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Author Topic: Drift in the Dark part 5  (Read 6752 times)

Colin Taylor

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Drift in the Dark part 5
« on: March 21, 2023, 04:34:02 AM »

Drift in the Dark
Part 5 of 8

What went wrong?
 
 The most likely eventuality was that the forecast wind issued by the Navy at Hawaii (ENE 15-18) was wrong and the actual wind (possibly ESE 27), combined with the wrong heading, caused 6 degrees of left drift instead of 2 degrees right drift.

Can we figure out what was the actual wind? (Figure 1, 5a, 5b)
https://photos.app.goo.gl/wTHnDCHj3uEPjrJL6
https://photos.app.goo.gl/WnksJaiynEr7EVqM6
 How do I get a 6 degree track deviation?  I started by plotting the 078oT track to Howland and the 157/337 sun-line. I then ‘fitted’ the search manoeuvre onto the sun-line to stop short of Howland by 20 NM. (A suitable strategy would be to either: go 1 hour North and 2 hours South or go 1 hour South and two hours North).  I then drew the deviated track from WP4 to the mid-point of the search manoeuvre about 170 NM North of Howland) and that gave about 6 degrees offset. 6 degrees includes the 2 degrees of drift in Noonan’s calculations using the forecast wind. In figure 5a you can see the effects during 10hrs 31mins from WP4. The triangle ABC (which is duplicated for clarity) comprises the planned track 078oT (AB), the track-made-good 072oT (AC) and the effect of the 'additional' wind over the same time period (BC). The additional wind-effect BC is 150 NM in 10.5 hours = 14 kts from direction 135oT. This is added to the forecast wind 068/18 in a vector triangle EFG to give the actual wind 097oT/27kts. EF is the forecast wind. GE is the additional wind. GF is the vector sum - the actual wind. In other words, the forecast wind and the additional wind are two imaginary components of the actual wind.
 Dashed line AX is the heading and airspeed, XB is the effect of the forecast wind, putting them on the planned track at B (DR1745). XC is the effect of the actual wind putting them on the 6 degree offset track at C. BC is the 'additional' wind. Using the new wind and Noonan’s headings based on the forecast wind, I then plotted the tracks and distances as the dashed line seen on the main chart.
 6 degrees offset over 1700 NM between WP4 and Howland puts them about 170 NM North of Howland, sufficient to go South at 120 kts groundspeed for 1 hr 15min and still be 20 NM short of Howland. This sounds a bit self-fulfilling, but it does explain how they got close enough to Howland for their radio calls to be so strong, yet not close enough to see Howland and how they used up three hours of fuel while remaining on the sun-line. Clearly, if they had continued South they would have seen the ship’s smoke but remember their mental picture was that, on the approach, they were close to on-track and they could not commit to one direction only. They had to look North and South.
 At 17:45Z, having got the sunrise timing, Noonan revised his ETA for the Howland sun-line and Earhart made the ‘200 out’ call. They thought they were at point B (WP10), 65 miles short of the 17:45 DR position. But I think they must have been on the sun-line where it crosses the 6 deg drift line North of WP10 (point C). The effect of the actual wind was to move them from the ‘still-air’ point X to the north end of the sunline (point C) instead of the forecast wind moving them from point X to point B.

How do we know this wind 097/27 is correct?

 The weather at the equator is dominated by the Inter-Tropical Convergence Zone (ITCZ).  Solar heating causes air to be drawn-in from North and South. In the Southern hemisphere, the South wind is deflected to the left by Coriolis effect, producing the South-East trade-winds. The North wind is deflected right in the Northern hemisphere giving the North-East trades. Although Coriolis effect is neutral at the equator, its effect is to generate rotation in air-masses at mid-latitudes which in turn affect the winds at the equator. The wind, squeezed between high pressure areas North and South of the Equator will be an Easterly. However, because the Earth’s axis of rotation is tilted, the ITCZ moves North in the Northern summer and the Sun is not over the Equator but is over the Tropic of Cancer at 23oN. The SE trades then push North of the Equator. (In the Northern winter the ITCZ moves South and the North-East trades push South of the Equator). You can see this in the charts reproduced from my Bartholomew’s Atlas.
https://photos.app.goo.gl/yYGNbT34LcmsTwnQ6
https://photos.app.goo.gl/zvZXDR5xctf5g4qv9
The forecasters may have assumed that the wind direction would change as it crossed the Equator; whereas in the Northern summer, the Equatorial latitudes are under the influence of the pressure patterns in the Southern hemisphere. This is not an absolute condition since the wind will be affected by local effects and tropical storms. Nevertheless, a North Easterly in the Northern summer is very unlikely. The South Easterly is much more reliable. That’s why they call them Trade-Winds!

 Also, there is a clue in the weather reports. This information has been there all along but appears to have been missed by previous researchers. The sea-level pressure was slightly lower at Howland, 28.83 in. Hg, compared with Nauru, 29.91 in. Hg. According to Buys-Ballots law, in the Northern Hemisphere, with your back to the wind the low pressure is on your left. In the Southern hemisphere the reverse is true and with your back to the wind, the low pressure is on the right. (Useful knowledge for the captain of a sailing-ship). So, on the Equator under the influence of the Southern pressure systems, moving Eastwards towards low pressure, the wind will be coming from the right, from the South East.

 Nesbit researched the Meteorological Office archive at Bracknell UK and says that the Met Office was reporting or forecasting a wind of E 25. Noonan himself reported a 23kt wind early on in the flight.

How to calculate a sun-line? (Figure 1)
 First, calculate a DR position at a time close to the time of sunrise and plot this on the chart. It does not matter if the flight is not exactly at this position, it is simply a known position on the chart. Using the almanac, calculate the time and direction of sunrise at the DR position. Draw the first sun-line through the DR position at 90 degrees to the direction of sunrise. In our case the direction is 067o True which gives the sun-line 157/337oT.
 Observe the sun-rise and note the time to the nearest half-second, when the first rays of sunlight emerge above the horizon (the calculations allow for the diameter of the sun). Correct the timing for the height of the aircraft above sea-level, to give the time of sunrise at sea-level.
 Compare the actual time of sunrise with the calculated time at the DR position. The time difference is converted to a distance using the speed of the terminator (the Earth shadow) moving across the surface, that is the speed of rotation of the surface of the Earth, at the particular latitude. Using that distance in an E-W direction draw a second sun-line parallel to the first. That is the line-of-position at the time of sunrise but your position could be anywhere on that line. Where the second sun-line crosses the DR track is the most-probable-position (MPP).
 Measure distance and time between the MPP and a previous fix to recalculate the head or tailwind component. Draw a third sun-line-of-position through the destination, measure the distance and calculate a new ETA. On the chart is shown the third sun-line through Howland and a notional sun-line at 200 NM to go.
 This method can correct for timing when the track is close to the direction of sunrise or correct for tracking when the track is 90 degrees to the sunrise. In our case the tracking remains a DR calculation.

Why were they NOT South of track?

 What extra wind would be needed to push them South of track? If they ended up at the South end of the sun-line where it crosses the 7 degree right drift line at ‘200 out’ at 17:45Z, the extra drift would need to be at least 7 degrees right to prevent them from seeing Baker Island on the run North. In this fictional scenario, they think they are at WP10, 65 miles short of the 17:45 DR position. They have been affected by an extra wind component additional to the forecast wind used in the DR calculations. The effect of the extra wind has been to move them from the DR1745 to the South end of the sunline. The triangle ABD comprises the planned track, the track-made-good with right drift and the effect of the wind over the same time period. The additional wind-effect is 180 NM in 10.5 hours = 18kts from direction 358oT. This is added to the forecast wind 068/18 in a vector triangle EFH to give the fictional wind 032/29. This is a North-Easterly and very improbable in the Northern summer. So I rule it out.


« Last Edit: April 25, 2023, 10:32:00 AM by Colin Taylor »
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Diego Vásquez

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Re: Drift in the Dark part 5
« Reply #1 on: March 22, 2023, 12:23:26 AM »

r1) I love your hand charts.  My dad was a civil engineer, and your charts remind me of when my dad was teaching me drafting as part of my 7th and 8th grade industrial arts classes. Much later I did some scale drawings by hand as an ancillary duty at work on occasion, and I stil do one every once in a great while in my retirement job.  People are amazed by them now, they can't believe they can be done without computer.

2)  Do you know, or have you corresponded with Gary Lapook? I'm still anxiously awaiting your final post, but I think you're going to splash AE  down in the same general area as Gary does, most of which area has not yet been searched.  You can PM me if you want to get in touch with Gary.   

Always nice to have something knew going on around here.  Especially if it doesn't involve major conspiracies and Japanese capture. 


Diego V. 
I want to believe.

Diego V.
 
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Colin Taylor

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Re: Drift in the Dark part 5
« Reply #2 on: June 02, 2023, 06:04:19 AM »

Well the lack of response is disappointing.

My point here is that the pressure distribution indicates a South Easterly wind and not a North Easterly as forecast. This is EVIDENCE that does not appear to have been noticed before. It explains why they were off-course.

Does nobody have anything to say about this?
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Jeff Christmas

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Re: Drift in the Dark part 5
« Reply #3 on: June 03, 2023, 07:43:59 PM »

Colin,

I've been out of pocket for a while and didn't see you posts until last night.

This data fits in well with one of my various lines of investigation which up until now I had considered to be mostly fanciful.  I am going to re-read your original post to be sure I fully understand what you posted.  I will comment further once I've had time to mull over.

One thing is for certain - you do have my attention!

Thank you for the post.

Sincerely,

Jeff Christmas
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