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POWEI THE BOOT

Latest Rutland Rear-engined Passenger Chassis has Unconventional Transmission Layout and Meadows Oil Engine : Improved Passenger Comfort and Engine Accessibility

OF the several advantages resulting from the rear engine position of the Rutland Clipper passenger chassis, the mostimportant is the high degree of engine accessibility afforded. The Clipper is thus endowed with all the virtues of conventional underfloor-engined designs, together with easier engine servicing for the operator without a pit, and greater passenger comfort by reason of the reduced engine noise.

The use of standard components in a variety of chassis has long been an established principle of Motor Traction, Ltd., who build the Rutland vehicles. This standardization policy accounts for the somewhat unconventional transmission layout of this rear-engined chassis, although the legal overhang limits prevalent in Great Britain must also be considered. Because of these limits it is rot possible to take the drive into the back-of the axle in a rear-engined design unless the engine is placed transversely in the chassis frame and angle drives are embodied in the transmission. In overseas areas where a rear overhang of up to 60 per cent, of the wheelbase is allowed, larger engines could be used, mounted longitudinally and, ;f desired, driving a pusher axle.

A transverse engine position does not offer the mine degree of accessibility as is obtainable with a longitudinally mounted unit, particularly with regard to ancillary components, so this layout was ruled out it the initial design period. It was decided, therefore, to mount the engine in line with the chassis and to drive the axle from the front, the means of doing this being to use a transfer box towards the front of the chassis.

By doing this, it has been possible to use a standard rear axle running a8 in the normal direction, whilst the engine and gearbox are also standard and interchangeable with those in a forward-engined chassis.

The location of the transfer box is such that it lies in a position where the tail of the gearbox would lie if an underfloor-engined .position were used. This has the effect of making even the propeller shaft a standard component, as the Clipper is available with an underfloor engine as a standard alternative.

It will be seen that the same chassis frame, axle, propeller shaft, and only a slightly modified engine and gearbox can be used for the underfloorengined version. Evidence of this intention to employ an horizontal engine midway in the chassis frame is provided by the relatively high chassis-frame height which is necessary with an underfloor-engined design and gives excellent ground clearance for a rear-engined chassis. This is of particular importance in the export field.

The Clipper tested, which is a development of the heavier rearengined export chassis, is aimed at the one-bus operator who, much as he. may like underfloor-engined designs, is handicapped for engine maintenance by the lack of a pit or hoist. The engine and gearbox unit, together with the radiator, are carried on a detachable sub-frame and, as has already been proved, it is possible to effect an engine change in 31 hours, using three men and a 6-ton hydraulic jack.

Several alternative power units are offered in the Clipper chassis, but the test vehicle was powered by a Meadows 4DC 330 oil engine developing 85 b.h.p. at 2,200 /.lm. The engine, which has a 14-in. diameter clutch, is mounted as a unil with a David Brown 45S four-speed synchromesh gearbox at three points Metacone mountings are used anc those in twin form at the rear of tlu engine are interesting in that the unii hangs from the chassis brackets anc safety bolts are fitted to avoid an chance of the mountings fracturini and the engine dropping to the ground. • The drive to the transfer box is through a two-piece propeller shaft, and the box, which contains single helical spur gears, is rubber mounted in the frame, using the same mounting points as would be employed for the rear of the power unit in the underfloor-engined chassis application.

In other respects the chassis specin cation is conventional. The frame is a straightforward assembly employ ing six cross-members. Girl ing hydraulic brakes with a Clayton Dewandre vacuum servo are employed and the test vehicle had an Eaton 16500 two-speed axle. Hydraulic clutch operationjs used but the accelerator linkage is through rods.

A Whitson 41-seat body of composite construction had been mounted on the test chassis and little impression of the engine position was ,conveyed by the seating layout. Indeed, the only effect noticeable inside the body is that the rear seat is 8 in. forward of the rear panel, the kick-board of this seat is flush with the forward edge of the cushion and the floor is slightly ramped upwards towards the rear, giving improved visibility to rear passengers.

Occupants of the back seat will be aware of the ventilation shaft running down the rear of the bus from.the roof: this acts as a heat and fume extractor from the engine compartment and does not supply fresh air to either the body or the engine.

Some of the seats had been removed for my test, as the payload consisted of 12 4-cwt. concrete blocks which were disposed equally down each side of the body. Allowing 1-1 cwt. per person, this test load was equivalent to just over 38 passengers, the timber battens which located the blocks compensating for the absent seats. The weight distribution was good, the tyre loadings being almost equal. The front axle loading was considerably lighter than normally experienced with equivalent underfloor-engined designs. '

The Vehicle, which had covered only 800 miles prior to my test, was taken to Titsey Hill for the first test and during the journey out to the hill I was able to observe the running characteristics of the Clipper from the passengers' angle.

As might be expected, the engine B9 noise level was extremely low and I was surprised at the quietness of the power unit even when sitting in the back seat.. Passengers in this position will become aware of the closeness of the power unit only when it is idling, very slight noise and vibration being apparent under this condition. I did not pay undue attention to this, however, as the engine compartment was in no way insulated.

I was disappointed in the amount of noise conveyed from the transfer box, but was given to understand that experimental bearings had been fitted temporarily and that the original bearings and a different grade of oil

Bill

produced much more silent running. The ride over varying types of surfaces was above criticism. Telescopic dampers at both axles were contributory to this, but it was apparent that a high degree of stability was imparted by the engine position, particularly during fast cornering.

Titsey Hill, which is almost a mile' long, with a general gradient of 1 in 6 and a steepest gradient of 1 in 5, was approached from the top, therefore a fade test was conducted first. For this, the Clipper was driven down the hill in neutral, with the foot brake applied to restrict the speed to 20 m.p.h. The descent was made in 3 minutes 10 seconds, and by

the time the coach had reached the lower slopes, heavy pedal pressure was required to keep the speed down.

A crash stop from 20 m.p.h. produced a Tapley meter reading of 32 per cent. which, when compared with the average Tapley meter reading of 67 per cent. obtained later in the day, shows that a certain amount of fade was present. Profuse smoking at the front drums suggested that these facings had faded whilst thz relatively cool rear brakeshad lost little efficiency. The test was severe, however, and such conditions are hardly likely to be repeated in normal service.

A climb of the hill was then made in an ambient temperature of 68° F. Before making this climb, the Clipper was taken for a brief run to bring the coolant temperature up to normal, and this normal temperature was recorded as 167° F. A five-minute climb to the summit produced a temperature rise of 6° F. in the coolant whilst the engine oil temperature rose by 11° F. to 168° F., the pressure dropping by only 2 p.s.i.

Whilst the climb could have been made in second gear, low axle ratio, the engine appeared to pull better in low gear, high axle ratio, and this combination was used for the steeper sections of the hill. The test was sufficient to prove, however, that the engine cooling is more than adequate for hilly operation in this country and would be sufficient for operation in most hot climates.

Returning to the 1-in-5 section, of the hill, a stop-start test was made, the hand brake holding the vehicle easily on this slope, and a satisfactory start was made in first gear with high ratio in the axle engaged. A certain amount of smoke was present in the exhaust during this re-start and slight hazing was observed during the non-stop climb also.

Up Succumbs Hill

In view of the good gradient performance of the Clipper, I elected (against the advice of the Rutland • representative) to take the chassis out to Succombs Hill, where there are two gradients of 1 in 4 severity, one of which occurs on a sharp bend. On both these gradients very successful smooth stop-start tests were carried out using first gear, low axle ratio and a three-quarter throttle. Once again, the Multi-pull hand brake showed itself capable of holding the vehicle on this gradient, although I prefer to see a straightpull hand brake on a passenger vehicle.

Fuel-consumption tests were conducted over a 20.5-mile out-andreturn route between .Caterham and Hobbs Barracks, East Grinstead. This route is undulating in nature and starts with a 31-minute climb which demands the use of third gear, high ratio. Despite such climbs and several traffic hold-ups, an average speed of 29.11 m.p.h. was maintained, and the use of just over 10+ pints of ,fuel indicated a consumption rate of 15.9 mpg: During this test the coolant temperature remained at between 160° F. and 165° F., the ambient temperature having dropped slightly since the hill-climb was made.

Acceleration tests produced satisfactory figures, in view of the low power-to-weight ratio. The best figures for the 0-30 m.p.h. tests were achieved by starting off in second gear with low axle ratio engaged, changing to third gear and then changing to high ratio, and the final change being a split one to top gear low ratio.

It was impossible to make the direct-drive tests with the higher axle ratio engaged because of transmission roughness, but the vehicle pulled away from below 10 m.p.h. in low axle ratio with only a slight vibration period between 9 and 13 m.p.h.

High Pedal Pressure

The brake tests were carried out along a level piece of concreted road adjacent to the Motor Traction factory in New Addington. High pedal pressure was required to produce satisfactory braking distances, but a pedal ratio which would give this effect had been deliberately chosen so as to avoid the chance of causing injuries to passengers during emergency conditions. Changing this ratio was relatively simple, alternative clevis holes being provided in the relay lever, and some tests carried out with a more advantageous ratio produced average Tapley meter readings of 85 per cent. without wheel-locking or deviation from a straight course.

This figure was decidedly unsuitable for passenger work, so the main tests were carried out with the harder pedal. The braking was quite smooth and progressive in the circumstances, with no wheel-locking, and there was very little evidence of time lag in the system. From both speeds, the average Tapley meter reading was 67 per cent. The Clipper is a pleasant vehicle to drive, although it is a little strange not to be able to hear the engine note. Several times this led me to suppose that the engine was not pulling well—an impression that was belied by glancing at the speedometer, which showed the road speed to be far higher than suspected.

A certain amount of work could be profitably done in connection with the pedal controls and the gear change: all the pedals are heavy in operation, whilst the gear change is inclined to be sloppy, although this is a feature often found on rearengined vehicles and one which is difficult to overcome without recourse to the use of electric, pneumaticor hydraulic operation.

Michelin X Tyres

The good road holding promotes confidence on corners, but the front tyres felt soft, and I put this down to the Michelin X-type tyres which were fitted. These have very soft walls and may tend to produce vague steering, but this characteristic 'is compensated by the increased life these tyres are claimed to give in service.

Access to the engine could hardly be bettered in any design. The engine compartment, which is the full width of the body, allows plenty of room on each side of the power unit. So much so, that it is intended to move the spare wheel and fuel tank into this space. This would then give additional luggage lockers below the floor, making the total capacity as great, if not greater, than that obtainable with a conventional rear boot.