Hot air balloon Totally Explained

   The hot air balloon is the oldest successful human-carrying flight technology, dating back to its invention by the Montgolfier brothers in Annonay, France in 1783. The first flight carrying humans was made on November 21, 1783, in Paris by Jean-François Pilâtre de Rozier and François Laurent d'Arlandes.
   Hot air balloons that can be propelled through the air rather than just being pushed along by the wind are known as airships or, more commonly, thermal airships.
   A hot air balloon consists of a bag called the envelope that's capable of containing heated air. Suspended beneath is the or wicker basket (in some long-distance or high-altitude balloons, a ) which carries a source of heat capable of producing a sufficient temperature gradient between the air inside the envelope and the surrounding air mass to give enough lift to keep the balloon and its passengers aloft. Unlike gas balloons, the envelope doesn't have to be sealed at the bottom since the rising hot air only exerts pressure on the upper hemisphere of the balloon to provide lift. In today's sport balloons the envelope is generally made from nylon fabric and the mouth of the balloon (closest to the burner flame) is made from fire resistant material such as Nomex.
   Recently, balloon envelopes have been made in fantastic shapes, such as hot dogs, rocket ships, and the shapes of commercial products.

History

Premodern Balloon

Unmanned hot air balloons are popular in Chinese history. Zhuge Liang of the Shu Han kingdom in the Three Kingdoms era used airborne lanterns for military signaling. These lanterns are known as Kongming lanterns (孔明灯). Yet the first known evidence of model flight in China employing the use of hot air comes from the Huainanzi, a Taoist book written by the Liu An in the 2nd century BC. This ancient Chinese text stated:
. He took off from downtown Bombay, India and landed south in Panchale. The previous record of had been set by Per Lindstrand on June 6, 1988 in Plano, Texas. As with all registered aircraft, oxygen is needed for all crew and passengers for any flight that reaches and exceeds an altitude of . The furthest that a hot air balloon has ever been flown is . On January 15, 1991, the Virgin Pacific Flyer balloon completed the longest flight in a hot air balloon when Per Lindstrand (born in Sweden, but resident in the UK) and Richard Branson of the UK flew from Japan to Northern Canada.
With a volume of 74,000 cubic metres (2,600,000 cubic feet), the balloon envelope was the largest ever built for a hot air craft. Designed to fly in the trans-oceanic jet streams the Pacific Flyer recorded the highest ground speed for a manned balloon at .
The longest duration hot air balloon flight ever made is 50 hours and 38 minutes made by Michio Kanda and Hirosuke Tekezawa of Japan on January 2, 1997.

Construction

A hot air balloon for manned flight uses a single-layered, fabric gas bag (lifting "envelope"), with an opening at the bottom called the mouth or throat. Attached to the envelope is a basket, or gondola, for carrying the passengers. The basket is usually made of wicker and rattan, but can be made of aluminium. Mounted above the basket and centered in the mouth is the "burner" which injects a flame into the envelope, heating the air within. The heater or burner is fueled by propane, a liquefied gas stored in pressure vessels, similar to high pressure forklift cylinders.

Envelope

Modern hot air balloons are usually made of light-weight and strong synthetic fabrics such as ripstop nylon, or dacron (a polyester).
During the manufacturing process, the material is cut into panels and sewn together, along with structural load tapes (webbing) that carry the weight of the gondola or basket. Vertical rows of triangular panels that are referred to as gores. Envelopes can have as few as 4 gores or as many as 24 or more.
Envelopes often have a crown ring at their very top. This is a hoop of smooth metal, usually aluminum and approximately in diameter, to which vertical load tapes attach.

Fabric coatings

The fabric (or at least part of it, the top 1/3 for example) may be coated with a sealer, such as silicone or polyurethane, to make it impermeable to air. It is often the degradation of this coating and the corresponding loss of impermiability that ends the effective life of an envelope, not weakening of the fabric itself. Heat, moisture, and mechanical wear-and-tear during set up and pack up are the primary causes of degradation. Once an envelope becomes too porous to fly, it may be retired and used as a 'rag bag': cold inflated and opened for children to run through. Products for recoating the fabric are becoming commercially available.

Envelope sizes

A range of envelope sizes is available. The smallest, one-person, basket-less balloons (called "Hoppers" or "Cloudhoppers") have less than 1,000 m³ (35,000 ft³) of envelope volume (for a perfect sphere this would mean a radius of around ). At the other end of the scale are the balloons used by large commercial sightseeing operations that carry well over two dozen people and have envelope volumes of up to 15,000 m³ (600,000 ft³). However, most balloons are roughly 2,500 m³ (100,000 ft³) and carry 3 to sometimes 4 people.

Vents

The top of the balloon usually has a vent of some sort. The most common type of vent is a disk-shaped flap of fabric called a parachute vent. The fabric is connected around its edge to a set of "vent lines" that converge in the center. (The arrangement of fabric and lines looks roughly like a parachute -- thus the name.) These "vent lines" are themselves connected to a control line that runs to the basket. A parachute vent is opened by pulling on the control line. Once the control line is released, the pressure of the remaining hot air pushes the vent fabric back into place. A parachute vent can be opened briefly while in flight to initiate a rapid descent. (Slower descents are initiated by allowing the air in the balloon to cool naturally.) The vent is pulled completely open to collapse the balloon after landing.
An older, and today less commonly used, style of vent is called a "Velcro-style" vent. This too is a disk of fabric at the top of the balloon. However, rather than having a set of "vent lines" that can repeatedly open and close the vent, the vent is secured by "hook and loop" fasteners (such as Velcro) and is only opened at the end of the flight. Balloons equipped with a "Velcro-style" vent typically have a second "maneuvering vent" built into the side (as opposed to the top) of the balloon.
Some hot air balloons have turning vents which are side vents which, when opened, cause the balloon to rotate. Such vents are particularly useful for balloons with rectangular baskets in order to align the wider side of the basket for landing.

Burner

The burner unit gasifies liquid propane, mixes it with air, ignites the mixture, and directs the flame and exhaust into the mouth of the envelope. The unit may consist of one or more individual burners of which the pilot may use one or more at a time to generate the desired heat. Each burner is characterized by a metal coil of propane tubing through which the flame shoots in order to preheat the incoming liquid propane.
   The burner unit may be suspended from the mouth of the envelope, or rigidly supported over the basket. The burner unit may be mounted on a gimbal to enable the pilot to aim the flame and avoid overheating the envelope fabric.
   The pilot actuates a burner by opening a propane valve, called a blast valve. The valve may be spring loaded so that it closes automatically, or it may stay open until closed by the pilot. The burner has a pilot light to ignite the propane and air mixture. The pilot light may be lit by the pilot with an external device, such as a flint striker or a lighter, or with a built-in piezo electric spark.
   A burner may have a secondary propane valve that releases propane more slowly and thereby generates a different sound. This is called a whisper burner and is used for flight over livestock to lessen the chance of spooking them. It also generates a more yellow flame and is used for night glows because it lights up the inside of the envelope better than the primary valve.
   Burners can generate heat on the order of 30 million BTUs (31,651,677 kilojoule).

Fuel tanks

Propane fuel tanks are usually cylindrical pressure vessels made from aluminum, stainless steel, or titanium with a valve at one end to feed the burner and to refuel. They may have a fuel gauge and a pressure gauge. The pressure necessary to force the fuel through the line to the burner may be supplied by the vapor pressure of the propane itself, if warm enough, or by the introduction of an inert gas such as nitrogen

Instrumentation

A balloon may be outfitted with a variety of instruments to aid the pilot. These commonly include an altimeter, a rate of climb (vertical speed) indicator, envelope (air) temperature, and ambient (air) temperature. A GPS receiver can be useful to indicate ground speed (traditional aircraft air speed indicators would be useless) and direction.

Combined mass

The combined mass of an average system can be calculated as follows

the envelope: 250 lb, 113 kg
basket: 140 lb, 63.5 kg
burner: 50 lb, 22.7 kg
3 fuel tanks with fuel: 3 × 135 lb = 405 lb, 184 kg
5 passengers: 5 × 150 lb each = 750 lb, 340 kg

the air in the envelope (100,000 ft³ at 0.062 lb/ft³ = 3.1 tons, 2,812 kg) - but at 120 °C, the density of dry air is 0.898 kg/m³ which is 0.056 lb/ft³, giving a weight of 2,551 kg For a total of 3,538 kg or about 3.9 tons

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