Technology

By technology I mean anything to do with the engineering aspects of a new bus, including how it would be manufactured. Thus, our candidates are of interest if they employed technology to solve an operating problem (like increasing passenger capacity) or helped the manufacturer be more profitable. If the technology proved durable and reliable, so much the better.

Routemaster

Even though its layout was conventional for the time, the Routemaster embodied lots of new technology, both in the body and the running units. This was a brave step considering that it was likely the bus would be built in the thousands. No wonder they took over eight years to get it right (and it still had huge teething troubles).

The essence of the RM is the bodywork. London Transport learned a lot about stressed skin construction when some of its facilities were turned over to making the fuselages of Halifax bombers during the war. The body of the new bus was designed to be strong enough to dispense with a chassis.

As much of the body as possible was made out of aluminium alloy, to avoid the weight and corrosion risk of steel and the tendency of wood to rot. Even the floors were made of corrugated alloy.

The Routemaster engine was either an AEC AV.590 or Leyland O.600 diesel, both putting out 115 bhp at 1,800 rpm. Two proven, not over-stretched, reliable workhorses.

The transmission was more interesting. Whereas the RT had a pre-selector gearbox, the RM was a true semi-automatic. It was an epicyclic unit built by AEC on Self Changing Gears patents, located in the wheelbase under the floor. The gear selector was mounted on the steering column.

The driver selected gear by gear as the bus accelerated. Changing down was rarely necessary except on gradients, and the gearbox reverted to neutral when the bus came to rest.

Whereas the pre-selector system on the RT could be very jerky in the wrong hands, the RM transmission was developed to be able to deliver smooth changes under full throttle.

Power assisted steering was also new, tuned not to be so light that the driver would be over-worked if it failed. It was specified following experience with the early prototypes.

Another major decision was to have hydraulic brakes. The attractions were less weight than an air system, combined with better responsiveness and avoiding the tendency of air brake valves to get contaminated with grit and rust. But a hydraulic system was more complex and needed skilled maintenance.

A front sub-frame was attached to the body structure, carrying the front wheels, suspension, engine and ancillaries. Independent front suspension reduced shock loads into the body structure. This was a new feature on a production bus.

A rear sub-frame carried the rear wheels and suspension and the final drive. Using coils and shock absorbers as on the front, the rear suspension was arranged to have those coils as close to the body side as possible, so decreasing any tendency for the bus to roll.

Coil springs were certainly an innovation, to give a better ride than traditional leaf springs and be less costly to maintain. Some earlier RMs had air suspension, but coil springs proved much less troublesome.

The vehicle’s component arrangements were perfectly suited to London Transport’s massive overhaul works at Aldenham. Built as a maintenance and stabling centre for underground trains, the building was stranded in south Hertfordshire when the Northern Line was never extended as planned.

It was turned into a giant factory where buses were taken to bits for reconditioning on a regular basis such that the bus that went in and the same bus that came out might have nothing in common except the bodyshell.

A Routemaster bus could arrive and have the front and rear sub-frames, and the gearbox, removed quickly. Units could be sent to various shops for reconditioning, whilst the body was brought back to as-new condition.

This process was facilitated by the fact that the bus was put together using very precise jigs at Park Royal, enabling universal interchangeability of parts. This was a step away from traditional coachbuilding methods that relied on a fair deal of hand work to get everything to fit together.

Dispensing with a chassis meant a great deal of weight could be saved. The RT was able to carry 56 seated passengers, yet the RM could carry 64 and weighed slightly less. In metric units, RM 1 came in at 6,833 kg.

The production Routemaster tipped the scales at 7,360 kg, mainly because of the fitment of interior heating and power steering and bigger destination displays, and relocating the radiator at the front instead of under the floor, .

The Routemaster was slightly heavier than the 300 super-light Leyland Titan PD2/20s fitted with MCW Orion bodies, bought by Edinburgh. But the Edinburgh vehicles were widely disliked as tinny and uncomfortable compared with the London product.

My rating for Routemaster technology: 7 out of 10.

D9

Now, the BMMO D9. What the Midland Red engineering operation lacked in scale, it made up for in ambition and panache. All of its in-house designs were radical in some way, and in some cases a decade or more ahead of what bigger manufacturers would make and operators would buy.

It developed the radical FEDD forward entrance double-decker as its standard big bus in the 1930s. In 1936 it built a transverse rear-engined single-deck bus, the REC. It was a pioneer in integral construction, use of glass reinforced plastic (GRP) and rubber suspension.

Perhaps it was the chance to work on such adventurous concepts that attracted talented designers and engineers to join the firm instead of taking jobs with any of the big automotive companies around Birmingham and Coventry. It is unlikely to have been a free bus pass.

During the 1950s BMMO had created a number of large single-deck models, as well as stunning coaches capable of hurtling down the new M1 motorway at 85 mph. The D9 embodied lots of the technology that had been proven on the big single-deckers, and added several new features.

However, we must not run away with the idea that BMMO was pursuing novelty for its own sake. Everything it did was about either saving money (especially by cutting production costs), saving weight or simplifying operations.

For the D9, the power unit was a conventional diesel engine. Compared with the Routemaster and the Lodekka, it had a bigger 10.5 litre capacity KL unit (made in-house), enabling it to produce 125 bhp at 1,700 rpm. Some BMMO double-deckers, like the D5, had a reputation for being rather under-powered, so the choice of this unit was meant to ensure available power was more than adequate. It did add a significant amount of weight though.

Previous BMMO double-deckers had manual gearboxes. The positive results from the trial of a Self Changing Gears semi-automatic epicyclic box in a D7 led to it being specified for the new bus. The gearbox was electrically controlled, but hydraulically operated. Other manufacturers, like Leyland, always chose air actuation and it was to be twenty years before they adopted the more responsive hydraulic system.

A robust underslung worm gear set took drive from the transmission to the rear wheels.

The biggest areas of mechanical innovation though were the brakes and the suspension.

In the 1950s disc brakes were only seen in high performance cars, yet BMMO chose to fit them to its S14 single-decker. They worked well and the decision was taken to fit them on the heavier D9. The whole braking system was hydraulic (like the Routemaster) with servo-assisted pedal control. There would also be a disc-type parking brake on the transmission.

During development it became clear that the rear disc brakes were regularly overheating and quickly wearing out, consequently rear drum brakes were installed for the production vehicles. Front disc brakes proved problematic in service, so early production D9s were retro-fitted with drums. The transmission brake was also dropped.

The suspension proved more successful. BMMO was already using the Metalastik rubber suspension and its compact envelope was attractive to achieve the maximum interior space. Independent front suspension was chosen as it enhanced ride and handling. The suspension layout required trailing radius rods anchored to the vehicle under-structure. This meant the front wheels had to be set back from the front end of the bus.

The front wheels therefore straddled the bulkhead between the driver’s cab and the lower saloon. As a consequence, the first seats in the lower saloon had to face inwards to cover the wheel-arch. On the other hand, this arrangement improved engine access and also permitted a more spacious driving compartment.

The body structure created an integral box to which the running components were attached. The skeletal steel structure was bought in from Metal Sections of Oldbury, with the panelling and fitting out done at the Central Works. Flat panelling was of aluminium, the inner panels being stressed. Extensive use was made of glass-reinforced plastic (GRP or glass fibre).

The dash panel, bonnet and parts of the cab interior used this material on the D9. BMMO’s commitment to GRP justified making the process of creating components as automated as possible. Thus a machine was purchased which could spray resin and glass filaments evenly across a mould. This could handle colour-impregnated gel which would become the surface of the final piece, saving money on priming and painting.

The front and rear domes, the entire roof, and the first and last window bay of the upper deck were moulded as a single GRP section which had to be manhandled into position. Only when this roof unit was attached to the bus body structure were the windows apertures cut out. There was no inner roof lining. The mould for the roof unit was a male type. This meant that the smooth surface that was the upper deck ceiling was against the metal mould. The outer surface was finished with a layer of fine-woven glass sheet to give a reasonably, but not perfectly, smooth finish.

Channel section GRP sticks were incorporated into the rood structure to add stiffness. This was done by having troughs in the mould into which the sections were laid on top of the initial resin-impregnated glass-fibre. Once production was under way, further experiments were done to refine the moulding techniques. Eventually, the inner surface of the roof unit was impregnated with white pigment for the interior and the outer surface in deep red for the Midland Red livery – saving money on paint and painters.

To strengthen other sections, like doors, the mould contained troughs into which paper ropes were placed to be surrounded by GRP. The spacing, thickness and number of ropes would allow just the right level of stiffness to be obtained.

One application of GRP cleverly took advantage of the machining going on at Central Works. The step treads of the stairs were surfaced with GRP sheets which had metal swarf mixed into them, creating a very slip-resistant surface.

The effect of using so much GRP was dramatic, as it offered weight savings of around 40% compared with aluminium doing the same job. The unladen weight of a D9 was was 7 tons 18 cwt, although that was actually four hundredweight heavier than the Routemaster RML which also had 72 seats. The big BMMO engine might have accounted for most of that difference. It was also claimed that the cost of fabricating the roof was half that of making a metal one, and similar cost savings would be possible on other parts.

The snag was that the roof turned out to be too light and flimsy. There was a tendency for the front dome to crack so that strengthening ribs and patching were often needed to ensure the front windows stayed put.

Overall, the D9 could be regarded as the most technically advanced of the three models, although it has to be admitted that some features would not have been available to the AEC or Bristol teams when they froze the design of their respective buses.

That said, it drew heavily on BMMO’s recent innovations on single-deck models, applying them to a double-decker that was markedly different to any other British half-cab double-decker.

Even though the automotive and manufacturing techniques were quite daring, Midland Red’s attitude to basic vehicle layout was conservative. For example, instead of applying technology to produce a low floor double-decker, it stuck with the raised floor on the lower deck.

The D9 proved to be a reliable and durable machine, although its poor brakes and weak single skin roof were problematic. Most lasted in service for around eleven years, but their relatively short life might have had more to do with fleet standardisation policies at NBC and WMPTE than the inherent longevity of the design.

My rating for D9 technology: 8 out of 10.

Lodekka

From a technical perspective the Bristol-ECW Lodekka is fascinating because it presents a journey towards an ideal solution to the lowbridge problem. Step one was the LD; step two was the F.

The first prototype took the drive from the gearbox and sent it down a prop shaft that was tucked against the off-side chassis rail to about two thirds of the way down the wheelbase. Here a differential unit split the drive. Power to the off-side rear wheels carried on a straight path to worm gear into the wheel.

Power to the near-side rear wheels was taken across the chassis, through a bevel box and down a prop shaft to a worm gear and the wheels. Thus the rear axle casing itself carried no drive but was part of the suspension system.

This was somewhat simplified in the second prototype when the differential was placed behind the gearbox, and power was fed through two prop shafts inside the chassis rails to separate worm drives for each rear wheel.

All these sets of gears and universal joints meant efficiency losses, and so in the pre-production LD type, the set-up was simplified still further. A single prop-shaft ran all the way from the gearbox to a double-reduction rear axle built by Bristol, again tucked up against the inside for the off-side chassis rail.

Every version had the drive angled away from the vehicle centre line by having the engine and gearbox set at six degrees off centre.

The consequence of all this was that the gangway height could be dropped such that there was no step from the platform into the lower saloon. The catch was that all the seats were on low platforms either side of the gangway so you had to step up to reach any of them.

The low floor was achieved by sweeping down the chassis cross members between the chassis rails. In the LD this meant having a number of intrusions into the gangway to cover components like the junction between the forward and aft sections of the prop shaft.

Nevertheless, this ingenious solution meant that conventional two plus two seating could be employed upstairs, yet the overall height of the bus could be 13 ft 5 in, more than a foot lower than conventional double-deckers.

One snag was that the position of the outriggers was fixed such that a window bay had to be incorporated that straddled the rear wheels, otherwise body strength would be compromised. This made a 30 foot long variant an ungainly looking creature.

The Lodekka could not be a pure integral because Bristol’s chassis works was in Bristol and ECW’s body factory was over 250 miles away in Lowestoft.

Completed chassis had to have enough stiffness to be able to be delivered by drivers perched on a makeshift seat and wrapped in whatever they needed to protect them from all the perils of the British weather.

The Bristol and ECW engineers were not entirely satisfied with the LD solution. They had cracked the lowbridge problem and achieved a stepless entrance into the lower saloon, but only by making compromises. The LD was also unable to accommodate a forward entrance.

Whilst the LD series buses were being built by the hundred, they worked to achieve the true goal, a low, completely flat floor on the lower deck.

This they arrived at with the F series Lodekka in 1958. Millions of miles of operating experience with the LD gave them the confidence to reduce the height of the chassis rails. This was compensated for by reinforcing the truss sections in the lower panels of the ECW body.

The chassis extended over the rear axle with two deep wheel arch members. These were supplemented by two even bigger wheelarch members at the outer extremes. Through inner and outer body attachments this meant that suspension loads could be efficiently transferred into the body structure.

A body pillar could be attached anywhere on either of the outer members, and the wheelbase could be varied to meet the needs of the market.

This improved design also meant that a forward entrance body was possible, without any step between the doorway and the main gangway.

Beyond the clever chassis design and the compact double reduction rear axle, the rest of the Lodekka did not display a great deal of innovation.

This conservatism was probably wise, because these buses ran everywhere from Penzance to Perth and beyond. Unlike at London Transport or Midland Red, working facilities varied enormously, and getting and retaining good mechanics was often a challenge away from big towns and cities.

Lodekkas had either a Bristol, Gardner or Leyland diesel giving around 115 bhp. Most had manual gearboxes, with some semi-automatics appearing only towards the end of the production run.

The LD series had old-fashioned leaf springs. The FLF kept these on the front but had air suspension on the rear. This enabled the floor height (and the overall height) to stay constant no matter how lightly or heavily the bus was loaded. Some operators retrofitted coil springs which were less troublesome.

The Lodekka was ground-breaking in another respect. Hundreds of examples were fitted with the Cave-Browne-Cave engine cooling and saloon heating system. This was invented by Wing Commander Cave-Browne-Cave, who became a Professor of Engineering at Southampton University.

The idea was to create a more efficient arrangement for cooling the engine and warming the interior than could be achieved by a traditional radiator. Hot water from the engine cooling circuit was piped up to a pair of small heat exchangers either side of the front destination display. The driver could open valves that would direct air warmed by passing across the heat exchangers into each saloon. Otherwise, the warmed air would pass out through vents on the side of the upper body.

The system was not a universal success, and some operators disconnected it and fitted a conventional radiator. It ceased to be offered as an option in 1966.

In summary, the great advance the Lodekka achieved was the solving the lowbridge problem. This included developing a complex, but reliable, rear axle. In doing so, Bristol and ECW created the first high volume stepless entrance bus.

Otherwise, the mechanics of the vehicle were kept simple to ensure it stood the best chance of running reliably with a wide range of operators in a wide range of operating conditions throughout Great Britain.

My rating for Lodekka technology: 6 out of 10.