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FODEN 24/28-TON EIGHT-WHEELER
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Page 72
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by Ron Cater, AMInstBE
ALTHOUGH the artic has ousted the eight-wheeler as the principal British trunk vehicle, for some applications the rigid eight is still the premier machine. Nowhere is this more true than in the top end of the tipper world.
The subject of this test, a Foden 8XB6 /24-26 ET had been built to order for A. S. Denniff Ltd., of Kiveton Park, Sheffield, and although its 17ft 9.25in. axle spread was insufficient for it to qualify at present for operation at 26 tons, it was tested at this weight—its gross plated figure.
Throughout the test the points that continually showed up were the extreme versatility of the I2-speed gearbox, and the lusty capability of the Gardner LXB 180 engine. Together these gave the vehicle the ability, to return quite surprising average speeds and to go almost anywhere I chose to take it. It climbed a gradient of 1 in 3, returned fuel consumptions of between 9.8 laden and 14.8 mpg unladen, despite very bad road conditions gave braking figures adequate to satisfy MoT requirements. But investigation into the brake test results revealed a delay between application and full effort in the system in the region of 0.75sec and had this been eliminated, overall stopping distances would have been considerably shorter. Unladen, the suspension was on the hard side, and when travelling on narrow and congested roads I found the steering to be somewhat inaccurate.
The vehicle carried an 18cu. yd. Cravens Homalloy fixed-sided light-alloy tipping body, tipped by Edbro front-mounted four-extension twin rams.
The Foden rules the driver rather than the other way about, and it is virtually impossible to do anything faster than the designers intended that it should be done. From the start the vehicle gives the impression of solid construction, and attempting to bash the gears in to mesh without first stopping the clutch spinning with the stop just cannot be done. The same applies to attempting snatch gear-changes.
By using the clutch stop it can be done, but this makes hard work of the job quite unnecessarily, and I feel it would be a very ambitious driver who would try to do it continuously. So flexible was the power unit on the test that the leisurely method of waiting for the revs to die, matching the road and engine speeds accurately and popping into the next ratio proved to be far and away the best. Even when completing the acceleration tests the hurry-up method failed to produce significantly better results, and from that point on I discarded it completely.
Quite the most important result from all this is that the transmission line in general must get a much easier life. The design compels the driver to change gear properly—in my book that can never be a bad thing.
I have long thought that vehicles should have a crawler gear for use either in emergencies or when manoeuvring in very close quarters. Even if it is not used more than half a dozen times for emergency starts throughout a vehicle's working life it will undoubtedly pay its way. The savings that result from reduced clutch wear alone are sufficient to make it worth while. The Foden I2-speed gearbox does, of course, provide the best of all worlds. There is a ratio for every condition and while the first flow combination coupled with the 5.2 to I final drive ratio on the test vehicle gave an overall first gear ratio of 63.9 to one, in fourth /overdrive the overall ratio was 3.9 to 1. This extremely high top-gear ratio results in the engine doing about 2,030 revs per mile and together with the Gardner engine is the key to the fuel economy of the vehicle when under normal working conditions.
It would be no use having this fantastic difference in gear ratios, however, if it were not possible also to have suitably spaced intermediate ones. Again the Foden gearbox fills the bill precisely. Although it was designed with the Foden two-stroke engine in mind, it is quite remarkable just how well the gearbox suits the Gardner engine. One has to keep very busy changing gear with the two-stroke, however, while when the Gardner LXB is fitted as in the test vehicle progress is surprisingly good with little or no fuss whatever. Once the outfit is on the road it is necessary only to use direct and overdrive ranges of gears. The progressive reduction of ratios is approximately 0.5 to one in each successive gear in these ranges and once a driver is accustomed to the vehicle the combination of splits that can be made is suitable for every condition.
The long, flat torque curve of the Gardner makes progress on undulating roads an extremely leisurely operation, and I found it quite a pleasant experience driving along the heavily trafficked AS in company with numerous other heavies, few apparently making such easy headway as I.
It was after leaving the confines of the Motor Industry Research Association test ground at Nuneaton—where all the traffic moves in one direction and one has ample room for manoeuvre—that my only complaint with the Foden became apparent. As soon as I started to motor north along A5—the first few miles of which at this point are quite narrow—I had to devote far too much attention to keeping the vehicle on its own half of the road. It seemed to me that the steering gear was completely dead within the range of a quarter turn on either lock and this meant that any correction due to changing cambers or irregular surfaces was made as a guess, rather than as it should be, through feel. Consequently for the first few miles I found myself wildly over-correcting and then having to check and recheck to get the machine travelling in a straight line. When I complained to Fodens about the steering, I was told that as the vehicle had covered less than 1,000 miles the steering gear was still relatively stiff.
Also, the power assistance ram used on the tipper chassis is more powerful than is really required to cope with a total weight on the front axles of 8.75 tons. The design has to take account of the higher degree of assistance needed for off-road conditions the vehicle will encounter, and I feel that the joint stiffness and extra ram power combined with a rather less-sensitive steering-load-sensing device than is desirable were jointly responsible. Despite assurances that when the stiffness wore off the steering would be right, I rather suspect that what really happens is that drivers become used to it.
Any driver who has shunted an eight-wheeler on soft ground where numerous moves have to be made to align with the tipping area will immediately, of course, see the vantage of having extra powerful, power-assisted steering gear.
The run north along AS involved 29.1 miles which was covered at a speed of around 40 mph. So little effort was needed on my part to keep the speed up in this range that I found myself constantly having to ease off. The pnly gears changed on this stretch were thirl and fourth high and low, a total ratio ran e difference of only 0.705 to 1. The lowet speed recorded on this section was 20 nph while the average speed over the rout was 27.2 mph. Fuel consumption on this stretch was 11.15 mpg.
High average
A full throttle run along M6 showed up several points. Despite having a maximum speed of only 58 mph, the 36.6-mile section from A5 junctipn to the A534 Sandbach turn-off was covered at an average speed of 51.2 mph. Over most of this part of the route a steady 55 mph was maintained on the clock—corrected this was in fact 52-53 mph. At this speed the Gardner was turning over at a leisurely 1,750 rpm, 100 rpm below its maximum. A check at the end of the run showed a fuel consumption figure of 11.1 mpg.
On this section the vehicle proved a bit on the noisy side. Fodens ought to do a little more to insulate the scuttle assembly in its glass-reinforced plastics cab for it was through here that most of the noise seemed to be coming. Where the bonnet is covered by a quilted plastics cover the noise is adequately damped but the scuttle acts as a very efficient sound box which should not be too difficult to insulate. The Gardner throttle control is notoriously heavy and requires quite Some ingenuity on the part of vehicle designers in order to achieve an acceptable pedttl pressure. It is not unusual to have to apply a first pedal-pressure of some 40Ib to accelerate the engine and thereafter a pOssure of 201b to hold the revs constant. As Gardner-engined vehicles go, the Foden was good from this point of view, the pedal not being over-heavy in operation.
An operational trial was carried out from a sand quarry at Sandiway, Cheshire, where the vehicle was loaded with 17 tons 12cwt 2qr of washed, sharp sand. Spotting under the digger presented no problems and this was one function that highlighted the ease of steering on soft ground. I left the pit at 11.13 a.m. to cover a route along A556 towards Knutsford onto B5082 via Lach Dennis and then the B5081 via Peover. We joined A50 back to Knutsford thence onto A5033, rejoining A556 and returning to Sandiway. The total distance covered was 29.3 miles and the time taken was precisely one hour. Spotting the vehicle for tipping took one minute, unpinning the tailboard 35sec and tipping the body 28sec. The load shot clean once the vehicle was moved forwards a few feet, only a small amount of wet sand sticking to the alloy floor of the Craven Hum alloy body. When it came to closing the body after tipping I would have appreciated some form of hand grip on the tail-gate which needed a slam to close it sufficiently to allow the locking pin to be pushed home. Even though it was made of light alloy, the tail-gate was quite heavy and difficult to grab hold of without trapping one's fingers between it and the body. The fuel consumption for the operational trial including tipping and spotting at loading and tipping points, plus negotiating 0.75 miles of unmade road, worked out at 9.8 mpg.
Unladen. the Foden proved to have rather hard suspension, and I considered that a vast improvement would result for the driver by fitting a suspension seat. Fuel consumption checked over a 13.8-mile route from Sandiway to Sandbach with the vehicle unladen was 14.8 mpg at an average speed of 33.4 mph.
After reloading the vehicle we took it back to Sandiway pit to see how it behaved in soft ground. As I had expected, it had sufficient traction to overcome normal soft ground through which it plodded with no signs of ever being stopped.
But when we had gone only 100 yd into some sharp sand, suddenly the rear wheels jumped twice and disappeared almost down to the hubs. I had been warned that this would happen, sharp sand acting, it appears, rather like marbles and just rolling one granule over the other and providing no traction at all.
We found out just how difficult the ground I had tried to negotiate was when a loading shovel mounted on huge sand tyres came to tow us out. Even with its four-wheel drive and hydrostatic transmission it spun first one wheel and then the other until it was obvious that we could not be moved.
By tipping the load and indulging in a lot more shovel work than I would ever volunteer to do, we got clear in a total time of 2hr 20min.
I think Fodens' test driver Tom Bowyer best summed up my own impression of the vehicle when he said: .!'Given a reasonably intelligent driver this truck should be a money spinner."
As tested, the Foden costs £7,892.