The Daedalus Project: Physiological Problems and Solutions

In April of 1985, a team of engineers and scientists at the rations showed that our pilot would be required to Massachusetts Institute of Technology began a research produce approximately 3.0 to 3.5 watts of mechanical program with the goal of flying an aircraft from the power per kilogram of body weight to fly at all. FurtherGreek island of Crete powered only by the muscles of more, because human-powered aircraft require signifthe pilot. The project was called Daedalus, in celebration candy more power to climb than to fly on the level and of the mythical Greek inventor who constructed wings of so generally fly within a few meters of the surface, there wax and feathers with which he flew from imprisonment would be no time to glide, and the pilot would be on Crete some 3,500 years ago. In some versions of the required to produce this power continuously, with no myth, Daedalus was accompanied by his son Icarus, rest, for the entire flight. who flew too dose to the sun, against his father's The metabolic cost to the pilot of maintaining the admonition, and fell to the sea when constant mechanical power produchis wings melted. tion of 3.0 to 3.5 watts per kilogram The route proposed in the DaeThe challenge of a humanof body weight is relatively easy to dalus project, from the port city of ligh determine. Potential energy is conHeraklion on Crete to the island of powered flight lasting verted into mechanical work by the Santorini (or Thira), was 119 km, t hours oxidation of stored fuels to generate more than three times the existing Up o SIX rs posed the high-energy compounds that are world record for human-powered unique physiological necessary for both the contraction flight, Bryan Allen's 35-km crossing L s 2 r and relaxation processes in skeletal in 1979 of the English Channel in the problems ana required muscle (see Ethan Nadel's article in Gossamer Albatross (Fig. 2). In the unique solutions American Scientist, July-August 1985, years since the record was set, adfor an expanded account of energy vances in aircraft tedhnology had conversion in skeletal muscle). It is made our more ambitious attempt possible, although generally accepted that in humans only about 24% of the much needed to be learned about the physiology of the potential energy of these stored fuels can be converted to human pilot. In fact, the fundamental challenge of mechanical work during the metabolic transfers human-powered flight is the limited ability of humans to (Astrand and Rodahl 1986); this value is known as the act as a power plant. Preliminary estimates of the mechanical efficiency. The remaining 76% is converted aircraft's performance, based on previous designs, indidirectly to heat during these transfers and is of no use to cated that the Daedalus flight would last four to six the pilot. Thus, in order to generate mechanical power at hours. Before an aircraft could be designed in detail, we the rate of 3.5 W/kg, the pilot would have to maintain a needed to learn more about the physiological limits of fuel-oxidation rate of 14.6 W/kg, which requires an long-duration exercise and about possible countermeaoxygen uptake of more than 44 ml 0Q/(min kg). The sures that would postpone the onset of fatigue. We pilot has to sustain this rate of oxygen uptake, without sought an engineering model for human power producpause, to maintain steady flight. This metabolic cost is tion that we could address with the same analytical tools approximately the same as that required to pedal a an aircraft designer would use in matching power plant bicycle over level ground at a world-class speed of to airframe. It was that goal which brought the authors37 km/hr (Whitt and Wilson 1982). a physiologist and an aeronautical engineer-into colThe problem unique to the Daedalus project was laboration. whether this energy production could be sustained for Because an aircraft engine must carry its own the anticipated four to six hours of the flight. A thorough weight, its performance is often expressed in power per review of the existing literature yielded no convincing unit weight or power-to-weight ratio. Preliminary calcudata for human power production of durations beyond about three hours, and no data taking the sizes or body