Highlights From the Forum
September 10 through 16, 2000
(click on the number to go directly to that message)
|1||Log Accuracy||10||That "Navy" Receiver|
|2||Re: The 281 Message||11||Re: Janet’s Questions|
|3||Takeoff and Climb Performance||12||Re: Takeoff and Climb Performance|
|4||Re: Fuel Reserves||13||The Point of the Project|
|5||Takeoff Performance||14||Lae Takeoff|
|6||Electra Instruments MTBF||15||Takeoff Distance|
|7||Please Welcome Mr. Gallagher||16||Re: Lae Takeoff|
|8||Takeoff Performance||17||Cambridge Analyzer Thoughts|
> I think we have
to accept what is recorded in the Itasca’s radio log as being
I agree with Ric.
I would add that we shouldn’t try to read too much literal meaning into the Itasca’s log entries of voice communications. The Itasca’s operators (all of whom except Bellarts were junior petty officers with relatively little operational experience) were accustomed to communicating principally via Morse code, which is slow and rhythmic compared to voice. Even at 30 words per minute, a high rate for CW, an experienced operator can keep up with the flow and maintain an accurate log. But conversational voice speed is on the order of 100 words per minute, and it was undoubtedly very difficult for the Itasca’s operators, with little experience on voice circuits, to keep accurate literal logs of Earhart’s voice transmissions. It would have been difficult even under ideal conditions, and paraphrasing what they heard was their only hope of keeping up. I think that much of what we see in the logs reflects paraphrasing under pressure, and we shouldn’t try to read more than general meaning into such entries.
Bob Brandenburg, #2286
Vern Klein wrote:
> We should not
forget that 1937 was a peak in the 11-year cycle of solar
Although 1937 was indeed a peak in the solar cycle, it is instructive to consider the day-to-day variability in the sunspot number (SSN) during that year.
The overall average SSN for 1937 was 145.1. The maximum, 223, occurred on 12 July, and the minimum, 14, occurred on 1 December. The month with the lowest average, 74.4, was November, and the month with the highest average, 145.1, was July. The SSN on 5 July was 91, which is significantly lower than the annual or monthly averages would suggest.
The optimum propagation path from Gardner to Wailupe at the time of the "281" message was via the F2 layer, with a single hop, i.e., no surface bounces involved.
It’s worth noting that sunspot number is not the only determinant of signal strength at the receiver. Path loss depends, among other things, upon the takeoff angle at the transmitter, the vertical angle above horizontal at which the energy radiated along the path leaves the transmitter antenna. In the case of a signal from Gardner Island at the time of the "281" message, the take off angle was 1 degree, which means relatively high absorption loss during refraction in the ionosphere. The takeoff angle also determines the antenna gain in the direction of the receiver, which for Earhart’s antenna was extremely low. Antenna radiation efficiency, which was quite low in Earhart’s antenna, determines how much of the total power input to the antenna is converted to radiated energy. The product of antenna gain, antenna input power, and radiation efficiency determines how much power is radiated in the direction of the receiver. In Earhart’s case, this was an extremely small value. You can read the details in the 8th edition.
The bottom line is that the signal strength, and thus the signal-to-noise ratio (SNR), at Wailupe for a signal from Gardner Island was so far below the detection threshold that there is no plausible hypothesis that would explain the "281" message having originated at Gardner Island.
For Doug Brutlag:
I am inclined to agree with Ric that there were no octane enhancers available to Amelia at Lae. Tetraethyl lead (TEL) was, of course, a basic fuel additive used to inhibit detonation (knock). Beyond adding TEL, in those days octane ratings were achieved through blending a straight run (distillation) gasoline with iso octane, for example. A lot depended upon the refining method and the source of the crude oil. Some fields yielded product with more beneficial aromatic content than others. California crudes were much better as a basis for aviation gasoline than say Pennsylvania crudes.
It is historically worth noting that many chemical compounds tended to inhibit detonation. C.F. Taylor in his book The Internal Combustion Engine lists 45 compounds. None, I should point out, were close to the effectiveness of TEL. Were any of these compounds available at Lae? I very strongly doubt it.
Your comments regarding takeoff with a massive overload are well taken. I followed the recent Lae takeoff film comments on the Forum with considerable interest. I developed an estimated weight statement (assuming 1,100 gallons of fuel) of 15,200 pounds. At that gross weight, the calculated takeoff distance is 2,900 feet. Yet apparently the takeoff film indicates a considerably shorter run possibly suggesting: 1) a considerably lower gross weight; or 2) the takeoff may not have been the last flight.
Because my baseline gross weight estimate cannot be entirely accurate, I looked at gross weights of 14,500 pounds and 15,300 pounds and again calculated takeoff distance. This was merely a sensitivity analysis without considering how the weight might have been added or taken away. This produced takeoff runs of 2,550 feet and 2,990 feet, respectively. (The calculations take into account a ground effect factor by the way.) The methodology I used is presented in Flight, by John D. Anderson, Jr., McGraw-Hill, 2000, pp. 421-426, although any aerodynamic text should cover this performance subject.
Put any reasonable tolerance on my numbers you wish, but to me there remains a puzzling inconsistency between the film representation, eye witness comments about Amelia’s takeoff roll, and calculated takeoff estimates. The major weight variable is fuel and if the takeoff roll was significantly less than 3,000 feet, there may not have been 1,100 gallons on board. I know this has been debated long ago, and only bring it up to illustrate what I perceive to be a significant discrepancy with respect to available information and analysis.
This is a long winded way of saying I completely share Mr. Brutlag’s thoughts about the very real problems associated with Amelia’s Lae takeoff. I wish we all had the answers.
Within the next day or so we should have a new Research Bulletin up on the website that includes several aerial photos of the airfield at Lae and 16 photos (some never before published) taken at Lae during Earhart’s and Noonan’s stay. Once you have a good feel for the lay-out at Lae I think you’ll agree with me that both the film and the still photo, without question, show the July 2nd take off. As I’ve said before, I see no inconsistency in the eyewitness accounts versus the film. If there is an inconsistency between the film and the calculations, I would look at the calculations.
In a nutshell, the airplane has to be lighter than your calculations say it is. There are only two ways to reduce the weight of an airplane -- make the load lighter or make the airplane itself lighter. The sources describing the fuel load seem very credible and are very specific. There were 1,100 U.S. gallons of gas aboard (give or take an insignificant amount). The factor we really don’t have a handle on is the empty weight of the airplane.
Your 2,550 foot takeoff run at a gross weight of 14,500 pounds exactly matches Chater’s estimate of what actually happened and also agrees with what is shown in the film. An 1,100 gallon fuel load (at standard temperature) would weigh 6, 600 pounds. Sixty gallons of "Stanavo 120" oil would be another-- what? -- 720 pounds? ( I’m guessing. l’ve forgotten what oil weighs.) Allow another 360 pounds for two people and we’re left with an empty weight for the airplane of 6,820 pounds. The advertised empty weight of the airline version Model 10E (including Western Electric radios and trailing wire) was 7,100 pounds. Is it unreasonable to think that Earhart’s stripped-down 10E Special, minus airline seats and accoutrements, might come in about 300 pounds or so under that?
Several months ago, I compared C-47/DC-3 cruise data (using comparable power-to-weight ratios and similar wing loading) with the L-10E numbers that have been published. The purpose was to (1) apply a test of reasonableness, and (2) attempt to validate a personal theory that Air Nautical Miles per (Unit) of Fuel would have improved during the late stages of the flight, regardless of AE’s technique.
The numbers for the first hour of flight didn’t match very well UNTIL I noticed a note in the C-47 manual that required the addition of 270 pounds of fuel for warm-up and takeoff. When the 270 pounds was added to the climb fuel, the fuel consumption curves for the first hour of flight paralleled rather nicely. One hundred gallons per hour passes the test of reasonableness.
Validation of my theory concerning fuel consumption during the later stages of the flight didn’t produce the results I expected. This was partially due to the fact that the C-47 has a low-RPM limit of 1700. As you probably know, low RPM is important in order to take advantage of lower internal friction losses in the engine.
Rate of Climb for the C-47 at 3,000 Density Altitude (comparable P/W ratio) are:
At 10,000 Density Altitude:
As a mattter of fact, Skeet’s exercise indicates that Kelly Johnson’s numbers are on the conservative side (which is what Kelly himself indicated to Earhart when he said, "Gallons per hour should run (a) little under figures given."
Published empty weight data for a standard 10E is 7,100 pounds as you indicate. Lockheed removed 566 pounds in the form of seats, lavatory, radio (Putnam would supply the radio) etc., bringing the empty weight down to 6,534 pounds. What you are neglecting in your empty weight assessment is the amount of weight Lockheed added to the airframe primarily in the form of extra wing and fuselage tanks. This brought the empty weight back up to 7,023 pounds. (I am using Lockheed numbers for Amelia’s airplane, not my own.)
Additional items were added by Lockheed in the form of a Sperry gryro, extra battery, radio, deicing equipment, structural tie down points, and fuel system plumbing amounting to 521 pounds, again Lockheed numbers. This brought the weight up to 7,544 pounds. Prior to licensing in June 1936, approximately 50 pounds were removed in the form of one 47 gallon fuel tank and the false flooring. Call the empty weight 7,500 pounds at that point in time.
Sixty gallons of oil at 7.5 pounds per gallon is 450 pounds. Add 1,100 gallons of fuel at 6 pounds per gallon (standard temperature) or 6,600 pounds. Using your crew weight of 360 pounds, minimum gross takeoff weight is 14,910 pounds. I say minimum because this does not include any work station for Noonan, a DF installation and lower antenna installation. I estimate 45 pounds additional weight bringing the gross to 14,955 pounds. (There would also have been some weight pickup due to aircraft usage which I have not tried to estimate, but the military did make such an allowance.) In any event, I believe the airplane weighed very close to 15,000 pounds when it took off from Lae if indeed it carried 1,100 gallons of fuel. At that gross weight, the calculated takeoff distance is in excess of 2,800 feet.
You state that: "If there is an inconsistency between the film and the calculations, I would look at the calculations." I have quoted the source of the method I used. I respectfully suggest that you, or someone you choose, perform these calculations and show me where I am in error.
I don’t question your methodology or your arithmetic. I think the key is in the empty weight. I have not seen the Lockheed documents you mention detailing the weight changes. Sounds like the last point at which you have a documented empty weight for the machine was when it was delivered in the summer of 1936 at ballpark 7,500 pounds. At that time it had the same transmitter and receiver and belly antenna it had when it disappeared. It also had a trailing wire antenna (length/weight?) that was removed and replaced by the Bendix loop and the dorsal vee for what I would guess would be a small net loss in weight (not the 45 pound increase you suggest).
The big bugaboo in all this has to be the repairs that were done after the Luke Field wreck. That whole airplane was pretty much taken apart and put back together with the benefit of the experience of the aborted first World Flight attempt. By that time everyone knew from bitter experience that weight was a major concern. That’s when the trailing wire went away along with the port side belly antenna. Photos also suggest that Manning’s elaborate navigator’s station was either eliminated or vastly trimmed. Sure would be nice to have an empty weight for the airplane on, say, May 19, 1937 when the airplane was inspected and signed off after the repairs were completed.
Finally, I wonder how much headwind you factored into the takeoff? There wasn’t much. Maybe five knots, looking at the smoke -- but we’re down to talking a few pounds and few feet -- and a little breeze on the nose can be significant.
Has anyone determined whether MTBF (mean time between failure) data for the Cambridge analyzer, Eclipse fuel meter, and other engine performance instruments still exist, perhaps in the archives of airlines that flew Model 10 Electras (like NorthWest Airlines)? Or, engine manufacturers like Pratt & Whitney? Also, what became of the Cambridge Instrument Company, Inc.?
According to the description of the Cambridge exhaust gas analyzer in "Aircraft Engine Maintenance for the Engine Mechanic" (Pitman Publishing Co., 1939) the exhaust gas analyzer was configured for one fuel octane rating. I don’t have any information about how the exhause gas analyzer would work if the fuel supply were switched from 100 to 87 octane during flight.
The only thing nicer than finding someone you’ve been looking for a long time is having them find you first. It is my pleasure and honor to introduce our newest forum subscriber. Better yet, I’ll let him introduce himself:
Hi my name is Gerry Gallagher and I live in Scotland. I have for some time been researching a family member that I had heard about as a child. My Grandfather used to tell my Mother who passed on to me the story of a relative who was in the Colonial service in the South Pacific. I am named after him although spelled Gerard instead of Gerald. My grandfather was James Bernard Gallagher. Our roots stem from Ireland although our branch has lived in Scotland for may years.
I immediately replied to Gerry’s email and asked for his phone number which he promptly supplied and I immediately rang him up. Gerry is a 45 year-old maritime attorney who lived in the States for several years. I’ll be sending him the information we already have on "Irish" and he’ll be asking his mother (who has lived in Oregon since 1963) whether she knows anything about what happened to Gerald’s personal effects, including the photo album.
I warned Gerry that by subscribing to the Earhart Forum he had stumbled into instant celebrity and he is braced for your questions, but please bear in mind that, at this point, we may know more about "Irish" than he does.
The theoretical takeoff performance is predicated on zero wind velocity.
I agree that an actual empty weight measurement after the rebuild would be awfully nice to have at hand. It apparently does not exist, and this does not surprise me in the least. A good weight and balance engineer would have maintained a log documenting changes made at the time, so it would not have been necessary to do an actual weighing. In any event, I was unable to locate this type of document at the time I had access to the Lockheed archives.
You are correct with respect to my weight data. It pertains to the summer of 1936. This is a good building block, however, upon which to estimate gross weight at a later date. It certainly is much better than trying to estimate weight numbers using published data for the Standard 10E, for instance.
I believe I have weight data in one of my textbooks that will suffice to approximate the weight of the trailing wire antenna. Will look that up and take it into account. Lockheed data did not estimate any weight for the navigator’s station, trailing antenna or a DF system. So whatever it was, it was additive. Estimate whatever number seems comfortable. My number of 45 pounds may be high, but we also know it was not zero.
I do not share your concern or uncertainty over what was done during the post-accident repairs. Weight was always a serious concern to Lockheed, even before the purchase documents were signed by the Putnams. There is documentation confirming this point.
To the best of my understanding, the Hawaii accident was not specifically due to the gross weight situation. Therefore, it seems safe to assume there was little or no weight addition due to structural modifications unless you have documentation to demonstrate otherwise. Nor can I think of any logical reason weight would have appreciably diminished (other than the long antenna).
Any significant weight reduction (or addition) after the accident would have to have been done judiciously or the center of gravity about the mean aerodynamic chord could have gone out of the allowable tolerance.
Removal of the trailing antenna at Burbank as you note, or in Miami as some have written, seems to me more a matter of Amelia’s disregard or disdain for radio communications. Regardless, there is no doubt that removing this equipment saved a bit of weight. This needs to be in the weight accounting estimate.
I agree that a weight and balance determination after the rebuild would be very helpful. I’m not sure I can construct a balance diagram, but it may be worth attempting. One variable in fuel consumption involves the aircraft angle of attack at any given point in time. In other words, could Amelia trim the aircraft to minimize drag at all points during the flight? If not, fuel consumption would have been higher than we might estimate. Just one more variable to ponder.
Anyone on the Forum that might be willing to help be do a rigorous weight and balance estimate?
If the film shows the July 2nd takeoff (and, as you know, I think it does), then the wind was not zero. I can’t look at the smoke in the film and provide a judgement of the wind other than to say "Eh, maybe 5 knots." but that could be a big 5 knots when we’re looking at tolerances this tight.
The Cambridge Fuel Analyzer was used both by the military and commercial air lines around the time Amelia Earhart had one in her Electra 10E. Thus a search of Air Corps and/or air line records might uncover MTBF data. Finding these data may be as illusive as agreeing on a gross weight for Amelia’s Lae takeoff . . .
I can think of no reason the Cambridge Analyzer would not adequately function with either 87 or 100 octane fuel. There may be a bit more tetraethyl lead in 100 octane, but this would result in only trace element variations in the exhaust gases considering that TEL was added in cubic centimeter quantities to the gallon.
The products of complete gasoline combustion are carbon dioxide and water vapor. Where the mixture ratio is such that combustion is less than efficient (most of the time for various reasons) the combustion products will also include unburned hydrocarbons and carbon monoxide. In fact, one measure of combustion efficiency is the ratio of carbon monoxide to carbon dioxide in the exhaust.
The basis of the Cambridge instrument was a Wheatstone bridge and the thermal conductivity of the combustion gas. Different gaseous mixtures will have different conductivities. Thus the exhaust gas composition can be directly related to the input mixture ratio.
If you are looking for possible failure modes, I would suggest the heated bridge wire spirals (most likely platinum) may have been the weak link (no pun intended) of this instrument. Shock, vibration and thermal degradation of the wire are likely culprits.
A box marked, "U.S. Navy" may not imply a direct transfer from the Navy.
With a letter dated, March 20, 1988, Fred Goerner sent a copy of a photo of a Bendix RA-1B Aircraft Receiver to Joe Gurr and asked if that was the receiver he installed aboard Amelia’s plane. The photocopy was from Donohue’s book, The Earhart Disappearance -- The British Connection.
The response to that question seems to be in Gurr’s letter dated, March 29, 1988. He makes reference to the Donohue book and says, "I did not personally install the receiver. Lockheed did, with a certain amount of advisory help from me."
It does seem odd that Gurr would not know what receiver that was -- if it was the Bendix RA-1B. The photo shows a prominent name-plate on both the receiver and the Remote Control. The latter was certainly in sight.
Perhaps the most interesting thing that can be made out on my rather poor copy is the Antenna terminal arrangement at the top left corner of the receiver panel. There are three terminals: "A", "DF" and "G".
This suggests that the "Coupling Unit" was needed by this receiver to transform the balanced Loop configuration to unbalanced, ground referenced, antenna input to the receiver. The "DF" antenna terminal may be a high-impedance input to some point in the 1st RF stage other than the low-impedance primary coil windings probably used by the "A" antenna terminal.
I also have a copy of the same photo from TIGHAR (Lombardo Report) from which I can make out that the knob right next to the antenna terminals is Marked, "ANTENNA SWITCH". I can make out switch positions "DF" and "TA" (Terminal A?) but can’t make out the third position. Oddly, there seems to be no such switch on the Remote Control.
The antenna switching may be handled by the "Coupling Unit" installed where it can be reached. Thus an antenna switch is not needed on the Remote Control. Such switching to an "A" or "DF" receiver connection is not seen in the RDF-1 circuitry we’ve been studying but that is not the same "Coupling Unit", it’s just a similar unit.
Did Amelia specifically say it was a Western Electric receiver under the co-pilot’s seat? I’m too lazy to search for the quote!
Do we have a schematic diagram of the Bendix RA-1B receiver?
Does Donohue cite a source for the caption under the photo of the Bendix receiver in his book? The photo is on page 154 in the book. The caption says, "... supplied by U.S. government to the Earhart and Dr. Richard Archbold expeditions..." This might, or might not, support Gurr’s story of the "Navy" receiver.
Yes, in Karachi Amelia specifically mentioned the Western Electric receiver under the copilot’s seat.
Donohue credits the photo of the Bendix RA-1B receiver, dynamotor, and remote to "Vernon Moore, Bendix Project Engineer."
Why are a box of records at the University of Wyoming, Noonan’s traffic tickets, the 1940’s plumbing system on Gardner Island., etc., ALWAYS more important to TIGHAR than finding the people at Pan Am who may have installed / changed / repaired Earhart’s communications equipment in Miami, the MTBF of the Cambridge gas analyzer, the problems that other Lockheed Model 10’s encountered with P & W engines during severe service, the radio propagation for 3105 KC on July 1-5, 1937, photos of the Electra’s instruments, radios, and antennas taken during the last flight, etc.?
In short, we try to focus our limited resources on avenues of research that will produce real evidence rather than just more speculation. Sometimes people like to chase pet subjects and there’s no harm in that as long as it doesn’t detract from the main focus of the investigation which is to figure out what really happened and why.
In reguard to Ric’s comments: Could a 10E stripped of its interior furnishings come in 300 lbs. less than a reported empty weight of 7100 lbs? I vote yes.
My AT-7 (military Twin Beech) with its 5 place interior, astro dome, & lighting came in at an empty weight of about 6000 lbs. give or take a couple hundred. A model D-18 which is the identical airframe to the AT-7 converted to a freighter, comes in about 400-500 lbs lighter. We have to factor in the weight of the auxillary fuel system, radios, survival gear, food, water, ect. The material I’ve read suggests that the aux tanking was not your typical ferry pilot set-up using 55 gallon drums, bladders, electric bendix pump hot-wired to the battery bus, but rather off the shelf or perhaps custom fuel tanks built to fit in the belly of a 10E. Does any of the surviving documentation include info or any clues as to the specs & weights of these items? I hate to keep bringing up the Twin Beech comparisons but they had similarities. I brought up the subject of octane enhancers as it was possible to draw more badly needed horses out of the Pratts in this scenario. Water/meth injection (ADI) was not yet developed or available.
Not to ask a stupid question Birch but did your analysis include a factor for the turf runway gradient? This would be a further degradation of takeoff performance compared to a hard surface runway as you well know, but can you compute a correction factor for it as I would speculate one would not find a chart in the manual. Was there much of slope either way?
Birch, you certainly know your petro chemicals & I won’t dispute your performance numbers. Both you & Ric make some valid points on this subject. In spite of it all I still cannot get in my mind how in fornication AE got this overloaded hog off that turf runway in the high density altitude without having mastered or being an "ace" if you will in a Lockheed 10E. In my opinion she did not & was not.
Doug Brutlag #2335
You mean you don’t believe she made the takeoff? That’s a pretty hard position to support. AE may have been no whiz at radio (to say the least), but by the time she got to Lae she had lots of time-in-type flying that particular machine into and out of all sorts of weird places with heavy fuel loads. The takeoff from Lae was an extreme case but she was rather obviously able to handle it.
Since there have been many differing opinions expressed regarding the ultimate disposition of historically notable aircraft, we should try to keep in mind that the single most important aspect of the search for AE/FN’s Electra (at least in my opinion) is to finally & definitively determine the answers to at least two of the 60+ year old questions which have occupied the minds of AE/FN searchers, ever since the last (documented) message was broadcast from the Electra to Itasca:
Until the aircraft is located, or the remains of the crew found, we can never know for certain the ’final’ answer to those two basic questions which presently, continue to be the ongoing subject of considerable conjecture, speculation & supposition!
Even if the remains of the aircraft & crew are found &/or recovered, the exact answers to these questions may never be fully or satisfactorilly explained unless, along with the remains, some further means of documenting such answers (diaries, journal pages, log notes or the original charts which FN actually utilized on this journey) is found, & thus the conjecture, speculation & suppositon will continue.
All of which would probably make the recovered Electra a prized museum piece, an icon to perpetuate the AE mystery, which has all the trappings of mythological proportions, for people really do love unexplained mysteries, as once the mystery is resolved, the Electra becomes, simply, another aircraft from the ’olden times’, taking up additional museum space, unless or until a ’hotter’ prospect comes on the scene.
I don’t question she made the takeoff Ric. I’ve always questioned her proficiency in the 10E though. Just seeing the numbers coming out of the Lae takeoff scenario the odds were very much in favor of Chuck Yeager or anyone else becoming toast. I’ve flown a Twin Beech in & out of our 2200 ft. grass runway where I live with known wind factors with 2 pilots & minimum fuel load. The other pilot with me was an experienced Twin Beech pilot checking me out who had 1200 hours in type and knew the machine inside and out-literally..he’s also and A&P & IA. Doesn’t make me the authority on this by no means, but we knew what we could fly, carry, where to abort, where & how to crash, and when we could feather a prop & go for it along with the numbers to make it fly. I have yet to see enough of this basic aviation technique(s) out of AE’s history to consider her any more than a notch or two above "amateur". At best I would consider her an "experienced amateur". When she went into the Electra, to my knowledge she had no previous multiengine experience. I believe she did get some training in the lockheed prior to the first world flight attempt but not near enough in my opinion to be safe or competent. Both of us have seen enough pileups to know that an aircraft is a poor classroom and on the job training is not something left to be done solo. The fact that she made it as far as she did could be used to contradict this statement and I’m not too stubborn to consider it. In any case she had a bull by the horns trying to fly the 10E. Anyone would have. She was definitely not a professional-not even close. I would put her somewhere between amateur & professional. I would put her light-years ahead of Linda Finch though-definely amateur-RANK AMATEUR at that.
I think her judgement was also lacking as the world flight attempt was without a doubt biting off way more than she could chew. I think Fred’s knowledge and experience was used in making some judgement calls which is why I support TIGHAR’s Gardner Island hypothisis.
Ok, enough of the pontification:
Doug Brutlag #2335
The answer to your question is yes, I should be able to factor in headwind velocity in calculating takeoff distance. Velocity is a component of the dynamic pressure q, and it is in the denominator of the takeoff distance equation. I will try and do this in the near future.
I believe you or someone on the Forum inquired about the variation in rolling friction or resistance of landing gear tires as a function of different takeoff surfaces. NACA report number 450 by Walter S. Diehl entitled "The Calculation of Takeoff Run" contains this type of data. This 1922 report can probably be downloaded from the NASA/NACA web site. NACA Report No. 583 investigated "The Rolling Friction of Several Airplane Wheels and Tires and the Effect of Rolling Friction On Takeoff." The author is J.W. Wetmore, and may be downloaded also. Technical Aerodynamics by Karl D. Wood, McGraw-Hill, 1947 presents similar data.
I would like to ask you some detail questions about your Twin Beech fuel system if you don’t mind. Please email me privately.
Earhart had owned and flown the 10-E for quite a number of hours in a variety of flights in the almost year before she left on her last flight. Kelly Johnson in his autobiography says she was a "very good pilot". Paul Mantz put her down as a pilot after she was lost, but this was after he had been let go as technical advisor and replaced by Kelly Johnson. Mantz was macho and probably a bit miffed and even jealous after that. He was widely known, widely respected as a pilot, and probably widely quoted, but that doesn’t necessarily mean that he was being honest or correct in his statements regarding Earhart’s abilities with the 10-E.
To quantify the issue, at the time the Electra came out of repairs on May 19, 1937 it had 181 hours and 17 minutes of total "flight time" as shown in the Bureau of Air Commerce Aircraft Inspection Report. Earhart was probably pilot in command for most of that time. The World Flight as far as Lae has been estimated by Elgen Long to have entailed another 161 hours of flying, all of which was done by Earhart. Even a conservative estimate would give AE something over 300 hours time in type at the time of the Lae takeoff.
In response to Ross Devitt’s question concerning the "cartridge" unit replaced at Lae, I reviewed an undated (1930s era) five page instruction manual for the Cambridge instrument system written by someone at Lockheed, possibly Kelly Johnson. I also again read Chapter 11 (entitled "Cambridge Aero Mixture Indicator," pp. 76-93) in the book Pilot’s and Mechanics Aircraft Instrument Manual, by G.C. DeBaud, The Ronald Press Co., New York, 1942. In both instances the assembly containing the Wheatstone bridge is referred to as the "analysis cell." This cell could be removed and replaced as you might expect.
A careful reading and study of the diagrams in both references suggests there is no other subassembly one could logically refer to as a "cartridge." So I think it is safe to say the cartridge and the analysis cell are one and the same.
While on the subject of the Cambridge analyzer, another consideration may be of interest to Forum members. The DeBaud book cited previously states that the instrument is accurate "to a maximum of 0.068 fuel-air mixture ratio," meaning 0.068 pounds of fuel per pound of air. (In terms of the reciprocal air-to-fuel ratio, this number becomes 1 / 0.068 = 14.7 pounds of air per pound of fuel.)
An independent 1941 experimental study of thermal conductivity analyzers (the basis of the Cambridge instrument) found "that every instrument practically ceased to function when the air-fuel ratio became leaner than 14 to 1." This work was done by J.L. Dilworth of the Department of Mechanical Engineering, Pennsylvania State College (now University). His work was presented in a paper to the Annual Meeting of the Society of Automotive Engineers on January 6, 1941. It was subsequently published in the S.A.E. Journal (Transactions), Vol. 48, No. 6, June 1941, pp. 235-239.
Kelly Johnson’s recommended fuel management scenario (see his telegrams) included Cambridge settings of 0.072 and 0.070, equivalent to air-fuel ratios of 13.9 and 14.3, respectively. Based upon the experimental data published by Dilworth, Amelia Earhart’s fuel analyzer was right on the ragged edge of accuracy if not over the edge at these settings. The Penn State data were published, of course, long after Kelly made his recommendations to Miss Earhart.
The bottom line based upon this Penn State work is that the Electra 10E engines were probably being fed a richer mixture than the analyzer indicated during the later stages of the flight to Howland.
So Janet, we don’t have MTBF data for the Cambridge unit, and I suspect the chance of running across such information is quite remote. I personally agree with you that it would be very interesting to have and with enough research might even be acquired. Corporations unfortunately tend to pay little attention to their histories and often destroy old records because of storage costs. The military might be a better possibility in this regard. Locating the right archive is a problem. Unfortunately, this type of travel and research is not within my retirement income budget.
However, the Penn State data published in the S.A.E. Journal may provide a basis for refining my fuel consumption estimates for the later stages of Amelia’s flight. Investigating the Cambridge analyzer may still pay a dividend, though not as you perceived. Had you not questioned MTBF I might not have looked a little deeper into the performance of this instrument.
The two benefits of Ric’s Earhart Forum which I have come to appreciate are: It not only informs, but makes you think.