Co-ordinating W.D. and Civilian Requirements in Six-wheelers.
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wE are convinced that the action of the War Department in extending its subsidy scheme to include medium-type six-wheelers which for W.D. work have to carry 3 tons on the road and 2 tons across country, will be a great stimulus to the employment of this most practicable form of vehicle for civilian transport, The War Department is to be congratulated upon having in the Royal Army Service Corps highly trained officers with perspicuity and a full knowledge both of civilian and army requirements. This knowledge is displayed in the fact that the subsidy is to be given for vehicles which, owing to the generous nature of the specification, can be designed to carry 4-ton, or possibly even 5-ton, loads when employed on good roads and in ordinary civilian transport.
We believe that everything possible should be done to encourage the rigid-frame six-wheeler, particularly for the carriage of heavy loads. It renders possible the extended use of pneumatic tyre's, and thus increases the maximum speed at which a vehicle can be run without undue vibration and damage to the road surfaces and foundations. As a result of this, the extent to which property adjacent to the highways is liable to be damaged by the Vibration transmitted from the roads will certainly be diminished, if not rendered altogether negligible. In addition, the vehicles themselves can, owing to the much better suspension afforded by the multi-wheeler, be built comparatively lightly, and the goods they carry are not nearly so liable to damage.
We have on many occasions enumerated the chief advantages of a well-designed multiwheeler. Experience with those already on the road has proved that, load for load, the wear on tyres is far less, owing to the obviating of wheelspin and the way in which the wheels can follow road inequalities in types such as that advocated by the W.D. specification.
The principal feature in this type is the manner in which equal loading of the driving wheels is ensured by the provision of torque rods conveying the drive from each axle direct to the chassis frame instead of entirely through the spring fulcrums of the bogie, although, even here, the War Department is quite open to consider other designs provided that they embody this property to the same satisfactory degree as has already proved practicable in the W.D. patented arrangement.
It always appears to us to be a mistake to lay down arbitrary rules which are apt to stultify the efforts of designers, thereby limiting progress, and we are pleased to note that this has not been done in the new specification. Even engine sizes have not been stated, it having been thought essential only to stipulate the performance expected and to leave manufacturers free to obtain this.
It is noteworthy also that the War Department retains to itself the right to test the capabilities of any new make or type of vehicle offered to it under the useful load for which it is offered for sale commercially. This is, in our opinion, an important safeguard for the user.
Scotland Yard and the Six-wheeled Bus.
THE news was given in the issue of this journal for April 26th that the London General Omnibps Co. was far advanced in the production of a six-wheeled bus for submission to the Public Carriage Department of Scotland Yard. We were able to forecast the specification of the vehicle and to disclose the interesting fact that it will include three differential gears—one to each axle of the rear bogie and one between the two axles—so that at no time can the whole of the torque on the transmission fall upon one axle alone. On Wednesday last the Public Carriage Department reached its decision upon the application of one of the leading commercial motor manufacturers for the approval, as a type, of its six-wheeled bus which has already been adopted in five provincial cities and towns, and has given satisfaction to the concerns operating it and to the public who use it.
The investigations conducted and the tests carried out by Scotland Yard upon the chassis submitted to it have been extremely thorough, and on Wednesday the type was approved and permission given for a small number of the vehicles to be constructed and sold for service in London. Each individual vehicle will, of course, have to be submitted for inspection and test to ensure that it conforms to the approved type and is in a condition suitable for service on the streets.
One bus-operating company has already opened negotiations for the purchase of some of the vehicles which will be built in accordance with the authorization of Scotland Yard, so that this summer will see six-wheelers operating in London on pneumatic tyres, and if the development of the use of the type be found to be desirable—that is, if the revenue from the larger-capacity bus be found sufficient to justify the high capital outlay —advantage to the travelling public, to the owners and tenants of property adjacent to the highway and to other road users must follow. Buses seating 68 passengers will carry over 30 per 'cent. more than the four-wheeled type, so that for a given volume of traffic the number of vehicles required can be 25 per cent. less if six-wheeled vehicles are used.
The Effects of Overloading and Overspeeding.
FF1WO of the greatest evils which militate against -Ithe efficient employment of commercial motor vehicles are overloading and overspeeding.
The former may perhaps be considered the worse evil, and the results of practising it become rapidly apparent—springs flatten out or break, the chassis becomes strained at every point, and in the case of solid tyres these split and leave their bands, whilst pneumatic tyres weaken at the walls and may burst. Even overloading on one occasion only may so strain a chassis that it is never again in really good condition.
Overspeeding, on the other hand, may be looked upon as being more subtle in its effect. It is equivalent to burning the candle at both ends, but it may take some considerable time before the reason for ensuing troubles may become apparent. Overspeeding must always be looked upon from a relative point of view. Some commercial vehicles are designed to run at fairly high speeds, and whereas 30 m.p.h. might be quite permissible in one case, it is totally inadmissible in others.
Impact forces increase very quickly with speed, and the shocks resultant therefrom are apt to cause rapid wear not only on the chassis but on the body, which is quickly racked so that every part of the vehicle may chatter. Overspeeding with a vehicle designed for quite moderate speeds may actually be most dangerous_ Racing a powerful engine built for slow speeds, and perhaps with a lubricating system not designed for very high-bearing pressures, may cause seizure, whilst the bursting of flywheels is by no means uncommon. Propeller shafts with fabric joints may not be perfectly true, or may whip under the effects of centrifugal force, and instances have occurred where these have pulled out, one end dropping on the road, and if this be the front end it may constitute a dangerous form of sprag.
Some well-known makers have adopted the practice of governing engine speeds to reasonable figures ; for instance, the new 4-tonner we describe in this issue is, in the normal model, governed to a road speed of 20 m.p.h., and in the case of the Colonial model to 161 m.p.h. Such speeds are quite sufficient for a vehicle of this capacity, and should never be exceeded, although even in the instances quoted the power units are designed for comparatively high-speed work.
Quite apart from the deleterious effect on the vehicle, high speeds have a very bad effect on the road, although this is not so appreciable when pneumatic tyres are employed. After all, excess Is never good ; moderation in everything is the only wise policy.