AEC MANDATORISCAMMER 30-TON-GROSS ARTIC
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VIAT, I wonder, does the average haulier look for when he is placing orders for new vehicles? Is it the fastest or fanciest achine? Is it the one that will give least trouble, or is it perhaps
one that comes from the factory giving the best after-sales Nice?
I have thought for many years now that the first concern when .ying vehicles should be the latter, with accessibility, reliability, consumption and price following in that order. The 30-32-ton EC Mandator with the AV760 engine, which was fully described COMMERCIAL MOTOR, September 11, 1964, and which is the bject of this test, just about fills my requirements exactly. It is rhaps a bit thirsty but is extremely capable of doing a hard day's )rk in the shortest possible time, a feature which has, of course, ways been associated with AECs.
The Mandator tested was coupled to a Scammell semi-trailer uipped with Rubery Owen suspension. The outfit, grossing just er 30 tons with driver and observer aboard, carried a payload 20.5 tons and returned laden fuel consumptions of 7.2 m.p.g. all road conditions.
I got the distinct impression that the differential ratio of 7.08 I was a bit on the low side from the point of view of getting good fuel consumption. Also I believe that the fairly low top speed —by today's standards—of 47 m.p.h. will encourage drivers to coast, particularly on motorways.
Considering the b.h.p. rating of approximately 196 net and the low axle ratio, the vehicle did not show up at all well when completing the motorway test. Its maximum speed of 47 m.p.h. made overtaking some of the older types of vehicle a long and rather embarrassing process, whilst to fall in behind them would have cut down the motorway average speed to the level of those obtainable on ordinary main roads.
Unfortunately, there was not even the compensation normally obtainable with a low-geared machine—that of tractability. When tackling a normal main road hill of about 1 in 25, road speed soon dropped off to the low 20s, necessitating dropping two and sometimes three gears. In this lack of ability to hold on to the higher gears on a gradient, I sensed that there was a shortage of fuel and that given just a touch more on the injector pump the tale may have been different.
I was told that this particular power unit carried a standard 5 per cent de-rating and this, I felt, was a mistake both from the point of view of performance and consumption. Even taking these criticisms into account the overall performance of the Mandator cannot really be said to be bad, as the acceleration is excellent and the capability of the machine to put up good average speeds without having to resort to very high top speeds is an advantage. High speeds, of course, are undesirable from many points of view and it may be that AEC has not been so backward looking as might at first be thought by fitting a 7.08 to I differential, although I would have preferred to have seen a 6.22 to 1 fitted.
With this gearing there is little difference in the acceleration rate irrespective of whether the vehicle is laden or empty, and this characteristic is a most desirable one, particularly if a large amount of metropolitan operations are included in the vehicle's daily round.
Much of the sluggishness of the unit in the upper range of engine speed was, I believe, due to a lack of fuel input as I got the distinct feeling that the engine was a bit starved when it got above 30 m.p.h. in direct-drive, with the last 4 m.p.h. possible in this gear being a sort Of half-hearted struggle, conquered by the slightest gradient.
These foregoing comments were the only ones that I could find to complain about with the Mandator's performance, as the handling was excellent and the level of noise in the cab very respectable. Vision from the "Ergomatic" could not, I feel, be bettered, whilst washers and wipers and good, sensible mirror equipment and quickdrop windows make bad-weather driving a not-so-gruesome task.
Brake tests produced adequate, if not spectacular, results. From all speeds stopping was progressive and certain, whilst there was a complete absence of deviation from a straight line. There is a bit too much loading on the brake pedal for my liking, this making "fine control" a bit difficult when checking the vehicle on a bumpy surface.
Results from 20 m.p.h. with full-pressure application were 33.2 ft. iverage distance—that is, 12.2 ft/sec.2—whilst a Tapley meter eading of 66 per cent was recorded. From 30 m.p.h. the average listance taken to stop the outfit was 65.25 ft.-14.9 ft/sec.2. rapley meter readings from 30 m.p.h. of 67 per cent were recorded m every stop made.
The secondary braking system on the Mandator is fed from a eparate reservoir and linked to triple-diaphragm chambers at the ractive-unit front axle and via a third line on to the semi-trailer xles. These chambers are activated through a hand-reaction valve ituated at the right-hand side of the instrument panel. Stops made iith this system from 20 m.p.h. produced Tapley meter readings of .0 per cent on each occasion. Again the outfit retained its stability uring braking and there were no anxious moments.
I was not very impressed with the handbrake, as although this is f the single-pull, air-assisted variety, I found it badly situated, lumsy to use and only just powerful enough. When doing the stopnd-start test on Bison Hill it was not possible to get the handbrake ) hold the vehicle when facing up the hill. It did just manage to old when facing down, although this entailed some pretty violent [Tort on my part.
The trouble with the handbrake is that it starts to take effect when le lever is almost under one's arm, when it.should, in fact, be operave in a position where the driver could apply some effort to it. ihilst talking about the handbrake I must also mention that to apply this with any zest whilst overdrive gear is selected results in one's hand becoming painfully trapped between the two levers.
Retardation results obtained with the handbrake, which is connected to the driving axle only, were very good. From 20 m.p.h. each stop made resulted in both driving-axle wheels locking and produced Tapley meter readings of 20 per cent. Throughout the brake tests this was the only occasion on which the tractive unit locked its wheels. On each of the full-pressure stops with the service brake, however, the offside leading axle of the semi-trailer locked.
When a fade test was carried out late in the day by coasting down Bison Hill against the brakes at 20 m.p.h., a full-pressure stop made with the service brakes from 20 m.p.h. produced a Tapley meter reading of 57 per cent, only 10 per cent lower than the results of the cold brake tests.
The hill climb showed that there would not be many gradients where this vehicle would find itself working that it could not easily surmount. Bison Hill, which has a total length of 0.75 mile, an average gradient of 1 in 10 and a steepest gradient of 1 in 6.5, was climbed in a total time of 5min. 36sec., when the lowest speed recorded was 3 m.p.h.
Ambient temperature at the time was 14°C (58°F) and when the coolant was checked at the start of the climb this registered 70°C (158°F). When checked at the end of the climb the coolant temperature had risen to 76°C (169°F). The dash-mounted thermometer which reads the temperature of the rearmost point of the cylinder head showed exactly 10°C higher readings on both occasions, my own readings being taken from the header tank of the cooling system.
One point that was noticeable when making the climb was the speed with which the vehicle accelerated once the steepest part of the climb was over. The lowest gear used was second and this was engaged for a total of 2min. 5see. on the steepest section. Where the gradient eased off the engine quickly soared to peak revs, crying out for a change of gear. This, unfortunately, could be achieved only by crashing through to the next higher ratio and here I would have appreciated some synchromesh or, alternatively, a clutch stop. The change was made, however, followed in quick succession by one more, placing the vehicle in fourth gear at the finish.
The brake fade test mentioned above was carried out during the descent of Bison and on reaching the bottom the vehicle was quickly turned round and taken back to the steepest part of the hill for the stop and restart test. It was here that the failure of the handbrake to hold the vehicle was recorded, but there was no reluctance on the part of the engine when the starts were made, these being easily accomplished.
When facing down the hill the handbrake proved just capable of holding, but the reverse start showed once again that adhesion is just becoming a problem at 30 tons gross with a single drivinl axle. Only by very careful application of power was it possible tc get the outfit under way in reverse, any heavy throttle applicatior resulting in immediate wheelspin. And this was in ideal road con. ditions.
General handling of the outfit proved to be good in all conditions. Whilst laden there was a slight tendency towards rollinE on corners, but directional stability was excellent. I experiencec no tendency of grabbing from the fifth-wheel, which so often spoil the handling of the larger artics, and found no problems with tlu semi-trailer lying in the gutter—also often a problem with a lorif trailer.
Quite substantial "bows" in the side raves of the semi-traile, were evident, pointing to a degree of flexibility in the main frame The trailer was of the latest Scammell design incorporatini rolled I-beams, the tops of which protrude through the floor tx floorboard level. It is provided with a substantial headboarc and Rubery Owen running gear as an option to the Scarnmel units.
There was little evidence of delay in the braking system of th4 semi-trailer and no tendency towards axle hop when braking Reaction to the hand valve controlling the secondary system wa: immediate on all occasions and the two-speed landing gear although very slow in operation, made a reasonably light job o landing the loaded trailer.
The neck of the trailer showed a 1.75in. droop when the tractiv: unit was removed whilst the trailer was loaded. A wheel-and screw type of handbrake was fitted for parking purposes and thi was linked to the leading trailer-axle only.