The Fuel-saving Fla rie
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By John F. Moon
A.IVI .1.R.T.E.
SINCE the current basic version of the Daimler Fleetline rear-engined double-decker bus chassis, with Gardner 6LX diesel engine, went into production in 1961, orders for some 1,500 of this model have been placed, and about 1,000 have been delivered to various municipalities and companies. This in itself speaks volumes for the success of this Daimler design, offering as it does the fuel economy for which the 6LX is renowned, whilst at the same time the chassis layout can accommodate 78-seat bodies with an overall height of 13 ft. S in. and flat floors in both saloons, with a step-free platform.
A somewhat hurried test of a highb ridge-bodied Fleetline running at a little more than 13-75 tons gross weight indicated good overall economy in this condition, and although time did not permit half-load and unladen fuel tests to be made, my own experience of this Gardner engine in vehicles of this type suggests that the half-load figures should be about 2 m.p.g. better than the full-load figures reported in the accompanying data panel, whilst the nonstop unladen result should have been about 16 m.p.g. Thus an overall figure in normal service taken over a considerable mileage would be in the region of I2 m.p.g. unless traffic density was particularly high.
Passengers should not be slow to appreciate Fleetline travel. For one thing, there is the obvious advantage of a rear-engined bus in that the level of engine noise is very much lower than in a forward-engined vehicle: in the upper saloon passengers would hardly be aware of the engine if there was the normal amount of conversation going on, whilst even downstairs the engine note is quite subdued, although in the case of the vehicle tested a certain amount of booming could be heard and felt in the lower saloon. This might, however, have been because one of the rearseat cushions had been removed to give access to the changeover taps in the fuel-test-tank circuit.
The Fleetline rides very well over fair and indifferent road surfaces, and particularly good is the very small amount of roll noticeable, even when cornering quite quickly on an adverse camber. As is usual with buses of this layout with a comparatively short wheelbase and a front overhang of more than 7 ft., some pitching can be felt when sitting towards the front of the vehicle in either saloon, but this is not particularly uncomfortable, and is not noticeable when sitting neater the rear of the vehicle. " Some bus drivers seem to be able to make jerky gear changes with virtually any type of transmission, but I find it hard to believe that even the most ham-fisted of drivers could change roughly with the Dairnatic box which is standard in the Fleetline. The C.A.V. electro-pneumatic change control is of the type normally used with semi-automatic transmissions of this nature, and in the case of the bus
tested the normal small five-gate switch control mounted on the left of the steering column had a sixth position which formed an interlock with the electrically operated jackknife doors at the front platform, this ensuring that, when all the various door switches were set correctly, a gear could not be engaged without the doors closing, and vice versa. whilst at the same time, the engine could not be started with the doors open. There are, however, ways of overriding the safety circuits.
Basic Specification The Daimler Pleetline design should by now be familiar to most operators of double-deck buses, so a brief look at its basic specification should suffice for the purposes of this report. The chassis-frame assembly is quite straightforward when compared with some low-height doubledecker models, and the standard wheelbase is 16 ft 3 in. Leftor right-hand drive can be accommodated quite easily, and the engine-and-gearbox unit is carried across the rear of the frame in a detachable sub-frame. Although most Fleetlines so far supplied have had the standard 6LX engine, which can be set for a maximum output of 150 b.h.p., but is often specified in derated form (as in the case of the vehicle tested), the 6LW .8.4-litre 112-b.h.p. diesel has been asked for in one or two cases, although personally I do not feel this unit would be much use in a full-length Fleetline running at nearly 14 tons gross, even though it might be satisfactory in special shorter models.
The standard type of hydraulic coupling is a 19-in.diameter open-circuit type, but in the interests of additional fuel economy an 18-in, coupling incorporating an automatic lock-up clutch can be supplied. The clutch action is dependent upon the speed of the output shaft, and starts to come into play at as low a speed as 600 shaft r.p.m., which does mean that there is slight coupling drag when the vehicle is stationary with a gear engaged, though this is by far and away outweighed by the fuel-economy advantages of direct drive at normal road speeds, whilst at the same time it in no way interferes with the smoothness of gear changing. The standard Diamatic gearbox has four forward speeds, and can be supplied with a fully automatic gearchange system if required. Integral with the box is the spiralbevel, right-hand-drive gearing, this lying between the box and the hydraulic coupling and reducing the height of the output flange in order to give the best possible propeller shaft angle. A dropped-centre, double-reduction rear axle is standard, the primary reduction gearing being spiral bevel, whilst the secondary reductions are straight spur gears carried as close as possible to the underslung springs: the use of this axle makes it possible to provide a completely stepless and central lower-saloon gangway.
All the springs are 4-in, wide, the dual-rate front springs having an effective length of 50 in., whilst the constant-rate rear springs are 62 in. long. Chromium-plated 1-5-in.diameter spring pins are employed, and the front suspension is controlled by Armstrong DAS.12 lever-type dampers, Armstrong telescopics being employed at the rear. Daimler worm-and-nut steering is employed, and a Hydrosteer hydraulic servo can be supplied: if the vehicle I tested is anything to go by, I feel it should be standard!
Daimler strut-type brakes incorporating automatic c8 adjusters are employed at both axles, the rear brakes being no less than 8 in. wide, and the brake units are actuated through a Bendix-Westinghouse dual-circuit air-pressure system, controlled by a dual E valve. The brake linings are 0-625-in, thick in all cases, and the total frictional area is 733 sq. in., the rear-brake area alone being 460 sq. in. Because of its weight distribution, the Fleetline has the same size of wheel and tyre at both axles, the standard tyre equipment being 10.00-20 (14-ply), although the vehicle tested had Michelin "X " 10.00-20s. An alternator is a standard item in the electrical system, and the fuel tank has a capacity of 35 gal.
In addition to the special items already mentioned, including the reduced engine output, the bus I tested was equipped with Clayton R.P. automatic lubrication and a Smiths magnetic-particle-drive fan, another potential power and fuel saver, besides helping to ensure that the engine operates at near its optimum temperature.
Walter Alexander (Coachbuilders) Ltd., Falkirk, built the 78-seat all-metal body of the bus tested, this having an unladen overall height of 14 ft. 4in. and being virtually continued on page 59
identical in design to the 50 Fleetlines supplied to Midland Red, the main difference being the addition of one seat over the nearside-front wheel arch, giving a total lowersaloon seating capacity of 34. In kerb condition, with full fuel tank, the test Fleetline weighed 8 tons 15.75 cwt., the rear-axle loading in this condition being 5 tons 1975. cwt. With securely battened iron weights aboard, plus myself and two Daimler people, the bus grossed 13 tons 16 cwt., of which 5 tons 0.75 cwt. were being carried by the front wheels. The bare chassis weight depends, of course, on the exact specification, but is approximately 5 tons 14 cwt., therefore the bodyweight in the case of this particular vehicle would have been about 31ons.
In a general sense, good retardation figures resulted from the brake tests, and if anything the Fleetline is above average for buses of this weight. However, under "emergency" conditions, when the brake pedal is depressed extremely quickly, there is a noticeable lag in the airpressure system (although this is not felt when braking normally), whilst excessive rear-wheel locking tended to increase the overall stopping distances relative to the maxi mum decelerations recorded by Tapley meter. When related to stopping distance, the Fleetline's retardations from the two test speeds were approximately 50 per cent, but the maximums were approximately 70 per cent, which is on the high side for passenger safety.
Fade no Problem
However, for normal circumstances the brakes are very good, and fade should not be a problem either, for the 26th stop made at the end of the six-stops-per-mile fuelconsumption test showed that the previous 25 stops (which had been made at about 0.2g average) carried out over a distance of 4.23 miles in about 20 min. had reduced the maximum efficiency by only 10 per cent. No• wheel locking occurred on this " fade " stop, suggesting that the rearbrake effect had been reduced by just the right amount.
It was a simple matter to obtain good acceleration figures between a standstill and 40 m.P.h., whilst the direct-drive acceleration rate was good also, the engine and transmission behaving perfectly smoothly at as low a speed as 8 m.p.h. while in this gear. The acceleration performances show that the Fleetline should not present too much obstruction to private-car traffic, which is an important point under present-day conditions in most towns. A higher engine governed speed would undoubtedly result in slightly better acceleration, of course, and in this respect it is perhaps unfortunate that the maximum road speed in third gear is only 26 m.p.h., meaning that acceleration above this speed is solely dependent upon top-gear performance. The speeds in bottom and second gears, incidentally, were recorded as 10 and 17 m.p.h.
As already observed, quite good fuel economy was shown during the three fuel tests made over a circuit of the Coventry by-pass. When making the non-stop run a maximum of about 32 m.p.h. was observed, as would occur in urban areas with a 30 m.p.h. speed limit, and during the runs involving stops, each stop was of 15 sec. duration, with the engine left idling (usually with the gear engaged). The average speeds quoted for the two stopping runs are based on the total time that the wheels were turning.
Gradient-restart tests were made in Cash's Lane, Coventry, the slope of which is not far short of 1 in 7. Tests were made both facing up and down the slope, and in each case the handbrake was just powerful enough to hold the vehicle without having to apply too much effort to the lever. I must confess to not having been entirely satisfied with the handbrake performance in general, however, as the best figure that I could get with it during the normal brake tests was 23 per cent, although admittedly the rear brake drums would still have been quite warm from the footbrake tests carried out immediately before. Quite smooth, although slow, restarts were made in bottom and reverse gears on the steep section of Cash's Lane, and, whilst these were satisfactory, I think they were near to the Fleetline's maximum gradient performance when fully laden.
As already remarked, few passengers would have reasonable cause for complaint in the case of the particular Fleetline that I tested, the accommodation being entirely satisfactory and being laid out to make the maximum use of the space available with the minimum of discomfort and the maximum frcedom of movement. There were a few creaks in the body, and l could not help wondering how effective the rear-installed body-heating system would be in really cold-weather, but on the credit side the hotweather ventilation is good, despite its simplicity, and the laden front-entrance height of only 1 ft. 1 in. above the road surface should make boarding the bus easy, even for crippled persons.
Steering Heavy From the driver's angle my main cause of complaint concerned the steering. This is far heavier than on any other bus of this weight that I have driven, making the Fleetline quite a handful to handle in narrow and congested streets, especially at low speeds. At normal speeds the steering has a dead feeling about it, whilst when reversing it is possible to turn the steering wheel only with the greatest of difficulty. Admittedly, the test bus was carrying the equivalent of 78 passengers, a conductor and a driver, and it would be rare for reversing to be necessary while carrying a full load during normal service. Nevertheless, for the steering to be so poor when fully laden suggests to me that there must be something basically wrong with it, and quite aside from the safety aspect this might even lead to excessive front-tyre wear.
In addition to the steering being heavy, the effort required to hold the accelerator pedal down against the Gardner governor seemed to me to be excessive also, despite the use of a Lockheed hydraulic linkage between the pedal and the engine. Gear changing presented no problems at all, of course, although a point in this connection was that the test vehicle was prone to top-gear slipping when making full-power changes. The driving position itself was perfectly satisfactory, whilst the overall range of vision was good. Unfortunately it appeared that the vehicle I tested had " lost its original nearside rear-view mirror during the course of earlier demonstration work, and the decentsized mirror which must have been there originally if the existing offside mirror was anything to go by had been replaced by a very small mirror ..which gave virtually no vision down the nearside of the bus.