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LONDON'S LEP BUS DESIGN.

The Prophetic Requirements of in the Evolution of Types of I for Work in London, fill

Yard in 1909 have Resulted are Proving their Suitability s, and even Overseas.

IN NO other country in the world has the motorbus developed to the wonderful extent which it has here. It is now almost 'within the range of possibility to travel from Land's End to the Highlands by public passenger conveyances of this type, but we must not forget the tremendous influence 'which has been exercised upon this progress by the pioneer buses of London. _

When first the authorities of Scotland Yard laid down certain regulations on which the construction of buses should be based, there were many serious criticisms as to the limits of weight which were imposed, and even suggestions that it would be impossible to produce satisfactory vehicles which would comply with themut have had who had the framing of the new rules had the satisfaction of seeing nat only the development of highly efficient vehicles for London service, but have also been able to note the influence of London bus design upon vehicles in many parts of the world, this influence even extending to chassis built for goods carrying.

The proof of this is to be found in the half dozen Tor so different makes of bus chassis other than the 'types placed on the streets by the London General Omnibus Co., Ltd., most of which have had very little difficulty in conforming to the rules imposed by Scotland Yard, and this despite the fact that these chassis were not originally constructed with this object in view. During our visits to various builders of Londontype vehicles, we have been surprised to note the very slight differences there are between the London and provincial models. Usually, it is mainly a question of seating accommodation in the body, but even in the case of bodies, the London-type doubledecker is sometimes employed With, possibly, some slight addition in the way of side protection to the driver's seat, and it has been proved that what is suitable for London should meet not only the needs of other of our big cities, but also those of the world. London, in fact, has proved an unrivalled testingground, and any vehicle which is found efficient and economical in London work is almost bound to be successful elsewhere, for not all the roads of the Metropolis are so smooth as those in its cents.] area.

The average bus operating in London may easily. cover 1,000 mileS per week all the year round, and what miles many of them are—constant declutching and clutching, gear changing and application of the brakes—and yet it is becoming an uncommon sight to see a stranded vehicle. In the Opinion of some, improvement ts being carried almost too far. At on thee, a motorbus announced its presence in no uncertain fashion, but now it approaches so silently as to be almost a menace from this cause only; if it were not that " safety first " is the ruling order and that the bus driver is without compeer.

As an example of the manner in which silence has been attained, it is interesting to note that cases are known in which drivers of a certain make of bus keep their engines idling at something like 700 r.p.m., in order to be certain that they have not stopped.

So far as we are aware, no efforts have yet been made to point out the differences and characteristic features of the various types of London bus, and the points to which attention has to be paid in order to Fet them passed by Scotland Yard. •We, therefore, intend, in this and subsequent articles, to deal with all the different makes se passed, and in this particular article we include certain interesting details concerning the Straker-Squire and the Thornycroft, but, first of all, we will give a brief outline of the most important of the 65 conditions with which those who Wish to 'run omnibuses on the streets of London have to comply.

So far as the chassis is concerned, this must not exceed a length of 21 ft., unless the platform is carried on the frame, when the total length may be 25 ft. A clearance of at least 10 ins; must be allowed as far back as the rear axle, or not less than 14 ft. 6 ins, from the durab-irons. The rear springs must be not less than 45 ins, between the outsides, and the front springs not less than 38 ins. ; the .wheelbase must be so arranged that not more than 7-24ths of the total length, including the body, overhangs the centre of the rear wheels. Not less than 5-ft. 6 ins. must be allowed for the track, and in no case must the front track be less than the rear.

The minimum tyre sizes are : front, 900 mm. by 100 mm. ; rear, 1,000 rum. by 90 mm., but where the vehicles weigh more than six tons larger wheels are rtquired, viz., for a five-ton axle weight 1.050 ram. eameter and, if possible, all wheels should be of the same size.

Another veryimportant consideration is that the breadth must not be greater than 7 ft. 2 ins, at any part.

Brakes are not deemed to be independent which act upon the same brake drums.

Wheel caps, hubs, etc., must not be projected more than 34 ins, from the wheel flange.

As regards the complete vehicle, the total laden weight, including a full fuel tank and the vehicle ready for service in every respect, must in no case exceed 84 tons, nor may the back axle weight be greater than five tons. In calculating the total laden weight, 140 lb. is allowed for each passenger, as well as for tbe driver and for the conductor.

In connection with the body, the most important dimensions are the inside height, which must not be less than 5 ft. 10 ins, or not greater than 6 ft., and from the ground to the spring of the roof or the edge of the drip hoards the height must not be greater, than 9 ft. ; the breadth must not exceed 7 ft. 2 ins. at any part, and the length is limited to 25 ft. The measurements for the seats are very important, and upon these, to a. great

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extent, depends the seating capacity of any particular type of vehicle. At least 16 ins., measured in a straight hue, must be allowed for each passenger' and where cross-seats are fitted there must be at least 26 ins, clear from the inside back .of one to the back of the seat in front.

We do not publish these extracts except as a rough guide to the main problems which have to be overcome. The full conditions can be obtained on application to the Public Carriage Office, New Scotland. Yard, London, 8.1/V.1.

The effect of these conditions on bus design ha been to produce a very satisfactory form of vehicle, which, owing to its low centre of gravity, has a high degree of Stability. Tests of the angle to which a loadod double-deck bus may be tilted before overturning takes place have been made with certain vehicles, and it has been shown that they can be forced over to an angle of something over. 40 degrees before • they overbalance. With the heavily constructed .bodies formerly employed this degree must have been considerably less.

The seating capacities of the various buses in use vary from 46 to 54 and they are now all of the 'type in which the majority, of the passengers sit in pairs facing forwards, whilst from four to eight are accommodated on facing seats at the rear, these usually being fitted in order to overcorne the difficulty of wheel arch intrusion. Various means have been adopted to increase the seating, capacity and yet keep withinthe police limitations, and the latest vehicles are a vast impiovement in this respect upon the old 34-seaters, a few of which are still in service. Body design has had a tremendous influence upon the matter, and this is being assisted in certain instances by carrying the dash forward so that part of the engine is accommodated behind it, as in the case of the 8traker-Squire, or placing the driver beside the engine, as was done first on the K-type buses and, later, on the Thornyeroft vehicles, thus allowing from two to four extra persons being carried.

We will now deal in particular with the -StrakerSquire vehicle. In this, the chassis has required practically no alteration from the standard A type, which has already been described by us in detail, and so well was the vehicle designed that, whilst giving ample strength, no trouble was experienced in complying with the weight restrictions ; in fact, with a chassis weight of 3 tons 10 cwt. and a body weight of 1 ton 6 cwt. 2 qrs., totalling 4 tons 16 cwt. 2 qrs. (the vehicle being built to carry 46 passengers), the total weight. of 7 tons 16 cwt. 2 qrs. is thus well within the limit.

No particular difficulty has occurred in obtaining silence, and, in so far as the gearing is concerned, each gearbox is run-in with oil for about eight hours before being built into the chassis. The only large alteration which has to be effected is the fitting of concentric drums in place of the single drums previously employed for the to sets of brake shoes.

The actual friction faces of the drums are still side

by side, but in the case of the outer drum this is belled out so that it can be bolted to the Ind-lee' out

side the inner drum. Other additions include a strap under the cardan shaft (which, incidentally, is one of the fittings required by the regulations), undershields for the gearbox and engine, and two small trays under the universal joints. Owing to the tremendous amount of declutching, a little troubli was at first experienced, as the saw steel single disc sometimes worked loose on its bolts, but the clutch has now been redesigned, and the disc is now splined on to its boss as well as being bolted. The springing is exactly the same as that employed on the standard A type. It is highly efficient, and is so designed that the tilting of the axle does not cause spring twist. At the front end the rear springs are fitted with hardened-steel balls working in chilled-ircn cups, whilst at the rear end are cast-iron slippers working on steel balls and completely enclosed, which take the place of the usual shackles. These slippers permit about I in. lateral movement in each direction, so that the springs can accommodate themselves to unequal displacements of the axle. Two taper coil springs give automatic stiffening of the springing under big deflections.

A small improvement in the braking is the use of adjustable screw stops, which were fitted in order to assist the levers to return to the off position.

Every chassis is fitted with a special impulse starter of the company's own make, and with this fitment it is only necessary to pull the engine slightly over compression.

• Dealing with the design of the body, this is in one with the rear platform, so that the whole body and platform can be removed together. The bracket for this platform enables it te be shortened some 6 ins. below the level of the top of the chassis frame, the ends of which are just in front of the entrance to the body. For the unladen vehicle this gives a distance

from the ground to the first step of 16 ins., from this step to the platform 13 ins, and from the platform into the body 9!:2; irks. Ample knee-room is provided; as a matter of fact, it is VI ins, over that required by the regulaeions.

Weight in the building of the body has been cut down without sacrificing the strength. For instance, the side standards are very light, but are reinforced by 1-in, by i-in. angle, steel. The platform brackets, of which there are two, are each 3 ins, wide and made of 1-in. mild steel. The chair-legs also are plated with 16 S.W.G. steel.

Efficient ventilation is provided by special windows at the sides, which are positively locked by screwhandles.

At each end of the body is a steel strengthening bracket, which stretches right across the vehicle and part of the Way down the pillars. This assists in giving a very rigid construction.

The following dimensions of the 46-seater StrakerSquire will be of interest :----Overall length, 24 ft. 10 ins. ; wheelbase, 15 ft. ; height to roof gutter,

B ft. ii ins.; width of body, 7 ft. 1 ; overhang from back axle, 7 ft. 2 ins. The front-axle weight of the chassis is 1 ton 14 cwt., and the back-axle weight 1 ton 16 cwt.•

The second of the vehicles with which we deal this week is that built by Sohn I. Thornycroft and Co., Ltd. The bus chassis in this case weighs 3 tons cwt. 1 qr., which allows rather more weight for the body. It can be built to carry as many as 50 people, and to permit the placing of the driver beside the engine. It is interesting to note that this weight compares with the 3 tons. 5 cwt.. of the standard J type chassis used for provincial buses. A great part of the saving is due to the use of cast-steel rear wheels, as these have proved considerably lighter than the plate type, whilst the small dash for the forward-control position in lieu of the full width dash employed elsewhere also assists in this respect. The actual weight of the complete bus with a Dodson body is said to be 4 tons 14 cwt. Springs of somewhat lighter type are utilized for London service. Another small modification required is the fitting of a second brake acting on independent rear-wheel drums in place of the transmission brake employed on the ordinary J type. Mechanical universal joints are also now employed in place of the leather disc type.

In order to conform to the regulation regarding the projection of wheel hubs, the . tyres which are employed at the rear are so fitted that the outer one projects about in.; this, combined with the use of tyres of somewhat narrow. section, permits a fairly large gap between the two tyres, and, consequently, entirely prevents the jamming of stones, etc., between them. This is a point of considerable interest, as such stones often ruin tyres by breaking the rubber from its vulcanite base, apart from causing a bad bump while running. In the Thornycroft chassis special attention has been paid to the question of silence. For instance, a secondary silencer is used for the exhaust. This is suspended at an angle from a back cross-member, the front end being supported by a neat bracket from a side-member of the chassis. In order to prevent the

possibility of rattle, the gear-change lever is providedwith a neat laminated steel spring at each side; this also assists in keeping the lever central when it is in the neutral position. Each of the forks for the brake connections has double spring washers between one side of the fork and the eye of the lever, hilt this is a feature which applies not only to bus chassis, but to all other chassis made by the company. In order to assist starting, a Simms impulse starter is employed, with the result that it is necessary merely to pull up the starting handle against compression, when the starting device ensures a fat spark. Adequate lighting is one a the most important features which must be attended to, and in the Thornyeroft this is effected by the use of two C.A.V. dynamos— one driven in line with the magneto and water pump and the other which is somewhat large-r, driven by a link-type belt.

The company do not build their own bus bodies, so that, in order to obtain details of the bodies fitted to theThornyeroft chassis, we had a chat with a representative of Christopher Dodson, Ltd., of Cobbold Road, London, N.W.10, who said that the weight of a 50-seater body, such as that fitted to the Thornycroft, is 23cwt. 2 qrs. Very little trouble, indeed, has been experienced in getting these bodies down to this weight. They are practically all wood, built with three-ply panels and the bodies now built are almost identical with tliat fitted on the first post-war independent bus to be placed on the streets of London—i.e.,

B36 ,

the "Chocolate Express "—except for a few minor details. For instances a certain amount of rattle was found to be caused, by the small window ventilators, but this trouble was entirely cured by fitting a small support under the ventilator at the front end. This takes the weight and thus relieves the hinges of this duty.

The pillars are constructed entirely of wood, but are steel-plated at the top and bottom. Much of the secret of obtaining lightness in this and other bodies of the same type lies in the vertical support pillars between the floor and the rocif, and which are also convenient for standing passengers. These pillars stop throbbing of the roof, which would otherwise. be caused by-movements of the passengers, and they add greatly to the stability of the whole vehicle, as the roof would otherwise tend to drop in its centre and cause the sides to bulge out.

The Thornycroft chassis is extended in a simple manner by the fitting of tapered inverted L-angle steel members, which are bolted to the main members of the chassis, a wedge-shaped steel packing piece being inserted between each frame member and its extension.

In order to provide efficient ventilation, apart from the small• windows previously referred to, dropwindows are provided at each side, but these can only be lowered to the level of the protecting rails. This is in order to prevent a passenger from extending his elbow outside the body. These frameless windows are carried in felt channels to avoid vibration.

A very interesting feature of the Dodson body is that all the rainwater is taken to the ends of the roof and down pipes on to the road, these two pipes at one end forming the canopy stanchions, and at the other end acting as a handrail on the platform. The Dodson provincial bus body is practically the same as that which we have just described in brief, except that the sides of the cab are extended to give greater protection to the driver.

The following are the main dimensions of the Thornycroft bus chassis :—Overall length, 24 ft. 5,!.ins.'; wheelbase, 15 ft. 6 ins. ; overhang (from centre a rear axle), 7 ft. oi in. ; back of petrol tank to end of frame extension, 18 ft. 74 ins. ; height from ground to first step, 18 ins. ; distance from first step to platform, 141ins,; height from platform into body, 8 ins.