Airships are defined as “lighter-than-air” aircrafts that produce lift thanks to the buoyancy of their lifting gas (helium or hydrogen) instead of the force produced by air flowing over surfaces such as wings or blades. This means that airships do not require engine power to stay afloat, unlike airplanes or helicopters. Airships are generally divided into three categories: non-rigid (also called blimps) that sustain their shape by a pressure differential between the internal lifting gas and the outside atmosphere; semi-rigid that contain an aerodynamically shaped rigid keel to provide support for the overall non-rigid envelope; and rigid airships that maintain their envelope shape thanks to a rigid framework and not by its internal pressure.
The history of modern airship designs is actually older than the engineering of modern airplanes. In 1900 Count Ferdinand von Zeppelin performed the first successful experimental flight of his rigid LZ-1 airship. The airship was 128 m long, 11.7 m in diameter, and its 11,298 m3 of volume filled with hydrogen produced 12,428 kg of lift. Although the history of airships can be traced back to the end of 18th century, jointly with the development of balloons, the first Zeppelins can be considered as the beginning of advanced airship aeronautics. For the first time they introduced some advanced techniques needed to overcome major issues with the mooring and ground handling, resistance to wind gusts, safe landing and attaching to the mooring station, weight balancing, lift control, manoeuvrability, etc. All these issues are still relevant even today in the design of airships.
By 1930s airships entered a massive military and civilian usage, with regular flights of luxury airships across the Atlantic Ocean. They were seen as the future of air travel and the technology that will dominate the sky. However, airplane technology had been advancing very fast at that time and airships were losing the race for the most efficient method of aerial transportation of cargo and passengers, where the economic driver is the specific power spent by the vehicle (maximum engine output power per gross vehicle weight per maximum speed) for a given maximum speed of travel
Then in May 1937 the large airship LZ-129 Hindenburg exploded during the landing procedure in Lakehurst, New Jersey, which killed 36 people. This event became a global news thanks to the popular radio broadcasting at that time. Even though this was not the largest airship tragedy, it played a major role in turning the public opinion against airships. Even today, one of the first associations to the word “airships” is the Hindenburg disaster, even though today’s safety regulations and materials used in airships dramatically reduce the risk of fire.
Since then, the airships have almost disappeared from the sky, while airplanes and helicopters dominate the aviation industry. Only a small number of blimps have been in a limited commercial or military use for surveillance and entertainment. This is in a stark contrast to the Hindenburg-class airships that remain the largest flying vehicles ever. With their 245 m in length and 41 m in diameter, Hindenburgs produced about 230 tonnes of useful lift that covered large gondolas, fuel, equipment, various cargo, about 90 passengers and luxury goods.
Although interest for airship development has never disappeared, it has increased within the last two decades. Modern versions of Zeppelins are now used for touristic flights, but the main driver for new developments came from the desire of U.S. military to explore new solutions for reconnaissance flight vehicles or transport of large and heavy cargo to world areas of limited or non-existent ground infrastructure. This was further enhanced by the civilian needs for environmentally friendly and sustainable ways of transport. The underlying rationale was that advancements in materials, engines, electronics, autonomous systems, and other relevant aeronautical technologies would enable breakthroughs in airship design and development.
At the same time, airships are still an obscure field of aeronautics, lacking rapid sizing methods that could enable simple early estimates of physical specifications of unconventional designs of airships. This resulted in a proliferation of unrealistic ideas and designs that are aesthetically appealing, but unsustainable (either from the engineering or business perspective) when used in real environments.
BorderUAS project is based on a novel rigid-type of airship design that has already been tested for its aerodynamic properties. Developed by one of BorderUAS consortium partners, HiperSfera Ltd, this airship is designed for a stationary or slowly moving operations that require long duration flights carrying lots of equipment, which is ideal for the border security tasks. Highly manoeuvrable at low speeds, HiperSfera Airship UAV provides robust flight control in all mission phases, including take-off and landing, and in all-weather scenarios.