Published 04 November, 2020; last updated 10 December, 2020

The Wright Flyer:

• flew around 0.080-0.18m/kJ
• and moved mass at around .022 – .061 kg.m/J

The Wright Flyer (Flyer I) was the first successful plane, built in 1903.¹

According to Wikipedia²:

• Empty weight: 605 lb (274 kg)
• Max takeoff weight: 745 lb (338 kg)

A 1904 article in the Minneapolis Journal says the plane consumed ‘a little less than than ten pounds of gasoline per hour’.³ A pound of gasoline contains around 20MJ⁴ So we have:

Hourly fuel consumption: 10lb/h x 20MJ/lb = 200MJ/h = 55kJ/s

We don’t know how reliable this source is. For instance, a 1971 book, The Write Brothers’ Engines and their Design does not give data on fuel consumption in their table of engine characteristics for lack of available comprehensive data⁵, suggesting that its authors did not consider the article strong evidence, though it is also possible that they didn’t have access to the 1904 article.

To confirm, we can estimate the plane’s energy use per second by a second means: combining the claimed power (energy/second) made use of by the engine, and a guess about how much fuel is needed to deliver that amount of energy.

According to Wikipedia, the plane had a 12 horsepower (9 kJ/s), gasoline engine.⁶ The 1904 Minneapolis Journal article put it at 16 horsepower (12 kJ/s), and Orville Wright, quoted by Hobbs (1971), puts it at ‘almost 16 horsepower’ at one point.⁷ Hobbs says that at one point this engine achieved 25 horsepower, though this probably isn’t representative of what was ‘actually utilized’.⁸ For that he gives a range of 8.25-16 horsepower.⁹ In light of these estimates, we will use 8.25-16 horsepower, which is 6.15-12 kJ/s.

A quote from Orville Wright suggests fuel consumption as 0.580lb of fuel per horsepower hour.¹⁰ This would imply 23% of energy was utilized from the fuel.¹¹

Hobbs notes that this seems low, but assumes a similar efficiency: 24.50%. Thus he presumably doesn’t find it implausible.¹²

According to Wikipedia, the thermal efficiency of a typical gasoline engine is 20%¹³. It seems that this has increased¹⁴, which would suggest that the typical figure was lower in 1903. We don’t think this undermines the more specific figures given above.

It seems likely that Hobbs number is best here, since he knows about Wright’s number, and may have more information than us about for instance the exact fuel being used. So we use 24.5%.

Combining these numbers, we have:

power spent = 6.15-12 kJ/s used by engine x 1 / 24.5% fuel energy needed to get one unit of energy used by engine, given inefficiency

= 25-49 kJ/s

We now have:

• energy expenditure calculated via motor power and efficiency: 25-49 kJ/s
• energy expenditure calculated via hourly fuel use: 55kJ/s

Neither figure seems clearly more reliable, so we will use the range 25-55kJ/s

Two of the Wright Flyer’s first flights were 120 feet in 12 seconds and 852 feet in 59 seconds.¹⁵ This gives speeds of 3m/s and 4.4m/s. We will use the second, since it better represents successful flight, still within the first days.

We now have (from above):

• speed = 4.4 m/s
• energy use = 25-55 kJ/s

Thus, on average each second the plane flies 4.4m and uses 25-55kJ, for 0.080-0.18m/kJ.

We have:

• Distance per kilojoule: 0.080-0.18m/kJ
• Mass: 274-338kg

This gives us a range of .022 – .061 kg.m/J

Primary author: Ronny Fernandez

1. “The Wright Flyer (often retrospectively referred to as Flyer I or 1903 Flyer) was the first successful heavier-than-air powered aircraft….The Wrights built the aircraft in 1903 using giant spruce wood as their construction material.^[2]“

   “Wright Flyer.” In Wikipedia, October 30, 2020. https://en.wikipedia.org/w/index.php?title=Wright_Flyer&oldid=986246127.

2. “Wright Flyer.” In Wikipedia, October 30, 2020. https://en.wikipedia.org/w/index.php?title=Wright_Flyer&oldid=986246127.
3. “At the speed of 1200 revolutions per minute the engine develops sixteen-brake horsepower, with a consumption of a little less than ten pounds of gasoline per hour.”
4. “Gasoline has an energy density of about 45 megajoules per kilogram (MJ/kg)”
   
   “Energy Density of Gasoline – The Physics Factbook.” Accessed November 3, 2020. https://hypertextbook.com/facts/2003/ArthurGolnik.shtml.
   
   45MJ/kg = 20.4MJ/lb
5. “No fuel consumption figures are given, primarily because no comprehensive data have been found. This is most probably because in the early flight years, when the Wrights were so meticulously measuring and recording technical information on the important factors affecting their work, the flights were of such short duration that fuel economy was of very minor importance.”

   Hobbs, Leonard S. The Wright Brothers’ Engines and Their Design. [For sale by Supt. of Docs., U.S. Govt. Print. Off.]; First Edition. Smithsonian Institution Press, 1971. https://www.gutenberg.org/files/38739/38739-h/38739-h.htm.

6. “Since they could not find a suitable automobile engine for the task, they commissioned their employee Charlie Taylor to build a new design from scratch, effectively a crude 12-horsepower (9-kilowatt) gasoline engine.^[4]
   
   “Wright Flyer.” In Wikipedia, October 30, 2020. https://en.wikipedia.org/w/index.php?title=Wright_Flyer&oldid=986246127.
7. “Speaking of the first engine, Orville Wright wrote, “Since putting in heavier springs to actuate the valves on our engine we have increased its power to nearly 16 hp and at the same time reduced the amount of gasoline consumed per hour to about one-half of what it was.””

   Hobbs, Leonard S. The Wright Brothers’ Engines and Their Design. [For sale by Supt. of Docs., U.S. Govt. Print. Off.]; First Edition. Smithsonian Institution Press, 1971. https://www.gutenberg.org/files/38739/38739-h/38739-h.htm.

8. “In the table, performance is given in ranges which are thought to be the most representative of those actually utilized. Occasionally performances were attained even beyond the ranges given. For example, the 4×4-in. flat development engine eventually demonstrated 25 hp at an MEP of approximately 65 psi.”

   Hobbs, Leonard S. The Wright Brothers’ Engines and Their Design. [For sale by Supt. of Docs., U.S. Govt. Print. Off.]; First Edition. Smithsonian Institution Press, 1971. https://www.gutenberg.org/files/38739/38739-h/38739-h.htm.

9. See first table in Appendix. It appears that the lower number is for the first flight, though this is confusing:

   “One important figure—the horsepower actually utilized during the first flight—is quite accurately known. In 1904 the 1904-1905 flight engine, after having been calibrated by their prony-brake test-fan method, was used to turn the 1903 flight propellers, and Orville Wright calculated this power to be 12.05 bhp by comparing the calibrated engine results with those obtained with the flight engine at Kitty Hawk when tested under similar conditions. However, since the tests were conducted in still air with the engine stationary, this did not exactly represent the flight condition. No doubt the rotational speed of the engine and propellers increased somewhat with the forward velocity of the airplane so that unless the power-rpm curve of the engine was flat, the actual horsepower utilized was probably a small amount greater than Orville’s figures. The lowest power figure shown for this engine is that of its first operation.”

   Hobbs, Leonard S. The Wright Brothers’ Engines and Their Design. [For sale by Supt. of Docs., U.S. Govt. Print. Off.]; First Edition. Smithsonian Institution Press, 1971. https://www.gutenberg.org/files/38739/38739-h/38739-h.htm.

10. “Orville Wright quotes an early figure of brake thermal efficiency for the 1903 engine that gives a specific fuel consumption of .580 lb of fuel per bhp/hr based on an estimate of the heating value of the fuel they had. This seems low, considering the compression ratio and probable leakage past their rather weak piston rings, but it is possible.”

    Hobbs, Leonard S. The Wright Brothers’ Engines and Their Design. [For sale by Supt. of Docs., U.S. Govt. Print. Off.]; First Edition. Smithsonian Institution Press, 1971. https://www.gutenberg.org/files/38739/38739-h/38739-h.htm.

    Note that the quote says bhp/h, but we think it must mean bhp.h.

    Also, bhp is ‘brake horsepower’, meaning horsepower measured empirically through a particular mechanism:

    ‘Brake horsepower (bhp) is the power measured using a brake type (load) dynamometer at a specified location, such as the crankshaft, output shaft of the transmission, rear axle or rear wheels.’
    
    “Horsepower.” In Wikipedia, November 3, 2020. https://en.wikipedia.org/w/index.php?title=Horsepower&oldid=986863945.

11. fuel/power = 0.580lb fuel / hp.h
    = 0.580 * 20MJ / hp.h
    = 11.6MJ/ 745J.h/s
    = 11600kJ / (0.745 * 3600 kJ)
    = 4.3.
    
    Thus power/fuel = 0.23.
12. “Assuming a rich mixture, consumption of all the air, and an airbrake thermal efficiency of 24.50% for the original engine…”
    
    Hobbs, Leonard S. The Wright Brothers’ Engines and Their Design. [For sale by Supt. of Docs., U.S. Govt. Print. Off.]; First Edition. Smithsonian Institution Press, 1971. https://www.gutenberg.org/files/38739/38739-h/38739-h.htm.
13. “Typically, most petrol engines have approximately 20%(avg.) thermal efficiency, which is nearly half of diesel engines. However some newer engines are reported to be much more efficient (thermal efficiency up to 38%) than previous spark-ignition engines.^[5]“
    
    “Petrol Engine.” In Wikipedia, August 20, 2020. https://en.wikipedia.org/w/index.php?title=Petrol_engine&oldid=973981680.
14. See above note.
15. “His first flight lasted 12 seconds for a total distance of 120 feet (37 m) – shorter than the wingspan of a Boeing 747, as noted by observers in the 2003 commemoration of the first flight.^[1][5]…The last flight, by Wilbur, was 852 feet (260 m) in 59 seconds, much longer than each of the three previous flights of 120, 175 and 200 feet (37, 53 and 61 m).”

    “Wright Flyer.” In Wikipedia, October 30, 2020. https://en.wikipedia.org/w/index.php?title=Wright_Flyer&oldid=986246127.