12 Tons 12 m.p.g. with an "Artie"
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By John F. Moon,
A.M.I.R.T.E.
HAULING a payload more normally associated with vehicles powered by 8-litre oil engines, the latest Dodge 12-ton prime mover, with Perkins R6 Mk. II oil engine, puts up a most irispiring road performance. In fueleconomy it has little to match it arid its power output is ample for .normal. British. working with vehicles of this weight.
In braking also the Dodge-Hands outfit showed itself to have a much better performance than is normally found with this class of vehicle. An added attraction of the .prime mover is its normal-control cab, which gives. comfortable seating for three persons and is quiet.
The wheelbase is appreciably. longer than that of a forward-control vehicle of comparable size, but this does not detract greatly from its mancefivrability and gives greater riding comfort and stability. Engine accessibility is also much better than would be possible with _a forwardcontrol layout.
l'he Dodge normal-control range of prime movers was introduced in June of this year and consists of four models—I 0-tonners and 12-tonners. Two have the Perkins R-6 Mk. II engine and two have the Leyland 0,350 unit. The basic chassis specification is similar, the 10-in -deep
-in.-thick frame being derived from the standard .7-ton normalcontrol chassis.
Eaton two-speed axles are standard equipment on all these chassis, a 16500 type being fitted to the lighter
models, whereas the 12-tonners have 18500 axles. Clayton DewandreGirling air-hydraulic brakes are fitted and the tractor has two-leading-shoe units on both axles. Moulded facings are used.
A timing valve is included in the air-pressure system to ensure that the semi-trailer brakes are applied slightly ahead of the tractor brakes, and two-line semi-trailer brake equipment. is fitted.
When the standard five-speed constant-mesh gearbox is used in conjunction with the R6 engine, the ratios_ are a little wider-spaced than in the Leyland engine application, to compensate for the slightly higher maximum torque output of the Leyland.
The Perkins R6 engine has been vindicated on the merit of its performance. during this test. Admittedly, its longevity could hardly be established during a two-day trial, but I have enough faith in the engine manufacturers tobelieve that the modifications that have been effected will give-trouble-free running.
A modified type of timing-chain tensioner, new timing-chain cover providing positive lubrication to the tensipner and an improved form of lubrication pump are among changes made in the original design.
The Hands semi-trailer used is of the latest type, with an exceptionally strong steel frame, having 15-in.-deep longitudinal members and pressedsteel cross-members, outriggers and rave rails welded in place. The 24-ft.-long platform is 7 ft. 2 in. wide. The Girling brakes are of the same size as those used on the driving axle of the prime mover, thereby introducing a desirable measure of standardization, and the air servo actuating them is located on the H-section axle of the semi-trailer.
The semi-trailer has a patent snapback undercarriage which is much more simple, quicker and less tiring to operate than the screw type which is offered as optional equipment. Standard S.A.E./S.M.M.T. coupling gear was provided.
As tested, the outfit was carrying a payload of 11 tons 161 cwt., and with myself and two Dodge representatives aboard the gross weight was 6+ cwt. in excess of the recommended figure.. The low front-axle loading suggested that the steering would be light, but in fact it was exceptionally heavy, particularly when manteuvring in tight corners.
During the test, castor action was found to be adequate without being fierce at small steering angles, but the effect disappeared progressively as the lock was increased, until at fulllock position the steering became extremely stiff to return.
This was my main criticism of the design and it is serious, because one of the normally accepted assets of an articulated outfit is its improved manceuvrability for, reduced driving effort. When this fault has been remedied, as I feel sure it must be, the Dodge prime mover will rate close to the top of its class among any in the world.
For the first tests the vehicle was
taken out to a level stretch of road running alongside Staines reservoir, where braking and acceleration figures were recorded. The first brake test was made from 20 m.p.h. and when the foot valve wasfully opened the brakes immediately took effect and a stopping distance of 201 ft. was recorded. This is equivalent to 65.5 per cent, efficiency, and when compared with the .maximum deceleration rate (recorded by the Tapley meter) of 72 per cent. shows that little lag was present in the system.
Unfortunately, as a result of this " crash " stop, it became clear that a similar stop from 30 m.p.h. would most probably result in the test load becoming dangerously loose and I did not feel that the risk was justi, fled. It is safe to assume, however, that a stopping distance of less than 50 ft. would have been recorded.
As it is, the figure obtained from 20 m.p.h. is much better than that obtained with any other articulated unit tested, let alone most of the rigid vehicles running at much lower gross weights. For the acceleration runs the Eaton axle was kept in low ratio the whole time and the figures obtained when accelerating from rest to 30 m.p.h. were satisfactory without being startling, bearing in mind the low powerto-weight ratio of 0.27 b.h.p. per cwt. gross weight. When driven normally in dense traffic the Dodge outfit was shown to be capable of keeping up with most heavy vehicles.
The low-speed pulling power and efficiency of the engine mountings were highlighted during the directdrive acceleration tests, made between 10 m.p.h. and 30 m.p.h. The power unit pulled smoothly from the lower speed, with low axle ratio engaged, and a steady acceleration rate was maintained up to 30 m.p.h. The times recorded are particularly good and speak well for the torque characteristics of this Perkins unit.
Consumption runs were carried out along a severely undulating route between Egham and Bagshot, the outand-return distance totalling 16 miles. A.5 shown by the consumption rate
and average-speed figures in the data panel, the Dodge was not spared during this test. Of the total running time of just over 33 minutes, only 27 minutes were spent in direct drive with either axle ratio engaged.
Evidence of the high-speed economy of the outfit is given by the time-load-mileage factor resulting from this test, 6,400 being one of the highest figures ever recorded by The Commercial Motor, The semi-trailer was disconnected in a lay-by at the western end of the Egham by-pass, this job being carried out single-handed in 2+ minutes. Then the prime mover was taken over the same course again and an this occasion practically the whole of the course was covered in top gear with high axle ratio engaged.
As the average speed of 34.1 m.p.h. shows, no time was lost on this test. Despite the high speed, no discomfort was experienced by either the driver or passengers, although no dampers were fitted. This is one of the advantages of a long-wheelbase tractor. Front dampers are, however, offered by the chassis makers.
These fuel-consumption tests were made under normal busy traffic conditions and the results are likely to be repeated in service in but the. hilliest areas of Great Britain.
As the subsequent hill-climb tests were to prove, economy has not been obtained at the expense of good gradient performance. A combination of a five-speed gearbox and twospeed axle is a great, help towards low fuel consumption. • • Titsey Hill, in Surrey, was chosen for the hill-climb and brake-fade tests. This gradient is nearly a mile long and its average severity is 1 in 6, the steepest section measuring 1 in 5. The run out to Titsey from Kew was made via Epsom, Reigate and Redhill, and took in some particularly long and severe main-road hills.
One long climb up the Reigate road just south of Epsom entailed a quarter of an hour of indirect-gear work and caused the coolant temperature to rise to 195° F., the air
temperature at the time being 83° F.
was continually surprised on such hills by the engine performance, and although on several occasions I was fully prepared to have to change into bottom gear, second gear, low axle ratio, was the lowest used.
At the bottom of Titsey Hill the coolant temperature was 179° F., ambient temperature being 84° F. A climb was then made in 121 minutes, . of which almost 9 minutes were spent im bottom gear, low axle ratio, and a coolant temperature rise of 11° F. was recorded.
It became obvious that I had held on to this lowest ratio far longer than need be, so the test was repeated and the second climb was made in 94 minutes and only two minutes were spent in bottom gear, low axle ratio.
Third-gear Finish
At the end of this clinib the radiator temperature had risen to 203° F., which is understandable because of the lower engine speed during the greater part of the ascent. Indeed, whereas the first climb was finished in "second low," on the second attempt the hilt, was breasted in "third high."
A particularly severe test of chassis and transmission strength was inadvertently conducted during this second climb when changing from 6. second low " to " first low." Thinking that the lower gear had not engaged fully, I let the clutch out to synchronize the engine speed for another change and found to my surprise that the gear had engaged.
The effect of letting in the clutch sharply at more than half engine speed was to lift the near-side front wheel off the ground by about 18 in., which says much for the toughness of the transmission components, let alone the frame flexibility.
Fierce Fade. Test A descent of Titsey Hill was then made in neutral with the brakes partially applied to restrict the speed to 20 m.p.h. This test lasted 31 minutes, at the end of which an emergency stop was made from 20 m.p.h.. producing a Tapley meter
reading of 37 per cent. Severe as this test was, the amount of fade was not inordinately great and showed the effectiveness. of the moulded facings when working at . high temperatures.
A peculiarity of the braking system, caused, presumably, by a slight discrepancy in adjustment, was that the off-side brakes on both tractor and semi-trailer were smoking much more heavily than those on the near side, the off-side semi trailer brakes" being the worst. During this descent the engine was kept at a fast idling rate to match the air-compressor output to the slight air leak that was occurring in one of the semi-trailer hose connections.
On the road the Dodge prime mover is pleasant to drive, other than the heavy steering effect. The engine is commendably quiet (so much so that I had to check to see whether any additional insulation had been applied to the bonnet—which it had not) and little engine heat penetrates into the cab.
During the two days of the test, however, the ambient temperature was for the most part above 80° F. and showed that additional cab ventilation would be beneficial, particularly as the fresh-air inlet behind the instrument panel, which relies on ram effect, provides little or no ventilation.
Wide Cab The cab is wide enough for three men without the centre passenger having to sit astride the gear lever. The driving seat is adjustable in fore and aft and vertical directions, whilst the passenger seat is fixed. The range of the driving-seat adjustment is not great, however, and the relationship of the seat to the steering wheel is Such that drivers of normal height will find the wheel higher and closer' to the chest than generally experienced with normal-control designs— rather after the Continental fashion. A shorter steering column would remedy this slightly unusual position.
The brake pedal has a reasonable amount of " feel " in it and does not encourage accidentally fierce braking when running light. The gear
change is sweet and the clutch action is light.
The road work left me with insufficient time to conduct maintenance tests, but a quick look round the chassis was sufficient to convince me that generally the components were laid to assist regular maintenance. So far as the power unit is concerned, the principal fault is the position of the dipstick, which is in line with the 'Kigass bottle mounted: on the interior near-side, wing panel.
Easy to Reach Access to the fuel-injection pump is reasonable, although it is rather low on the near side of the cylinder block and therefore slightly shrouded by the passenger toe-box. The injectors, which are located vertically in the top of the cylinder head, are particularly easy to reach. The main fuel filter, although partially obscured by the fresh-air hose, can be stripped in situ without much difficulty.
The gearbox and rear axle have combined filler and level plugs, and the brakes have the normal GirIing external adjusters, two for each front brake and one for each 'rear brake.
The spare wheel is stowed in a low-slung carrier on the off side immediately behind the cab, where it is secured by two bolts which fit the wheelbrace. The two batteries are covered by a wooden lid which is retained by one wing nut and a spring clip.
The Dodge 243 AR.6 prime mover has a basic mice of £1,752, to which must be added £395 7s. 10d. purchase tax in Great Britain. The Hands 12-ton 24-ft. semi-trailer costs £723, plus £8 for the 18-in. headboard.