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Author Topic: Battery life on AE's plane?  (Read 26774 times)

Randy W Kerr

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Battery life on AE's plane?
« on: December 25, 2010, 12:14:00 PM »

I have been wandering around the site looking for any information on expected battery life for the Electra.  My reason is that everywhere it seems assumed that AE made a wheels down landing on Niku.  This practice runs contrary to everything I have been taught about off-field landings on unsure surfaces. ( I hold a Commercial certificate)  The dangers of tucking your nose under and flipping your plane landing on soft sand or a rough reef top would lead me to choose a wheels up landing.  But every thread that mentions it suggests that the radios needed the #2 engine running to charge the battery.  Anyone have figures on battery life??
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Phil O'Keefe

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Re: Battery life on AE's plane?
« Reply #1 on: December 25, 2010, 12:30:05 PM »

I don't know the answer to your question in terms of battery life, but it's probably irrelevant - drop the Electra into salt water and it's going to short out the electrical system - including the batteries and the radio.
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Randy W Kerr

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Re: Battery life on AE's plane?
« Reply #2 on: December 25, 2010, 12:33:18 PM »

Ding ding..the light just went on.  Even if they landed at low tide they would have flooded soon after.
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Ric Gillespie

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Re: Battery life on AE's plane?
« Reply #3 on: December 25, 2010, 12:56:34 PM »

The portion of the reef where the available evidence suggests that the landing was made is smooth enough ride a bicycle, let alone land an Electra with big fat tires.
At low tide the reef is dry.  At high tide the water is not high enough to reach either of the batteries or any of the radio components.
Nearly all of the credible post-loss radio signals occur at times when the water level on the reef was low enough to run an engine.
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Randy W Kerr

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Re: Battery life on AE's plane?
« Reply #4 on: December 25, 2010, 01:13:17 PM »

"The portion of the reef where the available evidence suggests that the landing was made is smooth enough ride a bicycle,"   I understood that from other sources, but having seen a lot of other reefs where that was not the case it occurred to me that not knowing the conditions wheels up might have been a thought.  Even with a low pass it can be hard to see the conditions clearly.  I speak as one who got to watch from the right seat as a nearly pristine Beech 18 was turned to scrap under similar circumstances.  Excuse me if I ask a few uninformed questions as I try to educate myself on the fascinating story.
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Martin X. Moleski, SJ

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Re: Battery life on AE's plane?
« Reply #5 on: December 25, 2010, 01:28:08 PM »

"The portion of the reef where the available evidence suggests that the landing was made is smooth enough ride a bicycle,"   I understood that from other sources, but having seen a lot of other reefs where that was not the case it occurred to me that not knowing the conditions wheels up might have been a thought.  Even with a low pass it can be hard to see the conditions clearly.  I speak as one who got to watch from the right seat as a nearly pristine Beech 18 was turned to scrap under similar circumstances.  Excuse me if I ask a few uninformed questions as I try to educate myself on the fascinating story.

See "Landing on the Reef?" for some details about the reef and the Electra undercarriage.

"Post-loss Radio Messages--Overview, Battery Life."
LTM,

           Marty
           TIGHAR #2359A
 
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Ric Gillespie

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Re: Battery life on AE's plane?
« Reply #6 on: December 25, 2010, 06:05:39 PM »

A couple things to keep in mind when considering how Earhart may have viewed her options upon arriving over Gardner:

- In 1937, intentional wheels-up landings in retractable gear aircraft were pretty much unknown and there was no such thing as "a standard ditching procedure" for the Model 10.

- From a crew survival standpoint, landing a land plane in the water is almost never preferable to even a crash-landing on land. 

- Earhart's professional and financial future was tied up in that uninsured airplane.  A water landing would mean the loss of the certain aircraft.

- At low tide, from the air, Nikumaroro looks like it is surrounded by an empty parking lot.
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Ted G Campbell

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Re: Battery life on AE's plane?
« Reply #7 on: December 25, 2010, 06:30:59 PM »

Keep in mind AE also knew what the craft would look like with a wheels up landing i.e. the first leg.
Ted Campbell
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Randy W Kerr

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Re: Battery life on AE's plane?
« Reply #8 on: December 25, 2010, 06:37:56 PM »

A couple things to keep in mind when considering how Earhart may have viewed her options upon arriving over Gardner:

- In 1937, intentional wheels-up landings in retractable gear aircraft were pretty much unknown and there was no such thing as "a standard ditching procedure" for the Model 10.

- From a crew survival standpoint, landing a land plane in the water is almost never preferable to even a crash-landing on land. 

- Earhart's professional and financial future was tied up in that uninsured airplane.  A water landing would mean the loss of the certain aircraft.

- At low tide, from the air, Nikumaroro looks like it is surrounded by an empty parking lot.
Understood...I was not advocating that a water landing was a good option, unless drilled and in a craft conducive to a quick exit water landings are a last resort...I was suggesting rather that bellying in on unknown terrain is usually the safest choice..the plane was going to be lost in any event...but hooking a wheel and flipping upside down could have been instantly fatal..not that the eventual outcome was different.  It is obviously a moot point in any event given the reality that a belly-landed aircraft would have rendered transmissions for the length of time they are believed to have occurred impossible.
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Re: Battery life on AE's plane?
« Reply #9 on: December 27, 2010, 08:28:18 AM »

Hello folks

I have just read this thread and refered to the battery life details which state.

"Both batteries were rated at 85 ampere-hours. If both were at full charge on arrival at Niku -- a reasonable assumption -- there would have been enough charge for about 90 minutes of transmission time. The total transmission time required for all of the credible post-loss signals is 451 minutes."

So, we have two 85 amp hour batteries total 170 A/hr, say we can take them down to about half capacity before they are of less use * ( if they are lead acid type ).
That gives us 85A/hrs in total.
The question I need to ask is, what is the current consumption of the radio on transmission? Or, what is its output power in watts and the battery voltage?
If we know this we can work it out more exactly. Does anyone have this information?

Regards

Antonia

* you would think though that they would continue to use the radio until it would no longer work at all  ( if they had access to it, dependent on weather/sea conditions ) meaning batteries very dead
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Martin X. Moleski, SJ

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Re: Battery life on AE's plane?
« Reply #10 on: December 27, 2010, 09:26:16 AM »

LTM,

           Marty
           TIGHAR #2359A
 
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Re: Battery life on AE's plane?
« Reply #11 on: December 27, 2010, 11:02:18 AM »

The question I need to ask is, what is the current consumption of the radio on transmission? Or, what is its output power in watts and the battery voltage?

"Radio equipment on NR16020"

"A Technical Analysis of the Western Electric Radio Communications Equipment Installed on Board Lockheed Electra NR16020"

"WE-13C Transmitter Harmonic Power Output"



My thanks, it has not failed to amaze me, the amount of work you folks have done on this.

Kind  reagrds

Antonia
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Martin X. Moleski, SJ

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Re: Battery life on AE's plane?
« Reply #12 on: December 27, 2010, 11:23:42 AM »

The question I need to ask is, what is the current consumption of the radio on transmission? Or, what is its output power in watts and the battery voltage?

"Radio equipment on NR16020"

"A Technical Analysis of the Western Electric Radio Communications Equipment Installed on Board Lockheed Electra NR16020"

"WE-13C Transmitter Harmonic Power Output"


My thanks, it has not failed to amaze me, the amount of work you folks have done on this.

You're welcome.  If you'd like to pull together some of the information from the sources--with links at the ready for each item--I'd be happy to pop your findings into "Radio equipment on NR16020".  No harm in summarizing and consolidating things ...
LTM,

           Marty
           TIGHAR #2359A
 
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Bob Brandenburg

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Re: Battery life on AE's plane?
« Reply #13 on: December 30, 2010, 11:31:29 AM »

Antonia,

The relationship between battery performance and the radio electrical load is very complex, and will be detailed in a forthcoming research paper.  Meanwhile, here's a brief overview of key points that bear on your question:

The batteries were Exide 6-FHM-13-1, 12-volt, lead-acid type, with 85 AH capacity.
 
Each battery could be switched onto or off the main electrical bus.  We assume both batteries were fully charged on arrival at Niku, and that Earhart kept one on the bus, with the other off-bus as a safety standby.   

The generator was an Eclipse type E-5, rated to provide 15 volts DC, mounted on the starboard (right) engine. A crucial question for our analysis was whether the E-5  would deliver 15 volts when the engine was idling at 900 RPM.  Paul Mantz, Earhart's technical advisor, said in 1937 that the Pratt & Whitney Wasp S3H1 engine -- the type used on the Electra -- burned 6 gallons per hour at 900 RPM.  TIGHAR verified the engine and generator performance in 2009, in an experiment using an S3H1 engine and an E-5 generator.  This result established that 900 RPM was the lowest speed Earhart could use for battery charging, and that she would burn 6 gph while doing so.

The time required to recharge the battery after a transmission period, and the associated engine fuel burn, are important considerations in the post-loss signals.   

Ideally, we would have the Electra battery charging specifications, but we have been unable to find that information.  We could not use a modern 85 AH battery as a proxy because we could not be sure that the the internal resistance and charging efficiency of the 1937 battery were the same as in a modern battery. Therefore, it was necessary to derive the battery's performance parameters from first principles, using published empirical research data for aircraft lead-acid batteries of the period. 

Aircraft lead-acid battery cells of the period had a specific gravity range of 1300 at full charge to 1110 at fully discharged, with corresponding voltage range of 12.86 volts to 11.81 volts.

The transmitter high-voltage power supply was a dynamotor that drew 65 amps at 12 volts, and thus could function at virtually full output even with the battery approaching zero charge. Hence, the combined available "end game" battery charge -- after all engine fuel was exhausted -- was 170 AH, if both batteries were fully charged at fuel exhaustion.

The credible post-loss signals occurred in clusters, or blocks. We assume that Earhart kept the engine running to operate the generator continuously during each block, rather than start and stop the engine for each transmission.  We have developed a computer model that does the time line bookkeeping, giving the battery state of charge (SOC) -- and fuel remaining -- after each credible signal, and after a user-specified recharging period following each signal block.  After we have identified all the credible post-loss signals, we'll plug them in to the model and see how battery charge and fuel cosnumption behaved over time.     

Of course, the amount of fuel Earhart had on arrival at Niku depends on when she landed. We don't know exactly when that was , but we know the latest possible arrival time, which was constrained by tide depth on the reef.  The maximum safe water depth for landing the Elctra was 6 inches (0.15 meter).  Signal propagaton analysis for the last Earhart signal heard by the Coast Guard cutter Itasca on July 2, 1937, gives us a bound on Earhart's distance from Niku then, and thus her earliest possiible arrival time.  These two limits bound the uncertainty of fuel remaing on arrival, and factor into our analysis.   

The tide level also constrained when Earhart could run the engine for battery charging.  The required propeller tip clearance was 24 inches (0.6 meter), so engine operation was impossible when the water level exceeded that limit.

Now, let's take a brief look at the dynamics of the electrical load and battery recharge.

The generator output current was regulator-limited to 50 amps. 

We assume an ambient current load of 8 amps during each signal block: radio receiver on (1 amp), transmitter in standby (6 amps for vacuum tube filaments), and the cockpit instrument lights (2 amps). 

The transmitter drew 65 amps when transmitting, raisng the total current load to 68 amps.   

With the transmitter in standby, the generator could supply the 8 amp ambient load and have current to spare for charging the battery.  But when the transmitter was keyed, the generator could supply only 50 of the required 68 amps.  The battery would supply the remaining 18 amps, losing 18 ampere-minutes (0.3 AH) of charge for each minute of transmission time. About 13 minutes of charging time was needed to restore charge for each minute of transmission time, if the starting battery SOC was near the top of the exponential charging curve. At lower starting SOC, where the curve is steeper, the recharge time was on the order of 2 minutes for each minute of transmission.     

Earhart's only way to monitor battery SOC was to watch the generator current output on the ammeter.  The current would decrease toward the 8-amp ambient load as the battery approached full charge.  But it could take a long time to get those last few ampere-hours into the battery if she wanted to recharge to 100%, and Earhart would have to be careful not to spend her precious fuel too lavishly.  We don't know what strategy she used, but we can experimentally investigate the range of options and their effects using the computer model mentioned above.

I hope this helps.  Let me know if you have other questions.

Bob
 

 

 



   
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Dan Swift

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Re: Battery life on AE's plane?
« Reply #14 on: December 30, 2010, 01:48:44 PM »

I have been wandering around the site looking for any information on expected battery life for the Electra.  My reason is that everywhere it seems assumed that AE made a wheels down landing on Niku.  This practice runs contrary to everything I have been taught about off-field landings on unsure surfaces. ( I hold a Commercial certificate)  The dangers of tucking your nose under and flipping your plane landing on soft sand or a rough reef top would lead me to choose a wheels up landing.  But every thread that mentions it suggests that the radios needed the #2 engine running to charge the battery.  Anyone have figures on battery life??

As a pilot myself, I have concluded that Amelia was deficient in two areas:  1.  She was not a great  pilot.  2. She thought she was a great pilot.  A very dangerous combination usually resulting in death by crash at some point.  She would have thought she could do anything in an airplane. 
TIGHAR Member #4154
 
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