Three types of welding are used in the construction of aeroplanes, hangars and aircraft carriers
METAL FUSELAGES are used for large and small aircraft. Fuselage structures for two Avro aeroplanes are shown in this photograph. In the foreground is a fuselage for a small two-seater, and behind it the fuselage for a three-engined commercial aircraft. All the joints between tubes and the various fittings, such as those for internal bracing wires, are fixed by welding.
EACH of the three well-known processes of welding — namely, oxyacetylene, electric resistance and electric arc welding — plays its part in the aeronautical industry. In the construction of the aircraft themselves the oxy-acetylene, or gas welding process, as it is more commonly called, is most used. Certain parts of aeroplanes are now mass-produced by electric resistance welding machines, and electric arc welding is used in the construction of aeroplane hangars and aircraft carriers. One of the earliest aeroplanes built in Great Britain, and flown by Lieut.-Colonel Moore-Brabazon, incorporated gas welding in its construction; but, later, aircraft designers used wood instead of steel. After some years the all-steel aeroplane came into its own again, and welding is now displacing riveting in aircraft construction.
The aircraft industry developed from the beginning in what might be called “the age of fusion welding” largely controlled by young men inspired from the very nature of their industry with great experimental enthusiasm. It is not therefore surprising that welding has, from the earliest days, had a part to play in the science of aircraft engineering.
Confined at first to fittings and to parts of the machine which had no considerable strains or stresses to withstand, the use of welded joints has been steadily extended until, today, the all-welded metal aeroplane frame is nearly standard practice in most British aircraft.
Metal replaced wood in fuselage construction and, later, welded joints replaced riveted joints for the following reasons. Aircraft engineers realized that, where joints must be made by metal fittings (as with the unwelded metal fuselage), the material is necessarily weakened, and that, whereas in a crash wood splinters, metal tubes bend, and metal tubes joined by welding rarely break at all.
The whole structure has the valuable quality of rigidity, as it cannot loosen at the joints. When repairs are necessary they can be easily effected by resort to the same oxy-acetylene welding process as was originally used to build the aeroplane. Moreover, where a number of tubes come together, complicated joints can be made without resort to elaborate jigs or tools. These joints are therefore much less expensive, and take much less time to make than would otherwise be necessary.
No metal formation can compare with the metal tube for combined strength and lightness. Tubes are therefore almost essential in aircraft construction. It is only necessary to try to imagine the production by any other method than welding of such complex joints as are used in the construction of an aeroplane, and to compare weight, cost and rigidity to realize the importance of welding in aircraft building.
A PETROL TANK being built by welding the sections together. Before a welder is permitted to work on the construction of aircraft or their parts, he has to pass tests laid down by the Air Ministry The tests involve the making of different types of welded joints, all of which have to pass tensile tests, and one of which has to pass a microscopic test also. When a welder has passed these tests he is given a stamp with which to mark his work.
Only the lighter and smaller types of British aeroplanes, therefore, are now made with wooden fuselages. The riveted steel fuselage is almost a thing of the past.
The following is a list of the chief welded parts of one well-known make of aeroplane: rudder bars, aileron gear, main rocker shafts, control units, jury struts, top and bottom main planes, controls, complete fuselage, engine frame, rudders, exhaust manifolds and pipes, chassis, air intake, centre sections, tail skids, complete rear fuselage.
The same makers began to use oxyacetylene welding in a small way about 1919, with a single operator. They now employ considerable number of whole-time welders, and expect to increase their number as production increases. Virtually all the welding is in the production of the parts detailed above, and includes both mild steel and aluminium.
The following tests are laid down by Air Ministry regulations for the certification of a welder engaged upon aircraft work: butt weld — to pass tensile and microscopic tests; fork weld — to pass tensile test; tee weld — to pass tensile test; strip weld — to pass tensile test.
When an operator has passed these tests a stamp is issued to him to enable him to mark his work as it is performed, and every weld comes under the eye of a member of the company’s inspection department.
Periodical Test to Destruction
In another well-known company of aircraft manufacturers, in addition to most of the parts in the list above, engine mountings are made as complete welded units. In a large aircraft carrying three engines, the main engine mounting and two of the nacelle mountings are made of welded mild steel tubes, as also are elevators and seating units. Brackets for exhaust pipes, buffer stops for winding gear, and oleo legs (shock-absorbing undercarriage legs) are all welded units.
The mild steel tubes in use are usually of 0·15 per cent carbon content, and must never exceed 0·2 per cent carbon content. All welded parts of the fuselage and other structural parts of the aeroplane must conform to the following: yield point of 17 tons (38,080 lb.) per square inch, and a maximum stress of 28 tons (62,720 lb.) per square inch. These figures may be compared with a tensile strength laid down for similar work in the United States of America of 5,000 lb. per square inch.
A form of procedure control is in use in all British aircraft factories where welded joints are in use. Welder’s work is continually checked in the company’s research department by periodical test to destruction. Materials are subjected to careful examination, and oxygen and acetylene are carefully tested for purity. The design, layout and preparation of welds are standardized in each factory.
The great problem, however, of the British aircraft manufacturer is to obtain welders of first-class technique in the highly specialized form of tube welding which the industry requires. When new welders are taken on, it is generally necessary to submit them, however competent they may be in ordinary commercial welding practice, to a rigorous training before they are able to pass the tests imposed, and so qualify for structural work.
Today, in the British aeroplane, the frame built almost completely of welded steel tubes is fast becoming standard practice, as it has been for some time in the United States and in Germany. Among the pioneers are A. V. Roe & Co., Ltd. In this company’s factory only the lightest types of aircraft are made with wooden fuselage, and the riveted steel aeroplane is no longer made. The company, after considerable research and test work, is standardizing a welded steel structure for all its new types of aeroplane.
WELDED JOINTS do not weaken the material in the same way as joints made with metal fittings. Another advantage of tubes joined by welding is that, although they will bend, they seldom break in a crash. When repairs to a welded metal airframe become necessary they can be easily effected by the same oxy-acetylene process as that used in the construction of the fuselage. This photograph shows a student welder working on an aeroplane fuselage.
The mild steel tubes (normally 0·15 per cent carbon content and never over 0·2 per cent), which are the raw material of fuselage framework, vary, according to their position and purpose in the frame and the size of the machine, from 10 to 22 gauge. The above analysis as to carbon content applies to ail bar and sheet metal as well as to tubes.
The tubes are first of all laid in jigs. The welder then arrives and tacks up (or tack welds) each joint. The fuselage side is then removed from the jig and completely welded (see the illustration at the bottom of this page), the operator requiring only an ordinary flat top bench for this purpose, as the previous tacking holds the job rigid enough for welding.
When the two sides have been so welded they are then placed in a jig and the cross struts are tacked in position. The work is then removed from the jig and the welder carries on as before. In the illustration at the top of this page are shown two types of fuselage, the small one for an Avro Avian two-seater, and the larger one for an Avro passenger-carrying machine, a three-engined monoplane carrying ten passengers, two pilots and luggage.
The large number and variety of the welds are obvious in this photograph. All fittings, such as those to take the cross wires in each section, are welded on.
Transportable Hangars
Engine mountings are made up as complete separate welded units and are not welded to the fuselage, as it is necessary for them to be detachable. The centre engine structure of the three-engined liner is a complete mounting; the structures for the engines to the left and right of it are in the form of nacelle mountings.
In addition to fuselage and engine mountings, complete tail unit and elevators are constructed throughout of solid drawn tubes welded together, as also are the seating units for two-seaters. In each of these comparatively simple seating units there may be some twenty welds, for all the metal attachments for seats and for fixing the unit in the body of the aircraft are welded on.
Oxy-acetylene welding has long been in use at the works of the De Havilland Aircraft Company. Here welding is used upon many parts of the machines manufactured by them, and on the Tiger Moth type of aircraft, which has been used in considerable numbers during recent years.
Invaluable research work in connexion with the welding of aircraft is carried out at the Royal Aircraft Establishment at Farnborough, Hampshire, and at other centres.
Electric arc welding, another form of welding in which bare or covered wire is used as an electrode for depositing metal in the joint to be welded, is used in the construction of aeroplane hangars. The Bellman Hangar, which is made of ordinary mild steel sections, has been especially designed for use in most parts of the world. It is simply made and can be rapidly erected. No foundations or guys of any kind are needed, nor is any timber used. Its extremely light weight — it is only one-fifth to one-tenth of the weight of a standard hangar — makes it easily and quickly moved from site to site as required.
A LARGE AIR LINER in the course of construction. The whole of the internal framework of this aeroplane is oxy-acetylene welded. Wooden fairings are frequently added to metal frameworks to give the desired contours to the aircraft. A covering of fabric or even of wood may be fixed outside the wooden fairings. To the left a smaller aircraft is seen under construction.
In face of competition, the Air Ministry have made the Bellman Transportable Hangar their standard type. They have tested it thoroughly and it has proved satisfactory. Hangars of this type have withstood the severest winds and blizzards known in the north of England for nearly seventy years.
This hangar can be made to a size of at least 95 feet span by 25 feet and to any length required; thus it is capable of housing the largest aeroplanes that in all probability will be required.
Because the hangar is made to standard units, unskilled labour of almost any type can be used to erect it. The covering can be either canvas or galvanized sheets. Where galvanized corrugated sheeting is used, it is of an “easy fix” type and arranged so that it can be rapidly set up. Doors are of canvas and are fitted with an overhead track and bottom guide. They are quick in operation. Alternative ' methods of providing a steel door can be arranged where a permanent type
of structure is required or where for other reasons this is advisable.
The principle involved is that of unit construction, the units being composed of standard rolled steel sections. These are then assembled together to any design and at any site which may be chosen. The covering is easily fixed by erectors merely pushing hook bolts through the hook holes. The units have been designed to be easily transportable and can be loaded into railway trucks or motor vehicles, or on pack mules and so forth, without any special lifting tackle or the need of loading facilities. Varying sizes of hangars can be constructed from the same units as the standard hangar. A Bellman Hangar is suitable either as a transportable or as a permanent hangar.
NOSE COWLINGS may be built up from thin metal sheets by means of welding. A completed nose cowling is shown at the top centre of this photograph; below it and to the left are parts used in its construction. On the right is a pattern used to mark out the metal sheets.
Head, Wrightson & Co., Ltd., have acquired the commercial rights of these hangars and have manufactured a large quantity for the British Government. This experience has enabled them to develop a technique of manufacture and erection which proves invaluable for rapid and efficient production.
Welding, which is now extensively used in the building of ships of all kinds — warships and mercantile vessels — is being used in the construction of Great Britain’s latest aircraft carriers.
The greatest advance yet made in the application of welding to warship construction is in the building of H.M. Aircraft Carrier Ark Royal, which was launched at Cammell Laird’s yard, Birkenhead.
This remarkable vessel is 800 feet overall in length, and is over 75 per cent arc welded. It is, at the time of writing, the longest ship ever built at Birkenhead. The keel was laid on September 16, 1935, and the vessel was launched on April 13, 1937. Considering the size of the ship — 22,000 tons — the time she was on the stocks compared favourably with that for any similar riveted vessel.
The vessel, which was designed by Admiralty constructors, has the largest deck surfaces in the Royal Navy, and these are largely welded.
Welding was mainly used to reduce the structural weight of the ship. This saving in weight allows more weight for armament and protection and for the storage of fuel. The following information should be interesting:
Area of welded decks: 40,000 square feet
Area of welded bulkheads: 200,000 square feet
Area of welded side and fore end plating: 68,000 square feet
Total: 308,000 square feet
From this somewhat brief illustrated outline it will be readily seen that welding now plays a considerable part not only in the manufacture of aeroplanes but in the construction of buildings and ships for their safe housing.
THE TUBES FORMING THE SIDE of a welded fuselage are first fitted into a jig which holds them true. They are then tack welded at all points where joints are to be made. The fuselage side is then removed from the jig and placed on a bench, while the joints are completed The tack welding is sufficiently strong to hold the tubes together while the welding is being finished.
No metal formation can compare with the metal tube for combined strength and lightness. Tubes are therefore almost essential in aircraft construction. It is only necessary to try to imagine the production by any other method than welding of such complex joints as are used in the construction of an aeroplane, and to compare weight, cost and rigidity to realize the importance of welding in aircraft building.
Welding was mainly used to reduce the structural weight of the ship. This saving in weight allows more weight for armament and protection and for the storage of fuel. The following information should be interesting: