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Fuel Consumption

Conclusion of the fuel consumption analysis

Kelly Johnson’s third Telegram modifying World Flight operating parameters is important because indications from direct evidence are that AE closely adhered to these recommendations for altitude, and for mid-segment power setting, speed and fuel consumption, throughout the World Flight.

Unfortunately, AE made no reference to actual fuel burn, and drawing conclusions in this area requires analysis from a broad spectrum of data.

Assembling various aircraft performance data elements from pre-mission preparations, and 30 days of the World Flight, provides information on engine settings, speeds, altitudes, etc. These can be used to assess BHP, from which specific fuel consumption (SFC) can be derived.

The engine’s specific fuel consumption (SFC) is an engineering parameter, defined as “pounds of fuel per brake horsepower per hour.” Since this term is difficult to put into perspective, a more useful metric is gallons per hour (GPH).

SFC can be directly converted to GPH, and related to miles per gallon, range, and endurance.

We examined Pratt-Whitney documents from the Smithsonian Institute for AE’s engines, Swenson and Culick’s SFC calculations, and flight handbook engine operating data for nearly the same engine installed in a North American T-6 single engine aircraft, as well as for the Lockheed 10A aircraft, in context with all other performance data.

While the lack of Electra 10E-specific operating data hampered the investigation, we found that published operating information also varies among sources. Examples include

For takeoff, the Pratt-Whitney R-1340-S3H1 engine has a 5-minute time limit at that power setting, per Pratt-Whitney documents.

The L487 report specifies setting takeoff power for 1 minute, then directs a power reduction “…as soon as it is safe…” (L487 p6). It does not define climb conditions.

Swenson and Culick discusses a climb power setting of 420 brake horsepower (BHP). The source of this specification is not provided.

Pratt-Whitney specifies 550 BHP for climb, in engine data charts.

For cruise power, Swenson and Culick does not discuss power settings. L487 specifies for AE’s initial gross weight, a cruise power setting must be 375-400 BHP.
The graph below is plotted from Pratt-Whitney engine data for AE’s engines. The GPH curve (parabola) is relatively flat in the range of 250-400 BHP typically used for cruise flight, producing a linear relationship of BHP and GPH.

Figure 16.jpg

Figure 16 - From Pratt-Whitney Engine Data

BHP setting is important to a mission fuel analysis, because fuel consumption is directly proportional to BHP and gross weight.

At initial heavy gross weights, higher BHP in the range of 375-400 BHP is required, while at lower gross weights (achieved at approximately one third of the mission distance) power can be reduced to more economical settings, such as 250 BHP, to maintain prescribed speeds and altitudes, and achieved desired ranges.

The table below compares sources of fuel consumption data, with the associated effect on the mission fuel used (Total Gallons Required).

Table 6 - Engine Fuel Consumption

As corroboration, the P&W R-1340-AN-1 engine in the North American T-6 aircraft achieves its best long-range cruise at 5,000-10,000 feet altitude, burning 22-23 GPH. For simplicity, we can double this value, to approximate a representative cruise value for the twin-engine Electra of 44-46 GPH.
Differences among source data are relatively reasonable for the 1937 period

AT-6 engine GPH data, doubled to approximate Electra fuel consumption, is within 10% of simple (non-weighted) averages for Kelly Johnson and Pratt-Whitney data.

Kelly Johnson and Pratt-Whitney GPH data are within 3% to 7%.

L487 specifies initial cruise fuel consumption of 57 GPH

Within 4%-8% of Pratt-Whitney data.

Within 5%-11% of Kelly Johnson data.

Kelly Johnson and L487 cruise fuel burn at 250 BHP is 39.2 GPH

Within 4% of Pratt-Whitney’s published chart data.

Two-thirds of the Lae to Howland mission was specified to be flown at 250 BHP, which was also used by AE during the Natal to Dakar Atlantic Ocean crossing, earlier on the World Flight.

Pratt-Whitney engine data examined, to date, is for standard conditions of pressure and temperature. The Lae to Howland environmental conditions in temperature were warmer than sea level standard, which increases fuel flow. Flying at high altitude, while not exceeding optimum altitude, has a small positive effect on reducing fuel flow for AE’s engines.
These effects could account for differences between Pratt-Whitney engine data, and Kelly Johnson flight test data.

MSI Analysis (Multi-Source Integration)
Despite the absence of specific Lockheed 10E Flight Manuals, flight tests, and variances in published data, we can reach reasonable conclusions using all available resources.

After departing Lae with 1080 US gallons, and arriving in the Howland area at 1912 GMT, Fuel Remaining values from Kelly Johnson, L487, and our specific analyses, are all among the 9 unique results from Swenson and Culick’s interesting and comprehensive sensitivity analysis.

These 9 unique results are shown on the following graph. These serve as increasing confidence in identifying reasonable values for fuel consumption, fuel remaining, endurance time after 1912 GMT, and where the Electra could be located.

Figure 17.jpg

Figure 17 - Swenson and Culick conclusions (Average 21.37 hours. Standard Deviation 1.58 hours)

Conclusions for Fuel Consumption
The conclusions from this analysis include

AE had sufficient fuel for the Lae to Howland flight under existing environmental conditions, for Paths A, B and C, plus adequate reserves for a terminal area search.

After 2013 GMT there were no further transmissions heard from NR 16020.

Given AE’s communication history, this is uncharacteristic.

AE transmissions are expected at 2030 GMT, 2045 GMT, and 2100 GMT.

This supports a theory of a pre-fuel exhaustion water impact, possibly between 2013 GMT and 2100 GMT.

This may result from a CFIT event, or a mission fuel over-burn.

The fuel consumption rates in GPH computed from Kelly Johnson, L487, and Pratt-Whitney engine data, reasonably agree with empirical data from AE flight logs and position reports, in the range of 250 BHP prescribed for mission cruise.

A summation of discrete, mission segment analyses can produce a more accurate result in fuel consumption, using BHP and SFC with all other data.

Reaching Gardner Island, at approximately 400 statute miles distant, at 120 mph would require 3 hours 22 minutes, after 2013 GMT, or 4 hours 22 minutes after arriving at Howland Island at 1912 GMT.

Only Case 4 and 5 in Swenson and Culick’s analysis enable this result.

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