How the Leyland National was developed
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A DETAILED description of the development of the Leyland National was provided by Mr Marcus Smith, an executive director of Leyland National Ltd and one of the men most closely concerned with the new vehicle. Mr Smith described the LN as "a bus aimed at meeting the future needs of a revitalized urban transport system".
Mr Smith began his paper by comparing the growth in the use of the car with the steady decline in bus passengers. Throughout the late Fifties and early Sixties there was urgent pressure, he said, to expand the performance of existing buses and to design as quickly as possible new vehicles to give the maximum benefit in earning capacity from within the permitted legal dimensions. However, the changes which evolved did not result in a more attractive service to the public and gave further impetus to use of the private car, said Mr Smith.
It was this situation together with major changes in the operating industry which formed the background to the evolution of the LN concept. Four vital elements affected the initial concept: to design a vehicle to meet the new objectives of public transport as a broad-based social service; to provide a vehicle whose economy of operation, reliability and performance would meet the demands to be put upon it; to design and produce a vehicle which would restore the profitability of manufacturing and form a springboard for the efficient support of the operating industry; and to produce a vehicle capable of competing in sophisticated international markets.
Mr Smith then examined a large number of points connected with the LN in some detail. This is a summary of what he said: Length: originally set at 10, 11 and 12m, what eventually evolved were two lengths, 10.3 and 11.3m, which were chosen because of trends towards greater seat comfort and marginal demand for a longer version.
Width: one of the easiest decisions to make, the 2.5m chosen is in fact unsuitable for use in north America and parts of Australia. Door width: UITP recommendation was 1200mm so LN played safe with 1205 mm. Step depth appeared to be as important as step height which was set at 10in, for interior steps and 18in. for exterior ones. Floor layout: flat floors were chosen throughout because of the dangers of sloping floors in wet weather conditions when heavy braking is applied.
Suspension: use of an air system gives constant control of step height and adds to lateral stability. Use of a leading-link principle in front suspension design eliminates "nose-dive" when braking.
Braking: by controlling load transference with the suspension, conventional airoperated drum brakes are adequate, though potentially preferable systems like multi-disc brakes and retarders were not available when the LN was first developed. Low-profile tyres on 22.5in. wheels allow increased air flow for brake cooling purposes.
Engine and transmission: though it was obvious early on that a high "off the kerb" performance was necessary, Mr Smith admitted that this was one of the most vexed questions LN had to face. During the research programme there were "strong indications" that operators had come to terms with the relationship between performance and fuel consumption. However, Mr Smith sounded an ominous note: "Currently we are going through a period of readjustment as the reality in terms of fuel costs of high power and automatic transmission is experienced in service." The Leyland 500 series engine was chosen and, though initially 150, 180 and 200 hp versions were considered, only the top two versions were adopted. These ratings gave "superb" performance, said Mr Smith.
Noise and air pollution: quiet engines with high power outputs will take some time to evolve but are feasible. Some compromise with performance may be required and ultimately higher costs will be involved.
Integral structure: choice of this method of construction was ideal for incorporating safety features for both driver and passengers, and the heating and ventilation system was designed as one with the vehicle structure.
US standards
Passenger safety: American standards for school buses were used as a basis and seating design was closely examined. Safety when boarding and alighting was also studied.
Driver safety: Swedish legislation was used to set the standard when the driver's environment was being planned.
Passenger environment: improvements in this area have been effected by attention to lighting and heating and ventilation. These latter systems use an air-based design rather than one involving water. Air conditioning is already practicable for export models.
Volume production: four common areas were designed which would be used on any length of vehicle and these together with a wide choice of materials allowed maximum economy in component cost and assembly. Vehicle life: though this may vary with changes in the economics of the operating industry this is set at 15 years at present.
Mr Smith went on to detail the varying stages of the main research and development programmes. He also gave some indications of the costs involved. A total capital expenditure of £7im was needed to get into production. A further £1.6m was used to cover the cost of the design, research and development programme.
Mr Smith concluded by saying that investment on the scale used in the LN project was necessary for the main services needed by the nation. "We look forward to the results of the LN project supporting parallel investment •and activity over the coming years in the bus operating industry," he said.