The Leyland National was truly a revolution in British bus design, all new from the ground up and designed to be quick and easy to manufacture and repair
The Leyland National was unveiled to the world in September 1970 when the fifth of seven prototypes — all of them built at Leyland before the Lillyhall factory was completed — was exhibited at the Commercial Motor Show at Earls Court in London. It was registered BTJ 857J.
The National was to be produced in two lengths, 11.3m (37ft) and 10.3m (33ft 9in), the maximum permitted for single-deckers having been increased to 12m in 1967. There was a choice of one door or two to the same dimensions and design, up to 52 seats on the 11.3m version and 44 at 10.3m (two-door buses had four fewer seats). The seats over the front wheels faced inwards, but the combination of low profile tyres developed by Goodyear and standard size wheels minimised wheelarch intrusion into the saloon.
Most of the assembly was riveted
The 1,421mm front and middle and 812mm back sections were common to both versions; the other five body bays were also 1,421mm on the 11.3m model but 1,218mm in the 10.3m version. These common sets of dimensions within each type made all panels and windows interchangeable.
This was part of an overall aim of building a bus that required a minimum number of unique spare parts and could be maintained and repaired without operators having to own an inordinate number of standby vehicles.
Built strongly in steel
The integral body was manufactured from steel, which was cheaper than aluminium, and treated with epoxy powder coating to protect it against corrosion. The underframe was largely built up from varying sizes of steel channel, with pressed steel cross-members in the suspension areas and pressed steel wheelarch risers. The side framing employed formed longitudinal members with pressed steel door frames, while steel truss members reinforced the wheelarches and doors.
Most of the assembly was riveted, with a high degree of tooling on the production line, so that a Leyland National could be built in about a third of the time taken by traditional coachbuilders. Sub-assemblies, however, were welded.
For ease and speed of repair, areas most likely to suffer body damage were free from welding and all side panels were attached by closely spaced rivets. Most of the body panels were made of steel, except below waist height where high-strength aluminium alloy was used.
It also was designed to minimise the damage and injury to occupants in a serious accident, employing a ring frame construction system with pillars and roof sticks manufactured by Pressed Steel Fisher, a sister company in Leyland’s car division. One of the prototypes was crash tested into a concrete block to prove the integrity of the structure.
The roofstick, which formed part of the ring frame, was the main structural member. This was an assembly of substantial depth forming a transverse member of high strength at the top of the pillar. The stick consisted of two pierced pressings secured back to back along the line of abutment of the flanges and around the circumference of the openings in the member.
The exterior roof panelling was one complete corrugated aluminium alloy structure, while the longitudinal roof members and cantrail were formed sections that also contained the ducts for the heating and ventilation system, which used a pod at the back of the roof — one of the Leyland National’s most distinguishing features — to circulate throughout the saloon.
Leyland considered that the heating and ventilation (with provision for air conditioning in export markets) was superior to conventional under-seat heaters which used hot water piped from the engine cooling system. It overcame the problem of condensation misting windows on wet days, but defied physics by blowing hot air down when its natural state is to rise.
The floor, with one step up to the front section and a second ahead of the drive axle, comprised two sections of resinbonded plywood attached directly to the underframe, while the seats were steel pressings individually trimmed and mounted to the body sides and floor.
Saloon lighting was by fluorescent tubes concealed by a translucent panel in the centre of the ceiling and running for its full length from behind the driver’s cab.
The headless wonder
One of the biggest changes from previous products in the Leyland stable was its engine. In place of the 11.1litre O.680 that powered the Panther, Leopard and Atlantean was Leyland’s all-new 8.2litre turbocharged 510, the horizontal version of the vertical 501 engine later offered in double-deckers.
Nine Bristol REs for NBC’s Bristol Omnibus Company and West Yorkshire Road Car subsidiaries were fitted with early production examples of the 510 engine; the first of these appeared at the same Earls Court exhibition as the prototype Leyland National and the other eight were in service from early 1971.
Leyland had developed the new engines to deliver the power outputs demanded in higher gross weight trucks. One of the weaknesses of the O.680 and its equivalent units in the AEC range was cylinder head gasket failure, which was eliminated in the 500 series by having no separate cylinder head; this also ensured water flow at the piston crowns, the hottest part of the engine. A downside was that replacement valves needed to be inserted from the bottom. The new engine was slimmer as it also had an overhead camshaft, with fewer moving parts in the valve operation.
Leyland’s original plan had been for the 500 — which inevitably became known as ‘the headless wonder’ — to be a larger capacity one of 11.4litres, but it decided at a relatively late stage to reduce it to 8.2litres in order to cut its weight.
Hindsight suggests this was a mistake, one that contributed to its unreliability, particularly in trucks, and lost Leyland many road freight customers.
It was offered on the Leyland National with three power outputs: 150 or 180hp at 2,000rpm or 200hp at 2,200rpm.
Transmission options were either a fouror five-speed gearbox with a choice of semi- or fully-automatic control. Leyland’s Pneumo-Cyclic gearbox was standard, but the ZF 2HP45 torque converter was offered for a time as a more expensive alternative, taken up by a handful of operators.
Leyland’s launch publicity said that the turbocharged engine enabled the bus to hold its own in all traffic conditions without impeding the flow of other vehicles. “It does not produce excess smoke or noise,” it added. Reality was a little different, as an unfortunate characteristic soon apparent and never cured was its tendency to emit exhaust smoke when starting, before the turbocharger kicked in.
Its newly designed rear axle was a double-reduction one with primary reduction by helical spur gearing and secondary reduction by spiral bevel. Rather than for the power to be transmitted directly from the gearbox to the axle, which was a weakness in earlier rear-engined single-deckers, it had a longer straight propshaft, which ran through the axle case and transmitted the drive through a primary gear pair to the pinion and crown wheel.
Ride quality was improved by air suspension on both axles, with minimal moving connections, and levelling valves set to avoid a diving effect when braking.
The electrical wiring also was all-new. In place of colour-coded separate wires bound together in bundles over 1in in diameter and difficult to feed through and locate on a bus body, it had a flat seven-core wire that was compact and also shaped to avoid incorrect plug assembly. This had an adhesive backing and could easily be fixed between trim and body panels.
It retained colour-coded harnesses in areas where individual connections to components were required, but these were much smaller and easier to manage. For ease of maintenance, the wiring was installed in lengths, plugged at each end so that if a fault was traced to one area, the electrician simply needed to unplug the section and replace it with another. To help trace and diagnose faults, a test panel was designed which could be plugged into the vehicle’s control panel.
Testing took place out of public gaze
Designed around people
Leyland also made great use of ergonomics, the study of the relationship between people and their working environment, to accommodate drivers and passengers as comfortably as possible.
The driver’s cab was designed from scratch, with controls placed according to how often a driver would need to use them; those in most use (e.g. lights and wipers) were the easiest to reach, followed by start/stop, parking brake and gearchange, then fare collection and finally passengers’ lighting and heating. Leyland said at the time that the cab was capable of accommodating a 95% stature distribution of all male and female bus drivers and made a point of adding that the switches were light enough for a female driver to operate throughout a shift.
At 18in, the steering wheel was smaller than those on most other buses and coaches, and with power assistance required only five turns to go from lock to lock. The controls for the horn, trafficators and headlamp dipper were on two stalks on the steering column, a feature first used on Triumph cars. The instrument panel, with red and yellow warning lights, was placed in the driver’s sight line just behind the steering wheel. It also contained the door operating controls.
It was one of the first buses designed for one-person operation. Consequently, the gear selector was located on a ledge on the right-hand-side of the cab on right-handdrive models, with a small lever for the air-operated parking brake directly behind. The area to the left of the steering wheel was reserved for fare collection.
As the cab was a standard one on all Leyland Nationals, the idea was that once given an initial course of instruction, a driver would be able to work on any of these vehicles, regardless of length.
Ergonomics also determined the height of the steps, width of the doors, ceiling height, the height of the side windows, position of handrails and pitch of the seats. In our October 1970 issue, Buses commented that the seats “have not merely been designed for a comfortable ride with, because of their slim profile, a singularly good pitch between the rows but also to employ materials which are particularly resistant to damage, malicious and otherwise”.
“Never before in Britain has a manufacturer put so much effort, expertise and expenditure into developing a single range of buses,” said Leyland in a brochure produced for the 1970 launch, adding, “It is more than just a bus; it is a whole new transport idea giving the operator a vehicle designed for his [sic] requirements, with an operating efficiency and reliability considerably in advance of other buses.”
It argued that all of its features contributed to the inherent safety of the National. “The bus gives safety not only in the event of an accident where its integral construction with massive ring frames absorbs impact, but also inside with the use of high intensity lighting, flat sure-grip floors, carefully designed seats and a smooth suspension system giving maximum stability at all times.”
Prototypes and testing
The first running prototype was completed by the autumn of 1969, registered XTC 351H. It and five others were dual-door vehicles to test what potentially might be the weakest structure, while the fourth prototype was a chassis only. None operated in passenger service.
The first of them looked like a cross between the 1967 Commutabus mock-up and the finished article, with styling by the Rover design studio. Refinements first seen on the bus at Earls Court in 1970, like the treatment of the front headlamp clusters, roof dome with destination box and illuminated pay-on-entry signs, and cantrail, were the work of the Italian car designer Giovanni Michelotti who had worked with Standard Triumph since the late 1950s and went on to design other cars in the early years of British Leyland.
Testing work, by Leyland’s development engineers, was undertaken at locations in the UK and mainland Europe away from public gaze. To establish how the design stood up in extreme temperatures, vehicles were driven at the height of summer in southern Spain and in sub-zero winter conditions in northern Finland, north of the Arctic Circle.
A prototype also was subjected to endurance testing over the cobbled Belgian pavé surface at the Motor Industry Research Association (MIRA) track near Nuneaton, which subjects a vehicle to 100 times the stresses it will encounter on a normal road surface, so takes fewer miles and less time to highlight potential weaknesses.
As Leyland wanted to maintain as much secrecy as possible for as long as possible, the one crucial part missing from these trials was real-life operational experience of buses in the hands of ordinary drivers, perhaps running late or otherwise distracted in the course of a typical shift. Consequently, some design issues did not become apparent until the first production vehicles entered service.
