By the time he was 14, he had designed and built a number of unconventional model planes, including an autogyro that flew for more than 12 minutes, outlasting the best efforts of adults entered in the same competition. Two years later, he tried his hand in real airplanes, earning a pilot's license.
He entered Yale in 1943, at the same time signing up for training as a Navy pilot. His studies were interrupted occasionally by flight training, but World War II ended before he graduated; he never saw combat.
In 1947, MacCready bought an Army surplus glider and, combining his Navy flight skills with his Yale training in meteorology, he soon became an expert glider pilot. He invented a system that is still used to calculate optimum flight speeds between thermal air currents.
A year later, MacCready earned a master's degree in physics at Caltech and won the first of three national soaring championships.
In 1951, he founded Meteorology Research Inc., which quickly became a leader in weather modification technology and the manufacture of remote-controlled aircraft for atmospheric research.
MacCready received a doctorate in aeronautics from Caltech in 1952, and in 1956, he became the first American to win the World Champion Soaring Contest.
Several years later, he founded AeroVironment, which produces electronic systems, surveillance aircraft and experimental, energy-efficient cars and boats. The firm also builds systems to monitor and reduce air pollution and hazardous waste.
MacCready often stressed the importance of independent thought.
"You will find that your teachers are sometimes wrong," he told a group of Santa Monica schoolchildren in 1998.
"Your parents will be wrong. Your schools will be wrong. If you look for the answers yourself, you will find that you can do better."
Nobel laureate Murray Gell-Mann, a close friend, attributed MacCready's creativity to his outlook.
"He approaches nature and daily life with an innocent sense of wonder," Gell-Mann told Time magazine in 1990.
"He approaches problems and learning about new things in the same way: without strongly held, preconceived notions. When he sees something, he takes a fresh view of it."
MacCready is survived by his wife, Judy; three sons, Parker, Tyler and Marshall; and two grandchildren.
Plans for a private memorial service are pending.
