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The Reference on Airships

Airship FAQ

(Answers to Frequently Asked Questions about Airships)

Q: What is an Airship?

A: An airship, also known as a dirigible, is a powered lighter-than-air craft. In other words, an airship is an aircraft that derives its lift from a lifting gas (usually helium or hot air) while it is propelled forward by an engine.

Q: What are Lighter-Than-Air Craft or Aerostats?

A: An aircraft is anything that flies. A lighter-than-air craft is any vehicle that flies because it is lighter than air. This includes (a) balloons and (b) airships, also known as dirigibles. Lighter-than-air craft are also known as aerostats, a term which is derived from the ancient greek words "aer" and "statos", i.e. standing or staying in the air. What makes a vehicle lighter than air, is the fact that it uses a lifting gas (i.e. helium or hot air) in order to be lighter than the surrounding air. The difference between airships and balloons are the following: Balloons simply follow the direction of the winds. In contrast, airships are powered and have some means of controlling their direction, usually with rudders.

Q: What Kinds of Airships are there?

A: There are four categories of airships, Rigid, Semi-Rigid, Non-Rigid and Hot Air Airships.

• Rigid Airships
  As their name implies, rigid airships have an internal frame. The Zeppelins and the USS Akron and Macon were famous rigid airships. The rigid structure, traditionally an aluminum alloy, holds up the form of the airship. In general rigid airships are only efficient when longer than 120 Meters (360ft.) because a good weight to volume ratio is (or was) only achievable for large airships. For a small airship the solid frame would have been too heavy. There is hope that the use of composite materials will change this.
• Semi-rigid Airships
  Semi-rigid airships were more poplular earlier this century. They usually comprise a rigid lower keel construction and a pressurized 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. One of the most famous representants of the type was Italia, the airship which General Umberto Nobile used on his attempt to reach the North Pole.
• Non-rigid Airships or Blimps
  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 overpressure. The only solid parts are the passenger car and the tail fins. All the airships currently flying for publicity use are of that type; the Goodyear Blimps, the Budweiser and the Metlife Blimps in the USA, and the Fuji Blimp in Europe.
• Hot Air Airships
  Hot air airships, also known as thermal airships, are counted as a fourth kind even though they are technically part of the non-rigid category. Hot air airships are derived from traditional hot air balloons. Early models were almost like balloons with an engine and tail fins added. Pretty soon envelopes were lengthened and the tail-fins and rudder were pressurized by air from the wash of the propeller. Newer hot air airships maintain their shape with internal overpressure in the whole envelope, a feature which older models did not have.

Q: Where does the term "Blimp" come from?

A: The popular story is that during World War II, a military general visited one of the many airship stations operated by the U.S. Navy. Trying to find out what material an airship was made from, he tapped his finger against the fully pressurized envelope of a non-rigid Navy airship. The general described the sound he heard, "blimp," and blimps have been called blimps ever since.

Q: Why do Airships Fly?

A: Why airships fly is explained by the Principle of Archimedes: "Bodies submerged into a fluid receive from it a lifting force which is equal to the mass of the displaced fluid." (This is the same principle that explains why boats float on water.) The airship is filled with a lifting gas (Hydrogen, Helium, hot air or natural gas). The air in which the airship finds itself has a higher specific weight than the lifting gas. The envelope filled with the light gas generates a lift that is equal to the weight of the displaced air. Like a (light) kork floating in (heavier) water, a helium or hydrogen filled balloon floats in the heavier air.

Q: What is the Lift of Helium and Hot Air?

A: As a rule of thumb, 1 cubic meter of hydrogen lifts 1.1 kilogram, 1 m3 of helium lifts 1 kg and 1 m3 of hot air lifts 300 grams. (In Anglo-American measures: 1000 cu. ft. of hot air lift a maximum of 20 lbs. and 1000 cu ft. of helium lift about 60 lb.) These figures are on the safe side and allow for variations in altitude, temperature, humidity and also purity of the helium.

Since the USA holds most of the natural Helium reserves worldwide it is readily available in local welding supply stores there. Outside of North America the situation varies. Usually it is specialized chemical companies that carry helium in their program.

Q: Can I get a Ride on the Blimp?

A: The answer is usually NO. Despite all the modern technology used in today's blimps they are cost effective only for advertising purposes. In relatively small blimps, passenger transportation is not profitable enough unless it is combined with an advertising mission. In the past, the small number of blimp rides which is available has been given to executives and clients of the advertisers/sponsors of the blimps.

Blimp rides were available in Las Vegas for ten months in 2000 (see www.vegas.com/blimp/ for images). Unfortunately, the blimp ride operation shut down in December 2000.

Q: How do I become an Airship Pilot?

A: There is a special pilot licence that is required for airships. In the USA the airship pilot rating was recently split into VFR (visual flight rules) and IFR (instrument flight rules) since modern airships are now able to fly under instrument flight conditions, i.e. at night or in the clouds. As for any other pilots licence, a special commercial rating has to be obtained for commercial flights.

Virtually all airship pilots are professionals employed by commercial airship operators. Regarding pilot training this means that unless you are willing to become a professional pilot - or can buy a blimp, and even then - opportunities for airship pilot training are very limited. The few airship pilots I know had commercial twin engine ratings for fixed wing aircraft before being hired to be trained as blimp pilots.

In anticipation of the eventual availability of formal airship pilot training courses, I have started to compile the Airship Pilot Life Stories. They are a collection of accounts by several professional airship pilots detailing how they got where they are today.

Q: I want to build an airship. Where do I start?

A: Unless you have several hundred thousand dollars to spend, you should probably consider building a radio-controlled airship or a manned hot air balloon instead. If the financial requirements do not deter you, a book called "Building Gas Blimps - A Practical Guide to Building Small Gas Blimps" by Robert J. Recks will provide you with more detail. The book is available for approximately US$80 directly from the author (e-mail r.recks@juno.com).

Q: Where can I find More Information?

A: You should make sure to read all the material in the Airship and Blimp Resources (www.MyAirship.com) because they contain information that goes far beyond the scope of this simple Airship FAQ. For more Questions and Answers you can also visit the What is an Airship page on the website of the Airship Association (www.airship-association.org) in the UK. It answers other questions about airships which you may have.