29835987 Role of Aerostats

Role of Aerostats

CHAPTER 1

INTRODUCTION

1.1 INTRODUCTION TO AIRCRAFTS:

An aircraft is a vehicle which is able to fly by being supported by the air, or in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift (as with balloons, blimps and dirigibles) or by using the dynamic lift of an airfoil (as with vehicles that plane the air with wings in a straight manner, such as airplanes and gliders, or vehicles that generate lift with wings in a rotary manner, such as helicopters or gyrocopters), or a thrust lift from jet engines.

Although rockets and missiles also travel through the atmosphere, most are not considered aircraft because they use rocket thrust instead of aerodynamics as the primary means of lift. However, rocket planes and cruise missiles are considered aircraft if they rely on lift from the air.

The human activity which surrounds aircraft is called aviation. Manned aircraft are flown by an onboard pilot. Unmanned aerial vehicles may be remotely controlled or self-controlled by onboard computers. Target drones are an example of UAVs.

1.2 CLASSIFICATION OF AIRCRAFTS:

FIG 1.1 Classification of aircrafts

Vindhya.V.S, 1GA05ME058, Dept of Mechanical Engineering

AIRCRAFTS

By method of lift By propulsion By use

MilitaryLighter than air-

aerostatsHeavier than air

-aerodynes

Fixed wing

Rotor craft

Other methods of lift

Powered Un powered

Propellers

Jet

Other methods of propulsion

Helicopters

Gliders

Balloons

Kites

Civil

Experimental

Model

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Role of Aerostats

1.21 BY METHOD OF LIFT:

Aircraft fall into two broad categories: Lighter-than-air, called aerostats, and heavier-than-air, called aerodynes.

LIGHTER THAN AIR- AEROSTATS:

FIG 1.2 Hot air balloons

Aerostats use buoyancy to float in the air in much the same way that ships float on the water. They are characterized by one or more large gasbags or canopies, filled with a relatively low density gas such as helium, hydrogen or hot air, which is less dense than the surrounding air. When the weight of this is added to the weight of the aircraft structure, it adds up to the same weight as the air that the craft displaces.

Small hot air balloons called sky lanterns date back to the 3rd century BC, and were only the second type of aircraft to fly, the first being kites.

Originally, a balloon was any aerostat, while the term airship was used for large, powered aircraft designs – usually fixed-wing though none had yet been built. The advent of powered balloons, called dirigible balloons, and later of rigid hulls allowing a great increase in size, began to change the way these words were used. Huge powered aerostats, characterized by a rigid outer framework and separate aerodynamic skin surrounding the gas bags, were produced, the Zeppelins being the largest and most famous. There were still no fixed-wing aircraft or non-rigid balloons large enough to be called airships, so "airship" came to be synonymous with these aircraft. Then several


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accidents, such as the Hindenburg disaster in 1937, led to the demise of these airships. Nowadays a "balloon" is an unpowered aerostat, whilst an "airship" is a powered one.

A powered, steerable aerostat is called a dirigible. Sometimes this term is applied only to non-rigid balloons, and sometimes dirigible balloon is regarded as the definition of an airship (which may then be rigid or non-rigid). Non-rigid dirigibles are characterized by a moderately aerodynamic gasbag with stabilizing fins at the back. These soon became known as blimps. During the Second World War, this shape was widely adopted for tethered balloons; in windy weather, this both reduces the strain on the tether and stabilizes the balloon. The nickname blimp was adopted along with the shape. In modern times any small dirigible or airship is called a blimp, though a blimp may be unpowered as well as powered.

HEAVIER THAN AIR- AERODYNES:

FIG 1.3 Different types of fixed wing aircraft

Heavier-than-air aircraft must find some way to push air or gas downwards, so that a reaction occurs (by Newton's laws of motion) to push the aircraft upwards. This dynamic movement through the air is the origin of the term aerodyne. There are two ways to produce dynamic up thrust: aerodynamic lift, and powered lift in the form of engine thrust.

Aerodynamic lift is the most common, with fixed-wing aircraft being kept in the air by the forward movement of wings, and rotorcraft by spinning wing-shaped rotors sometimes called rotary wings. A wing is a flat, horizontal surface, usually shaped in cross-section as an aerofoil. To fly, air must flow over the wing and generate lift. A flexible wing is a wing made of fabric or thin sheet material, often stretched over a rigid frame. A kite is tethered to the ground and relies on the speed of the wind over its wings, which may be flexible or rigid, fixed or rotary.

With powered lift, the aircraft directs its engine thrust vertically downwards.

The initialism VTOL (vertical take off and landing) is applied to aircraft that can take off and land vertically. Most are rotorcraft. Others, such as the Hawker Siddeley Harrier, take off and land vertically using powered lift and transfer to aerodynamic lift in steady


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flight. Similarly, STOL stands for short take off and landing. Some VTOL aircraft often operate in a short take off/vertical landing mode known as STOVL.

A pure rocket is not usually regarded as an aerodyne, because it does not depend on the air for its lift (and can even fly into space); however, many aerodynamic lift vehicles have been powered or assisted by rocket motors. Rocket-powered missiles which obtain aerodynamic lift at very high speed due to airflow over their bodies, are a marginal case.

Fixed-Wing Aircraft:Airplanes or aero planes are technically called fixed-wing aircraft.The forerunner of the fixed-wing aircraft is the kite. Whereas a fixed-wing aircraft relies on its forward speed to create airflow over the wings, a kite is tethered to the ground and relies on the wind blowing over its wings to provide lift. Kites were the first kind of aircraft to fly, and were invented in China around 500 BC. Much aerodynamic research was done with kites before test aircraft, wind tunnels and computer modeling programs became available.

The first heavier-than-air craft capable of controlled free flight were gliders. A glider designed by Cayley carried out the first true manned, controlled flight in 1853.

Besides the method of propulsion, fixed-wing aircraft are generally characterized by their wing configuration. The most important wing characteristics are:

• Number of wings – Monoplane, biplane, etc.• Wing support – Braced or cantilever, rigid or flexible.• Wing plan form – including aspect ratio, angle of sweep and any variations along

the span (including the important class of delta wings).• Location of the horizontal stabilizer, if any.• Dihedral angle – positive, zero or negative (anhedral).

A variable geometry aircraft can change its wing configuration during flight.

A flying wing has no fuselage, though it may have small blisters or pods. The opposite of this is a lifting body which has no wings, though it may have small stabilizing and control surfaces.

Most fixed-wing aircraft feature a tail unit or empennage incorporating vertical, and often horizontal, stabilizing surfaces.

Seaplanes are aircraft that land on water, and they fit into two broad classes: Flying boats are supported on the water by their fuselage. A float plane's fuselage remains clear of the water at all times, the aircraft being supported by two or more floats attached to the fuselage and/or wings. Some examples of both flying boats and float planes are amphibious, being able to take off from and alight on both land and water.


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Role of Aerostats

Some people consider wing-in-ground-effect vehicles to be fixed-wing aircraft, others do not. These craft "fly" close to the surface of the ground or water. An example is the Russian ekranoplan (nicknamed the "Caspian Sea Monster"). Man-powered aircraft also rely on ground effect to remain airborne, but this is only because they are so underpowered—the airframe is theoretically capable of flying much higher.

Rotorcraft:

FIG 1.4 Rotodyne

Rotorcraft, or rotary-wing aircraft, uses a spinning rotor with aerofoil section blades (a rotary wing) to provide lift. Types include helicopters, autogyros and various hybrids such as gyrodynes and compound rotorcraft.Helicopters have powered rotors. The rotor is driven (directly or indirectly) by an engine and pushes air downwards to create lift. By tilting the rotor forwards, the downwards flow is tilted backwards, producing thrust for forward flight.

Autogyros or gyroplanes have unpowered rotors, with a separate power plant to provide thrust. The rotor is tilted backwards. As the autogyro moves forward, air blows upwards through it, making it spin.(cf. Autorotation).

US-Recognition Manual (very likely copy of German drawing)This spinning dramatically increases the speed of airflow over the rotor, to provide lift. Juan de la Cierva (a Spanish civil engineer) used the product name autogiro, and Bensen used gyrocopter. Rotor kites, such as the Focke Achgelis Fa 330 are unpowered autogyros, which must be towed by a tether to give them forward ground speed or else be tether-anchored to a static anchor in a high-wind situation for kited flight.

Gyrodynes are a form of helicopter, where forward thrust is obtained from a separate propulsion device rather than from tilting the rotor. The definition of a 'gyrodyne' has changed over the years, sometimes including equivalent autogyro designs. The most important characteristic is that in forward flight air does not flow significantly either up or down through the rotor disc but primarily across it. The Heliplane is a similar idea.

Compound rotorcrafts have wings which provide some or all of the lift in forward flight. Compound helicopters and compound autogyros have been built, and some forms of gyroplane may be referred to as compound gyroplanes. Tiltrotor aircraft (such as the V-22 Osprey) have their rotors horizontal for vertical flight, and pivot the rotors vertically


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Role of Aerostats

like a propeller for forward flight. The Coleopter had a cylindrical wing forming a duct around the rotor. On the ground it sat on its tail, and took off and landed vertically like ahelicopter. The whole aircraft would then have tilted forward to fly as a propeller-driven aeroplane using the duct as a wing (though this transition was never achieved in practice).

Some rotorcraft have reaction-powered rotors with gas jets at the tips, but most have one or more lift rotors powered from engine-driven shafts.

OTHER METHODS OF LIFT:

• A lifting body is the opposite of a flying wing. In this configuration the aircraft body is shaped to produce lift. If there are any wings, they are too small to provide significant lift and are used only for stability and control. Lifting bodies are not efficient: they suffer from high drag, and must also travel at high speed to generate enough lift to fly. Many of the research prototypes, such as the Martin-Marietta X-24, which led up to the Space Shuttle were lifting bodies (though the shuttle itself is not), and some supersonic missiles obtain lift from the airflow over a tubular body. The flat bodies of recent jet fighters also produce lift, as in the F-14 Tomcat's "pancake".

• Powered lift types rely on engine-derived lift for vertical takeoff and landing (VTOL). Most types transition to fixed-wing lift for horizontal flight. Classes of powered lift types include VTOL jet aircraft (such as the Harrier jump-jet) and tiltrotors (such as the V-22 Osprey), among others. A few examples rely entirely on engine thrust to provide lift throughout the flight. There are few practical applications. Experimental designs have been built for personal fan-lift hover platforms and jetpacks or for VTOL research (for example the flying bedstead).

• The FanWing is a recent innovation and represents a completely new class of aircraft. This uses a fixed wing with a cylindrical fan mounted spanwise just above. As the fan spins, it creates an airflow backwards over the upper surface of the wing, creating lift. The fan wing is (2005) in development in the United Kingdom.

1.22 BY PROPULSION

UNPOWERED:

Gliders:Heavier-than-air unpowered aircraft such as gliders (i.e. sailplanes), hang gliders and Para gliders, and other gliders usually do not employ propulsion once airborne. Take-off may be by launching forwards and downwards from a high location, or by pulling into the air on a tow-line, by a ground-based winch or vehicle, or by a powered "tug" aircraft. For a glider to maintain its forward air speed and lift, it must descend in relation to the air (but not necessarily in relation to the ground). Some gliders can 'soar'- gain height from


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Role of Aerostats

updrafts such as thermal currents. The first practical, controllable example was designed and built by the British scientist and pioneer George Cayley, who many recognize as the first aeronautical engineer. Balloons: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). A wing-shaped hybrid balloon can glide directionally when rising or falling; but a spherically shaped balloon does not have such directional control.

Kites:Kites are aircraft that are tethered to the ground or other object (fixed or mobile) that maintains tension in the tether or kite line; they rely on virtual or real wind blowing over and under them to generate lift and drag. Kytoons are balloon kites that are shaped and tethered to obtain kiting deflections, and can be lighter-than-air, neutrally buoyant, or heavier-than air.

POWERED:

Propellers:A propeller or airscrew comprises a set of small, wing-like aero foils set around a central hub which spins on an axis aligned in the direction of travel. Spinning the propeller creates aerodynamic lift, or thrust, in a forward direction.

A tractor design mounts the propeller in front of the power source, while a pusher design mounts it behind. Although the pusher design allows cleaner airflow over the wing, tractor configuration is more common because it allows cleaner airflow to the propeller and provides a better weight distribution. A contra-prop arrangement has a second propeller close behind the first one on the same axis, which rotates in the opposite direction. A variation on the propeller is to use many broad blades to create a fan. Such fans are traditionally surrounded by a ring-shaped fairing or duct, as ducted fans. Many kinds of power plant have been used to drive propellers.

The earliest designs used man power to give dirigible balloons some degree of control, and go back to Jean-Pierre Blanchard in 1784. Attempts to achieve heavier-than-air man-powered flight did not succeed fully until Paul MacCready's Gossamer Condor in 1977.The first powered flight was made in a steam-powered dirigible by Henri Giffard in 1852. Attempts to marry a practical lightweight steam engine to a practical fixed-wing airframe did not succeed until much later, by which time the internal combustion engine was already dominant.

From the first controlled powered fixed-wing aircraft flight by the Wright brothers until World War II, propellers turned by the internal combustion piston engine were virtually the only type of propulsion system in use. The piston engine is still used in the majority


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Role of Aerostats

of smaller aircraft produced, since it is efficient at the lower altitudes and slower speeds suited to propellers.

Turbine engines need not be used as jets (see below), but may be geared to drive a propeller in the form of a turboprop. Modern helicopters also typically use turbine engines to power the rotor. Turbines provide more power for less weight than piston engines, and are better suited to small-to-medium size aircraft or larger, slow-flying types. Some turboprop designs (see below) mount the propeller directly on an engine turbine shaft, and are called propfans.

Since the 1940s, propellers and propfans with swept tips or curved "scimitar-shaped" blades have been studied for use in high-speed applications so as to delay the onset of shockwaves, in similar manner to wing sweepback, where the blade tips approach the speed of sound. The Airbus A400M turboprop transport aircraft is expected to provide the first production example: note that it is not a propfan because the propellers are not mounted direct on the engine shaft but are driven through reduction gearing.

Other less common power sources include:

• Electric motors often linked to solar panels to create a solar-powered aircraft.• Rubber bands, wound many times to store energy, are mostly used for flying

models.

Jet:

FIG 1.5 Jet Engined Boeing 777

Air-breathing jet engines provide thrust by taking in air, burning it with fuel in a combustion chamber, and accelerating the exhaust rearwards so that it ejects at high speed. The reaction against this acceleration provides the engine thrust.

Jet engines can provide much higher thrust than propellers, and are naturally efficient at higher altitudes, being able to operate above 40,000 ft (12,000 m). They are also much more fuel-efficient at normal flight speeds than rockets. Consequently, nearly all high-speed and high-altitude aircraft use jet engines.


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Role of Aerostats

The early turbojet and modern turbofan use a spinning turbine to create airflow for takeoff and to provide thrust. Many, mostly in military aviation, use afterburners which inject extra fuel into the exhaust.Use of a turbine is not absolutely necessary: other designs include the crude pulse jet, high-speed ramjet and the still-experimental supersonic-combustion ramjet or scramjet.These designs require an existing airflow to work and cannot work when stationary, so they must be launched by a catapult or rocket booster, or dropped from a mother ship.

The bypass turbofan engines of the Lockheed SR-71 were a hybrid design – the aircraft took off and landed in jet turbine configuration, and for high-speed flight the afterburner was lit and the turbine bypassed, to create a ramjet.

The motorjet was a very early design which used a piston engine in place of the combustion chamber, similar to a turbocharged piston engine except that the thrust is derived from the turbine instead of the crankshaft. It was soon superseded by the turbojet and remained a curiosity.

Helicopters:

FIG 1.6 Helicopters

The rotor of a helicopter, may, like a propeller, be powered by a variety of methods such as an internal-combustion engine or jet turbine. Tip jets, fed by gases passing along hollow rotor blades from a centrally mounted engine, have been experimented with. Attempts have even been made to mount engines directly on the rotor tips.

Helicopters obtain forward propulsion by angling the rotor disc so that a proportion of its lift is directed forwards to provide thrust.

Others methods of propulsion:• Rocket-powered aircraft have occasionally been experimented with, and the

Messerschmitt Komet fighter even saw action in the Second World War. Since then they have been restricted to rather specialized niches, such as the Bell X-1 which broke the sound barrier or the North American X-15 which traveled up into space where no oxygen is available for combustion (rockets carry their own oxidant). Rockets have more often been used as a supplement to the main power plant, typically to assist takeoff of heavily loaded aircraft, but also in a few experimental designs such as the Saunders-Roe SR.53 to provide a high-speed dash capability.


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• The flapping-wing ornithopter is a category of its own. These designs may have potential, but no practical device has been created beyond research prototypes, simple toys, and a model hawk used to freeze prey into stillness so that it can be captured.

1.3 BY USE:

The major distinction in aircraft types is between military aircraft, which includes not just combat types but many types of supporting aircraft, and civil aircraft, which include all non-military types.

Military:

FIG 1.7 HAL Dhruv helicopterA military aircraft is any fixed-wing or rotary-wing aircraft that is operated by a legal or insurrectionary armed service of any type. Military aircraft can be either combat or non-combat:

• Combat aircraft are aircraft designed to destroy enemy equipment using its own armament.

• Non-Combat aircraft are aircraft not designed for combat as their primary function, but may carry weapons for self-defense. Mainly operating in support roles.

Combat aircraft divide broadly into fighters and bombers, with several in-between types such as fighter-bombers and ground-attack aircraft (including attack helicopters).Other supporting roles are carried out by specialist patrol, search and rescue, reconnaissance, observation, transport, training and Tanker aircraft among others.

Many civil aircraft, both fixed-wing and rotary, 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 the UK and the Commonwealth. Even the small fabric-covered two-seater Piper J3 Cub had a military version, the L-4 liaison, observation and trainer aircraft. 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 military gliders were used during World War II to land troops.

Civil:Civil aircraft divide into commercial and general types, however there are some overlaps.


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Commercial:Commercial aircraft include types designed for scheduled and charter airline flights, carrying both passengers and cargo. The larger passenger-carrying types are often referred to as airliners, the largest of which are wide-body aircraft. Some of the smaller types are also used in general aviation, and some of the larger types are used as VIP aircraft.

General aviation:General aviation is a catch-all covering other kinds of private and commercial use, and involving a wide range of aircraft types such as business jets (bizjets), trainers, homebuilt, aerobatic types, racers, gliders, warbirds, firefighters, medical transports, and cargo transports, to name a few. The vast majority of aircraft today are general aviation types.

Within general aviation, there is a further distinction between private aviation (where the pilot is not paid for time or expenses) and commercial aviation (where the pilot is paid by a client or employer). The aircraft used in private aviation are usually light passenger, business, or recreational types, and are usually owned or rented by the pilot. The same types may also be used for a wide range of commercial tasks, such as flight training, pipeline surveying, passenger and freight transport, policing, crop dusting, and medical evacuations. However the larger, more complex aircraft are more likely to be found in the commercial sector.

For example, piston-powered propeller aircraft (single-engine or twin-engine) are common for both private and commercial general aviation, but for aircraft such as turboprops like the Beech craft King Air and helicopters like the Bell Jet Ranger, there are fewer private owners than commercial owners. Conventional business jets are most often flown by paid pilots, whereas the new generations of smaller jets are being produced for private pilot

Experimental:Experimental aircrafts are one-off specials, built to explore some aspect of aircraft design and with no other useful purpose. The Bell X-1 rocket plane, which first broke the sound barrier in level flight, is a famous example.

The formal designation of "experimental aircraft" also includes other types which are "not certified for commercial applications", including one-off modifications of existing aircraft such as the modified Boeing 747 which NASA uses to ferry the space shuttle from landing site to launch site, and aircraft homebuilt by amateurs for their own personal use.

Model:A model aircraft is a small unmanned type made to fly for fun, for static display, for aerodynamic research (Reynolds number) or for other purposes. A scale model is a replica of some larger design.


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Role of Aerostats

CHAPTER 2

INTRODUCTION TO AEROSTATS

2.1 INTRODUCTION

An aerostat is a lighter than air object that can stay stationary in the air. Aerostats include free balloons, airships, moored balloons and tethered Helikites. An aerostat's main structural component is its envelope, a lightweight skin containing a lifting gas to provide buoyancy, to which other components are attached.Aerostats are so named because they use "aerostatic" lift which is a buoyant force that does not require movement through the surrounding air mass. This contrasts with aerodynes that primarily use aerodynamic lift which requires the movement of at least some part of the aircraft through the surrounding air mass.However, in reality most aerostats (except spherical balloons) obtain lift from both aerodynamic lift and pure gas lift at some time or other.The word aerostat was originally French and is derived from the Greek aer (air) + statos (standing).

2.2 TYPES OF AEROSTATS

1) Moored balloons: They are systems that are connected to the surface via one or more tethers. In contrast to the other types of aerostats, moored balloons are non-free flying. Some moored balloons obtain aerodynamic lift via the contours of their envelope or through the use of fins or other appropriately shaped surfaces (e.g. Helikites.)

2) Free balloons – They are Free-flying buoyant aircraft that move by being carried along by the wind. Types of free balloons include hot air balloons and gas balloons.

3) Airships – They are Free-flying buoyant aircraft that can be propelled and steered. Some airships obtain aerodynamic lift via the shape of their envelope or through the addition of fins or other shape. These types of craft are called hybrid airships.

FIG 2.1 Moored Balloons FIG 2.2 Airships


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2.3 HISTORY OF AEROSTATS

FIG 2.3 Montgolfier brothers’ first hot air balloon

The first enunciation of the principles on which aerial navigation must depend was by Roger Bacon, in the twelfth century. This indefatigable student had discovered that air possesses weight, and he therefore conceived that if a hollow globe of thin brass were filled with “liquid fire or ethereal air" it would float in the atmosphere as a hollow vessel floats upon water. To what he referred by liquid fire and ethereal air can not be determined; but these are generally known as akhemistic terms for rarefied air. But Bacon made no attempt to sustain his theory. It therefore fell into oblivion, and we hear of no efforts in this direction until the middle of the eighteenth century, when Cavallo experimented rather unsuccessfully with hydrogen.

In 1782, Stephen and Joseph Montgolfier, wealthy paper manufacturers at Annonay, noting that clouds and smoke rise in the air, concluded that a bag, made of light material, would also rise if inflated with 6inoke or some similarly expanded substance. They therefore made a small balloon,* of fine paper, and filled it with rarefied air by a fire of chopped wool and straw kindled underneath. When fully inflated, the apparatus rose with such ease that the brothers were encouraged to exhibit the discovery on a much larger scale. On this occasion a linen bag, twenty-five feet in diameter, was used. It rose rapidly to a height of one thousand feet, and, after some time, fell at a distance of three miles from its starting point. The discovery now attracted the attention of the French Academy,


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at whose request the brothers went to Paris, and there constructed a new balloon, seventy-four feet by forty-one, elegantly ornamented, and weighing one thousand pounds. When released from the ropes, this, with a load of five, hundred pounds, reached an elevation of one thousand five hundred feet, where, unfortunately, a gust of wind overturned it, and caused such material injury that a new machine was necessary for further experiments. The investigations of the French Academy appeared to prove that man could, by means of the new discovery, navigate the atmosphere; and it was not long before persons of sufficient daring were found to undertake aerial voyages. Montgolfier having offered to make a balloon of more durable texture, M. Pilatre de Rozier consented to be the first aeronaut. The new machine was seventy-four feet by forty-eight, weighed about one thousand two hundred pounds, and was ornamented with the zodiacal signs and the royal insignia. In this M. Pilatre made several ascensions, and on one occasion, accompanied by the Marquis d'Arlandes, attained a height of three thousand feet, and descended about five miles from Paris.

Ascensions in the Montgolfier balloons were always dangerous, and were never very extensive. To remedy these defects, Dr. Black recommended hydrogen as a substitute for rarefied air. Acting upon his suggestions, the French Academy employed Messrs. Roberts to construct, under the supervision of Prof. Charles, a silken balloon, thirteen feet in diameter. When set free, this almost instantly attained a height of three thousand feet, and, after remaining suspended for three quarters of an hour, descended fifteen miles from Paris. This experiment was so successful, that a larger balloon, of twenty-seven feet diameter, was immediately made. In this, on December 1st, 1785, Prof. Charles with M. Roberts ascended six thousand feet, and, after an absence of one hour and three-quarters, descended twenty-seven miles from Paris. Here M. Roberts left the car, and, there being still some ascensive power, Prof. Charles re ascended, rising almost immediately nine thousand feet, and ultimately, by throwing over ballast, ten thousand feet. When he left the surface the thermometer stood at 51° F., bat in ten minutes it sank to 21°. When he started the sun had set, but when he attained the extreme height it was again visible. This ascension is important, as it first proved the existence of counter currents in the atmosphere.

FIG 2.4 Navigable Balloon Created by Giffard


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Role of Aerostats

In the same year M. Blanchard, with Dr. Jeffries, an American physician, crossed from Dover to Calais in two hours and one-half. The voyagers were several times in great danger, but especially when nearing the French coast. They were met with great consideration, and M. Blanchard received twelve thousand livres from the king. M. Pilatre de Rozier attempted to rival Blanchard by crossing in the opposite direction. In order to avoid the dangers encountered by the latter, he fastened a small Montgolfier balloon to the car. Scarcely had he risen three thousand feet, when the upper balloon took fire from the lower: a fearful explosion followed, and the aeronaut was soon afterwards found in a fearfully mangled condition. This was the first fatal accident—there have been many since.

Previous to 1821 few aerial voyages were made. The manufacture of hydrogen was expensive, and balloons were so clumsily constructed that none but foolhardy men would risk their lives in them. In that year Mr. Green, who during his life made more than two hundred ascensions, conceived that light carbureted hydrogen or illuminating gas, would answer equally well and be far less expensive. His experiments were successful, and gave a wonderful impetus to the science.


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CHAPTER 3

TYPES OF AEROSTATS

3.1 MOORED BALLONS

INTRODUCTION:

A moored balloon is an inflated fabric structure, often shaped like an airship and filled with a lifting gas such as helium or hot air, which is restrained by a cable attached to the ground or a vehicle. Moored balloons differ from airships and free balloons in that it is not free-flying.

Moored balloons are sometimes called aerostats. However, the term aerostat can also be used to refer to all lighter than air systems. In this broader sense of the term, moored balloons are a type of aerostat.

TYPES OF MOORED BALLOONS:

1) Spherical balloons generally without fins or other appendages to provide stability. These are most often are used to carry passengers or for advertising;

2) Elongated (i.e., "blimp-shaped") balloons usually with fins to provide aerodynamic stability;

3) Non-blimp shapes that use appendages for stability and/or secondary lift (e.g. Helikites).

Spherical balloons:Spherical balloons have the lowest surface-area-to-volume ratio and they lift well in low or no wind. However, unless they are very large, in most winds they quickly begin to be pushed to the ground. In light winds, very large rounded balloons are used to lift people for recreational flight.

Elongated balloons:Blimp-shaped balloons were originally designed as barrage balloons just before the First World War. Thousands of blimps were used in both world wars, but they have changed little in design since the First World War. The British L.Z. type of the Second World War was based upon the French Caquot type of 1915. A British L.Z. barrage was sent to the USA in 1942 where it was copied and became the ZK Type made by the Goodyear Tire & Rubber Company. Today most blimps are used for advertising in fair weather. Some massive blimps are used for lifting radar or surveillance cameras.

Blimps are more or less sausage-shaped, to reduce frontal area and wind resistance. They


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Role of Aerostats

have stern fins to keep the balloon pointing into the wind. When they are correctly made, blimps are more stable than spherical balloons; however, their large ratio of surface area to volume requires blimps to be large so that they can lift a sufficient payload to be efficient. Generally, blimps must be large also to cope with high winds. Their long, thin shape necessitates a device to equalize pressure in the envelope, called a ballonet, if they are to rise over 900 feet in altitude and to cope with large atmospheric temperature changes.

When set at an angle to the wind, blimps can produce aerodynamic lift especially from their stern fins. When blimps do this it is called "kiting". As the wind increases further this lift causes the stern to rise and the nose to lower. The low nose is further pushed down by the wind leading to an instability called "porpoising". To reduce porpoising the tethers are set to further raise the nose in high winds, however this increases the drag on the blimp causing the blimp to lose height and the tether to lay over to give "quatenary" problems. The handling and cost implications of the blimps large size means they are not commonly used by the general public. However, the military sometimes use large blimps for surveillance and radio relay due to their ability to stay in the air for long periods of time in reasonable weather.

Non-Blimp shaped balloons:

FIG 3.1 Helkite

Helikites are probably the most commonly used worldwide at present, with thousands produced each year. Helikites are generally very small compared to other aerostats and fly in all but the most extreme weathers. They are a combination of an oblate-spheroid balloon and a kite. Thus both the wind and helium push Helikites upwards so they can fly to 6000 ft with ease even with no ballonet. Helikites are very stable in foul and have introduced the concept of the "personal aerostat".

HISTORY OF MOORED BALLOONS:

Designed by Albert CAQUOT, French engineer, in 1914, the barrage balloons of World War I and World War II were examples of moored balloons.


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FIG 3.2 Barrage balloons used in world war 1 and world war 2

As early as 1901, already visionary, Albert Caquot performed his military service in an airship unit of the French army. At the beginning of First World War, he naturally led an airship unit as first lieutenant. He noticed the poor wind behavior of the spherical balloon. In 1914, he designed a new sausage-shaped dirigeable equipped with back stabilizers, able to hold in 90 km/h winds. This balloon is known as “Caquot dirigeable”. During three years, France manufactured "Caquot dirigeables" for all the allied forces, including English and United States armies. This balloon gave to France and its allies an advantage in military observation which significantly contributed to the allies’ supremacy in aviation and eventually to the final victory.

Barrage balloons were sometimes more trouble than they were worth. In 1942 Canadian and American forces began joint operations to protect the sensitive locks and shipping channel at Sault Ste. Marie along their common border among the Great Lakes against possible air attack. During severe storms in August and October of 1942 some barrage balloons broke loose, and the trailing cables short-circuited power lines, causing serious disruption to mining and manufacturing. In particular, the metals production vital to the war effort was disrupted. Canadian military historical records indicate that "The October incident, the most serious, caused an estimated loss of 400 tons of steel and 10 tons of Ferro-alloys."

Following these incidents new procedures were put in place, which included stowing the balloons during the winter months, with regular deployment exercises and a standby team on alert to deploy the balloons in case of attack.

Barrage balloons or moored balloons played a very important role in World War 1 and World War 2. Balloons were intended to defend against dive bombers flying at heights up to 5,000 feet (1500 m), forcing them to fly higher and into the range of concentrated anti-aircraft fire—anti-aircraft guns could not traverse fast enough to attack aircraft flying at low altitude and high speed. By the middle of 1940 there were 1,400 balloons, a third of them over the London area.


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3.2 FREE BALLOONS:

INTRODUCTION TO FREE BALLOONS:

FIG 3.3 Hot air balloons

A balloon is a type of aircraft that remains aloft due to its buoyancy. A balloon travels by moving with the wind. It is distinct from an airship, which is a buoyant aircraft that can be propelled through the air in a controlled manner.

The "basket" or capsule that is suspended by cables beneath a balloon and carries people, animals, or automatic equipment (including cameras and telescopes, and flight-control mechanisms) may also be called the gondola.

TYPES OF BALLON AIRCRAFT:

There are three main types of balloon aircraft:

• Hot air balloons obtain their buoyancy by heating the air inside the balloon. They are the most common type of balloon aircraft. "Hot air balloon" is sometimes used incorrectly to denote any balloon that carries people.

• Gas balloons are inflated with a gas of lower molecular weight than the ambient atmosphere. Most gas balloons operate with the internal pressure of the gas being the same as the pressure of the surrounding atmosphere. There is a type of gas balloon, called a super pressure balloon, which can operate with the lifting gas at pressure that exceeds the pressure of the surrounding air, with the objective of limiting or eliminating the loss of gas from day-time heating. Gas balloons are filled with gases such as:

o 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).

o Helium - the gas used today for all airships and most manned balloons.o Ammonia - used infrequently due to its caustic qualities and limited lift.o Coal gas - used in the early days of ballooning; it is highly flammable.

• Rozière 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.


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HISTORY OF BALLOONS:

Unmanned hot air balloons are popular in Chinese history. Zhuge Liang of the Shu Han kingdom, in the Three Kingdoms era (220-280 AD) used airborne lanterns for military signaling. These lanterns are known as Kong Ming lanterns (孔明灯).

FIG 3.4 Kong Ming lanterns

In 1710 in Lisbon, Bartolomeu de Gusmão made a balloon filled with heated air rise inside a room. He also made a balloon named Passarola (English: Big bird) and attempted to lift himself from Saint George Castle in Lisbon, but only managed to harmlessly fall about one kilometer away.

Following Henry Cavendish's 1766 work on hydrogen, Joseph Black proposed that a balloon filled with hydrogen would be able to rise in the air. The first recorded manned flight was made in a hot air balloon built by the Montgolfier brothers on November 21, 1783. The flight started in Paris and reached a height of 500 feet or so. The pilots, Jean-François Pilâtre de Rozier and François Laurent d'Arlandes, covered about 5 1/2 miles in 25 minutes.

Only a few days later, on December 1, 1783, Professor Jacques Charles and Nicholas Louis Robert made the first gas balloon flight, also from Paris. Their hydrogen-filled balloon flew to almost 2,000 feet (600 m), stayed aloft for over 2 hours and covered a distance of 27 miles (43 km), landing in the small town of Nesles-la-Vallée.

The first military use of a balloon was at the Battle of Fleurus in 1794, when L'Entreprenant was used by the French Aerostatic Corps to watch the movements of the enemy. On April 2, 1794, an aeronauts corps was created in the French army; however, given the logistical problems linked with the production of hydrogen on the battlefield (it


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required constructing ovens and pouring water on white-hot iron), the corps was disbanded in 1799.

3.3 AIRSHIPS:

INTRODUCTION TO AIRSHIPS:

FIG 3.5 Zeppelin NT Airships

An airship or dirigible is a "lighter-than-air aircraft" that can be steered and propelled through the air using rudders and propellers or other thrust. Unlike other aerodynamic aircraft such as fixed-wing aircraft and helicopters, which produce lift by moving a wing, or airfoil, through the air, aerostatic aircraft, such as airships and hot air balloons, stay aloft by filling a large cavity, such as a balloon, with a lifting gas.

TYPES OF AIRSHIPS:

• Non-rigid airships (blimps) use a pressure level in excess of the surrounding air pressure to retain their shape during flight.

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.

Rigid airships (Zeppelin is almost synonymous with this type) 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 and can be made to virtually any size.

Metal-clad airships were of two kinds: rigid and non-rigid. Each kind used a thin gastight metal envelope, rather than the usual rubber-coated fabric envelope. Only four metal-clad ships are known to have been built, and only two actually flew: Schwarz's first aluminum rigid airship of 1893 collapsed, while his second flew; the non-rigid ZMC-2 flew 1929 to 1941; while the 1929 non-rigid Slate "City of Glendale" collapsed on its first flight attempt.

Thermal airships use a heated lifting gas, usually air, in a fashion similar to hot air balloons.

HISTORY OF AIRSHIPS:


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FIG 3.6 Blanchard crossing the English Channel

The father of the dirigible was Lieutenant Jean Baptiste Marie Meusnier (1754–93). On 3 December 1783, he presented a historic paper to the French Academy: "Memoire sur l'equilbre des Machines Aerostatique" (Memorandum on the balance of aerostatic machines). The 16 water-color drawings published the following year depicted a 260-foot-long (79 m) envelope with internal ballonets that could be used for regulating lift, and this was attached to a long carriage that could be used as a boat if the vehicle was forced to land in water. The airship was designed to be propelled in the air by three airscrew propellers and steered with a sail-like aft rudder. In 1784, Jean-Pierre Blanchard fitted a hand-powered propeller to a balloon, the first recorded means of propulsion carried aloft. In 1785, he crossed the English Channel with a balloon equipped with flapping wings for propulsion, and a bird-like tail for steerage.

In March 1851,Dr William Bland sent designs for his 'Atomic Airship' to the Great Exhibition at the Crystal Palace in London where a model was displayed. His idea was to supply power to an elongated balloon with a steam engine installed in a car. Bland believed that with two airscrews the machine could be driven at 80 km/h (50 mph) and could fly from Sydney to London in less than a week. The first person to make an engine-powered flight was Henri Giffard who, in 1852, flew 27 km (17 mi) in a steam-powered airship. Paul Haenlein flew an airship with an internal combustion engine running on the coal gas used to inflate the envelope over Vienna, the first use of such an engine to power an aircraft in 1872. The first fully controllable free-flight was made in a French Army airship, La France, by Charles Renard and Arthur Constantin Krebs in 1884. In 1884 and 1885, it made seven flights.

The "Golden Age of Airships" began in July 1900 with the launch of the Luftschiff Zeppelin LZ1. This led to the most successful airships of all time: the Zeppelins. These were named after Count von Zeppelin who began experimenting with rigid airship designs in the 1890s. At the beginning of World War I the Zeppelin airships had a framework composed of triangular lattice girders, covered with fabric and containing separate gas cells. Multi-plane, later cruciform, 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.

Although airships are no longer used for passenger transport, they are still used for other purposes such as advertising, sightseeing, surveillance and research. CHAPTER 4


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ROLE OF AEROSTATS

4.1 AEROSTATS USED FOR POWER GENERATION:

4.11 SOLAR POWER:

DISADVANTAGES OF PRESENT SYSTEM:

The development of new and cost effective methods to harness renewable energy has become crucial to maintain the energy supply which underpins our society, and solar power is one of the main candidates to make a substantial contribution to fulfill our future energy requirements.One of the major issues in the use of ground based photovoltaic panels to harvest solar power is the relatively low energy density available which is compounded by the fact that the power output of the devices is strongly dependent on the latitude and weather conditions.These factors have particularly hindered the diffusion of photovoltaic (PV) in several countries with cloudy climates (e.g. North European Countries). On the other hand, areaswith high solar irradiations (e.g. African deserts) are remote from most users and the losses over thousands of miles of cables and the political issues entailed in such a large project, severely reduce the economic advantages.

CONCEPTS TO OVERCOME PRESENT SYSTEM DISAVANTAGES:

A completely different approach was proposed by Glaser in the 1970s, and his idea has captured the imagination of scientists up to this day. The basic concept was to collect solar energy using a large satellite (that would be able to capture the full strength of the solar radiation continuously), and transmit it to the ground using microwave radiation. The receiving station would then convert the microwave radiation into electric energy to be made available to the users. The original concept was revisited in 1995 in view of the considerable technological advances made since the 70s, and research work on this concept is still ongoing. However a mixture of technical issues (such as the losses in the energy conversions and transmission), safety concerns (regarding the microwave beam linking the satellite with the ground station), and cost, have denied the practical implementation of this concept. The latter is a substantial hurdle as the development of Satellite Solar Power (SSP) cannot be carried out incrementally, in order to recover part of the initial cost during the development, and use it to fund the following steps, but it requires substantial funding upfront before there is any economical return.


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FIG 4.1 Illustration of aerostat used for solar power generation

As a compromise between Glaser’s (SSP) and ground based PV devices, concept to collect the solar energy using a high altitude aerostatic platform was established. This approach allows most of the issues related to the weather condition to be overcome, as the platform will be above the clouds except for very extreme weather situations. At the same time, as the platform is above the densest part of the troposphere, the sun beam will travel though considerably less air mass than if it was on the ground (in particular for early morning and evening) and this will further improve the energy output. Therefore this method enables considerably more solar power to be collected than on the ground .In addition, the mooring line of the platform can be used to transmit the electric energy to the ground in relative safety and with low electrical losses. Although this approach enables between 1/3 and 1/2 of the energy that could be harvested using a SSP, the cost of the infrastructure is orders of magnitude lower, and this approach allows an incremental development with a cost to first power that is a few orders of magnitudes smaller than that necessary for SSP.Most researchers up till now have proposed harvesting energy at high altitude by exploiting the strong winds existing in the high atmosphere by using Flying Electrical Generators, that are essentially wind turbines collecting wind power at altitudes from few hundred meters to 10 km or more kilometers altitude (to exploit the powerful jet stream currents).The extraction of this energy using the type of machines proposed for example by Roberts in is relatively complex in mechanical terms.

DISAVANTAGES OF THE CONCEPT:

One of the issues is that in low wind the machine (that is heavier then air) needs to reverse its energy flow and take energy from the ground to produce enough lift to support itself and the tether. Alternative designs like the MAGENN in overcome this problem


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using a lighter-than-air approach so that the buoyancy keeps it in flight all the time. However the mechanical complications are still considerable.

4.12 WIND ENERGY

Modern society depends heavily on the availability of efficient energy resources. Unfortunately, the major sources of energy are from depleting nonrenewable reserves such as coal and oil. Among the possibilities for renewable energy are solar, hydroelectricity, wind, and biomass energy sources. However, many of these new technologies centre on incremental improvements to the energy problem, making it difficult to foresee an era when humankind will sever its ties to nonrenewable energy sources. One source of energy that has received significant attention from humans over the years is wind. The extraction of energy from the wind dates back hundreds of years, and is most commonly associated with windmills for pumping water or grinding grain by generating rotational motion from an array of blades. Typical windmills and wind turbines, beginning with the Hallady-Perry windmill design of the 1920s and 1930s, have been continually refined, altered, and developed over the decades in attempts to improve efficiency. This has often only created small improvements in the system output. These systems have evolved modestly to modern wind turbine systems.

DISADVANTAGES OF THE PRESENT SYSTEM:

The modern wind turbine systems have basically reached the peak of their capability. At best, current ground-based wind turbine technology can only supplement a small fraction of the total energy grid. This is due to a number of contributing factors: 1) the variability of the wind source at low altitudes, 2) the costs of constructing wind farms, and 3) the small power output from individual wind turbines. These three factors combine to give a relatively inefficient power generation method compared to the need for large-scale power production. Furthermore, the size of onshore wind farms is limited by the production of noise.

CONCEPTS TO OVERCOME PRESENT SYSTEM DISAVANTAGES:

The need alleviate some of the deficiencies has spawned a significant number of proposals for wind turbines placed at high altitudes where the wind energy source is more powerful and more consistent. The prevalence of wind at altitude is due to the fact that the Earth’s surface creates a boundary layer effect so that winds generally increase with altitude according to a power-law at low-altitudes. The true wind patterns depend on a complex interaction of solar flux, the Earth’s rotation, and a variety of other factors so that winds at higher altitudes are generally present even when the wind at ground level may be nonexistent.


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The idea of using airborne windmills for electricity generation was investigated at least as far back as the 1930’s. The company Sheldahl, Inc. placed a French-made generator on a tethered balloon in the late 1960s and generated about 350 Watts of power. Riegler and Riedler proposed the idea of using a turbine wind generator mounted on a tethered balloon or aerostat. Six symmetrically arranged wind turbines (double bladed, horizontal axis turbines) were proposed to be attached to the balloon just behind its center of gravity. To keep a wind generator aloft, it may be more desirable to keep the system at altitude using lift generated from the aerostat. Tethered aerostats require lift provided by the helium inside the aerostat. In the presence of wind, extra lift is provided due to aerodynamics. To make the design very efficient for generating lift at high altitude, it may also be possible to augment the aerostat with a fixed wing. According to Riegler and Reidler, balloons up to 200000 m3 are almost certainly feasible, whereas higher volumes will require further research and development. An alternative concept was proposed by Ockels, where power is generated by a series of high-lifting wings or kites that move a cable through an electric generator.

FIG 4.2 Laddermill

The Laddermill concept makes use of lifting bodies, called kites or wings, connected to a cable that stretches into the higher regions of the atmosphere. The lower part of the cable, about 10% of the total length is wound around a drum. The tension that the kite creates in the cable pulls it off the drum, thus driving the generator. The actual Laddermill will have several wings connected in the upper section of the cable. The installed power of a Laddermill can be higher than that of conventional windmills. Since the wings are high up in the air, their size is not limited like the blades of a conventional windmill. Large controllable kites are thus an enabling technology for the Laddermill.


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4.2 MILTARY USE OF AEROSTATS:

4.21 AEROSTATS USED FOR SURVEILLANCE:

Airships and aerostats have been used historically for military surveillance and antisubmarine warfare. Unlike fixed-wing aircraft or helicopters, aerostats and airships are “lighter-than-air (LTA)”; typically using helium to stay aloft.The US Navy disbanded its last airship unit in1962, and military use of lighter-than-air platforms (LTA) has been limited to Air Force custodianship of a dozen aerostats.

FIG 4.3 Helikite being used for aerial surveillance

However, a number of developments have combined to draw increased attention toward LTA platforms. First, U.S. domination of airpower in military conflicts has been overwhelming since 1991. Threats to LTA platforms appear to be very low by historical standards. Second, the military’s demand for “persistent surveillance,” a function for which aerostats appear to be well suited, is growing. Network-centric warfare approaches, increased emphasis on homeland security, and growing force protection demands in urban environments all call for “dominant battle space awareness.” Third, growing airlift demands have spawned studies on using airships as heavy lift vehicles. Fourth, growing budget pressures have encouraged the study of potential solutions to military problems that may reduce both procurement and operations and maintenance spending. LTA platforms may fit into this category. Finally, recent advances in unmanned aerial vehicles suggests that future airships may also be remotely piloted, or fly autonomously.The most well established LTA platform today is the Tethered Aerostat Radar System (TARS). TARS’ primary mission is surveillance for drug interdiction. Each aerostat can lift 2,200 lbs of sensors to a height of 12,000 feet, and can detect targets out to 230 miles. The aerostat can stay aloft for months.

4.22 AEROSTATS USED FOR FIRE CONTROL:The US army has been conducting research based into LTA systems. One of them is a two different aerostat-borne radar systems. One radar will perform over-the horizon surveillance to detect the cruise missile. The second radar will track the cruise missile and guide an intercepting weapon. This process is called “fire control.”


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FIG 4.4 Tethered aerostat radar systems

The feasibility of a High Altitude Airship (HAA) for homeland defense is also being investigated by defense organizations all over the world.Like TARS, HAA would be unmanned, and provide over-the-horizon surveillance. However, it would not provide fire control-quality tracks, and unlike an aerostat, HAA could move to avoid weather or change radar coverage. The HAA would operate at high altitudes and has been likened to a low flying, and relatively inexpensive satellite. This altitude might enable a small number of airships to survey the entire country.There has been research to develop a stratospheric airship-based sensor that can remain airborne for years. It is hoped to detect both air and ground targets at long range. The Integrated Sensor Is Structure program will develop technologies to enable large and lightweight radar antennas to be integrated into an airship platform. This approach exploits the platform’s size and complies with the platform’s weight and power limitations. Major technical challenges include developing ultra-lightweight antennas, antenna calibration technologies, power systems, and airships that support extremely large antennas.

FIG 4.5 Lockheed-Martin’s High altitude Airship Concept

Other more main uses of aerostats in military are for scientific research, weather observation and carrying of heavy payloads at high altitudes for a long period of time.


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There are several aircrafts flying at high altitudes unfortunately these vehicles are either payload limited, duration limited or both. Aerostats, which are tethered balloons, are capable of lifting heavy payloads about a fixed location for extended durations.

4.3 AEROSTATS USED FOR COMMUNICATION

4.31 AEROSTATS USED FOR EMERGENCY COMMUNICATION SYSTEMS:

New requirements for the protection of the public at large entertainment events, security for key industrial and government facilities, domestic transportation infrastructure and border crossings require the development of new platforms for wide-area communications and situational awareness for incident response. Such incidents include environmental emergencies, industrial, transportation accidents and acts of terrorism. These surveillance platforms include satellites, conventional aircraft, uninhabited aerial vehicles (UAVS), airships and tethered aerostats. One of the most promising and economical of these platforms is the use of tethered aerostats that can be moved easily and deployed rapidly by a small group of operators. Tethered aerostats can provide highly portable and affordable platforms for ad hoc emergency services for weeks or months before a scheduled event and after an emergency incident. The integrated communications and sensor system on tethered aerostats is used for emergency response. Such systems can also be used for short-term security at large public events such as major sporting events and political events as well as for seasonal environmental studies when they are not needed by emergency responders. The emergency communication equipment deployed would include cellular, security force radios and Wi-Fi, all connected to the Internet by satellite when the high speed cellular infrastructure is not available. The sensors would also include chemical, biological, radiological detection and monitoring capabilities. Acoustic and video surveillance would also be included in this sensor monitoring system.

FIG 4.6 Aerostat carrying payload of communication system


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4.32 AEROSTATS USED FOR LOW COST INTERNET ACCESS:

Tethered Aerostats are being also being used to provide low cost internet access to rural areas. Wireless bridges can provide connectivity up to 10 Km. The conventional approach is to mount antennae (typically directional) on a high tower which is then connected to the wireless bridge. These antennae look at client side antennae through line of sight (LOS) connectivity for internet access. It is the cost of these high towers (50 to 100 meters) at the base station which makes deployment of such wireless networks expensive. Further, these towers, once erected, are not re-locatable to other areas where communication needs may arise. The PoE cable carries data as well as power from ground to the router box mounted below the aerostat. The receiver antenna at client location which may be in the range of 10 to 30 km from the aerostat spot location can easily receive these signals. Thus, both data and telecommunication is achieved by such a noble technique which costs almost 8 to 10 times lesser than the tower networks. Other advantages of this technique are as below.1. Very less infrastructure required.2. Relocation of the system to anywhere within operational range is possible. This includes flood areas, earthquake areas, and other natural disaster affected areas where communication network is not yet established.3. Very less launching area is required.

4.4 AEROSTATS USED FOR SPACE RESEARCH:

4.41 AEROSTATS USED FOR PLANETARY EXPLORATIONS:

An aerobot is an aerial robot, usually used in the context of an unmanned space probe or unmanned aerial vehicle.

While work has been done since the 1960s on robot "rovers" to explore the Moon and other worlds in the Solar system, such machines have limitations. They tend to be expensive and have limited range, and due to the communications time lags over interplanetary distances, they have to be smart enough to navigate without disabling themselves.

For planets with atmospheres of any substance, however, there is an alternative: an autonomous flying robot, or "aerobot". Most aerobot concepts are based on aerostats, primarily balloons, but occasionally airships. Flying above obstructions in the winds, a balloon could explore large regions of a planet in great detail for relatively low cost.

Balloons have a number of advantages for planetary exploration. They can be made light in weight and are potentially relatively inexpensive. They can cover a great deal of ground, and their view from a height gives them the ability to examine wide swathes of terrain with far more detail than would be available from an orbiting satellite. For exploratory missions, their relative lack of directional control is not a major obstacle as there is generally no need to direct them to a specific location.


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A balloon designed for planetary exploration will carry a small gondola containing an instrument payload. The gondola will also carry power, control, and communications subsystems. Due to weight and power supply constraints, the communications subsystem will generally be small and low power, and interplanetary communications will be performed through an orbiting planetary probe acting as a relay. Typically, the balloon enters the planetary atmosphere in an "aeroshell", a heat shield in the shape of a flattened cone. After atmospheric entry, a parachute will extract the balloon assembly from the aeroshell, which falls away. The balloon assembly then deploys and inflates.

Once operational, the aerobot will be largely on its own and will have to conduct its mission autonomously, accepting only general commands over its long link to Earth. The aerobot will have to navigate in three dimensions, acquire and store science data, perform flight control by varying its altitude, and possibly make landings at specific sites to provide close-up investigation.

FIG 4.7 AN ILLUSTRATION OF THE VEGA MISSION

The first, and so far only, planetary balloon mission was performed by the Space Research Institute of Soviet Academy of Sciences in cooperation with the French space agency CNES in 1985. A small balloon, similar in appearance to terrestrial weather balloons, was carried on each of the two Soviet Vega Venus probes, launched in 1984.

4.5 OTHER USES OF AEROSTATS:

4.51 ADVERTISING:Aerostats are being extensively used for advertising especially Blimps and hot air balloons. Blimps are used for advertising and as TV camera platforms at major sporting events.


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FIG 4.8 Goodyear blimp

The most iconic of these are the Goodyear blimps. Goodyear operates three blimps in the United States, and the Lightship group operates up to 19 advertising blimps around the world. Airship Management Services owns and operates three Skyship 600 blimps. Two operate as advertising and security ships in the North America and the Caribbean. Goodyear Blimps have adorned the skies since 1925. Moored balloons are sometimes used for advertisement, either by lifting up advertisement signs, or by using a balloon with advertisements on it. Often both methods are combined. It is not uncommon to use specially designed balloons. By suspending a light source within the envelope, the balloon can be made to glow at night, drawing attention to its message. 4.52 SIGHTSEEING:

FIG 4.9 TETHERED BALLOON CARRYING PASSENGERS UPTO A HEIGHT OF 1000FT


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The hot air balloon is the oldest successful human-carrying flight technology and is a subset of balloon aircraft. Recently, balloon envelopes have been made in all kinds of shapes, such as hot dogs, rocket ships, and the shapes of commercial products.A hot air balloon consists of a bag called the envelope that is capable of containing heated air. Suspended beneath is a gondola or wicker basket (in some long-distance or high-altitude balloons, a capsule), which carries passengers and (usually) a source of heat, usually an open flame.

4.53 BIRD SCARING:

FIG 4.10 Allsopp Helikite

The name Helikite relates to a combination of a helium balloon and a kite to form a single, aerodynamically sound tethered aircraft, that exploits both wind and helium for its lift. The balloon is generally oblate-spheroid in shape although this is not essential.

Helikites can fly in far higher winds than balloons, blimps and most normal kites. They are lighter than air so also fly without wind. They fly far higher and in far worse weather than normal tethered aerostats and seldom require a ballonet. Helikites have made possible the concept of "personal aerostats" that are small enough for one person to easily operate and yet will fly far higher and in worse weather, than most huge blimp-shaped aerostats.

The Helikite birdscarer is a lighter-than-air combination of a helium balloon and a kite. Helikites fly up to 200ft in the air with or without wind. Although they do not look like hawks, they fly and hover high in the sky behaving like birds of prey. Helikites successfully exploit bird pests’ instinctive fear of hawks and can reliably protect large areas of farmland.

4.54 TRANSPORTATION:

Airships were the first aircraft to enable controlled, powered flight, and were widely used before the 1940s, but their use decreased over time as their capabilities were surpassed by those of airplanes. Their decline continued with a series of high-profile accidents, including the 1937 burning of the hydrogen-filled Hindenburg near Lakehurst, New Jersey, and the destruction of the USS Akron.


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FIG 4.11 Hot air balloon over Cappadocia

In recent years, the Zeppelin Company has reentered the airship business. Their new model, designated the Zeppelin NT made its maiden flight on 18 September 1997. There are currently four NT aircraft flying, a fifth completed in March 2009 and an expanded NT-14 (14,000 cubic meters of helium, capable of carrying 19 passengers) also under construction. Several companies, such as Cameron Balloons in Bristol, United Kingdom, 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 inflated with hot air (as in a balloon) to provide the lifting force, instead of helium. A small gondola, carrying the pilot and passengers, a small engine, and the burners to provide the hot air are suspended below the envelope, below an opening through which the burners protrude.


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Documents

29835987 Role of Aerostats