THE RENOWN ON AN EXACTING COURSE
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Road Test No. 100.
Our One Hundredth Road-test Report Deals With the A.E.C. Renown Sixwheeled Passenger-carrying Chassis : A High Degree of Comfort Afforded by a Model which Possesses Distinc tive Performance Characteristics
AT one time six-wheelers achieved a considerable measure of popularity for passenger services; then followed a temporary reaction. Now, after vast improvements, the type is becoming a feature of many transport undertakings. For example, there are some 1,400 vehicles of the Renown class at work in London; they are, of course, products of the Associated Equipment Co., Ltd., Southall, Middlesex.
It is indeed appropriate that this, our one hundredth road-test report, should concern so outstanding a model, which is typical of the latest practice in chassis construction. The principal features of the Renown chassis are the 120 b.h.p. engine driving through a single-plate 3a28 clutch to a four-forward-speed gearbox—with a silent "third "—the power thence being conveyed to the two live axles of the bogie, a longitudinal differential being used between the axles. This type of chassis is made in two mean-wheelbase lengths, 16 ft. 6 ins. and 18 ft. 7 ins.; this test relates to the latter.
The actual chassis handed over to us was brand new and, in consequence, somewhat stiffer in operation than the average. The test platform carried large weights which corresponded to 66 passengers and a normal type of double-saloon body. Actually, this model is used to carry from 60 to 72 passengers, or 35 in a single-deck body. In all cases the gross weight with a normal body is below the M. of T. limits.
For our test we loaded the chassis to within 11 cwt. of the 12-ton limit and regarded the number of passengers as midway between the figures specified; 66 is the number popularly carried by a Renown when fully laden. Detailed weights are given in the accompanying panel.
Trials of the braking abilities were the first specific item. For normal purposes the servo-operated six-wheel brakes amply suffice, and the effort demanded of the driver is trifling—an important matter in urban service. So smooth is the retardation that the casual observer is apt to think that the stopping distances are long ; use of the tape shows that the figures are pleasingly low—in fact, not so great as those of many four-wheeled doubledeckers carrying 15 fewer persons. For instance, the bus can stop, from 35 m.p.h., in little over twice its length.
The hand brake, affecting the wheels of the bogie, is of generous power and is easily released after hard application. On 1 in 8 it comfortably holds the fully laden vehicle. Individual or master adjustments are easily effected and there is no fear of "slacking back."
On the other hand the acceleration from rest through the gears, or on the direct drive, is pleasingly rapid for the class of vehicle. Bearing in mind that the engine had covered less than 100 miles, its performance in this respect was gratifying. Details of these tests can be gathered from an accompanying graph.
As regards gear changes, these can be carried out quickly and quietly when the clutch stop is set to the driver's taste—a matter of a moment. The example tested, being new, was rather stiffer to operate than a service vehicle, but it responded to conventional methods of double-declutching. All the controls are well placed and call for the minimum amount of effort. Automatic regulation of the firing point relieves the driver of the bulk of the work in this connection.
A.D.C. worm-and-nut steering is employed on the latest models ; it functions with consistent ease and the amount of castor action is well suited to double-decker work.
In these days bus routes are
schemed to cover really hilly districts, therefore we decided to include a round of steep ascents in our general running, also in the route covered while on fuel-consumption trials. With the 6.75-to-1 final drive ratio, the chassis was capable of starting on a slope of 1 in 6. As either of two lower ratios can be supplied the vehicle is capable of working under the worst conditions that a double-decker could be
operated. The clutch stop allows a change-up after restart on first gear ; normally second gear suffices for getting away from rest. The overall ratios suit the engine, which has a useful speed range from 300 r.p.m. to 3,000 r.p.m.
Considerable thought has been devoted to the question of cooling; the normal temperature of the water is about 168 degrees F., whilst the Still-tubed radiator dissipates heat so rapidly that a 1-mile climb on the indirect gears raises the temperature by a mere 17 degrees F. Thus the engine is kept up to a pleasant and economical heat under usual conditions, but strenuous work causes no risk of boiling.
During the ascent of Brockley Hill we covered .8 mile (.5 on third gear, .1 on second and .2 on first gear) at 11.2 m.pib,.—a high speed for a 12-ton machine — on an average gradient of 1 in 11, with a steepest pitch of 1 in 9. Other severe hills were Cocks Hill, near Barnet (1 in 6), Stanmore Hill (1 in 12, length 1,116 yds.) and many shorter stretches of 1 in 10.
Fuel consumption was measured on two bases. First the chassis was driven over an up-and-down course with three stops per mile ; these were of varying duration, in order to simulate bus work. The returns were 4.4 miles and 4.9 miles, each on a measured gallon of spirit.
Later, the vehicle was run in suburban traffic as an express coach or bus—still, of course, carrying the full load. The returns in this case were 5.9 miles and 6.4 miles, again on separate measured gallons of commercial petrol. In both cases, as can be seen by a study of the data panel, the average speeds were those which would be expected under service conditions.
The particular chassis, being of 18 ft. 7 ins, wheelbase, is designed to have a turning circle of 66 ft. diameter, thus complying with the Conditions of Fitness Regulations. We found that the left circle was actually less than the required amount by 2 ft. 8 ins., but the right lock required setting as the circle was 3 ft. 5 ins, too great. There was ample tyre clear
ance at both sides and the desired result could have been obtained by setting the stops— the chassis had not been through the final test shop.
Turning now to the question of comfort as considered from the pas sengers' viewpoint. The principle of the six-wheeler halves the vertical rise at the rear end, due to passing over any hump or hollow, but the extra wide frame which can be used, owing to the employment of single tyres and springs directly below the frame channels, tells its story unmistakably in the direction of unusually good stability when cornering at high speeds. The Renown shows no tendency to sway, and this must decrease the risk of sideslip.
The spreading of the• gross weight over three axles, and in almost even amount, means that the axle weight is 10 cwt. below the limit, even with a full load and the full complement of standing passengers.
The results of the braking tests, coupled with the smoothness of restarting on steep hills, shows that the special torque blade between the live axles is fulfilling with efficiency its function. The design in this respect is unique and simple from the maintenance point of view ; it involves the minimum number of bearing surfaces. Both the overhead-camshaft engine and the "silent third" ,gearbox operate quietly ; on third gear the most prominent sound is the " rush" of exhaust gases from the tail pipe. From the point of view of the public this matter is of the ut most importance; after the clanging of a tram. the silent passage of a Renown is a pleasing contrast.
Two other features are vvorthy of special comment. The brake facings are no less than in. thick, so that renewals should be infrequent— which means economy of maintenance. The placing of the reversed camber springs below the frame channels gives a low loading line (21 ins, at the centre and 11 ins. at the platform) and minimizes the frame kick-up.
In brieT the A.E.C. Renown is a model of the moment and one which is bound to prove an important factor in passenger-carrying problems of the future. Its performance, as revealed by our comprehensive test, yustifies its cognomen.