Energy efficiency of MacCready Gossamer Albatross

Updated Nov 9, 2020

The MacCready Gossamer Albatross:

  • covered around 2.0—4.6 m/kJ
  • and moved mass at around 0.1882 —0.4577 kg.m/J

Details

The MacCready Gossamer Albatross was a human-powered flying machine that crossed the English Channel in 1979.1 The pilot pedaled the craft, seemingly as if on a bicycle. It had a gross mass of 100kg, flying across the channel,2 and flew 35.7 km in 2 hours and 49 minutes.3 The crossing was difficult however, so it seems plausible that the Gossamer Albatross could fly more efficiently in better conditions.

We do not know the pilot’s average power output, however:

  • Wikipedia claims at least 300W was required to fly the craft4
  • Chung 2006, an engineering textbook, claims that the driver, a cyclist, could produce around 200W of power.5
  • Our impression is that 200W is a common power output over houres for amateur cycling. For instance, one of our researchers is able to achieve this for three hours.6

The best documented human cycling wattage that we could easily find is from professional rider Giulio Ciccone who won a stage of the Tour de France, then uploaded power data to the fitness tracking site Strava.7 His performance suggests around 318W is a reasonable upper bound, supposing that the pilot of the Gossamer Albatross would have had lower performance.8

To find the energy used by the cyclist, we divided power output by typical efficiency for a human on a bicycle, which according to Wikipedia ranges from .18 to .26.9

Distance per Joule

For distance per energy this gives us a highest measure of:

35.7 km / ((200W * (2 hours + 49 minutes))/0.26) = 4,577 m/MJ

And a lowest measure of:

35.7 km / ((318W * (2 hours + 49 minutes))/0.18) = 1,993 m/MJ

Mass per Joule

For weight times distance per energy this gives us a highest measure of:

(100kg * 35.7 km) / ((200W * (2 hours + 49 minutes))/0.26) = 0.4577 kg*m/j

And a lowest measure of:

(100kg * 35.7 km) / ((318W * (2 hours + 49 minutes))/0.17) =  0.1882 kg*m/j

Notes

  1. “The Gossamer Albatross is a human-powered aircraft built by American aeronautical engineer Dr. Paul B. MacCready‘s company AeroVironment. On June 12, 1979, it completed a successful crossing of the English Channel to win the second £100,000 (£509644 today) Kremer prize.[1]

    “MacCready Gossamer Albatross.” In Wikipedia, October 7, 2020. https://en.wikipedia.org/w/index.php?title=MacCready_Gossamer_Albatross&oldid=982283381.

  2. “The empty mass of the structure was only 71 lb (32 kg), although the gross mass for the Channel flight was almost 220 lb (100 kg). “

    “MacCready Gossamer Albatross.” In Wikipedia, October 7, 2020. https://en.wikipedia.org/w/index.php?title=MacCready_Gossamer_Albatross&oldid=982283381.

  3. “Allen completed the 22.2 mi (35.7 km) crossing in 2 hours and 49 minutes, achieving a top speed of 18 mph (29 km/h) and an average altitude of 5 ft (1.5 m).”

    “MacCready Gossamer Albatross.” In Wikipedia, October 7, 2020. https://en.wikipedia.org/w/index.php?title=MacCready_Gossamer_Albatross&oldid=982283381.

  4. “To maintain the craft in the air, it was designed with very long, tapering wings (high aspect ratio), like those of a glider, allowing the flight to be undertaken with a minimum of power. In still air, the required power was on the order of 300 W (0.40 hp), though even mild turbulence made this figure rise rapidly.[2]

    “MacCready Gossamer Albatross.” In Wikipedia, October 7, 2020. https://en.wikipedia.org/w/index.php?title=MacCready_Gossamer_Albatross&oldid=982283381.
  5. Chung, Yip-Wah. Introduction to Materials Science and Engineering. CRC Press, 2006. p89
  6. https://www.strava.com/activities/272615649/overview
  7. Strava. “Yellow Jersey – Giulio Ciccone’s 158.8 Km Bike Ride.” Accessed November 9, 2020. https://www.strava.com/activities/2525139293.
  8. For an upper value, we used a combination of two metrics given on the website. The first metric is his “weighted average power” for the Tour de France stage, which was 318W. Weighted average power is a way of averaging power over a ride with highly variable power which gives higher weight to higher power portions of the ride, and is used by athletes and coaches to estimate the maximum power that a rider could sustain for a long time, if they had a steady power output. The second metric is Ciccone’s maximum power from his Tour race applied over the duration of the MacCready flight (2 hours and 40 min) which is 5W/kg body weight. For the pilot, Allen, riding with the same power per body weight (65 kg), this would be equivalent to 322W, a similar value to his weighted average power. We use the lower of the two values, 318W.
  9. “The required food can also be calculated by dividing the output power by the muscle efficiency. This is 18–26%. “

    “Bicycle Performance.” In Wikipedia, October 9, 2020. https://en.wikipedia.org/w/index.php?title=Bicycle_performance&oldid=982652996.


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