LEAVI [HE NOISE BEHIND
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T°WARDS the front of the Foden rear-engined coach the noise of the power unit is practically inaudible to the passenger, and it is only at the rearmost seats that the combination of supercharger whine and exhaust note can be heard at anything like normal level. Because of the concentration of power and transmission units behind the axle, it is difficult to arrange the exhaust system without introducing a trans_ verse silencer pipe at the rear, and most of the noise at present can be attributed to reflected exhaust note. This is particularly noticeable in towns, where the sound is reflected by buildings, or in narrow byways with hedges. In open country the noise level in all parts of the body is considerably lower than with a forwardor amidship
mounted power unit. .
Rear-engined passenger chassis are no longer novel, but few manufacturers can boast of fitting the power unit" in this position without encroaching on passenger space or sacrificing accessibility. Both these details have been observed in the Foden, which has the engine slung low in the frame, and arranged transversely in the chassis to occupy less space and have all units exposed readily for maintenance at the rear.
The spiral-bevel drive between the clutch and gearbox is preferable to the arrangement of some other models of this type, and as the radiator is mounted behind the clutch housing the design includes a fan -operated from the clutch output shaft. The gearbox • is secured approximately at right angles to the crankshaft and projects down towards the underslung worm-drive of the axle to neutralize the angle of the propeller-shaft couplings when the vehicle is loaded.
The fuel pump, injectors and dynamo are arranged at the rear for easy servicing, and the exhaust manifold sweeps down below frame level to discharge the gases into a transversely mounted expansion chamber and then into a short silencer. Developments are now in prngress to incorporate an improved silencer, and for the tailpipe to project alongside the frame at the rear. This model is also available with a Gardner 6LW unit, carried transversely at the real, but when the two-stroke engine is fitted the Supercharger draws its air supply through a Tallow air fitter.
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With the 32-gallon fuel tank suspended at the 'rear overhang, between the -• offside wheels -and radiator, and.the battery carried amidships in the chassis, there is ample luggage space between the wheels on both sides of the frame, thus there is no loss of capacity due to the engine occupying the normal boot accommodation at the rear.
The Foden hydraulic braking system, with twoleading-shoe operation in both directions, has the ' pump driven from the front of the engine crankshaft, and' fluid under pressure is supplied to the booster mounted externally on the frame, adjacent to the power unit. There is a mechanical linkage between the brake pedal and booster. The variable-leverage hand brake occupies a position to the near side of the driving seat, with the lever in the horizontal position. The lever is connected to a conventional relay of rods and by a chain which engages on an eccentrically mounted sprocket, so that the initial free movement is taken up rapidly and the subsequent effective travel is assisted by the sprocket passing " Over. centre."
• Like other Foden passenger chassis, the rear-engined model has a cruciform bracing at the centre of the frame, but the rear overhang is upswept by ins, to provide clearance under the engine. Beyond the front axle the depth of the side rails is decreased by 2i ins., thus providing a frame height, when loaded, of 2 ft. 5f ins, for a front-entrance bus. When 10.00 by 20-in. tyres are used, the frame height is increased by 1 in. The spare wheel is carried below the front overhang and is equipped with a built-in winch for easy handling.
When I arrived at the Foden works in Sandbach for the test there were three chassis at my disposal, including one with a Metalcraft 41-seater body, which had been loaned by Hollinsheads, of Scholar Green, To get a clear picture of the advantages of the rear engine it is preferable to ride in a complete vehicle, where the difference in noise level can be best appreciated.
The coach was loaded with 36 bags of gravel, each weighing 10 stone, which were placed between all seats except at the engine bay. As the complete vehicle was not equipped with a super-low ratio to the gearbox it would have been unwise to tackle Mow Cop so, after the weighing procedure, the coach was headed towards .Congleton and the Pennines Without a human payload, but with the off-side driving window open. the note of the Foden two-stroke c5
engine exhaust could be heard in the front seats, but it is conceivable that under operating conditions, with passengers on board and all windows closed, the driver might not discern the engine note above the normal undercurrent of conversation.
The Foden engine is remarkably free from vibration and its smoothest range is between 1,050 to 1,700 r.p.m., corresponding to a road speed of 25-40 m.p.h. Above this speed, the general tone encroaches on a -" sports roar" which, although liked by the drivers, might not be so well appreciated by all passengers. I would not care to say all the answers have been found in insulating the general engine-noise level, but the Foden is definitely one of the quietest rear-engined models having a compression-ignition unit that I have yet travelled in. To the passengers occupying the rear seats there can be no doubt that the engine is behind the axle, but with a pressurized engine compartment, sound-deadening material fining the surrounding panels, and a heavier insulation baffle between the engine and body, the Foden could be the nearest approach to the quietness of trolleybus travel.
Fast Climbing Congleton, with a double turn in the main street, is a test of manceuvrability, and it was only because of a slight misjudgment that one rear wheel climbed the kerb at the first corner. Soon after leaving the town, we crossed the main North road, and started climbing Dumbers Hill. The Foden soared up the incline, and by making early gear changes, we scaled the first 1-in-8 section in the second ratio. After flattening out to 1 in 12 for 200 yards, the gradient again stiffened, and here low gear was required for 3i minutes.
Altogether the first and second gears were in use for about 10 minutes, but the radiator water temperature kept within 100 degrees F. of ambient, which at the top of the Pennine Range was 49 degrees F. This indicates there was ample air flow through the tube stack. When bodying a rear-engined model, close collaboration is c6 required by the bodybuilder, because adequate louvring is essential to obviate restriction of air flow to the radiator.
A swift run back to Sandbach proved the suspension well suited to most requirements, and travel in all parts of the body was indeed smooth. In addition to doubleacting shock absorbers at all wheels, the Foden has a " double-decker " safety clip at the main spring eyes, and vernier adjustment of the suspension can be obtained by the tension on the clips.
Weight Distribution Because of the ratio of weight distribution between axles, the suspension and steering are little affected by the rear position of the engine, but with the recirculatory ball steering, the manual effort is light in any case. The Foden PVRF proved extraordinarily safe for fast cornering on dry roads, and even with abuse there was only a slight tyre squeal, and no tendency to roll.
Consumption trials were made starting from the works, because, at present, the Foden rear-engined model is not equipped with means for distance recording, so the test had to be made over a course of known distance. The first run of 34.2 miles represented a normal coach coastal service, and included town driving in Middlewich, Northwich, Knutsford and Holmes Chapel, with a total of 12 stops in the circuit. The Foden cruised along at a steady 35-38 m.p.h. without fuss, and at this speed the passengers occupying the rear seats would be aware of only a quiet hum coming from the engine compartment. I sat in the centre, and later at the front of the coach, and there was practically no noise to be heard from the power unit or exhaust.
The average speed for this trial worked out to 28.1 m.p.h. and the quantity of fuel used weighed 20 lb. 11 oz., corresponding to precisely 2i gallons. This gives a consumption rate of 12.2 m.p.g. which is indeed satisfactory for a vehicle tested complete with body, and making on average, a stop every three miles.
Then followed an inter-urban trial, with one stop per mile, over a shorter circuit through Middlewich. and with a turning point in Holmes Chapel. The axle ratio was well suited for the stage-carriage work and besides operating a fast schedule, the fuel consumption rate was very little more than for the first trial. Ignoring the 1-minute stops, and counting only the time the wheels were revolving, the average speed was 28.5 m p.h., and the fuel consumption rate 11.97 m pg. The favourable consumption rate may have been influenced by local conditions because, apart from a slight hill in and out of Middlewich, the course was relatively level.
I selected the Foden-engined chassis for the braking tests, because it would not be fair to risk damaging the
tyres on the coach loaned by an operator. There is a good level road running through the Foden works, with a stretch of concrete midway, which is ideal for optimum braking tests. I was not prepared for such effective retardation in the first emergency application on The pedal from 30 m.p.h., and after being catapulted from my seat on to one of the heavy iron castings, I finished up sharply against the temporary driving cab. There can be nothing lacking in the Foden braking system for the vehicle to stop in 47 ft., measured by the pistol method, from 30 m.p.h. The maximum Tapley reading recorded during a series of trials was 76 per cent. Hand-brake tests proved the link up between the lever and wheels to be extremely powerful, and both rear wheels were locked with the chassis loaded to full capacity The Tapley meter indicated 42 per cent, for the hand-brake performance, and by the stop-watch the distance was 36 ft. from 20 m.p.h.
I used the same stretch of road for the acceleration test; incidentally, there would be a slight difference in performance between the coach and chassis, because the latter was equipped with 10.00 by 20-in. tyres, but the variation being of such negligible proportions, no compensation has been made in the data panel.
The driver of the Foden two-stroke-engined chassis soon realizes that the best performance is obtained by keeping up the engine revolutions, the maximum torque of 350 lb.-ft. being at 1,500 r.p.m., therefore, he is not likely to try accelerating from 10 m.p.h. in top gear. Because of this, I ignored the customary top-gear acceleration, and made trials starting with the normal first gear engaged, and passing through the second and third ratios to reach 30 m.p.h. With this technique it took 13.8 seconds to reach 20 m.p.h., and 32.3 seconds to 30 m.p.h.
As the chassis was equipped with a super-low gear, and the trials progressed so smoothly that there was time to spare, I decided to make an assault on the famous Mow Cop. Driving to the foot of the hill I found difficulty in making faultless gear changes because of the initial stiffness of the gear shift. Possibly the automatic lubrication system had not had sufficient use to charge the relay bearings, because there was no indication of stiffness to the coach which had covered under 2,000 miles.
Over Mow Cop The squeaks and thuds of the movement between the temporary cab and the chassis frame, by far exceeded any noise from the engine, and my performance on the chassis was not impressive. I was not unwilling to pass over driving to the works representative who appeared less concerned with the noise, and more accustomed to snicking the gear lever into the neutral position with just the right amount of pressure.
The Foden literally roared up Mow Cop, and superlow was brought into play as we approached the Railway Inn, where the grade is 1 in 3.8. A great cloud of dust was swept up by the exhaust, because not many vehicles venture the climb, and the top dressing of the road is fairly loose. Viewed from the rear, it must have been spectacular to see the Foden disappear over the crest of the hill. with one side of the road practically obliterated by the dust screen.
Reversing down to the Inn, the hand brake was again proved efficient by holding the chassis, loaded to 10 tons 12 cwt, stationary, and full points were awarded when the driver engaged gear and accelerated the vehicle up the hill without letting the wheels roll back an inch.
After turning, the descent was made in quick time, the brakes being in constant use because the retarding force of a two-stroke engine during overrunning is less than the conventional four-cycle unit. Such treatment found no weakness in the Foden brakes, and an emergency application at the level crossing produced a Tapley reading of 65 per cent.
In the heavier oil-engined passenger range, the Foch:it rear-engined vehicle undoubtedly sets a new standard for smooth and quiet running.