Aero Engines - Promise of Solar Power

An aircraft that draws fuel from a free, limitless source and promises zero-carbon emission flight—a seemingly impossible dream at present.

If all goes as planned, perhaps three years from now, a strange looking aircraft will get airborne somewhere in Switzerland and circumnavigate the globe. Remarkably, this craft will require only the rays of the sun as fuel. In these difficult times, when the skyrocketing price of oil is threatening to deal a body blow to the air transport industry, could anything be more mouth-watering than the prospect of switching to free, nonpolluting solar power? The revolutionary Solar Impulse will have four propellers mounted on a wingspan of approximately 80 m—a little over that of the 555-seat Airbus A380—and yet, will carry only one pilot in a cramped cockpit. The expansive wingspan serves two purposes. First, it will minimise the induced drag and reduce the power required to maintain the plane in cruise flight and second, it will provide a greater surface area to mount the all-important solar cells. Since it has only one pilot, a practical limit of three to four days airborne time will be observed. However, once the technology is proven and the capacity of onboard batteries sufficiently enhanced, it should be relatively simple to accomplish non-stop circumnavigation of the globe, this time with two pilots.

Solar planes, unmanned and manned, have been flying for decades, mainly on short, daytime flights. Solar Impulse will probably be the first manned solar aircraft to fly in total darkness. Some time in 2009 it should undertake a preliminary 36-hour day-night-day flight at a top speed of just 70 km an hour—a speed at which an average motorcyclist could race ahead of it. The challenge will be to use minimal power during the day to keep flying while charging the batteries sufficiently to continue operating the electrically powered engines when flying by night.

The Predecessors

The maiden flight of an unmanned solar-powered aircraft, the Sunrise I, took place on November 4, 1974. It took a few more years to refine the technology for the next step: a pilot onboard. Ultra-light airplane designer Dr Paul MacCready accepted the challenge. On May 18, 1980, the Gossamer Penguin, weighing just 31 kg, got airborne with Dr MacCready’s 13-year-old son Marshall at the controls and made a brief solar-powered flight. However, the official credit for the first sustained flight relying entirely on solar power should go to Janice Brown who achieved the feat on August 7, 1980.