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Energy efficiency of The Spirit of Butt’s Farm

Published 18 November, 2020; last updated 10 December, 2020

The Spirit of Butt’s Farm:

  • covered around 31.67 m/kJ
  • and moved mass at around 0.16 – 0.086 kg⋅m/J


The Spirit of Butt’s Farm was a record setting model airplane that crossed the Atlantic on one gallon of fuel.1 Fully fueled it weighed 4.987 kg, dry it weighed 2.705 kg.2

The record setting flight used 117.1 fluid ounces of fuel.3 The straight line distance of the flight was 3,028.1 km.4 It was powered by 88% Coleman lantern fuel, mixed with lubricant.5 Coleman fuel is based on naphtha 6, so we can use the energy density of naphtha—31.4 MJ/L7—as a rough guide to its energy content, though naphtha appears to vary in its content, and it is unclear whether Coleman fuel consists entirely of naphtha.

From all this, we have:

Distance per energy = 3,028.1 km / (117.1 fl oz * 0.88 * 31.4 MJ/L)

= 31.67 m/kJ

For weight times distance per energy we will calculate a best and a worst score. To calculate the best score we will use the fully fueled weight, and to calculate the worst score we will use the dry weight. All other values are the same in both calculations. 

Best score:

Distance*mass/energy = 4.987 kg * 31.67 m/kJ

= 0.16 kg⋅m/J

(4.987 kg * 3,028.1km) / (117.1 US fluid ounces * 31.4MJ/litre) = 0.1389 kg*m/j

Worst score:

Distance*mass/energy = 2.705 kg * 31.67 m/kJ

= .086 kg⋅m/J

Primary author: Ronny Fernandez


Photo by Ronan Coyne, licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license, unaltered.

  1. The Spirit of Butts’ Farm (also known as TAM 5) was the first model aircraft to cross the Atlantic Ocean on August 11, 2003…Fuel tank: Approx. 118 US fluid ounces (3.5 l)” [118 US fluid ounces = 0.92 US liquid gallons according to Google]

    The Spirit of Butts’ Farm.” In Wikipedia, September 29, 2019.

  2. From Wikipedia:
    Weight: Dry: 5.96 lb (2.705 kg); Fully fueled: 10.99 lb (4.987 kg)[11]

    The Spirit of Butts’ Farm.” In Wikipedia, September 29, 2019.

  3. “The flight used 99.2% of its fuel…Fuel tank: Approx. 118 US fluid ounces (3.5 l)”

    The Spirit of Butts’ Farm.” In Wikipedia, September 29, 2019.

    Multiplying these values we find that the vehicle crossed the Atlantic using 99.2%*118 = 117.1 fluid ounces
  4. “It was recognized by the FAI as a double world record[2] flight for its duration of 38h 52 min 19 sec[3] and straight-line distance of 1,881.6 mi (3,028.1 km) using an autopilot,[4]…”

    The Spirit of Butts’ Farm.” In Wikipedia, September 29, 2019.

  5. From Wikipedia:
    Fuel: Coleman lantern fuel with 16 US fl oz (470 ml) of Indopol L-50 lubricant additive per 1 US gal (3,785 ml). Single fuel tank in the fuselage at the CG point [12] (normal: alcohol)

    The Spirit of Butts’ Farm.” In Wikipedia, September 29, 2019.

  6. “…Coleman Camp Fuel, which is a common naphtha-based fuel used in many lanterns and stoves”

    “Coleman Fuel.” In Wikipedia, August 22, 2019.

  7. Liquid Fuel MJ / liter

    Naphtha 31.4

    “List of Common Conversion Factors (Engineering Conversion Factors) – IOR Energy Pty Ltd.” Accessed November 17, 2020.

power_of_evolution/evolution_engineering_comparison/energy_efficiency_of_the_spirit_of_butts_farm.txt · Last modified: 2022/09/21 07:37 (external edit)