POTTED PERFORMANCE

30th April 1954, Page 93

30th April 1954

Page 93

Page 95

Page 96

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Page 93, 30th April 1954 — POTTED PERFORMANCE

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THERE have been many changes in vehicle component design and oil engines have been put into lighter classes of chassis since April, 1950, when a summary of performance was presented graphically in The Commercial Motor. It is, therefore, opportune to collate the results of tests made since that date to afford a more up-to-date picture of vehicles now available for the home and overseas markets.

Economic production required that similar units to those used in the sturdy and powerful machines built to satisfy overseas conditions in the immediate post-war years should be employed in domestic models. In the result the home operator often lolled that the larger engines and leavier components affected fuel economy, this being noticed particuarly in passenger vehicles and the naximum-load four-wheelers.

A light class of passenger chassis las now been developed, and the '

cruiser" range of 7-8-ton goods hassis extended in the second phase if post-war design, and small threerid four-cylindered oil engines are leing installed in vehicles of 12-cwt.-ton payload capacity. There is ealthy competition between makers f small compression-ignition units, ,hich is noticed in the wider range of

oil engines now available and the tendency to reduce prices.

Fuel-injection equipment is one of the most expensive components in an oil engine, but simpler and less costly units are being developed. Ultimately they should cheapen the smaller engines, thereby adding to their popularity in vans and light lorries covering relatively low annual mileages.

In four years, over 120 road tests have been conducted by The Commercial Motor on British, American, German and Swedish vehicles, both in this country and abroad. There have also been trials of local conversions of petrol-engined chassis, in which have been installed a comparable-size oil engine.

Only British chassis are included in the accompanying graphs. The ranges tested are representative of all types, including battery-electric localdelivery vehicles and all-wheel-drive cross-country chassis, in addition to vans, lorries, articulated combinations and the new lightweight buses and coaches.

The road trials are thorough and

which might affect performance, particularly braking.

In Chart 1, the Trojan 1-ton van shows unusual fuel economy, giving about 39 m.p.g. on long-distance runs and 274 m.p.g. in local service when carrying a full payload. The Perkins three-cylindered oil engine is an optional power unit in the Trojan.

Thawing snow was responsible for extensive wheel-locking during the tests of the Austin 15-cwt. pick-up and Morris Cowley 10-cwt. van. The effect of poor road conditions during braking tests can be assessed by cornraring the 56-ft. stopping distance recorded with the Morris Cowley van with the 33 ft. returned by the pickup version on a good dry road. In the 3-6-ton class the Scammell and Jen Tug articulated units, which are built for local haulage, are included. The Jen Tug Mk. 11 tractor, using the Austin 40 b.h.p. petrol engine, has a maximum speed of below 30 m.p.h., therefore its performance is not shown in the acceleration or braking charts. During the trials it reached 20 m.p.h. from rest in 22.8 sec. and 25 m.p.h. in 34 sec. From 20 m.p.h. it was stopped

in 341 ft., which corresponds to 0.39g.

The increase in the number of 3-tonners with oil engines is noteworthy. Models tested include the Dennis, Dodge, Guy, Seddon and Thornycroft. Apart from the Thornycroft, which has its own make of engine, they have Perkins four-cylindered engines, that in the Dennis Stork being mounted horizontally amidships. The Bedford 5-ton oil-engined truck was one of the first to be tried under commercial service conditions and the fuel-consumption rate shown was obtained in fast driving between Luton and Cornwall. When driving for 300 miles at a stretch along the difficult roads of Britain, and in countries noted for hills and traffic, there can be virtually no part-throttle work, which was the case when the Bedford was taken to the West Country and back.

The Guy Otter is shown with two sets of results, tests being made with Perkins P6 and Gardner 4LK oil engines. Fuel-consumption trials with the Guy Otter were staged over a 35mile out-and-return course which combined a fair measure of hills.

The Thornycroft 3-4-ton chassis and the Thames 5-tonner were tried in bad weather, and the braking performance of the Austin 5-tonner was measured after it had been through dust-andwater inoculation on the Motor Industry Research Association's proving ground at Nuneaton.

Apart from the Bedford and Commer 7-tonners, all other 6-8-ton four-wheeled chassis tested had oil engines. When • the Bedford, with a Perkins 108 b.h.p. engine, was first made available, it was tried out over a 580-mile course from Luton to Newcastle, across to Carlisle and back to Luton, all within 201 hours, which included stops for refuelling, refreshment and changing drivers. Although the run was "hard" on fuel, the trial proved that the Bedford was suitable for continuous trunk haulage.

The Foden light 8-tonner uses the four-cylindered blown two-stroke oil engine which, being exceptionally small, occupies relatively little space in the three-seat cab. The Foden 2.72-litre oil engine provides about average acceleration, as revealed when reaching 30 m.p.h, from rest in 47 sec., but it v4 parison. Being produced for operation only on hard-top roads in Britain it has a single driving axle, which, with reduced transmission efficiency losses, shows to advantage in fuel consumption. The Albion, E.R.F., Foden, Leyland and Sentinel tested all had double-drive bogies.

The Leyland was particularly penalized in the fuel trials, because it had small-section tyres and a low-ratio final ‘'rive. which were specified by the operator.

A six-eylindered two-stroke oil engine of 4:09-litre capacity was used in the Foden, which, as tested, had a 12-speed main and auxiliary gear bo x. the auxiliary unit having pre-selective ratios, Articulated vehicles with smallengined tractors show up well in economy, which is to be st.vm in the E.R.F. and Guy units, both of which had a gross weight of over 15 tons.

It is, unusual to complain of he when trying out a chassis, but hot tarred. loads were responsible for practically full-distance wheel-locking in the Sentinel tests and the tyres picked up heavily on the softened road when the Bristol was tried.

In articulated outfits there is a time delay in the braking system, because. to prevent jack-knifing, the shoes on the semi-trailer are arranged to work slightly ahead of those on the tractor. Although this delay would not be shown by an inertia-throw meter, it is measured in terms of stopping distance with the equipment used by The Commercial Motor.

Another Bristol model, thelight single-decker, is included in the passenger-vehicle charts, again for comparative purposes only, because it is supplied solely to the British Transport Commission. Two fuel-consumption graphs have been drawn to show continuous running and tests with one and four stops per.mile. In both, the lightweight models are shown to be the more economical and generally their acceleration rate is comparable with that of the heavier vehicles...

The Leyland Tiger Cub has been tested as a bus, and with a modified power unit in the coach chassis. Uprating the engine hasenabled the high performance of the bus to be retained in the coach version without impairing economy.

Fourand six-wheel-drive units, and other special types of goods chassis and tractors are normally subjected to off-the-road trials, but the acceleration, braking and fuel-consumption rates are measured on hard-top roads.

Battery-electric vehicles are tested over standard routes at Watford, a 15-mile course being planned for the driver-operated models and a short but hilly route for pedestrian-controlled units. These vehicles are tested with standard batteries and carry threequarters load to represent conditions of leaving the depot fully laden and returning with empty trays or bottles of about half the nominal load.