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SILENT SPEED

11th August 1950, Page 34
11th August 1950
Page 34
Page 35
Page 36
Page 34, 11th August 1950 — SILENT SPEED
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Which of the following most accurately describes the problem?

By L. J. COTTON,, m.i.R.T.E.

BEARING the characteristics of its namesake, the Leyland Royal Tiger is quick off the mark, glides in motioh and, with the addition of the Aphonic injector, is almost noiseless. Its smoothness was exemplified during the full-consumption trials which I carried out, when some spanners, inadvertently left perched on a frame outrigger. bracket, remained there. during a seven-mile run.

With the co-operation of Leyland Motors, Ltd., I tested one of the first Royal Tiger production models conforming to the revised home regulations.for length and width. So that I could compare engine noise, I was' also provided with a similar vehicle

equipped with the former standard high-pressure injectors.

Driving each vehicle in turn, I required no noise-measuring apparatus to determine which was the quieter operating unit. The Aphonic injector is effective in ironing out all Vibration, and reducing noise, with

out being expensive in fuel. Repeated efforts to produce a smoky exhaust, under all conditions of engine speed and load, failed completely.

The Royal Tiger P.S.U.1/13, as the single-deck bus I tested is designated, is one of a new range of 16 "tailor made" underfloor engined passenger chassis, built for both home and overseas requirements. The range was first described in "The Commercial Motor" on April 28. The P.S.U.1/13, which is a home model, has a frame 30 ft. long with 15-ft. 7-in, wheelbase, and

is 8 ft. wide. It has a front overhang of 6 ft. 5 ins., and the length of frame behind the rear axle is 7 ft. 7 ins.

Three Entrance Positions A feature of the Leyland range of flat-engined models is that the batteries, spare wheel and fuel tank can be arranged to suit bodies with forward, central or rear entrances. In the chassis tested, these components were carried on the, rear overhang, so that a forward or central entrance could be used.

The Leyland 9.8-litre 0.600 directinjection oil engine is installed amidships in the frame, with the Cylinders projecting towards the crown of the road and the crankshaft in line with the spiral-bevel drive of the rear axle. Both cylinder heads and manifolds are outside the frame side members, which is advantageous when servicing injectors, adjusting valve clearances or replacing cylinder heads complete. An interesting feature of the induction system is that the air supply is drawn through the cleaner and passed through a boxed-in outrigger bracket before being delivered to the manifold. This is an effective and inexpensive method of reducing induction noise.

The fuel-injection pump is attached to the engine sump and can be removed conveniently from the near side of the frame, or through a floor trap, which would normally be provided in the body. An electric remote control operates a solenoid controlling the fuel-pump rack to stop the engine. This arrangement also resets the rack in readiness for the next start.

Fan Closely Shrouded

Operating in a close-fitting shroud and rotating at 1 times engine speed, the fan shares a common jackshaft drive from the front of the engine. The radiator, which has no header tank, is arranged below frame level immediately behind the front axle.

As in the Leyland-M.C.W. Olympic integral-construction bus, to which the Royal Tiger is complementary, the engine, clutch and gearbox are of unit construction, flexibly mounted at the rear and supported forward on a rubber-bonded bush. Helical gearing is used for the fourspeed gearbox, the three higher ratios being in constant mesh and engaged through synchromesh arrangements. A Hardy Spicer mechanically jointed shaft is used between the gearbox and spiral-bevel drive of the rear axle.

The test vehicle had the Clayton Dewandre triple-servo system of braking, with an engine-driven exhauster operating in conjunction with a large-capacity reservoir mounted on the frame side member.

Like the Olympic, the Royal Tiger has a divided track rod, the push-pull rod from the steering drop arm being connected to a bell-crank lever pivoted on the axle beam. The bell crank in turn takes -effect at stub axles through the rods. This steering linkage lightens controls and improves steering accuracy.

The axles are attached to the frame by semi-elliptic springs, which are secured through Leyla hdMetalastik rubber-bonded shackle pins to absorb rotary movement between the pin and spring eye.

Except for a slight sweep over the rear axle. the frame assembly is level

and fitted with outrigger brackets, so the body can be built directly on the frame without need for packing. Equipped with 10.00 by 20-in, lowpressure tyres, the frame of a chassis for a front-entrance body is, when unladen, 3 ft. 11 ins, above ground level and the centre of the frame is about an inch higher.

Five tons of castings were carried during my test to represent a bus body and a full complement of passengers. This weight possibly erred on the generous side. After an initial run with this chassis, to demonstrate the value of the Aphonic injector, the vehicle equipped with high-pressure injectors was dispatched back to Leyland while I continued with the performance tests.

Sheep Hill and Whittle Hill were climbed comfortably in the indirect ratios, and I tested for incomplete combustion by making numerous stops and pulling away from rest with full throttle at low revolutions and at the top end of the governed range. There was not a trace of unburned fuel to be found in the exhaust, and a puff of blue lubricating-oil haze was visible only after prolonged idling.

When driving the Royal Tiger, I was at first conscious_ of the additional 12-in, front overhang, when compared with the Olympic, which was subject to Road Test No. 193, reported in "The Commercial Motor" on January 27. After negotiating a few difficult corners with extreme caution, 1 had soon "tamed" the Royal Tiger. The light and accurate steering, good suspension and simple and rapid gear change inspire confidence.

Because a rain storm threatened, measured the braking efficiency at the first opportunity. The tripleservo vacuum system afforded effortless retardation that was smooth and without bounce from the suspension. The results show that the delay between the application of the pedal and the operation of the shoes was extremely brief, for a series of tests yielded an average of 26 ft. from 20 m.p.h. and 57 ft. from 30 m.p.h.

Compared with the acceleration figures obtained during the Olympic test, the Royal Tiger is at a disadvantage by 1.5 secs. from 0-30 m.p.h., when passing through the gears. The Olympic, which conformed to the former Construction and Use Regulations, was tested at 9 tons 91, cwt. gross and was

equipped with 9.00 by 20-in. tyres, whereas the Royal Tiger weighed. 10 tons 41 cwt. gross and had 10.00 by 20-in. tyres.

An analysis of the acceleration tests yielded results of 0-30 m.p.h. in 22.5 secs., and 0-40 m.p.h. in 43.7 secs. Direct-drive trials from 10-30 m.p.h. produced a time factor of 32.9 secs. The high power and high torque of the Leyland 0.600 engine are obvious from the rapid acceleration through the gears and the flexibility in direct drive.

Three Fuel Tests

The test vehicle had the standard axle ratio of 4.625 to I, but ratios of 4.111 and 5.143 to 1 are available. As the course planned for the consumption trials was reasonably favourable, I made three independent tests. The first, simulating coach service, was over an out-andreturn course of 14 miles with a stop half-way to make the turn.

After allowing for standing time, the average speed worked out to 29 m.p.h. and the consumption rate to 13.66 m.p.g. It was on the outward leg of the course that the spanners were left on the outrigger bracket. A check of the tool kit showed that no loose tools were missing.

The inter-urban service trial with one stop per mile yielded a return of 12.3 m.p.g. During this test, 35 m.p.h. was not exceeded and a 15-sec. halt was made at each point. In the local-service test the fast acceleration from rest proved that the axle ratio was correct for a normal give and course. Although town work is usually heavy on fuel, the consumption rate of 9.02 m.p.g. is far from high, and is at least proof that the Aphonic injector is not detrimental to economy.

The swept-circle measurement indicated that the Royal Tiger was well within the limits prescribed in the proposed amended regulations.

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