In 1956, a Minneapolis investor and four engineers who had been working in the research and mechanical division of the General Mills company, founded Raven Industries in Sioux Falls. They planned to continue their work on high altitude gas balloons, but they also thought they could develop a new kind of improved hot air ballon. They knew that hot air could provide enough bouyancy to lift a balloon, but no one had yet developed a safe, reliable system design.
Their prototype featured a chair for the pilot. After trying a number of fuel options, including kerosene, they settled on propane, which they planned to carry aloft in two converted oxygen tanks salvaged from a World War II bomber.
The bottom of the balloon envelope was held open by bicycle wheel rim. A rope at the top of the balloon tied the fabric together like a sack. When the time came to land, a pilot would allow the air in the balloon to cool. Just before touchdown, the pilot would trigger an explosive charge to dislodge the rope and open the sack. The entire top of the balloon would burst open, releasing the bouyant hot air nearly all at once.
On October 20, 1960, pilot Ed Yost became the first person to fly a modern hot air balloon untethered.
Yost and other engineers, designers, and aviators at Raven improved their design rapidly.
On April 13, 1963, Yost and co-pilot Don Piccard became the first to fly a modern hot air balloon across the English Channel. Other firsts and aviation records would follow. Longest time aloft, first crossing of the Atlantic, and on and on. Pilots flying Raven balloons and those designed and manufactured by Yost set altitude, distance and other records for decades.
While adventurers piled up records, hot air ballooning became a sport and recreational activity for aviators all over the world.
Today, there are about 10-thousand hot air balloon pilots worldwide and 5-thousand in the United States. Contemporary balloons vary in shape and size but the basic designe developed by Yost and others in the late 1950s and 1960s is still in use today.