DENNIS UBILANT MAKES ASY WORK OF 12-TON LOAD
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SINCE the description of the new Dennis Jubilant 12-ton, rigid six-wheeler appeared in our issue dated December 7, we have been given an opportunity of subjecting one of these machines to ocr usual road test. For the benefit of those readers who did not see " The Commercial Motor" for the date mentioned and by way of a .refresher to those who did, here is a brief description of the main features of this new heavy goods vehicle..
It is powered by a Dennis 06 sixeylindered oil engine, which. is a unit of the direct-injection type, the b,h.p. being 100 at 1,800 r.p.m The drive is taken through a two-plate dry clutch to a five-speed overdrive gearbox, in which the oi/erdrive ratio is of the preselective type From the main gearbox a Layrubjointed shaft transmits to an auxiliary gearbox, and from this unit a HardySpicer shaft, with needle-roller joints, conveys the drive to the first wormdriven axle. Another Hardy-Spicer A26 . shaft runs from the first axle to the second; there is a third differential in the first axle to even out the torque between the two units The twin rear-axle assembly is suspended on trunnion-mounted springs, a notable feature in the design. of the chassis at this point being the use of a massive fabricated stiffener which spans the frame and takes the torque arms at the top, and the cross tube, on which the springs are trunnioned, at the bottom.
All brakes are of the Girling 2LS type, those controlled by the foot being hydraulically operated via a Clayton Dewandre vacuum servo. The hand brake has a Neate-type control, which provides for graduated application and release.
Dennis worm-and-nut type steering, in conjunction with a sprung wheel,s and well-disposed controls make for remarkable ease of control, as we were to prove for ourselves.
As is our customary practice, we first took the vehicle on to the weighbridge, which showed us that the total gross weight, with driver and passenger, was 19 tons 6 cwt.---14 tons 4 cwt. 1 qr. 20 lb on the driven axles, and 5 tons 1 cwt 2 qrs 8 lb.
on the front axle. Of the total 12 tons, in i-ton weighs, represented the payload.
As we had elected to carry out the acceleration and braking tests first, we ran out to a stretch of road in the Godaiming area. This initial run gave us a useful introduction to the Jubilant, particularly as to its splendid manoeuvrability, ease of gear change and light but strictly directional steering Indeed, in its general handling, the machine could give points to some vehicles of much smaller pay-load capacity Having had experience of the Dennis 06 oil engine in a Lancet .111 single-deck bus, we looked forward to a fairly lively performance, and in this we were not disappointed Its excellent torque at moderate r.p.m. showed up on a number of stiff "pimples," it being possible to hold the overdrive ratio on quite respectable up-grades, a preselected changedown to fourth seeing us over the top of the majority.
As to the engine's powers of acceleration, we obtained amean figure of 24 secs, in reaching 20 m.p.h. from rest and passing through
the gears, From a rolling start, with the speedometer hovering on 10 m.p.h. in fourth speed, the Jubilant reached 20 m.p.h. in the mean time of 19 secs.
A notable feature of this test, as the times will show, was the manner in which the engine "got behind the load." even on the return run, which was slightly on the up-grade.
We used the same stretch of road for our braking tests, and on these we obtained a mean figure of efficiency of 65 per cent., which is somewhat unusual On the outward run we pulled up the vehicle in 19 ft. from 20 m p.h., and in the opposite direction in 21 ft. from the same road speed In both cases these distances are well within the length of the vehicle, a point which is shown in one of the accompanying pictures.
While on the subject of braking, we would mention that the brake pedal does not follow the foot as pressure on it is released, the slight lag, no doubt, being caused by the servo It should be made clear, however, that this has no effect on the braking should the pedal have not fully returned when another application is called for. In the, case of the lever, this could, with advantage, have been a couple of inche3 nearer the hand when in the fully released position, a matter for adjustment only We did, however, appreciate the Neate control, and we tested this out on a gradient of about 1 in 7.
For the hill-climbing test we used a gradient known as Coombe Bottom, which boasts of a maximum up-grade of 1 in 6, this coming on a sharp lefthand bend.
The writer of the present article knows this hill well, having used it for test purposes, over 20 years ago, when on the staff of "The Light Car." Little did he think then that he would be using a hill of such a nature to prove out the hill-climbing qualities of a vehicle of a gross weight of close on 20 tons!
On the lower stretches we made good headway on third gear at about 16 m.p.h., and at 10 m.p.h. we dropped into second. Momentarily, we were able to get back into third, and after another change down to second, we kept at a steady 9 m.p.h. Unfortunately, however, the lady driver of a Y.M.C.A. van, who was coming down the hill, did tlx right thing at the wrong moment, which meant changing down to the normal gearbox first earlier than was necessary.
It was thought that recourse would have to be made to the auxiliary box to give us low first, and this proved to be so. To engage this gear one operates the auxiliary-box control in the same mannzr as the normal gear lever, double-declutching in the usual manner. In this ratio the Jubilant had ample power reserve, and it took us up the 1-in-6 portion and around the tight bend in a most reassuring manner
Once clear of the bend we stopped on a 1-in-7 stretch, and got away comfortable on the normal first gear. Gruelling climb as Coombe Bottom represents, there was no signs of undue heat or objectionable fumes in the cab; in fact, the cooling water at the summit showed a temperature of only 173 degrees F., against an atmospheric temperature of 52 degrees F.
To complete the trial therremained the fuel consumption test, and for this we ran over a give-and-take stretch of the London-Portsmouth Road. The test tank, which was affixed to the chassis just behind the cab, was filled with a measured gallon of fuel, and the machine was driven until the fuel in the gauge glass reached the " bottom nut" On the outward run we recorded 9.8 miles, and on the homeward trip, on a second gallon, of course, we covered 9.2 mites The mc.In figure was thus 9.5 m.p.g. It should be mentioned that little gear changing was called for, there was practically no traffic to impede us, and the overall average speed worked out at 25 m.p.h —no mean achievement for a vehicle of this type The driver of a Dennis Jubilant will appreciate the comfortable driving position, the remarkably easy gear change, the general ease of control and the roomy cab from which the degree of visibility is excellent.
To sum up this road test we can say, with some conviction that, while in our hands, it gave a performance somewhat above the average, and we would go as far as to say that we thoroughly enjoyed the trip.