WE are living in a day of changing locomotive fashions. Because of the competition of travel in the air and on the roads, the incessant demand is for speed, speed, and yet more speed on rails. So far as it concerns locomotive power, this demand is affecting not only the interior of the steam locomotive, but also its exterior. For it is realized – as it has already been realized in the design of aeroplanes and of racing motor cars – that in the higher ranges of speed, the influence of air resistance on the moving vehicle is considerable. Maximum speeds can still be increased’ if proper attention is paid to streamlining.
Steam locomotive externals are rapidly changing in this way, and the engine that forms the main subject of this chapter – No.6400 of the Canadian National Railways – is a typical example of progress in modern locomotive design. From the early days of railways the locomotive in Great Britain has always been thought of as something more than a mere piece of machinery. Trouble has been taken by locomotive engineers to develop a graceful outline and to conceal the working parts as much as possible.
Distinctive colours have been used by different railways for their engines, and these well-kept liveries have had some publicity value. What is more, this “cleaned-up” exterior, as the Americans have described it, is proving of value from the streamlining point of view. American locomotives, on the other hand, as well as those on the mainland of Europe, have kept a large proportion of their “works” outside. One of the advantages of having the “works” outside as much as possible is increased accessibility. Only in recent years has there been a definite move on the North American continent towards the improvement of locomotive externals.
This move has coincided with the demand for railway speeds higher than ever previously known. For continuous running speeds of 80 miles an hour or so, and maximum speeds up to 90 and even 100 miles an hour, fully streamlined locomotive exteriors have become necessary. It is the streamlined casing which makes the outline of No. 6400 and her four sisters differ entirely from that of other engines on the Canadian National system.
It has been ascertained from experiments in wind tunnels that complete streamlining cuts down air resistance by 40 to 45 per cent at high speed and that the power output necessary for a completely streamlined locomotive, when all resistances are taken into account, is less by 10 per cent at 80 miles an hour and by 12½ per cent at 110 miles an hour than that required for a non-streamlined engine of the same type. The streamlining of No. 6400 of the Canadian National Railways, however, is only partial.
Considerable advances in speed are being made on North American railways, and in these advances the two great railways of Canada – the Canadian National and the Canadian Pacific – may well claim to have taken a lead. In recent years, however, they have been outstripped in the race by various railways in the United States. The enormous size of the modern American locomotive, and the reasons for it, must now be explained, for No. 6400 of the Canadian National Railways, and others of her class, are – at the time of writing – the largest and heaviest streamlined engines so far built. This monster machine, in full running trim with tender, weighs 296 tons, compared with the 166 tons of one of the London and North Eastern Railway’s Silver Link streamlined engines with tender. No. 6400 is carried on sixteen wheels and her tender on twelve, as compared with Silver Link’s twelve wheels and eight-wheeled tender. Yet the track gauge of 4 ft 8½-in on which the two engines run is identical.
One reason for this difference in weight and size is that railway pioneers in America were not handicapped as were those in Great Britain, who had to carry their lines through valuable land. In America more space could be spared for the tracks, and level crossings, in many instances, took the place of bridges. These conditions permitted the development, on a more ample scale, of the rolling stock. Thus the American locomotive designer can plan an engine extending up to 16 feet above track level, compared with the 13 feet or so which is possible on a British railway.
The American engine may also be proportionately wider, but must still clear tunnels, bridges and the various other structures that are closely adjacent to the line. In view of the limited dimensions to which railway locomotives must be built, because of these loading gauge restrictions, this extra space has a remarkable influence on locomotive development.
But it needs more than the mere fact of an ample constructional space to justify the building of locomotives of such enormous size. This justification is found in the weight of modern American rolling stock. Partly because of the haphazard methods of railway operation in the early days of North American railways, leading to frequent and disastrous accidents, the travelling public demanded that coaches should be built entirely of steel, to give them a better chance of survival without telescoping in the event of collision or derailment.
This process of strengthening has gone on steadily with the building of vehicles of greater weight and size, and to-day the cars composing a modern North American express are from 70 to 80 feet long, are carried on two six-wheeled bogies, and weigh 75, 80 or even 85 tons apiece. Compared with this, a British twelve-wheeled dining or sleeping car weighs at most 43 to 46 tons, and an ordinary main-line corridor coach from 30 to 35 tons.
An important express in Canada may load up to twelve, thirteen, or fourteen heavy steel cars, and occasionally even more, with a total weight behind the engine tender of 1,000 to 1,200 tons, whereas in Great Britain express trains weighing as much as 600 tons are rare. Because of the length of many North American journeys, the proportion of sleeping-car accommodation in the long-distance trains is high. This helps to increase the proportion of the “tare” or empty weight of the stock to the number of passengers that it carries. Thus the tractive power of a modern express locomotive in Canada must be considerable and the proportions of No. 6400 are thereby explained.
The arrangement of the wheels which carry this streamlined giant first needs consideration. At the leading end of No. 6400 is a four-wheeled track, or bogie, pivoted under the centre of the engine smokebox, to enable the engine to traverse smoothly and easily the curves in the track. Of such immense size is the firebox, that the rear end of the engine also requires a four-wheeled bogie for its support. Between the two bogies are the four pairs of coupled wheels.
So that the power developed in the cylinders may be taken up at the rails, and not dissipated by slipping, it is essential that there shall be adequate adhesion, or grip. Six wheels or three coupled axles are more common in passenger service, but the weight borne by three axles would not provide adequate adhesion in so large and powerful a locomotive as No. 6400. Her four pairs of coupled wheels carry as much as 105½ tons of the engine’s weight, or an average of nearly 26½ tons on each pair. The second pair of coupled wheels from the leading end are the driving wheels proper ; the coupled wheels are 6 ft 5-in in diameter. Roller bearings are provided to all axle-boxes.
Rckoning from the chimney end, with the four wheels of the leading bogie first, then the eight coupled wheels and finally the four wheels of the trailing bogie, we have an engine of the 4-8-4 wheel arrangement. The nearest approach to this in Great Britain is the Cock o’ the North class of the London and North Eastern Railway, having the 2-8-2 wheel arrangement and similarly using eight coupled driving wheels.
Mechanical Stoking
These provide adequate adhesion for the extremely heavy gradients round the East Coast from Edinburgh to Aberdeen, but single pairs of wheels front and rear, with liberty for limited radial movement, are used instead of the two bogies. Compared with 4-8-4 No. 6400 of the Canadian National Railways, which weighs 170 tons without tender, Cock o’ the North of the London and North Eastern Railway weighs but 107 tons.
American and Canadian locomotive engineers are not generally in favour of the British plan of dividing up the cylinder power of modern locomotives into three or four units in place of two. One advantage of three-cylinder or four-cylinder propulsion is that the engine is better “balanced”, especially when running at high speed; against this division must be set the matter of greater complication of working parts and higher constructional cost. In Great Britain the division of cylinder volume into three or four units has been partly necessary because, with the limited space in which to build, two cylinders of sufficient size could not be mounted outside the engine frames in the clearance available.
No such limitation besets the Canadian locomotive designer, and No. 6400 is equipped with two exceptionally large cylinders with a diameter of 24-in, and a piston travel, or “stroke”, of 30-in. The motion operating the piston-valves is of the Baker-Pilliod type, arranged so that the steam supply to the cylinders can be cut off, when the engine is well under way, early in the stroke. The higher working pressure offers a correspondingly increased capacity for expansion.
Steam is generated in the giant boiler of No. 6400 at the high figure of 275 lb per square inch. Hitherto the highest pressure in British locomotives (with the exception of the experimental No. 10000 of the LNER, which carried a water tube boiler of special design) has been 250 lb per square inch, as in the LNER streamlined Pacifics of the Silver Link type, the LMS Pacifics and Royal Scots and the GWR Kings. At the rear end the boiler barrel of No. 6400 is 7 ft 2-in in diameter; at the front end it tapers to
6 ft 6-in.
The firegrate has an area of 74 square feet, and it would be beyond the power of any fireman to feed it by hand. Mechanical firing is therefore provided, the coal being brought forward by a worm and screw gear from the tender on to the firegrate, at a speed which the fireman can regulate according to the demand for steam. Inside the firebox two “thermic syphons” provide for rapid, circulation, and assist the process of steam-raising. After generation the steam is superheated, as is the practice on all modern locomotives. The object is to prevent cylinder condensation at the end of the stroke.
Coupled to No. 6400 is a tender which fittingly matches this enormous machine. Carried on twelve wheels, it accommodates 11,700 gallons of water and 20 tons of coal, and has a little over twice the capacity of the eight-wheeled tenders fitted to the Pacific locomotives of the LNER, which were the largest in Great Britain early in 1937. As the photograph above reveals, No. 6400’s tender consists chiefly of a large barrel-shaped water-tank, on top of which is placed, at the leading end, the hopper containing the coal. The driver’s cab and the tender front are connected in such a way that the crew is completely enclosed – a provision greatly appreciated when the engine is travelling at full speed through the intense cold of a Canadian winter. One novel feature of the tender is a “track sprinkler”, whereby a fine spray of water can be directed on to the track at places where it is dusty, so that the dust may be kept down and prevented from entering the carriages.
The total length of engine and tender falls short of 100 feet by only a narrow margin – the figure is 94 ft 8-in. By the ordinary tractive force calculation the maximum tractive effort that No. 6400 can exert, at 85 per cent of the working pressure (the customary allowance), is 52,450 lb, or nearly 23½ tons – a mighty pull indeed. The general arrangement of the streamlining of No. 6400 was decided after exhaustive tests had been made with models in a wind tunnel at Ottawa. The casing is really “semi-streamlined”, for the cylinders, motion and wheels have been left uncovered to permit of easier access for examination and repairs.
The front appearance of No. 6400 differs completely from that of most other Canadian or American locomotives. The usual circular smokebox front, carried on a saddle, is concealed by a rounded nose. This is extended downwards almost to rail level by an apron which takes the place of the ordinary cowcatcher, or lattice arrangement of steel bars, designed to clear the track of obstructions.
Recessed into the nose is the powerful electric headlight such as is carried by all North American locomotives; inside it is the small turbo-generator which supplies current for this headlamp and other lamps carried on the engine, and also for the air-brake compressors. When it is necessary to couple the chimney end of No. 6400 to a train, or to attach a pilot locomotive, a coupler appears from behind a door in the lower part of the nose, where normally it lies out of action.
Another lengthy casing extends along the top of the boiler from the chimney end right back to the cab, and is the chief contribution to the unusual appearance of the locomotive. Built into this are the chimney, dome, sand-boxes and safety valves, which are usually mounted above the top of the boiler.
If certain special precautions had not been taken, especially when the engine was being worked at high speed on a short cut-off, the exhaust steam from the chimney would drift along the top of this streamlined casing and obscure the front windows of the driver’s cab. Special louvres have, therefore, been formed in the rounded nose, and through these a strong current of air is forced when the engine is travelling fast. This draught is carried upwards in such a way that it catches the exhaust emerging from the chimney and lifts it high above the cab.
Further provision for the driver’s unobstructed view ahead is made by the fitting of a revolving disk of high-grade glass which forms part of the front window of the cab on the driving side, and this ensures a clear view in all weather conditions. Rain and snow are thrown off through centrifugal force.
Certain safety regulations did not permit the concealment of the whistle behind the streamlined casing, and it is therefore mounted in a prominent position abreast of the hidden chimney. The hooter of No. 6400 is operated not by steam, but by compressed air from the brake reservoir.
To such an extent is the publicity value of a smart locomotive now realized in Canada and the United States that cheerful colour schemes have become a standard feature of locomotive finish in North America. No. 6400 is no exception to this new rule. The front of the locomotive is painted black, but the long, narrow panel or “apron” of the running board, extending the whole length of the engine, is finished in the standard green shade of Canadian National passenger cars, with gold stripes above and below. These gold stripes begin at the front of the nose and sweep round to the running-board apron in graceful curves which accentuate the streamline effect.
In the middle of the apron, immediately above the driving wheels and in the middle of the nose below the recessed headlamp, appears the number “6400” in bronze figures on a red background. The numbers, on raised plates on either side of the upper part of the smokebox, correspond in a way to motor-car number-plates, and are illuminated at night from within.
The cab sides and the tender also are painted green, and on the side of the coal hopper on the tender appears the Canadian National “trade mark” – a rectangular panel, set at an angle, with the words “Canadian National” in gold on a red background. Above the running board, the “jacket” of the engine, including the outer covering of the boiler and the streamlined casing above, is of specially planished steel which needs no paint, but is rubbed with an oiled cloth to retain its natural bluish-grey colouring.
A 533-Miles Working
Five engines of this class are in service, and their principal task is to operate the fast and heavy passenger services between Montreal, Toronto and the United States border at Sarnia. This is a through locomotive working of 533 miles, and in Great Britain would be equivalent to running a locomotive unchanged with the “Flying Scotsman”, the “Aberdonian” or the “Royal Highlander” for the entire journey between King’s Cross or Euston and Aberdeen. At present the longest British locomotive workings are those of the LMS between Euston and Glasgow, a distance of 401½ miles.
It is in connexion with these lengthy Canadian through workings that the large size of No. 6400’s firegrate is of such value. Despite the fact that North American fuel is inferior in calorific value to the fuel used in Great Britain, it is possible, with the help of mechanical appliances for “shaking up” the grate while the engine is running, and so getting rid of ash and preventing the coal from clinkering, to keep a good, clean fire for an indefinite distance. The mechanical firing ensures also that no undue strain is imposed on the fireman. One engine-crew does not work the engine throughout this 533-miles run, but crews are changed at the important divisional locomotive points, while the engine herself uncomplainingly carries on.
The Canadian National tracks do not come to an end at the border station of Sarnia. The Grand Trunk Railway which, after its absorption by the Canadian National, provided the greater part of the Canadian National tracks in the Eastern States of Canada, also penetrated well into the United States. Thus to-day the Canadian National tracks extend almost as far as the great Middle West city of Chicago.
The “International Limited” and the “Inter-City Limited” expresses of the Canadian National Railways connect Montreal and Toronto directly with Detroit and Chicago. Beyond Sarnia the trains are taken over by other large 4-8-4 express locomotives somewhat similar in design to No. 6400.
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