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Author Topic: SkyVector  (Read 7658 times)

Todd Attebery

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SkyVector
« on: January 29, 2015, 01:58:38 PM »

In light of the "PREPONDERENCE OF EVIDENCE - #1" on facebook, I thought I would point out a tool that might be of interest to some of the navigators in the forum.

SkyVector.com has online aeronautical charts and allows for some quick navigational calculations.   It has always bothered me that the great circle route from Howland to Niku is not 157 deg true. (It's about 159.)  It may have been discussed in the forum before, but I just wanted to see how far off they would have been in terms of nautical miles.

I put together a putative route consistant with the 337-157 line as linked below.   Niku is the next to last waypoint with Howland at the end for reference.

http://skyvector.com/?ll=-1.672613944860546,-176.36865234379562&chart=304&zoom=5&plan=N.AY.LAE:G.-4.105369350978441,159.5544433640483:G.-1.347165897221681,-176.12841796879223:G.-0.3200666971407293,-176.56420898442334:G.-0.2706288789462717,-176.40490722660863:G.-4.676348538149383,-174.53704833986362:G.0.8085669081673698,-176.64367675786198
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Martin X. Moleski, SJ

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Re: SkyVector
« Reply #1 on: January 29, 2015, 02:39:40 PM »

It has always bothered me that the great circle route from Howland to Niku is not 157 deg true. (It's about 159.) 

The discrepancy doesn't bother me.

If the Niku hypothesis is true, it does not involve flying from Howland to Niku, but from somewhere:
  • far enough away from Howland and Baker for them to have failed to make visual contact;
  • close enough to Howland to account for the strong radio signals at the end of transmissions;
  • close enough to Niku to get them to the reef before the tide would have frustrated a safe landing;
  • close enough to Niku to leave them with enough gas to be able to transmit for four or five days;
  • within a broad corridor slanted more or less 357-157 that would bring them within sight of Niku.
This "broad corridor" could be 15 to 20 miles wide, I suppose.  They might have been able to spot Niku from eight or ten miles away--either from the east or west side of the island.  They might have aimed elsewhere, but drifted in sight of Niku.   

The guess that navigators have made is that the bearing of the final line they were trying to fly came not from a desire to navigate from the vicinity of Howland to the vicinity of Niku, but from a Line of Position (LOP) that Fred would have drawn on his charts at dawn. 
LTM,

           Marty
           TIGHAR #2359A
 
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Ric Gillespie

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Re: SkyVector
« Reply #2 on: January 30, 2015, 10:19:00 AM »

We're getting a good response to the Preponderance of Evidence series on the Facebook page.  I'm finding that it's also useful for me to walk through the evidence in sequence (as it were). 
Late last night Billings and someone else mounted something of an attack with predictable comments and links.  I cleaned them out and will continue to ban their ilk.  The purpose of the series is to inform, not debate.
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Neff Jacobs

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Re: SkyVector
« Reply #3 on: February 17, 2015, 09:10:05 PM »

Todd,
Noonan stated in a letter he could get a Fix +/- 10 miles.   Fred being a navigator I presume +/-10 nautical miles, statute miles *1.15.

A navigators rule of thumb says you get lost by 10% over time.   If flying 150 mph, add +/-15 miles to the width of your course for each hour flying DR

In the case of the LOP  Fred lost the sky during the overcast and got a LOP some time after sun up.
To get the right idea on SkyVector  Pick a time between 0618 and 0718 Howland time when the sun would have been at an azimuth of 67 degrees and start with two points +/-10 miles from the center line.  Add a quarter mile to the distance from center for each minute you presume Fred is flying DR.   If you continue this to Niku the LOP will be almost +/-60 miles.  I like to use 0645 and have Fred turn into the LOP at 0745, makes the LOP +/-17.5 miles or about 35 miles wide when he turned into it.  You can assign different times from a sunrise LOP to 718 and see the effect of different times.   I hope this helps you visualize how flying DR works.
Neff 
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