Sunraycer—The GM Solar-Powered Car

Solar Challenge race tests new technology–Carol Hazard

Hughes News Special Edition for Australia, September 1987

Transcribed by Faith MacPherson

 

A Hughes team is developing the power system for a solar-powered car that General Motors has entered in the 1987 Solar Challenge race in Australia.

The race, which is scheduled to being Nov. 1, will cover 1950 miles in the outback from Darwin to Adelaide.

GM’s entry is one of 25 vehicles representing nine countries that have been entered. Howard Wilson, Hughes vice president in charge of GM projects, is overall project manager for the company’s participation.

According to Ervin Adler, project manager for Space and Communications Group’s work on the car, the end result may spawn a new age of electric-powered commuter vehicles and demonstrate innovative approaches for using solar power on Earth.

The Group team assigned to the out-of-the-ordinary project is modifying technology that it has used for decades to power spacecraft. It will apply its expertise in solar cells, solar panels, and batteries to build an efficient power source for the vehicle.

Based on a mandated daily schedule from 8 a.m. to 5 p.m. and depending upon weather conditions, the race is expected to last no longer than seven days. Any vehicle lagging behind the lead by two full day will be disqualified.

Without disclosing details, Mr. Adler said that GM’s entry is “larger than a compact car, ultra-lightweight, and highly streamlined.”

According to the rules, the vehicle cannot be taller or wider than 6 ½ feet and no longer than 19 ½ feet.

“Anything goes, as long as it complies with the rules,” said Mr. Adler.

The project must be completed by October to allow for transportation to Australia.

“With so little time left, we’ll have to push to get it done,” said Mr. Adler. “It’s a challenge, but it’s also fun.”

GM is providing electric drive and suspension systems, aerodynamic testing, and design consultation for the vehicle through several organizations.

Other team members, Group Lotus PLC of London and Holden’s Motor Company of Australia, both GM international subsidiaries, are developing race strategy and logistics support.

AeroVironment, Inc., of Monrovia, Calif., has been retained by GM to contribute its expertise in lightweight structures and materials, low-speed aerodynamics, and low-powered aircraft.

AeroVironment designed and built the Gossamer Condor, the first maneuverable human-powered aircraft, and the Solar Challenger, a solar powered aircraft that set records in its crossing of the English Channel.SunraycerPIC

Hughes News Quarterly International July-September, 1987

Sunraycer

Sunraycer Description and Race Results—Jack Fisher

The Challenge

Early in 1987 GM’s Australian Division contacted GM headquarters in Detroit to inquire about the corporation’s interest in participating in the Pentax World Solar Challenge to be held in Australia later that year. Roger Smith, GM CEO at the that time, was interested and a team was formed, consisting of GM, Hughes Aircraft, and AeroVironment, to design a solar-powered car that came to be called the Sunraycer. Time was of the essence as only about 10 months remained to design, build and test the car.

The race was to begin on November 1 and was to cover a distance of about 1900 miles on the Stuart Highway between Darwin in Australia’s Northern Territory and Adelaide in South Australia. This two-lane highway is only partially paved. The cars are to be solar powered with the solar panel area limited to 8 m 2(projected area). Any size battery can be used but must be charged only by the solar panel. Racing will take place daily between 8 am and 5 pm with maintenance and battery charging allowed from 6am to 8 am and 5 pm to 7 pm. Six drivers plus an unlimited support team are allowed for each car with the drivers ballasted to 85 kg. A major concern on the Stuart Highway was the presence of large tractor-trailers, known locally as road trains. Each participating car had to undergo a stability test passing a tractor-trailer driving in the opposite direction at 100 km/hr.

Australia

Car Design

The design approach adopted was to minimize weight, aerodynamic drag and rolling friction. This necessitated a solar panel that was contoured to the shape of the car rather than a flat panel that could be raised to face the sun while racing. The contoured panel, however would be raised to face the sun during the two daily battery charging opportunities. The car body, only 3.3 feet in height, was a lightweight honeycomb composite over an aluminum tube frame that in wind tunnel tests had a drag coefficient of only 0.125 based on the frontal area.

Two cars were built—a development model with silicon solar cells that provided an output of 1000 watts and the racing model with a combination of silicon (20%) and gallium-arsenide (80%) cells that provided 1400 watts. The silver zinc battery had a capacity of 3-kilowatt hours. The solar panels and battery were both designed and built by Hughes SCG.

The controls consisted of a throttle, brakes and a two-mode cruise control operating at a fixed speed or fixed battery current. An option for regenerative braking returning energy to the battery was also provided. A lightweight dc brushless 2 horsepower electric motor operating at 92% efficiency provided torque to a chain drive on the left rear wheel. The car weight (without driver) was only 385 pounds. GM did not disclose the cost for the Sunraycer development, but it is estimated to be in the order of $2 million.

Software

Software was developed at SCG to simulate racing conditions and predict vehicle performance. This software, developed on a Macintosh personal computer, by Joe Gurley and Mike Cassidy was also used during the race for tactical support. An SCG systems engineer, probably Mike Cassidy, traveled with the support team in Australia to provide tactical support for race operations using this software.

The software provided an electrical system simulation that took into account ambient conditions including rolling friction, aerodynamic drag, sun angle, wind, and grade to provide an optimal speed control law. This allowed the determination taking into account the diurnal variation of the solar aspect angle a minimum and maximum operating speed. In the early morning and late afternoon the minimum speed could be maintained using the battery while during midday holding the speed to the maximum allowed battery charging.

Testing

A ¼-scale model was tested in Caltech’s GALCIT wind tunnel and the full-scale development model was tested in a GM wind tunnel. The development model was operated for 3000 miles at GM’s Mesa Proving Ground in Arizona. As a result of this testing the suspension system was redesigned. The race vehicle was completed only a few days before shipment to Australia and underwent only limited testing.

Race Results

The Sunraycer won the pole position for the start of the race with a speed of 33 mph and completed the race in 44 hr 54 min at an average speed of 42.8 mph almost 24 hr ahead of second place car. The only problems encountered during the race were three flat tires. In June 1988 at the GM proving ground in Arizona the Sunraycer set a new world speed record of 48.7 mph for a solar powered land vehicle. GM donated the car to the Smithsonian where it is on permanent display at the Museum of American History.

 

 

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