Energy Harvesting via Ballonet Altitude Control; The History and Future of Airships

My technical project focuses on harvesting energy from the change in altitude of a ballonet controlled airship. We created a nonrigid airship using mylar sheets for the outer envelope to contain the helium. The helium is the lighter-than-air gas that provides the buoyant lifting force. The ballonet is a secondary balloon that is stored inside the outer envelope which controls the amount of lifting force the helium can provide. The volume of the ballonet is controlled using a valve to either fill the ballonet with air using an air compressor or to release air into the atmosphere. As the ballonet is inflated with air, the density of the helium increases which reduces its lifting capacity and allows the airship to descend. Releasing the air inside the ballonet decreases the density of helium and allows the airship to ascend.

The airship is connected to a wooden frame using a fishing line wound around four pulleys. Connected to one of the pulleys is a brushed direct current (DC) motor operating as a generator. As the airship displaces vertically it rotates the pulley and creates an electrical potential difference between the two terminals of the motor. The two terminals of the DC motor are connected through a charging circuit. The charging circuit detects current polarity which corresponds with the airship’s direction of travel. This information is sent to an Arduino to control a 4-channel relay module to output the correct polarity to charge a nickel-metal hydride battery. The Arduino powers a secondary circuit which shares a common ground with the charging circuit and monitors sensor data such as pressure, current, voltage, and power.

The STS portion of my project focuses on the history of airships. It begins with the engineers that laid the foundation for air travel to even be considered. Otto von Guericke showed the tremendous forces that can be generated from a vacuum in his Magdeburg hemisphere demonstration. This earliest design of an airship was a vacuum airship proposed by Francesco Lana de Terzi. Building on Guericke’s vacuum pump, Boyle experimented with mercury in a J-tube to establish the inverse relationship between pressure and volume, which we now know as Boyle’s law.

After Terzi, many engineers attempted to find novel solutions for airships. The Montgolfier brothers are credited for the first manned hot air balloon, but it was only possible because of Bartolomeu Lourenço de Gusmão’s model hot air balloon demonstration in Portugal. Jacques Charles and the Robert brothers transitioned to hydrogen filled airships, the primary lifting gas used in airships throughout history, and released an unmanned airship that flew for 45 minutes.

At this point, engineers had no problems designing airships that could support the weight of a human, so they changed their focus to steerable airships, or dirigibles. Henri Giffard manufactured one of the earliest steerable airships, using hydrogen gas for lift and a steam engine with propellers for directional control. Jean-Baptiste Meusnier de La Place proposed a similar design and is credited with giving airships their familiar ellipsoidal shape. Alberto Santos-Dumont expanded on his work years later and successfully created the first practical dirigible that could travel long distances by winning the “Deutsch de la Meurthe Prize.” This was a pivotal moment in history because we could now use airships to travel between two locations.

Dirigibles increased competition in the airship industry. The earliest dirigibles would remain uncontested in the air during combat, so every country raced to manufacture their own airships. Ferdinand von Zeppelin was one of the most notable names during this period. He created the Zeppelin, a rigid, steerable airship. The destructive capabilities of the Zeppelin was clear at the start of World War I when Germany repeatedly launched aerial attacks on Britain. After the war, Zeppelins were still used as passenger ships for air travel, proving their reliability. As quickly as dirigibles gained popularity, their decline was also rapid. The numerous U.S. airship accidents, the Hindenburg disaster, and advancements in airplane technology meant that airships began to fade away.

The possibility of airships making a return has been debated, especially as sustainability has become increasingly important over the years. Airships produce very low carbon emissions and could play an important role in the long-distance transportation of goods. My technical project focuses on maximizing the airship's role in contributing to a sustainable future. By harvesting energy, we can reduce waste by storing it for future use, similar to other energy capture technologies. Lighter-than-air aircraft generate nearly free lift, and we can convert some of that energy into stored energy. Airships may not serve the same purpose they once did, but they can still play an important role in sustainability.