CHIEFTAIN Happ
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18 tons Gross Says John F. Moon, A.M.I.R.T.E. THE growing popularity of 12ton-payload articulated outfits has lead several vehicle manufacturers to introduce tractive units suitable for operation with this size of semi-trailer. One of the newest is the Albion Chieftain 7-ft. 8-in.-wheelbase unit, which has been designed for use with -Scammell automatic coupling gear at a gross train weight of 171 tons.
The tractive unit is a typical Albion product, both for its use of sound engineering principles arid a relatively small power unit. The combination produces a robust and economical vehicle with an entirely adequate road performance. It is, furthermore, the only tractive unit of this size with an easy-access forward-step cab, the cab used being the all-steel assembly adopted for Clydesdale and other Chieftain chassis.
A comprehensive road test of one of these Albion-Scammell vehicles proved the good fuel economy claimed, a consumption rate of 12.5 m.p.g. being returned at an average speed of 27.8 m.p.h. at a gross train weight of 18 tons 21 cwt. In view of the low power-to-weight ratio the acceleration and hill-climbing performances were unexpectedly good.
The Chieftain tractive unit is powered by the Albion EN.335 fourcylindered oil engine introduced last November and notable for its use of a C.A.V. DPA distributor fuel-injection pump. This 5.5-litre unit is rated to develop 94 b.h.p. at 2,200 r.p.m., with a peak torque output of 252 lb.-ft.
The standard gearbox is the familiar Albion five-speed constant-mesh unit, c6
which is available with a sixth overdrive ratio of 0.76 to 1. This additional ratio raises the maximum speed from 34 m.p.h. in direct top to 44 m.p.h. when the standard rear-axle ratio of 7.71 to 1 is specified.
Useful as this additional speed is, however, a more particular advantage of the overdrive is that it permits a reduction in engine speed at normal cruising speeds, with reduced engine wear and improved fuel economy. This applies to an even greater degree when running unladen, as shown by the consumption rate of 19.4 m.p.g. obtained with an empty semi-trailer at a gross weight of 6 tons 24 cwt. The gearbox is unit-mounted with he engine and the 13-in.-diameter 1.utch, with sprung centre plate, is cctuated by the recently introduced klbion annular clutch withdrawal nechanism, which provides automatic rear adjustment.
A short propeller shaft with Hardy :nicer 1510 needle-roller universal aints takes the drive to the Albion ouble-reduction rear axle. The Iection front axle is conventional, xcept for its use of Glacier DU ,.t.f.e.-lead thrust washers at the kingins. Marles cam-and-double-roller teering with a ratio of 24.7 to 1 is mployed.
Short-wheelbase tractive units of
is type are not normally renowned Dr good riding characteristics, but -le Albion is an exception. The long -ant springs-54 in.—are a help, and re controlled by double-acting tele
scopic dampers. The overslung semielliptic springs at the rear are 45+ in, long, and both sets •of springs have 3-in.-wide leaves.
Girling two-leading-shoe brake units fitted to the tractive unit are similar to those employed on Chieftain load carriers. A Hydrovac suspended vacuum servo boosts the system and there is an additional Hydrovac, triggered by the tractive-unit system, which acts as a slave for operation of the semi-trailer brakes through the coupling gear. This Hydrovac slave servo is a feature of the Scammell Mark 118 coupling gear, as is the incorporation of a further vacuum
servo for the coupling release mechanism.
The chassis-frame side members are swept down behind the rear axle to accommodate the ramps of the Scam melt coupling gear. The layout is such that 8.25-20-in. tyres can be employed without raising the coupling height unnecessarily, thereby permitting a rear-axle loading of 6 tons. Bolting is used throughout Although the test outfit had been taken out of service with the Albion transport fleet, it had covered only 16,500 miles before it was handed over for test. Other than having had the braking system checked and a fueltest tank fitted, the vehicle was exactly as received from the transport department. Cast-iron weights totalling exactly 12 tons had been placed evenly along the length of the drop-sided body, and ready for the road the semitrailer axle, to which were fitted Michelin 9.00-20-in. "X " tyres, was loaded to 9+ tons.
Squally weather was not helpful, but no inherent instability in the outfit was exhibited. Even when driven fairly quickly .along narrow country roads, the vehicle could be handled with confidence.
The first series of tests was conducted on a 1-in-6 gradient known as Crarae Hill, in the Westerton area of Glasgow. Facing up this gradient the tractor hand brake alone would hold the outfit after it had been helped on by light use of the foot brake. The lever controlling the vacuum valve for the semi-trailer brakes was then applied and the tractor brake released, but the power available was not sufficient to prevent rolling back.
I then made a commendably smooth bottom-gear restart with little of the " kangarooing " so often unavoidable with articulated outfits drawn by shortwheelbase tractive units. The outfit was next turned round, so that it faced down the slope, and this time the tractive-unit hand brake held it without assistance from the foot brake, although, again, the semi-trailer brake was not quite capable of preventing movement.
An attempted restart in reverse failed because of lack of engine power, c7 but neither on this occasion nor when facing up the hill did any wheelspin take place.
A fairly fast run over somewhat difficult roads was then made out to Buchlyvic for the start of a 20-mile out-and-return fuel-consumption run. Half the distance was over fairly undulating ground and the rest over reasonably level roads. The complete distance was covered at an average of 27.75 m.p.h. without at any time exceeding 33 m.p.h., and the resulting consumption rate of 12.5 m.p.g. gives the highly satisfactory time-load-mileage factor of 6.302.
Later, the same route was used for c8 an unladen test and, although traffic reduced the average speed slightly, the consumption rate improved by 6.9 m.p.g. to 19.4 m.p.g. An operator unfortunate enough to have to run his articulated outfit unladen on return journeys could expect 15-16 m.p.g. overall, which is good for any vehicle capable of handling a 12-ton payload.
Although it cannot be pretended that this outfit is exceptionally lively, the gearbox has well-chosen ratios and is easy to use, and this helps to make the most of the available acceleration performance. The figures recorded from a standstill to 30 m.p.h. were decidedly better than I would have expected, considering the availabi power.
The good direct-drive performanc from 10-20 m.p.h. emphasizes th remarkable low-speed pulling powe of the relatively small power uni although, as can be seen from th figures in the data panel, the perfot mance tails off slightly when engin speed is increased.
When making the standing-sta, runs, second gear was used up to m.p.h., third up to 13 m.p.h. an fourth up to 22 m.p.h.
Braking tests were made on th second day of my test during an hot or so when the roads were dry and was a little disappointed with the performances recorded. The retardation performances from both the test speeds would be upset slightly by the fact that the off-side driving-wheel brakes tended to grab slightly, and this was shown up even more when making tests with the tractor hand brake alone from 20 m.p.h.
During the tractor hand brake tests I was able to produce 90-ft.-long skid marks from the off-side driving wheels, although the Tapley meter recorded a maximum retardation of only 23 per cent. Slightly lower efficiency-22 per cent.—was obtained when the semitrailer braking control was actuated by itself from the same speed.
The Clyde was crossed by ferry to reach the site of hill-climbing and brake-fade tests. The gradient used is known as Gleniffer Braes and is 1.3 miles long, with an average gradient of 1 in 13 and sections of up to 1 in 8.
Adequate Cooling Ambient temperature was 63° F. and the climb was made in a total time of 9 minutes 48 seconds, and the engine-coolant temperature rose from its normally low value of 130° F. to 166° F. Despite this rather marked increase, I am confident that the cooling system is adequate for prolonged hill working, as the system is pressurized to raise the boiling point to above 212° F.
Minimum speed during this ascent was 7 m.p.h., which shows that the Chieftain tractive unit is not as slow up hills as its specification might suggest. This speed was recorded in second gear, a ratio employed for a total of 6 minutes 16 seconds.
When running on the governor in this gear, a certain amount of exhaust smoke was observed. I am told that smoking and occasionally reluctant cold starting are shortly to be cured by raising the compression ratio from 16 to 1 to 16.9 to 1 and by altering the shape of the combustion depressions in the piston crowns from hemispherical to toroidal formation.
Coasted Downhill To check fade resistance, I coasted the outfit down the hill in neutral while using the foot brake to keep the maximum speed to 20 m.p.h.—a severe test on a hill of this length. Before the bottom of the hill had been reached the vacuum gauge showed the vacuum to be dangerously low and I had to speed up the engine.
The descent lasted 3 minutes 49 seconds and, although both myself and my passenger agreed that when the pedal was fully depressed hardly any retardation took place, the Tapley meter registered 43 per cent. This was undoubtedly deceptive and possibly the meter had been jerked up to this reading during the descent, because all the brakes were smoking severely and the pedal travel had increased considerably.
A big four-cylindered unit such as
this is to be found these days only in Albion chassis, but the engine behaves commendably smoothly and quietly, and is obviously a " four " only when it is idling. The gearbox is a delight to use, as always, and the clutchpedal travel is short enough to allow depression without the driver lifting his heel from the floor.
Only a slight amount of pitching can be felt in the cab on rough roads and on reasonable surfaces the ride is steady. The semi-trailer followed well, with no tugging or pushing, and the steering was light and positive, with a comfortable amount of castor action. When hauling the semi-trailer unladen the ride was not appreciably different from that when carrying a full load.
Full-circle Turn Manceuvrability of outfits such as this increases as the wheelbase is shortened and the tractive unit alone could turn between kerbs in 34 ft., whilst a U-turn with the semi-trailer coupled occupied little more space. A full-circle turn required 51 ft. between kerbs, because of the need to keep clearance between the cab rear corner and the semi-trailer side board.
Coupling and uncoupling are rapid —14 seconds and 16 seconds, respectively, from the moment I left the cab seat until I regained it. Because of the vacuum release mechanism, appreciable manual labour is required only in applying and releasing the semitrailer parking brake.