Petroleum. Chemical Composition of Petroleum

Petroleum

 Oil has been used for lighting purposes for many thousand years. In areas where oil is found in shallow reservoirs, seeps of crude oil or gas may naturally develop, and some oil could simply be collected from seepage or tar ponds.

            The Sumerians, who lived in the Tigris-Euphrates valley 4000 B.C. and are thought to form the cradle of civilizations, used asphalt widely in construction and ornamental works. In the Bible, Noah is commanded to build an ark that also includes instructions for caulking the vessel with pitch (Genesis 6:14). There is also reference to the use of tar as a mortar when the Tower of Babel was under construction (Genesis11:3).

            Approximately 2000 years ago, Arabian scientists developed methods for the distillation of petroleum, which were  introduced  into Europe by way of Spain. This represents a documented use of the volatile derivatives of petroleum which led to a continued interest in petroleum and its derivatives as medicinal materials and materials for warfare, in addition to the usual construction materials.

            The Egyptians were the first to adopt the practice of embalming their dead rulers and wrapping the bodies in cloth. Starting with 1000 B.C., asphalt was used in mummification. Historically, we know of tales of eternal fires where oil and gas seeps would ignite and burn. One example dating back to 1000 B.C. is the site where the famous oracle of Delphi would be built, and 500 B.C. Chinese were using natural gas to boil water.

            Petroleum is perhaps the most important substance consumed in modern society. It provides not only  raw materials  for  the ubiquitous plastics and other products, but also fuel for energy, industry, heating, and transportation.

            The  fuels  that are derived  from petroleum supply more than half of  the world’s  total supply of energy. Gasoline, kerosene, and diesel oil provide fuel for automobiles, tractors, trucks, aircraft, and ships. Fuel oil and natural gas are used to heat homes and commercial buildings, as well as  to generate electricity. Petroleum products are the basic materials used  for  the manufacture of synthetic fibers for clothing and in plastics, paints, fertilizers, insecticides, soaps, and synthetic rubber. The uses of petroleum as a source of raw material in manufacturing are central to the functioning of modern industry.

            Products we get out of oil include ink, crayons, bubble gum, dishwashing liquids, deodorant, eyeglasses, CDs and DVDs, tires, ammonia, heart valves, and many others.

            Petroleum is scattered throughout the earth’s crust, which is divided into natural groups or strata, categorized in order of their antiquity.      

            The word petroleum, derived from the Latin petra and oleum, means  literally  rock oil and  refers  to hydrocarbons that occur widely  in  the  sedimentary rocks in the form of gases, liquids, semisolids, or solids.

            The origin of petroleum is still disputable for the scientist of the entire world. Among the existing theories about the origin of petroleum and gas the greatest distribution was received by the organic theory of the mixed origin, according to which the animal and vegetative residuals participate in petroleum and gas formation (natural hydrocarbon systems (NHCS)). Therefore all combustible minerals are called caustobioliths (from Greek, caustos- combustible, bios - life, lithos - stone). These residuals under the influence of complicated chemical and biochemical processes turned into putrid silt (sapropel), into which residuals of highly organized plants could be admixed.

            Putrid silt and humus substances loaded in salt-water pools, were subjected to further modifications, gradually turning into gum-form substance (initial phase - diagenesis). Due to high temperatures and pressure more deep chemical and biochemical transformations of these substances happened which resulted in formation of complicated hydrocarbon mixtures (main phase of formation - catagenesis).

            There is an alternative theory about the formation of oil and gas deposits that could change estimates of potential future oil reserves. According to this theory, oil is not a fossil fuel at all, but was formed deep in the Earth's crust from inorganic materials. The theory was first proposed in the 1950s by Russian and Ukranian scientists. Geologists argue that formation of oil deposits requires the high pressures only found in the deep mantle and that the hydrocarbon contents in sediments do not exhibit sufficient organic material to supply the enormous amounts of petroleum found in supergiant oil fields. The idea of the theory is that hydrogen and carbon, under high temperatures and pressures found in the mantle during the formation of the Earth, form hydrocarbon molecules which have gradually leaked up to the surface through cracks in rocks. The organic materials which are found in petroleum deposits are easily explained by the metabolism of bacteria which have been found in extreme environments similar to Earth's mantle.

In the crude state petroleum has minimal value, but when refined it provides high-value liquid fuels, solvents, lubricants, and many other products.

Petroleum is a mixture of gaseous, liquid, and solid hydrocarbon compounds that occur in sedimentary rock deposits throughout the world and also contains small quantities of nitrogen-, oxygen-, and sulfur-containing compounds as well as trace amounts of metallic constituents.

Petroleum and the equivalent term crude oil cover a wide assortment of materials consisting of  mixtures of hydrocarbons and other compounds containing variable amounts of sulfur, nitrogen, and oxygen, which may vary widely in volatility, specific gravity, and viscosity. Metal-containing constituents, notably those compounds that contain vanadium and nickel, usually occur in the more viscous crude oils in amounts up to several thousand parts per million and can have serious consequences during processing of these feedstocks. Because petroleum is a mixture of widely varying constituents and proportions, its physical properties also vary widely and the color is from colorless to black.

Petroleum occurs underground, at various pressures depending on the depth. Because of the pressure, it contains considerable natural gas in solution. Petroleum underground is much more fluid than it is on the surface and is generally mobile under reservoir conditions because the elevated temperatures (the geothermal gradient) in subterranean formations decrease the viscosity.

Crude petroleum is a mixture of compounds boiling at different temperatures that can be separated into a variety of different generic fractions by distillation. And the terminology of these fractions has been bound by utility and often bears little relationship to composition.

The molecular boundaries of petroleum cover a wide range of boiling points and carbon numbers of hydrocarbon compounds and other compounds containing nitrogen, oxygen, and sulfur, as well as metallic (porphyrinic) constituents. However, the actual boundaries of such a petroleum map can only be arbitrarily defined in terms of boiling point and carbon number. In fact, petroleum is so diverse that materials from different sources exhibit different boundary limits, and for this reason alone it is not surprising that petroleum has been difficult to map in a precise manner.

Oil chemical and physical (fractional) composition can vary not only with the location and age of the oil field but also with the depth of the individual well. Indeed, two adjacent wells may produce petroleum with markedly different characteristics.

           

ULTIMATE  (ELEMENTAL)  COMPOSITION

With  few  exceptions,  the  proportions  of  the  elements  (carbon, hydrogen,  nitrogen,  oxygen, sulfur,  and  metals)  in  petroleum  (whatever  and  wherever  the  source)  vary  over  fairly  narrow limits:

Carbon,  83.0%  to  87.0%

Hydrogen,  10.0%  to  14.0%

Nitrogen,  0.1%  to  2.0%

Oxygen,  0.05%  to  1.5%

Sulfur ,  0 .05%  to 6.0%

Metals (Ni and V), <1000 ppm.

The narrow range of variation is quite surprising when the variation of the precursors is considered and even more surprising when one considers the wide variation in physical properties from the lighter, more mobile crude oils at one extreme to the heavier asphaltic crude oils at the other extreme. In addition, when the many localized or regional variations in maturation conditions are assessed, it is perhaps surprising that the ultimate compositions are so similar. Perhaps this observation, more than any other observation, is indicative of the similarity in nature of the precursors from one site to another.

CHEMICAL COMPONENTS

Petroleum contains an extreme range of organic functionality and molecular size. In fact, the variety is so great that it is unlikely that a complete compound-by-compound description for even a single crude oil would be possible.

            In very general terms (and as observed from elemental analyses), petroleum, heavy oil, bitumen, and residua are a complex composition of: (1) hydrocarbons; (2) nitrogen compounds; (3) oxygen compounds; (4) sulfur compounds; and (5) metallic constituents.

The hydrocarbon content of petroleum may be as high as 97% by weight (e.g.,in the lighter paraffinic crude oils) or as low as 50% by weight or less as illustrated by the heavy asphaltic crude oils. Nevertheless, crude oils with as little as 50% hydrocarbon components are still assumed to retain most of the essential characteristics of the hydrocarbons. It is, nevertheless, the nonhydrocarbon (sulfur, oxygen, nitrogen, and metal) constituents that play a large part in determining the processability of the crude oil. But there is more to the composition of petroleum than the hydrocarbon content. The inclusion of organic compounds of sulfur, nitrogen, and oxygen serves only to present crude oils as even more complex mixtures, and the appearance of appreciable amounts of these nonhydrocarbon compounds causes some concern in the refining of crude oils. Even though the concentration of nonhydrocarbon constituents (i.e., those organic compounds containing one or more sulfur, oxygen, or nitrogen atoms) in certain fractions may be quite small, they tend to concentrate in the higher boiling fractions of petroleum. Indeed, their influence on the processability of the petroleum is important, irrespective of their molecular size and the fraction in which they occur.

The presence of traces of nonhydrocarbon compounds can impart objectionable characteristics to finished products, leading to discoloration or lack of stability during storage. On the other hand, catalyst poisoning and corrosion are the most noticeable effects during refining sequences when these compounds are present. It is therefore not surprising that considerable attention must be given to the nonhydrocarbon constituents of petroleum as the trend in the refining industry, of late, has been to process more heavy crude oil as well as residua that contain substantial proportions of these nonhydrocarbon materials.

           

HYDROCARBON CONSTITUENTS

The isolation of pure compounds from petroleum is an exceedingly difficult task, and the overwhelming complexity of the hydrocarbon constituents of the higher molecular weight fractions as well as the presence of compounds of sulfur, oxygen, and nitrogen, are the main causes for the difficulties encountered. It is difficult on the basis of the data obtained from synthesized hydrocarbons to determine the identity or even the similarity of the synthetic hydrocarbons to those that constitute many of the higher boiling fractions of petroleum. Nevertheless, it has been well established that the hydrocarbon components of petroleum are composed of paraffinic, naphthenic, and aromatic groups. Olefin groups are not usually  found  in  crude  oils,  and  acethylenic  hydrocarbons  are  very  rare  indeed.  It  is  therefore convenient  to  divide  the  hydro carbon  components  of  petroleum  into  the  following  three classes:

1. Paraffins,  which  are  saturated  hydrocarbons  with  straight  or  branched  chains,  but without  any  ring  structure

2. Naphthenes,  which  are  saturated  hydrocarbons  containing  one  or  more  rings,  each  of which  may  have  one  or  more  paraffinic  side  chains 

3. Aromatics,  which  are  hydrocarbons  containing  one  or  more  aromatic  nuclei,  such  as benzene,  naphthalene,  and  phenanthrene  ring  systems,  which  may  be  linked  up  with (substituted)  naphthene  rings  or  paraffinic  side  chains.

The relationship between the various hydrocarbon constituents of crude oils is one of  hydrogen addition  or  hydrogen  loss  (Figure  2.1).  This  is  an  extremely  important  aspect of petroleum composition and there is no reason to deny the occurrence of these interconversion  schemes  during  the  formation,  maturation,  and  in situ alteration  of  petroleum.

Saturated hydrocarbons can be linear, i.e. straight-chain (general formula C_nH_{2n + 2}) wherein the carbon atoms are joined in a snake-like structure, branched (general formula C_nH_2n+2, n > 3) wherein the carbon backbone splits off in one or more directions.      

The members of the series (in terms of number of carbon atoms) are named as follows: methane, CH₄; ethane, C₂H₆; propane, C₃H₈; butane, C₄H₁₀; pentane, C₅H₁₂; hexane, C₆H₁₄; heptane, C₇H₁₆; octane, C₈H₁₈, and so on.

            Generally, the boiling point of hydrocarbons rises 20 - 30 °C for each carbon added to the chain. A straight-chain hydrocarbon will have a boiling point higher than a branched-chain one due to the greater surface area in contact, thus the greater van der Waals forces, between adjacent molecules.

Fuels and Lubricants (F&L).

Fuels and  Lubricants (F&L). Sources of FL Raw Materials. Nonrenewable Primary Energy Resources

All types of equipment and machinery have been greatly improved mechanically and designed to run under far more severe operating conditions. Fuels, lubricants, and other oil products, likewise, have been greatly improved and adapted for exacting operating requirements. The selection of the proper product for the specific application thus has become more important than ever before. The proper transportation, storage, and handling of products to ensure that they reach the point of usage with their properties unchanged from their manufacture are also important.

Since F&L derived from oil in the refining processes make up the most of all F&L used, they will be referred to and analyzed in this discipline course as the main object. According to the international standard ISO 8681 (International organization for standardization), all oil products are classified into five main classes named with alphabetic indexes (table 1).

Table 1

Classification of petroleum products according to ISO 8681

Class	Product
F	Fuel
L	Lubricants, industrial oils and related products
W	Paraffin
B	Bitumen
S	Solvents and raw material for the chemical industry

Fuel is any material or individual substance that can be burned or altered to obtain different kinds of energy for heating and/or moving objects. Fuel releases its energy through chemical reactions, such as combustion and oxidizing. An important property of a useful fuel is that its energy can be stored to be released only when needed, and that the release is controlled in such a way that the energy can be harnessed to produce work. The application of energy released from fuels ranges from heat for cooking and from powering weapons to combustion and generation of electricity.

            Fuels are usually categorized according to four main indications into groups, grades, brands and kinds:

            a) based on their origin – there are natural and synthetic (artificial);

            b) based on their chemical structure – hydrocarbon and non-hydrocarbon;

            c) based on their state of matter – gaseous, liquid and solid;

            d) based on the engine type (gasoline, diesel fuel, jet fuel, gas oil, rocket fuel).

            ISO 8216/0 sets the general classification of the oil origin fuels (table 2). 

Table 2

General classification of fuels according to ISO 8216/0

Class	Category	Title
	G	Gaseous fuel. Gaseous fuel of petroleum origin consisting mainly of methane and (or) ethane
F	L	Liquefied gaseous fuel. Gaseous fuel of petroleum origin consisting mainly of propane, propene and (or) butane and butene
	D	Distillate fuel. Fuel of petroleum origin except for liquefied petroleum gases and fuels. Include gasoline, kerosene, gas-oil and diesel fuel. Heavy distillates may contain a small amount of residuals
	R	Residual fuel. Petroleum fuel containing residual fractions of distillation
	C	Petroleum cokes. Solid fuel of petroleum origin consisting mainly of carbon, obtained through the process of cracking

           

            The work of engines, mechanisms and machines is accompanied by friction of contacting and moving surfaces. Lubricants are individual substances or materials that are used for decreasing of wear of rubbing details and decreasing the loss of power expended on friction in any mechanism.

            All lubricants are subdivided into three basic groups:

            1. The lubricants, which under normal conditions are liquids (oils).

            2. Consistent (plastic, flexible) lubricating materials (lubricating pasty greases).

            3. Solid lubricants that might be used as oil additives and grease additives, or as individual lubricants.

            Natural resources such as coal, petroleum, oil and natural gas take thousands of years to form naturally and cannot be replaced as fast as they are being consumed. Eventually natural resources will become too costly to harvest and humanity will need to find other sources of energy. At present, the main energy sources used by humans are non-renewable as they are cheap to produce. Natural resources, called renewable resources, are replaced by natural processes during a reasonable amount of time. Soil, water, forests, plants, and animals are all renewable resources as long as they are properly conserved. Solar, wind, wave, and geothermal energies are based on renewable resources. Renewable resources such as the movement of water (hydropower, including tidal power; ocean surface waves used for wave power), wind (used for wind power), geothermal heat (used for geothermal power); and radiant energy (used for solar power) are practically infinite and cannot be depleted, unlike their non-renewable counterparts, which are likely to run out if not used wisely.

            A non-renewable resource is a natural resource which cannot be produced, re-grown, regenerated, or reused on a scale which can sustain its consumption rate. These resources often exist in a fixed amount, or are consumed much faster than nature can recreate them. Fossil fuel (such as coal, petroleum and natural gas) and nuclear power are examples. In contrast, resources such as timber (when harvested sustainably) or metals (which can be recycled) are considered renewable resources

            Fossil fuels are fuels generally thought to be formed by natural resources such as anaerobic decomposition of buried dead organisms. Fossil fuels range from volatile materials with low carbon:hydrogen ratios like methane, to liquid petroleum to nonvolatile materials composed of almost pure carbon, like anthracite coal. It is generally accepted that they are formed from the fossilized remains of dead plants and animals by exposure to heat and pressure in the Earth's crust over hundreds of millions of years.

Fossil fuels are easy to transport, store, and use, and they have very high energy capacity per unit of mass.

            It was estimated that in 2007 primary sources of energy used by mankind consisted of

            petroleum 35,0%,

            coal 27,0 %,

            natural gas 23,0%,

amounting to an 85 % share for fossil fuels in primary energy consumption in the world.

Non-fossil sources in 2007 included

            hydroelectric 6,0 %,

            nuclear 8,0 %, and geothermal, solar, tide, wind, wood, waste

amounting 1 percent.

           

World energy consumption has been growing about 2.3% per year.

            Petroleum is by far the most commonly used source of energy, especially as the source of liquid fuels, and its use is projected to continue at least at the current levels for at least two decades .

            Figure 1.1. Trends and the projected trend for the use of fossil fuel resources and other fuel resources until 2020.

            Fossil fuels are non-renewable resources because they take millions of years to form, and reserves are being depleted much faster than new ones are being formed. The production and use of fossil fuels raise environmental concerns. A global movement toward the generation of renewable energy is therefore under way to help meet increased energy needs.

           

Total fuel reserves of the Earth are estimated at the level of 12,5 trillion tons of equivalent fuel (1 kg of equivalent fuel = 29,4 MJ/kg (~7000 kcal);

1 kg of wood = 19,5 MJ/kg,

1 kg of coal = 33 MJ/kg,

1 kg of oil = more than 50 MJ/kg.

However only 3,5 trillions tons of these resources may be extracted and used with modern technological methods.

           

Hydrocarbon Sources for FL production

            Most of FL are produced using petroleum as a main raw material. Oil is refined in different processes to produce large variety of derived products.

            Petroleum products may also be supplied in whole or in part from natural gas.       Crude oil emerging from the well is accompanied by a large volume of natural gas, about 100 m³ of gas per barrel of oil on the average (1 barrel = 158.94 L). The quantity of natural gas produced per barrel of oil decreases with the age of the oil field. More than two-fifths of the gas obtained from oil wells is returned to the ground to maintain the pressure in the oil pools and thus increase the ultimate oil recovery.

            Though natural gas is predominantly methane, it contains other saturated hydrocarbons and gasoline vapors. The liquids extracted from gas constitute an important supplement to our petroleum resources. Today they are about one-tenth the volume of the crude oil taken from the ground.  The heavier hydrocarbons are recovered and sold as liquefied petroleum gas (LP-Gas), natural gasoline, solvents, and raw materials for the manufacture of plastics and chemicals, among other uses.

            Petroleum is the cheapest but not the only possible source of liquid fuels. Petroleum substitutes can be obtained from oil sands (also called tar sands), large beds of which are found in Canada and Venezuela. These sands are basically a mixture of sand, clay, water, and a form of petroleum called “bitumen,” which is very viscous and dense material.

            Coal, which is almost pure carbon, can be changed to liquid fuels by combining it chemically with hydrogen. This process today is also more costly than the production of these fuels from petroleum. Processes are available to recover the oil from the shale but at a cost today which generally speaking is higher than the cost of producing petroleum from wells.  Shale oil recovery and hydrogenation of coal are now economical in some European countries which are located far from crude-oil supplies in the ground.  

taken from Mykola Zakharchuk

UNIT ASSEMBLY IN AIRCRAFT PRODUCTION

Assembled units of an aircraft (helicopter) with small amount of parts which have specified design and technological requirements (each unit generally has separate assembly drawing) are the objects of Unit Assembly.

Technological units of an aircraft (helicopter) are:

1. Flat frame units which form the outline of an aircraft (spars, ribs, frames, beams).

2. Spatial frame units ("spiders" of a wing, skeletons of the equipment).

3. Panels of an airframe, and parts (framework), joined to the skin (or reinforced primary structure).

4.Constructions (assembly units) such as doors, covers, hatches, dashboards, fairings.

5. Units and panels of inborn systems and airborne equipment (control panels, collectors, seats, gears). These assemblies are usually referred as mechanical assembly.

The constituent components (sub-assemblies) which are assembled separately and joined to the unit are called Sub-Units. They usually do not have any separate assembly drawings.

Assembly is a combination of technological operations for installation of parts and units in its own position assigned by assembly drawing. Joining of these sections in assembly units are conducted by methods specified in the process documentation.

These two large stages of assembly should be precisely marked and optimized during development and realization

Let's consider regulations (rules, principles), which should be used at development and realization of these stages of the master schedule assembly.

It is known, that for positioning of work pieces, parts or articles in selected coordinate system surfaces, lines, points are used. These surfaces are called Bases.

According to their purpose, Bases are subdivided into constructional (designer), technological and measuring. The technological Bases, in their turn, are divided in positioning and assembly bases.

Positioning bases are the surfaces, lines, points which are used for positioning of work pieces, parts or articles with regard to selected coordinate system. Such definition is usable for all operations of processing and assembly.

At the first stages of development of master schedules, all possible versions of positioning bases for an article on the basic operations are considered. Then the scheme of basing is layed out. This is a sketch where the adopted sets of positioning bases are marked

The combination of scheme of basing, methods and facilities of parts installation and positioning is called method of assembly. There are three groups of assembly methods applied in aircraft production. At first the mutual positioning of parts is considered by matching of positioning bases of parts to the joint. Secondly, positioning bases of parts, match with positioning bases of assembly equipment (presence of mechanical contacts). Thirdly, positioning bases of parts, match positioning bases are created by optical-mechanical-coordinate systems by no mechanical contact.

The methods of assembly with positioning bases on parts are (without use of an assembly device) distinguished by different kind of positioning bases, which are as follows:

a) Assembly by mating surfaces of interfaced parts or assembly by installing on a base part, i.e. assembly by drawing;

b) Assembly by marks on some (base) parts;

c) Assembly by technological (assembly) holes in parts of an assembled packet.

The methods of assembly with assembly device are as follows:

a) Assembly on bases - surfaces, which includes:

- any surfaces (which do not form the outlines)

- external surface of a skin which form the outlines

- internal surface of a skin;

- outer surfaces of a skeleton ("from a skeleton");

b) Assembly on bases - holes, which includes:

- structural holes under attachment bolts (HAB);

- technological locating-base holes (LBH);

- technological coordinate-fixing holes (CFH).

For unit assembly, the optical-mechanical coordinate system method is not applied practically.

Assembly Bases are the surfaces, lines, points of mating parts which directly form a joint. In other words these are the surfaces prepared by special way and coordinated according to the kind of joint.

The assembly base and units in a joint are restricted to some degrees of freedom. Therefore they may be considered as supplementary or positioning bases.

Combination of assembly bases of parts in a unit is evident from the assembly drawing. The character of real assembly process depends on coordination of assembly bases (if it is required).

Measuring Bases are the surfaces used for determination (definition) of relative position of article refer to means of measurement.

The selection of bases at article design, part and manufacture affects the accuracy of assembly unit and efficiency indexes of an assembly (technological cost price, labor-intensiveness, duration) process.

It is necessary to follow on three principles of basing:

1.       Principle of identity (unity) of bases: the technological bases should coincide with design or bases and materialized in it.

Such method corresponds to more common principle of machine-building technique. There should be a shortest path of transferring the sizes from the drawing up to an article. Rejection of special (arbitrary) technological bases eliminates intermediate calculations so-called base sizes. Thus errors can be reduced.

As example of keeping this principle (see fig.) is arrangement of placing holes (PH) of a rib wall on the basic constructional horizontal axis of a wing. By this, the coordination of positioning bases of a part and assembly device becomes simpler.

2.       Principle of combination (coincidence) of bases: positioning bases it is necessary to select those surfaces of parts, which are assembly bases at the given stage of assembly or it could be considered in future assembly bases.

Following this rules allows to increase the accuracy of assembly and to reduce volume of adjustment.

As you can see in a fig 2.1, this principle is provided for bands – its outline are positioning and assembly bases simultaneously. Positioning and assembly bases of fitting attachment does not coincide. The violation of this principle of combination (coincidence) of bases results to attachment fitting with a band adjustment by removal of allowance compensation of a gap by the gasket (on a place).

3.       Principle of permanency of bases: once selected positioning bases should be saved at all stages of assembly and manufacture of parts. The positioning bases at first assign for assembly units, then for sections, panels, units and, at last, for parts.

For a unit (see fig. 2.1) such base should be an attachment hole because it used for a rib installation by next stage of assembly of the assembly unit, and also securing a part at its machining, for example, at milling a foot of attachment fitting.

The principles of basing should be taken into account when selecting the sequence of the installation of parts in an assembly position. Parts, which assembly bases can serve as positioning supplied on assembly first (principle of combination (coincidence) of bases). Then, in order of geometrical deposition on assembly supplied parts and units participating in formation of outlines or ensuring rigidity.

THE MANUFACTURING PROCESS IN AVIATION

There are six major subassemblies which make up an aircraft: 1) the fuselage or body, 2) the empennage or tail assembly, 3) the wings, 4) the landing gear assemblies, 5) the powerplant or jet engine, and 6) the flight control systems and instruments.

Just as in automotive manufacturing, the aircraft industry uses assembly lines for manufacturing. The production volume is much lower in aircraft, but the idea is the same. In aircraft manufacturing, a series of "positions" and "setbacks" are used to indicate the stage of the aircraft assembly. For example, if 16 positions are used to manufacture an aircraft, the 16th position would be the beginning of assembly, starting with either the nose section or wing spar buildups, and the 1st position would entail the installation of the engines and nacelle assemblies (the "nacelle" is the streamlined body which houses the engine). Position 0 indicates that the plane is "out the door" (OTD) and ready for pre-flight inspection and flight test. "Setbacks" indicate the stage a subassembly or "buildup" is within a position. For example, a wing assembly may only encompass one position, but within this position there may be three setbacks. Regardless of position or setback, assembly work is constantly ongoing. Even though one position may have more priority than others, other positions are simultaneously assembled so that both assemblies will be ready for mating at the proper time. The painting and work on the interior of the aircraft – adding seats and cabinets, for example – are done last as they can vary from aircraft to aircraft.

The production of an aircraft relies on the precise and accurate alignment and mating of each one of the major subassemblies. For subassembly production and assembly mating, a series of floor assembly jigs (FAJs) are used. These jigs hold, support, and locate the individual workpieces or subassemblies until they can be riveted, bonded, or bolted in place. Rigidity of the assembly jigs is critical to prevent misalignment, so most of these tools are large and heavy. Some of the jigs are permanently installed, while others are on rollers so they can be moved to the assembly line when needed.

Fuselage Assembly

The fuselage group is the first main assembly to be produced. The fuselage group consists of the nose structure assembly, forward cabin structure assembly, aft cabin structure assembly, and the tailcone assembly. The aircraft is essentially assembled from the back forward.

1.                 The first part of the fuselage to be assembled is the aft cabin barrel assembly (see illustration marked "Position 4, Setback 0"). The cabin barrel is assembled in the vertical direction in a floor assembly jig. The cabin barrel jig incorporates all the frame assemblies, skins, and supporting structures necessary to complete the aft cabin barrel assembly. Details and sub-assemblies are provided with tooling holes and locators set to contour templates which define the aircraft's loft or contour. Next, an aft cabin intermediate jig is used to assemble three primary components: the aft cabin barrel, the aft pressure bulkhead (which serves as the boundary of the pressurized section of the fuselage), and the wing attach fittings.

2.                 The nose and forward cabin structures are assembled next (see "Position 3, Setback 1"). The nose section jig assembles the forward frame wheel well assembly, skin assemblies, and supporting structures. The forward cabin buildup jig assembles the windshield frame, cabin door frame, forward pressure bulkhead, supporting structure, and skins.

3.                 The forward and aft cabin sections are now mated using a cabin mate jig. Both cabin sections are located in the jig through the use of tooling holes which coordinate both the forward and aft pressure bulkheads (see "Position 3, Setback 0").

4.                 While the cabin sections are being built, the upper and lower tailcone sections are also being assembled. The tail-cone mate jig is used to connect and align the upper and lower tailcone subassemblies (see "Position 2, Setback 2" and "Position 2, Setback 1").

5.                 The three primary fuselage sections, nose, forward and aft cabin assembly, and tailcone are located and assembled using a fuselage mate jig. The forward and aft cabin sections are loaded into the jig first, followed by the nose and tailcone sections. Engine mount brackets, forward and aft, are now installed onto the structural engine beams which extend out from the fuselage. Mounting holes are also aligned. These will be used to attach the vertical stabilizer to the tailcone and the aft canted bulkhead (the aft canted bulkhead "caps" off the end of the tailcone section). (See "Position 2, Setback 0").

Empennage or Tail Assembly

The empennage or tail assembly is the next section to be assembled. It consists of the vertical fin, rudder, horizontal stabilizer, and elevators. The rudder is the primary control surface for yaw or side to side movement usually used to turn the aircraft. Two elevators are mounted on the trailing edge of the horizontal stabilizer and are used to control the pitch or up and down motion of the air-craft.

The horizontal stabilizer frame buildup jig is used to assemble the leading edge and spar assemblies, along with the vertical attach fittings, stringers (aluminum extrusions which are used to provide structural support for sheet metal skins), skins, and supporting structures (see "Position 1, Setback 2").

Elevator frame buildup, trim tab assembly, and skinning jigs are used to assemble the right and left hand elevators. The trim tabs are movable control surfaces attached on the trailing edge of the elevators, used to hold the aircraft in level flight during cruise conditions (somewhat analogous to cruise control in a car). After the elevator frame and trim tabs are constructed, the skinning jig is then used to assemble the frame and trim tab assemblies along with the tip, leading, and trailing edge skins.

The vertical fin buildup jig is used to assemble the leading edge, spar, and bonded skin assemblies, along with the horizontal attach side plates and the supporting structure required to complete the vertical fin section. The fastener locations in the tailcone are established by the airframe alignment jig to ensure the vertical fin's relationship to the wing and engine attach points.

Rudder frame buildup, trim tab assembly, and skinning jigs are utilized in assembling the rudder assembly. After the rudder frame and trim tab is completed, the skinning jig is then used to assemble the frame and trim tab assemblies, along with the leading and trailing edge skins.

The empennage section of the aircraft is completed after the elevators, horizontal stabilizer, vertical stabilizer, and rudder are assembled (the rudder is usually installed last along with the flight control systems). (See "Position 1, Setback 1"). The empennage section is then mated to the aircraft tailcone section (see "Position 1, Setback 0").

Wing Assembly

The wing assembly is next and typically consists of the center wing section, outboard wing sections, and aileron and flap assemblies. The ailerons are movable control surfaces, usually hinged to the outer wing, which help provide control in roll about the longitudinal axis of the plane. The flaps are movable control surfaces, mounted inboard on the wing, which are able to hinge down-ward. These increase low-speed lift and add drag, allowing the aircraft to make steep approach landings without gaining excess airspeed.

Aileron frame buildup and skin and rivet jigs are used to assemble the left and right hand aileron assemblies. After the aileron frame is completed, the skin and rivet jig is used to load the aileron frame, skin and doublers (used for extra strength), then rivet the assembly complete. The aileron frame is located by pinning the hinge bearings and the inboard and out-board rib webs (the ribs are primary structural members running across the aileron). The ailerons are usually installed last, along with the flight control instruments and flaps.

Flap frame buildup and skin jigs are used in constructing the left and right hand flap assemblies. The flap frame is completed first. Then the flap skin jig assembles the bonded upper skin and trailing edge skin, flap spar section, leading edge assembly and end ribs and interconnect clevises.

The building of the outboard wing section involves the use of many different jigs for drilling, riveting, and buildup. The main tool used is the outboard wing buildup jig, which assembles the forward outboard wing assembly, rear spar assembly, trailing edge bonded skin assemblies, and the supporting structure (see "Position 1, Setback 3").

The construction of the center wing section also requires the use of many different buildup jigs. The primary tool used here is the center wing buildup jig, which assembles the center section subassembly, wheelwell structure, rib and skin assemblies, and the supporting structure (see "Position 1, Setback 2").

The wing assembly mate jig assembles both the left and right outboard wings with the center wing. The wing sections and center section are located in the jig by locators and contour boards. The center section is loaded first, followed by the left and right outboard wings (see "Position 1, Setback 1"). The completed wing assembly is then mated to the fuselage section (see "Position 1, Setback 0").

Landing Gear Assembly

There are two different landing gear assemblies: the nose and main landing gears. Both use retraction systems which are electrically controlled and hydraulically actuated. The main landing gear (MLG) is usually a trailing link type, and retracts inboard into the wing. The nose landing gear (NLG) retracts forward into the fuselage nose section, and is enclosed by doors. The landing gears are assembled away from the main assembly line and are brought to the line when needed, usually when the fuselage and wings are being mated (see "Position 1, Setback 0").

Powerplant-Jet Engine

A business jet is typically powered by two turbofan jet engines located on each side of the rear fuselage in nacelle assemblies. The nacelle assemblies consist of an inlet section, a cowl or outer housing, an exhaust nozzle section, and a bleed air system, which diverts hot air to the wing and nacelle leading edges for deicing. Bleed air is also used for cabin heating and pressurization. The large sheet metal panels which form the cowl are typically roll formed. Some of the other sheet metal parts, such as the nose cap on the nacelle inlet section, are formed using a female die in a draw press. Nacelle assemblies are built separately away from the line and then brought back for installation (see "Position 1, Setback 0").

Flight Control Systems

The flight control systems are usually installed last, along with the ailerons, flaps, and rudder. There are many different flight control systems which go into a modern air-craft. The following is a partial list of the major systems: aileron control system; aileron trim system; speedbrake system; flap interconnect system; rudder control system; rudder trim control system; elevator control system; elevator trim control system; pressurization system; windshield anti-ice system; wing anti-ice system; oxygen system; pitot static system. (See "Position 1, Setback 0").

Out the Door

Before the aircraft leaves the factory, all electrical and mechanical systems undergo a functional test. Examples of items checked are fuel calibration, hydraulic systems, gear blow down and lock, warning lights and horns, and avionics. After the engines and flight control systems are installed, the aircraft is ready to go out the door for engine testing and flight test. The aircraft is put through numerous performance and systems tests before it is approved for delivery to the customer. Before delivery, the aircraft is sent to be painted, after which the interior is finished. (See "Position 0, Setback 0").

Quality Control

The quality of aircraft depends on good design, documentation, and electronic record keeping to meet Federal Aviation Administration (FAA) regulations and certification requirements. The windshields, wing leading edges, engines and other critical components must meet the FAR 25 (Federal Aviation Regulation) bird strike requirements before the aircraft is certified for commercial use. Many different forms and checklists are used throughout the manufacturing process to detail the history of each part made. Various laboratory tests and standardized aerospace material specifications have been developed specially for aircraft. To check how well bonded panels have adhered, they are placed in a water tank for ultrasonic testing. Stress testing is used extensively. A section of the aircraft is assembled and then placed in a test fixture which simulates actual use under varying conditions. Some of the tests are run until the parts fail, to see if the design safety factor is acceptable.

Byproducts/Waste

Environmental protection laws have developed stringent codes limiting water flows and emissions from aircraft manufacturing facilities. In compliance with federal laws, aircraft companies have been using fewer solvents and looking for better ways to clean parts, such as steam vapor degreasing systems. Aluminum chips and scrap material are the major byproducts of the aircraft industry, and are recycled.

The Future

Technological change is a major driving force in the evolution of aircraft manufacturing. Many developments underway involve computerized controls and automation designed to improve economy and quality and lower energy consumption and pollution. More assembly operations, such as riveting, may become completely automated. "Smart" sensors – sensors with predictive abilities involving fuzzy logic and artificial intelligence – are becoming more prevalent. Artificial intelligence or "fuzzy controls" enable the sensors to predict changes needed in the settings due to changes in load or production volume. In addition to these developments, increasing economic and environmental needs will bring further technical refinements to aircraft manufacturing.

Where To Learn More

Books

1.     Bright, Charles D. The Jet Makers. The Regents Press of Kansas, 1978.

2.     Gunston, Bill. Jane's Aerospace Dictionary, 3rd edition. Jane's Information Group Ltd, 1988.

3.     Phillips, Almarin, A. Paul Phillips, Thomas R. Phillips. Biz Jets: Technology and Market Structure in the Corporate Jet Aircraft Industry. Kluwer Academic Publishers, 1994.

4.     Porter, Donald J. The Cessna Citations. TAB Books, 1993.

5.     Rowe, Frank Joseph and Craig Miner. Borne on the South Wind: A Century of Aviation in Kansas. The Wichita Eagle and Beacon Publishing Co., 1994.

6.     Todd, Daniel. The World Aircraft Industry. Auburn House Publishing Company, 1986.

7.     Winant, John H. Keep Business Flying: A History of the National Business Aircraft Association, Inc. 1946-1986. The National Business Aircraft Association, Inc., 1989.