A few nice Aluminium Doors images I found:
Wood
Image by Joost J. Bakker IJmuiden
Wood is a hard, fibrous tissue found in many plants. It has been used for centuries for both fuel and as a construction material for several types of living areas such as houses. It is an organic material, a natural composite of cellulose fibers (which are strong in tension) embedded in a matrix of lignin which resists compression. In the strict sense wood is produced as secondary xylem in the stems of trees (and other woody plants). In a living tree it transfers water and nutrients to the leaves and other growing tissues, and has a support function, enabling woody plants to reach large sizes or to stand up for themselves. Wood may also refer to other plant materials with comparable properties, and to material engineered from wood, or wood chips or fiber.
People have used wood for millennia for many purposes, primarily as a fuel or as a construction material for making houses, tools, weapons, furniture, packaging, artworks, and paper. Wood can be dated by carbon dating and in some species by dendrochronology to make inferences about when a wooden object was created. The year-to-year variation in tree-ring widths and isotopic abundances gives clues to the prevailing climate at that time.
Formation
Wood, in the strict sense, is yielded by trees, which increase in diameter by the formation, between the existing wood and the inner bark, of new woody layers which envelop the entire stem, living branches, and roots. Technically this is known as secondary growth; it is the result of cell division in the vascular cambium, a lateral meristem, and subsequent expansion of the new cells.
Growth rings
Where there are clear seasons, growth can occur in a discrete annual or seasonal pattern, leading to growth rings; these can usually be most clearly seen on the end of a log, but are also visible on the other surfaces. If these seasons are annual these growth rings are referred to as annual rings. Where there is no seasonal difference growth rings are likely to be indistinct or absent.
If there are differences within a growth ring, then the part of a growth ring nearest the center of the tree, and formed early in the growing season when growth is rapid, is usually composed of wider elements. It is usually lighter in color than that near the outer portion of the ring, and is known as earlywood or springwood. The outer portion formed later in the season is then known as the latewood or summerwood. However, there are major differences, depending on the kind of wood.
Knots
A knot on a tree at the Garden of the Gods public park in Colorado Springs, Colorado (October 2006).A knot is a particular type of imperfection in a piece of wood; it will affect the technical properties of the wood, usually for the worse, but may be exploited for artistic effect. In a longitudinally sawn plank, a knot will appear as a roughly circular "solid" (usually darker) piece of wood around which the grain of the rest of the wood "flows" (parts and rejoins). Within a knot, the direction of the wood (grain direction) is up to 90 degrees different from the grain direction of the regular wood.
In the tree a knot is either the base of a side branch or a dormant bud. A knot (when the base of a side branch) is conical in shape (hence the roughly circular cross-section) with the tip at the point in stem diameter at which the plant’s cambium was located when the branch formed as a bud.
During the development of a tree, the lower limbs often die, but may persist for a time, sometimes years. Subsequent layers of growth of the attaching stem are no longer intimately joined with the dead limb, but are grown around it. Hence, dead branches produce knots which are not attached, and likely to drop out after the tree has been sawn into boards.
In grading lumber and structural timber, knots are classified according to their form, size, soundness, and the firmness with which they are held in place. This firmness is affected by, among other factors, the length of time for which the branch was dead while the attaching stem continued to grow.
Knots materially affect cracking (known in the US as checking, and the UK as shakes) and warping, ease in working, and cleavability of timber. They are defects which weaken timber and lower its value for structural purposes where strength is an important consideration. The weakening effect is much more serious when timber is subjected to forces perpendicular to the grain and/or tension than where under load along the grain and/or compression. The extent to which knots affect the strength of a beam depends upon their position, size, number, and condition. A knot on the upper side is compressed, while one on the lower side is subjected to tension. If there is a season check in the knot, as is often the case, it will offer little resistance to this tensile stress. Small knots, however, may be located along the neutral plane of a beam and increase the strength by preventing longitudinal shearing. Knots in a board or plank are least injurious when they extend through it at right angles to its broadest surface. Knots which occur near the ends of a beam do not weaken it. Sound knots which occur in the central portion one-fourth the height of the beam from either edge are not serious defects.
Knots do not necessarily influence the stiffness of structural timber, this will depend on the size and location. Stiffness and elastic strength are more dependent upon the sound wood than upon localised defects. The breaking strength is very susceptible to defects. Sound knots do not weaken wood when subject to compression parallel to the grain.
In some decorative applications, wood with knots may be desirable to add visual interest. In applications where wood is painted, such as skirting boards, fascia boards, door frames and furniture, resins present in the timber may continue to ‘bleed’ through to the surface of a knot for months or even years after manufacture and show as a yellow or brownish stain. A Knot Primer paint or solutuion, correctly applied during preparation, may do much to reduce this problem but it is difficult to control completely, especially when using massproduced kiln-dried timber stocks
Heartwood and sapwood
A section of a Yew branch showing 27 annual growth rings, pale sapwood and dark heartwood, and pith (centre dark spot). The dark radial lines are small knots.Heartwood is wood that, as a result of tylosis, has become more resistant to decay. Tylosis is the deposition of chemical substances (a genetically programmed process). Once heartwood formation is complete, the heartwood is dead. Some uncertainty still exists as to whether heartwood is truly dead, as it can still chemically react to decay organisms, but only once (Shigo 1986, 54).
Usually heartwood looks different; in that case it can be seen on a cross-section, usually following the growth rings in shape. Heartwood may (or may not) be much darker than living wood. It may (or may not) be sharply distinct from the sapwood. However, other processes, such as decay, can discolor wood, even in woody plants that do not form heartwood, with a similar color difference, which may lead to confusion.
Sapwood is the younger, outermost wood; in the growing tree it is living wood, and its principal functions are to conduct water from the roots to the leaves and to store up and give back according to the season the reserves prepared in the leaves. However, by the time they become competent to conduct water, all xylem tracheids and vessels have lost their cytoplasm and the cells are therefore functionally dead. All wood in a tree is first formed as sapwood. The more leaves a tree bears and the more vigorous its growth, the larger the volume of sapwood required. Hence trees making rapid growth in the open have thicker sapwood for their size than trees of the same species growing in dense forests. Sometimes trees (of species that do form heartwood) grown in the open may become of considerable size, 30 cm or more in diameter, before any heartwood begins to form, for example, in second-growth hickory, or open-grown pines.
The term heartwood derives solely from its position and not from any vital importance to the tree. This is evidenced by the fact that a tree can thrive with its heart completely decayed. Some species begin to form heartwood very early in life, so having only a thin layer of live sapwood, while in others the change comes slowly. Thin sapwood is characteristic of such species as chestnut, black locust, mulberry, osage-orange, and sassafras, while in maple, ash, hickory, hackberry, beech, and pine, thick sapwood is the rule. Others never form heartwood.
There is no definite relation between the annual rings of growth and the amount of sapwood. Within the same species the cross-sectional area of the sapwood is very roughly proportional to the size of the crown of the tree. If the rings are narrow, more of them are required than where they are wide. As the tree gets larger, the sapwood must necessarily become thinner or increase materially in volume. Sapwood is thicker in the upper portion of the trunk of a tree than near the base, because the age and the diameter of the upper sections are less.
When a tree is very young it is covered with limbs almost, if not entirely, to the ground, but as it grows older some or all of them will eventually die and are either broken off or fall off. Subsequent growth of wood may completely conceal the stubs which will however remain as knots. No matter how smooth and clear a log is on the outside, it is more or less knotty near the middle. Consequently the sapwood of an old tree, and particularly of a forest-grown tree, will be freer from knots than the inner heartwood. Since in most uses of wood, knots are defects that weaken the timber and interfere with its ease of working and other properties, it follows that a given piece of sapwood, because of its position in the tree, may well be stronger than a piece of heartwood from the same tree.
It is remarkable that the inner heartwood of old trees remains as sound as it usually does, since in many cases it is hundreds, and in a few instances thousands, of years old. Every broken limb or root, or deep wound from fire, insects, or falling timber, may afford an entrance for decay, which, once started, may penetrate to all parts of the trunk. The larvae of many insects bore into the trees and their tunnels remain indefinitely as sources of weakness. Whatever advantages, however, that sapwood may have in this connection are due solely to its relative age and position.
If a tree grows all its life in the open and the conditions of soil and site remain unchanged, it will make its most rapid growth in youth, and gradually decline. The annual rings of growth are for many years quite wide, but later they become narrower and narrower. Since each succeeding ring is laid down on the outside of the wood previously formed, it follows that unless a tree materially increases its production of wood from year to year, the rings must necessarily become thinner as the trunk gets wider. As a tree reaches maturity its crown becomes more open and the annual wood production is lessened, thereby reducing still more the width of the growth rings. In the case of forest-grown trees so much depends upon the competition of the trees in their struggle for light and nourishment that periods of rapid and slow growth may alternate. Some trees, such as southern oaks, maintain the same width of ring for hundreds of years. Upon the whole, however, as a tree gets larger in diameter the width of the growth rings decreases.
Different pieces of wood cut from a large tree may differ decidedly, particularly if the tree is big and mature. In some trees, the wood laid on late in the life of a tree is softer, lighter, weaker, and more even-textured than that produced earlier, but in other trees, the reverse applies. This may or may not correspond to heartwood and sapwood. In a large log the sapwood, because of the time in the life of the tree when it was grown, may be inferior in hardness, strength, and toughness to equally sound heartwood from the same log. In a smaller tree, the reverse may be true.
Hard and soft woods
There is a strong relationship between the properties of wood and the properties of the particular tree that yielded it. For every tree species there is a range of density for the wood it yields. There is a rough correlation between density of a wood and its strength (mechanical properties). For example, while mahogany is a medium-dense hardwood which is excellent for fine furniture crafting, balsa is light, making it useful for model building. The densest wood may be black ironwood.
It is common to classify wood as either softwood or hardwood. The wood from conifers (e.g. pine) is called softwood, and the wood from dicotyledons (usually broad-leaved trees, e.g. oak) is called hardwood. These names are a bit misleading, as hardwoods are not necessarily hard, and softwoods are not necessarily soft. The well-known balsa (a hardwood) is actually softer than any commercial softwood. Conversely, some softwoods (e.g. yew) are harder than many hardwoods.
Engineered wood products have properties that usually differ from those of natural timbers. (see below)
Color
In species which show a distinct difference between heartwood and sapwood the natural color of heartwood is usually darker than that of the sapwood, and very frequently the contrast is conspicuous (see section of yew log above). This is produced by deposits in the heartwood of chemical substances, so that a dramatic color difference does not mean a dramatic difference in the mechanical properties of heartwood and sapwood, although there may be a dramatic chemical difference.
Some experiments on very resinous Longleaf Pine specimens indicate an increase in strength, due to the resin which increases the strength when dry. Such resin-saturated heartwood is called "fat lighter". Structures built of fat lighter are almost impervious to rot and termites; however they are very flammable. Stumps of old longleaf pines are often dug, split into small pieces and sold as kindling for fires. Stumps thus dug may actually remain a century or more since being cut. Spruce impregnated with crude resin and dried is also greatly increased in strength thereby.
Since the latewood of a growth ring is usually darker in color than the earlywood, this fact may be used in judging the density, and therefore the hardness and strength of the material. This is particularly the case with coniferous woods. In ring-porous woods the vessels of the early wood not infrequently appear on a finished surface as darker than the denser latewood, though on cross sections of heartwood the reverse is commonly true. Except in the manner just stated the color of wood is no indication of strength.
Abnormal discoloration of wood often denotes a diseased condition, indicating unsoundness. The black check in western hemlock is the result of insect attacks. The reddish-brown streaks so common in hickory and certain other woods are mostly the result of injury by birds. The discoloration is merely an indication of an injury, and in all probability does not of itself affect the properties of the wood. Certain rot-producing fungi impart to wood characteristic colors which thus become symptomatic of weakness; however an attractive effect known as spalting produced by this process is often considered a desirable characteristic. Ordinary sap-staining is due to fungous growth, but does not necessarily produce a weakening effect.
Structure
Wood is a heterogeneous, hygroscopic, cellular and anisotropic material. It is composed of cells, and the cell walls are composed of micro-fibrils of cellulose (40% – 50%) and hemicellulose (15% – 25%) impregnated with lignin (15% – 30%).
Sections of tree trunk
A tree trunk as found at the Veluwe, NetherlandsIn coniferous or softwood species the wood cells are mostly of one kind, tracheids, and as a result the material is much more uniform in structure than that of most hardwoods. There are no vessels ("pores") in coniferous wood such as one sees so prominently in oak and ash, for example.
The structure of hardwoods is more complex. The water conducting capability is mostly taken care of by vessels: in some cases (oak, chestnut, ash) these are quite large and distinct, in others (buckeye, poplar, willow) too small to be seen without a hand lens. In discussing such woods it is customary to divide them into two large classes, ring-porous and diffuse-porous. In ring-porous species, such as ash, black locust, catalpa, chestnut, elm, hickory, mulberry, and oak, the larger vessels or pores (as cross sections of vessels are called) are localised in the part of the growth ring formed in spring, thus forming a region of more or less open and porous tissue. The rest of the ring, produced in summer, is made up of smaller vessels and a much greater proportion of wood fibers. These fiber are the elements which give strength and toughness to wood, while the vessels are a source of weakness.
In diffuse-porous woods the pores are evenly sized so that the water conducting capability is scattered throughout the growth ring instead of being collected in a band or row. Examples of this kind of wood are basswood, birch, buckeye, maple, poplar, and willow. Some species, such as walnut and cherry, are on the border between the two classes, forming an intermediate group.
Earlywood and latewood in softwood
earlywood and latewood in a softwood; radial view, growth rings closely spaced in a Pseudotsuga taxifoliaIn temperate softwoods there often is a marked difference between latewood and earlywood. The latewood will be denser than that formed early in the season. When examined under a microscope the cells of dense latewood are seen to be very thick-walled and with very small cell cavities, while those formed first in the season have thin walls and large cell cavities. The strength is in the walls, not the cavities. Hence the greater the proportion of latewood the greater the density and strength. In choosing a piece of pine where strength or stiffness is the important consideration, the principal thing to observe is the comparative amounts of earlywood and latewood. The width of ring is not nearly so important as the proportion and nature of the latewood in the ring.
If a heavy piece of pine is compared with a lightweight piece it will be seen at once that the heavier one contains a larger proportion of latewood than the other, and is therefore showing more clearly demarcated growth rings. In white pines there is not much contrast between the different parts of the ring, and as a result the wood is very uniform in texture and is easy to work. In hard pines, on the other hand, the latewood is very dense and is deep-colored, presenting a very decided contrast to the soft, straw-colored earlywood.
It is not only the proportion of latewood, but also its quality, that counts. In specimens that show a very large proportion of latewood it may be noticeably more porous and weigh considerably less than the latewood in pieces that contain but little. One can judge comparative density, and therefore to some extent strength, by visual inspection
No satisfactory explanation can as yet be given for the exact mechanisms determining the formation of earlywood and latewood. Several factors may be involved. In conifers, at least, rate of growth alone does not determine the proportion of the two portions of the ring, for in some cases the wood of slow growth is very hard and heavy, while in others the opposite is true. The quality of the site where the tree grows undoubtedly affects the character of the wood formed, though it is not possible to formulate a rule governing it. In general, however, it may be said that where strength or ease of working is essential, woods of moderate to slow growth should be chosen.
Earlywood and latewood in ring-porous woods
Earlywood and latewood in a ring-porous wood (ash) in a Fraxinus excelsior ; tangential view, wide growth ringsIn ring-porous woods each season’s growth is always well defined, because the large pores formed early in the season abut on the denser tissue of the year before.
In the case of the ring-porous hardwoods there seems to exist a pretty definite relation between the rate of growth of timber and its properties. This may be briefly summed up in the general statement that the more rapid the growth or the wider the rings of growth, the heavier, harder, stronger, and stiffer the wood. This, it must be remembered, applies only to ring-porous woods such as oak, ash, hickory, and others of the same group, and is, of course, subject to some exceptions and limitations.
In ring-porous woods of good growth it is usually the latewood in which the thick-walled, strength-giving fibers are most abundant. As the breadth of ring diminishes, this latewood is reduced so that very slow growth produces comparatively light, porous wood composed of thin-walled vessels and wood parenchyma. In good oak these large vessels of the earlywood occupy from 6 to 10 per cent of the volume of the log, while in inferior material they may make up 25 per cent or more. The latewood of good oak is dark colored and firm, and consists mostly of thick-walled fibers which form one-half or more of the wood. In inferior oak, this latewood is much reduced both in quantity and quality. Such variation is very largely the result of rate of growth.
Wide-ringed wood is often called "second-growth", because the growth of the young timber in open stands after the old trees have been removed is more rapid than in trees in a closed forest, and in the manufacture of articles where strength is an important consideration such "second-growth" hardwood material is preferred. This is particularly the case in the choice of hickory for handles and spokes. Here not only strength, but toughness and resilience are important. The results of a series of tests on hickory by the U.S. Forest Service show that:
"The work or shock-resisting ability is greatest in wide-ringed wood that has from 5 to 14 rings per inch (rings 1.8-5 mm thick), is fairly constant from 14 to 38 rings per inch (rings 0.7-1.8 mm thick), and decreases rapidly from 38 to 47 rings per inch (rings 0.5-0.7 mm thick). The strength at maximum load is not so great with the most rapid-growing wood; it is maximum with from 14 to 20 rings per inch (rings 1.3-1.8 mm thick), and again becomes less as the wood becomes more closely ringed. The natural deduction is that wood of first-class mechanical value shows from 5 to 20 rings per inch (rings 1.3-5 mm thick) and that slower growth yields poorer stock. Thus the inspector or buyer of hickory should discriminate against timber that has more than 20 rings per inch (rings less than 1.3 mm thick). Exceptions exist, however, in the case of normal growth upon dry situations, in which the slow-growing material may be strong and tough."
The effect of rate of growth on the qualities of chestnut wood is summarised by the same authority as follows:
"When the rings are wide, the transition from spring wood to summer wood is gradual, while in the narrow rings the spring wood passes into summer wood abruptly. The width of the spring wood changes but little with the width of the annual ring, so that the narrowing or broadening of the annual ring is always at the expense of the summer wood. The narrow vessels of the summer wood make it richer in wood substance than the spring wood composed of wide vessels. Therefore, rapid-growing specimens with wide rings have more wood substance than slow-growing trees with narrow rings. Since the more the wood substance the greater the weight, and the greater the weight the stronger the wood, chestnuts with wide rings must have stronger wood than chestnuts with narrow rings. This agrees with the accepted view that sprouts (which always have wide rings) yield better and stronger wood than seedling chestnuts, which grow more slowly in diameter."
Earlywood and latewood in diffuse-porous woods
In the diffuse-porous woods, the demarcation between rings is not always so clear and in some cases is almost (if not entirely) invisible to the unaided eye. Conversely, when there is a clear demarcation there may not be a noticeable difference in structure within the growth ring.
In diffuse-porous woods, as has been stated, the vessels or pores are even-sized, so that the water conducting capability is scattered throughout the ring instead of collected in the earlywood. The effect of rate of growth is, therefore, not the same as in the ring-porous woods, approaching more nearly the conditions in the conifers. In general it may be stated that such woods of medium growth afford stronger material than when very rapidly or very slowly grown. In many uses of wood, total strength is not the main consideration. If ease of working is prized, wood should be chosen with regard to its uniformity of texture and straightness of grain, which will in most cases occur when there is little contrast between the latewood of one season’s growth and the earlywood of the next.
Monocot wood
Trunks of the Coconut palm, a monocot, in Java. From this perspective these look not much different from trunks of a dicot or coniferStructural material that roughly (in its gross handling characteristics) resembles ordinary, "dicot" or conifer wood is produced by a number of monocot plants, and these also are usually called wood. Of these, bamboo, botanically a member of the grass family, has considerable economic importance, larger culms being widely used as a building and construction material in their own right and, these days, in the manufacture of engineered flooring, panels and veneer. Another major plant group that produce material that often is called wood are the palms. Of much less importance are plants such as Pandanus, Dracaena and Cordyline. With all this material, the structure and composition of the structural material is quite different from ordinary wood.
Water content
The churches of Kizhi, Russia are among a handful of World Heritage Sites built entirely of wood, without metal joints.Water occurs in living wood in three conditions, namely: (1) in the cell walls, (2) in the protoplasmic contents of the cells, and as free water in the cell cavities and spaces. In heartwood it occurs only in the first and last forms. Wood that is thoroughly air-dried retains from 8-16% of water in the cell walls, and none, or practically none, in the other forms. Even oven-dried wood retains a small percentage of moisture, but for all except chemical purposes, may be considered absolutely dry.
The general effect of the water content upon the wood substance is to render it softer and more pliable. A similar effect of common observation is in the softening action of water on paper or cloth. Within certain limits, the greater the water content, the greater its softening effect.
Drying produces a decided increase in the strength of wood, particularly in small specimens. An extreme example is the case of a completely dry spruce block 5 cm in section, which will sustain a permanent load four times as great as that which a green (undried) block of the same size will support.[citation needed]
The greatest increase due to drying is in the ultimate crushing strength, and strength at elastic limit in endwise compression; these are followed by the modulus of rupture, and stress at elastic limit in cross-bending, while the modulus of elasticity is least affected.
Fuel
Main article: Wood fuel
Wood has a long history of being used as fuel, which continues to this day, mostly in rural areas of the world. Hardwood is preferred over softwood because it creates less smoke and burns longer. Adding a woodstove or fireplace to a home is often felt to add ambiance and warmth.
Construction
Wood can be cut into straight planks and made into a wood flooring.
The Saitta House, Dyker Heights, Brooklyn, New York built in 1899 is made of and decorated in wood.[8]Wood has been an important construction material since humans began building shelters, houses and boats. Nearly all boats were made out of wood until the late 19th century, and wood remains in common use today in boat construction.
Wood to be used for construction work is commonly known as lumber in North America. Elsewhere, lumber usually refers to felled trees, and the word for sawn planks ready for use is timber.
New domestic housing in many parts of the world today is commonly made from timber-framed construction. Engineered wood products are becoming a bigger part of the construction industry. They may be used in both residential and commercial buildings as structural and aesthetic materials.
In buildings made of other materials, wood will still be found as a supporting material, especially in roof construction, in interior doors and their frames, and as exterior cladding.
Wood is also commonly used as shuttering material to form the mould into which concrete is poured during reinforced concrete construction.
Engineered wood
Wood used in construction includes products such as glued laminated timber (glulam), laminated veneer lumber (LVL), parallam and I-joists. On the one hand these allow the use of smaller pieces, and on the other hand allow bigger spans. They may also be selected for specific projects such as public swimming pools or ice rinks where the wood will not deteriorate in the presence of certain chemicals. These engineered wood products prove to be more environmentally friendly, and sometimes cheaper, than building materials such as steel or concrete.
Wood unsuitable for construction in its native form may be broken down mechanically (into fibers or chips) or chemically (into cellulose) and used as a raw material for other building materials such as chipboard, engineered wood, hardboard, medium-density fiberboard (MDF), oriented strand board (OSB). Such wood derivatives are widely used: wood fibers are an important component of most paper, and cellulose is used as a component of some synthetic materials. Wood derivatives can also be used for kinds of flooring, for example laminate flooring.
Next generation wood products
Further developments include new lignin glue applications, recyclable food packaging, rubber tire replacement applications, anti-bacterial medical agents, and high strength fabrics or composites. As scientists and engineers further learn and develop new techniques to extract various components from wood, or alternatively to modify wood, for example by adding components to wood, new more advanced products will appear on the marketplace.
Furniture and utensils
Wood has always been used extensively for furniture, including chairs and beds. Also for tool handles and cutlery, such as chopsticks, toothpicks, and other utensils, like the wooden spoon.
In the arts
Artists can use wood to create delicate sculptures.
Stringed instrument bows are often made from pernambuco or brazilwood.Main article: Wood as a medium
Wood has long been used as an artistic medium. It has been used to make sculptures and carvings for millennia. Examples include the totem poles carved by North American indigenous people from conifer trunks, often Western Red Cedar (Thuja plicata), and the Millennium clock tower , now housed in the National Museum of Scotland[ in Edinburgh.
It is also used in woodcut printmaking, and for engraving.
Certain types of musical instruments, such as those of the violin family, the guitar, the clarinet and recorder, the xylophone, and the marimba, are made mostly or entirely of wood. The choice of wood may make a significant difference to the tone and resonant qualities of the instrument, and tonewoods have widely differing properties, ranging from the hard and dense african blackwood (used for the bodies of clarinets) to the light but resonant European spruce (Picea abies) (traditionally used for the soundboards of violins). The most valuable tonewoods, such as the ripple sycamore (Acer pseudoplatanus), used for the backs of violins, combine acoustic properties with decorative color and grain which enhance the appearance of the finished instrument.
Sports and recreational equipment
Many types of sports equipment are made of wood, or were constructed of wood in the past. For example, cricket bats are typically made of white willow. The baseball bats which are legal for use in Major League Baseball are frequently made of ash wood or hickory, and in recent years have been constructed from maple even though that wood is somewhat more fragile. In softball, however, bats are more commonly made of aluminium (this is especially true for fastpitch softball).
Many other types of sports and recreation equipment, such as skis, ice hockey sticks, lacrosse sticks and archery bows, were commonly made of wood in the past, but have since been replaced with more modern materials such as aluminium, fiberglass, carbon fiber, titanium, and composite materials. One noteworthy example of this trend is the golf club commonly known as the wood, the head of which was traditionally made of persimmon wood in the early days of the game of golf, but is now generally made of synthetic materials.
Medicine
In January 2010 Italian scientists announced that wood could be harnessed to become a bone substitute. It is likely to take at least five years until this technique will be applied for humans.
Capital Airlines de Havilland DH 4A Comet
Image by james_gordon_los_angeles
CAPITAL AIRLINES PURCHASE COMETS' was the headline in the Enterprise magazine - the internal magazine of the de Havilland Company. It referred to a (then) recent joint announcement by Capital and de Havilland which disclosed an order for 14 Comet aircraft.
Thus it appeared that de Havilland had done what every other non-American manufacturer needed to do, broken into the United States airliner market in the face of home competition. The argument went: with a foot hold in the U.S. market many more 'knock on' sales could be hoped for. So the announcement was of very great significance.
The agreement specified that the Comets would be powered by Rolls-Royce engines, and including spares, the cost was put at some £19 million/USD 7 million (year 2000 = £263/43). Deliveries were to commence in late 1958 with four Comet Mk.4s and late in 1959 with ten of the special variant the Mk.4A.
J.H. Slim Carmichael, who was President of Capital Airlines, said of the deal, The decision to purchase the Comet has been made after a most comprehensive and detailed study of all flight equipment either in production or projected, both in the United States and England. The economical and operating characteristics of the Comet 4A are ideally suited to the Capital system. The Comets will go into service on our major and most competitive routes.
Apparently the same basis for determining economic criteria were used when Capital purchased Viscounts. (ed note - The only financing Capital had available was through the Bank Of England and only for British built aircraft). Projections made before the Viscount purchase had proved accurate when it was introduced on Capital routes in 1955. The Comet order was placed because Capital now wanted a range of pure-jets to operate some 200 mph faster than anything else they then had in use. Capital was one of the biggest domestic carriers in the USA as was illustrated by figures for 1955 which showed that Capital carried 2½ million passengers over some 31 million miles!
Capital's Mk.4As were to be furnished to accommodate 74 passengers in the utmost luxury by having 68 persons seated four abreast in two large cabins and six in a forward lounge. The expectation was that passengers would be carried in unprecedented smoothness and quietude, even surpassing the qualities of the earlier Comet models while the speed and economy also show a marked advance. The 4A was to be assembled at Chester as well as Hatfield, England.
The Mk.4A was launched in June 1956 as a short range version of the Comet. The fuselage was stretched and the wing span was reduced. Maximum takeoff weight was reduced to 152.5Klb. The Mk.4A died, when the launch customer Capital Airlines cancelled the order. As a result no Mk 4A was ever built.
Unfortunately Capital suffered sudden financial difficulties, a period of uncertainty and numerous fatal incidents, it was forced to give up some of its routes to rival carriers and was absorbed into United Airlines. The foothold into the US market was lost and the Mk.4A was never produced.
The de Havilland DH 106 Comet was the world's first commercial jet airliner to reach production. Developed and manufactured by de Havilland at the Hatfield, Hertfordshire, United Kingdom headquarters, it first flew in 1949 and was a landmark in aeronautical design. It featured an extremely aerodynamically clean design with its four de Havilland Ghost turbojet engines buried into the wings, a low-noise pressurised cabin, and large windows; for the era, it was an exceptionally comfortable design for passengers and showed signs of being a major success in the first year upon launching.
However, a few years after introduction into commercial service, Comet airframes began suffering from catastrophic metal fatigue, which in combination with cabin pressurisation cycles, caused two well-publicised accidents where the aircraft tore apart in mid-flight. The Comet had to be withdrawn and extensively tested to discover the cause; the first incident had been incorrectly identified as having been caused by an onboard fire. Several contributory factors, such as window installation methodology, were also identified as exacerbating the problem. The Comet was extensively redesigned to eliminate this design flaw. Rival manufacturers meanwhile developed their own aircraft and heeded the lessons learned from the Comet.
Although sales never fully recovered, the redesigned Comet 4 series subsequently enjoyed a long and productive career of over 30 years. The Comet was adapted for a variety of military roles, such as surveillance, VIP, medical and passenger transport; the most extensive modification resulted in a specialised maritime patrol aircraft variant, the Hawker Siddeley Nimrod. Nimrods remained in service with the Royal Air Force (RAF) until they were retired in June 2011, over 60 years after the Comet's first flight.
Development
Design studies for the DH 106 Comet 1944–1947
During the Second World War, the Brabazon Committee was formed on 11 March 1943 to determine Britain's postwar airliner needs. One of the recommendations set a design target of a pressurised, transatlantic mailplane that could carry a ton of payload at a cruising speed of 400 mph (640 km/h).[8] Challenging the widely held scepticism of jet engines as too fuel-hungry and unreliable, committee member Sir Geoffrey de Havilland, head of the de Havilland company, used his influence and the company’s expertise with jets to specify a turbojet-powered design.[7] The committee accepted the proposal, calling it the "Type IV" (of five designs), and awarded the production contract to de Havilland’s Type 106. The first-phase designs focused on short and intermediate range mailplanes with a small passenger compartment and as few as six seats, later redefined as a long-range airliner with 24-seat capacity. Out of all the Brabazon designs, the DH 106 was seen as the riskiest in terms of both introducing untried design elements and for the financial commitment involved.[7] Nevertheless, British Overseas Airways Corporation (BOAC) found the Type IV’s specifications attractive, initially proposing a purchase of 25 aircraft and, in December 1945, when a "firm contract" was laid out, revising the number to 10.
A design team was formed in 1946 under the leadership of Chief Designer Ronald Bishop, who had been responsible for the Mosquito fighter-bomber. A number of unorthodox configurations were considered, all of which were subsequently rejected. The Ministry of Supply was interested in the most radical of the proposed designs and issued Operational Requirement OR207 to Specification E.18/45 for two experimental DH 108s ordered as proof-of-concept aircraft to test swept-wing configurations in both low-speed and high-speed flight.
Even before the DH 108s were completed, further requests from BOAC necessitated a redesign of the DH 106 from the original four-engined (Halford H.1 Goblin-powered) 24-seat airliner to a larger 36-seat version to specification 22/46 in September 1946. With no time to develop the technology required for the tailless configuration, Bishop opted for a more conventional 20˚ swept-wing design with unswept tail surfaces, married to an enlarged fuselage accommodating 36 passengers, arranged four abreast with a central aisle. Four new, more powerful Rolls-Royce Avons were to be incorporated in pairs buried in the wing roots, but Halford H.2 Ghost engines were eventually specified as an interim solution while the Avons cleared certification. The redesigned DH 106 was named the DH 106 Comet in December 1947. First revised orders for both BOAC and British South American Airways for a combined total of 14 aircraft had a projected delivery schedule set for 1952.
During 1947–1948, de Havilland undertook an extensive research and development phase, utilising a number of stress test rigs at Hatfield for small components and large assemblies. Sections of the pressurised fuselage were subjected to the conditions of a flight at altitude in the company’s decompression chamber. The DH 108s were also modified to test the DH 106′s power controls.
The first flight of the first prototype DH 106 Comet (carrying Class B markings G-5-1) took place on 27 July 1949 from Hatfield, and lasted 31 minutes. The pilot was de Havilland Chief Test Pilot John Cunningham, a famous wartime night-fighter pilot, who later commented, "I assumed that it would change aviation, and so it has proved. It was a bit like Concorde. Also on board were co-pilot Harold Tubby Waters, engineers John Wilson (electrics) and Frank Reynolds (hydraulics), along with flight test observer Tony Fairbrother. Fairbrother commented, The world changed as our wheels left the ground.
G-5-1 was publicly displayed at the 1949 Farnborough Airshow before beginning flight trials. A year later, the second prototype made its maiden flight. On 2 April 1951, this aircraft was delivered to the BOAC Comet Unit at Hurn under the registration G-ALZK and carried out 500 flying hours of crew training and route proving.[22] Both prototypes were distinguished by large main wheel units that were replaced by four-wheeled bogies on each main leg for the subsequent production series.
The British Government considered the development of the Comet a highly ideological matter, as high-ranking officials perceived the need to meet foreign competition and surpass them when there was the opportunity to do so:
During the next few years, the UK has an opportunity, which may not recur, of developing aircraft manufacture as one of our main export industries. On whether we grasp this opportunity and so establish firmly an industry of the utmost strategic and economic importance, our future as a great nation may depend.
—Duncan Sandys, Minister of Supply, 1952.
Design
The Comet is an all-metal low-wing cantilever monoplane powered by four jet engines, approximately the length of a Boeing 737, carrying fewer people in a significantly more spacious environment. The earliest Comets had 11 rows of seats with four seats to a row in the 1A configuration used by Air France; BOAC used an even roomier arrangement of 36 seats on 45-inch (1,100 mm) centres. The Comet’s four-place cockpit held two pilots, a flight engineer, and a navigator. The cabin was quieter than those of propeller-driven airliners. Amenities included a galley that could serve hot and cold food and drinks, a bar, and separate men’s and women’s washrooms. For emergencies, life rafts were stored in the wings near the engines and life vests were stowed under each seat bottom.
The clean, low-drag design featured many unique or innovative design elements, including a swept-wing leading edge, integral wing fuel tanks, and four-wheel bogie main undercarriage units designed by de Havilland. Two pairs of de Havilland Ghost 50 Mk1 turbojet engines were buried in the wings close to the fuselage. Chief Designer Bishop chose this configuration because it avoided the drag of podded engines and allowed a smaller fin and rudder, since the hazards of asymmetric thrust were reduced. The engines’ higher mounting in the wings also reduced the risk of ingestion damage (foreign object damage [FOD]), a major problem for turbine engines. These benefits were compromised by increased structural weight and general complexity, including armour for the engine cells (in case of an engine explosion) and a more complicated wing structure. This arrangement also carried higher risk of catastrophic wing failure in case of an engine fire, cited as the main reason the Boeing Aircraft Company chose podded engines in their subsequent jet bomber and airliner designs. The fuel system incorporated underwing pressure refuelling, developed by Flight Refuelling Ltd, which allowed much faster refilling of fuel tanks than was possible previously.
The Comet was originally intended to have two hydrogen peroxide-powered de Havilland Sprite booster rockets for takeoff under hot and high altitude conditions from airports such as Khartoum and Nairobi. These were tested on 30 flights, but the Ghosts were considered powerful enough without them, although Sprite fittings were kept on production aircraft. The later Comet 4 was highly rated for its takeoff performance from high altitude locations such as Mexico City. Newer and more powerful AJ.65 Avon engines replaced the Ghosts on the Comet 2. High engine performance combined with a low weight (compared to the Boeing 707 and Douglas DC-8), and exceptionally clean design all contributed to its high performance. Early-model Comets had the advantage of requiring low maintenance, the de Havilland Ghost engines being a key contributing factor. Mounting the engines in a low-wing position combined with numerous service panels allowed for "easy" and efficient maintenance.
The Comet’s thin metal skin was composed of advanced new alloys (Directorate of Technical Development 564/L.73 and DTD 746C/L90) and was both chemically bonded using the adhesive Redux and riveted, which saved weight and reduced the risk of fatigue cracks spreading from the rivets. When it went into service with BOAC on 2 May 1952, the Comet was the most exhaustively tested airliner in history. After the Comet entered production, for safety reasons, and to limit the damage to the specimens, a water tank was used instead of the decompression chamber. The entire forward fuselage section was tested for metal fatigue by repeatedly pressurising to 2.75 pounds per square inch (19.0 kPa) overpressure and depressurising through more than 16,000 cycles, equivalent to about 40,000 hours of airline service. The windows were tested under a pressure of 12 psi (83 kPa), 4.75 psi (32.8 kPa) above the normal service ceiling of 36,000 ft (11,000 m). One window frame survived a massive 100 psi (690 kPa), about 1,250% over the maximum pressure it would encounter in service.
In 1953, Sud-Est’s design bureau, while working on the Sud Aviation Caravelle, licensed several design features from de Havilland, a company Sud had previously collaborated with on earlier licenced designs, including the DH 100 Vampire. [N 12] The entire nose and cockpit layout from the Comet 1 was grafted onto the Caravelle.
Operational history
Introduction
The first production aircraft (G-ALYP) flew on 9 January 1951 and subsequently was on loan to BOAC for development flying by the Comet Unit. On 22 January 1952, G-ALYS was the first Comet to receive a Certificate of Airworthiness, six months ahead of schedule. As part of the BOAC route proving trials, on 2 May, G-ALYP took off on the world’s first jetliner flight with fare-paying passengers, beginning scheduled service to Johannesburg. The last Comet from the initial order (G-ALYZ) began flying in September 1952, carrying cargo along South American routes while simulating passenger schedules.
The Comet was a hit with passengers including Queen Elizabeth, the Queen Mother and Princess Margaret, who were guests on a special flight on 30 June 1953 hosted by Sir Geoffrey and Lady de Havilland, and thus became the first members of the British Royal Family to fly by jet.[48] A total of 30,000 passengers was carried during the first year of service. For the travelling public, the Comet offered flights about 50% faster than advanced piston-engined types such as the Douglas DC-6 (490 mph for the Comet compared to 315 mph for the DC-6B), and its rate of climb was also far higher, which could cut flight times in half. In August 1953 BOAC scheduled the Comet London to Tokyo in 35 hours, compared to 85 hr 35 min for their Argonaut; Pan Am’s DC-6B flight 2 was scheduled 46 hr 45 min. Smooth, quiet jet flight was a new experience for passengers used to piston-engined airliners (although passengers of today would consider it noisy, particularly when seated aft of the wing). BOAC’s Comets featured the BOAC-designed slumberseat; a comfortable, reclining design, allowing for greater leg room in front and behind. The large picture window view and accommodations for a table setting for a row of passengers afforded a feel of comfort and luxury atypical of airliners of the period. One of the most striking aspects of flight on the Comet was the quiet, vibration-free flying touted by BOAC.
Commercial success was widely expected, with a profitable passenger load factor as low as 43%. The Ghost engine was smooth, relatively simple, fuel-efficient above 30,000 ft (9,144 m),[N had low maintenance costs, and enabled operations above weather the competition had to fly through. At the height of Comet's early flying career, the BOAC Comet 1 fleet flew routes such as London-Singapore, London-Tokyo, and London-Johannesburg several times a week.
Early accidents and incidents
On 26 October 1952, a BOAC flight departing from Ciampino airport near Rome failed to become airborne and ran into rough ground at the end of the runway. Two passengers sustained only minor injuries, but the aircraft was a total loss. On 3 March 1953, a new Canadian Pacific Airlines Comet 1A (CF-CUN), known as "Empress of Hawaii," being delivered to Australia, also failed to become airborne on takeoff from Karachi, Pakistan. The aircraft plunged into a dry drainage canal and collided with an embankment, killing all five crew and six passengers on board, the first fatal crash of a passenger jet airliner.
Both of these accidents were originally attributed to pilot error as over-rotation had led to a loss of lift from the leading edge of the aircraft's wing. It was later determined the wing profile led to a loss of lift at high angle of attack, and the engine inlets suffered from a lack of pressure recovery in these conditions as well. The wing leading edge was re-profiled with a pronounced droop and a wing fence was added to control spanwise flow. A fictionalised investigation into these takeoff accidents was the subject of the 1959 novel, Cone of Silence by Arthur David Beaty, a former BOAC captain. Cone of Silence was made into a film in 1960, and Beaty also recounted the story of the Comet's takeoff accidents in a chapter of his 1984 non-fiction work, Strange Encounters: Mysteries of the Air.
The next fatal accident involving passengers was on 2 May 1953, when a BOAC Comet 1 (G-ALYV) crashed in a severe tropical storm six minutes after taking off from Calcutta/Dum Dum (now Netaji Subhash Chandra Bose International Airport), India, killing all 43 on board. The crash was attributed to structural failure of the airframe with witnesses observing the wingless Comet on fire plunging into the Indian Ocean.
India Court of Inquiry
A court of inquiry was convened by the Central Government of India to examine the cause of the accident.[N 17] The conclusions of the inquiry focused on the extreme negative G forces encountered in the thundersquall. A large proportion of the aircraft was recovered and reassembled at Farnborough.[59] The break-up was found to have begun with a left-hand elevator spar failure in the stabiliser. The immediate focus was on the severe turbulence encountered that induced down-loading, which subsequently precipitated the loss of the wings. Examination of the cockpit controls led to a belief that the pilot may have inadvertently overstressed the aircraft when pulling out of a steep dive by over-manipulation of the fully powered flight controls.
Recommendations from the court revolved around the enforcement of stricter rough air speed limits. The tragedy led to two significant developments: all Comets were equipped with "weather radar" and the introduction of Q feel, a system that ensured that control column forces (invariably called "stick forces") would be proportional to control loads. The artificial feel was the first of its kind to be introduced in any aircraft. The Comet 1 and 1A had been criticised for a lack of feel in their controls, although test pilot John Cunningham contended, it flew extremely smoothly and responded to the controls in the best way de Havilland aircraft usually did.
DH.106 Comet 1 of BOAC at London Heathrow on 2 June 1953
[edit] Comet disasters of 1954
Main articles: BOAC Flight 781 and South African Airways Flight 201
Rome’s Ciampino airport, the site of the first Comet hull loss, was again the origin of more disastrous Comet flights just over a year later. On 10 January 1954, 20 minutes after taking off from Ciampino, Comet G-ALYP ("Yoke Peter"), BOAC Flight 781, broke up in flight and crashed into the Mediterranean off the Italian island of Elba, with the loss of all 35 on board. With no witnesses to the disaster and only "sketchy" and incomplete radio transmissions left behind, there appeared to be no obvious reason for the crash. Engineers at de Havilland immediately recommended 60 modifications aimed at any possible design flaw while the Abell Committee met to determine potential causes of the crash.
Abell Committee Court of Inquiry
Media attention centred upon sabotage; other speculation ranged from "clear-sky" turbulence to an explosion of vapour in an empty fuel tank. The committee soon focused on six potential aerodynamic and mechanical causes: control flutter (which had led to the loss of the de Havilland DH 108 Swallow prototypes), structural failure due to high loads or metal fatigue of the wing structure, failure of the powered flight controls, failure of the window panels leading to explosive decompression, or fire and other engine problems. The committee concluded fire was the most likely cause of the problem, and a number of changes were made to the aircraft to protect the engines and wings from damage which might lead to another fire.
The cost of solving the Comet mystery must be reckoned neither in money nor in manpower.
During this investigation, the Royal Navy conducted recovery operations. The first wreckage was discovered on 12 January and the search continued until August, by which time, 70% of the main structure, 80% of the power section and 50% of the aircraft systems/equipment had been recovered. The forensic reconstruction effort was only lately underway when the Abell Committee reported their findings. On 4 April, Lord Brabazon wrote to the Minister of Transport, "Although no definite reason for the accident has been established, modifications are being embodied to cover every possibility that imagination has suggested as a likely cause of the disaster. When these modifications are completed and have been satisfactorily flight tested, the Board sees no reason why passenger services should not be resumed." Comet flights resumed on 23 March 1954.
On 8 April 1954, Comet G-ALYY ("Yoke Yoke"), on charter to South African Airways, was on a leg from Rome to Cairo (of a longer flight from London to Johannesburg), when it crashed in the waters near Naples. The fleet was immediately grounded once again and a large investigation board was formed under the direction of the Royal Aircraft Establishment (RAE). Prime Minister Winston Churchill tasked the Royal Navy with helping locate and retrieve the wreckage so that the cause of the accident could be found.[69] The type’s Certificate of Airworthiness was revoked and line production suspended at Hatfield while the BOAC fleet was grounded.
[edit] Cohen Committee Court of Inquiry
An illustration showing the recovered (shaded) parts of the wreckage of the de Havilland Comet 1 G-ALYP "Yoke Peter" and the forward ADF aerial window in the cabin roof where the initial fatigue failure occurred – after an illustration in Air Disasters (1989).
On 19 October 1954, a court of inquiry was set up under the chairmanship of Lord Cohen to examine the causes of the Comet crashes.[70] Investigators under the leadership of Sir Arnold Hall, Director of the RAE at Farnborough, began considering fatigue as the most likely cause of both accidents and initiated further research into measurable strain on the skin. With the recovery of large sections of G-ALYP from the Elba crash and G-ALYU, an extensive "water torture" test eventually provided conclusive results. Stress around the window corners was found to be much higher than expected, and stresses on the skin were generally more than previously expected or tested. This was due to stress concentration, a consequence of the windows’ square shape, the levels of stress at these corners could be two or three times that across the rest of the fuselage.
Before the Elba accident, G-ALYP had made 1,290 pressurised flights and at the time of the Naples accident, G-ALYY had made 900 pressurised flights. Dr. P.B. Walker, Head of the Structures Department (RAE) said he was not surprised by this, noting that the difference was about 3 to 1, and previous experience with metal fatigue suggested a total range of 9 to 1 between experiment and outcome in the field could result in failure. Thus, if the tank test result was "typical", aircraft failures could be expected at anywhere from 1,000 to 9,000 cycles. Engineers subjected an identical airframe, G-ALYU, to repeated re-pressurisation and over-pressurisation, and on 24 June 1954, after 3,057 flight cycles (1,221 actual and 1,836 simulated), G-ALYU burst open. Hall, Geoffrey de Havilland and Bishop were immediately called to the scene, where the water tank was drained to reveal the fuselage had ripped open at a corner of the forward port-side escape hatch cutout. A further test reproduced the same results. By then, the RAE had reconstructed about ⅔ of G-ALYP at Farnborough and found fatigue crack growth from a rivet hole at the low-drag fibreglass forward "window" around the Automatic Direction Finder, had caused a catastrophic breakup of the aircraft in high altitude flight.
The rivet problem was exacerbated by the punch rivet construction technique employed. The windows had been engineered to be glued and riveted, but had been punch riveted only. Unlike drill riveting, the imperfect nature of the hole created by punch riveting may cause the start of fatigue cracks around the rivet. Hall, the principal investigator, concluded, "In the light of known properties of the aluminium alloy D.T.D. 546 or 746 of which the skin was made and in accordance with the advice I received from my Assessors, I accept the conclusion of RAE that this is a sufficient explanation of the failure of the cabin skin of Yoke Uncle by fatigue after a small number, namely, 3,060 cycles of pressurisation.
The Cohen Court closed on 24 November 1954. Although the court found that the basic design of the Comet was sound, nonetheless, de Havilland began a refit programme that involved strengthening the fuselage and wing structure, employing thicker gauge skin and replacing all square windows and panels with rounded ones.
As is often the case in aeronautical engineering, other aircraft manufacturers learned from, and profited by, de Havilland’s hard-learned lessons. Although the Comet had been subjected to the most rigorous testing of any contemporary airliner, the "dynamic stresses" of pressurisation were not well known, and the Comet had pushed ‘the state-of-the-art’ beyond its limits. According to John Cunningham, representatives from American manufacturers such as Boeing and Douglas (privately) "admitted that if it hadn’t been for our [de Havilland's] problems, it would have happened to one of them.
Resumption of service
The Comet did not resume commercial airline service until 1958.[78] Following the structural problems of the early series, all remaining Comets were withdrawn from service, with de Havilland launching a major effort to build a new version that would be both larger and stronger. The square windows of the Comet 1 were replaced by the oval versions used on the Comet 2, which first flew in 1953, and the skin sheeting was thickened slightly. The remaining Comet 1s and 1As were either scrapped or modified with oval window rip-stop doublers (a thick, structurally strong ring of material that prevents a crack from spreading further), but a program to produce a Comet 2 with more powerful Avons was delayed. All production Comet 2s were modified to alleviate the fatigue problems and most of these served with the RAF as the Comet C2. Development flying and route proving with the Comet 3 allowed BOAC to accelerate the certification of what was destined to be the most successful variant of the type. On 24 September 1958, the Comet 4 received a Certificate of Air Worthiness and, the next day, BOAC took delivery of its first two Comet 4s.
The Comet 4 enabled BOAC to inaugurate the first regular jet-powered transatlantic services to begin that same year, albeit the westward North Atlantic crossing still required a fuel stop at Gander International Airport, Newfoundland. BOAC got publicity by being the first across the Atlantic with the London to New York crossing on 4 October 1958, but by the end of the month Pan Am was flying the Boeing 707 along the same route and in 1959-60 the Douglas DC-8 would be ready. The American jets were larger, faster, longer-ranged, and more cost-effective to operate than the Comet. In analysing the route structure the Comet could fly effectively, BOAC reluctantly cast about for a successor and, by 1958, had entered into an agreement with Boeing to purchase the 707.
In 1959 BOAC began shifting its Comet operations from the Atlantic run to other routes and releasing the Comet to the associate companies, the moves resulting in the Comet 4′s ascendancy as a premier airliner being relatively brief. Besides the 707/DC-8 duo, the imminent introduction of the Vickers VC10 meant the Comet’s competitors assumed more of the role initially pioneered by the Comet, that of high-speed, long-range passenger service.[82] Orders from other air carriers were gradually falling off in the 1960s with a total of 76 of the Comet 4 family delivered from 1958 to 1964. BOAC retired its Comet 4s from revenue service in 1965, but other operators continued flying Comets in commercial passenger service until 1981. Dan-Air played a significant role in the fleet’s later history and, at one time, owned all 48 remaining airworthy civil Comets. On 14 March 1997, a Comet 4C (XS235) which had been acquired by the British Ministry of Technology and used for radio, radar and avionics trials, made the last documented Comet flight.
Variants
Comet 1
DH106 Comet 1 preserved in the colours of BOAC G-APAS, this aircraft also served with the RAF as XM823, now at RAF Cosford
The square-windowed Comet 1 was the first model produced, a total of 12 aircraft in service and test. Following closely the design features of the two prototypes, the only noticeable change was the adoption of four-wheel bogie main undercarriage units, replacing the single main wheels. Four 5,050 lbf (22.5 kN) Ghost 50 Mk 1 (later 5,700 lbf (25 kN) Ghost DGT3 series) engines were fitted. The span was 115 ft (35.05 m), length 93 ft (28.35 m), Maximum Takeoff Weight 105,000 lb (47.628 kg) with 36–48 passenger configurations.
An updated Comet 1A was offered with higher allowed weight and water-methanol injection; 10 were produced. In the wake of the 1954 disasters, all Comet 1s and 1As were brought back to Hatfield, first placed in a protective "cocoon" and retained for testing.[85] All were substantially damaged in stress testing or were scrapped entirely.
Comet 1X: Two RCAF Comet 1As were rebuilt with heavier-gauge skins to a Comet 2 standard for the fuselage, and renamed Comet 1X.
Comet 1XB: Four Comet 1As were upgraded to a 1XB standard with a reinforced fuselage structure and oval windows. Both 1X series were limited in number of pressurisation cycles.[86]
DH 111 Comet Bomber
Originally proposed in 1948 as the "PR Comet", a "high-level photo reconnaissance" adaptation of the Comet 1, de Havilland further developed a bomber variant to Air Ministry specification B35/46 as the DH 111 Comet Bomber with a submission to the Air Ministry on 27 May 1948. The substantially altered airframe powered by four 5,700 lbf (25 kN) Ghost DGT3 engines, was designed around the special bomb, and featured a narrowed fuselage along with a bulbous nose to accommodate the H2S Mk IX radar; the crew of four would be housed in a pressurised cockpit under a large bubble canopy. Additional fuel tanks carrying 2,400 imperial gallons (11,000 L) were built into the fuselage to attain a range of 3,350 miles (5,390 km). The DH 111 proposal was evaluated by the Royal Aircraft Establishment but serious concerns regarding weapons storage led to a negative RAE review. The capability of the proposed V bomber trio also made the DH 111 redundant and further development work at de Havilland was abandoned on 22 October 1948.
Comet 2
The Comet 2 had a slightly larger wing, higher fuel capacity and more powerful Rolls-Royce Avon engines, which all improved the aircraft’s range and performance; some of these changes had been made to make the aircraft more suitable for transatlantic operations.[88] Following the Comet 1 disasters, these models were rebuilt with heavier gauge skin and rounded windows, and the Avon engines featuring larger air intakes and "outward-curving" jet tailpipes.[N 21][89] A total of 12 of the 44-seat Comet 2s were ordered by BOAC for the South Atlantic route.[90] The first production aircraft (G-AMXA) flew on 27 August 1953. Although these aircraft performed well on test flights on the South Atlantic, their range was still not suitable for the North Atlantic. All but four Comet 2s were allocated to the RAF with deliveries beginning in 1955. Modifications to the interiors allowed the Comet 2s to be used in a number of different roles. For VIP transport, the seating and accommodations were altered while provisions for carrying medical equipment including iron lungs was incorporated. Specialised ELINT and electronic survelillance capability was later added to some airframes.
Comet 2X: Limited to a single Comet Mk 1 powered by four Rolls-Royce Avon 502 turbojet engines and used as a development aircraft for the Comet 2.
Comet 2E: Two Comet 2 airliners were fitted with Avon 504s in the inner nacelles and Avon 524s in the outer ones. These aircraft were used by BOAC for proving flights during 1957–1958.
Comet T2: The first two of 10 Comet 2s for the RAF were fitted out as crew trainers, with the first aircraft (XK669) flying for the first time on 9 December 1955.
Comet C2: Eight Comet 2s originally destined for the civil market were completed for the RAF and assigned to No. 216 Squadron.
Comet 2R: Three Comet 2s were modified for use in radar and electronic systems development, initially assigned to No. 90 Group (later Signals Command) for the RAF. In service with No. 192 and No. 51 Squadrons, the 2R series were equipped to monitor Warsaw Pact signal traffic and operated in this role from 1958.
Comet 3
The Comet 3, which flew for the first time on 19 July 1954, was a lengthened Comet 2 powered by Avon M502 engines developing 10,000 lbf (44 kN) with greater capacity and range, including the addition of wing pinion tanks. The Comet 3 was destined to remain a development series since it did not incorporate the fuselage-strengthening modifications of the later series aircraft, and was not able to be fully pressurised.[95] Only two Comet 3s were constructed with G-ANLO, the only "flying" Comet 3, demonstrated at the Farnborough SBAC Show in September 1954. The other Comet 3 airframe was not completed to production standard and was used primarily for ground-based structural and technology testing during development of the similarly sized Comet 4. Nine additional Comet 3 airframes were not completed and their construction was abandoned at Hatfield.[96] In BOAC colours, G-ANLO was flown by John Cunningham in a marathon round-the-world promotional tour in December 1955. As a flying testbed, it was later modified with Avon RA29 engines fitted, as well as replacing the original long-span wings with reduced span wings as the Comet 3B and demonstrated in British European Airways (BEA) livery at the Farnborough Airshow in September 1958. Assigned in 1961 to the Blind Landing Experimental Unit (BLEU) at RAE Bedford, the final testbed role played by G–ANLO was in "autoland" experiments. When retired in 1973, the airframe was used for foam arrester trials before the fuselage was salvaged at BAE Woodford, to serve as the mock-up for the Nimrod.
Comet 4
The Comet 4 was a further improvement on the stretched Comet 3 with even greater fuel capacity. The design had progressed significantly from the original Comet 1, growing by 18 ft 6 in (5.64 m) and typically seating 74 to 81 passengers compared to the Comet 1′s 36 to 44. The Comet 4 was considered the definitive series, having a longer range, higher cruising speed and higher maximum takeoff weight. These improvements were possible largely because of Avon engines with twice the thrust of the Comet 1′s Ghosts.
BOAC ordered 19 Comet 4s in March 1955, with G-APDA first flying on 27 April 1958. Deliveries to the airline began on 30 September 1958 with two 48-seat aircraft.[99] BOAC’s G-APDC initiated transatlantic Comet 4 service and the first scheduled transatlantic passenger jet service in history, flying from London to New York with a stopover at Gander, Newfoundland on 4 October 1958. Rival Pan Am’s inaugural Boeing 707 service began later that month.
BEA’s Comets received a welcome response from crews and passengers but they were not so well liked by the baggage handlers. The baggage/cargo holds had doors directly underneath the aircraft, so each item of baggage or cargo had to be loaded upwards from the top of the cab of the baggage truck, through the little hole, then slid along the hold floor to be stacked inside. Likewise, the individual pieces of luggage and cargo had to be retrieved slowly with great effort on arrival.
American operator Capital Airlines ordered 14 Comet 4s in July 1956.[103] The Comet 4A was designed for short-range operations and had a stretched fuselage with short wings (lacking the pinion (outboard wing) fuel tanks of the Comet 4). This order was cancelled but the aircraft were built for BEA as the Comet 4B, with a further fuselage stretch of 38 in (97 cm) and seating for 99 passengers. The first Comet 4B (G-APMA) flew on 27 June 1959 and BEA aircraft G-APMB began Tel Aviv to London-Heathrow service on 1 April 1960.
The last Comet 4 variant was the Comet 4C with the same longer fuselage as the Comet 4B coupled with the longer wings and extra fuel tanks of the original Comet 4, which gave it a longer range than the 4B. The first Comet 4C flew on 31 October 1959 and Mexicana began scheduled Comet 4C flights in 1960. The last two Comet 4C fuselages were used to build prototypes of the Hawker Siddeley Nimrod maritime patrol aircraft. Comet 4C (SA-R-7) was ordered by Saudi Arabian Airlines with eventual disposition to the Saudi Royal Flight for the exclusive use of King Saud bin Abdul Aziz. Extensively modified at the factory, the aircraft included a VIP front cabin, a bed, special toilets with gold fittings and was distinguished by a resplendent green, gold and white colour scheme with polished wings and lower fuselage that was commissioned from aviation artist John Stroud. Following its first flight, the special order Comet 4C was described as "the world’s first executive jet.
Comet 5 design
The Comet 5 was proposed as an improvement over previous models, including a wider fuselage with five-abreast seating, a wing with greater sweep and podded Rolls-Royce Conway engines. Without support from the Ministry of Transport, the proposal languished as a "paper project" only.
Hawker Siddeley Nimrod
Main article: Hawker Siddeley Nimrod.
The last two Comet 4 fuselages produced were modified as prototypes to meet a British requirement for a maritime patrol aircraft for the Royal Air Force, designated Type HS 801. This variant became the Hawker Siddeley Nimrod and was built at the Hawker Siddeley factory at Woodford Aerodrome. Entering service in 1969, five Nimrod variants were produced. The final Nimrod aircraft were retired in June 2011.
Capital Airlines ordered the Comet 4 in July 1956 which were to be supplemented by 10 Comet 4As, a variant modified for Capital. Following financial problems and the takeover by United Airlines, the order was cancelled.
FOR SALE – 1989 R32 Nissan Skyline GTR – Rear
Image by Daft Photos
Nissan Skyline GT-R
Year: 1989
KM: 118,XXXKM
Car was ordered last year from Keizenauto as a mint bone stock car. That is what I got. A super clean, gun metal Skyline GTR. That said, as most, if not all JDM cars, quite a bit of work was needed to make this car run properly.
The car was sent to Teknica Industries in Île Bizzard in Montréal.
Louis-Philippe, the owner took over the project him self since the car had
become a project car for the magazine Québec Tuning and a showpiece for the drift series Drift Mania Castrol DMCC.
From that point on, we order 4000$ worth of parts from Japan and the USA.
You will find the list below, but in the end, the idea was to make the
drive and the looks of this car as stock and reliable as possible. Which is
what we got after putting a new aluminum Koyo Rad, a new battery and tie
down as well as new gaskets, seals, belts and fluids. A new gauge pod was
added as well as a Clarion 5 inch retractable DVD player. I also had to get
two of the Weeds racing wheels sanded and painted to eliminate major
scratches.
Once the car was to our satisfaction, it was inspected by the SAAQ (who gave it the thumbs up), plated and insured.
The car now runs awesome. It pulls very hard from 3,000rpm until the 7,000
rpm redline and idles very smooth. The brakes are very good and the
transmission (which uses a Nismo short shifter) is simply erotic to use.
i.e. short, precise and with out any grinding what so ever. The exhaust and
the intake (both aftermarket) allow the car to scream a little louder then
stock. But I can not stress enough how the sound remains soft, inside out.
I drove the car during 500km before getting fed up with the fully adjustable
Quantum coilovers. Yes, they are high end racing coil-overs and worth quite a few bucks. But Québec roads are simply to rough for them. So I purchased a set of used bone stock GT-R shocks with an adjustable bone stock GT-R strut tower bar, and had them installed (I still have the Quantum coilovers). At the same time, we replaced one of the HID bulbs that were dead.
The result is now a car that drives much smoother then before. Yes, the
rides look a little high. I also miss the feel the handling of the Quantum
suspension but the compromise is worth it (in Québec Only). The rear left
shock (on the stock GTR shocks) also feels like it is reaching the end of it
life span. I would give it 5,000km and then it will need replacement.
Other then that, the car is stock and mint inside out. From a critical point
of view, the outside rear left corner has a scratch and could use a little
finesse work. The rest of the body is A1 and the overall condition is as
good as it gets. The interior is perfect. Aside a few scratch on the
steering wheel (I also have a choice of two new MOMO steering wheels), all 4 seats, carpets (original with GTR logo), shifter (stock), dash, are in
perfect condition and all originals. Since I replaced the gauges with
original stock ones, they work with out any problem (including boost gauge,
power distribution gauge, etc.).
I am now at the point where I have to let her go. I have new priorities in
life (other then cars) which requires, like every other thing, money.
The car is priced at ,500 It is a fairly stiff price as I had to put in a
lot of work, money and time to get to this. This is not a modified car that
has lost value on it’s mods but a car that was worked on so it could hold
it’s value. The only thing that needs to be done as we speak are new upper
arm bushings so the car can be aligned properly.
The car can also keeps it’s role in Québec Tuning magazine. The new owner is more then welcome to sponsor his new parts and to describe in the magazine the ups and downs of these new parts and accessories. It can also choose to keep the car bone stock and simply relate to our readers the ups and downs regarding owning a collectible like this car.
I did my best to describe everything I know about this car. If you have any
other questions, please let me know @ alex.crepault@driftmania.ca. The car is also available with a free or discounted sponsorship to the Castrol DMCC series, which are coming back in 2008 to Downsview Park (Toronto), as well as in 3 other locations across Canada.
Other information
Compression test done:
Cyl#1 160 Cyl#2 160
Cyl#3 165 Cyl#4 165
Cyl#5 165 Cyl#6 165
No ABS
HICAS still active
ATTESA system still active
Tires = 75% good
Power door lock works
Power windows works
GTR key
Parts orders from Japan:
Tie Rod
Intake Mani Gaskets (actually 2 sets of 3)
Timing Belt x 2
Tensioner
Tensioner Spring
Idler
Intake Turbo Gasket x 2
Upper Rad Hose
Lower Rad Hose
Thermostat
Spark Plugs x 6
Oil Filter x 3
Fuel Filter
Injector insulator/oring kit
All front belts
Other parts ordered
Engine oil
Transmission oil
Aluminium rad coolant
Koyo aluminium radiator
Battery
GTR stock shocks
GTR stock gauge and gauge pod
Batteru tie down
Gtr stock strut tower bar
Clarion 5 inch DVD player
MOMO steering wheels (optional)