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Fuel Remaining

The critical factor reviewed in depth

The amount of fuel remaining in the Electra at 1912 GMT is important because it determines how long the aircraft could stay airborne, and how far it could fly, before fuel exhaustion.

The amount of fuel remaining is a function of how much fuel was consumed.

This analysis is a challenge due to the need for estimation in the absence of empirical data.

Direct evidence from AE, and World Flight data, corroborate that mission segments were flown adhering closely to the accurate Kelly Johnson specifications.

It was not possible to conduct test flights on the aircraft to acquire necessary performance data because there are very few remaining Lockheed Electra 10E aircraft. The one article we photo-documented is not flyable.

In order to make an assessment of fuel consumption, and the possible amount remaining, other data were examined.

Fuel Consumption
Constants used in this analysis are

Fuel weight is 6 pounds per gallon (also used by Swenson and Culick).

Maximum endurance speed is 120 mph at 40 GPH.

Estimated from L487 and Pratt-Whitney engine data (35-40 GPH).

Takeoff fuel quantity is 1080 US gallons (Swenson and Culick).

The following resources were examined

Kelly Johnson Telegrams.

“Range Study of Lockheed Electra Bi-Motor Airplane,” Lockheed Report 487 dated 4 June 1936.

AE Flight Notes, Flight Performance history, and direct evidence of performance.

“Aircraft Engine Characteristics Summary,” Pratt-Whitney dated 1 May 1951.

“Flight Operation Instruction Chart,” detailing aircraft performance for the North American AT-6 SNJ with the Pratt-Whitney R-1340-AN-1 (very similar to -S3H1).

Jeppesen Flight Planning software interpolating L487, Kelly Johnson and AE Flight Notes data.

Each of these resources is limited to some extent, in its usefulness.

Lockheed Report 487 is largely analytical, reflecting computations vice actual aircraft performance. The L487 Report includes brake horsepower, however, it does not specifically cover engine power settings frequently used and reported by AE in her flight notes.

None of the three Kelly Johnson telegrams (issued post-L487 Report) containing flight test data mention the gross weight of the Electra as tested, the speed associated with each power setting, outside air temperature, or the brake horsepower at which fuel consumption data were recorded.

From the Kelly Johnson flight test data, notably the third Telegram to AE, mission profile recommendations were made for altitude, power setting, and fuel consumption. These recommended settings were grouped into 3-hour segments, reflecting that Electra aircraft performance is relatively unaffected by small gross weight changes.

Aircraft Gross Weight
The gross weight of the aircraft and the power from its engines are important to climb rate, cruise speed, and fuel consumption.

For constant altitude, constant speed cruise flight, lift must balance weight, and engine power must balance the total vehicle drag from all sources.

An aircraft design axiom is that an “aircraft climbs on its engines.” Excess engine power beyond that required for cruise flight where vehicle drag is balanced by engine power, can be used to climb, and where excess power is limited, climb rate is also limited.

Report L487 indicates climb rates at AE’s operating weight, should be in the range of 600-700 feet per minute. However, Pellegreno reported routinely requiring 20 minutes to reach 1,000 feet, after takeoff. L487 optimum initial cruise altitudes were 2,000-4,000 feet. Kelly Johnson modified the initial cruise altitude to 8,000 feet.

In practice, climbing the heavy Electra to 8,000 feet, 10,000 feet, or higher, likely required 30-60 minutes at high power settings of approximately 500-550 BHP and high fuel consumption ranging from 95-110 GPH (Pratt-Whitney).

AE’s Electra gross weight is important because the mission routinely operated at high gross weight. Takeoff from Lae was at approximately 15,500 pounds, 47.6% above design maximum gross weight. The Lae to Howland mission average gross weight was approximately 22.9% above design maximum gross weight.

One concern was that if the Kelly Johnson flight tests were performed at significantly “lower-than-actual-mission” aircraft weights, the resulting profile recommendations could result in AE experiencing less climb rate, slower aircraft speed, and higher fuel consumption throughout the World Flight.

Our assessment is that Kelly Johnson’s data was accurate.

The empirical data from Kelly Johnson’s flight tests are very close to Pratt-Whitney engine data, and likely resulted from either testing the Electra at actual operational weights, or from computational corrections to test data, producing the three Telegrams recommending the following fuel consumption planning data.

3 hours at 60 GPH for 180 gallons

3 hours at 51 GPH for 153 gallons

3 hours at 43 GPH for 129 gallons

10 hours at 38 GPH for 380 gallons

This data agrees well with fuel consumption data we derived by calculations from Pratt-Whitney engine data supplied by the Smithsonian Institution, and from flight handbooks for other aircraft using the same engine as in AE’s Electra.

Kelly Johnson specified settings for 3-hour cruise segments, however, he did not specify takeoff, climb or descent fuel consumption data.

Combining Pratt-Whitney engine data, with Kelly Johnson’s recommendations and data, offers a more complete profile of fuel consumption.

Takeoff using 10 gallons

1 hour climb using 110 gallons

3 hours at 60 GPH using 180 gallons

3 hours at 51 GPH using 153 gallons

3 hours at 43 GPH using 129 gallons

8.5 hours at 38 GPH using 323 gallons

0.5 hours descent at 30 GPH (estimated) using 15 gallons

Total 920 gallons required from takeoff to 1912 GMT

Fuel Consumption and Time Remaining From All Analyses
Below summarizes the solutions for mission fuel consumed, and fuel remaining upon arrival at where AE thought Howland should be, at 1912 GMT.

If AE began with 1080 gallons, and flew this Kelly Johnson profile (”adjusted” for takeoff, climb and descent) requiring 920 gallons, the total fuel remaining would have been 160 gallons at 1912 GMT, or 4 hours endurance.

Computer flight profile modeling of data largely from Kelly Johnson and L487 data, also indicate the total fuel remaining would have been 160 gallons at 1912 GMT, or 4 hours endurance.

While our Jeppesen software model results, in terms of fuel used, corroborate the Kelly Johnson/L487 Report, our further analysis offers increased accuracy in this area.

Swenson and Culick’s analysis concluded that AE had enough fuel for 20 hours 38 minutes total mission time. Subtracting the known mission time of 19 hours 12 minutes, results in approximately 1 hour 26 minutes remaining endurance.

This represents 57.3 gallons remaining at 1912 GMT.

Our research, using a specific flight profile segment analysis technique, results in a total mission fuel burn of 957 gallons. Under the best circumstances AE should have arrived at time 1912 GMT with 123 gallons, enough for 3 hours 04 minutes endurance.

This figure could have been reduced due to malfunction of the Cambridge Fuel Analyzer and increased fuel consumption en route due to cruise altitude choices, winds or other factors.

“…Gas is Running Low…”
For the Oakland to Honolulu flight, AE planned to have 4 hours of fuel remaining, a “…good safety margin…” by her own account. AE also planned on having enough fuel on the Honolulu to Howland flight, 8 hours fuel remaining, to return to Honolulu from Howland in the event of an aborted landing situation.
Below 4 hours fuel quantity, even were it planned, AE would likely consider this a low fuel quantity situation, as she reported at 1912 GMT.

With fuel remaining of 4 hours, per Kelly Johnson/L487, and software modeling solutions, it is not likely that AE would have reported a low fuel condition.

With fuel remaining of 1 hour 26 minutes, per Swenson and Culick, it is likely AE would have reported a low fuel condition, but possibly with a sense of urgency, due to the extreme nature of her fuel quantity, with just 57.6 total gallons remaining.

Our analysis of 3 hours 04 minutes fuel remaining falls within the range for AE to report a low fuel condition, but without a sense of urgency. This figure could have been reduced due to malfunction of the Cambridge Fuel Analyzer and increased fuel consumption en route due to cruise altitude choices, winds or other factors.

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