavy octant. Unless the aircraft has a dome, sometimes aircraft structure (eg: wings, window framing) gets in the way. Sometimes the star is too high to be seen from behind a standard vertical window.

Noonan was a very good navigator. He’d pre-compute his star altitudes and bearings and plan the shot well ahead of time. He also, if I remember correctly, would only take 2-body shots rather than 3.

Taking a 2-body shot is fine. Planning ahead, the navigator would select two stars that are about 90deg different in bearing rather than the 3-body shots and 120deg separation.

Even so, the air navigator of the time would draw a circle around the fix – the size of the circle depends on a number of factors. The error in the fix is why Noonan likely did not aim directly at Howland Island – there is a landfall procedure used at the time where you would deliberately aim left or right of the island destination and then then definitively turn towards the island at the right time.

The good thing about a 2-body and a 3-body shot is that it gives a definite fix. However, once the stars go to bed, the Sun becomes the primary navigation source and because you can only get 1 LOP from the Sun, your fix becomes the Sun line coupled with your estimated ground track. The estimated ground track can be significantly different from your actual track so unless you can get a shot of the Moon at a good angle to the Sun, your daylight celestial fixes are estimates that are only as good as your dead reckoning skills.

To answer your question more directly – yes, 3-body fixes can be shot all night long. It is one reason, I believe, that Noonan planned the flight so that they would arrive at Howland Island near sunrise after a long passage at night – he would be able to take fixes all night (perhaps at 1 hour intervals) so that, in the critical final approach to Howland, he’d minimize the run during daylight when they’d lose the crossing LOP to give a definitive fix.

[manxcat]

To: kollsmanUser
Thank you for your excellent explanations! As for Gary LaPook’s website: I believe that I was the one who first posted it to this message board. I asked a question regarding LaPook’s analysis of Noonan’s 1937 World Flight navigation that wasn’t answered on the message board. It regards Noonan’s navigation from Natal, Brazil to Dakar, Africa… which actually ended up at Port St. Louis, Africa instead.
LaPook seemed to harshly criticize Noonan’s supposed navigational ‘error’, which resulted in missing Dakar by around one hundred miles. Despite the fact that LaPook’s work proved that the change in destination was a command decision, to an alternate airport, presumably because of bad weather around Dakar. LaPook mentioned something about Noonan flying too far east if he intended to route to St Louis. Also, Earhart, supposedly wrote in one of her books that she refused a new course given to her by Noonan, which she apparently thought would have been the best course had she taken it. However, LaPook said that if she had followed that course… she and Noonan would’ve likely been lost in the jungle, rather than at sea.
My question is why was LaPook so hard on Noonan? He seemed to be saying that Noonan’s navigation was the probable cause of their missing Howland Island.
The sub-heading of this article is “Navigation to Dakar” on the fredienoonan web-site. If you have the time to look at this section, I would be interested in hearing your thoughts.
Thanks & Have a Nice Day,
–Joseph

[kollsmanUser]

I did not recall GL criticizing Noonan’s Dakar planning so I went back and re-read it. I still do not see anything in there critical of Noonan’s methods. GL goes so far as to say that the Dakar planning was used as an example in AFM 51-40. He does have some fairly harsh words for AE who was not a navigator but none for Noonan.

Perhaps you are referring to GLs text regarding the shift in destination to St. Louis, Senegal, with there being few notes on the chart? That sounds to me like it was a case of changing the destination on the fly based on decisions that were made based on requirements that we do not know about. It does sound very much like they hit the African coast fairly closely to where Noonan expected them to.

Looking at Noonan’s planning and in-flight execution, it seemed to follow a lot of best practices of the time.

GL’s comment about “But from this point Noonan’s navigation becomes strange” does not appear to be a reference to Noonan suddenly getting sloppy but, rather, lack of notation on the chart that the destination changed.

I’m guessing here but I know that GL carries Noonan in high esteem.

[manxcat]

To Kollsman,
I’ve copied the last two paragraphs of LaPook’s “, Navigation to Dakar below:
“But what if they had unusual winds or the plane flew at a different speed than planned or Earhart
didn’t stay on the correct heading? Well all those things were taken into account when figuring
the band of uncertainty so none of those things change the conclusion that there was less than one
chance in a million that they hit the coast like Earhart said they did based on a review of
Noonan’s chart work.
If the math isn’t convincing then lets look at it with just common sense. Noonan had just missed
his landfall on the continent of Africa by more than two hundred miles and now Earhart was
going to have him navigate her to a one mile long island in the middle of the Pacific. As my kid
would say, “I don’t think so!”
The first Amelia Earhart Commemorative World Flight was successfully completed in 1967 by Pilot Ann Pellegreno. A Lockheed Electra was rebuilt to match Earharts, except that the smaller Wasp Junior engines were used in 1967 flight. The plane work was performed by Lee Koepke, who went along on the World Flight. Pellegreno’s entire crew were top experts in their fields with navigator William L. Polhemous being probably the best. He was the founder and president of Polhemous Navigation services back in 1967. He performed periscopic sextant sightings every half hour along with wind directons and speed throughout the night before arriving at Howland the following morning. After the Commemorative flight he became president of the Institute of Navigation for several years. I have a copy of his Amelia Earhart report to the I.O.N., which is hard to get. If you’re interested in it I can send it to you, but it will have to be in hard-copy form via the snail-mail. We would have to exchange regular Email addresses to make this work.
Of course, I am interested in your opinions regarding the LaPook paragraphs above and the Polhemous Report it you decide to review it.
Joseph
manxcat2@sbcglobal.net

[kollsmanUser]

I read those two paragraphs very differently – I see them as them being critical of AE and supportive of Noonan.

“…so none of those things change the conclusion that there was less than one
chance in a million that they hit the coast like Earhart said they did based on a review of
Noonan’s chart work.”

This passage says that AE’s statement was wrong as it does not match the data that was on Noonan’s chart.

‘If the math isn’t convincing then lets look at it with just common sense. Noonan had just missed
his landfall on the continent of Africa by more than two hundred miles and now Earhart was
going to have him navigate her to a one mile long island in the middle of the Pacific. As my kid
would say, “I don’t think so!”’

Again, this passage is supportive of Noonan. Read it this way: “If Noonan had navigated to Africa and missed by more than 200 miles common sense says that AE would not have confidence in his abilities so would not keep Noonan as her navigator to hit a 1 mile long island in the middle of the Pacific. It is unlikely that she would have kept him if he was that bad a navigator.”

[Author]

Posts