Highlights From the Forum
October 21 through 27, 2001
(click on the number to go directly to that message)
|1||Signal Strength Quantifiers||Mike Everette|
|2||Opening Coconuts||J. Dubb|
|3||Search Altitude||Tom MM|
|4||Reef Landing||Skeet Gifford|
|5||Pan Am in the South Pacific||Don Neumann|
|6||Re: Reef Landing||Skeet Gifford|
|7||Dental Records||Dan Brown|
|8||Winslow Reef||Roger Kelley & Others|
Some more input on signal-strengths, and things to think about.
Signal strength is a function of several variables. In order to measure it, and use it to derive anything like meaningful approximations of distance from the source, certain things must be known:
Signal strength is measured in terms of MICROVOLTS.
One might logically assume that the more microvolts are presented to thereceiver, the closer the transmitter is to it... well, yeah, BUT:
Not always. Sometimes transmitted energy is concentrated in one direction more-so than another, due to antenna characteristics. More below...
Now, in order to obtain an actual measurement of signal strength in microvolts at a receiving point, the following are required.
As I said last night, “S-meters” on receivers of that day (and many in present time) were NOT so calibrated. The scales were totally arbitrary, despite any numbers which may appear thereupon.
When I worked in an AM broadcasting station, we were required to make periodic checks of our antenna radiation pattern... it was directional, i.e, it concentrated most of the power in a particular direction, by means of multiple towers. We had to maintain the pattern within precise limits.
The way the pattern was measured, was by means of a calibrated receiver, called a FIELD INTENSITY METER. This device uses a calibrated antenna as well. The field-intensity meter was transported to a number of points distributed around the “shape” of the directional pattern, each a number of miles from the station, and signal strength measured. If the measurements were not within a certain tolerance, precalculated by engineers at the time the station was constructed and part of the FCC filing data for the license, the pattern was “out” and we had to find out why... maybe due to mistuning of the coupling network at the transmitter or the antenna tower itself when the temperature or humidity changed, or broken parts of the “ground screen” under the towers, bad guy-wire insulators etc etc etc.
The point is, for a given transmitting power and antenna, we knew to expect certain signal intensities at certain distances from the station.
Now how does this relate to AE?
NO quantitative measurements were ever made, or at least none survive if they were, of the radiation pattern of her aircraft’s antenna. Whether the ntenna exhibited a “lobe” or a “null” in the direction of a given receiver, will make a tremendous difference in the observed signal strength at the receiver.
Most aircraft antennas will exhibit pronounced directional characteristics at the relatively low frequencies used by AE, because the meatl aircraft structure is so close to the actual antenna wire and because the aircraft itself is often of a size close to the wave length of the signal, or a fraction of the wave length. So, for instance, the wings or fuselage of an aircraft, if their length approaches ¼ or ½ wave length, will often greatly influence the directivity of the antenna.
NOTHING is absolutely known about the antenna’s efficiency, or exactly how much power it radiated. From its physical characteristics we can (and HAVE, thanks to the great work of Bob Brandenburg and others) make a number of predictions about that. It is very likely that the efficiency was low; that it exhibited a loss and radiated somewhat less power than was actually generated by the transmitter.
We know SOME things about the state of the signal path in July 1937 (again thanks to Bob Brandenburg) but we don’t have ALL the answers. We also DON’T KNOW FOR ABSOLUTE CERTAIN what her antenna height was at any given time, i.e. what altitude she was flying. We are PRETTY SURE that some times she was at about 1000 feet.
The reason the antenna height is important, is that it determines the line-of-sight radio horizon; but at these frequencies (3105/6210 KHz) the radio horizon is not that absolute a factor. “Ground wave” signals, or non-skip propagated signals, can travel well beyond the horizon with considerable strength.
Modern aircraft VHF communications between 118-136 MHz have a much more definite horizon. The wave propagation mechanics are very different at low HF (AE’s case) from those at VHF. THIS IS IMPORTANT to understanding how this all works. Many modern-era aviators don’t realize the difference. Understand this too: The field strength of the signal decreases as distance from transmitting source to receiver increases, no matter what the frequency. And over a given path, the decrease, or attenuation, varies in accordance with a number of factors, some meteorological, some determined by the type of surface over which the path travels. (In AE’s case it was sea surface; this won’t change much.)
As for the receiving antenna, it was a structure of convenient size and arrangement for the Itasca... a wire hanging in the breeze. The exact characteristics of this antenna, its efficiency, directionality, how much signal voltage it would deliver to the receiver at the frequency in question, are unknown. The Itasca’s receivers themselves were standard type communications receivers, NOT calibrated field intensity meters. If they had an S-meter at all, that meter – as I said last night – tells one NOTHING about the absolute signal strength. All it says is, “the signal is weak” or “the signal’s stronger.” And, it’s a tuning aid.
As for reported signal strengths in terms like “S-5” this really does not have any relationship to the meter reading. In fact a signal reading high on the S-meter scale can still be covered up in strong noise.
The operator in those days used a scale of 1 to 5. S-1 means “signal very weak, in the noise, barely intelligible if readable at all.” S-2 means “weak signal, still in noise, but readable, maybe with difficulty.” S-3 means “signal stronger, noise, but readable.” S-4 means “fairly strong signal, some noise, very readable.” S-5 means “very strong, clear signal.”
Like I said last night: This is SUBJECTIVE. There is a LOT of room for interpretation. An operator’s ears might tell him/her that a signal is S-1 if any appreciable amount of noise is heard. Or, that a signal is NOT S-5 if there is ANY NOISE AT ALL heard. It’s a judgement call. Different operators hearing the same signal may disagree.
And, again like I said last night, the S-meter readings are NOT CALIBRATED NUMBERS.
Even a modern receiver with an S-meter scaled from S-1 to S-9 and then in terms of “dB over S-9” is a totally arbitrary scale, unless the meter is calibrated to a known signal strength in terms of microvolts... only a handful of manufacturers ever actually established such references. So a higher S-meter reading just means “Louder,” “REALLY loud,” or “BODACIOUS” signal! It has NOTHING to do with the amount of microvolts.
An important technical point: A receiver’s S-meter operates only when the receiver is operated with the automatic gain control circuit (aka Automatic Volume Control, abbreviated AGC or AVC) is activated. Many operators of the mid-30s era preferred to operate with the AGC DISABLED until they actually acquired the signal. One reason for this was that noise bursts would cause the AGC to keep the receiver “blocked” for a period, maybe one or two seconds, which could cause the call to be missed.
Even when operating with the AGC off, the operator would still report the strength as S-1 through S-5. So some of the Itasca operators’ signal reports MAY NOT BE REFERENCED TO A METER after all!
As for correlation of such reports with actual signal strength in microvolts, which result in pinpointing a distance? NO WAY. And anyone who thinks they can read this into it, is working with an uncalibrated brain.
Yes, experience will tell you that under certain conditions, certain things MAY BE TRUE, but that does not mean they are true. NUMBERS, or QUANTITATIVE MEASUREMENTS, are the determining factor. But you must be careful how those numbers are obtained, and to what standard they are referenced.
In this case there aren’t enough hard numbers. Elgen Long doesn’t have any. I stand by my position that his, and other such inferences not derived from hard data, are totally bogus. TIGHAR has a lot more hard numbers than Elgen; but we don’t have all the numbers.
LTM (who passed Algebra II)
This is my first post to the forum, so here goes with my two cents on coconuts. When I was 20 years old I was sailing on a square rig ship in the south Pacific. We stopped in at one of the small low atolls in the Marquesas. My buddy and I decided to walk about 1.5 miles along the beach to an iron ship that went aground near the turn of the century. After we got there we tried to find a coconut for a nice cool drink (ha-ha).
There were lots of coconuts on the ground. All eaten into by some creature and no good. There were lots green coconuts in the trees, all inaccessible to us. Finally after much tramping through the heavy brush we found a tree bent over enough to climb and got some down. We each had our sailors knives, 5″ blade, sharp, strong. We worked those things open bored through the little “eyes” and each got about a cup and a half of the coconut water. (You are right , it is a little fizzy) After all the work we agreed that we lost more water through perspiration finding and opening those things than they had in ’em.
Keep in mind these points: We were young, we were in shape, we were used to the tropics. We had been climbing around the rigging on a tall ship for months. We had had a good nights sleep the night before, we started off well hydrated. We had hats, we had shoes, we had knives. We were not injured. We still had a hard time with those coconuts. Natives open a coconut with a machete, or use the pointed stick in the ground method, but most importantly, they have had practice. I feel that a castaway could easily be found dead in the MIDDLE of a coconut grove. AE and FN might not have had all it takes to get a coconut open. In short, (after a long post) opening a coconut is a non-trivial matter.
What does TIGHAR assume describes the flight altitudes to Niku? On the one hand, I hear low altitude to remain under the cloud bases to spot the island, which may pop up anytime at very short sight distances from the aircraft. However, grinding along for 3-4 hours at 1,000 - 2,000 feet can require a fairly rich and un-economical mixture for safety and power. On the other hand, I seem to hear higher altitudes mentioned. That implies clear visibility and longer sight distances, certainly below and possibly above, which begs a few other important questions.
Anyway, back to this one. What flight assumptions are used in TIGHAR’s estimate for the fuel endurance? Do they need to climb to at least – maybe 8,000 to 10,000 ft or can they drone along on the deck and still make it with a reasonable reserve? Do they make it one way and not the other?
TIGHAR assumes that AE and FN followed Johnson’s altitude recommendations enroute to Howland then descended to 1,000 when they were trying to pick up the island visually. What altitude they may have maintained while running down the LOP is a matter of speculation but my guess would be that they stayed low. Yes, they’d burn more fuel down low but they’d also burn a lot of fuel climbing up above the clouds and they wouldn't be able to look for land from up there. However, they should have had enough fuel to do either and still make it to Gardner.
There have been a couple of references to the probability of a successful landing on the portion of the reef north of the Norwich City. Ric, Gary, Mark and I walked that portion of the reef, and with a Pentax PS-300, measured that portion of the reef which could reasonably serve as a runway for landing. The useable length, landing to the south (no obstacle to clear) was 2,700 feet. Additionally, most of the team members were on the most southerly portion of the reef for the plaque dedication ceremony.
1) Although we did not plot the position of the many pot-holes in the reef, it should have been possible to make a successful landing there last September. I remember saying that “...the landing would be a crap-shoot,” but I would hesitate to put a number on the likelihood of success. There are just too many variables, the most significant of which is that we don’t know what the reef condition was in 1937.
2) The cockpit visibility cut-off angle could also be an issue. Using a diagram of the L-10, I determined that with the airplane in a 3-point attitude, the pilot looking over the nose would be able to see the surface not closer than 100 feet from the position of the airplane.
3) The published landing speed for the L-10 is 65 miles per hour (57 knots). Reference my C-47 flight manual, I determined the landing ground roll for a weight (18,000 lbs) which called for a touch-down speed of 65 mph. Zero wind was assumed, although there is usually a prevailing light, left-quartering headwind (for a landing to the south) at that location. Deceleration rates are calculated from the published landing distances. Note that the surface description is from the manual. More recent flight manuals use other terms:
Frankly, I was a little surprised at the rather modest deceleration rates when compared to those of a modern airplane. The autobrake system on a Boeing airplane typically has five selections of deceleration rates, ranging from 4 ft/sec2 to 11 ft/sec2. Deceleration is determined by the inertial platform, which is also the source for performance and navigation requirements. If the requested deceleration rate is being met by engine reverse thrust, then the brakes will not apply. Carbon-fiber, anti-skid brakes make a difference. But I digress.
Footing on the outer reef was rather good, as opposed to closer-in areas that were slicker than greased (pick your substance). Bottom line: even though the surface is obviously wet, the braking response should be good due to the rough surface. For the pilots on the forum, I’d compare it to a wet, well-grooved runway. I’d say that the 1,350 landing distance number is reasonable. In any event, there was sufficient flat surface to land and stop a Lockheed L-10.
The landing distance I opined on the reef was clearly a WAG, and would have required a deceleration rate of 8 ft/sec2. Reasonable – for a 767 with a touchdown speed of 57 knots(g).
What, I wonder, would be the effect of – say – an inch of standing water? One fact that was apparent from our detailed inspections of the reef surface versus tidal state is that the reef flat on some parts of the island is higher than at other parts. For example: when the water level is a good 12 inches below the surface level of the reef at the blasted landing channel, the reef surface north of the Norwich City still has a film of standing water. Clearly the reef flat there is lower than at the channel. There are periods during unusually low tides when the reef north of the shipwreck is really dry, but it’s much more common for there to be at least some standing water in that area.
How much standing water would impose enough resistance to a 35 inch tire at 65 mph to to cause a 7,000 pound airplane to go up on its nose? If we had a feel for that we’d have a better handle on how big or small the tidal window might be for a successful landing.
Just a note about an article I found on the PanAm website that I found rather interesting & somewhat illuminating.
I’ve searched this site before & corresponded on their message board, but I must have missed this article: “;South by West, the Route to New Zealand” which describes in great detail the March 17th 1937 survey flight from California to New Zealand, via Hawaii, Kingman Reef & American Samoa.
Seems that Pan Am had been planning & surveying this route by ship since 1934, so that FN would (as Chief Navigator at the time) probably have had, at least some working knowledge of this route planning project & the various island groups in the general vicinity of the planned route, perhaps even access to the various maps & charts being prepared & utilized in the project.
Ironically, after leaving California for Hawaii, the Pacific Clipper actually saw AE’s Electra enroute, on her (abortive) first round-the-world attempt, which never got off the ground in Hawaii. The article clearly emphasizes the critical importance of the radio DF system employed at the time by Pan Am, in permitting their flight to locate Kingman Reef, even during a rainstorm.
Curiously, they had no difficulty in making visual contact of the vessel North Wind (anchored at Kingman) or the tiny, narrow strip of sand, showing barely above low tide at the time, in spite of the poor weather conditions.
They also mentioned their great interest in obtaining information about & the importance of all the other island groups to the NE & NW of Samoa.
Given the detailed planning & preparation that Pan Am exerted in this effort & particularly the ultimate success they enjoyed in applying their own radio DF system, it does seem rather tragic that the AE/FN team rejected the offer of Juan Trippe to have his people “monitor” the flight around the world.
I might also mention that there is a map of the Pacific Ocean, showing the Clipper routes to China & New Zealand, as part of the “South by West” article, & when you print-out the map enlargement, there is a solid line from Lae, NG to the Gilberts, then a dotted line to Howland Island with a (?) mark on the dotted line.
I checked with the webmaster for the PanAm website & he could not provide me with any date the map was printed or any information about its origin. However, he did confirm that the map was part of the original 10 page article that was published by PanAm in 1938 & found later in the company's archives.
Though my Webtv isn’t clear enough to read the names, all of the Phoenix Islands appear to be in their generally proper locations, also, there is a block in the lower right hand corner containing the scale for the map & some additional printing (possibly the name of the map's publisher) which I can’t read either.
Maybe one of you computer experts can enhance the the map’s detail to determine its origin & possibly its date.
That line to Howland with the question mark has got to be a reference to the Earhart flight.
>What, I wonder,
would be the effect of – say – an inch of standing water?
Two good questions.
Intuitively, all pilots understand that an inch of standing water (and also sand or snow) decelerates the airplane on landing and inhibits acceleration on takeoff. I was able to locate a reference for calculating this effect in: Aircraft Performance Engineering, Joop Wagenmakers, Prentice Hall, 1991. Referencing slush, he states, “The tyre drag may be calculated by using the frontal area of the submerged part of the tyre and Cd = 0.75 as the drag coefficient in the drag equation.” Elsewhere he states that slush has a density 50 to 80 percent that of water.
It would be necessary to know the width of the “tyre” to calculate the contribution of standing water to total deceleration of the airplane. As to the second question, how deep must the water be to cause the airplane to tip onto its nose, one would have to know both the specific location of the center of mass of the airplane and the downward force that up-elevator exerts during the landing roll. Perhaps one of the engineers on the forum (Walt?) could give it a go.
Tire width was 15 inches. These calculations are worth doing and, in fact, necessary if we’re going to accurately establish the window of opportunity when the airplane could have been landed on the reef that day.
Fred Goerner recruited Theodore D. McCown, an anthropologist at the University of California – Berkeley, to examine the skeletal remains possessed by Goerner. McCown received a letter from Horace L. Cartee of Miami FL, who performed dental work on AE the day before the flight left Miami. The letter from Cartee referred to Collins W. Sword as AE’s general dentist in Miami.
Horace Leslie Cartee (b. 3 October 1899 in Carter KY, d. 21 July 1978 probably in or near Miami FL) graduated from the University of Louisville School of Dentistry in 1923. He moved to Florida in 1926, married Miss Frank Alma Peters of Miami in 1931, and they had one daughter, Almalee. Cartee had a distinguished career as an oral surgeon and was active in national and international professional organizations. He was Vice-President, President-Elect, and President of the state East Coast District Dental Society between 1936 and 1939. A Mason and a Shriner, Cartee was also active in the social and civic life of Miami, including the Law Enforcement League of Dade County, the Miami Chamber of Commerce, the Committee of One Hundred, the Century Club, the Kiwanis Club, the Biscayne Bay Yacht Club, the Miami Country Club, and the Coral Reef Yacht Club. In short, he seems to have been a candidate to socialize with the Putnams.
Collins W. Swords (b. 4 November 1891 in Big Cane LA, d. probably 1950 in or near Miami FL) was from a prominent family in St. Landry Parish LA. Swords graduated from the Northwestern University School of Dentistry in 1912. He moved to Florida some time after 1914. He was the state East Coast District Dental Society’s delegate to the Florida State Dental Society (later known as the Florida Dental Association) from 1945 to 1947, therefore he and Cartee likely knew each other well.
Last October I contacted Samuel B. Low, Associate Dean of the University of Florida’s College of Dentistry, for advice on how to track down dental records from the 1930's in Florida. Dr. Low’s opinion was that it is unlikely any survive, and he knew of no additional resources within the College. Neither the Florida Dental Association nor the American Association of Oral and Maxillofacial Surgeons (formerly known as the American Society of Oral Surgeons; Cartee was President-Elect in 1949) responded to requests for information. The University of Louisville Archives and Records Center has no information on Cartee other than his academic records. Cartee never published anything in the Journal of Oral Surgery or the Journal of Oral and Maxillofacial Surgery. The Northwestern University School of Dentistry is closed.
For any forum members in south Florida, obituaries for Swords (1950) and especially Cartee (1978) in the Dade, Broward, or Palm Beach County newspapers may mention the names of other dentists who might have taken their active patients and preserved their records after they retired. Notices to patients may have appeared in the newspapers before they closed their practices, which could provide a clue to who received the records. Almalee Cartee may be able to provide relevant information.
The correspondence, manuscripts, reports, and photographs of McCown (b. 1908, d. 1969) are preserved at the Bancroft Library at UC-Berkeley. If among them, the letter from Cartee would make a great “Original Document” on the TIGHAR website.
Dan Brown, #2408
Whew! Good work. Anybody want to check out the Bancroft Library at UC-Berkeley?
>>In the past
various forum members have inquired about Winslow Reef which
Rather than landing, I would submit that if our disillusioned aviators came upon the 4 Winslow reefs and the reefs were properly identified, a direct bearing to any other location would have been gained. Note that there are 4 exposed reefs in the immediate vicienty, not one. Therefore, 4 times more likely to visually acquire.
However, several questions come to mind. Not having large scale charts of the area between Howland and Nikumaroro I ask the following:
1. How far off the LOP are the Winslow Reefs?
Other than a navigation check point, I don’t think the Winslow Reefs would be of much use.
Somebody want to plot that out?
From Dan Postellon
I wouldn’t want to have to land there, though. It sounds like the “cays”/sandy islands come and go with the storms, and might be awash most of the time. Sounds like Kingman reef, only smaller. Note the shipwreck on the detailed map. I wonder if every rock and island in the Pacific has at least one shipwreck (hopefully not a castaway as well)
I wonder if the “shipwreck” is really the metal frame mentioned.
From Alan Caldwell
Roger, for those who are interested here is the pertinent paragraph of your URL cite.
As a pilot it doesn’t sound inviting. And I would like to assume the yacht that saw the tower structure knew what they were looking at. Tower framework wouldn't look like a wrecked airplane, ... right? <G>
From Randy Jacobson
Still, the Colorado aviators flew right over the area, and still could not see it. Even if AE and FN did land there, they were soon underwater.
From Tom MM
What interesting stuff – directly in conflict with much that we have heard. I have to admit that I’m a little dubious.
Some quick observations:
1. I’ve compared Shippke’s chart with several small scale charts commercial covering the area, and they agree fairly closely. No commerical chart that I have seen comes close to the large scale of his chart.
2. If you superimpose Lambrecht’s sketch chart on Schippke’s, it would appear that the Colorado flights did indeed cover this area thoroughly. On 7 July, they would have flown directly over the “Doric Crain” reef (Reef and Sandbank on Lambrecht’s sketch). On 8 July, the search passed within 4-5 NM at most from all the features on Schippke’s chart except for the “Hanston Reef”. Their first turn on the search pattern was very close to “Belle Blue Reef”.
3. Lambrecht’s location of Winslow Reef is roughly 10-15 NM ESE of where it is located on modern charts. Nevertheless, the search pattern would have brought them almost directly over the modern location.
4. Shippke’s text clearly describes Winslow Reef at or obove the surface, while modern charts indicate a depth of about 36 feet.
5. Interestingly, among his sources is Lambrecht’s report(?). Lambrecht, of course, did not find anything reef related.
6. I’m totally baffled about the steel tower remains on “Gigant Rock” on Winslow. This makes almost no sense given the remoteness of the location, the clear difficulty of close approach, and the utter lack of a good reason for the effort. I doubt that a navigational safety light would have been worth installing and maintaining, and it did not sound like a good place to stay, even for short periods. The first storm surge would make things very unpleasant. Maybe it is the frame of the Electra, nose down. (OK, JUST KIDDING).
Winslow has been a very confusing issue. On the one had, we have charts, developed from reliable and credible observations that show at least “Reef and sandbank” formation in the general area. On the other hand, from what I have heard, they are not visible today. Now we have O’Brayan in 1932 showing substantial features and Lambrecht with a flight of searchers with observers not seeing a thing in 1937. Later, in 1967, they are back and now have the remains of a steel tower. The tide range (low to high) is not great enough in this region to explain the sudden appearances and disappearances. Also, in these clear waters a reef 30 or so feet down or the surface disturbance related to it should have been discernable to Lambrecht, unless the sea was rough enough to be whitecaps everywhere. But that would have made the search for anything, including AE and FN all but impossible. If volcanic activity is involved, it certainly is an active area.
I did notice on the Scripps Institute site a page titled “Scripps Log, February 26 - March 5, 1999 vol. 36 no. 8.” Part way down, we find “R/V Melville, Nova Leg 2 Weekly Report – The Melville has now completed the fourth week of its marine geological/geophysical investigation of seamounts and atolls in the Gilbert/Tokelau region. We sampled and surveyed the northern portion of this chain, between Howland Island and Winslow Reef.”
I think TIGHAR looked into Winslow at one time. Was Scripps contacted to see what info they can provide on this slippery eel?
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