TIGHAR
Amelia Earhart Search Forum => General discussion => Topic started by: Tim Gard on July 05, 2014, 04:39:16 AM
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Having considered this line from Betty's note book for some time, I think the statement is relevant to the state of charge of the battery.
Given that the transmitter consumed current at an higher rate than the generator could supply, it became incumbent on the person transmitting to allow sufficient non-transmission time for the generator to recover the charge.
It sounds as though the panic precipitated one of the users to exceed the duty cycle and thereby hazard the next scheduled start especially if high water forced a shutdown before the battery's charge could be restored.
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Tim...I was kinda wonderin exactly what you are referring too? I guess I missed a posting of some sorts along the way. Anyway, while we're on the subject of watchin the battery..something came to my mind and want you forum members to help me out on this. I work in a battery manufacturing plant here in Kansas and know alot about the process and longevity of batteries. One thing I do know is that batteries need distilled water or acid when they become low or are overused or exposed to heat. When batteries are subjected to heat...they evenutally will lose a cell and the life of the battery if not cared for properly. I'm assuming that Amelia and Fred never took precautionary measures on the Electra like having an extra battery on board or maintenance kit to maintain the battery. Another thing that hasnt been mentioned is if this is the case and the only water resource they had to fill the batteries was salt water...then this could be very damaging. Plus, if you fill a warm battery up with cold water...its almost the same principle of filling up a radiator with cold water when its extremely boiling. Very damaging. But, corrosion is most likely the number reason why that battery failed. Like your car batteries...if your posts aren't well cleaned then you eventually lose power. I wonder if that was the case?
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Tim...I was kinda wonderin exactly what you are referring too? I guess I missed a posting of some sorts along the way.
Anyway, while we're on the subject of watchin the battery..something came to my mind and want you forum members to help me out on this.
I haven't seen any evidence to suggest the batteries that started those big radials were defective or neglected. The Darwin photo shows the team were very aware of the needs of the Electra (Oleo Oil, engine oil etc).
Batteries will need distilled water added at short intervals if they are being overcharged or have shorted cells.
I have seen evidence that Amelia kept her transmissions brief because the generator on the starboard engine could not provide all the current the transmitter needed during transmission. That means any transmission drained the battery (or batteries depending on what Amelia had on line at that instant). Those brief transmissions are one reason why Itasca could not take a bearing on the Electra.
"Watch that battery" is consistent with the brief transmissions operating practice. It may also be that if the voltage fell below a particular level the transmission quality would be compromised, true for the July 8th 1937 transmissions consistent with operating with the generator offline.
Notice that the initial post of this thread is the anniversary of the transmission recorded in Betty's notebook.
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"Watch that battery" is consistent with the brief transmissions operating practice. It may also be that if the voltage fell below a particular level the transmission quality would be compromised, true for the July 8th 1937 transmissions consistent with operating with the generator offline.
It could be argued that there was nothing to watch, in that there was no meter that showed the state of charge of the batteries, but I would counter that they surely knew that if the charge in the batteries was allowed to become insufficient to start the engine - they were screwed. "Watch that battery!" could mean simply "I think you're transmitting too much! Give the battery a chance recover."
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I started driving long before the advent of sealed batteries, and I'm pretty sure there had been very little change in lead-acid battery technology from the time I started driving a car and Amelia's day. Adding water was a relatively rare thing to have to do, and although distilled water was preferred, almost no one bothered - tap water was virtually always used. Obviously the limiting factor in Amelia's case was the lack of gasoline, or the inability to start or run the engine because of flooding. If they could physically run the engine and had gasoline, they could always recharge the battery, although without a battery gauge it would have been rather a hit or miss operation. I would run the engine without the radio turned on, for a bit longer than the length of time that I had used the radio. I would guess the critical factor to have probably been the gasoline supply.
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This scientific paper sheds some light on how the battery charge state can be affected by various factors Tim. An interesting chapter covers 'Human, System, and Facility Safety – Threat of Fire and Explosion' Quote: "This outgassing scenario, while rare, can become an issue typically under unusual conditions, like abnormal over-voltage to the battery or abnormal high ambient heat conditions"
http://www.battcon.com/PapersFinal2008/ODonnellPaper2008PROOF_6.pdf (http://www.battcon.com/PapersFinal2008/ODonnellPaper2008PROOF_6.pdf)
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If the battery charge state was of concern to the flyers, so that a restart could be performed after the tide receded, does that imply they were aware that fuel was not approaching exhaustion on July 5th 1937 (validated by subsequent transmissions)?
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If the battery charge state was of concern to the flyers, so that a restart could be performed after the tide receded, does that imply they were aware that fuel was not approaching exhaustion on July 5th 1937 (validated by subsequent transmissions)?
Hard to say. The fuel gauges were not all that precise and they probably had no way to "stick" the tanks, so it would be hard for them to know when the rule was "approaching exhaustion' - however you define that. It could be that they figured they would just keep going until they ran out of gas.
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My first thought on measuring the available fuel, after the gauges of course, would be a dipstick. A quick run through the Luke Field post-crash inventory shows nothing like that was carried then (doesn't mean it wasn't on the second flight), but ... if you REALLY want to know if there's gas left, how hard would it be to whittle something from the ample flotsam on the beach or along the jungle's edge? It would not tell you how many gallons were left, but it could, with careful calibration, tell you how much of what was left you were burning up every time you fired up the engine to transmit.
LTM, who finds no paint as interesting as dry paint,
Monty Fowler, TIGHAR No. 2189 ECSP
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My first thought on measuring the available fuel, after the gauges of course, would be a dipstick.
Note that the fuselage tanks are filled through ports on the side of the fuselage, so the filler necks do not go straight down to the tanks. How you gonna stick those tanks?
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What conclusions can we draw about the fuel remaining in the 100 octane tank?
Is it possible to conclude that the after takeoff level was still present after arrival and shutdown at Gardner?
Did Amelia switch to that tank as part of a potential go round procedure before arrival at Gardner?
Did the reduced gross weight mitigate the need for using 100 octane under takeoff power?
My take is that as much 100 octane as possible was preserved post Lae departure because it was scarce and it would be needed to depart Howland.
If Amelia's expectation at touchdown Gardner was that she would soon be refuelled and continue the flight from Gardner, then either way she would need to preserve the 100 octane.
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Ric asks "How you gonna stick those tanks?"
I'll offer one possible answer: "you don't." You pump all remaining fuel in those tanks up to the 118 gallon starboard "header tank" (my terminology) that has the sight-glass gage next to the cockpit door, which (I'm guessing) feeds the engines through the selector valve. The cockpit had a manual fuel pump that could be selected to pump from any tank, as I recall. I think it might be safe to assume it could pump to the tank that has the sight-glass. Once the fuel level is below the bottom of the sight-glass, you've only got some fixed small quantity of fuel remaining, unless you discover a tank you hadn't previously tried pumping from, perhaps a forgotten tank partly full of 80 octane that you hadn't used since takeoff.
I don't recall confirming that the tank with the sight-glass was even a fuel tank, so this is supposition on my part.
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What conclusions can we draw about the fuel remaining in the 80 octane tank?
Is it possible to conclude that the after takeoff level was still present after arrival and shutdown at Gardiner?
Did Amelia switch to that tank as part of a potential go round procedure before arrival at Gardiner?
Did the reduced gross weight mitigate the need for using 80 octane under takeoff power?
My take is that as much 80 octane as possible was preserved post Lae departure because it was scarce and it would be needed to depart Howland.
If Amelia's expectation at touchdown Gardiner was that she would soon be refuelled and continue the flight from Gardiner, then either way she would need to preserve the 80 octane.
Tim, there was no 80 octane fuel on board the aircraft. Most of the fuel was 87 octane, later called 80/87 octane, with 100 octane reserved for takeoff. See here. (http://tighar.org/Projects/Earhart/Archives/Forum/FAQs/fuel.htm)
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If the battery charge state was of concern to the flyers, so that a restart could be performed after the tide receded, does that imply they were aware that fuel was not approaching exhaustion on July 5th 1937 (validated by subsequent transmissions)?
Tim, the Electra had two batteries (http://tighar.org/wiki/Lockheed_Electra_10E_Special_-_NR16020) on board, either of which could be connected or disconnected from the main buss for starting, radio use or charging. This one allow them to start the engine and use one battery for the radio while saving the other for starting the engine. Your guess is as good as anyone else's as to whether or not this is what they did.
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If the battery charge state was of concern to the flyers, so that a restart could be performed after the tide receded, does that imply they were aware that fuel was not approaching exhaustion on July 5th 1937 (validated by subsequent transmissions)?
Tim, the Electra had two batteries (http://tighar.org/wiki/Lockheed_Electra_10E_Special_-_NR16020) on board,
Yes. I'm aware of that and commented so ...
"That means any transmission drained the battery (or batteries depending on what Amelia had on line at that instant)."
They kept one fully charged battery isolated during the transmissions to mitigate the risk of losing them both as per Bob Brandenburg's text at your link.
That means the concern was directed towards the online battery.
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What conclusions can we draw about the fuel remaining in the 80 octane tank?
Is it possible to conclude that the after takeoff level was still present after arrival and shutdown at Gardiner?
Did Amelia switch to that tank as part of a potential go round procedure before arrival at Gardiner?
Did the reduced gross weight mitigate the need for using 80 octane under takeoff power?
My take is that as much 80 octane as possible was preserved post Lae departure because it was scarce and it would be needed to depart Howland.
If Amelia's expectation at touchdown Gardiner was that she would soon be refuelled and continue the flight from Gardiner, then either way she would need to preserve the 80 octane.
Tim, there was no 80 octane fuel on board the aircraft. Most of the fuel was 87 octane, later called 80/87 octane, with 100 octane reserved for takeoff. See here. (http://tighar.org/Projects/Earhart/Archives/Forum/FAQs/fuel.htm)
Many thanks. The post has been edited.
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My first thought on measuring the available fuel, after the gauges of course, would be a dipstick.
Note that the fuselage tanks are filled through ports on the side of the fuselage, so the filler necks do not go straight down to the tanks. How you gonna stick those tanks?
Perhaps they could have used the bamboo pole that was used to pass messages back and forth.
It appears that it might have been flexible enough to reach the bottom Starboard corner of each tank.
But an accurate reading would require the aircraft to be on level ground.
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My initial impression was that the statement was driven by an ammeter showing discharge for an extended period.
Bob Brandenburg refers to the presence of an ammeter and the interpretation of its readings.
I could imagine myself saying "Watch that battery" under the same pressure.
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Yes. I'm aware of that and commented so ...
"That means any transmission drained the battery (or batteries depending on what Amelia had on line at that instant)."
They kept one fully charged battery isolated during the transmissions to mitigate the risk of losing them both as per Bob Brandenburg's text at your link.
That means the concern was directed towards the online battery.
Sorry I missed that Tim. Thanks for the correction.
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Ric asks "How you gonna stick those tanks?"
I'll offer one possible answer: "you don't." You pump all remaining fuel in those tanks up to the 118 gallon starboard "header tank" (my terminology) that has the sight-glass gage next to the cockpit door, which (I'm guessing) feeds the engines through the selector valve. The cockpit had a manual fuel pump that could be selected to pump from any tank, as I recall. I think it might be safe to assume it could pump to the tank that has the sight-glass. Once the fuel level is below the bottom of the sight-glass, you've only got some fixed small quantity of fuel remaining, unless you discover a tank you hadn't previously tried pumping from, perhaps a forgotten tank partly full of 80 octane that you hadn't used since takeoff.
I don't recall confirming that the tank with the sight-glass was even a fuel tank, so this is supposition on my part.
Does the lowest photo down show the visigauge? (http://tighar.org/smf/index.php/topic,496.msg6381.html#msg6381)
Your description makes good sense. I think those rods are pull to activate. Much easier to pull than rotate and if they did rotate, lining them up is futile.
If the visigauge shows an adequate level - meaning the transmission fuel burn is not rapidly nearing bottom, then there is no imminent fuel shortage crisis.
If that be the case then you do need to preserve battery for a future start.
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Yes, a "Visigauge" might have been the brand of sight glass, but a friend offered a correction to my "possible answer" - the hand pump in the cockpit (called a "stripper pump") could only pump to a selected wing tank, not to what I called the "header tank" in the fuselage. The fuel system diagram shows the arrangement of valves, plumbing and tanks, but not the sight glass.
So, to modify my previous possible answer - one would use the stripper pump to pump all other tanks dry into a convenient wing tank, possibly one with a gauge.
It's worth noting that aircraft fuel gauges are not to be used to measure fuel quantity, but only to indicate the presence of fuel to the most approximate degree, if that. I don't know how this might have been taught in Amelia's day, but in modern times it's drilled into flight students. If a gauge reads "E", the tank might be half full, or empty. If it reads "F", it might be half full, or full. If Amelia reported running short of fuel, and was relying on a gauge, then she might have been running on fumes, or had a half tank left.
The sight glass might have been connected to an oil tank, but that's also conjecture on my part. We just don't know.
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I've given further thought to this and it forced me to address the following question.
How soon after the Lae departure did AE effect the tank change from 100 octane to the lower octane?
Answer: As soon as possible after becoming airborne.
Eyewitnesses reported the Electra dipping towards the ocean, then recovering. At first I thought that was the Electra coming out of ground effect, but now I think it was both 1st power reduction and 1st tank change.
My reasoning follows:
Since AE had only to clear sea level, it gave her the option of using an efficient and slow cruise climb of 50 - 100 ft/min, rather than a step climb that guaranteed burning 100 octane at maximum rate (60 US Gal per hour?). The reduced weight from the fuel burn aided in the climb performance.
AE had to first reduce power to select the lower octane fuel in order to avoid blowing holes in pistons through detonation/pre-ignition, as well as reduce power to conserve fuel and lean back to 43 US gal per hour.
Having dipped the tanks just before departure, having used a defined period for startup, taxi, takeoff and climbout, having selected away from the 100 octane tank, AE now knew how much fuel remained in that tank especially having performed the procedure on so many previous departures.
That means AE knew how much 100 octane remained upon arrival at Gardiner and also knew preserving that fuel gave her a known running time for the starboard engine once she selected that tank.
This reasoning is why her focus was heavily on the state of the battery "Watch that battery" rather than transmitting for all they were worth pending an imminent and permanent stopping of the starboard engine due to fuel exhaustion.
Because I agree with Bill de Cleef's 1200 RPM minimum for charging, my estimate is that the 100 octane reserve provided for 4 hours running of the starboard engine at half cruise consumption (21.5 divided by 2 US gal / hour = 10.25 US gal / hour).
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I've given further thought to this and it forced me to address the following question.
How soon after the Lae departure did AE effect the tank change from 100 octane to the lower octane?
Answer: As soon as possible after becoming airborne.
Answer: No way to know but it would seem reasonable that she would change tanks as soon after takeoff as possible.
Eyewitnesses reported the Electra dipping towards the ocean, then recovering. At first I thought that was the Electra coming out of ground effect, but now I think it was both 1st power reduction and 1st tank change.
I would not switch tanks until I had reached a safe altitude - at least a couple thousand feet. Again, no way to know what she did.
Since AE had only to clear sea level, it gave her the option of using an efficient and slow cruise climb of 50 - 100 ft/min, rather than a step climb that guaranteed burning 100 octane at maximum rate (60 US Gal per hour?). The reduced weight from the fuel burn aided in the climb performance.
I don't think she had any choice. The thing would barely fly at that weight. The balls-to-the-wall anticipated fuel burn for the first hour of flight, according to British researcher Roy Nesbit (see attached excerpt from a 1993 TIGHAR report), was 100 gph.
AE had to first reduce power to select the lower octane fuel in order to avoid blowing holes in pistons through detonation/pre-ignition, as well as reduce power to conserve fuel and lean back to 43 US gal per hour.
According to Nesbit's table, which agrees with the Kelly Johnson telegrams (http://tighar.org/Projects/Earhart/Archives/Documents/Kelly_Johnson.html), Earhart wouldn't achieve 43 gph until 7 hours into the flight.
Having dipped the tanks just before departure, having used a defined period for startup, taxi, takeoff and climbout, having selected away from the 100 octane tank, AE now knew how much fuel remained in that tank especially having performed the procedure on so many previous departures.
Where does it say she did any of that?
That means AE knew how much 100 octane remained upon arrival at Gardiner and also knew preserving that fuel gave her a known running time for the starboard engine once she selected that tank.
If your speculation is correct.
This reasoning is why her focus was heavily on the state of the battery "Watch that battery" rather than transmitting for all they were worth pending an imminent and permanent stopping of the starboard engine due to fuel exhaustion.
It makes sense that she would be concerned about the state of the battery.
Because I agree with Bill de Cleef's 1200 RPM minimum for charging, my estimate is that the 100 octane reserve provided for 4 hours running of the starboard engine at half cruise consumption (21.5 divided by 2 US gal / hour = 10.25 US gal / hour)
In 1937, Paul Mantz told a newspaper reporter that Earhart could charge her batteries at 900 RPM burning 6 gph. We confirmed that by experimentation in 2009 at Covington Aircraft Engines in Okmulgee, OK. We put an R-1340 on a test stand connected to an Eclipse E-5 generator just like Earhart's and were able to get a positive charge of 14.25 volts (enough to trip the set point and allow the battery to charge) at 900 RPM burning 6 gph.
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Having dipped the tanks just before departure, having used a defined period for startup, taxi, takeoff and climbout, having selected away from the 100 octane tank, AE now knew how much fuel remained in that tank especially having performed the procedure on so many previous departures.
Where does it say she did any of that?
Having already covered vast expanses cossetting her 100 octane, AE has no motive to depart from that MO at Lae. Her Howland departure is as dependent on preserving the 100 octane as was the Lae departure itself. AE needs assurance of the remaining quantity of 100 octane before she can attempt the next takeoff. In doing so, the burn rate of the previous flight is also confirmed.
Also, running with a power setting so high that 100 octane is a must, creates a coffin corner. Once the 100 octane is gone, AE is left piloting an Electra that cannot fly on the remaining low octane fuel without destroying both engines. That implies an earlier power reduction to have been practical, necessary and advisable.
Because I agree with Bill de Cleef's 1200 RPM minimum for charging, my estimate is that the 100 octane reserve provided for 4 hours running of the starboard engine at half cruise consumption (21.5 divided by 2 US gal / hour = 10.25 US gal / hour)
In 1937, Paul Mantz told a newspaper reporter that Earhart could charge her batteries at 900 RPM burning 6 gph. We confirmed that by experimentation in 2009 at Covington Aircraft Engines in Okmulgee, OK. We put an R-1340 on a test stand connected to an Eclipse E-5 generator just like Earhart's and were able to get a positive charge of 14.25 volts (enough to trip the set point and allow the battery to charge) at 900 RPM burning 6 gph.
I recall the test conclusion being that AE used a "2 to 1".
Mantz' comment taken literally says the batteries could be charged at 900 RPM. It doesn't state 900 RPM to be capable of providing the generator's max current.
"Watch that battery" relates to the transmission duty cycle which becomes complex.
1. Transmitting with the engine at that RPM which also produces max current (1200 RPM), reduces the load on the batter(y/ies).
2. Transmitting with the engine at that RPM which also produces max current (1200 RPM), reduces the time to recharge the batter(y/ies) once the transmission cycle has completed.
3. The battery can be recharged at 900 RPM but the recharge will take longer because the current output is less.
4. The longer the recharge time, the greater the fuel burn.
5. Higher RPM means the battery load will be least and the recharge time will be least.
6. 900 RPM will impact the transmission quality due to voltage drop.
Integrating all that info is the ammeter, which tells the simple truth that the battery is or isn't being recharged or does not need charging (centred on 0).
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Having already covered vast expanses cossetting her 100 octane, AE has no motive to depart from that MO at Lae. Her Howland departure is as dependent on preserving the 100 octane as was the Lae departure itself. AE needs assurance of the remaining quantity of 100 octane before she can attempt the next takeoff. In doing so, the burn rate of the previous flight is also confirmed.
I agree that she would naturally want to conserve her 100 octane but I don't think it's possible to say exactly when she switched tanks. What I see you doing that worries me is that you decide what seems logical and reasonable to you and then you state it as a fact. If you do that you're building a house of cards.
Also, running with a power setting so high that 100 octane is a must, creates a coffin corner. Once the 100 octane is gone, AE is left piloting an Electra that cannot fly on the remaining low octane fuel without destroying both engines. That implies an earlier power reduction to have been practical, necessary and advisable.
Where do you get that? As far as I know she can run those engines at full throttle and at max RPM on 87 octane without hurting them.
"Watch that battery" relates to the transmission duty cycle which becomes complex.
You just did it again. Your statement is an opinion, not a fact. If you don't make a clear distinction you lose track of what you actually know.
1. Transmitting with the engine at that RPM which also produces max current (1200 RPM), reduces the load on the batter(y/ies).
2. Transmitting with the engine at that RPM which also produces max current (1200 RPM), reduces the time to recharge the batter(y/ies) once the transmission cycle has completed.
3. The battery can be recharged at 900 RPM but the recharge will take longer because the current output is less.
4. The longer the recharge time, the greater the fuel burn.
5. Higher RPM means the battery load will be least and the recharge time will be least.
6. 900 RPM will impact the transmission quality due to voltage drop.
I'd like to see the numbers that support your statements. Our tests show that the generator charge does not max out at 1200 RPM. There is no way to know what RPMs she used to charge the battery. What we do know is that she could have used as little as 900 RPM.
Integrating all that info is the ammeter, which tells the simple truth that the battery is or isn't being recharged or does not need charging (centred on 0).
Yes, and I think all we can say about "Watch that battery" is that it might be a warning not to let the battery get run down to the point where they would not be able to start the engine.
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Where do you get that? As far as I know she can run those engines at full throttle and at max RPM on 87 octane without hurting them.
That then obviates the need to carry, isolate and take off using 100 octane. Why she didn't previously burn it while it was available then fully top up the 100 octane tank at Lae to give herself the best chance makes no sense. Her fuel carrying awareness was such that she chose to leave such items as a life raft behind, yet preserved a partially full tank of 100 octane defies rationale.
"Watch that battery" relates to the transmission duty cycle which becomes complex.
You just did it again. Your statement is an opinion, not a fact. If you don't make a clear distinction you lose track of what you actually know.
I see your point.
I've spent a long time pondering the variables. My electrical engineering background amplifies the importance and emphasis AE placed on the statement.
The ammeter is all she has to ascertain the battery condition, which relates to the next start which is also dependent on having the fuel to support same. For as long as the ammeter reads discharge the situation is in crisis. Because the ammeter integrates the voltage and current peaks to produce a reading, it also reports the rate of recharge.
Low RPM low transmission time = short recharge time, reduced fuel burn but ineffective communication.
Low RPM high transmission time = long recharge time, increased fuel burn but effective communication.
High RPM low transmission time = shortened recharge time, increased fuel burn but ineffective communication.
High RPM high transmission time = shortened recharge time, increased fuel burn but effective communication.
The ammeter's reading showing a more rapid rate of battery recharging is the stress yardstick.
The sooner it comes out of discharge the better.
The sooner it comes out of charge and falls back towards 0, even better still.
I'd like to see the numbers that support your statements. Our tests show that the generator charge does not max out at 1200 RPM.
I agree completely.
The max current output is likely to occur even higher than 1200 RPM.
There is no way to know what RPMs she used to charge the battery. What we do know is that she could have used as little as 900 RPM.
I agree.
Again it is not likely to be as low as 900 RPM. The lower the RPM figure the less efficient the battery recharge process due to the non-linear response of the batteries. That is the longer the engine will have to be run to recover. The higher the RPM the lower the recharge time giving the best return for the fuel burn. Again the ammeter tells the story.
At higher RPM the needle spends less time in heavy discharge.
Integrating all that info is the ammeter, which tells the simple truth that the battery is or isn't being recharged or does not need charging (centred on 0).
Yes, and I think all we can say about "Watch that battery" is that it might be a warning not to let the battery get run down to the point where they would not be able to start the engine.
My focus remains:
1. If they thought fuel exhaustion was imminent then "damn the torpedos, full steam ahead".
2. If they thought fuel exhaustion was not imminent due to some reassuring factor, then "watch that battery."
I'm building the case that the policy of preserving the 100 octane was still in practise on arrival at Gardiner Island and that provided the reassurance of an effective restart.
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I recall the test conclusion being that AE used a "2 to 1".
Mantz' comment taken literally says the batteries could be charged at 900 RPM. It doesn't state 900 RPM to be capable of providing the generator's max current.
Mr. Gard, It is my understanding that max current is controlled by the voltage regulator which is normally 14.2 volts. Any more than that you will eventually boil the batteries and ruin them. Mantz I am sure determined that the generator on the Electra would put out 14.2 volts at 900 RPM. Less than that would discharge the batteries and eventually stall the engine. You could run that engine at 1800 RPM and you would still only by generating 14.2 volts to the battery. So your premise that 1200 RPM would charge the batteries faster is false. What affects the length of time the generator takes to charge the batteries is the load on them i.e. lights etc. With no load, the time it takes to completely recharge is the same at 900 RPM as it is at 1200 RPM given Mantz's testing. We are not talking alternators here. That is a whole different kettle of fish.
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Mr. Gard, It is my understanding that max current is controlled by the voltage regulator which is normally 14.2 volts.
You're assuming that because the generator could make 14.2 volts at 900 RPM no load, that it could make the same voltage at full load at that RPM.
The answer is that it can't. Max current output will occur at 14.2 volts and when the the armature windings are passing through the field at that RPM which provides same. That figure does not occur at minimum RPM.
Any more than that you will eventually boil the batteries and ruin them.
Agree.
It is certainly the job of the voltage regulator to regulate the voltage and regulating the voltage down to that level prevents boiled batteries.
Mantz I am sure determined that the generator on the Electra would put out 14.2 volts at 900 RPM.
Agree.
Less than that would discharge the batteries and eventually stall the engine.
Agree that the batteries would become discharged.
Disagree that the engine would stall:
1. The engine used magnetos for spark ignition so completely independent of battery state.
2. When a generator drops below charge voltage, the cut out relay breaks the circuit between battery and generator. That prevents the battery from discharging into and through the generator which also takes the load off the engine. It's as if the generator isn't even there.
You could run that engine at 1800 RPM and you would still only by generating 14.2 volts to the battery.
Agree, however the increased rate of armature windings passing the field increases the generator's ability to provide current.
So your premise that 1200 RPM would charge the batteries faster is false.
Even with an alternator you will see the battery recharge faster with an increase in RPM because the rotor is passing the field windings at a more rapid rate.
With a generator you will see the battery recharge faster with an increase in RPM because the armature windings are passing the field windings at a more rapid rate.
What affects the length of time the generator takes to charge the batteries is the load on them i.e. lights etc. With no load, the time it takes to completely recharge is the same at 900 RPM as it is at 1200 RPM. We are not talking alternators here. That is a whole different kettle of fish.
Increasing the load on a generator can decrease the rate of recharge of the battery if the generator's current limit for that RPM is exceeded.
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Where do you get that? As far as I know she can run those engines at full throttle and at max RPM on 87 octane without hurting them.
That then obviates the need to carry, isolate and take off using 100 octane. Why she didn't previously burn it while it was available then fully top up the 100 octane tank at Lae to give herself the best chance makes no sense. Her fuel carrying awareness was such that she chose to leave such items as a life raft behind, yet preserved a partially full tank of 100 octane defies rationale.
"Watch that battery" relates to the transmission duty cycle which becomes complex.
You just did it again. Your statement is an opinion, not a fact. If you don't make a clear distinction you lose track of what you actually know.
I see your point.
I've spent a long time pondering the variables. My electrical engineering background amplifies the importance and emphasis AE placed on the statement.
The ammeter is all she has to ascertain the battery condition, which relates to the next start which is also dependent on having the fuel to support same. For as long as the ammeter reads discharge the situation is in crisis. Because the ammeter integrates the voltage and current peaks to produce a reading, it also reports the rate of recharge.
Low RPM low transmission time = short recharge time, reduced fuel burn but ineffective communication.
Low RPM high transmission time = long recharge time, increased fuel burn but effective communication.
High RPM low transmission time = shortened recharge time, increased fuel burn but ineffective communication.
High RPM high transmission time = shortened recharge time, increased fuel burn but effective communication.
The ammeter's reading showing a more rapid rate of battery recharging is the stress yardstick.
The sooner it comes out of discharge the better.
The sooner it comes out of charge and falls back towards 0, even better still.
I'd like to see the numbers that support your statements. Our tests show that the generator charge does not max out at 1200 RPM.
I agree completely.
The max current output is likely to occur even higher than 1200 RPM.
There is no way to know what RPMs she used to charge the battery. What we do know is that she could have used as little as 900 RPM.
I agree.
Again it is not likely to be as low as 900 RPM. The lower the RPM figure the less efficient the battery recharge process due to the non-linear response of the batteries. That is the longer the engine will have to be run to recover. The higher the RPM the lower the recharge time giving the best return for the fuel burn. Again the ammeter tells the story.
At higher RPM the needle spends less time in heavy discharge.
Integrating all that info is the ammeter, which tells the simple truth that the battery is or isn't being recharged or does not need charging (centred on 0).
Yes, and I think all we can say about "Watch that battery" is that it might be a warning not to let the battery get run down to the point where they would not be able to start the engine.
My focus remains:
1. If they thought fuel exhaustion was imminent then "damn the torpedos, full steam ahead".
2. If they thought fuel exhaustion was not imminent due to some reassuring factor, then "watch that battery."
I'm building the case that the policy of preserving the 100 octane was still in practise on arrival at Gardiner Island and that provided the reassurance of an effective restart.
Tim,
You seem to labor under some basic misconceptions about 100 octane fuel and perhaps as to how the DC generator on the Electra operated, as Mark Samuels has pointed out.
100 octane would have had nothing to do with 'ease of starting'. It was used for take-off at high power settings to offset detonation, that's the only reason the ship bothered to have a reserve of 100 octane. At start or low power settings, it makes essentially no difference whatsoever to the engine or how it performs.
As to what I read earlier regarding your take on the take-off at Lae, I doubt seriously that Earhart switched tanks immediately, etc., etc. as accounting for her fairly dramatic run-off the end and drop toward the water, etc. Why would any pilot taking off in a heavily loaded airplane choose that moment to swiitch tanks from 100 octane to 80? Earhart did some nutty things in her time - especially with radios, but I don't recall fuel mishandling - and that's prime-time for screwing that up royally. There would be no harm in continuing on 100 octane for some time, especially while still under climb power (even with the power reduced). I don't recall all the limits on the engine off-hand, and perhaps there was a 1 or several minute limit at METO, but it matters not - the 100 octane could be burned quite happily, indefinitely. More likely she might have wanted to conserve a bit for take-off at Howland (seems like they had none, but I'm not clear on that at moment).
As to the electrical generation - Samuels is basically correct, although I would agree that voltage falls off on a DC brush type generator as RPM falls. That said, it WILL charge well down to at least around 900 RPM, and I believe TIGHAR actually has test data showing lower RPMs than that on a live engine of the same type (which is important to determining how much fuel might have been available to charge the batteries, and in turn power the radios).
Perhaps I've not read all of your suppositions well, but note as well that the radio depended directly on battery state; one could not get enough current out of that puny generator to power the radio transmitter directly. Transmissions had to be limited with an eye on battery state, then the battery charge replenished.
Your discourse is interesting, but to me also a bit convoluted, frankly (not to personally criticize, just to point out that it's confusing to the whole point, at least as I understand it). It might be profitable to consider these points and read up on what Jacobsen and others have contributed here as to these things - and consider that the matter isn't so complex: fuel available on the ground (regardless of octane) would have been the stuff of transmissions, for as long as it - or the bird, lasted. The engine could consume, if memory serves, as little as around 6 - 8 gallons an hour probably at a battery-charging low RPM. But please don't take my word for that (I'm hip shooting the details from memory anyway), it can be looked up on this site.
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Even with an alternator you will see the battery recharge faster with an increase in RPM because the rotor is passing the field windings at a more rapid rate.
With a generator you will see the battery recharge faster with an increase in RPM because the armature windings are passing the field windings at a more rapid rate.
That is a common misconception. Have you ever tried to charge a dead battery with an alternator by driving around for a couple hours. You will wake up in the morning with another dead battery. An alternator is designed to top off a battery, not fully charge it. The alternator will put out the voltage to keep the ignition system running and the engine as long as you don't have your lights and heater on. Turn the key off and you'll be getting out the jumper cables again.
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Tim,
You seem to labor under some basic misconceptions about 100 octane fuel
Jeff,
If AE did specifically plan to depart Lae using 100 octane, then she needs to do just that.
In order for the carbs to be full of 100 octane before starting the takeoff roll one needs to have allowed sufficient time for that process to occur. Interconnecting fuel lines need time to be purged of the lower octane fuel.
Startup, taxi and particularly runup is a reasonable way of ensuring that.
and perhaps as to how the DC generator on the Electra operated, as Mark Samuels has pointed out.
Mark has considered the Electra's generator to be a perfect device, devoid of frequency response, internal resistance and RPM sensitivity. I'm sure it was quite efficient for its time, but perfect it was not.
100 octane would have had nothing to do with 'ease of starting'.
I don't remember saying that.
In order for the carbs to be full of 100 octane before starting the takeoff roll one needs to have allowed sufficient time for that process to occur. Interconnecting fuel lines need time to be purged of the lower octane fuel.
Startup, taxi and particularly runup is a reasonable way of ensuring that.
It was used for take-off at high power settings to offset detonation, that's the only reason the ship bothered to have a reserve of 100 octane. At start or low power settings, it makes essentially no difference whatsoever to the engine or how it performs.
Agreed. I don't recall saying differently.
As to what I read earlier regarding your take on the take-off at Lae, I doubt seriously that Earhart switched tanks immediately, etc., etc. as accounting for her fairly dramatic run-off the end and drop toward the water, etc. Why would any pilot taking off in a heavily loaded airplane choose that moment to swiitch tanks from 100 octane to 80?
We share the same purport- that AE carried 100 octane of necessity.
So when did AE deselect 100 octane? Why not 1st power reduction if she had to reduce power anyway?
Earhart did some nutty things in her time - especially with radios, but I don't recall fuel mishandling - and that's prime-time for screwing that up royally. There would be no harm in continuing on 100 octane for some time, especially while still under climb power (even with the power reduced).
Are you now arguing against the need for 100 octane for the Howland departure, yet you just argued that it was necessary for Lae?
More likely she might have wanted to conserve a bit for take-off at Howland (seems like they had none, but I'm not clear on that at moment).
Then you *do* agree there was a need to switch tanks ASAP?
As to the electrical generation - Samuels is basically correct, although I would agree that voltage falls off on a DC brush type generator as RPM falls.
Agreed.
That said, it WILL charge well down to at least around 900 RPM,
I haven't said it wouldn't charge. I am saying that at 900 RPM:
1. It will take a damn long time to charge.
2. It will not output full current.
The driving fact here is the need to provide current for the transmitter which is not possible at 900 RPM.
and I believe TIGHAR actually has test data showing lower RPMs than that on a live engine of the same type (which is important to determining how much fuel might have been available to charge the batteries, and in turn power the radios).
I've seen the video. Note my "2 to 1" quote.
Perhaps I've not read all of your suppositions well, but note as well that the batteries depended directly on battery state; one could not get enough current out of that puny generator to power the radio transmitter directly. Transmissions had to be limited with an eye on battery state, then the battery charge replenished.
Which is exactly why low RPM won't cut it. AE was paranoid enough about the battery condition when the engine was running cruise power and she was trying to communicate with Itasca. How did she feel when the engine was running less than cruise power and she was attempting the same thing?
Your discourse is interesting, but to me also a bit convoluted, frankly (not to personally criticize, just to point out that it's confusing to the whole point, at least as I understand it). It might be profitable to consider these points and read up on what Jacobsen and others have contributed here as to these things - and consider that the matter isn't so complex: fuel available on the ground (regardless of octane) would have been the stuff of transmissions, for as long as it - or the bird, lasted. The engine could consume, if memory serves, as little as around 6 - 8 gallons an hour probably at a battery-charging low RPM. But please don't take my word for that (I'm hip shooting the details from memory anyway), it can be looked up on this site.
After lengthy consideration some things have become obvious to me. I accept they may not be obvious to you.
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That is a common misconception. Have you ever tried to charge a dead battery with an alternator by driving around for a couple hours. You will wake up in the morning with another dead battery. An alternator is designed to top off a battery, not fully charge it. The alternator will put out the voltage to keep the ignition system running and the engine as long as you don't have your lights and heater on. Turn the key off and you'll be getting out the jumper cables again.
Many times and successfully too so I can't relate to your anecdote unless you are describing a flat battery that has sulphated because it was left fully discharged for an extended period. Such a battery will have shorted cells.
Such a battery *might* be recovered by the use of a specialised charger that charges and discharges in cycles to restore the plate material.
Otherwise I have successfully recovered heavily discharged batteries with alternators many times.
We are not discussing neglected and sulphated batteries here.
We are discussing the responsible management of 2 batteries that had only recently proven their good condition by repeatedly starting 2 big radial engines.
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Mark has considered the Electra's generator to be a perfect device, devoid of frequency response, internal resistance and RPM sensitivity. I'm sure it was quite efficient for its time, but perfect it was not.
Ah, never said that, I've had my troubles with generators in my day.
That said, it WILL charge well down to at least around 900 RPM,
I haven't said it wouldn't charge. I am saying that at 900 RPM:
1. It will take a damn long time to charge.
2. It will not output full current.
The driving fact here is the need to provide current for the transmitter which is not possible at 900 RPM.
Maybe what you fail to understand is that the generator on the Electra L10 E had an max output of 50 amps against a draw of 65 amps required by the transmitter not withstanding other things that might have required power. The radios had to be shut down long enough for the generator to get the 85 amp hour batteries up to charge. My understanding is they used the smaller battery for starting the engine and the larger one by the navigators desk for powering the radios.
http://tighar.org/smf/index.php/topic,252.msg2222.html#msg2222
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... Have you ever tried to charge a dead battery with an alternator by driving around for a couple hours. You will wake up in the morning with another dead battery. An alternator is designed to top off a battery, not fully charge it. The alternator will put out the voltage to keep the ignition system running and the engine as long as you don't have your lights and heater on. Turn the key off and you'll be getting out the jumper cables again.
I have done that many times and as long as the battery and charging system was healthy, it worked just fine with no need for jumper on next start.
On the other hand, with a completely dead battery and no 14 volt charger or vehicle available to jump from, then trying to jump from a fully charged 12 Volt boat battery (twice the size of the cars battery) would not start it. I just bought a pocket-size Cobra JumPak 400 Amp that is supposed to provide three 3 second jump starts from a full charge, if I ever leave my parking lights on again... :-[
One of the advantages of an aircraft (or auto) with an alternator over a generator is that an alternator will continue to charge at an idle RPM.
Best way for her to judge RPM needed would have been to watch the Ammeter while transmitting. Generator could not put out enough for a positive reading at any RPM but she could find the minimum RPM for a minimum discharge reading and then lean the fuel mixture to the maximum for that RPM. This would produce the most fuel efficient RPM for maximum battery charging, if she was doing a minimum of transmitting, her batteries could remain fully charged at a lower RPM and she could listen longer for less fuel.
One of the disadvantages is that an alternator will not self-excite and if the battery is completely dead, the alternator won't put out at all.
Push starting won't work at all but I have jump-started many autos with alternators and the excite current from the jumper cable was enough to excite the alternator and it charged just fine. Even providing enough charge in the battery (lights, heater and all) for subsequent starts after running a while, but battery should still be charged if possible as they last longer if fully charged.
Landed at Grand Cayman many years ago and after a few days, wanted to fly to Little Cayman. Battery was completely dead (a reading light on a 'hot-buss' had been left on), so I had Cayman Airways use a Ground Power Cart to start the engines, flew to Little Cayman, shut down and battery was still completely dead. The Battery switch activated a relay powered from the battery side, so even with Alternators producing plenty of current, there was nothing to close that battery relay to send current to the battery. Only battery charger was a little 12 Volt at the Dive Shop, charged a 24 Volt battery over several days by contacting a plate in the middle and charging each half of the battery separately.
Turbine (Jet) engines do not use alternators (some single engine models have a backup alternator), they have Starter/Generators, Battery supplies 600 to 1800 amps (at 24 volts) to spin it up to 20% RPM and then after it is lit-off and passing 40% or so, the automatic controller transforms the starter into a generator that can produce many 100's of amps.
I agree that she would have wanted to allow enough ground running to assure that the carburetors were full of 100 octane before take-off, but engines would start just as easily on lower octane. It would be especially dangerous to attempt a take-off on a nearly empty (usually below 1/4 ) tank.
100 octane was necessary for that extra 100 Horsepower per-side (increased supercharger boosted compression) and if she lost one engine at anywhere near her take-off weight, she was already in the coffin corner no matter how much power was available from the other engine. That Lockheed did not even have feathering props...
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Tim,
You seem to labor under some basic misconceptions about 100 octane fuel
Jeff,
If AE did specifically plan to depart Lae using 100 octane, then she needs to do just that.
In order for the carbs to be full of 100 octane before starting the takeoff roll one needs to have allowed sufficient time for that process to occur. Interconnecting fuel lines need time to be purged of the lower octane fuel.
Startup, taxi and particularly runup is a reasonable way of ensuring that.
and perhaps as to how the DC generator on the Electra operated, as Mark Samuels has pointed out.
Mark has considered the Electra's generator to be a perfect device, devoid of frequency response, internal resistance and RPM sensitivity. I'm sure it was quite efficient for its time, but perfect it was not.
100 octane would have had nothing to do with 'ease of starting'.
I don't remember saying that.
In order for the carbs to be full of 100 octane before starting the takeoff roll one needs to have allowed sufficient time for that process to occur. Interconnecting fuel lines need time to be purged of the lower octane fuel.
Startup, taxi and particularly runup is a reasonable way of ensuring that.
It was used for take-off at high power settings to offset detonation, that's the only reason the ship bothered to have a reserve of 100 octane. At start or low power settings, it makes essentially no difference whatsoever to the engine or how it performs.
Agreed. I don't recall saying differently.
I see that now - I could have read your post more thoroughly I suppose.
As to what I read earlier regarding your take on the take-off at Lae, I doubt seriously that Earhart switched tanks immediately, etc., etc. as accounting for her fairly dramatic run-off the end and drop toward the water, etc. Why would any pilot taking off in a heavily loaded airplane choose that moment to swiitch tanks from 100 octane to 80?
We share the same purport- that AE carried 100 octane of necessity.
So when did AE deselect 100 octane? Why not 1st power reduction if she had to reduce power anyway?
Could have, but makes more sense to me to reduce power first (and I'll just about guarantee that she would not have immediately upon departing the end of the runway - that settling was a thing too close), thence switch tanks when all up and away with some margin. There's no need to be that stingy - there was ample 100 octane for the Lae and Howland take-offs if reasonably managed.
Earhart did some nutty things in her time - especially with radios, but I don't recall fuel mishandling - and that's prime-time for screwing that up royally. There would be no harm in continuing on 100 octane for some time, especially while still under climb power (even with the power reduced).
Are you now arguing against the need for 100 octane for the Howland departure, yet you just argued that it was necessary for Lae?
I've said nor argued any such thing. In fact, to repeat - there was ample 100 octane for both take-offs with reasonable management. The dramatic cowboy power reduction and tank switching off the end of the cliff as you envision isn't necessary and no reasonable pilot that I know of would manage a take-off that way.
More likely she might have wanted to conserve a bit for take-off at Howland (seems like they had none, but I'm not clear on that at moment).
Then you *do* agree there was a need to switch tanks ASAP?
You argue for argument's sake. No need to switch as you have described; I've already said what I think is reasonable.
How much 100 octane do you think she would have burned in 5 minutes at take-off and initial climb? If the bird was burning 100 gallons an hour it would be less than 10 gallons out of 100, so why would you want to switch tanks after just peeling your sphincter off the grass at Lae and nursing the bird low across the water for a few hundred yards?
As to the electrical generation - Samuels is basically correct, although I would agree that voltage falls off on a DC brush type generator as RPM falls.
Agreed.
That said, it WILL charge well down to at least around 900 RPM,
I haven't said it wouldn't charge. I am saying that at 900 RPM:
1. It will take a damn long time to charge.
2. It will not output full current.
The driving fact here is the need to provide current for the transmitter which is not possible at 900 RPM.
It wasn't even possible to provide enough current for the transmitter even at full throttle, but only about half the 65 amps the radio drew when transmitting at a higher power setting. Read what Bradenburg and others have offered on the details (http://tighar.org/wiki/Electra).
and I believe TIGHAR actually has test data showing lower RPMs than that on a live engine of the same type (which is important to determining how much fuel might have been available to charge the batteries, and in turn power the radios).
I've seen the video. Note my "2 to 1" quote.
Perhaps I've not read all of your suppositions well, but note as well that the batteries depended directly on battery state; one could not get enough current out of that puny generator to power the radio transmitter directly. Transmissions had to be limited with an eye on battery state, then the battery charge replenished.
Which is exactly why low RPM won't cut it. AE was paranoid enough about the battery condition when the engine was running cruise power and she was trying to communicate with Itasca. How did she feel when the engine was running less than cruise power and she was attempting the same thing?
Where do you get the information on Earhart's 'paranoia'? I'd overlooked that she suffered from that (although she might have benefitted had she realized how her own habits were out to get her). There is a balance to fuel conservation and periodic transmitting (see linked material); there is no reason for a high power setting to make such transmissions.
Your discourse is interesting, but to me also a bit convoluted, frankly (not to personally criticize, just to point out that it's confusing to the whole point, at least as I understand it). It might be profitable to consider these points and read up on what Jacobsen and others have contributed here as to these things - and consider that the matter isn't so complex: fuel available on the ground (regardless of octane) would have been the stuff of transmissions, for as long as it - or the bird, lasted. The engine could consume, if memory serves, as little as around 6 - 8 gallons an hour probably at a battery-charging low RPM. But please don't take my word for that (I'm hip shooting the details from memory anyway), it can be looked up on this site.
After lengthy consideration some things have become obvious to me. I accept they may not be obvious to you.
Obvious is in the eye of the beholder; many things are obvious to me. I invite your scrutiny of the many words posted in this forum and related material herein on the topic; perhaps more will become obvious to you should you do so.
It is obvious to me that supposing Earhart rashly switched tanks at the worst possible moment would have gained her nothing but risk, and that there is no reason to conjecture so far to test the hypothesis of a Niku landing; I fail to see the point of it, however obvious it may be to you, that's all.
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Jeff,
I'm delighted that you don't argue for the sake of arguing, that you don't believe in saturating your posts with tons of quotes and that you are not one of those people who echoes the equivalent of expressing the finger like you say some drivers do.
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Maybe what you fail to understand is that the generator on the Electra L10 E had an max output of 50 amps against a draw of 65 amps required by the transmitter not withstanding other things that might have required power. The radios had to be shut down long enough for the generator to get the 85 amp hour batteries up to charge. My understanding is they used the smaller battery for starting the engine and the larger one by the navigators desk for powering the radios.
The term I've used previously is "transmission duty cycle".
I'll be ending the sport for you and Jeff in this thread now.
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Well said Art.
I agree with every word.
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Jeff,
I'm delighted that you don't argue for the sake of arguing, that you don't believe in saturating your posts with tons of quotes and that you are not one of those people who echoes the equivalent of expressing the finger like you say some drivers do.
I'm delighted that you are delighted, Tim.
I guess there's just something about clairvoyants who extrapolate bits and pieces of technical lore into 'the answer' that draws those things out in me. I think it is pure fop. The icing on the cake is all the over-parsing of 100 octane use - 'gas is gas' when it comes to cranking an engine and charging a battery.
One thing is for damn sure - if you are a pilot, you are one I'd never fly with given your cowboy view of take-off / climb power management: whatever her faults and propensity for losing her way, Earhart way outclassed the judgment you've expressed in that regard here. So maybe it comes down to defending the lady in some way.
Have a nice day.
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I am reminded that there was ample 100 octane available at Howland according to the Black Cruise Report (http://tighar.org/Projects/Earhart/Archives/Documents/Reports/BlackCruise.pdf).
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In fairness to you, Tim, I'll more carefully comment on the particulars here that appear tortured to me -
I've given further thought to this and it forced me to address the following question.
How soon after the Lae departure did AE effect the tank change from 100 octane to the lower octane?
Answer: As soon as possible after becoming airborne.
Eyewitnesses reported the Electra dipping towards the ocean, then recovering. At first I thought that was the Electra coming out of ground effect, but now I think it was both 1st power reduction and 1st tank change.
My reasoning follows:
Since AE had only to clear sea level, it gave her the option of using an efficient and slow cruise climb of 50 - 100 ft/min, rather than a step climb that guaranteed burning 100 octane at maximum rate (60 US Gal per hour?). The reduced weight from the fuel burn aided in the climb performance.
AE had to first reduce power to select the lower octane fuel in order to avoid blowing holes in pistons through detonation/pre-ignition, as well as reduce power to conserve fuel and lean back to 43 US gal per hour.
Having dipped the tanks just before departure, having used a defined period for startup, taxi, takeoff and climbout, having selected away from the 100 octane tank, AE now knew how much fuel remained in that tank especially having performed the procedure on so many previous departures.
That means AE knew how much 100 octane remained upon arrival at Gardiner and also knew preserving that fuel gave her a known running time for the starboard engine once she selected that tank.
Most respectfully, Tim -
Why the urgency to switch tanks so quickly at a very busy and potentially hazardous point in the flight? It gains nothing. A safer approach to your notion of a gentle cruise climb (which is itself something most of us would favor) would be to allow the craft to find a stabilized climb and gain safe altitude, throttling back when safe (and respecting any METO time limits). There would be no urgency to switch tanks - 100 octane would be fine, and there was an ample supply awaiting NR16020 at Howland as delivered by the Itasca.
How much 100 octane would be consumed by using this reasonable conservatism? Assuming warm-up, taxi, take-off and the first 5 minutes of climb to gain some safety margin, all pulling from the 100 octane reserve, would use something on the order of perhaps 10 gallons at the outside (but don't take my word for it, dig into the real numbers and do the math). That hardly makes a compelling point of reaching for fuel tank controls and making a switch on the sea deck just after sailing off the end of the grass runway at Lae: fly the airplane first, gain some comfort margin, then tidy up the long-term needs. That's especially true for single pilot ops in an airplane like the Electra (Fred was in the back - the lady wanted to do it herself).
Your reasoning as to Earhart somehow wishing to preserve 100 octane so as to 'know what was left in tank' (if I follow your logic, in part) seems to be pure conjecture as we have nothing from Earhart suggesting such a concern. Further, the presence of 100 octane vs. 80 octane at the end of the day means nothing because for battery charging: fuel is fuel (perhaps you didn't intend the distinction, but somehow I read it in the sum of your point).
This reasoning is why her focus was heavily on the state of the battery "Watch that battery" rather than transmitting for all they were worth pending an imminent and permanent stopping of the starboard engine due to fuel exhaustion.
Because I agree with Bill de Cleef's 1200 RPM minimum for charging, my estimate is that the 100 octane reserve provided for 4 hours running of the starboard engine at half cruise consumption (21.5 divided by 2 US gal / hour = 10.25 US gal / hour).
You are of course free to agree with anyone's opinion on 'minimum for charging', but the fact is that generator and engine combination have been demonstrated as adequately charging for the purpose we're talking about at around 900 RPM, and with very low fuel consumption - around 8 GPH.
"Watch that battery" was a necessity: no matter how much engine power Earhart applied, the poor little Eclipse generator could only give about 1/2 of what the radio transmitter demanded. The battery would necessarily deplete, even if Earhart were running the right engine at full boost / high power, 100 octane and all.
'Standby' (receiving) was a bit different - the generator could provide for that and battery charging. Yes, higher RPMs would charge marginally faster - but fuel consumption does not increase on a linear scale, but goes up exponentially when one bumps the shiny knobs forward. Patience...
Doesn't some inner pilot instinct tell you 'conserve' when you have very limited fuel and a need to transmit as-can? Watch "Island in the Sky" (written by Gann, portrayed by John Wayne and notable others) for a fair demonstration of the dilemma of transmitting on old sets and power demands: it left shitty choices. Somehow my pilot instincts - which seem to agree with what we know about even Mantz's views, are that the least smelly choice would be, if one could start an engine, to use modest power, 'watch the battery' and periodically make 'burst' transmissions.
If Earhart actually did ever say "watch that battery", then I believe (my opinion) that she was well attuned to these things and carefully managing all that we've discussed. Despite her other shortcomings - ground loops, off course arrival in Africa, radio nonsense, the lady managed to fly a respectfully demanding transport 3/4 of the way around the world without significant mishap - not bad. That take-off at Lae was a piece of fine work by anyone's standard: I'd bet not one man watching that day would have eagerly traded places - it could have easily gone wrong and been turned into a smoking hole. As you rightly pointed out elsewhere of late, tail-draggers aren't very forgiving to bad man-handling.
Her keeping her cool and dropping into ground effect as she sailed off the end of the runway was an impressive move, whatever the reason - and none of us will ever know for sure how expected or not that maneuver was. It might have been a momentarily desperate response to very marginal take-off performance that day (been there with south Georgia pines in the windshield), or it could have been one of those near-joyful acts of conservative energy conservation to gain the best energy state for safety that looks more dramatic than it really is. She apparently handled it well - I don't recall any dramatic report of it from the flying community - just one of those one-off things that turned out well and wasn't too shocking under the circumstances of the day.
I bother to elaborate on all this for the sake of the lady's character and judgment - not out of chivalry, but of common sense: some of her basic stuff was pretty darn sound, and I have severe doubts (my judgment) that she would over-gun the engines in a fuel-limited situation for the sake of overly aggressive transmission times.
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Maybe what you fail to understand is that the generator on the Electra L10 E had an max output of 50 amps against a draw of 65 amps required by the transmitter not withstanding other things that might have required power. The radios had to be shut down long enough for the generator to get the 85 amp hour batteries up to charge. My understanding is they used the smaller battery for starting the engine and the larger one by the navigators desk for powering the radios.
The term I've used previously is "transmission duty cycle".
Ah yes, that pesky "transmission duty cycle". Seems that Ms Earhart was well aware since she, on a number of occasions transmitted that she would listen at different periods on the hour. Unfortunately as it were, she was transmitting and listening on the wrong frequency, I think.
I'll be ending the sport for you and Jeff in this thread now.
Thank you, its been fun but not 'real fun'. ;)
Hold the Heading Tim, we'll get there sooner or later. ;D