Over 90 per cent British content in Ailsa decker
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AILSA'S double-decker, announced today, is the only front-engined model available on the British market. Its Volvo engine is its single non-British component and the complete bus — Ailsa's underframe allied to Alexander bodywork — is well over 90 per cent UK-produced. The doubledeck project has involved some of the closest co-operation ever between vehicle manufacturer and coachbuilder, though there is no reason why other bodies may not be fitted later.
The double-decker began three years ago when the following parameters were set: reliability, simplicity, front-engine, serviceability and proven components. Various positions for the engine were considered: under the floor, under the stairs, behind the front axle and on one side. But the most logical place, in terms of
ease of boarding, cooling, sensible suspension, loading and maintenance had to be amidships, it was decided.
It was at this time that the importance of the TD70 engine was fully appreciated. Without its high power /size ratio, provision of adequate performance and an acceptable entrance would have proved impossible. The TD70 was also well proven, being used to power Volvo's successful F86 truck range at gross weights up to 32 tons.
The Ailsa underframe — it is not drivable without the body — is a jig-built, all-welded construction which uses standard rectangular steel members. As the photographs show, unbroken cross-frames are used to provide — when linked to the body's side members — the strength inherent in integral designs. The longitudinals are broken by these cross-members.
Simplicity has also dictated the use of high-mounted leaf springing and a simple cam-operated air brake system at front and rear. I understand that a more sophisticated pre-production model featuring refinements like air suspension, Lockheed power hydraulic brakes and possibly a "quiet" engine may be built soon.
Working from front to rear, the frame supports firstly the engine. A lot of effort has been devoted to developing the maximum airflow over the engine from the front-mounted radiator. In line with the need for serviceability, the Volvo unit can be removed easily. With the radiator unbolted it is simply slid out on the front two underframe members. Ailsa hopes to market a special trolley for facilitating engine removal.
Next component in the driveline is the 171in. fluid flywheel coupling. This is the size normally used with Volvo's TD100, 235 bhp engine so it is to be expected to give few problems with the "small" engine. It is mounted directly behind the engine, directly in the airstream to ensure adequate cooling.
Front axle is a standard Kirkstall model fitted with 11.00 by 25.5 tyres. Front overhang is 9ft 10-1-in. Having mounted its engine forward of the front axle Ailsa has tried to get all other major components as far back as possible. The Self Changing Gears G340 four-speed gearbox is mounted in the centre of the vehicle. It is controlled by a Hawker Siddeley unit on the left of the dashboard and has inhibitors to prevent gearchanges at unsuitable revolutions. It can be offered as a fully automatic unit if required but the first prototype has two, three and four hold positions. The vehicle always starts from rest in first gear. The gearbox has to be dropped out for maintenance. I understand that a manual gearbox version of the bus is not ruled out. But it would have weight, space and linkage problems and Ailsa is not very keen to build anything but fully automatics.
Drop-centre axle The only major component which is new and designed specifically for the Ailsa bus is the rear axle. This is of the drop-centre variety and designed by Norman Watson jointly with Hamworthy Axles who are producing it. It is the only major component to have needed pre-production evaluation and the axle has run without major snags in a 32-ton tractive unit for more than 34,000 miles. Many of the axle's parts are used in dump trucks.
Before designing the axle, engineers studied various drop-centre axles, including ones made by Bussing and Fiat. Three Bristol Lodekka axles were also purchased. The drop-centre axle was chosen because of its importance in a low-bridge doubledecker. Such a vehicle is likely to be built before full production starts but the market is relatively small. Continuing its serviceability theme, Ailsa has designed its axle so that it can be stripped without removal from the vehicle. This was one of the strongest objections operating engineers had to current buses.
Both the half-shaft and differential can be removed without the use of even a pit. The rear axle — which is thought to be the first in a British bus with hub reduction — has a final drive ratio of 5.45:1 giving the bus a top speed of 50 mph and gradeability of 1 in 6.25.
To further compensate for the weight of the front engine, the batteries, either lead acid or alkali, are mounted at the very rear together with the 45gal fuel tank. The electrics are supplied by a special harness developed in conjunction with Rists Cables. This is in sub assemblies form for easy replacement and has plugged connections.
The body looks little different from the outside than the standard Alexander unit. This is deliberate because spares for this well-tried unit are widely available. The only distinguishing feature from the front
is the Ailsa grille — similar to that used on Volvo trucks. In fact, this familiar appearance conceals some extensive development work "under the skin" which had taken place during the past 18 months. The Alexander body is usually fitted to substantial chassis, so Alexander has modified its body. Essentially, extra strength has been added by means of an additional longitudinal' truss panel below waist level which goes the full depth from waist to skirt, Further strengthening above the doors has been included to carry the additional load imposed by the front engine.
Obviously . the attachment of the body side-members to the outriggers of the underframe is crucial to the vehicle's strength. To ensure lasting protection from corrosion a zinc chromate treatment is applied to all joints where the steel underframe meets the aluminium body. Another major difference between the Ailsa's body and that used for other double-deck models is the change in wheelbase (to 16ft 3in.).
Inside the vehicle, of course, there are plenty of differences. The 78-seat, singledoor show model (a two-door model will follow shortly) has the staircase immediately behind the driving compartment. The stairs are forward ascending and maintain a continuous radius curve. Like much of the front end of the body, the staircase and luggage compartment underneath is a one-piece grp moulding.
Seating layout in the 6ft 0#in, lower deck is conventional though there are two pairs of rear facing seats over the back axles. The front end of the 5ft 84in. upper deck has the staircase on the right — coming out directly behind the front screen — and three single seats on the nearside to allow an adequate gangway.
Plastics cover The engine is housed in a plastics cover lined with 2in. of sound insulation material. This cover is about 30in wide at the bottom tapering to 114in. at the top. The cover is 36in. high. The cover forms a continuous barrier between driver and passengers. Obviously the critical factor of any front-engined passenger vehicle intended for one-man operation is passenger access. This is much better than 1 would have thought possible. The bus grant door (a three-piece front-folding device) opens to reveal two steps. The first step is 12-13in. high (depending upon loading) and the second 8+in. The first step of the stairs is 10+in. high and the narrowest part of the entrance gangway is about 21in. according to my measurements.
The distance from the outside edge of the front step to the base of the engine cover is about 38in. Though this is nearly 15in. less than the equivalent measurement for an Alexander body on an Atlantean of Fleetline, there seemed to be ample room. I did feel, however, that the mounting of certain types of fare collection apparatus might be a little difficult without impinging on the access space.
Entry to the driving compartment is via a 21in. wide door 32in. from the ground. There is one step provided. Once in the seat there is ample space, however.