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Readers Look at Future Design

9th January 1959, Page 70
9th January 1959
Page 70
Page 73
Page 70, 9th January 1959 — Readers Look at Future Design
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Which of the following most accurately describes the problem?

I WRITE to congratulate the technical editor, John Moon, on his most interesting article on the trunk road vehicle of the future. I am prepared to accept almost all his ideas with little or no reservation. Also, I am delighted to find that he supports my advocacy of air cooling for such vehicles. However, I rlIUSt question his choice of the two-stroke cycle.

It is, of course, unarguable that a two-stroke engine develops more power for its size than a four-stroke, but by the same token, it produces more heat. I hesitate to suggest that it would be impossible to disperse the. extra heat, but it presents a substantial problem.

Assuming that this dispersal is feasible it will call for the fitting of larger fins, and as fin diameter determines the overall length of an air-cooled engine the high-power two-stroke tends to lose its size advantage relative to the four-stroke of equivalent power.

The cooling of large air-cooled two-strokes is further complicated by the fact that the lower part of each cylinder barrel has to accommodate at least one port, so that it is impossible for uniform finning to be continued throughout the length of the barrel.

Fortunately, judging by Lofthouse's excellent drawings— which also call for congratulations—there is ample room -for a four-stroke engine in the position chosen by Mr. Moon.

Stutton, nr. Ipswich. E. N. FARRAR.

IT was with great interest that I read the article "A I Vehicle for Motorways" in the December 12 issue of The Commercial Motor. However, I would have placed the appearance of a vehicle such as that envisaged by your technical editor in the more immediate future than the next 15 or 20 years. For such a long-term view, I think the following considerations would have more weight.

It is interesting to reflect that the road-holding of cars in general was immensely improved when designers discarded the concept of an open-section chassiswith stiff springs in favour of torsionally rigid chassis (or integral chassis-body structures) and comparatively soft springing.

Up to the present, heavy commercial vehicles, using, as they do, a basically constant-rate suspension and having to keep the difference between laden and unladen heights within practical limits whilst coping with vast variations of load, have been unable to employ a sufficiently low-rate and long-travel suspension to accommodate ground-surface irregularities without considerable torsional flexure of the chassis.

With the advent, however, of practicable variable-rate suspension systems the chassis may be made as torsionally rigid as possible, and the suspension may be left to tackle the "lumps and bumps" by itself. Another advantage of long-travel suspensions on multi-wheelers is that balance beams between the front and rear axles of bogies could be dispensed with without the risk of overloading one axle or the other on uneven ground. This would obviate the phenomenon where bogies are continually bouncing from one axle to the other when travelling at speed.

The springing medium could be rubber, air, or even oil (as used in some aircraft undercarriages). The last might fit conveniently into the hydraulic power system.

How about employing independent suspension, particularly at the front? Correctly designed, this would reduce wheel shimmy and improve stability and road-holding.

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Independent suspension at the rear could result in a useful increase in stability and reduction of unsprung weight. However, the mechanical complexity .would be great and any suspension geometry involving a varying camber angle might have some odd effects with twin-tyred rear .wheels.

Perhaps an assembly of (light alloy?) castings could be used, consisting of a • rear-mounted engine, gearbox, and differentials, with a suspension Similar to that of the Skoda dump truck, using single-tyred wheels. All moving parts could be served by a common lubrication system. Part of the assembly could take structural loads, Skoda-fashion, to reduce weight.

The use of a considerably smaller overall wheel diameter than the current fashion dictates would bring attendant advantages in the reduction of unsprung weight, of undesirable gyroscopic effects on the front wheels and a possible reduction of tyre running costs. It would also permit a lower platform height, which would lower the centre of gravity of the laden vehicle, thus improving stability. Whether the advantages of a lower platform height would offset the inconvenience of its being non-standard would, of course, depend on the type of operation in which the vehicle would be engaged.

To sum up, I would say that if the high-speed potential of the motorways is to be effectively and safely realized, the road-holding and braking of heavy vehicles are features that will need the most careful attention. I believe that the development of brakes is proceeding along satisfactory lines, but I would like to see a little more initiative in chassis and suspension design.

• Hatfield, Herts. C. BATTEN.

[One of the principal objects in mind when formulating the design of this-vehicle was to keep the cost low, and this was why as simple a suspension system as possible was employed. Independent suspension at the front bogie of an eight-wheeler would be somewhat complicated, particularly, with the use of rubber, air or hydraulie suspension, and certainly cost would rule out its employment at the rear bogie.

Similarly, a conventional engine location was adopted so that a more or less 'Standard unit could be employed, and, of course, with the tilt cab as drawn, engine accessibility would be considerably better than would be possible with a rear-mounted unit. In any event, it would be difficult to mount the engine at the rear of the chassis if, as Mr. Batten suggests, smaller wheels were employed.—En.]

I READ with interest the most stimulating artiele in your

issue of December 12, covering the design of a vehicle for the motorways, but I do question whether your technically-minded readers would approve of a future design which has so much unsprung axle weight. One can only conclude that the use of I.R.S. and I.F.S. produces insufficient dividends, especially having regard to the running surface on the motorway and the moderate average speeds to offset the cost, weight and extra maintenance.

Even if this position be accepted, I cannot understand why worm-driven axles have been incorporated in the design. Surely, for a motorway, with its limited gradients, a single driving axle would be all that is required? The percentage of time that double driving axles are essential in a year in southern England is small indeed, and, as you so rightly say, double drive with a third differential has no great advantage for winter conditions—it merely allows for even tyre wear.

On the other hand, the troubles we have had in practice (Continued on page 817)

with double driven axles without a third differential at moderate speeds are considerable, and at motorway speeds would result in very rapid tyre wear, or, alternatively, abnormal axle wear. In any case a double-reduction axle with the first reduction spiral or hypoid and the second helical or straight spur, would provide the capacity to deal with the torque at starting and slogging speeds, and the frictionless running so necessary at higher speeds. I am sure I can safely predict that worm axles will be as dead on the new heavies in 10 years as they are now on the modern so-called light vehicles—and for exactly the same

reasons. R. W. AMEY,

Oxford. Director, Amey's Transport (Oxford), Ltd.

Accessibility from a Fitter's Viewpoint

FROM the paragraph "Off the Beam" under "Bird's Eye

View" in The Commercial Motor dated December 5, it seems that "The Hawk" wishes to improve his knowledge regarding the inaccessibility of the components on some commercial vehicles.

The place to learn of such things is a maintenance shop. There he could question any litter, or even listen to a man trying to reach a part that is hidden from sight and can be touched only if he had fingers a foot long.

As a vehicle fitter I worked on more p.s.v. models than goods vehicles, so that my remarks may not apply to the latter. The modern slab front makes any simple job difficult and on some types the engine can be reached only by climbing in with it. Brake-shoe springs are usually out of sight and require two men and a" hook-up" to remove and refit. To remove the shoes often requires the removal

of the hub. Then there are the dozens of nuts that would seem to require rubber ring spanners, and the trapdoors in bodies which are too small or in the wrong places. One thing in particular strikes me, that is the more modern the design the more difficult it is to work on and the longer it takes to do a job. Perhaps it is all the extra fancy bits that add to the difficulty.

If any designer writes to you to say that he knows modern vehicles require working on less often, he should talk to a few vehicle fitters to see what they think. In my view many designers are "crackers," and do not have much idea of what happens to their brain children once these are on the road.

Grimsby. C. S. BETTINSON.

A Scottish Peck at "The Hawk" I HAVE to take The Hawk" to task for his flippant reply to the reasonable request of Robt. Walling, motoring correspondent of the Evening Standard, when he asked: What impact force would result if a 14 tons gross vehicle hit a halted vehicle at a speed of 70 m.p.h." Although a little weak in mathematics, I would say that it would approximate that of a large, plush car doing 110 m.p.h. In any case the end is the same and a butcher's mincing machine could do the job equally as well, whilst keeping the residue in a tidy heap. Arsenic in the comfort of one's own home would not impede following traffic.

One of life's maxims is not to cross your bridges until you come to them, there might be no bridge to cross. Let's not start a vehicle class war on the motorways, but Work together for safety and speed.

Glasgow. A.R.W.

Tags

Organisations: I.R.S.
People: Batten, John Moon
Locations: Glasgow, Oxford

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