Hot Air Ballooning
Updated: Feb 23
Science Cafe welcomed John Wilcher, a previous Café presenter (see- November 2021 report). Before settling in Sherborne, he was medical doctor with a career in research and a professor of molecular biology. He has an abiding interest in geology, particularly the inferior oolite of Dorset, for which he has published several papers and a passion for hot air ballooning. It was for the latter that he made a returning visit to Sherborne Science Café.
Despite humankind’s long-term stewardship of the Earth, it is only recently that they have been able to leave terra firma and ascend into the skies. Until 1783, nobody had flown.
The first to claim the record of free flight were the Montgolfier brothers, Joseph-Michel (1740-1810) and Jacques-Etienne (1745-1799) of the town of Annonay, in France. They came from a family of papermakers and had noted in their factory, that hot air caused drying paper to rise. Using this observation, they planned a balloon, built out of paper and inflated from below by a fire (with care taken to protect the fabric of the balloon). Hot-air balloons achieve their effect because heat pushes individual air molecules further apart reducing the density of the gas. If this gas or hot air is contained by a canopy, it is lighter than the surroundings and the canopy rises, although at the time it was believe that ‘phlogiston’ held the lifting properties and that smoke held the key to lift. It is probable that the efficacy of hot air to achieve flight had been noted before. Zhuge Liang (181-234 AD), for example, a Chinese statesman and military strategist, had used paper bags, inflated with hot air, to carry messages between his armies.
On the 4th June 1783, a first (unmanned) ascent at Annonay by the Montgolfiers achieved a 10 minute flight to an altitude of ~2,000m and a distance of 2km. After this success, the brothers moved their experimentation to Paris, with a greater audience to demonstrate their new mode of transport, to solidify their claim of first flight and to attract the influential attention of the King.
In Paris, they collaborated with wallpaper manufacturer, Jean-Baptiste Réveillon, developing a balloon made of taffeta, coated with a fireproofing of alum, enveloping a volume of 37,500ft3 (1,060m3). Despite metrification, balloon volumes still tend to be measured in cubic feet.
The next flight in the aforementioned balloon ‘Aerostat Reveillon’ (which was intended to be manned) was scheduled for 19th September 1783. There was concern of the possible effects of altitude on the aeronauts. The King, Louis XVI, generously suggested sending a couple of convicts aloft, obviously regarding them as expendable in the interests of science. Instead, a sheep (considered an approximation of human physiology), duck and rooster (high and low altitude birds respectively) were included on this ascent indicating that, even in the very early stages of flight, there were concerns of the effects on human physiology. The animals all survived, perhaps underwhelmed by the knowledge they were the first aeronauts (see Fig. 1).
Fig 1: The first balloon flight with passengers (a sheep, a duck and a rooster) took off on Sept. 19tth 1783.
On 15th October 1783, on a tethered balloon, Étienne Montgolfier and physicist Pilâtre de Rozier, became the first humans to achieve controlled flight with ascents of several tens of metres. One month later, the first free flight by hot air was made by de Rozier and an army officer, Marquis d’Arlandes, to an altitude of 3,000ft, a fight distance of 9km in 25 minutes. 400,000 spectators assembled to watch, probably the population of Paris at that time (see Fig. 2).
Fig. 2: First free ascent of a hot-air balloon with human passengers, on Nov. 21, 1783 by Jean-François Pilâtre de Rozier and the Marquis d´Arlandes
The French Montgolfier brothers caught the public imagination in France and Britain with their demonstrations of hot-air ballooning. Enthusiasts in the scientific world raced to make accounts of their own flights. John Seldon, an FRS, ascended with French aeronaut Jean-Pierre Blanchard from Chelsea in London in 1784 (see Fig. 3). Unfortunately, the Frenchman discarded the terrified Sheldon’s equipment as the balloon struggled to lift thereby missing an opportunity to bring back scientific data.
Fig. 3: Spectacle and Utility Grand Aerostatic Balloon, 1784. Seldon and Blanchard’s panicky ascent
But hot air ascent was not the only option for an aspiring aeronaut. Jacques Alexandre César Charles (1746-1828), inventor and mathematician, after researching Boyle’s Law, (PV=k) conceived the idea of obtaining lift using a hydrogen balloon. The first hydrogen balloon flew unmanned on the 27th August 1783 from the site of the yet to be conceived Eiffel Tower. It enclosed a volume of 1,236ft3 (35m3) and lifted 9kg of weight and designed by Charles and brothers (‘Les Frères’) Robert (both engineers). It took two days generate the necessary hydrogen by reacting together ½ ton of sulphuric acid and ¼ ton of scrap iron at the launch site. Again, there was another hugely enthusiastic turnout by Parisians with 400,000 believed to be present. It flew well, landing 20km away at Gronesse, terrifying agricultural workers who promptly destroyed it.
The successful proving flight was followed on 1st December 1783 by a manned flight piloted by one of the two brothers (Les Frères Robert) and Charles himself. The canopy was of rubberised silk.
A flaw of the first hydrogen balloons was that there was no way to release hydrogen from the canopy. The ascent often became dangerously uncontrolled. One early flight went to 9000 ft with oxygen deprivation affecting the aeronauts, and thankfully landed safely 30 miles away from the release site. Such balloons are nowadays used for high altitude stratospheric research. Charles (noted for his ‘Charles Law’, another gas law) later became professor of physics at the Academie de Sciences in 1795 for his contributions to science.
The hydrogen balloon offered better lift for a given canopy volume than a Montgolfier balloon (therefore a smaller canopy was needed- see Fig. 4). Hot air needed to be continually generated whereas hydrogen remains contained. The advantage of longevity in the air gave the hydrogen balloon an ascendancy over the hot air variety for nearly 200 years. The competing modes of ballooning (hot air viz-a-viz hydrogen) became known as Montgolfières and Charlières.
Fig. 4: Comparison of required volumes and diameters of sphere with a lifting capacity of 1,000kg
A further technical development, by Francois Rozier (1754-1785), used separate chambers for hydrogen lifting gas as well a chamber for hot-air (see Fig. 5), a Montgolfière/Charlière hybrid. Rozier built such a balloon for a channel crossing. On its first flight, the canopy deflated and crashed, killing Rozier, the first aeronaut death. The Rozier design (a Rozière) permitted better control of buoyancy allowing longer flight. The lifting gas gave neutral buoyancy, the hot-air the ability to manoeuvre vertically with minimal fuel use.
Fig. 5: the Rozier balloon (or simply a Rozière) is a hybrid with separate chambers for a non-heated lifting gas (hydrogen or helium) and for a heated lifting gas (as in a hot-air balloon)
This reduction of fuel consumption has allowed Rozières and their crews to achieve very long flight times, as much as several days or even weeks.
The versatility of the hydrogen balloon confirmed its primacy and Montgolfières became a curiosity, though the combustibility of hydrogen as a lifting gas was always an ever-present danger (e.g. destruction of the R101 airship). After WW2, helium became available and therefore a possible, safer, substitute for hydrogen.
In the 1960’s several influences brought back a resurgence in ballooning. Notable explorer, Anthony Smith, led a Sunday Telegraph Balloon Safari expedition from Zanzibar to East Africa and then across the Ngorongoro crater. The following year he crossed the Alps. Fred Dolder, another intrepid balloonist, made a series of dramatic ascents across the Alps. Both explorer’s escapades were well publicised in the mainstream press and raised the profile of ballooning considerably.
During the post war period, hydrogen and helium especially had become easier to source and the continuing disincentive for moving to the less dangerous Montgolfières was that there was no practical method of creating enough hot air to sustain a large canopy. Butane gas cylinders were available though poor in practical use. At this time, propane gas, a better heating gas, coupled with light-weight burners, demonstrated an effective method of generating lots of hot air and the scene was set for a revolutionary transition with a shift of emphasis back to Montgolfierès. That transition came quicky. John was, for example, at a ballooning event in 1965 at Badminton. One of the hydrogen balloons briefly came to grief and various members of the public went to assist, one such member was casually smoking and ignited the escaping hydrogen and rubberised fabric. It was a wake-up call to the dangers of hydrogen balloons when perhaps a better alternative was now available.
The most technical balloon journey was some 23 years’ ago. On March 21, 1999, Swiss psychiatrist Bertrand Piccard and English balloon instructor Brian Jones became the first team to fly nonstop around the world by balloon (Breitling Orbiter 3) setting records for distance and duration and winning a million-dollar prize offered by Anheuser-Busch. Although the courage and dedication of the aeronauts was part of the success, technology was key in the form of a new balloon design, real-time data of jet-stream pathways and communications technology. This 20-year quest set a new milestone in the 200-year history of ballooning. Two previous attempts had ended in failure.
The 10-ton Breitling Orbiter 3 (see Fig. 6) was designed to hold 15% more helium than its predecessor, Orbiter 2 which had used an experimental kerosene fuel that proved inefficient, prompting a switch to propane. Solar panels, suspended below the gondola, charged five lead acid batteries and supplied energy for equipment on board. Propane burners provided the heated air needed to keep the balloon aloft. In case of an emergency, the lower part of the balloon was detachable, leaving the remaining upper half attached and functioning as a parachute. The gondola in which Piccard and Jones lived was equipped with a toilet, writing desks, sleeping bunks, satellite telephones, and a fax machine.
Fig. 6: Breitling Orbiter 3 ascending over the Alps
Plans for the flight were less than ideal. Iraq, at war, was near to their planned route and the Chinese government, sensitive about balloon overfights, restricted the craft to south of latitude 260. Piccard and Jones began their journey in the Swiss village of Chateaud'Oex, ascending into the morning air amid the cheers of thousands of spectators. The two pilots rotated eight-hour shifts, one piloted, whilst the other slept.
They flew southwest over Mauritania to catch the jet stream flowing eastward. With the assistance of their flight team, using computer models and transmitting live data to/from Switzerland, they manoeuvred to stay in optimum parts of the jet stream so that their path eastward was as controlled and on schedule as possible. This was crucial, especially as they flew over China. Speeds in the Jetstream were in the low hundreds (m.p.h.)
They flew over Mauritania on March 21st, after a total of 19 days, 21 hours, and 47 minutes of flight. The Breitling Orbiter 3 landed in Egypt, bringing an end to a journey of 26,050 miles (41,923 km).
The successful balloon circumnavigation by Piccard and Jones stands as an impressive technological accomplishment. Whilst drifting high above the world and its problems, they had cause to reflect on global problems beneath. The impact of their adventure is perhaps best expressed in the words of Piccard: "During our three-week flight, protected by our high-tech cocoon, we have flown over millions of people suffering on this Earth, which we were looking at with such admiration. Why are we so lucky? At this moment it occurs to me that we could use the largest portion of the Budweiser Cup million-dollar prize to create a humanitarian foundation, the Winds of Hope, to promote respect for man and nature." (See https://www.windsofhope.org/index.html) suggesting that some explorers, at least, have a focus on the greater good, not merely their own achievements.
Fig. 7: preparing for a mass ascent at Bristol International Balloon Fiesta
Hot air ballooning continues to thrill and inspire, from the manufacture of aesthetically, graceful canopies, usually made by Cameron’s of Bristol, to awe-inspiring record-breaking flights, and the relaxed beauty of a mass balloon ascent at the annual Bristol International Balloon Fiesta (see Fig. 7), the largest such event in Europe.