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[Alan Harris]

You are, of course, assuming . . . that all of the receivers involved were properly calibrated and that there would be no difficulty reading the dial to the least significant digit.

Actually I wasn't assuming those things at all, I was casually over-simplifying to a degree with which you are not comfortable.  Reading it again, I'm not that comfortable either.    To be more accurate and still be brief, it should have said ". . . would be prima facie suspect as to credibility."  Or to be more long-winded, it could have said that a received signal further off 3105 than known calibration limits of the receiver would lose credibility; that a signal observed to vary in frequency while monitored would have little/no credibility; and that if the same station received 2 separate signals within a fairly short time that were significantly different in frequency, at least one of those signals would be of very doubtful credibility.  Reading back over that, I think I prefer the brief version.   

. . . assuming--something frowned upon among the engineers of my acquaintance . . .

Matter of opinion, I guess, but in mine and my instructors', engineers make assumptions all the time.  That is what distinguishes engineering from pure science and enables things to actually be designed and built within a practically useful time frame.  Apart from basic science and math, engineering education consists largely of training in such things as what previous assumptions have been found to be sound and useful over time, estimating risks or inaccuracies involved in assumptions made, etc.  Engineers read the books assiduously but they don't re-research and rewrite the books before starting each new project.

[Dan Kelly]

You are, of course, assuming--something frowned upon among the engineers of my acquaintance ......

Father Moleski that made me laugh out loud.

About 15 years ago I was working on an engineering project where we were using big overhead blower ducts to carry finely crushed ore from where it was trucked in, to the smelters. The big pylons and the ducts (roughly 2 yards in diameter) were being designed by an engineering company that were partners with the company I was contracting for. Anyway their designers assumed that the site was on an even slope, and none of our engineers checked their calculations. Anyway these huge pylons and the mountings were being fabricated off site by another engineering company who just fabricated what they were told to build.

Anyway things were going real well until the site construction manager discovered that the ducts were all of sudden going upwards at a steady angle while the pylons were not reaching the same height. Turned out that the engineer responsible for the overall design hadn't noticed that the ground level actually flattened out. I bet that if we had continued these huge ducts would have been in Earth orbit by now.  

I reckon everyone assumes sometime or other even philosophers       

[Martin X. Moleski, SJ]

Actually I wasn't assuming those things at all, I was casually over-simplifying to a degree with which you are not comfortable.  Reading it again, I'm not that comfortable either.    To be more accurate and still be brief, it should have said ". . . would be prima facie suspect as to credibility."  Or to be more long-winded, it could have said that a received signal further off 3105 than known calibration limits of the receiver would lose credibility; that a signal observed to vary in frequency while monitored would have little/no credibility ...

I haven't worked a lot with old-time tube radios.  If this was a common phenomenon, either because of defects in the transmitter or receiver, and if the person operating the radio was truthful in reporting their observation of their instrument, it simply "is what it is."

. . . assuming--something frowned upon among the engineers of my acquaintance . . .

Matter of opinion, I guess, but in mine and my instructors', engineers make assumptions all the time. ...

If the assumptions are sound, the bridge probably won't collapse; if the assumptions are groundless, people may die.  Canadian engineers wear iron rings on their pinky fingers to remind themselves of what can happen if they make the wrong kind of assumptions.

[Bob Lanz]

Actually I wasn't assuming those things at all, I was casually over-simplifying to a degree with which you are not comfortable.  Reading it again, I'm not that comfortable either.    To be more accurate and still be brief, it should have said ". . . would be prima facie suspect as to credibility."  Or to be more long-winded, it could have said that a received signal further off 3105 than known calibration limits of the receiver would lose credibility; that a signal observed to vary in frequency while monitored would have little/no credibility ...

I haven't worked a lot with old-time tube radios.  If this was a common phenomenon, either because of defects in the transmitter or receiver, and if the person operating the radio was truthful in reporting their observation of their instrument, it simply "is what it is."

. . . assuming--something frowned upon among the engineers of my acquaintance . . .

Matter of opinion, I guess, but in mine and my instructors', engineers make assumptions all the time. ...

If the assumptions are sound, the bridge probably won't collapse; if the assumptions are groundless, people may die.  Canadian engineers wear iron rings on their pinky fingers to remind themselves of what can happen if they make the wrong kind of assumptions.

Interesting story about the Canadian Engineers iron rings Marty.  That said, the cost of my Professional Liability Insurance always reminded me of what could happen if I made the wrong kind of assumptions.   

[Ranchodoug]

The tidal data is from EasyTide. It's for Hull Island. My understanding is Niku tides lag Hull by about 10 minutes.

I checked the transmit times against the radio database here and it appears to match.

I also added the height of the Electra's wheels (52") ...It looks like AE/FN were in the Electra for at least the first three nights.

Is is possible for you to post the raw data from the "Easy Tide" site that you used for Hull Island?

Here you go. They are unfortunately not machine readable.

At any rate, based on the original 52" height in the Brandenberg study the wheels barely got wet at the highest tide, and the high/low tides had nothing to do with the transmit times (this was mentioned). I wonder if propagation wasn't just better at night.

With the revised location (22") there are times where there wasn't enough propeller clearance for a credible transmission (0200-0800 July 3-4 Niku time). The Electra need to be at least 30" above the tidal datum (this is a small amount). A revised tidal chart is posted.

Thanks Jeff Carter for the very insightful way of looking at the transmissions.

Posted w/o attribution.

[John Ousterhout]

'Just a reminder that one assumption to remain aware of is that the necessary propeller tip clearances assumes fully inflated tires on a flat surface.  A flat aircraft tire obviously brings a prop tip considerably closer to surface.  Likewise, a wheel sitting in a depression also brings the prop tip closer to the surface.  In the reef landing and transmitting hypothesis, there may be some correlation between transmit times and decreasing tip clearance. 

[Alan Harris]

The more I look at Purdue photos, the more I am inclined to think (or: opine, speculate: choose any or all of those) that the prop clearance on level ground was significantly more than the 24 inches I've seen assumed.

Photos such this one from Assab, Africa.  Unless the man is remarkably short, it certainly appears that the prop tip would be closer to the top of a typical leg rather than at typical 24" knee height.

Other photos suggestive to me include ones from Indonesia; Dakar, Africa; and Massawa, Africa.

Comparing both to persons in the photos and to the height of the Electra's MLG tires (which are believed to be 35" or 36" unloaded diameter), my personal estimate for prop clearance is more in the range of 32" to 36".

Note that I am not stating this as a fact.  Also please note that I am aware of the effects of perspective in photos, and that dimensions of objects not in the same spatial plane, etc. can be deceiving, and don't need reminding of that.  I'm just relating my interpretation of what I see.

I started looking at the photos for this because I was messing around with some scaled sketches of the Electra for my own amusement, and it seemed, using the assumed 9-foot props and ~35" tires, that I was having to "squat" the gear down more than seemed right to get the prop tips down to 24" from ground.  I do not offer this as "evidence" because, as I said, it is just me messing around.

[Joe Cerniglia]

Joe, I didn’t use a spreadsheet. Your numbers, which appeared unbelievably small, motivated me to look at the post-loss signal catalog. Once there, I scrolled through each page noting the non-Itasca signals that were listed, without qualification, as having a frequency of 3105 kHz. That method constituted my "filter".

If I’d included the 3105 kHz non-Itasca signals with the frequency tagged either “assumed” or “approximately”, the result would have been something like: 67 total,  41 (61%) credible, 16 (24%) uncertain, and 10 (15%) not credible.
 

Do you draw any conclusions from the ratios you observed?

Yes. The numbers you posted don’t reflect the content of the post-loss signal catalog.

Chuck

Chuck,
I've had a chance to sit down and correct my earlier tally of the 3105 kHz signal receptions on the Signal Catalog spreadsheet. I did a manual count (includes approximates) and came up with the following:
85 total,  44 (52%) credible, 22 (26%) uncertain, and 19 (22%) not credible. 

A spreadsheet with minor modifications to reflect the calculations is attached.  Note that this iteration of the spreadsheet is not meant to supersede the earlier one, only to reflect my specific purpose in this particular exercise with the 3105 kHz signals.

I double-checked my counts using the DCOUNTA function in Excel at cell E195 in the worksheet titled "Signal Catalog."  I also created a column to indicate whether or not I included a given signal as part of my 3105 kHz total.  This column may be found at Column R and is labeled "3105 reception (not transmission)."  The value for each cell in this column is simply "yes" or "no."  By using the arrow in cell R1, you can filter on the "yes" values to view which rows I selected.  You can filter on the "no" values to view which rows I did not select.  Note that Itasca transmissions were counted as "no."

While my math was wrong earlier (due to a faulty assumption on my part regarding Microsoft Excel filters), the database itself is, to my knowledge, correct and in exact correspondence to the signal catalog that is on the TIGHAR website.  If it is not, please tell me about it, and where it diverges, so that I can make the necessary adjustment.

The reason I originally undertook the exercise was to investigate a poster's claim that a signal received on 3105 kHz stood an inordinately high chance of receiving a rating of credible.  That nearly half (48%) of the signals received on or near 3105 kHz were assigned a rating other than "credible" seems to indicate to me that numerous other criteria, in addition to the frequency of the signal, were applied to the signal credibility ratings.  A quick perusal of the "Qualifying Factors" column (Column L) should confirm this observation.  Again, if anyone feels differently, please let me know so that I can reassess if I am missing something.

Joe Cerniglia
TIGHAR #3078 ECR

[John Kada]

The more I look at Purdue photos, the more I am inclined to think (or: opine, speculate: choose any or all of those) that the prop clearance on level ground was significantly more than the 24 inches I've seen assumed.

Photos such this one from Assab, Africa.  Unless the man is remarkably short, it certainly appears that the prop tip would be closer to the top of the leg rather a typical 24" knee height.

Other photos suggestive to me include ones from Indonesia, Dakar, Africa, and Massawa, Africa.

Comparing both to persons in the photos and to the height of the Electra's MLG tires (which are believed to be 35" or 36" unloaded diameter), my personal estimate for prop clearance is more in the range of 32" to 36".

Note that I am not stating this as a fact.  Also please note that I am aware of the effects of perspective in photos, and that dimensions of objects not in the same spatial plane, etc. can be deceiving, and don't need reminding of that.  I'm just relating my interpretation of what I see.

I started looking at the photos for this because I was messing around with some scaled sketches of the Electra for my own amusement, and it seemed, using the assumed 9-foot props and ~35" tires, that I was having to "squat" the gear down more than seemed right to get the prop tips down to 24" from ground.  I do not offer this as "evidence" because, as I said, it is just me messing around.

Another photo that may be of interest was taken in Burma

[Alan Harris]

Another photo that may be of interest was taken in Burma

Thanks, John, you are indeed correct.  I don't know how I missed that one.  If anything, my own estimate for prop clearance height just went further upward with that one.

[Dan Kelly]

I wonder what the variance in height was when the aircraft was loaded and unloaded - if any. On the reef it would have been quite light so maybe less compression on the gear?

[Gary LaPook]

The tidal data is from EasyTide. It's for Hull Island. My understanding is Niku tides lag Hull by about 10 minutes.

I checked the transmit times against the radio database here and it appears to match.

I also added the height of the Electra's wheels (52") ...It looks like AE/FN were in the Electra for at least the first three nights.

Is is possible for you to post the raw data from the "Easy Tide" site that you used for Hull Island?

Here you go. They are unfortunately not machine readable.

At any rate, based on the original 52" height in the Brandenberg study the wheels barely got wet at the highest tide, and the high/low tides had nothing to do with the transmit times (this was mentioned). I wonder if propagation wasn't just better at night.

With the revised location (22") there are times where there wasn't enough propeller clearance for a credible transmission (0200-0800 July 3-4 Niku time). The Electra need to be at least 30" above the tidal datum (this is a small amount). A revised tidal chart is posted.

Thanks Jeff Carter for the very insightful way of looking at the transmissions.

Posted w/o attribution.

I was wondering where you got the height of 22 inches for the revised location on the surface of the reef but I see you calculated it by comparing the graph that Ric produced with the UK tide data.
Comparing the height of the same high tide, July 9, 1937 at 7:06 am, from the UK tide data site showing 4.6 feet, 53 inches, with the height of the same tide on the graphic from TIGHAR of 0.82 meters, 33 inches, it is clear that the difference, 22 inches, is the height of the reef surface as determined by TIGHAR. I have attached annotated copies of each that shows this.

gl

https://tighar.org/smf/index.php?action=dlattach;topic=916.0;attach=4688

https://tighar.org/smf/index.php/topic,916.msg21293.html#msg21293

[Ric Gillespie]

Apologies for the tardiness of this reply but I'm just now catching up with recent contributions to this thread.

I agree that the photos cited suggest more prop clearance than the 24 inches we have been using.  That distance is based upon the Harney Drawings and it may be that there is a scaling error there.  The best way to check would be to measure the clearance on an existing 10E that has the same props and tires as NR16020.  There are two surviving Electras in 10E configuration:
• c/n 1015 used by Linda Finch in her 1997 world flight and later bought by the late Mike Kammerer.  The Seattle Museum of Flight is currently trying to raise the money to buy the airplane from Kammerer's heirs. Last I heard it was stored in a hangar in Santa Fe, NM.
• c/n 1042 is owned by Grace McGuire. At last report it was stored at Gillespie Field near San Diego.

I don't think either aircraft is fitted with the big fat Goodyear Airwheels that were on NR16020.

If the length of the prop blades and the height of the prop shaft off the ground are the same for the R-985 equipped 10A as on the R-1340 equipped 10E, we could measure the clearance on c/n 1052 at the New England Air Museum.  It has Goodyear Airwheels.  I'm not an aeronautical engineer, but it seems to me that the prop shaft would have to be in the same place regardless of engine size.

If it is true that the clearance is greater than we have used in our calculations of when the engine could be run to charge the batteries, the Post-Loss Radio hypothesis may be stronger than we thought.  At present, we have a few occasions when credible messages were received at times when the engine could not be run due to the water level on the reef, but it may be that we can legitimately move that red "propeller clearance" line up a bit. For example, if 32" is the right number for prop clearance, the red line on the attached graph moves up to .8 meter and all of the credible messages sent on the night of July 3-4 can be sent with the engine running.

All the talk about tide heights completely misunderstands the calculation of water levels on the reef at Niku.  I don't have time to explain it again.

[Dan Swift]

In the Assab, Africa picture, the prop is almost at its lowest point.....and where is falls on the gentlemen directly in front of it......on me is about 29-30".  I am exactly 6' tall. 

[Ric Gillespie]

In the Assab, Africa picture, the prop is almost at its lowest point.....and where is falls on the gentlemen directly in front of it......on me is about 29-30".  I am exactly 6' tall.

His head is even with the lower lip of the cowling.  If we can find a photo of either AE (5' 7or 8") or FN (6 ft) standing in the same relative location, regardless of the prop orientation, we should be able to estimate Mr. Assab's height.