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Lighter Than Air

Lighter than air

The expression lighter than air refers to objects, usually aircraft, that are buoyant in air because they have an average density that is less than that of air (usually because they contain gases that have a density that is lower than that of air). Examples include balloons, airships, and aerostats. The opposite expression, heavier than air, refers to aircraft, such as aeroplanes and helicopters, that have a greater density than air.

Derivation

At low densities, the behaviour of gases is well approximated by the ideal gas law :

pV = nRT

where

p

is pressure,

V

is volume,

n

is the number of moles of gas,

T

is absolute temperature, and

R

is the universal gas constant. Dividing both sides by

V

R

and

T

gives :

p/RT = n/V.

Now multiply each side by

A

, the molecular mass of the gas in question: :

pA/RT = nA/V

Notice that

nA

, the number of moles multiplied by the mass per mole, is simply the total mass of the gas. And mass divided by volume is density. So, :

\rho = pA/RT

where

\rho

is the density of the gas. This equation shows that a gas with low density can be achieved by:
- Lowering

p

, the pressure;
- Lowering

A

, the molecular mass;
- Raising

T

, the absolute temperature; or
- Some combination of the above.

R

is a physical constant and so cannot be changed.

Low pressure

The average density of an aircraft can be reduced, at least in principle, by creating a partial vacuum. The concept of an airship supported by the buoyancy of a vacuum has been explored in science fiction, but in practice the strength of the envelope must be so great in order to resist crushing by external atmospheric pressure that its weight exceeds the lift created by the vacuum. It may be possible in the future to construct a vacuum airship from advanced materials.

High temperature

The density of a gas can also be reduced by raising its temperature. Heated air is widely used in practice as a lifting gas in hot-air balloons (although, to be strictly accurate, the gas in a hot-air balloon is not just air, but also the products of combustion of the balloon's burner).

Low molecular mass

Since the average molecular mass of air is 28.8, any gas with a lower molecular mass will be lighter than air, even at the same temperature and pressure. This makes it possible to create a balloon with a thin, light envelope, and no need for constant heating. Assuming:
- the gas is composed of normal elements (i.e. no strange matter); and
- appropriate materials are chemically stable, and gases at reasonable temperatures then the laws of chemical valence enable all of the possible choices to be enumerated quickly. The heaviest possible atom that could meet these criteria is silicon. Silicon has an atomic mass of 28.1, so with just 0.7 atomic mass units left over, it would have to be a monatomic gas. Unfortunately, silicon does not become a gas until it reaches a temperature of over 2,000°C. The next lightest atom is aluminium, with an atomic mass of 27. The spare 1.8 units gives room for just one hydrogen atom, but AlH would not be stable, and plain Al is not a gas until 2500°C. Next would be magnesium, mass 24.3. With 3.5 units spare, it could combine with up to 3 hydrogen atoms. The stable number would be two, giving magnesium hydride, MgH₂. Unfortunately, neither magnesium hydride nor magnesium are gases at reasonable temperatures. Proceeding in the same way through progressively lighter elements produces the following list of all stable materials with a molecular mass under 28.8 and a boiling point under 800°C: All of these 14 gases—and no others!—are lighter than air at the same temperature and pressure. A number of them are clearly unsuitable to use as a lifting gas in a balloon, however. There are seven (carbon monoxide, ethylene, diborane, hydrogen cyanide, acetylene, methyllithium and hydrogen fluoride) which combine poor lift (mass close to 28.8) with highly objectionable properties. Nitrogen has negligible lift. Neon is harmless, and offers a modest degree of lift; however it costs roughly the same as helium, another noble gas with far superior lift. Four of the remaining five (ammonia, methane, helium, and hydrogen) have been used as balloon gases. Ammonia and methane have generally only been used for small scale experimental uses, since they are inferior to hydrogen on nearly every account. In particular, ammonia has sometimes been used to fill weather balloons, while methane—in the form of town gas or illuminating gas—has been used when nothing better was available. However, due to its relatively high boiling point, ammonia could potentially be refrigerated and liquified, allowing for an airship to easily reduce lift and add ballast. Hydrogen and helium have been the most common choices for lifting gases. Hydrogen offers slightly superior lift, but the difference is negligible; helium is usually preferred whenever it can be obtained because it is not flammable. Many countries have banned the use of hydrogen as a lifting gas. The German Zeppelin Hindenburg is the frequently cited example for risks posed by hydrogen. However Addison Bain in 1997 published a paper discounting the role of hydrogen as a cause of the fire on the Hindenburg. Instead he focused attention on the role of the skin material of the Zeppelin which contained the ingredients used in Thermite, a rocket propellant ingredient. There is an ongoing debate about Bain's analysis and the safety of hydrogen as a lifting gas. Other researchers have recently conducted analyses and experiments that substantially refute Bain's theory. (See Hindenburg disaster for a detailed discussion of this controversy.) The relatively high cost of helium compared to hydrogen has led several researchers to reinvestigate the safety issues of hydrogen as a lifting gas with some positive conclusions regarding its use given sufficient crew and ground handling team training. The one remaining gas, water, is worth a comment. Although it is not a gas at normal temperatures, its vapour pressure may allow it to contribute significantly to the lift of other gases, such as the combustion products in a hot air balloon. Unfortunately this situation is unstable; if the air cools, then lift-generating water vapour may become lift-sapping water droplets. However this process should occur quite slowly owing to water's high latent heat capacity. At higher altitudes—where the boiling point of water is below the ambient temperature—a pure water vapour balloon is easier to implement. Nonetheless, two research efforts are currently underway to build steam-based aircraft (See section below.)

External links

- [http://www.centennialofflight.gov/essay/Lighter_than_air/LTA-OV.htm Lighter-than-air - An overview]
- [http://www.blimpinfo.com/ The Lighter-Than-Air Society]
- [http://www.flyingkettle.com/ The Flying Kettle Steam Balloon Project]

Aircraft

An aircraft is any machine capable of atmospheric flight. flight. This is a wide-bodied long-haul aircraft]]

Categories and classification

Aircraft fall into two broad categories:

Heavier than air

- Heavier than air aerodynes, including autogyros, helicopters and variants, and conventional fixed-wing aircraft: aeroplanes in Commonwealth English (excluding Canada), airplanes in North American English. Fixed-wing aircraft generally use an internal-combustion engine in the form of a piston engine (with a propeller) or a turbine engine (jet or turboprop), to provide thrust that moves the craft forward through the air. The movement of air over the airfoil produces lift that causes the aircraft to fly. Exceptions are gliders which have no engines and gain their thrust, initially, from winches or tugs and then from gravity and thermal currents. For a glider to maintain its forward speed it must descend in relation to the air (but not necessarily in relation to the ground). Helicopters and autogyros use a spinning rotor (a rotary wing) to provide lift; helicopters also use the rotor to provide thrust. The abbreviation VTOL is applied to aircraft other than helicopters that can take off or land vertically. STOL stands for Short Take Off and Landing. Mainly used internationally.

Lighter than air

STOL
- Lighter than air aerostats: hot air balloons and airships. Aerostats use buoyancy to float in the air in much the same manner as ships float on the water. In particular, these aircraft use a relatively low density gas such as helium, hydrogen or heated air, to displace the air around the craft. The distinction between a balloon and an airship is that an airship has some means of controlling both its forward motion and steering itself, while balloons are carried along with the wind.

Types of aircraft

:See also: List of aircraft There are several ways to classify aircraft. Below, we describe classifications by design, propulsion and usage.

By design

A first division by design among aircraft is between lighter-than-air, aerostat, and heavier-than-air aircraft, aerodyne. Examples of lighter-than-air aircraft include non-steerable balloons, such as hot air balloons and gas balloons, and airships (sometimes called dirigible balloons) such as blimps (that have non-rigid construction) and rigid airships that have a rigid frame. The most successful type of rigid airship was the Zeppelin, although there were some accidents such as the Hindenburg Zeppelin which was destroyed in a fire at Lakehurst, NJ, in 1937. In heavier-than-air aircraft, there are two ways to produce lift: aerodynamic lift and engine lift. In the case of aerodynamic lift, the aircraft is kept in the air by wings or rotors (see aerodynamics). With engine lift, the aircraft defeats gravity by use of vertical thrust greater than its weight. Examples of engine lift aircraft are rockets, and VTOL aircraft such as the Hawker-Siddeley Harrier. Among aerodynamically lifted aircraft, most fall in the category of fixed-wing aircraft, where horizontal airfoils produce lift, by profiting from airflow patterns determined by Bernoulli's equation and, to some extent, the Coanda effect. The forerunner of these type of aircraft is the kite. Kites depend upon the tension between the cord which anchors it to the ground and the force of the wind currents. Much aerodynamic work was done with kites until test aircraft, wind tunnels and now computer modelling programs became available. In a "conventional" configuration, the lift surfaces are placed in front of a control surface or tailplane. The other configuration is the canard where small horizontal control surfaces are placed forward of the wings, near the nose of the aircraft. Canards are becoming more common as supersonic aerodynamics grows more mature and because the forward surface contributes lift during straight-and-level flight. The number of lift surfaces varied in the pre-1950 period, as biplanes (two wings) and triplanes (three wings) were numerous in the early days of aviation. Subsequently most aircraft are monoplanes. This is principally an improvement in structures and not aerodynamics. Other possibilities include the delta-wing, where lift and horizontal control surfaces are often combined, and the flying wing, where there is no separate vertical control surface (e.g. the B-2 Spirit). A variable geometry ('swing-wing') has also been employed in a few examples of combat aircraft (the F-111, Panavia Tornado, F-14 Tomcat and B-1 Lancer, among others). The lifting body configuration is where the body itself produce lift. So far the only significant practical application of the lifting body is in the Space Shuttle, but many aircraft generate lift from nothing other than wings alone. A second category of aerodynamically lifted aircraft are the rotary-wing aircraft. Here, the lift is provided by rotating aerofoils or rotors. The best-known examples are the helicopter, the autogyro and the tiltrotor aircraft (such as the V-22 Osprey). Some craft have reaction-powered rotors with gas jets at the tips but most have one or more lift rotors powered from engine-driven shafts. A further category might encompass the wing-in-ground-effect types, for example the Russian ekranoplan also nicknamed the "Caspian Sea Monster" and hovercraft; most of the latter employing a skirt and achieving limited ground or water clearance to reduce friction and achieve speeds above those achieved by boats of similar weight. A recent innovation is a completely new class of aircraft, the fan wing. This uses a fixed wing with a forced airflow produced by cylindrical fans mounted above. It is (2005) in development in the United Kingdom. And finally the flapping-wing ornithopter is a category of its own. These designs may have potential but are not yet practical.

By propulsion

ornithopter adapted as a floatplane]] Some types of aircraft, such as the balloon or glider, do not have any propulsion. Balloons drift with the wind, though normally the pilot can control the altitude either by heating the air or by releasing ballast, giving some directional control (since the wind direction changes with altitude). For gliders, takeoff takes place from a high location, or the aircraft is pulled into the air by a ground-based winch or vehicle, or towed aloft by a powered "tug" aircraft. Airships combine a balloon's buoyancy with some kind of propulsion, usually propeller driven. Until World War II, the internal combustion piston engine was virtually the only type of propulsion used for powered aircraft. (See also: Aircraft engine.) The piston engine is still used in the majority of aircraft produced, since it is efficient at the lower altitudes used by small aircraft, but the radial engine (with the cylinders arranged in a circle around the crankshaft) has largely given way to the horizontally-opposed engine (with the cylinders lined up on two sides of the crankshaft). Water cooled V engines, as used in automobiles, were common in high speed aircraft, until they were replaced by jet and turbine power. Piston engines typically operate using avgas or regular gasoline, though some new ones are being designed to operate on diesel or jet fuel. Piston engines normally become less efficient above 7,000-8,000 ft (2100-2400 m) above sea level because there is less oxygen available for combustion; to solve that problem, some piston engines have mechanically powered compressors (blowers) or turbine-powered turbochargers or turbonormalizers that compress the air before feeding it into the engine; these piston engines can often operate efficiently at 20,000 ft (6100 m) above sea level or higher, altitudes that require the use of supplemental oxygen or cabin pressurisation. During the forties and especially following the 1973 energy crisis, development work was done on propellers with swept tips or even scimitar-shaped blades for use in high-speed commercial and military transports. Pressurised aircraft, however, are more likely to use the turbine engine, since it is naturally efficient at higher altitudes and can operate above 40,000 ft. Helicopters also typically use turbine engines. In addition to turbine engines like the turboprop and turbojet, other types of high-altitude, high-performance engines have included the ramjet and the pulse jet. Rocket aircrafts have occasionally been experimented with. They are restricted to rather specialised niches, such as spaceflight, where no oxygen is available for combustion (rockets carry their own oxygen).

By usage

The major distinction in aircraft usage is between military aviation, which includes all uses of aircraft for military purposes (such as combat, patrolling, search and rescue, reconnaissance, transport, and training), and civil aviation, which includes all uses of aircraft for non-military purposes.

Military aircraft

Combat aircraft like fighters or bombers represent only a minority of the category. Many civil aircraft have been produced in separate models for military use, such as the civil Douglas DC-3 airliner, which became the military C-47/C-53/R4D transport in the U.S. military and the Dakota in Britain and the Commonwealth. Even the little fabric-covered two-seater Piper J3 Cub had a military version, the L-4 liaison, observation and trainer aircraft. In the past, gliders and balloons have also been used as military aircraft; for example, balloons were used for observation during the American Civil War and World War I, and cargo gliders were used during World War II to land intruding German troops in many European countries in the 1940/42 period, while Allied troops used them in Europe after D-Day . Combat aircraft themselves, though used a handful of times for reconnaissance and surveillance during the Italo-Turkish War, did not come into widespread use until the Balkan War when first air-dropped bomb was invented and widely used by Bulgarian air force against Turkey. During World War I many types of aircraft were adapted for attacking the ground or enemy vehicles/ships/guns/aircraft, and the first aircraft designed as bombers were born. In order to prevent the enemy from bombing, fighter aircraft were developed to intercept and shoot down enemy aircraft. Tankers were developed after World War II to refuel other aircraft in mid-air, thus increasing their operational range. By the time of the Vietnam War, helicopters had come into widespread military use, especially for transporting and supporting ground troops.

Civil aviation

helicopter]] Civil aviation includes both scheduled airline flights and general aviation, a catch-all covering other kinds of private and commercial use. The vast majority of flights flown around the world each day belong to the general aviation category, ranging from recreational balloon flying to civilian flight training to business trips to firefighting to medevac flights to cargo transportation on freight aircraft. Within general aviation, the major distinction is between private flights (where the pilot is not paid for time or expenses) and commercial flights (where the pilot is paid by a customer or employer). Private pilots use aircraft primarily for personal travel, business travel, or recreation. Usually these private pilots own their own aircraft and take out loans from banks or specialized lenders to purchase them. Commercial general aviation pilots use aircraft for a wide range of tasks, such as flight training, pipeline surveying, passenger and freight transport, policing, crop dusting, and medical transport (medevac). Piston-powered propeller aircraft (single-engine or twin-engine) are especially common for both private and commercial general aviation, but even private pilots occasionally own and operate helicopters like the Bell JetRanger or turboprops like the Beechcraft King Air. Business jets are typically flown by commercial pilots, although there is a new generation of small jets arriving soon for private pilots.

External links

History
- [http://www.nasm.si.edu/ Smithsonian Air and Space Museum] - Excellent online collection with a particular focus on history of aircraft and spacecraft
- [http://invention.psychology.msstate.edu/Tale_of_Airplane/taleplane.html Virtual Museum]
- [http://www.centennialofflight.gov/essay/Prehistory/PH-OV.htm Prehistory of Powered Flight]
- [http://www.hq.nasa.gov/office/pao/History/SP-468/contents.htm The Evolution of Modern Aircraft (NASA)]
- [http://www.check-six.com Check-Six] - Information on historic aircraft crashes including the X-15 and Flying Wing
- [http://www.anythingplanes.net Aircraft community ] Information
- [http://www.aircraft-info.net Aircraft-Info.net]
- [http://www.airliners.net/info/ Airliners.net]
- [http://www.HomebuiltAircraft.com HomebuiltAircraft.com]- Information Portal about Homebuilt Aircraft
- [http://www.DefenceTalk.com Airforces ]
- [http://www.challoner.com/aviation/index.html Series of Photo Essays on British Aviation]
- [http://www.usenet-replayer.com/webrings/aviation.html Pictures of Aircraft] published on Usenet
- [http://www.sulman4paf.tk PAF Procedures and Information, Wallpapers, Picture Gallery, Updated News] Patents
- US[http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=821393.WKU.&OS=PN/821393&RS=PN/821393 821393] -- Flying machine -- O. & W. Wright Category:Aircraft Category:Aviation zh-min-nan:Hui-hêng-ki ko:항공기 ms:Pesawat udara ja:航空機 simple:Aircraft

Air

Air is a name for the mixture of gases present in the Earth's atmosphere. Compressed air is often used in scuba diving as a shallow water breathing gas and to inflate buoyancy devices. Compressed air is also used as the means of transmission of energy to pneumatic tools.

Composition of air

By volume, air is about:
- 78.084% Nitrogen (N₂)
- 20.947% Oxygen (O₂)
- 0.934% Argon (Ar)
- 0.033% Carbon Dioxide (CO₂) With trace amounts of:
- Neon (Ne)
- Helium (He)
- Krypton (Kr)
- Sulfur dioxide (SO₂)
- Methane (CH₄)
- Hydrogen (H₂)
- Nitrous Oxide (N₂O)
- Xenon (Xe)
- Ozone (O₃)
- Nitrogen dioxide (NO₂)
- Iodine (I₂)
- Carbon monoxide (CO)
- Ammonia (NH₃) The amount of water vapor in the air varies considerably depending on weather, climate, and altitude. See Humidity. The molecular mass of air is approximately 28.96443 g/mole (molecular weight of standard air - CRC, 1983).

External link

- [http://mistupid.com/chemistry/aircomp.htm Composition of Air] Category:Atmosphere Category:Psychrometrics Category:HVAC ko:대기 ms:Udara ja:空気 simple:Air

Density

: For other senses of "density", see density (disambiguation). Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. The higher an object's density, the higher its mass per volume. The average density of an object equals its total mass divided by its total volume. A denser object (such as iron) will have less volume than an equal mass of some less dense substance (such as water). The SI unit of density is the kilogram per cubic metre (kg/m³) :

\rho = \frac

where :ρ is the object's density (measured in kilograms per cubic metre) :m is the object's total mass (measured in kilograms) :V is the object's total volume (measured in cubic metres) Under specified conditions of temperature and pressure, density of a fluid is defined as described above. However, the density of a solid material can be different, depending on exactly how it is defined. Take sand for example. If you gently fill a container with sand, and divide the mass of sand by the container volume you get a value termed loose bulk density. If you took this same container and tapped on it repeatedly, allowing the sand to settle and pack together, and then calculate the results, you get a value termed tapped or packed bulk density. Tapped bulk density is always greater than or equal to loose bulk density. In both types of bulk density, some of the volume is taken up by the spaces between the grains of sand. Also, in terms of candy making, density is affected by the melting and cooling processes. Loose granular sugar, like sand, contains a lot of air and is not tightly packed, but when it has melted and starts to boil, the sugar loses its granularity and entrained air and becomes a fluid. When you mold it to make a smaller, compacted shape, the syrup tightens up and loses more air. As it cools, it contracts and gains moisture, making the already heavy candy even more dense.

Other units

Density in terms of the SI base units is expressed in terms of kilograms per cubic metre (kg/m³). Other units fully within the SI include grams per cubic centimetre (g/cm³) and megagrams per cubic metre (Mg/m³). Since both the litre and the tonne or metric ton are also acceptable for use with the SI, a wide variety of units such as kilograms per litre (kg/L) are also used. Imperial units or U.S. customary units, the units of density include pounds per cubic foot (lb/ft³), pounds per cubic yard (lb/yd³), pounds per cubic inch (lb/in³), ounces per cubic inch (oz/in³), pounds per gallon (for U.S. or imperial gallons) (lb/gal), pounds per U.S. bushel (lb/bu), in some engineering calculations slugs per cubic foot, and other less common units. The maximum density of pure water at a pressure of one standard atmosphere is 999.972 kg/m³; this occurs at a temperature of about 3.98 °C (277.13 K). From 1901 to 1964, a litre was defined as exactly the volume of 1 kg of water at maximum density, and the maximum density of pure water was 1.000 000 kg/L (now 0.999 972 kg/L). However, while that definition of the litre was in effect, just as it is now, the maximum density of pure water was 0.999 972 kg/dm³. During that period students had to learn the esoteric fact that a cubic centimetre and a millilitre were slightly different volumes, with 1 mL = 1.000 028 cm³. (often stated as 1.000 027 cm³ in earlier literature).

Measurement of density

A common device for measuring fluid density is a pycnometer. A device for measuring absolute density of a solid is a gas pycnometer.

Density of substances

Perhaps the highest density known is reached in neutron star matter (see neutronium). The singularity at the centre of a black hole, according to general relativity, does not have any volume, so its density is undefined. The most dense naturally occurring substance on Earth is iridium, at about 22650 kg/m³. A table of densities of various substances:

Substance	Density in kg/m³
Iridium	22650
Osmium	22610
Platinum	21450
Gold	19300
Tungsten	19250
Uranium	19050
Mercury	13580
Palladium	12023
Lead	11340
Silver	10490
Copper	8960
Iron	7870
Tin	7310
Titanium	4507
Diamond	3500
Basalt	3000
Granite	2700
Aluminium	2700
Graphite	2200
Magnesium	1740
PVC	1300
Seawater	1025
Water	1000
Ice	917
Polyethylene	910
Ethyl alcohol	790
Gasoline	730
Aerogel	.003
any gas	0.0446 times the average molecular mass, hence between 0.09 and ca. 10.0 (at standard temperature and pressure)
For example air	1.2

Note the low density of aluminium compared to most other metals. For this reason, aircraft are made of aluminium. Also note that air has a nonzero, albeit small, density. Aerogel is the world's lightest solid.

Balloon (aircraft)

Balloons are a type of lighter than air aircraft that remain aloft due to their buoyancy. Balloons travel by moving with the wind. They are distinct from airships which are buoyant aircraft which can be propelled through the air in a controlled manner. They are also distinct from aerostats which are balloons that are moored to the ground rather than free flying. aerostats aerostats aerostats

Types of balloon aircraft

There are four main types of balloons:
- hot air balloons obtain their buoyancy by heating the air inside the envelope. They are the most common type of balloon aircraft.
- gas balloons filled with an unheated gas such as:
- hydrogen - not widely used for aircraft since the Hindenburg disaster because of high flammability except for some sport balloons as well as nearly all unmanned scientific and weather balloons.
- helium - the gas used today for all airships and most manned balloons in the United States
- ammonia - used infrequently due to its caustic qualities and limited lift
- coal gas - used in the early days of ballooning, high flammability
- Rozier balloons use both heated and unheated lifting gases. The most common modern use of this type of balloon is for long distance record flights such as the recent circumnavigations.
- superpressure balloons that allow the lifting gas to be pressurized in flight [with the objective of limiting or eliminating the loss of gas from day-time heating]

History

The hot air balloon was first developed as a children's toy round about the 2nd or 3rd century AD in China. It has been proposed that some ancient civilisations developed manned hot air balloon flight. For example it has been proposed that the Nazca lines (which can only be seen from the air) presuppose some form of manned flight, and a balloon was the only possible available technology that could have achieved this. Julian Nott designed and built a balloon using woven cotton fabric and a Torta reed gondola, both readily available to the peoples who made the Nazca lines. Heating the air in the balloon with a wood fire, Nott flew over the Nazca Plains. Nott comments that there is no evidence of any kind that that ancient peoples did fly but this flight proved beyond doubt that most early civilizations could have flown: all they needed was a loom and fire. In 1709 in Lisbon, Bartolomeu de Gusmão made a balloon filled with heated air rise inside a room. He also made a balloon named Passarola (Port. Big bird) and attempted to lift himself from Saint George Castle, in Lisbon, but only managed to harmlessly fall about one kilometre away. Following Henry Cavendish's work on hydrogen, of 1766, Joseph Black proposed that a balloon filled with hydrogen would be able to rise in the air. The first recorded manned balloon flight in history was made in a hot air balloon by the Montgolfier brothers in 1783. Within a few days, Professor Jacques Charles made the first gas balloon flight. Gas balloons became the most common type from the 1790s until the 1960s. The first steerable (also known as a dirigible) balloon was attempted by Henri Giffard in 1852. Powered by a steam engine it was too slow to be effective. Like heavier than air flight, the internal combustion engine made dirigibles, especially blimps, practical, starting in the late ninteenth century. Ed Yost reinvented the design of hot air balloons in the late 1950s using rip-stop nylon fabrics and high powered propane burners to create the modern hot air balloon. His first flight of such a balloon in 1960 triggered the entire modern sport balloon movement.

Balloons as flying machines

A balloon is conceptually the simplest of all flying machines. The balloon is a fabric envelope filled with a gas that is lighter than the surrounding atmosphere. As the entire balloon is less dense than its surroundings, it rises, taking along with it a basket, attached underneath, that carries passengers or payload. The first balloons capable of carrying passengers used hot air to obtain buoyancy and were built by the brothers Josef and Etienne Montgolfier in Annonay, France. Balloons using the light gas hydrogen for buoyancy were flown less than a month later. They were invented by Professor Jacques Charles and first flown on December 1, 1793. Gas balloons have greater lift and can be flown much longer than hot air, so gas balloons dominated ballooning for the next 200 years. In the 19th century, it was common to use town gas to fill balloons; it was not as light as hydrogen gas, but was much cheaper and readily available. town gas, England. The inset shows detail of the gondola]] The third balloon type was invented by Pilâtre de Rozier and is a hybrid of a hot air and a gas balloon. Gas balloons have an advantage of being able to fly for a long time and hot air balloons have an advantage of being able to easily change altitude so the Rozier balloon was a hydrogen balloon with a separate hot air balloon attached. In 1785, Pilâtre de Rozier took off in an attempt to fly across the English Channel but the balloon exploded a half-hour into the flight. This unfortunate accident earned de Rozier the title "The First to Fly and the First to Die". It wasn't until the 1980s that technology once again allowed the Rozier balloons to become feasible. Jean-Pierre Blanchard made the first piloted balloon flight in North America on January 9, 1793. Although a balloon has no propulsion system, a degree of directional control is possible through making the balloon rise or sink in altitude to find favorable wind directions. Both the hot-air, or Montgolfière, balloon and the gas balloon are still in common use. Montgolfière balloons are relatively inexpensive as they do not require high-grade materials for their envelopes, and they are popular for balloonist sport activity. Light gas balloons are predominant in scientific applications, as they are capable of reaching much higher altitudes for much longer periods of time. They are generally filled with helium. Although hydrogen has more lifting power, it is explosive in an atmosphere full of oxygen. With a few exceptions, scientific balloon missions are unmanned. There are two types of light-gas balloons: zero-pressure and superpressure. Zero-pressure balloons are the traditional form of light-gas balloon. They are partially inflated with the light gas before launch, with the gas pressure the same both inside and outside the balloon. As the zero-pressure balloon rises, its gas expands to maintain the zero pressure difference, and the balloon's envelope swells. At night, the gas in a zero-pressure balloon cools and contracts, causing the balloon to sink. A zero-pressure balloon can only maintain altitude by releasing gas when it goes too high, where the expanding gas can threaten to rupture the envelope, or releasing ballast when it sinks too low. Loss of gas and ballast limits the endurance of zero-pressure balloons to a few days. 1793] A superpressure balloon, in contrast, has a tough and inelastic envelope that is filled with light gas to pressure higher than that of the external atmosphere, and then sealed. The superpressure balloon cannot change size greatly, and so maintains a generally constant volume. The superpressure balloon maintains an altitude of constant density in the atmosphere, and can maintain flight until gas leakage gradually brings it down. Superpressure balloons offer flight endurance of months, rather than days. In fact, in typical operation a Earth-based superpressure balloon mission is ended by a command from ground control to open the envelope, rather than by natural leakage of gas. For air transport balloons must contain a gas lighter than the surrounding air. There are two types:
- hot air balloons: filled with hot air, which by heating becomes lighter than the surrounding air; they have been used to carry human passengers since the 1790s;
- balloons filled with:
- hydrogen - although highly flammable still used in Europe (see Hindenburg disaster)
- helium - safe but very expensive. Large helium balloons are used as high flying vessels to carry scientific instruments (as do weather balloons), or even human passengers. Cluster ballooning uses many smaller gas-filled balloons for flight (see [http://www.clusterballoon.org/intro/intro.html An Introduction to Cluster Ballooning]).

Balloons in the military

Cluster ballooning)]] The first military use of a balloon was at the Battle of Fleurus in 1794, when it was used by French Revolutionary troops to watch the movements of the enemy. Hot air balloons such as The Enterprise were used by military observers in the American Civil War (1861-65), the project was headed by Thaddeus Lowe, who headed the balloon corps from 1861-1863. The use of military observers in balloons during the Civil War resulted in a warfare first, when Union guns fired on the Confederates using only the information that the aeronaut provided, and without seeing the enemy for themselves. Hydrogen-filled ballons were also widely used during World War I (1914-1918) to detect enemy troop movements and to direct artillery fire. Observers phoned their reports to officers on the ground who then relayed the information to appropriate destinations. Because artillery was such an important factor in World War I, balloons were frequent targets of opposing aircraft. Though balloon companies of all combatants were protected by antiaircraft guns and patrolling fighters, casualties were frequently heavy. The Aeronaut Badge was established by the United States Army in World War I to denote service members who were qualified balloon pilots. Observation balloons were retained well after the Great War, being used in the Russo-Finnish conflicts (1939-40 and 1941-45). The Japanese launched thousands of balloon bombs to the US and Canada, carried in the jet stream; see fire balloons. Also, the British used balloons to carry incendiary devices to Germany between 1942 and 1944, see Operation Outward.

Airship

1931]] An airship is a buoyant aircraft that can be steered and propelled through the air. Unlike aerodynamic aircraft which stay aloft by moving an airfoil through the air in order to produce lift, airships stay aloft primarily by means of a cavity (usually quite large) filled with a gas of lesser density than the surrounding atmosphere. Airships are also known as dirigibles from the French dirigeable, meaning "steerable". The term airship is sometimes informally used to mean a machine capable of atmospheric flight. The term zeppelin is a genericized trademark that originally referred to airships manufactured by the Zeppelin Company. In modern common usage, the terms zeppelin, dirigible and airship are used interchangeably for any type of rigid airship, with the terms blimp or airship alone used to describe non-rigid airships. In modern technical usage however, airship is the term used for all aircraft of this type with zeppelin referring only to aircraft of that manufacture and blimp referring only to non-rigid airships. In the early days of airships, the primary lifting gas was hydrogen. Until the 1950s, all airships, except for those in the United States continued to use hydrogen because it offered greater lift and was cheaper than helium. The United States (until then the sole producer) was also unwilling to export helium because of its rarity and the fact it was considered a strategic material. However, hydrogen is flammable when mixed with air, a quality that has caused disasterous effects. The buoyancy provided by hydrogen is actually only about 10% greater than that of helium. So the issue became one of safety versus cost. American airships have been filled with helium since the 1920s and modern passenger-carrying airships are, by law, now prohibited from being filled with hydrogen. Some small experimental ships still use hydrogen. Other small experimental airships are filled with hot air in a fashion similar to a hot air balloon. They are sometimes called hotships. In contrast to airships, balloons are buoyant aircraft that generally rely on wind currents for movement, though vertical movement can be controlled in both.

Types

balloon
- Rigid airships (for example, Zeppelins) have rigid frames containing multiple, non-pressurized gas cells or balloons to provide lift. Rigid airships do not depend on internal pressure to maintain their shape.
- Non-rigid airships (blimps) use a pressure level in excess of the surrounding air pressure in order to retain their shape.
- Semi-rigid airships, like blimps, require internal pressure to maintain their shape, but have extended, usually articulated keel frames running along the bottom of the envelope to distribute suspension loads into the envelope and allow lower envelope pressures.
- Metal-clad airships have characteristics of both rigid and non-rigid airships, utilizing a very thin, airtight metal envelope, rather than the usual rubber-coated fabric envelope. Only two ships of this type, Schwarz's aluminium ship of 1897 and the ZMC-2, have been built to date.
- Hybrid airship is a general term for an aircraft that combines characteristics of heavier-than-air (airplane or helicopter) and lighter than air technology. Examples include helicopter/airship hybrids intended for heavy lift applications and dynamic lift airships intended for long-range cruising. It should be noted that most airships, when fully loaded with cargo and fuel, are typically heavier than air, and thus must use their propulsion system and shape to generate aerodynamic lift, necessary to stay aloft; technically making them hybrid airships. However, the term "hybrid airship" refers to craft that obtain a significant portion of their lift from aerodynamic lift and often require substantial take-off rolls before becoming airborne.

History

The development of airships was necessarily preceded by the development of balloons. See balloon (aircraft) for details.

Airship Pioneers

Airships were among the first aircraft to fly, with various designs flying throughout the 19th century. They were largely attempts to make relatively small balloons more steerable, and often contained features found on later airships. These early airships set many of the earliest aviation records. In 1784 Jean-Pierre Blanchard fitted a hand-powered propeller to a balloon, the first recorded means of propulsion carried aloft. The first person to make an engine-powered flight was Henri Giffard who, in 1852, flew 27 km (17 miles) in a steam-powered airship. Charles F. Ritchel made a public demonstration flight in 1878 of his hand-powered one-man rigid airship and went on to build and sell five of his aircraft. Paul Haenlein flew an airship with an internal combustion engine on a tether in Vienna, the first use of such an engine to power an aircraft. In 1880, Karl Wölfert and Ernst Baumgarten attempted to fly a powered airship in free flight, but crashed. In the 1880's a Serb named Ogneslav Kostovic Stepanovic also designed and built an airship. However the craft was destroyed by fire before it flew. In 1883, the first electric-powered flight was made by Gaston Tissandier who fitted a 1-1/2 horsepower Siemens electric motor to an airship. The first fully controllable free-flight was made in a French Army airship, La France, by Charles Renard and Arthur Krebs in 1884. The 170 foot long , 66,000 cubic foot airship covered 8 km (5 miles) in 23 minutes with the aid of an 8-1/2 horsepower electric motor. In 1888, Wölfert flew a Daimler-built petrol engine powered airship at Seelburg. In 1896, a rigid airship created by Croatian engineer David Schwarz made its first flight at Tempelhof field in Berlin. After Schwarz's death, his wife, Melanie Schwarz, was paid 15,000 Marks by Zeppelin for information about the airship. In 1901, Santos Dumont, in his airship "Number 6", a small blimp, won the Deutsch de la Meurthe prize of 100,000 francs for flying from the Parc Saint Cloud to the Eiffel Tower and back in under thirty minutes. Many inventors were inspired by Santos-Dumont's small airships and a veritable airship craze began world-wide. Many airship pioneers, such as the American Thomas Scott Baldwin financed their activities through passenger flights and public demonstration flights. Others, such as Walter Wellman and Melvin Vaniman set their sights on loftier goals, attempting two polar flights in 1907 and 1909, and two trans-atlantic flights in 1910 and 1912. The beginning of the "Golden Age of Airships" was also marked with the launch of the Luftschiff Zeppelin LZ1 in July of 1900 which would lead to the most successful airships of all time. These Zeppelins were named after the pioneer Count Ferdinand von Zeppelin. Von Zeppelin began experimenting with rigid airship designs in the 1890's leading to some patents and the LZ1 (1900) and the LZ2 (1906). At the beginning of WW1 the Zeppelin airships had a cylindrical aluminium alloy frame and a fabric-covered hull containing separate gas cells. Multi-plane tail fins were used for control and stability, and two engine/crew cars hung beneath the hull driving propellers attached to the sides of the frame by means of long drive shafts. Additionally there was a passenger compartment (later a bomb bay) located halfway between the two cars.

Airships in the First World War

WW1 The prospect of using airships as bomb carriers had been recognised in Europe well before the airships themselves were up to the task. H. G. Wells described the obliteration of entire fleets and cities by airship attack in The War in the Air (1908), and scores of less famous British writers declared in print that the airship had altered the face of world affairs forever. On 5 March 1912, Italian forces became the first to use dirigibles for a military purpose during reconnaissance west of Tripoli behind Turkish lines. It was World War I, however, that marked the airship's real debut as a weapon. Count Zeppelin and others in the German military believed they had found the ideal weapon with which to counteract British Naval superiority and strike at Britain itself. More realistic airship advocates believed the Zeppelin was a valuable long range scout/attack craft for naval operations. Raids began by the end of 1914, reached a first peak in 1915, and then were discontinued after 1917. Zeppelins proved to be terrifying but inaccurate weapons. Navigation, target selection and bomb-aiming proved to be difficult under the best of conditions. The darkness, high altitudes and clouds that were frequently encountered by zeppelin missions reduced accuracy even further. The physical damage done by the zeppelins over the course of the war was trivial, and the deaths that they caused (though visible) amounted to a few hundred at most. The zeppelins also proved to be vulnerable to attack by aircraft and antiaircraft guns, especially those armed with tracer bullets. Several were shot down in flames by British defenders, and others crashed 'en route'. In retrospect, advocates of the naval scouting role of the airship proved to be correct, and the land bombing campaign proved to be disastrous in terms of morale, men and material. Many pioneers of the German airship service died bravely, but needlessly in these propaganda missions. They also drew unwanted attention to the construction sheds which were bombed by the British Royal Naval Air Service. Meanwhile the Royal Navy had recognised the need for small airships to counteract the submarine threat in coastal waters, and beginning in February 1915, began to deploy the SS (Sea Scout) class of blimp. These had a small envelope of 60-70,000 cu feet and at first utilised standard single engined planes (BE2c, Maurice Farman, Armstrong FK) shorn of wing and tail surfaces as an economy measure. Eventually more advanced blimps with purpose built cars, such as the C (Coastal), C
- (Coastal Star), NS (North Sea), SSP (Sea Scout Pusher), SSZ (Sea Scout Zero), SSE (Sea Scout Experimental) and SST (Sea Scout Twin) classes were developed. The NS class, after initial teething problems proved to be the largest and finest airships in British service. They had a gas capacity of 360,000 cu feet, a crew of 10 and an endurance of 24 hours. Six 230 lb bombs were carried, as well as 3-5 machine guns. British blimps were used for scouting, mine clearance, and submarine attack duties. During the war, the British built over 225 non-rigid airships, of which several were sold to the Russia, France, the US and Italy. Britain, in turn, purchased one M-type semi-rigid from Italy whose delivery was delayed until 1918. Eight rigid airships had been completed by the armistice, although several more were in an advanced state of completion by the wars end. The large number of trained crews, low attrition rate and constant experimentation handling techniques meant that at the wars end Britain was the world leader in non-rigid airship technology. Royal Navy Airplanes had essentially replaced airships as bombers by the end of the war, and Germany's remaining zeppelins were scuttled by their crews, scrapped or handed over to the Allied powers as spoils of war. The British rigid airship program, meanwhile, had been largely a reaction to the potential threat of the German one and was largely, though not entirely, based on imitations of the German ships. Royal Navy]]

Airships in the Inter-war period

Airships using the Zeppelin construction method are sometimes referred to as zeppelins even if they had no connection to the Zeppelin business. Several airships of this kind were built in the USA and Britain in the 1920s and 1930s, mostly imitating original Zeppelin design derived from crashed or captured German World War I airships. The British R33 and R34, for example, were near identical copies of the German L-33, which crashed virtually intact in Yorkshire on September 24 1916. Despite being almost three years out of date by the time they were launched in 1919, these sister ships were two of the most successful in British service. On July 2 1919 R34 began the first double crossing of the Atlantic by an aircraft. It landed at Mineola, Long Island on July 6, 1919 after 108 hours in the air. The return crossing commenced on July 8 because of concerns about mooring the ship in the open, and took 75 hours. Impressed, British leaders began to contemplate a fleet of airships that would link Britain to its far-flung colonies, but unfortunately post-war economic conditions lead to most airships being scrapped and trained personnel dispersed, until the R-100 and R-101 commenced construction in 1929. Another example was the first American-built rigid dirigible ZR-1 "USS Shenandoah" , which flew in 1923, while the Los Angeles was under construction. The ship was christened on August 20 in Lakehurst, New Jersey and was the first to be inflated with the noble gas helium, which was still so rare at the time that the Shenandoah contained most of the world's reserves. So, when the Los Angeles was delivered, it was at first filled with the helium borrowed from ZR-1. The Zeppelin works were saved by the purchase of what became called the USS Los Angeles by the United States Navy, paid for with "war reparations" money, owed according to the Versailles Treaty. The success of the Los Angeles encouraged the United States Navy to invest in larger airships of its own. Germany, meanwhile, was building the Graf Zeppelin, the first of what was intended to be a new class of passenger airships. Interestingly, the Graf Zeppelin burned un-pressurised blau gas, similar to propane, as fuel. Since its density was similar to that of air, it avoided the weight change when fuel was used. Initially airships met with great success and compiled an impressive safety record. The Graf Zeppelin, for example, flew over 1 million miles (including the first circumnavigation of the globe by air) without a single passenger injury. The expansion of airship fleets and the growing (sometimes excessive) self-confidence of airship pilots gradually made the limits of the type clear, however, and initial successes gave way to a series of tragic rigid airship accidents. In fact, with the exception of the Graf Zeppelin, most of the world's most famous airships eventually crashed. propane Although USS Los Angeles flew successfully for 8 years, the U.S. Navy eventually lost all three of its American-built rigid airships to accidents. USS Shenandoah flew into a thunderstorm over Ohio in 1925 and broke into pieces. USS Akron was caught by a microburst and driven down into the surface of the sea off the shore of New Jersey in 1933. Both storm-related losses led to great loss of life. USS Macon broke up after suffering a structural failure in its upper fin off the shore of Point Sur in California in 1935. All but 2 of the 83 people aboard Macon survived the crash thanks to the issue of life jackets and inflatable rafts in the interval since the Akron disaster. Britain suffered its own airship tragedy in 1930 when R 101, a ship far advanced for its time but rushed to completion and sent on a trip to India before she was ready, crashed in France with the loss of 48 out of 54 aboard. Because of the bad publicity surrounding the crash, the Air Ministry grounded the competing R 100 in 1930 and sold it for scrap in 1931. The most spectacular and widely remembered airship accident, however, is the burning of the Hindenburg on 6 May 1937, which caused public faith in airships to evaporate in favour of faster, more cost-efficient (albeit less energy-efficient) airplanes. What is generally not remembered is that of the 97 people on board, 62 got out alive. There were 36 dead: 13 passengers, 22 aircrew, and one American groundcrewman. Most probably, the airplane became the transport of choice also because it is less sensitive to wind. Aside from the problem of manoeuvring and docking in high winds, the trip times for an upwind versus a downwind trip of an airship can differ greatly, and even crabbing at an angle to a crosswind eats up ground speed. Those differences make scheduling difficult.

Airships in the Second World War

The greatest number of airships in use during the Second World War were blimps used to form anti-aircraft defences. Thousands were put up tethered to the ground by steel cables to form obstacles to German aircraft flying on bombing missions over England. American construction of airships for civilian purposes was halted in the 1930s by a series of fatal crashes. However, military development of airships was continued in the US. While Germany determined that airships were obsolete for military purposes in the coming war and concentrated on the development of airplanes, the United States pursued a program of military airship construction even though it had not developed a clear military doctrine for airship use. At the Japanese attack on Pearl Harbor on 7 December 1941 that brought the United States into World War II, it had 10 non-rigid airships:
- 4 K-class : K-2, K-3, K-4 and K-5 designed as a patrol ships built from 1938.
- 3 L-class : L-1, L-2 and L-3 as small training ships, produced from 1938.
- 1 G-class built in 1936 for training.
- 2 TC-class that were older patrol ships designed for land forces, built in 1933. The US Navy acquired them from Army in 1938. Only K and TC class airships could be used for combat purposes and they were quickly pressed into service against Japanese and German submarines which at that time were sinking US shipping in visual range of US coast. US Navy command, remembering the airship anti-submarine success from WWI, immediately requested new modern anti-submarine airships and on 2 January 1942 formed the ZP-12 patrol unit based in Lakehurst from the 4 K airship. The ZP-32 patrol unit was formed from 2 TC and 2 L airship a month later, based at US Navy (Moffet Field) in Sunnyvale in California. An airship training base was created there as well. In the years 1942-1944, approximately 1400 airship pilots and 3000 support crew members were trained in the military airship crew training program and the airship military personnel grew from 430 to 12400. The US airships were produced by the Goodyear factory in Akron, Ohio. From 1942 till 1945, 154 airships were built for the US Navy (133 K-class, 10 L-class, 7 G-class, 4 M-class) and 5 L-class for civilian customers (serial number L-4 to L-8). The primary airship tasks were patrol and convoy escort near the US coastline. They also served as an organisation center for the convoys to direct ship movements and course, and were used during naval search and rescue operations. Rarer duties of the airships included aerophoto reconnaissance, naval mine-laying and mine-sweeping, parachute unit transport and deployment, cargo and personnel transportation. They were deemed quite successful in their duties with the highest combat readiness factor in the entire US air force (87%). They were extremely successful in their primary goal of anti-submarine warfare as the below numbers illustrate: During the war some 532 ships were sunk near the coast by submarines.
- 1942: 454 ships sunk near the US coast, 4-13 airships in service
- 1943: 65 ships sunk near the US coast, 17-53 airships in service
- 1944: 8 ships sunk near the US coast, 56-68 airships in service
- 1945: 3 ships sunk near the US coast, 53-48 airships in service Not a single ship of the 89,000 or so in convoys escorted by blimps was sunk by enemy fire. Airships engaged submarines with depth charges, or rarely from other on-board weapons. They were very successful since they could match the slow speed of the submarine and bomb it until its destruction. Additionally, submerged submarines had no means of detecting an airship approaching. Only one airship was ever destroyed by U-boat: on the night of 18/19 July 1943 a K-class airship (K-74) from ZP-21 division was patrolling the coastline near Florida. Using radar, the airship located a surfaced German submarine. Due to the failure of the depth charge release mechanism, the airship was unable to release the bombs during the bombing run and the German returned fire. The (K-74) received serious damage and was forced to make a water landing. The crew was rescued by patrol boats in the morning, but one crewman died from a shark attack. The U-Boat responsible was sunk a few hours later. Some US airships saw action in the European war theater. The ZP-14 unit operating in the Mediterranean area from June 1944 completely denied the use of the Gibraltar Straits to Axis submarines. Airships from the ZP-12 unit took part in the sinking of the last U-Boat before German capitulation, sinking U-881 on 6 May 1945 together with destroyers Atherton and Mobery. The Soviet Union used a single airship during the war. The W-12, built in 1939, entered service in 1942 for paratrooper training and equipment transport. It made 1432 runs with 300 metric tons of cargo until 1945. On 1 February 1945 the Soviets constructed a second airship, a Pobieda-class unit (used for mine-sweeping and wreckage clearing in the Black Sea) which later crashed on 21 January 1947. Another W-class - W-12bis Patriot was commissioned in 1947 and was mostly used for crew training, parades and propaganda.

Continued use

Although airships abandoned carrying passengers, they continued to be used for other purposes. In particular, the US Navy as above. 1945 In recent years, the Zeppelin company has reentered the airship business. Their new model, designated the Zeppelin NT made its maiden flight on September 18, 1997. There are currently three NT aircraft flying. One has been sold to a Japanese company, and was planned to be flown to Japan in the summer of 2004. However, due to delays getting permission from the Russian government, the company decided to transport the airship to Japan by ship. An airship was flown over Athens during the 2004 Summer Olympics as part of security anti-terrorism measures. Blimps continue to be used for advertising and as TV camera platforms at major sporting events. Several companies, such as Cameron Balloons in Bristol, UK, build hot-air airships. These combine the structures of both hot-air balloons and small airships. The envelope is the normal 'cigar' shape, complete with tail fins, but is not inflated by helium, but by hot air (as in a balloon), which provides the lifting force. A small gondola, carrying the pilot (and sometimes between 1 and 3 passengers), a small engine and the burners to provide the hot air is suspended below the envelope, below an opening through which the burners protrode. The advantages with the hot-air airship are that is costs less to buy and maintain than a standard modern blimp and it can be quickly deflated at the end of a flight, meaning it is easily transported on a trailer or truck, without the need for expensive storage arrangements. Such craft usually are very slow moving, with a typical top speed of 15-20 mph. They are used mainly for advertising, but several have been used in rainforests for wildlife observation, because they could easily be transported into remote areas.

Present-day research

Recently, several companies have begun exploring the possibilities of airships with their potentially huge lifting capacities, near-VTOL (Vertical Take-Off and Landing) capabilities, and potentially lower freight costs, though none has demonstrated economic viability yet. In addition to the research on conventional blimp designs, several unconventional prototype designs continue to be investigated. One example is a design commissioned by the United States Military for a massive solar powered spy and communication blimp, 25 times larger than the Goodyear Blimp, which it is hoped will be able to carry tons of payload far above the range of antiaircraft weapons. The company developing the design, JP Aerospace, claims to have long-range plans to develop an "orbital airship" capable of lifting cargo into low earth orbit with a marginal transportation cost of $1 per short ton per mile of altitude. Contracts are underway with Lockheed for high-altitude airships (HAAs). Airships are being investigated as a possible alternative to LEO (low Earth orbit) satellite communications. One proposed system involves sending unmanned airships high above cities at 70,000 feet (21 km). These aircraft would provide cellular voice and data service to a city with service similar to what LEOs provide. Due to the fact that these would be located in the stratosphere, one company currently working on this calls their proposed airships "Stratellites". With the September 11 terrorist attacks, the U.S. military has been forced to reassess threats and evaluate strategies for aerial defence. Two major defense contractors are pitching the zeppelin as a potential piece in the homeland security jigsaw. Military planners envision unmanned airships as high-altitude radar platforms keeping watch for anything threatening U.S. airspace. In February 2005, the US Department of Defense announced a research program named the WALRUS HULA [http://www.darpa.mil/tto/programs/walrus.html] [http://www.defenseindustrydaily.com/2005/10/us-cbo-gives-ok-to-hula-airships-for-airlift/index.php] to explore the development of very large airships. The primary goal of the research program is determine the feasibility of building an airship capable of carrying 500 short tons (450 metric tons) of payload a distance of 12,000 miles (20,000 km) and land on an unimproved location without the use of external ballast or ground equipment (e.g. masts.)

Fiction

Airships were a popular theme in scientific romance (prototypical science fiction) and adventure fiction published in the late 19th century and the earliest years of the 20th century. The theme of aeronautical exploration was most famously explored in this period by Jules Verne (The Clipper of the Clouds) and H. G. Wells (The War in the Air). After the invention of the airplane, airships were largely forgotten by mainstream fiction, and today appear mainly in historical fiction and alternate history (particularly the steampunk genre and the work of Michael Moorcock, most notably The Warlord of the Air). In his "Anome" trilogy (The Anome aka The Faceless Man, The Brave Free Men, and The Asutra), Jack Vance depicts a system of airships tethered to unmanned monorail dolleys which keep them on fixed courses. In Philip Pullman's trilogy His Dark Materials (The Golden Compass, The Subtle Knife, and The Amber Spyglass), which takes place in a parallel universe, airships are the only method of air travel. Airships' strengths and weaknesses are well portrayed in these novels: their great lifting capacity makes them valuable for transporting supplies and soldiers, but they are easily destroyed. In Theodore Judson's post-apocalyptic Fitzpatrick's War, the neo-feudal Yukon Confederacy makes heavy use of airships as military and civilian transports. Kim Stanley Robinson in his Mars Trilogy envisages rigid airships being used as a major form of transport for the emerging settlements of Mars. Kenneth Oppel's novel Airborn, a young adult adventure set in an alternate history in which airship travel is common, won the 2004 Governor General's Award for children's literature. [http://www.airborn.ca/ www.airborn.ca]. There is also a sequel, Skybreaker. In Philip Reeve's Hungry City Chronicles , which takes place in the distant future, airships are the primary form of travel because of the mobile nature of cities in the books. In the series, it is mentioned that airship technology had advanced beyond the imaginations of the "Ancients". Airships include freighters, sky yachts, fighter airships and immense air destroyers. In Jasper Fforde's Thursday Next series the airship is a significant and popular form of transport. David Brin's 1990 Hugo nominated near-future, post global-warming science fiction novel, "Earth" (set in 2038), portrays a future where there is regular use of airships for passenger transportation. China Miéville's Bas Lag novels (Perdido Street Station, The Scar, Iron Council) feature airships ("dirigibles") as a common mode of transport; they are used as taxis and military scouts. The Scar featured two large war airships controlled by the pirate city of Armada: The Arrogance (a captured New Crobuzon airship used as a crow's nest) and the Trident. Philip Jose Farmer's Riverworld novels feature a giant rigid and several non-rigid airships which are used to reach the north pole of the Riverworld More than a few video games, such as Crimson Skies, Skies of Arcadia and the Final Fantasy series, utilize airships in their fictional worlds as a major mode of transportation. (In some cases (most notably in the Final Fantasy series), the "airship" is actually a ship with wings, propellers, etc..) Also, in Command & Conquer Red Alert 2, the Soviets' most lethal conventional weapons are their extremely tough but slow Kirov Airships, which drop incredibly powerful bombs.

References

- Rich Archbold and Ken Marshall,Hindenberg, an Illustrated History, 1994 ISBN 0446517844
- William F. Althoff , USS Los Angeles: The Navy's Venerable Airship and Aviation Technology , 2003, ISBN 1574886207
- Peter Brooks , Zeppelin: Rigid Airships 1893-1940 , 2004, ISBN 0851778453
- Charles P. Burgess, Airship Design, (1927) 2004 ISBN 1410211738
- Wilbur Cross, Disaster at the Pole, 2002 ISBN 1-58574-496-4
- Arthur Frederick et al., Airship saga: The history of airships seen through the eyes of the men who designed, built, and flew them , 1982, ISBN 0713710012
- Manfred Griehl and Joachim Dressel, Zeppelin! The German Airship Story, 1990 ISBN 1-85409-045-3
- Gabriel Alexander Khoury (Editor), Airship Technology (Cambridge Aerospace Series) , 2004, ISBN 0521607531
- Alexander McKee, Ice crash, 1980, ISBN 0312403828
- Andrzej Morgała, Sterowce w II Wojnie Światowej (Airships in the Second World War), Lotnictwo, 1992
- Ces Mowthorpe, Battlebags: British Airships of the First World War, 1995 ISBN 0905-778-138
- US War Department , Airship Aerodynamics: Technical Manual, (1941) 2003 , ISBN 1410206149

External links

General

- [http://spot.colorado.edu/~dziadeck/airship.html Airship Home Page] - Provides a list of airship related websites. Also contains airship mailing list.
- [http://www.hotairship.com/ Airship and Blimp Resources] - This site focuses more on how to build your own airship with a particular focus on hot air airships (a.k.a "hotships")
- [http://lists.sculptors.com/mailman/listinfo/airships Airships Mailing List] - A forum for the discussion and design of lighter-than-air craft.

Associations

- [http://www.airship-association.org/ The Airship Association] - British based association for people interested in all things to do with airships.
- [http://www.blimpinfo.com/ Lighter than Air Society] - US based association for people interested in all things to do with airships.
- [http://www89.pair.com/techinfo/ABAC/abac.htm The Association of Balloon and Airship Constructors] - Maintains an extensive technical library on airship technology old and new.

Historical

- [http://www.nlhs.com/ Navy Lakehurst Historical Society] - airship history with a focus on activities at the historically most active airship base in the US.
- [http://www.aht.ndirect.co.uk/ Airships Online] - website of the Airships Heritage Trust. It contains an extensive history relating British Airships from 1900 to the present day.
- [http://www.history.navy.mil/branches/lta-m.html US Navy Airship History]
- Ferdinand von Zeppelin, US [http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=621,195.WKU.&OS=PN/621,195&RS=PN/621,195 621,195] Patent, "Navigable Ballon". March 14, 1899.
- [http://specialcollections.wichita.edu/collections/ms/99-01/99-1-bio.html Harold G. Dick Airship Collection] - biography of Harold G. Dick
- [http://specialcollections.wichita.edu/exhibits/haldick/haldickpostcards.html Postcards from Harold G. Dick Airship Collection]
- [http://specialcollections.wichita.edu/exhibits/haldick/haldick.html The Golden Age of the Great Passenger Airships: The Collection of Harold G. Dick]
- [http://www.centennialofflight.gov/essay/Lighter_than_air/Beginning_of_the_Dirigible/LTA6.htm US Centennial of Flight Commission]

Manufacturers and commercial operators

- [http://www.airship-association.org/net.html Airship Association Net Links Page] for a comprehensive list of companies throughout the world focusing on the development of airships.
- [http://www.americanblimp.com American Blimp Corporation] In association with The Lightships Group, this company builds and operates the world's largest fleet of airships.
- [http://www.gefa-flug.com GEFA-FLUG GmbH - The Air Company] -- makers of hot air airships
- [http://www.zeppelin-nt.com/index_e.htm Zeppelin Luftschifftechnik GmbH] -- The Zeppelin Company and the Zeppelin NT.
- [http://www.goodyearblimp.com/ The Goodyear Blimps] -- The most famous modern airships. These aircraft are owned and operated by the Lockheed Martin Corporation.
- [http://www.airshipman.com/ Airship Management Services] -- Operators of several type-certified airships including the Fuji Blimp. These aircraft were originally built by the Westinghouse Corporation with the designation Skyship 600. They also own and operate a sightseeing airship in Switzerland under the name [http://www.skycruiser.co.uk/ Skycruiser Switzerland]
- [http://www.cameronballoons.co.uk/airships.htm Cameron Airships] -- Hot air airships manufactured by Cameron Balloon - the world's largest manufacturer of hot air balloons.
- [http://www.lindstrand.co.uk/Airship.html Lindstrand Airships] - Hot air airships manufactured by hot air balloon company Lindsrand - a subsidiary of Cameron Balloon.
- [http://aas.augurballoons.com/ Augur Aerostatic Systems] -- Russian company making both gas and hot air airships

Experiments, prototypes and one-offs

- [http://www.21stcenturyairships.com 21st Century Airships Inc.] Developers of spherical, finless airships. From June 12, 2003 until December 13, 2004, a 21st Century Airship craft held the absolute FAI altitude record for airships of 6,234 m (20,450 ft).
- [http://www.aerosml.com/main.htm Aeros Corporation] - In addition to producing several small airships, this company is one of the winners of Phase I funding from DARPA for Project WALRUS.
- [http://www.usairships.com/ USA Airships]
- [http://www.myairship.com/database/whitedwarf.html White Dwarf] - A small, human-powered airship
- [http://www.endlessflyers.com/nice-calvi.htm Zeppy] - Human powered airship -- website in French.

Designs under development

- [http://www.lockheedmartin.com/wms/findPage.do?dsp=fec&ci=14477&rsbci=12972&fti=0&ti=0&sc=400 Lockheed-Martin HAA Project]
- [http://www.sanswire.com/ Sanswire Stratellite]
- [http://www.dynalifter.com/ Dynalifter]
- [http://www.atg-airships.com Advanced Technologies Group] Until August of 2005, when it went into receivership, this company was developing a range of products such as UAV's - Unmanned Aerial Vehicles, heavier-than-air airships and HAPS' - High Altitude Platform Stations for telecommunication.

Proposed designs

- [http://www.airship.org/ Vertical Airships]
- [http://rigid.tripod.com/english.html Airship Holland]
- [http://www.nagyairship.com/ Nagy High Speed Airship]
- [http://www.millenniumairship.com/ Millennium Airship]
- [http://www.quantumaerostatics.com/ Quantum Aerostatics]
- [http://www.hacinc.us/ Hybrid Aircraft Corporation]
- [http://www.ahausa.com/ Advanced Hybrid Aircraft] Category:Airships Category:Aeronautics ja:飛行船

Aerostat

The term "aerostat" has two meanings. In the first, broader sense, it includes all lighter than air aircraft. The term "aerostat" comes from the fact that buoyancy is technically said to provide aerostatic lift in that the force upwards arises without movement through the surrounding air mass. This contrasts with aerodynamic lift which requires the movement of at least some part of the aircraft through the surrounding air mass. The second, narrower and more techical usage refers only to moored balloons. This article focuses on the narrower use of the term. For a discussion of the other types of bouyant aircraft, see balloon (aircraft), airship, and lighter than air. Thus, in the narrower sense, an aerostat is a tethered or moored balloon often shaped like an airship and usually filled with helium. Aerostats differ from airships and balloons in that airships and balloons are both free flying whereas aerostats are tied to the ground. The barrage balloons of World War I and World War II were examples of aerostats. Today, Aerostats are used primarily as long duration sensor platforms. Surveillance aerostats have also been used in the 2004 American occupation of Iraq. Utilizing a high-tech optics system to detect and observe enemies from miles away and have been used accompanying foot patrols in Baghdad.

Aerostats in Science Fiction

Aerostats are commonly used in science fiction, though they are often envisioned as having a vacuum based displacement rather than helium; doing such appears to require the construction of a very large craft or the use of super-strong rigid materials. Aerostats of fiction are typically not tied to the ground, but rather remain stationary through the use of propulsion systems and internal sensors and controls. Category:Balloons

Helicopter

]] , a four seat development of the R22]] A helicopter is an aircraft which is lifted and propelled by one or more horizontal rotors (propellers). Helicopters are classified as rotary-wing aircraft to distinguish them from conventional fixed-wing aircraft. The word helicopter is derived from the Greek words helix (spiral) and pteron (wing). The engine-driven helicopter was invented by the Slovak inventor Jan Bahyl. The first stable, fully-controllable helicopter placed in production was invented by Igor Sikorsky. Compared to conventional fixed-wing aircraft, helicopters are much more complex, more expensive to buy and operate, relatively slow, have shorter range and restricted payload. The compensating advantage is maneuverability: helicopters can hover in place, reverse, and above all take off and land vertically. Subject only to refuelling facilities and load/altitude limitations, a helicopter can travel to any location, and land anywhere with enough space (a diameter of length 1.5 times the rotor disk).

Applications

Helicopters have many uses, both military and civil, including troop transportation, infantry support, firefighting, [http://www.tropicaled.com/helicopter2.htm shipboard operations], business transportation, casualty evacuation (including MEDEVAC, and air/sea/mountain rescue), police and civilian surveillance, carrying goods (some helicopters can carry slung loads, accommodating awkwardly shaped items), or as a mount for still, film or television cameras. Helicopters suffer from significantly higher operating and maintenance costs compared with fixed wing aircraft. The costs are due to inherent mechanical complexity and greater power requirements for a given gross weight. For these reasons, helicopters are not economically viable for commercial transportation. Speed and range limitations also constrain commercial applications.

History

police] Since around 400 BC the Chinese had a flying top that was used as a children's toy. This toy eventually made its way to Europe via trade and has been depicted in a 1463 European painting. Incidentally, the Wright brothers as children were given a rubber-band-powered version of this toy invented by Alphonse Penaud and were very much fascinated by it and built their own copies. "Pao Phu Tau" was a 4th century book in China that described some of the ideas in a rotary wing aircraft. The first somewhat practical idea of a human carrying helicopter was first conceived by Leonardo da Vinci around 1490, but it was not until after the invention of the powered aeroplane in the 20th century that actual models were produced. Developers such as Jan Bahyl, Oszkár Asbóth, Louis Breguet, Paul Cornu, Emile Berliner, Ogneslav Kostovic Stepanovic and Igor Sikorsky pioneered this type of aircraft, with Juan de la Cierva introducing the first practical autogiro in 1923 that was to be the basis for the modern helicopter. A flight of the first fully controllable helicopter was demonstrated by Raúl Pateras de Pescara 1916 in Buenos Aires, Argentina. The German Focke-Wulf Fw 61 was the first practical helicopter. It first flew in 1934. The Bell 47 designed by Arthur Young was the first helicopter to be licensed (in March 1946) for use in the United States. Reliable helicopters capable of stable hover flight were developed decades after fixed wing aircraft. This is largely due to higher engine power density requirements when compared with fixed wing aircraft. Igor Sikorsky is reported to have delayed his own helicopter research until suitable engines were commercially available. Improvements in fuels and engines during the first half of the 20th century were a critical factor in helicopter development. The availability of lightweight turboshaft engines in the second half of the 20th century led to the development of larger, faster, and higher performance helicopters. Turboshaft engines are the preferred powerplant for all but the smallest and least expensive helicopters today.

Generating lift

A conventional aircraft is able to fly because the forward motion of its angled wings forces air downwards, creating an opposite reaction called lift that forces the wings upwards. A helicopter uses exactly the same method, except that instead of moving the entire aircraft, only the wings themselves are moved, in a circular motion. The helicopter's rotor can simply be regarded as rotating wings (hence the military appellation of "rotary wing aircraft"). lift

Conventional layout

There are several possible design layouts for arranging a helicopter's rotors. The most common design is the Sikorsky-layout, which is used by approximately 95% of all helicopters manufactured to date. It is as follows: turning the rotor generates lift but it also applies a reverse torque to the vehicle, which would spin the helicopter fuselage in the opposite direction to the rotor. At low speeds, the most common way to counteract this torque is to have a smaller vertical propeller mounted at the rear of the aircraft called a tail rotor. This rotor creates thrust which is in the opposite direction from the torque generated by the main rotor. When the thrust from the tail rotor is sufficient to cancel out the torque from the main rotor, the helicopter will not rotate around the main rotor shaft. The world's largest and smallest series-produced helicopters follow this principle. The Mil Mi-26 can lift 27 metric tons, the Robinson R22 has a crew of two and a gross weight of 1300 lbs (590 kg). Almost all civilian helicopters have the main rotor and tail rotor system. The world's fastest helicopter, the Westland Lynx can perform aerobatic loops and rolls with this conventional rotor system. aerobatic (Poland)]] Sometimes the blades of a tail rotor are not separated by the same angle, but laid out in an X-shape, which is supposed to reduce the noise levels for military use (e.g. AH-64 Apache). If the tail rotor is shrouded (i.e., a fan embedded in the vertical tail) it is called a fenestron. The fenestron rotor system on the model EC120 helicopter uses a shaft driven system and gearbox to turn the fan. It is less efficient but the advantages are that less noise is generated, it's safer for people that may walk near it and there is less chance of the blades being damaged by objects because it's shrouded, unlike the traditional tail rotor. Other helicopters use a Notar (an acronym meaning no tail rotor) design: they blow air through a long slot along the tail boom, utilizing the Coanda effect to produce forces to counter the torque. Notars adjust thrust by opening and closing a sliding circular cover near the end of the tail boom. The amount of power required to prevent a helicopter from spinning is significant. A tail rotor can use up to 30% of the engine's power, and this power does not help the helicopter produce lift or forward motion. To reduce this waste during cruise, the vertical stabilizer is often angled to produce a force which helps counter the main rotor torque. At high speeds, it is possible for the vertical stabilizer to counteract the entire torque, leaving more power available for forward flight. This is commonly known as slip-streaming and can make hovering turns difficult on windy days. Another reason for the angled vertical stabilizer is to make it possible to stage a successful high-speed, run-on landing, in case of the tail rotor failure or damage. Many military helicopters, especially attack types, have short wings called stub wings to add lift during forward motion. They are also used as external mounts for weapons. In extreme cases, such as that of the Mil Mi-24, the wings are large enough to obstruct airflow down from the rotors, making the helicopter all but unable to hover.

Alternative layouts

Mil Mi-24]] There are alternatives to Sikorsky's layout, which save the weight of a tail boom and rotor. Such design

Lighter than air

Derivation

Low pressure

High temperature

Low molecular mass

See also

External links

Aircraft

Categories and classification

Heavier than air

Lighter than air

Types of aircraft

By design

By propulsion

By usage

Military aircraft

Civil aviation

Related topics

External links

Air

Composition of air

See also

External link

Density

Other units

Measurement of density

Density of substances

See also

Balloon (aircraft)

Types of balloon aircraft

History

Balloons as flying machines

Balloons in the military

See also

Airship

Types

History

Airship Pioneers

Airships in the First World War

Airships in the Inter-war period

Airships in the Second World War

Continued use

Present-day research

Fiction

See also

References

External links

General

Associations

Historical

Manufacturers and commercial operators

Experiments, prototypes and one-offs

Designs under development

Proposed designs

Aerostat

Aerostats in Science Fiction

Helicopter

Applications

History

Generating lift

Conventional layout

Alternative layouts