Title: National and universal
Pages: 46 - 49
Author: Alan Townsin
Text: National and universal
Alan Townsin describes the Leyland National, Britain's first mass-produced public transport bus
At first glance the new Leyland National looks little different to most other modern single-decker buses. So what makes it so special? The essential factor is the manufacturing philosophy on which it is based. For, surprising though it may seem, the "pressed-steel revolution", which radically altered car production nearly 40 years ago, has not hitherto made any impact on bus manufacture in Britain and relatively little in the world.
There are many reasons for this. Bus manufacture is a small industry by comparison with car or even goods vehicle manufacture. The total annual demand for single-deckers, excluding coaches and minibuses, is only about 2000 vehicles per year in Britain. Seven British chassis makers share most of this market; of these, four are part of the British Leyland empire, two are American-owned (though both of these, Bedford and Ford, are more concerned with coaches) and one, Seddon, is independent. There are about ten major models and numerous minor variations of wheelbase, plus engine and transmission options. Single-deck bus bodywork comes from at least seven major factories, most of which use several chassis types.
Up to now, it has been economically possible to retain a largely "bespoke" character in the bus building business. With vehicle orders calling for perhaps 30 units at a time it is practicable to include many variations of design. But the increasing cost of labour is one factor making a change of method more attractive. Another is the formation of the State-owned National Bus Company as successor to the two largest bus-operating groups in Britain, the Tilling Group (itself State-owned since 1948) and the British Electric Traction bus interests.
Both Tilling and BET had their own standardisation schemes. But the NBC, with a 22 000 vehicle fleet - though less than half this total consists of single-deck buses - is the largest in the world. So new possibilities for standardisation have arisen. At about the same time, the formation of the British Leyland Motor Corporation produced a combine with skills in varied methods of production. So the concept of a specialised bus factory, jointly owned by British Leyland and the NBC on a 50-50 basis, was evolved. The Leyland National Co Ltd's premises at Lillyhall, near Workington, are brand new and specifically designed for the manufacture of a bus built in much the same way as a modern car. It is intended that the factory will have a capacity of up to 2000 buses per year, about equal to the entire British demand. NBC can be expected to take perhaps half of this. Their new-vehicle programme for 1971 calls for 1142 single-deck buses, including types with which the Leyland National hardly competes. The first NBC order for Leyland National is 500 vehicles, presumably for delivery in 1972.
Production is due to begin late in 1971, and although starting a new factory building with a new vehicle is a prodigious task, Leyland's engineers seem confident that all will be ready in time. In the early stages, production will be aimed at the home market. Initial reactions at this autumn's Earls Court Commercial Vehicle Show were encouraging, with firm orders from both a municipal operator and a dealer acting on behalf of independent concerns. Leyland will also have their eyes on the State-owned Scottish Bus Group, operating the largest single-deck bus fleet in Britain outside the NBC. But the key to the long term future of the Leyland National lies in its concept as a "universal" bus, saleable without major alteration in almost any country with a market for the big single-decker.
With this background, Leyland's engineers could and did carry out an immense programme of research and development
The Leyland National prototype, above, will be Britain's first integrally built series-produced bus. Seating is not yet finalised but is likely to be similar to the prototype's, left
Top: section shows engineering. Above: hoop frames - pressed steel side and roof supports - are linked to floor underframing. Roof panel is one sheet of corrugated aluminium. Right: seating layouts for the 103m version. Far right, air distribution is from roof-mounted heater. Opposite: lights in dash illuminate to signal operational. Driving controls are intended for easy touch use by men or women.
on the new bus. Initial design work began three years ago, before the NBC even existed, and although the basic concept of the vehicle and its major mechanical and structural features are now settled, much work continues, especially on internal design. No figures have been published but it is certainly a multi-million pound project. On the one hand, a major effort has been made not only to meet all known national legal requirements in every major bus-operating country but also to force the trend of safety legislation spreading from countries like the United States and Sweden over the next decade. On the other hand, British Leyland's production expertise - and notably the skills in production of pressed steel bodywork at the Pressed Steel plant in Cowley - enable new methods of bus manufacture to be used.
Integral construction of buses is far from new in itself. It has been common practice in many countries since shortly after (in one or two cases before) the second world war. Some of London's trolleybuses built in 1939 were integral and Leyland were themselves concerned in the production of a successful mainly-export integral bus, the Leyland-MCW Olympia, from 1950. But the Leyland National makes use of the strength obtained by pressing components made from relatively thin-gauge material, and this is still rare on bus work. Part of the reason is the complexity of bus structure - on the National, computers have been used to analyse components, sub-assemblies and their relationship to the vehicle as a whole.
Hitherto, British operators have shown no enthusiasm for integral construction for the good reason that separate body and chassis could give at least equally satisfactory service, often at lower cost, and without any noticeable effect on weight. In recent years, however, rear engined single-deckers (chosen largely to give low floor levels near the entrance) have proved a difficult proposition, largely because of the considerable engine weight overhang behind the rear axle.
All these factors have led to the concept of the Leyland National. It is to be built in two lengths, 10.3m and 11.3m, the latter seeming likely to be the more popular as buses of around 11m have been found the most economic and practical in many countries. The exact length chosen has been selected as the best in relation to seating layout and space required to give a convenient and safe driving compartment. It is significant that the Ministry of Transport bus grant length, precisely 11m, has been rejected as being less satisfactory. The same applies to the other basic dimensions. The 11.3m version will carry up to 78 passengers as a standee bus.
The form of construction is based largely on what Leyland engineers call hoop frames. The floor underframing is linked to pressed steel members forming the pillars and roof sticks, producing a series of hoop frames linked together with longitudinal members and cruciform pressed brackets at waist and roof levels. The roof framing contributes greatly to the vehicle's beam strength and is deep enough to provide the main heating and ventilating duct between the outer roof panel (remarkable in being formed in one sheet of corrugated aluminium) and the inner ceiling panels.
This in turn helps to allow a low floor level, since the underframe does not have to provide much of the vehicle's beam strength. A stepped floor has been chosen, as on London Transport's Red Arrow buses, to provide room for the engine under the rear floor. But unlike most such buses, both front and rear floors are horizontal except for the wheelarches (themselves minimised in size by analysis of road wheel movement using a computer). A standardised step height of approximately 10in (254mm) is used for all internal steps to make movements into, through and out of the bus simpler.
The main floor height is 2ft 1in (634mm), 3in lower than the bus grant figure for this type of vehicle. Part of the secret of the low build of the bus lies in the use of low-profile tyres, specially developed for the National by Goodyear. These are claimed to be 4in less in diameter than conventional tyres. Yet the wheels are of the standard 20in diameter type almost universal on heavy commercial vehicles and providing important air space round the brakes.
All versions of the Leyland National are to have the same basic engine, the Leyland 510 six-cylinder 8.2 litre in-line unit in its horizontal form. This is a turbo-charged unit and will be available in versions developing 150, 180 or 200bhp - the 150bhp rating being about as high as British operators require for an 11m single-decker bus. It is a "slim" engine, which contributes to the ability to provide a level floor at the rear of the bus.
Transmission, as on most modern British heavy duty buses, is by fluid coupling and epicyclic gear box which can be arranged to give fully or semi-automatic control. The rear axle is an ingenious design. Normally on rear, underfloor engined buses, the propeller shaft must be exceptionally short to keep the overhang of the engine assembly behind the axle to the minimum. This introduces angularity problems if the suspension is to be reasonably supple. On the National, the propeller shaft passes through the main axle casing to couple to an input flange on a gear case mounted on the front of the axle.
The suspension, by air bellows, is indeed supple by bus standards. The softness is comparable to that of modern cars. Steering is power-assisted; an unusual feature on a vehicle of this size is the use of the rack-and-pinion steering system not hitherto seen above the private car range. This is mounted on the front axle beam, making the provision of left-hand steering particularly simple as the connection between it and the steering column is by universally-jointed shaft. Particular emphasis has been laid on the comfort and convenience of the driving compartment. The steering wheel is of 18in diameter, which may seem large by car standards but compares with the 22in wheel used on most other Leyland bus models. All other controls are designed for easy touch use.
The entire water system is confined to the rear of the bus. As well as the conventional engine cooling radiator near the power unit, a heat exchanger unit to provide saloon heating is mounted at roof level. The unit supplies heating and demisting via the roof duct to the vehicle as a whole. Slots direct demisting air over the side windows as well as the windscreen. In addition, heated air is directed downwards at the entrance and exit doorways to minimise loss of heat when the doors are open at stops. The system is claimed to be capable of maintaining a comfortable temperature inside the bus when the outside temperature is down to 23ºF. A second heater unit can be provided for colder climates and air-conditioning is offered as a further option.
It was somewhat ironic that the Leyland National, as exhibited at Earls Court, revealed so little of the immense design effort put into it. The interior was by no means finalised and thus much of the visual impact of the exhibit was concentrated on items subject to further change. The external appearance has been cleaned up by Michelotti but the changes made are little more than superficial - the vehicle remains a functional design in which appearance is mainly determined by practical consideration.