Aero-statics


Aero-static means "air at rest." Aero-statics applies to Hot Air Balloons, and Lighter-Than-Air Craft (also know as blimps, zeppelins and airships). In the aero-static condition, the craft is supported by displacing air. By Archimedes' Principle, the buoyant force is equal to the weight of the fluid (in this case air) displaced.


Ballooning Firsts

In 1783 the two french Montgolfier Brothers, Jacques Étienne and Joseph Michel, wealthy papermakers of Annonay, France, sent up a balloon filled with hot air. Shortly after, spurred by their success, the French physicist, chemist, and aeronaut Jacques Alexandre César Charles released a balloon filled with hydrogen, which made a successful two-hour flight, covering 43 km (27 mi).

The same year also marked the first actual balloon ascent by humans, when the French physicist Jean François Pilâtre de Rozier made flights near Paris, first in a captive balloon and later in a free balloon.

Two years later the French aeronaut Jean Pierre Blanchard, accompanied by John Jeffries, an American, made the first balloon crossing of the English Channel.

The first balloon ascent in America was made at Philadelphia on January 9, 1793. In 1836 The Great Balloon of Nassau, of 2410 cu m (85,000 cu ft) capacity, sailed 800 km (500 mi) from London to Weilburg, Germany, in 18 hr. During the Franco-German War of 1870, balloons were used for military observation by the armies of both nations, and the French minister Léon Gambetta made a dramatic escape from the besieged city of Paris by balloon. A long-standing distance record for the flight of manned balloons was set in 1914, when the balloon Berliner traveled from Bitterfeld, Germany, to Perm, Russia, some 3052 km (about 1897 mi). Armies in World War I made extensive use of balloons, especially for military observation.

Sport Ballooning

Interest in ballooning as a sport was stimulated by the Gordon Bennett Balloon Trophy Races. The competition was held annually, except during World War I, from 1906, when the American journalist James Gordon Bennett donated the trophy, to the start of World War II, when the races were discontinued.

Sport ballooning still enjoys limited popularity in Europe, where hydrogen-filled balloons are used almost exclusively. In the United States in recent years a resurgence in interest has taken place in sport ballooning, using hot-air balloons that are kept aloft with butane or propane burners.

Altitude Records

High ascents in balloons have been made by a number of aeronauts. In 1931 the Swiss physicist Auguste Piccard ascended into the stratosphere in a spherical, airtight, metal cabin suspended from a specially constructed, hydrogen-filled balloon of 14,000 cu m (494,400 cu ft) capacity, reaching an altitude of 15,797 m (51,793 ft). The following year he reached 16,507 m (54,120 ft). In 1935, two U.S. Army captains, Orvil Anderson and Albert William Stevens, ascended 22,080 m (72,395 ft).

In August 1957, Major David Simons, a U.S. Air Force surgeon, ascended to about 31,110 m (about 102,000 ft), remained in the air 32 hr, and drifted 652 km (405 mi) from his takeoff point. The flight was designed to chart the reactions of humans at high altitudes. On August 27, 1960, Captain Joseph Kittinger bailed out of a polyethylene plastic balloon at 31,354 m (102,800 ft), setting a new altitude record for balloon flight and a new record for parachute descent. On May 4, 1961, the Americans Malcolm Ross and Victor Prather set a record of 34,679 m (113,700 ft) on a flight launched from a U.S. Navy aircraft carrier.

Distance Records

The first transatlantic balloon flight ended on August 17, 1978, after setting a distance record of 5000 km (3108 mi) and an endurance record of 137 hr 6 min. The helium-filled Double Eagle II, manned by the American businessmen Ben Abruzzo, Max L. Anderson, and Larry Newman, took off from Presque Isle, Maine, on August 11 and landed in Miserey, France. The endurance record was broken by two Americans, Troy Bradley and Ben Abruzzo's son Richard, who took off from Bangor, Maine, on September 15, 1992. In the world's first transatlantic race, they were blown off course and landed near Fez, Morocco, 146 hours later.

Kittinger made the first solo transatlantic crossing when he flew his helium-filled Rosie O'Grady's 5690 km (3535 mi) from Caribou, Maine, to the Italian Riviera near Savona, September 14-18, 1984.

The first around the world balloon flight was made by the Breitling Orbiter in 1999.

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Modern Scientific Ballooning

Three types of balloons are in common use for meteorologic research.

The rubber, or neoprene, balloon is used for vertical soundings, either as a radiosonde-carrying balloon that transmits meteorological information, or as a pilot balloon, a small balloon sent aloft to show wind speed and direction. The balloon, inflated with a lifting gas (hydrogen, helium, ammonia, or methane), stretches as it ascends into thin air. When the balloon has stretched from three to six times its unstressed length (that is, when its volume has increased 30 to 200 times its original amount), the skin ruptures, destroying the balloon.

The zero-pressure plastic (usually polyethylene) balloon is used to carry scientific instruments to a predetermined density level. The plastic balloon is filled only partly with gas while on the ground. As the balloon ascends, the expanding gas fills the envelope. This type of balloon has a valve that automatically discharges excess gas when the balloon reaches its constant-density altitude, so that the balloon can maintain this altitude. When the sun sets, the gas cools, the volume decreases, and the balloon descends to the ground, unless ballast is released.

The superpressure balloon is a nonextensible balloon that is sealed to prevent the release of gas. By the time the balloon reaches its constant-density level, the free-lift gas has become pressurized. Variations in the air pressure caused by the heat of the sun produce changes in the internal gas pressure, but the volume of the balloon remains fixed. So long as the balloon remains under pressure, therefore, it continues to float at its predetermined constant-density level.

The highest unmanned research balloon flight was made from Chico, California, in October 1972, reaching an altitude of 51,850 m (170,000 ft).

Around the world each day radiosonde balloons make over 1000 soundings of the winds, temperature, pressure, and humidity in the upper atmosphere (see METEOROLOGY). These flights are made almost exclusively from land areas. As a result, adequate measurements of the atmosphere are made over less than 20 percent of the globe. To obtain coverage over ocean areas, Global Horizontal Sounding Technique (GHOST) balloons have been flown experimentally from the southern hemisphere.

Contributed by: Vincent E. Lally

"Balloon," Microsoft (R) Encarta. Copyright (c) 1994 Microsoft Corporation. Copyright (c) 1994 Funk & Wagnall's corporation.

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Hot Air Balloon

A hot air balloon consists of a large pliant bag made of paper, varnished silk, or other suitable nonporous material. The earliest hot air balloons often carried a brazier to replenish the supply continuously. In modern hot-air sport ballooning, the air is heated by a propane burner.

When did mankind first fly? (or How the Country Bumpkins beat out the Big City Bureaucrats)


Math Associated with Hot Air Balloons

Circumference and area of a circle.

Use Simpson's Rule to find the volume of the envelope.

Use Simpson's Rule to find the surface area of the envelope. Use this to determine how much material is needed and to estimate the weight.

Use trigonometry to measure the altitude of the balloon.

Science Associated with Hot Air Balloons

Gas Laws. Boyle's Law. Charles and Gay-Lussac's Law (the Lighter than Air Guys). Avogradro's Law.

NASA atmospheric models.

Archimedes' Principle.

Heat loss through insulation.

Technology Associated with Hot Air Balloon

Using the gas laws to estimate the weight of the gas within the envelope.

Use NASA atmospheric models to estimate the density of the displaced atmosphere.

Use Archimedes' Principle to relate the weight of the displaced air to the buoyancy on the balloon

Determine an appropriate material for the balloon.

Predict the altitude of the baloon. Consider the reduced displacement, reduced amount of gas in the envelope and the heat loss on the trip to altitude.

Problem Statement

Design the lowest cost Hot Air Balloon that will take an atomspheric test device (3x5 card) to an altitude of 200 feet above ground level.

Estimate the static lift of your balloon. The test device requires that the balloon have a 18 gage galvanized wire ring at the bottom with a minimum diameter of 10 inches. The test device will include the heat source, a method of measuring the temperature inside the envelope, and a way to measure lift.

Construct the balloon. Weigh it empty.

Measure the static lift. Compare it to your prediction.

Launch your Hot Air Balloon carrying the atmopheric test device. Measure the altitude attained using ground telemetry. Compare the maximum altitude to the design specification.

Investigate the modern uses for Hot Air Baloons.

Links

NASA Atmosphere Model

Charles' Law

Animated Boyle's Law

Engineer's Edge

Books to get

Lighter Than Air: An Illustrated History of the Development of Hot-Air Balloons and Airshipsby David Owen

Hot Air Balloons by Ailsa Spindler and Clive McFadden

Equipment

Visit Kevlin.com and get an Air Blower, industrial to try out

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Lighter-than-Air Craft

Lighter-Than-Air craft is a common term for both rigid airships and blimps.

Modern airships are filled with helium. Helium has the great advantage of being nonflammable, but it is twice as heavy as hydrogen and has 7 percent less lifting power. Hydrogen weighs 1.14 kg/cu m (0.071 lb/cu ft) less than air at standard atmospheric pressure and temperature, and a hydrogen balloon of 28.3 cu m (1000 cu ft) is able to lift, therefore, about 32 kg (about 70 lb).

Using the Ideal Gas Law for LTA craft:

Finding Displacement

The volume of the gas bag can be determined by numerical methods or solid geometry.

The displacement is determined by multiplying the volume of the gas bag by the specific weight of air. The specific weight of air can be determined by the idea gas laws, or from mass density tables.

To use mass density, multiply the mass density by the gravity constant

example: at STP the mass density of air is 0.002377 slugs per cubic foot, g = 32.174 ft/sec2

Specific Weight of Air = 0.002377 x 32.174 = 0.0764 lbs./cubic foot

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