Sitka spruce for airplane construction is imported kiln dried and rift sawn, the usual specification being 3 to 6 inches thick by 6 inches and wider, 18 to 40 feet long with 10 to 15 per cent 10 to 17 feet admitted. A very superior grade of No. 2 clear and better is used and is selected piece by piece after the severest tests by the airplane builders' inspector. The lumber not only must be free of knots and other defects but great attention is paid to the grain, which must be of the close, fine type and must be absolutely straight from end to end, cross, curly, or coarse grain being unsuitable for airplane work. In the early days of airplane construction West Virginia spruce (Picea rubra) was used but has been superseded by Sitka for some years.

Next in importance is ash, used for longerons and other parts requiring strength, toughness, and elasticity. Of all the species the native timber is considered the best for airplane work. This wood is very carefully selected and must be free from any cross grain. It is customary for construction companies to purchase ash in the log, cut through and through, seasoned for approximately one year to the inch. When cutting these planks into the required parts, care is taken that the piece shall have two of its sides parallel with the medullary rays; otherwise the shrinkage may cause alteration in the shape which would in turn disorganize the fittings.

American black walnut or Honduran and Nicaraguan mahogany are the woods chiefly used for making propellers, but for this purpose black walnut has no superior. The propellers are built up in laminations from straight-grained wood, preferably quarter sawn, because lumber sawn in this manner retains its shape better, shrinks less in width, and takes glue better, enabling a superior joint to be obtained. In the early days of airplane construction in Great Britain, French walnut was exclusively used for propellers for no particular reason except that it was well known and plentiful and considerably used in that country. It does not, however, possess the qualities of American black walnut and has now been entirely superseded by the latter. Mahogany is sometimes used for seaplane floats, these being laminated from thin boards. During the war experiments were also made with red cypress for propellers, but it was found unsuitable, and some of the stock imported at that time is still stored in importers' yards.

Birch is used chiefly in the form of plywood and is manufactured in the United Kingdom out of imported Canadian logs, white birch being preferred. It is used chiefly for the fuselage of airplanes and seaplanes and for the floats of the latter also. In order, however, to prevent its absorbing moisture it is constantly varnished, otherwise additional weight will be taken up in the form of water. Other uses of plywood is the building up of wings, ribs, spars, tank coverings, partitions, and instrument boards.

Among other woods used in airplane construction may be mentioned yellow poplar for instrument boxes and fittings; also the lighter fancy hardwoods for interior finish.

The adoption of the all-metal plane has developed a market for a wood heretofore little known in Great Britain, namely balsa. This peculiar wood is extraordinary light in weight, being approximately one-half that of cork, and is now being used for filling up the tubular construction parts of metal planes. With the develop

ment of the metal the demand will probably increase. Apart therefore from this species it may reasonably be taken for granted that the demand for wood for airplane construction will continue to decrease until it ceases to be a factor in the lumber market-a condition likely to be reached in the near future.

PATTERN MAKING

The white pine (Pinus strobus) of North America has long been a favorite wood for pattern making in the United Kingdom on account of its soft even grain, making it easy to work, and its ability to stay flat and hold its shape after working.

No statistics are available showing the quantity of pattern-making wood imported into the United Kingdom so it is impossible to give even an approximate idea of the quantity consumed for this purpose.

The principal consumers of pattern-making wood in the United Kingdom are the shipbuilding (including the British Admiralty), engineering, and railroad industries, and upon the activity of the first two largely depends the demand.

Pattern woods are handled by softwood importers who purchase their supplies through regular agents. They are located principally in the largest ports nearest these industries, such as Liverpool, Glasgow, Manchester, Belfast, and Newcastle-on-Tyne, and the woods are distributed by them to the consumers, who usually operate their own pattern shops.

CANADIAN WHITE PINE

Of the woods used for pattern making, Canadian white pine, or "Quebec yellow pine" as it is called in the United Kingdom, has the largest sale. It has been used for very many years and is firmly established. Pattern makers assert that patterns made of this species retain their shape and can be used over and over again. The specifications usually called for are first, second, third, and fourth quality deals, 3 by 7 inches and wider; first, second, and "unsorted" (first, second, third, and fourth, averaging third) quality sidings, 1, 114, 12, and 2 by 7 inches and wider, and hewn wany timber. Some Canadian exporters put up special grades of their own which are well known to the trade. This timber is imported hewn on all four sides with a heavy wane on each corner, and sold as "wany pine." A usual specification runs from 15 to 36 feet in length by 15 to 24 inches deep. When very wide boards, or a thickness greater than 3 inches, or long lengths are required, wany pine logs are purchased and cut into the desired dimensions in the consumers' own shop. The quantity of logs used, however, forms a very small part of the total.

OTHER SPECIES

Other species used for pattern making are California sugar pine, western white pine, Port Orford cedar, and Siberian and east Asiatic kedar (a soft pine). These are gradually gaining a foothold as a substitute for Canadian white pine, but so far, with the exception of the Manchurian or Siberian kedar, without much success, the British trade preferring the expensive Quebec white pine. A little Central American mahogany is also used for special patterns.

PROSPECTS FOR AMERICAN WOODS

Although Canadian white pine is still the favorite and most used wood in the United Kingdom for pattern making, it is becoming scarcer and more expensive and substitutes may eventually supplant it.

The United States, as the principal producer of other suitable species, will probably find its sales of these species slowly increasing but, in any event, the total quantity of lumber consumed by the pattern-making industry is comparatively small.

The final decision as to what species shall be used in the pattern shops of the large shipbuilding, engineering, and railroad companies is largely in the hands of the works manager and unless his approval is gained other factors carry little weight. White pine has been used for so many years that great difficulty is always experienced in getting users to consider any other species-even when there is a material price differential in its favor.

COFFINS

Oak and elm are chiefly used for the better kind of coffins in Great Britain, the cheaper one being made to a considerable extent of American sap gum, or hazel pine, as it is called, while those used for the very poor are made out of any cheap wood finished to resemble the more expensive species. An interesting development in this respect has been a process whereby ordinary cheap wood is made to resemble oak or other species desired by means of a transfer.

In discussing the different woods used in the manufacture of coffins it must be understood that only the tops and sides are referred to, sap gum or almost any inexpensive wood generally being used for the bottoms.

English, American, and Japanese oak are all used, no difference being made between them by the coffin manufacturers. The American and Japanese lumber, however, while having a higher first cost, is preferred on account of its being graded and sawn square edged, unlike the native, which is obtained by sawing logs through and through and sold ungraded.

The United States furnishes both red and white oak of the northern and southern varieties for coffin manufacture in the United Kingdom, the majority coming from the Southern States. For some unexplainable reason certain sections prefer the white oak, while in others the red is more often called for.

The grade known as "prime coffin" is imported in thicknesses of 5%, 34, and 1 by 12 inches and wider, the quantity of 12-inch boards usually being limited to not over 10 per cent of the total number of the pieces shipped. As great a proportion of 17-inch and wider boards as possible are desired, not less than 25 per cent of the total pieces generally being required by the buyer, these being used for lids, while the narrower boards are for the sides. The usual lengths are 12 feet and longer, not over 10 per cent of the pieces may be 12 feet but any number of pieces 6 feet 6 inches and 7 feet may be included, as they are the lengths most used and entail the minimum

of waste.

Southern elm in the same specification as oak is also imported in small quantities from the United States. Elm from native sources

furnishes most of the stock used for coffins of the less expensive kind, it being one of the most common species indigenous to Great Britain. It is used both 3⁄44 and 1 inch thick, depending upon the price of the coffin.

Native elm and oak lumber is obtained by sawing logs through and through, which are sold log run to the coffin manufacturers. By this method many of the boards obtained are defective and considerable waste takes place in the factory.

The boards obtained by this method of sawing are generally wider at one end than the other; in other words, they taper. This irregularity of width, however, is not objected to by the coffin manufacturers as, by making use of the taper, the amount of waste lumber is materially less than when regular lumber with parallel edges is used. A taper of not over 2 inches is ordinarily allowed on boards used for sides, a usual specification being 14 to 12 inches, 15 to 13 inches, and 16 to 14 inches. Tops may taper even more, a usual specification being 26 to 23 inches or 22 to 18 inches in width.

In measuring tapered lumber, the width for the purpose of calculating the sale contents is taken in the middle of the piece. The boards are sold to the coffin manufacturers sawn on one or both edges; in either event the saw cut is parallel to the side of the log so as to take full advantage of the extreme width, but in most cases the lumber is simply sold as it comes from the log with the wane left on.

Canadian elm is also used to a small extent, being imported either as lumber or logs which are cut into lumber on arrival.

In addition to the species mentioned, occasionally coffins are made of North Carolina pine, but it is not considered as good as either oak or elm, and it is more expensive than the species generally used for the cheaper coffins.

PLYWOOD AND VENEER

PLYWOOD

Owing to the high cost of producing plywood in Great Britain it can not be manufactured except for special purposes, the chief of which is for the construction of seaplane bodies, gondolas for airships, and ordinary airplane fuselages. Canadian birch is used largely for this purpose, the north European variety not being large enough or sufficiently free from defects to make the sizes required. To a lesser extent mahogany is also used, but the greater proportion is birch.

The plywood used for this purpose is of exceptionally large size, sheets as large as 8 feet wide by 60 feet long and 1% and 3% inch thick being manufactured. In addition to being cemented with a special glue in the ordinary manner it is also stitched with linen thread, the stitching being spaced according to the strains to which it is likely to be subsequently put. When for flying boats and motor-boat hulls or other purposes where extreme smoothness of finish is desired, the stitching is countersunk below the face of the outer plys so that when varnished a surface which offers little resistance to either air or water is produced.

In the latter part of 1926 there was launched for the Air Ministry the first passenger and mail-carrying flying boat specially designed

for that purpose. It had accommodations for six passengers and 1,000 pounds of mail. The hull of this boat was made of only five lengths of stitched plywood. Two lengths each 50 feet long were used for the keel, two of the same length for the sides, and one for the deck.

At a public meeting held in London to celebrate the completion of a trip from England to Australia and back it was stated that the machine used was largely constructed of plywood.

While for military purposes the all-metal plane has been adopted by the British Government, plywood is bound to retain great importance for airplane construction. Its freedom from atmospheric influences and ability to stand up under extremes of heat and cold and dryness and moisture make it a particularly suitable material for this purpose.

Not only in the fuselage is plywood used, but it also enters largely into the building up of the wings, ribs, spars, tank coverings, partitions, and instrument boards.

Plywood panels. In addition to the plywood used for aeronautical purposes there is an important trade in the manufacture of high-class plywood panels for wainscoting, display windows of stores, railroad passenger and Pullman cars, trolley cars, flush-surfaced doors, and table tops, the use of veneer giving an opportunity for matched panels and wood decoration obtainable in no other way. These are made by applying a veneer of mahogany, oak, or walnut on a core of some less valuable plywood, such as north European birch, alder, okoumé, or sometimes Douglas fir. Okoumé, however, is seldom used except for mahogany veneer. Domestically made panels are seldom used in stock sizes but are generally ordered to special dimensions to fit the particular job for which they are required.

The manufacture of plywood panels is sometimes undertaken by the larger furniture and talking-machine manufacturers themselves, sound wormy chestnut being favored by some for the core.

Metal-faced plywood.-There has been on the British market for several years a plywood having a metal sheet on both faces. The increased strength thus obtained and resistance to fire make it particularly suitable for many purposes, especially for fireproof curtains or doors, partitions, panels, motor-cycle side cars, and light commercial vehicle bodies. While the demand is not of great proportions at present, there would seem to be a wide field for this kind of plywood in Great Britain provided its price does not prove prohibitive.

VENEER

The British veneer industry has been established for many years and has reached a high standard of excellence. It is principally occupied with the manufacture of fine veneers such as mahogany, oak, and walnut, although many fancy woods, such as sycamore, satinwood, and sabicu are made to meet individual desires.

In addition to the fancy hardwoods, there is also made a small quantity of American yellow poplar veneer out of imported logs, this species being much esteemed as a base on which the other veneers are laid.

While no statistics are available, it is estimated that a total of about 80,000,000 feet of veneer of all kinds is produced each year.

Methods of production. The rotary, sliced, and sawn methods of manufacture are all used, the latter principally for curl veneers and those made from the denser hardwoods.