TESTING A THORN CROFT-EAGLE 7-TONNER
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SPEEDY, the designation of the Thornycroft chassis which, detachably coupled to an Eagle semi-trailer, is the subject of this report, although a strictly appropriate name, is, nevertheless, a little misleading, for it suggests low
"weight, high gear ratios, streamlining and . even, perhaps; flimsiness. The speed is certainly there, but one is first impressed more by solidity than lightness, by slogging power than mere velocity, and by bulk and strength rather than the characteristics of slenderness that its name involuntarily brings to mind.
It is comparatively easy for one experienced in the road behaviour of many makes and types of commercial vehicles to form an opinion of the capacity of the machine under observation to carry more load than that on board at the time, or otherwise— to decide whether it is correctly laden, or under or overladen for its powers. With regard to the Thornycroft in question, we are confident that another ton at least could be added to the seven, with which we conducted this test, without its per formance or safety being appreciably impaired.
While on the subject of weight, it will be seen that, in the accompanying data panel, the unladen weight of the complete vehicle, with full equipment, is given as 4 tons 14 cwt.
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Of this amount 5 cwt. can be accounted for by the spare wheel, the demonstrator's tool kit, a large seat rigged up for the third passenger who accompanied us, the oil, water and petrol carried, and certain other oddments., whilst the jockey wheels, their legs and winding gear scale another 5 cwt. or thereabouts. Thus, this machine as a permanently coupled articulated six-wheeler weighs, for registration purposes, 4 tons 4 cwt. On discovering this fact we put the obvious question: Why has not the odd 4 cwt. been pared off to bring the outfit into the 4-ton class? We were informed, in reply, that a lighter semi-trailer was available if the prospective purchaser stipulated that 4 tons must not be exceeded. The standard model, however, apparently is just outside the limit, and when equipped with a sided body would, of course, be more so. The difference in taxation is £20.
We suggest that steps should be taken to produce the standard model. in slightly lighter form, but we hope, if this should be done, that none of. the many excellent features of the existing chassis will be sacrificed. The power unit, for example, is on the large side and, accordingly, has ample power for its job. It is, nevertheless, economical and, furthermore,
possesses marked characteristics of flexibility and freedom from vibration. Incidentally, . it is equipped with a governor mounted on the induction pipe and driven by flexible cable. Magneto ignition is employed.
Substantial construction is found in the transmission, and the rear axle is a solid-looking unit. The frictional area of the brake shoes is larger than the average, whilst the actuating mechanism is massively made and has not been simplified, to save weight, at the risk of diminished efficiency. , • , There are two brake cross-shafts, one operated by the band lever and the other by the pedal through a Westinghouse vacuum cylinder. From these common rods run to the hubs, lost-motion links serving to transmit the pull from one to the other, while allowing either control to be used without affecting the other.
A flexible tube connects the vacuum valve with two cylinders on the trailing unit, one for each wheel. There is a large vacuum tank included in the system.
• Excellent retardation is afforded, as an accompanying graph shows, and, despite the fact that the roads on which we tested the brakes were wet, locking of the wheels occurred only when the hand brake was used in addition to the vacuum system. The extra braking force thus exerted upon the driving wheels definitely caused them to slide, but, nevertheless, the machine never diverged from a straight course.
• On a gradient of about 1 in 8 the hand brake, used alone, quickly reduced the speed of the vehicle from quite a high figure, but, unaided, would not bring it to rest. It was, however, found to be just capable of holding the machine on this slope.
Despite the length of pipe-line, the time lag did not appear to be great, but we had no opportunity of making separate tests for delay in the operation of the trailing wheels.
The maximum road speed permitted by the governor is about 39 m.p.h. Occasions when circumstances permitted its use were somewhat infrequent on the course over which we took this Thornycroft outfit, but, judging by the ease with which 30 m.p.h. could be attained, favourable conditions would not be indispensable for the maintenance of high average speeds. In this respect, the big engine scores heavily, and even with only the four widely spaced
ratios (see accompanying table) no time is lost through inability to
accelerate because of a slight up grade or similar handicap.
Another point should be mentioned
in this connection. The rigidity of the outfit, with regard to frame construction and the resistance of the suspension system to lateral forces, is' such that its cornering powers are
exceptionally good.
Fairleign Hill, to the south of Basingstoke, was used for •a hillclimbing test. It has a maximum gradient of about 1 in 8 and, from the village at its
foot to the summit, is 1.3 mile long. The average speed for this distance was 11 m.p.h., and, on the
steepest section, we progressed in first gear at about 4 m.p.h. with plenty of power in hand. As the slope eased second gear was engaged ; later, when the speed rose to about 14 m.p.h., third and fourth gears were used.
Thornycrofts are regularly tested for consumption over a specified course, which has been accurately mapped and measured for the purpose. It follows, from the Basingstoke works, the Salisbury road so far as Whitchurch. There it turns south towards Bullingdon, and later, roughly, east, returning to the starting point by the BasingstokeWinchester road. The exact length of the circuit is 28 miles, and it includes no fewer than seven quite steep gradients.
That known as Bullingdon Hill is the iv'orst; its upper stretches necessitated the employment of " first " on this trial, for we respected the tradition and used the official course for our test.
A one-gallon tank had been rigged up for our needs, and this was filled with a measured quantity before starting. Its contents carried us 8.1 miles. The succeeding gallon carried us 7.1 miles; the third, 7.8 miles. The final five miles— downhill nearly all the way—required 3.25 pints. Thus, the average rate of consumption for the 28 miles was 8.22 m.p.g. This figure may be relied upon, as the conditions are
probably harder than average.
As mentioned earlier, the Eagle semi-trailer was of the quick-coupling type. Accordingly, we timed the period necessary to disconnect the two units, and ascertained that in three minutes the jockey wheels can be lowered to raise the front end of the trailing unit until the king-pin is clear of the lower half of the turntable on the tractor. The operation
is hard work for two men of normal physique.
In build, this semi-trailer seemed a suitable complement to the Thornycroft tractor. It is substantial, properly equipped and provided with a secure king-pin locking device, whilst the attachment gear is sprung to relieve fore and aft shocks.
The whole outfit, as should have been gathered from the foregoing, seems essentially sound and built to endure. Its margin of safety is wide, and the inner boundary thereof should rarely be reached, even by overloaders and hard drivers. That is the opinion formed after close on 100 miles of testing.