Solar Challenger

by Don Monroe (1981)

I wrote this article in 1981, and it has not previously been published. It is based on my own observations and talking with Paul MacCready.

Janice Brown, former schoolteacher from Ca1ifornia in her early thirties, is planning to fly a small a1rplane from Paris to London some day this June. She expects to cover the 350-km distance in about six hours, without using a drop of fuel. The flight of the Solar Challenger, as the airplane is called, will climax an 18-month effort led by aeronautical scientist Dr. Paul MacCready, of Pasadena, California, to make a long distance flight with a solar-powered airplane. The Solar Challenger is powered directly by the sun, without batteries.

The Solar Challenger was conceived by MacCready and created by a team of engineers and model airplane builders. But because of the weight and cost of solar cells, and because they produce energy only under bright light, there will never be a significant number of airplanes powered by direct conversion of solar energy. MacCready says, "The least useful application of solar cells that I can think of is powering an airplane." Gasoline-powered airplanes will remain more practical, because of the energy efficiency of fossil fuel, and because they can be flown without sunlight.

So why is MacCready doing it? Observing the failure of government leaders to effectively respond to the energy crisis, he realized that he as an individual could do something that might have an impact. He believed in the great potential of solar cells as an alternative energy source. Continued research should yield eventual breakthroughs in production methods, resulting someday 1n low costs, just as has happened in other areas of the semiconductor field. And solar cells don't pollute. "I felt that a long distance flight with the Solar Challenger would focus public attention on solar cells, and help stimulate the public awareness and support which would speed their development and utilization. Rapid growth of the solar cell field would lessen our dependence on imported oil," says MacCready.

Early last year, MacCready was in a unique position. He had earned the title "father of human-powered flight" by winn1ng aviation's largest prizes: the £50,000 Kremer Prize for demonstrating the first successful human-powered aircraft, the Gossamer Condor, on August 23, 1977; and the £100,000 Kremer Cross-Channel Prize for a f1ight of the human-powered Gossamer Albatross from England to France on June 12, 1979. So he had experience in low-speed flight and ultralight airframes. Talented people, some having worked on his human-powered-flight projects, surrounded him. So he knew how to obtain financial backing, having secured DuPont sponsorship for the Gossamer Albatross project. And he had the ability to bring all these elements together to attack the problem in an effective way.

In the late winter of 1980, he gathered a group of talented people, defined the problem, and set about designing the airplane and seeking sponsorship. Ray Morgan, a brilliant young engineer and experienced hang glider pilot, took a leave of absence from Lockheed Aircraft Corporation to become manager. First, with DuPont support again, Morgan and his group completed the Gossamer Penguin, which had been designed as a possible backup aircraft for the cross-Channel flight. It wasn't needed, and construction hadn't been completed. The Gossamer Penguin, similar to the Gossamer Albatross but 3/4 the size, provided a test bed to try out ideas pertaining to the power system and to build experience with solar power.

Bob Boucher, president of Astro Flight, Inc., in Venice, California, a small company that makes model airplane kits and small electric motors as powerplants for them, served as the powerplant expert on the project. Boucher, under air force contract, in the mid-seventies, had pioneered solar-powered flight by building and flying two unmanned solar-powered aircraft, Sunrise I and Sunrise II. These airplanes, with wingspans of approximately 10 meters, had been developed to demonstrate the possibility of long duration flights using only the sun's rays for power. Boucher designed the motor installation, the solar cell array, and for the initial flights of the Gossamer Penguin, the battery installation.

Thirteen-year-old, 37-kg Marshall MacCready, Paul's youngest son, was the first test pilot on the Gossamer Penguin. He made about 50 battery-powered flights, and then completed his contribution with two short hops under solar power on May 18, 1980. Janice Brown, weighing 45 kg, was then brought in as project pilot, continuing to make solar-powered flights in the Gossamer Penguin, making a 2.5-km flight at Edwards Air Force Base, California on August 7, 1980.

Flight tests of the Solar Challenger began November 1980. The airplane was first flown under battery power because they didn't want to risk losing any of the 16,128 solar cells, worth over $100,000, in an inadvertent mishap while learning to fly the airplane. Starting with short hops down the runway, the team quickly developed enough confidence to attempt higher and longer flights. This phase of testing, at Shafter Airport, near Bakersfield, Calif., was concluded with a 1 1/2-hour flight at heights reaching 500 meters above the ground. The motor was used for only 15 minutes; the remainder of the flight was conducted using indirect solar power, rising air (thermals).

On November 20, 1980, at El Mirage field in Southern California's Mojave Desert, Janice made the first solar-powered flights of the Solar Challenger. After a week of 3-7 minute flights using the low winter sun (which provided only a fraction of the energy which will be available in late spring and summer, with the midday sun more directly overhead), Morgan then took the airplane to Marana Air Park, near Tucson, Arizona. There, they hoped to make a 100-km flight attempt. Experiencing unusually cloudy weather, many flights were made nonetheless, and Janice was able to leave the airport twice for short distances, gaining valuable off-field landing experience. After a week in Arizona, Morgan returned to Southern California, to make some modifications in the motor and propeller installation, then went back to Arizona in mid-January to resume distance attempts, warming up for the June European flight.

Where does this all lead? Aside from being fun, MacCready feels the project is a "significant and legitimate technical challenge," and the team continues to break new ground in low speed, ultralight flight. And who knows? Janice's flight to London just might lead to reduced dependence on fossil fuel.

Solar Challenger Physical Data
Weight (without pilot) 88 kg.
Wing 14.3 m
Horizontal tail 4.0 m
Wing 23.2 m2
Horizontal tail 9.3 m2
Length 8.8 m
Propeller diameter 3.4 m
Power rating (@ 7500 rpm) 1865 watts (2.5 hp)
Dimensions: length 19 cm
diameter 7.6 cm
Cruise speed (indicated) 35-55 kph
(20-30 kt)


by Don Monroe (March 31, 2010)

After this article was written, Steve Ptacek became the project pilot. Ptacek flew the solar-powered aircraft from Corneille-en-Verin Airport, near Paris, to Manston Royal Air Force Base, England, near Dover, a distance of 163 miles, on July 7, 1981. Flight duration was 5 hours, 23 minutes.

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