The gas balloon was born on December 1st, 1783, ten days after the first manned hot-air balloon flight (November 21st). It is composed of a large envelope connected to the suspension hoop (or load ring) by net or ropes (depending on technologies). The suspension hoop forms a junction between the envelope and the gondola. It usually takes 3 to 4 hours to prepare a gas balloon. The envelope is filled with helium, hydrogen or any other gas less dense than air. Gas balloon can lift almost one kilogram per m3 (in the case of hydrogen).
The envelope is a gas-tight cloth sphere made of rubberized cotton fabric. At the top of the envelope is a valve allowing lifting gas to escape. At the bottom of the envelope is a tube used to fill the balloon known as an appendix. The appendix is used as a pressure relief for the lifting gas as it expands with the heat of the day. A rope set can act on the valve from the basket.
Gas balloons use ballast that is thrown overboard to control ascent or descent operations. Ballast can be in the form of sand or water. To expedite the descent, the valve is opened. Gas balloon are equipped with same instruments as hot-air balloon.
Both hot-air and gas balloon flights are delightful except that a gas balloon flight is a long adventure and a real journey that can last several days. And when you finally decide to alight on ground, it’s necessary to perform a real technical manoeuvre.
Today gas balloon are used primarily for sport, national and international competitions, but also for records (distance, duration and altitude).
Unlike hot-air balloon, gas balloon survived all times, no doubt because of its early military use.
Reference: Pilâtre de Rozier Organisation