In the 1950s, Yost’s own interests turned toward reviving the lost practice of manned hot-air ballooning. This technology had first been invented in France by in the late 18th century by pioneers led by the Montgolfier brothers, but under the Montgolfier system the balloon’s air was heated by a ground fire prior to the balloon being released. The inherent danger of this type of balloon flight led to the system being abandoned when hydrogen and later helium became available.
One of Yost’s key engineering insights was that a hot-air balloon could be made to carry its own fuel. The invention of relatively light burners fueled by bottled propane made it possible for the balloonist to re-heat the air inside the balloon for a longer flight. Yost’s invention improved modern hot-air balloons into semi-maneuverable aircraft. Yost’s other hot-air balloon patents included nonporous synthetic fabrics, maneuvering vents, and deflation systems for landing. Yost also designed the distinctive “teardrop” shape of the hot air balloon envelope itself. This hot-air balloon image has become an icon, used for example on the standard license plate of motor vehicles registered in New Mexico.