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Author Topic: Navigating the LOP with the offset method.  (Read 197533 times)

Monty Fowler

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Re: Navigating the LOP with the offset method.
« Reply #135 on: June 06, 2011, 07:48:16 PM »

Gary, you've heard the one about trying to nail Jell-O to the wall? Same thing as trying to have a reasoned discourse with Mr. Van Asten. He is right. Regardless of anything remotely resembling logic that anyone else may try to apply to the discussion at hand.

Except for the tiny little fact that neither he nor anyone else in this discussion was there on that fateful day. The only two people who were are dead. So trying to recreate what happened on that day, using math, a seance, a Cray supercomputer, God or the Great Pumpkin, is nothing more than an intellectual exercise. In the end, it proves nothing - and it still doesn't put Amelia and Fred on Howland Island, unfortunately. My
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Chris Owens

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Re: Navigating the LOP with the offset method.
« Reply #136 on: June 06, 2011, 09:00:42 PM »


Except for the tiny little fact that neither he nor anyone else in this discussion was there on that fateful day. The only two people who were are dead.

Ahh.. So you're part of the "they're dead" cover-up conspiracy as well.  :P
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #137 on: June 06, 2011, 11:38:00 PM »

Mr. Lapook ,

According to your replies I would not have explained "looking at the same time by two sextant types" , etc. The key to overcome the misunderstanding is the following : the N.A. or any other source gives GMT of sunrise U.L. @ 175453 GMT . It here concerns the visible (also named ´apparent´-) sun , for which the true sun must be 53´below the horizon . Hence , if you go to look to sunrise U.L. with the marine sextant , you actually see the sun for @ GMT 175453 - 3m50s = 175103 Greenwich Apparent Time . The sun rises with 13´8 / time minute , so 53´/ 13´.8 = 3m50s after 175103 GAT , sun´s centre is in the horizon , elevation zero . Now you have 2 alternatives :  I . @ 175453 GMT you observe with the marine sextant . You now see the sun with a LHA which is 57´.5 larger than it would be @ 175453 GAT. It will last 3m50s (53´/ 13´.8) before the true sun (centre) is in the horizon , the LHA having diminished with 57´.5 . II . @ 175453 GAT you observe with the bubble sextant , the LHA has the correct opening since you view the true sun . During the time lag 175103 GAT to 175453 GAT however , the MEAN sun traveled from 175453 GAT to 175843 GMT by the time equation , equally being 3m50s . Balance : since you fly on GMT schedule , given that you observe by marine sextant , whereas you used the bubble sextant @ sunset last evening ,  you will seemingly arrive at precomptud  Zulu time at your next initial point . However , actually , you will be there 3m50s early. If the initial point is at the "alter to offset course" place , you will consequently arrive 3m50s short of the precomputed Turn-Off-Point on the from sunrise advanced LOP .

I from experience know that this reasoning about time lags is a dreadful blackbox , inscrutable and demanding for many hours of study , but that´s just how it is.
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #138 on: June 07, 2011, 02:02:12 AM »

G.Lpk. Yes , alternatively with marine / bubble sextant .
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #139 on: June 07, 2011, 02:13:02 AM »

G.Lpk . Yes I can , and not through earth , since 3m50s rise time after 175103 GAT the true sun is in the (celestial) horizon , 3m50s equation slow on the mean sun , to see it by bubble sextant @ 175843 GMT.
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #140 on: June 07, 2011, 02:15:55 AM »

Mt.Fwr . What do you think about "Fun with hypotheses" ?
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #141 on: June 07, 2011, 02:23:46 AM »

Mr. Lapook ,

Excuse , I went vertigo for a while , the correct term for both cases is : Greenwich Hour Angle.
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #142 on: June 07, 2011, 02:27:47 AM »

Chr.Ows . Not in a few words . Plse see EJN 2008-2011 and follow comments to/from mr.Lapook who is a sharp referee.
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #143 on: June 07, 2011, 02:49:19 AM »

Mr.Lapook ,

No . A sparrow is a bird , but not all birds are sparrows . Precision analysis shows GHA 88-43-10 sunrise central 175453 GAT to be interconnected with LHA 88-03-18 sunset central 071545 GAT : both GAT since it concerns the bubble sextant observation(s) , one facultative (@ rise), one real (@ down) . Draw the angles circle and you will see.
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #144 on: June 07, 2011, 02:16:59 PM »

Chr.Owns . in very short terms : Noonan established position @ sunrise near Nukumanu , high altitude , by the bubble sextant . He thereof precomputed sunrise next morning to be @ 175453 GMT in position 178-47-W : 00-09´-N , 150 mls off Howland. For accuracy he now used  , low flying 1,000 ft , the marine sextant . The bubble sextant registers on the true sun . The marine sextant registers on the visible sun , upper limb @ sunrise. Between the visib. sun in the horizon and te true sun in the horizon existed an astronomical time difference of 3m50s. Henceforth ,  by not again using the bubble sextant @ sunrise he saw U.L. 3m50s too early , although the watch hands stood 175453 ,  thereof estimating to be 150 mls off , but actually they were 3m50s x 150 mph = 9.6 mls more , i.e. 160 mls off . Steering on the offset course for the island (100 mls out) was also 3m50s early and an erroneous Turn Off Point taken on a line 10 mls west of Howland on chart . At 1912 GMT (fuel reserves for 1h05m) the inbound flight , course  157T , was completed , but the island did not run up below the A/c progression line , since it was 16 mls (10 + 6 chart error) on the port bow. As a result Howland remained beyond visual range , RDF exercitions failed , and A/c proceeded (337T) until fuel ran out.
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #145 on: June 07, 2011, 02:58:36 PM »

G.Lpk. No computation in navigation was " very short" , therefore navigators precomputed by homework , mostly before flight , sometimes during flight . All short methods (Pinto , Dreisonstok , Lieuwen , Ageton , H.O.214 , H.O.249) are for practical air navigation only time saving if precomputation before flight is accomplished.
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Chris Owens

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Re: Navigating the LOP with the offset method.
« Reply #146 on: June 07, 2011, 05:09:51 PM »

Chr.Owns . in very short terms : Noonan established position @ sunrise near Nukumanu , high altitude , by the bubble sextant . He thereof precomputed sunrise next morning to be @ 175453 GMT in position 178-47-W : 00-09´-N , 150 mls off Howland. For accuracy he now used  , low flying 1,000 ft , the marine sextant . The bubble sextant registers on the true sun . The marine sextant registers on the visible sun , upper limb @ sunrise. Between the visib. sun in the horizon and te true sun in the horizon existed an astronomical time difference of 3m50s. Henceforth ,  by not again using the bubble sextant @ sunrise he saw U.L. 3m50s too early , although the watch hands stood 175453 ,  thereof estimating to be 150 mls off , but actually they were 3m50s x 150 mph = 9.6 mls more , i.e. 160 mls off . Steering on the offset course for the island (100 mls out) was also 3m50s early and an erroneous Turn Off Point taken on a line 10 mls west of Howland on chart . At 1912 GMT (fuel reserves for 1h05m) the inbound flight , course  157T , was completed , but the island did not run up below the A/c progression line , since it was 16 mls (10 + 6 chart error) on the port bow. As a result Howland remained beyond visual range , RDF exercitions failed , and A/c proceeded (337T) until fuel ran out.

In other words, what you're saying is that
  • Noonan was planning to use the offset method to intercept Howland,
  • At the time he was deciding when to turn off, they were flying at 1,000 feet,
  • He used the marine sextant rather than the bubble sextant to take a sunrise sight, but failed to apply the refraction correction, which put him ~10 miles West of where he thought he was.
  • Noonan was using charts that had Howland's position off by 6 miles.
  • Combined error of chart + failure to correct for refraction put him 16 miles W of where he wanted to be at the point they turned and began flying the 337T course
  • They flew down the 337T course until they ran out of fuel, at which point they ditched and sank.

Thank you.  I suspect that if you had laid out this theory beforehand, you would have had less resistance from people on this forum.
The theory is internally consistent, as far as I can tell, but it does depend on a large number of assumptions that are untestable.
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Monty Fowler

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Re: Navigating the LOP with the offset method.
« Reply #147 on: June 07, 2011, 05:49:27 PM »

"... but it does depend on a large number of assumptions that are untestable." Bingo.

One of the main assumptions, to me, being that Noonan got stupid and sloppy near the end, knowing that his own life was on the line. I'm sorry, Mr. Van Asten, you can throw all the numbers up against the wall and hope some of them stick, but that just doesn't compute, as they say.
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #148 on: June 07, 2011, 10:34:35 PM »

Chr.Owns . in very short terms : Noonan established position @ sunrise near Nukumanu , high altitude , by the bubble sextant . He thereof precomputed sunrise next morning to be @ 175453 GMT in position 178-47-W : 00-09´-N , 150 mls off Howland. For accuracy he now used  , low flying 1,000 ft , the marine sextant . The bubble sextant registers on the true sun . The marine sextant registers on the visible sun , upper limb @ sunrise. Between the visib. sun in the horizon and te true sun in the horizon existed an astronomical time difference of 3m50s. Henceforth ,  by not again using the bubble sextant @ sunrise he saw U.L. 3m50s too early , although the watch hands stood 175453 ,  thereof estimating to be 150 mls off , but actually they were 3m50s x 150 mph = 9.6 mls more , i.e. 160 mls off . Steering on the offset course for the island (100 mls out) was also 3m50s early and an erroneous Turn Off Point taken on a line 10 mls west of Howland on chart . At 1912 GMT (fuel reserves for 1h05m) the inbound flight , course  157T , was completed , but the island did not run up below the A/c progression line , since it was 16 mls (10 + 6 chart error) on the port bow. As a result Howland remained beyond visual range , RDF exercitions failed , and A/c proceeded (337T) until fuel ran out.

Your posterior conclusions are correct (not "refraction correction" , but that is detail) . The sunset fix parameters deliver  the time-coordinates group for the sunrise fix , hence the uncertainties are possibly less than you suggest.

In other words, what you're saying is that
  • Noonan was planning to use the offset method to intercept Howland,
  • At the time he was deciding when to turn off, they were flying at 1,000 feet,
  • He used the marine sextant rather than the bubble sextant to take a sunrise sight, but failed to apply the refraction correction, which put him ~10 miles West of where he thought he was.
  • Noonan was using charts that had Howland's position off by 6 miles.
  • Combined error of chart + failure to correct for refraction put him 16 miles W of where he wanted to be at the point they turned and began flying the 337T course
  • They flew down the 337T course until they ran out of fuel, at which point they ditched and sank.

Thank you.  I suspect that if you had laid out this theory beforehand, you would have had less resistance from people on this forum.
The theory is internally consistent, as far as I can tell, but it does depend on a large number of assumptions that are untestable.
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #149 on: June 07, 2011, 10:53:12 PM »

"... but it does depend on a large number of assumptions that are untestable." Bingo.

One of the main assumptions, to me, being that Noonan got stupid and sloppy near the end, knowing that his own life was on the line. I'm sorry, Mr. Van Asten, you can throw all the numbers up against the wall and hope some of them stick, but that just doesn't compute, as they say.

To quote A.Einstein : if only one sticks that will do (and it does).
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