Lighter_than

Lighter than Air

Balloons and airships are called lighter than air aircraft. The aircraft fly because the whole structure is lighter than the air surrounding it.

Balloons: These are filled with hot air or heated helium.

Airships: An aircraft consisting of a cigar-shaped balloon that carries a propulsion system (propellers), a steering mechanism, and accommodations for passengers, crew, and cargo. The balloon section is filled with a lighter-than-air gas-either helium, which is non-flammable, or hydrogen-to give the airship its lift. The balloon maintains its form by the internal gas pressure in the non rigid (blimp) and semi rigid types of airships; the latter in addition has a rigid keel. The rigid type maintains its form by having a metal framework that holds its shape regardless of the internal gas pressure; inside the hull are a number of small gas-filled balloons.
- Non-rigid: Non-rigid airships, also known as Blimps, are the most common form nowadays. They are basically large gas balloons. Their shape is maintained by their internal gas pressure. The only solid parts are the passenger gondola slung beneath the ship, and the tail fins. All the airships currently flying for publicity use are of that type. E.g. the Goodyear Airships
- Rigid: As their name implies, rigid airships have an internal frame. The rigid structure creates the form of the airship and a more aerodynamic shape. This is like the Zeppelin Airship pictures below: It has a frame which is covered in material.
- Semi Rigid: Semi-rigid airships were more popular earlier this century. They usually comprise a rigid lower keel construction and a pressurised envelope above that. The rigid keel can be attached directly to the envelope or hung underneath it. The airships of Brazilian aeronaut Alberto Santos-Dumont were semi-rigids.

Balloons

The first hot-air balloons were invented by two French brothers, Joseph Michel and Jacques Etienne Montgolfier. Their first successful flight was on 19 September 1783, at the Royal Palace at Versailles, outside Paris. The passengers were a sheep, a duck and a rooster. Why ‘a sheep, a duck and a rooster’? Nobody knew if there would be air to breathe high above the ground. It was best to find out before risking a man’s life. Almost 200 years later the Russians and the Americans adopted the same approach when they sent a dog and a monkey into space before risking a man’s life.
Exactly nine weeks after their first flight, the Montgolfier brothers launched the first balloon with human passengers. Originally the plan was to use two criminals who had been sentenced to death; the argument being that if they didn’t survive, their deaths would be no loss. But if it were successful it wouldn’t do for two criminals to be famous, so they had to get two volunteers.
On 21 November the Marquis d’Arlandes and Jean Pilatre de Rogier travelled about 9 km in a Montgolfier balloon.

Airships

Zepplin Airship

In 1760 the scientist, Henry Cavendish, discovered and isolated a gas, which was lighter than air. Cavendish called his discovery “inflammable air” because it would burn very easily; we call his discovery hydrogen. On 1 December 1783, Jacques-Alexandre Charles, a French physicist, made the first flight in a hydrogen balloon. The first real airship was the cigar-shaped, hydrogen balloon built by the Frenchman, Henri Giffard, in 1852. Although Giffard’s airship had a small lightweight steam engine driving a propeller, and he managed to fly 27 km from Paris to Trappes, it was unstable and underpowered.

In 1901, using a small petrol engine, Alberto Santos-Dumont, a Brazilian living in France, flew his airship from St Cloud to Paris, circled the Eiffel Tower, and returned to St Cloud. The petrol engine was powerful enough and light enough to be a viable power source for airship flight. We should also bear in mind that there were also improvements in the design of propellers. The most important name in airships is undoubtedly Count Ferdinand von Zeppelin. The German aristocrat began experimenting with airships with the flight of his LZ1 in September 1900. For the next seventeen years until his death in 1917, von Zeppelin continued to experiment with and improve his airships and after his death his company continued his work.

At first airships were slow and cumbersome but as improvements were made in engine technology and in streamlining, airship performance improved. The airship Graf Zeppelin flew commercially from 1928 offering safety, luxury, comfort and reliability. In 1929 it completed a 21-day round-the-world flight. It was many years before aeroplanes took the place of Airships in commercial atlantic crossings.

The largest airship was the Hindenberg. It was 245m long, 41m in diameter, and had a capacity of almost 200,000 cubic metres of hydrogen. The Hindenberg made its first commercial flight from Germany to America in 1937. Arriving at its landing site at Lakehurst, New Jersey, the Hindenberg was only seconds away from completing its voyage when it burst into flames and was completely destroyed, with the loss of 35 lives. The shock and the horror of the loss of the Hindenberg effectively marked the end of airships.

Travelling by Airship

In the late1920s and 1930s travelling by airship was the last word in luxury and elegant travel. Airships such as the Graf Zeppelin with a top speed of 129 km/h (80 mph) could easily compete with transatlantic liners.As early as 1909, an airline, DELAG, had been established in Germany to operate airships.

The only major difficulty airships had was that they relied on hydrogen, a very flammable and highly dangerous gas, for lift. The USA had the only viable supply of helium, a much safer non-flammable gas, but for political and commercial reasons was unwilling to supply other countries.To overcome the dangers of hydrogen airships, passengers had to take precautions. Shoes with nails in the soles, which could produce a spark, were forbidden and passengers had to wear felt slippers.

Luggage was examined and anything that could be regarded as a fire risk was removed and stored carefully until arrival at the destination .Cooking was done on special electric stoves to avoid the use of naked flames, and smoking was forbidden except in a special room built inside a bigger room. So important was the need to guard against sparks or fire that the air pressure in the smoking room could be regulated so that when the door was opened air naturally flowed into the smoking area.

Weight was of crucial importance in operating an airship so only lightweight materials were used, even the grand piano in the salon was made of aluminium rather than wood. The quality of the music has not been recorded!The one thing, which airships alone could provide, was spectacular views. An airship could easily fly slowly at low altitude so the passengers could see shipping or observe whales, but the real spectacle was the approach to New York. Passengers had unrivalled views of well-known landmarks such as the Statue of Liberty and the Manhattan skyline.

Text and graphics courtesy of The Flight Experience, Sponsored by Bombardier Aerospace.