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Author Topic: Navigating the LOP with the offset method.  (Read 195642 times)

h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #225 on: June 16, 2011, 02:21:01 AM »

Nonsense , if you preset 31´ and you are not @ 1,000 feet the local horizon line does not match the instrument´s horizon mirror line , and you must ascend / descend .

Except that there is no such thing as the "instrument´s horizon mirror line" so you have nothing to compare with the local horizon (the visible sea horizon.) Mr. van Asten, have you never looked through a marine sextant?

That is the purpose of the bubble in the bubble sextant, to provide a level reference independent of the sea horizon and marine sextants do not have such a reference. Find someone who has a marine sextant and take a look through it.

gl

Instrument horizon mirror line is the horizon as reflected in the field of vision , coming from the variable inclination reflector.
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #226 on: June 16, 2011, 02:30:58 AM »

“Most people believe that they were down at 1000 feet when they thought they were near the
island and at that point (and not before) they had been compelled to descend below a low cloud
layer in order to search for Howland. “

I believe that the 1912 GMT transmission gives their altitude as 1000 feet.  No motive is given in the transmission for the descent. 

The splendid article, "Log Jam," records this as 07:42 a.m. Itasca time.

Previous altitude reports were all from early in the flight: 7000, 10000, 8000.

In Log Jam we read that @ 1912 the fuel reserves were for 1/2 hour and @ 2013 they amounted to 150  gallons (?)
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #227 on: June 16, 2011, 03:22:37 AM »

You don't have to, I'm done.

I first communicated with Mr. van Asten after I read his two articles that are just full errors. I was making a friendly effort to help him understand how this navigation really works.  I think that it is obvious to everyone that he is not interested in learning anything. He always goes back to his 0719:30 observation, the one that lead to the position report that was received in Lae one  minute and a half prior to that observation! I was always taught that time goes in only one direction, from earlier to later. Apparently in Mr. van Asten's parallel universe time can run in the opposite direction.  Don't try to confuse him with the facts.

So, I give up, he will have to carry on without my help.

I appreciate your efforts very much, Gary.  Thanks!

All representative sources , the Hooven report included , let know that the position tranmission 159-07-E  ; 04-33.5-S was received 0720 GMT @ Lae ; some sources mention "0520 p.m." , evidently local time congruent with 0720 GMT .
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Martin X. Moleski, SJ

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Re: Navigating the LOP with the offset method.
« Reply #228 on: June 16, 2011, 09:42:13 AM »

... Hopefully my long explanations have served to demystify the process for other readers of these posts so that they can see now that it isn't voodoo or even rocket science. It has some complications but it is a rational process when you see how it all works.

You've helped me a lot.

Celestial navigation is awesome.  It is an example of "standing on the shoulders of giants."  Our amazing GPS units use the same kind of spatial logic along with the added precision that comes from astonishingly accurate clocks and clever databases.   What a great achievement!
LTM,

           Marty
           TIGHAR #2359A
 
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Gary LaPook

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Re: Navigating the LOP with the offset method.
« Reply #229 on: June 16, 2011, 11:19:05 AM »

... Hopefully my long explanations have served to demystify the process for other readers of these posts so that they can see now that it isn't voodoo or even rocket science. It has some complications but it is a rational process when you see how it all works.

You've helped me a lot.

Celestial navigation is awesome.  It is an example of "standing on the shoulders of giants."  Our amazing GPS units use the same kind of spatial logic along with the added precision that comes from astonishingly accurate clocks and clever databases.   What a great achievement!

----------------------

Thanks for that.

gl
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #230 on: June 16, 2011, 12:51:52 PM »

You may safely assume that in the course of 23 years I have consulted all representative flght manuals . When commencing the 055 T offset @ 1815 for the correct longitude sun´s altitude  was 04-26 , at the end @ 1859 it was 21-00 . On the erroneous offset the respective elevations were 04-21 and 16-00 , all figures rounded to arcmin. I already mentioned by comment that the 16-00 / 21-00 difference may be a weakness of determination , also since textbooks prescriptions ask for repeated observation like you say . Because for the article I had to do the work alone (no old style navigators available , no readers) , and against deadlines , combined with the menace of  making the treatise unreadable due to too many details , I decided for the text & diagrams as published . I have worked for 20 years in the sciences during my professional career , there is not any reason for which I would venture  to " wiggle out" (as you call it) from a problem . There is namely , a possibility (not yet computed) that the offset entire track was longer than 132 mls because instead of having made good 348 mls @ 175453 GMT , only 337 mls had been made good , this has influence on the ETA time-position groups .

-----------------------------------------------------
Mr. van Asten,

If there really was a difference between the 16 degree altitude of the sun at the erroneous interception that you claim compared to the 21 degree altitude that you calculate for the correct LOP then the difference between them, 5 degrees, would produce an error of 300 NM, pretty hard for Noonan to be that wrong! AS I posted before, the correct altitude at the turn off point onto the correct LOP was 16° 04.5' at 1859 GMT.

There is something wrong with your computations of these altitudes.

Here is link to the U.S. Naval Observatory site that will do the computations for you so you won't get the wrong answers.

http://aa.usno.navy.mil/data/docs/celnavtable.php

Readers of these posts can go to that site themselves and check Mr. van Asten's computations themselves. Just put in the date, time, and the coordinates for Howland (0° 48' N, 176° 38' W) to calculate the sun's altitude at Howland and any place along the correct LOP through Howland. Look at the column marked "Hc" which is the standard abbreviation for "computed altitude." "Zn" = azimuth and "GHA is Greenwich Hour Angle. While you are at it you can check out Mr. van Asten's calculation of GHA of the sun for 175453 GMT, just enter in that time and look at the GHA column. Mr. van Asten said in his prior posts that the GHA of the sun at that time was 88° 43.2', did he get it right? I said the GHA at 175453 GMT was  87° 45.7', did I get it right?
 

And no, I do not assume that you have  consulted all representative flght manuals since you have failed to cite to any of them in your posts or in our other correspondence.

gl

88-03-14 is GHA-mean sun ; 87-45-45 is GHA-true sun , the latter used for determining LHA , nothing wrong with this .

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