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Re: Amelia Earhart's aerial navigation
From: Gary LaPook
Date: 2009 Nov 29, 03:49 -0800
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From: Gary LaPook
Date: 2009 Nov 29, 03:49 -0800
You wrote:
"4. It needs to be noted shooting an off-the-nose rising sun shot from 5,000ft altituude would give a Nav a dip correction of nearly seventy-miles. So without the correction Noonan would have thought he was apx 70 miles nearer Howland than he actually was. At a higher altitude it would have been even greater; so when possible was a let down initiated?"
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A sunrise shot from 5,000 feet would have a dip of 68 minutes. The refraction correction for a minus 68 minute sight is minus 45 minutes and the semi-diameter is minus 16 minutes giving an Ho of minus 2 degrees and 9 minutes. Noonan would not have known what refraction correction to use since his table only covered altitudes above 6 degrees. The minus 45 minute correction I mentioned comes from the correction table in the modern Air Almanac and was not available in Noonan's time.
gl
(The following is a repeat of my response on the Amelia Earhart navigation- basic information thread)
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I don't understand your concern about dip since Noonan was using a Pioneer bubble octant and you do not apply a dip correction to bubble sextant observations. See:
http://www.fer3.com/arc/imgx/A-5-Manual.pdf
No correction for coriolis either since the flight was at the equator.
If by "dipped-shot" you mean visually observing the sunrise in relationship to the visible horizon then you would have to allow for dip the same as if you were using a marine sextant set for zero degree altitude. But why would Noonan do that since he had a bubble octant to use? The dip correction table in Dreisonstok only tabulates corrections up to an altitude of 4,000 feet so to use that table he would have to be below 4,000 feet. Of course if he could do square roots in his head or on a slide rule then he could have computed the dip correction for any altitude (assuming he knew the formula.) If using a marine sextant the sextant altitude (Hs) of the sun at sunrise (appearance of the upper limb) as observed from 10,000 feet is zero degrees, lined up with the visible horizon. The dip from this altitude is 97 minutes so the apparent altitude (Ha) that you would enter the refraction table with is minus 1 degree and 37 minutes. The refraction correction for a sight from 10,000 feet for an Ha of minus 1 degree and 37 minutes is minus 50 minutes. Include semi-diameter and the observed altitude (Ho) is minus 2 degrees and 43 minutes. If this sight was taken with a bubble sextant then the Hs would be minus 97 minutes, the same as the dip so you don't have to apply the dip correction. You then end up with the same Ho after applying refraction and semi-diameter..
This brings out the real problem with taking an altitude below horizontal, that of determining the refraction correction. The 50 minute correction I just mentioned comes from the modern Air Almanac correction table and this table was not available to Noonan. He carried Dreisonstok and the Nautical Almanac for 1937. I have attached the refraction correction tables from these tables and the lowest altitude that they provide a refraction correction for is 6 degrees above the horizon. The other commonly available sight reduction tables of the time, H.O. 211 and Weems Line of Position Book, also had refraction tables limited to altitudes above 5 degrees 30 minutes. Noonan would have no way to compute a refraction correction.
Some people have claimed that Noonan just observed the sunrise, computed an LOP from that observation, advanced it to pass through Howland, flew to the LOP using just DR based on his ground speed, turned on to the LOP and started looking for Howland. Basically they are claiming that Noonan must have opened the door and thrown his octant away after he saw the sunrise. Does this make any sense? The sun rose at Howland at 0615 Itasca time, 1745 Z ( I just noticed the typo in my prior post, 1645 Z should have been 1745 Z) and it had climbed above 6 degrees a half hour later at 1815 Z. We have all been taught to avoid low altitude sights due to variability in the refraction and Noonan would also have avoided low altitude sights. In fact, he was constrained to take sights above 6 degrees by his refraction table, he had no choice and he could not take a lower altitude. He would have continued to use his bubble octant to take sights after the sun was above 6 degrees and would have taken additional sights after he had turned onto the LOP to ensure staying on it to Howland. At this point he would have a clear view of the sun through the left window since the relative bearing would be 270 degrees (assuming he intercepted the LOP northwest of Howland which makes the most sense) and he had taken several sights near this relative bearing on the way to Hawaii. Another reason Noonan could not take negative altitudes is that the Pioneer instrument only has a scale from zero to ninety degrees, no negative altitudes. I have attached a photo of the scale of this type of octant showing it set on zero
Another reason he could not use negative altitudes is that the sight reduction tables he was using, H.O. 208, Dreisonstok, had no provision for computing negative altitudes. In fact none of the other sight reduction tables of the time provided for computing negative altitudes, not H.O. 211, Weems, Hughes, or Nories. Even when inspection tables were developed they too did not provide for negative altitudes. H.O. 214 only has altitudes above 5 degrees, H.O. 218 only above 10 degrees, and H.O. 229 only above zero. The only tables that provide for negative altitudes in H.O. 249 which were a much later development and provided negative altitudes for use by our Air Force flying B-52s at high altitudes on the way to Russia in case the only available star might be a low altitude shot. But even then, B-52 navigators would prefer to use higher altitude sights.
You seem concerned with the viewing opportunities for Noonan. AE wrote on page 47 in "Last Flight," "The plane had been fitted with special windows" for use by the navigator. These side windows were larger than standard and made out of flat glass to eliminate unwanted refraction. We know from the Hawaii and Atlantic charts that he was able to take sights in all direction and up to 75 degrees high. I have attached a table of the relative bearings and altitudes shot while flying to Hawaii and to Dakar. You can see that Noonan was able to take sights in every direction and at many altitudes. The Pioneer octant makes it easy to take high altitude shots because the index prism is located at the front of the instrument only one inch back from the front. This allows you to place the octant right up against the window and it only takes an 8 inch high window to allow sights up to 80 degrees. Also the eyepiece in 9 inches back making it easy to place the octant well in front of you against the window. This is different from the MA-1 where the index prism is 4 inches back from the front requiring a much taller window to allow high altitude shots.
gl
Ronald P Barrett wrote:
"4. It needs to be noted shooting an off-the-nose rising sun shot from 5,000ft altituude would give a Nav a dip correction of nearly seventy-miles. So without the correction Noonan would have thought he was apx 70 miles nearer Howland than he actually was. At a higher altitude it would have been even greater; so when possible was a let down initiated?"
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A sunrise shot from 5,000 feet would have a dip of 68 minutes. The refraction correction for a minus 68 minute sight is minus 45 minutes and the semi-diameter is minus 16 minutes giving an Ho of minus 2 degrees and 9 minutes. Noonan would not have known what refraction correction to use since his table only covered altitudes above 6 degrees. The minus 45 minute correction I mentioned comes from the correction table in the modern Air Almanac and was not available in Noonan's time.
gl
(The following is a repeat of my response on the Amelia Earhart navigation- basic information thread)
---------------------------------------------------------------------------------------------------------------------
I don't understand your concern about dip since Noonan was using a Pioneer bubble octant and you do not apply a dip correction to bubble sextant observations. See:
http://www.fer3.com/arc/imgx/A-5-Manual.pdf
No correction for coriolis either since the flight was at the equator.
If by "dipped-shot" you mean visually observing the sunrise in relationship to the visible horizon then you would have to allow for dip the same as if you were using a marine sextant set for zero degree altitude. But why would Noonan do that since he had a bubble octant to use? The dip correction table in Dreisonstok only tabulates corrections up to an altitude of 4,000 feet so to use that table he would have to be below 4,000 feet. Of course if he could do square roots in his head or on a slide rule then he could have computed the dip correction for any altitude (assuming he knew the formula.) If using a marine sextant the sextant altitude (Hs) of the sun at sunrise (appearance of the upper limb) as observed from 10,000 feet is zero degrees, lined up with the visible horizon. The dip from this altitude is 97 minutes so the apparent altitude (Ha) that you would enter the refraction table with is minus 1 degree and 37 minutes. The refraction correction for a sight from 10,000 feet for an Ha of minus 1 degree and 37 minutes is minus 50 minutes. Include semi-diameter and the observed altitude (Ho) is minus 2 degrees and 43 minutes. If this sight was taken with a bubble sextant then the Hs would be minus 97 minutes, the same as the dip so you don't have to apply the dip correction. You then end up with the same Ho after applying refraction and semi-diameter..
This brings out the real problem with taking an altitude below horizontal, that of determining the refraction correction. The 50 minute correction I just mentioned comes from the modern Air Almanac correction table and this table was not available to Noonan. He carried Dreisonstok and the Nautical Almanac for 1937. I have attached the refraction correction tables from these tables and the lowest altitude that they provide a refraction correction for is 6 degrees above the horizon. The other commonly available sight reduction tables of the time, H.O. 211 and Weems Line of Position Book, also had refraction tables limited to altitudes above 5 degrees 30 minutes. Noonan would have no way to compute a refraction correction.
Some people have claimed that Noonan just observed the sunrise, computed an LOP from that observation, advanced it to pass through Howland, flew to the LOP using just DR based on his ground speed, turned on to the LOP and started looking for Howland. Basically they are claiming that Noonan must have opened the door and thrown his octant away after he saw the sunrise. Does this make any sense? The sun rose at Howland at 0615 Itasca time, 1745 Z ( I just noticed the typo in my prior post, 1645 Z should have been 1745 Z) and it had climbed above 6 degrees a half hour later at 1815 Z. We have all been taught to avoid low altitude sights due to variability in the refraction and Noonan would also have avoided low altitude sights. In fact, he was constrained to take sights above 6 degrees by his refraction table, he had no choice and he could not take a lower altitude. He would have continued to use his bubble octant to take sights after the sun was above 6 degrees and would have taken additional sights after he had turned onto the LOP to ensure staying on it to Howland. At this point he would have a clear view of the sun through the left window since the relative bearing would be 270 degrees (assuming he intercepted the LOP northwest of Howland which makes the most sense) and he had taken several sights near this relative bearing on the way to Hawaii. Another reason Noonan could not take negative altitudes is that the Pioneer instrument only has a scale from zero to ninety degrees, no negative altitudes. I have attached a photo of the scale of this type of octant showing it set on zero
Another reason he could not use negative altitudes is that the sight reduction tables he was using, H.O. 208, Dreisonstok, had no provision for computing negative altitudes. In fact none of the other sight reduction tables of the time provided for computing negative altitudes, not H.O. 211, Weems, Hughes, or Nories. Even when inspection tables were developed they too did not provide for negative altitudes. H.O. 214 only has altitudes above 5 degrees, H.O. 218 only above 10 degrees, and H.O. 229 only above zero. The only tables that provide for negative altitudes in H.O. 249 which were a much later development and provided negative altitudes for use by our Air Force flying B-52s at high altitudes on the way to Russia in case the only available star might be a low altitude shot. But even then, B-52 navigators would prefer to use higher altitude sights.
You seem concerned with the viewing opportunities for Noonan. AE wrote on page 47 in "Last Flight," "The plane had been fitted with special windows" for use by the navigator. These side windows were larger than standard and made out of flat glass to eliminate unwanted refraction. We know from the Hawaii and Atlantic charts that he was able to take sights in all direction and up to 75 degrees high. I have attached a table of the relative bearings and altitudes shot while flying to Hawaii and to Dakar. You can see that Noonan was able to take sights in every direction and at many altitudes. The Pioneer octant makes it easy to take high altitude shots because the index prism is located at the front of the instrument only one inch back from the front. This allows you to place the octant right up against the window and it only takes an 8 inch high window to allow sights up to 80 degrees. Also the eyepiece in 9 inches back making it easy to place the octant well in front of you against the window. This is different from the MA-1 where the index prism is 4 inches back from the front requiring a much taller window to allow high altitude shots.
gl
Ronald P Barrett wrote:
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A number of matters more with Navigator Noonan trying to shoot a below the horizon sun shot from a plane with no astrodome and and a slot-front window in the ITCZ.
1. In looking at the pictures of the L-10AE, I feel there is no way an aft cabin shot of the sun rise could be accomplished due to the fat wing chord and engine nacelle being in the visual path. Like I said prior one does need to do an engineering study of the visual paths or views possible from all the L-10AE's windows using as best as is known sextant:by a navigator if possible as you need to know what you are looking for. The view of the sun would have been slightly to the left of the flight center line of the flight path of apx 080 degrees. The sun rise azimuth was to be 067 degrees at that time/date.
2. If one studies the front cockpit windows you see that the view from the cockpit seat as Ruth Richter Holden (owner of the current flying L-12A Electra ) stated to me, "Like looking out a mail box slot." That says a lot. I found the sister ship to AE's Electra up at the Canadian Air museum and you can see by their picture details of the cockpit window Noonan might have been sighting through. So he had to have his head way up in the crown of the cockpit area, to get the sextant to be able to sight out over the glare shield and out the bottom edge of the window. HUMM???
3. Upon further analysis: would Noonan have been sighting through the left cockpit window pain? Were the frames in the way? If he could shoot...could he see over the engine nacelle? If so was he shooting through a prop into the sun? What were the real glare/optical problems. They look horrific to me.
4. It needs to be noted shooting an off-the-nose rising sun shot from 5,000ft altituude would give a Nav a dip correction of nearly seventy-miles. So without the correction Noonan would have thought he was apx 70 miles nearer Howland than he actually was. At a higher altitude it would have been even greater; so when possible was a let down initiated?
5. Looking at the picture does any one think we need to look at the visual/sighting paths possible for Noonan's sun-rise celestial observations?
Thanks, Ron Barrett, USAF Ret Nav & President of Air Force Navigators Observers Association (www.afnoa.org)
--- On Fri, 11/27/09, Gary LaPook <glapook@pacbell.net> wrote:
From: Gary LaPook <glapook@pacbell.net>
Subject: Re: [NavList 10825] Re: Amelia Earhart's aerial navigation
To: navlist@fer3.com
Date: Friday, November 27, 2009, 7:19 AM
Greg Rudzinski wrote:
A few more questions. The abrupt ending of voice radio transmission
implies trouble. Is it possible that the batteries/magneto and or fuel
pump failed then causing a ditch short of Howland on the LOP
approach ? What were there chances without a life raft?
Greg
On Nov 18, 9:59 pm, Gary LaPook <glap...@pacbell.net> wrote:
> Greg Rudzinski asked:
>
> Maybe Gary can comment on the following:
> 1. Time tick before departure.
> 2. Sobriety of Noonan.
> 3. Life raft.
> 4. Radio antenna.
> 5. Head winds.
> 6. Celestial opportunities.
> 7. Sleep deprivation.
> 8. Was it possible to fly right over Howland Island and not see it?
> 9. Was Howland charted correctly.
> 10.What would have been a better less risky route?
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I think I have answered most of these questions already except:
There are other possible explanations for the sudden loss of radio calls from AE. In her last call she announced that she was changing frequency to her daytime freq of 6210 kHz and may have not operated the radio controls correctly. And remember tube type radios had sudden failures regularly.
It would not have been a magneto problem since each engine has two independent magnetos and the engine will run perfectly well on just one(that is why you have two.) To lose electrical power to the radio would take a simultaneous failure of both the battery and the generator, unlikely. However, if the generator had failed sometime before and AE hadn't noticed this on her ammeter then the battery would have gradually run down and the radio would have eventually stopped working.
There is no reason to believe that they did not have a life raft.
I believe that they did ditch northwest of Howland on or near the LOP due to some type of failure but I have no idea what.
6. They reported clouds several times but that doesn't mean that there were clouds continuously so as to prevent celestial sights. They should have been on top of most clouds during the night. AE cabled Putnam that Noonan needed star sights so if they couldn't get them they would have turned around. In addition to the sun, the moon would have been well positioned to give good cuts as they approached Howland. It was about 76 high at the start but coming down and we know from a noon sun sight while crossing the Atlantic that he could get a sight 75 high so should have been able to shoot the moon.
7. I remember flying 14 hours after having been up 16 hours already so landed after being awake for 30 hours. I got out of the plane, sat down of the tarmac, leaned back against the tire and was asleep in an instant. But it didn't hit me until after I had landed and I had no trouble flying the NDB approach to the airport. Remember Noonan wasn't banished to the nav station, he sat in the co-pilot seat to take sights too. The autopilot did most of the flying and Noonan also could fly the plane while AE grabbed a nap and Noonan could also have napped between taking sights.
8. Itasca reported that Howland was surrounded by clear skies for a 40 mile radius and Itasca was making smoke so it should have been impossible to fly over it without seeing it.
10. The original plan was to fly around westbound and to refuel in the air over Midway Island since there was no airport there, only a seaplane base. The Navy put the kibosh on that idea, the felt AE was not skillful enough to attempt aerial refueling. There were no other airports available, in fact there was no airport on Howland, they had to bulldoze one for AE.
> Excellent post Gary. Thanks.
>
> A few more questions. The abrupt ending of voice radio transmission
> implies trouble. Is it possible that the batteries/magneto and or fuel
> pump failed then causing a ditch short of Howland on the LOP
> approach ? What were there chances without a life raft?
>
> Greg
>
> On Nov 18, 9:59 pm, Gary LaPook <glap...@pacbell.net> wrote:
>
>> Greg Rudzinski asked:
>>
>> Maybe Gary can comment on the following:
>> 1. Time tick before departure.
>> 2. Sobriety of Noonan.
>> 3. Life raft.
>> 4. Radio antenna.
>> 5. Head winds.
>> 6. Celestial opportunities.
>> 7. Sleep deprivation.
>> 8. Was it possible to fly right over Howland Island and not see it?
>> 9. Was Howland charted correctly.
>> 10.What would have been a better less risky route?
>>
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Or post by email to: NavList@fer3.com
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