A BUSMAN'S DREAM F HOME
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New Midland "Red" Double-decker Shows Admirable Handling and Comfort on Test : High Standard of Hill-climbing Ability, Acceleration and Fuel Economy By John F. Moon, A.M.I.R.T.E.
FIRST-CLASS conditions for driver, conductor and passengers alike are given by the latest " home-made " double-decker—the D.9 72-seater--of the Birmingham and Midland Motor Omnibus Co., Ltd. It fully illustrates the advantages that an operator can gain by designing and constructing his own passenger vehicles.
It must surely be one of the most confidence-inspiring buses to handle in heavy traffic: even I, whose experience of driving double-deckers is limited, thoroughly enjoyed taking a laden D.9 through the heart of Birmingham in morning and evening rush-hour traffic, and none of the observers who were riding behind me seemed to have the slightest qualms about my ability to negotiate the numerous hazards successfully.
Distinctive among vehicles of this type, because of its pronounced front overhang, it is a 30 ft. by 8 ft. highbridge design with 32 seats in the lower saloon and 40 in the upper compartment., Integral construction has been adopted in the interestsof weight-saving, and this accounts for the low licensing weight of 7 tons 181 cwt. This form of construction can cause problems Of noise and vibration' in the passenger saloons, but the D.9 is as smooth
and quiet to ride in as any double-decker with separate body and chassis construction.
Since the prototype was described in The Commercial Motor on September 5, 1958, several design modifications have been carried out for incorporation in production vehicles, 195 of which are to be built. The most important change is that disc brakes are no longer used at the rear —not because of lack of efficiency, but because the discs were closely shrouded by the inner wheels and the body panels, Which caused overheating, to the detriment of
the hubs. The adoption of drum brakes at the rear has enabled the transmission hand brake to be dispensed with and the hand-brake lever actuates the rear shoes in the conventional way.
The suspension owes much to recent Sand C-type single-deckers, in that similar Metalastik rubber components are employed at front and rear. The independent front suspension, calling for anchorages for the trailing radius arms ahead of the wheels, is the primary reason for the set-back front-wheel location.
The shortened wheelbase has reduced the turning circle B24 and, possibly more important, the overhang provides engine accessibilityrivalled only by that of rear engines.
Although the layout of the front suspension is almost identical to that of Midland "Red " single-deckers, the rear system .is 'slightly different, in that the units are located in planes. parallel to the rear axle, instead of being angled, as on the single-deckers. This is partly because the near-side tear suspension assembly would encroach on the loading-Platform space if -the original layout had been adopted and partly because the designers wanted maximum roll stiffness. Longitudinal axle location has had to be provided by using trailing radius arms, as at the front wheels.
The B.M.M.O, Mk. II 10.5-litre direct-injection engine, although 'capable of producing 160 b.h.p. and 543 lb.-ft. torque, is down-rated to give 125 b.h.p. (net) at 1,700 r.p.m. and 463 lb.-ft. torque at 1,000 r.p.m. A Self Changing Gears Fluid-friction combined hydraulic coupling and centrifugal clutch assembly gives smooth operation in conjunction with the Self-Changing Gears RV28 semiautomatic gearbox and, because of its centrifugal clutch, also provides a higher degree of fuel economy than is obtainable from a conventional hydraulic coupling.
The self-contained four-speed gearbox is mounted amidships and is controlled by a small five-position electrical switch mounted on the left of the cab, where I found it appreciably more convenient to use than when outrigged from the steering column. The box gives smooth changes if the control lever is moved swiftly and, although such sharp movements make staccato noises ii the cab, these cannot be heard in either passenger saloo Continuous-flow powered hydraulic braking of Lockheed design is employecrand boost is derived from a hydraulic pump driven from the rear of the gearbox, so that its i output increases with road speed. This layout gives an exceptional degree of braking " feel " and a light pedal
pressure at normal road speeds. The pedal pressure required increases as the speed reduces, but it never• becomes excessive. This type of braking system has a big advantage over normal air-pressure designs in that exact control can be maintained at all times, irrespective of the number of passengers being carried.
The Marles steering has Hyclrosteer hydraulic assistance, the setting of which has been regulated so as not to make the steering too light. A happy compromise has been arrived at, and the bus can be lightly steered round the sharpest corners and through the narrowest of city-traffic gaps without any risk of undesirable wander on the open road. The front wheels carry Michelin .20 " X " tyres. on B7.5 rims, whilst at the rear the 6.00 in. wheels carry 10.00-20-in. (12-ply) equipment.
Body and framing are of B.M.M.O. design, but the underframe and lower body-side frame assemblies (including the inner stress panels) are constructed by Metal Sections, Ltd., Oldbury. They are all-steel, and the main cladding panels are of light alloy, but elsewhere in the body glass-fibre mouldings are used extensively.
A one-piece moulded roof, incorporating glass-fibre hoop sticks bonded to the panel during assembly, eliminates all metal components. Other plastics components include the driver's and emergency doors, front bulkhead, radiator grille, front cowl, bonnet, cab panels, staircase assembly, rear corner panels, and the front and rear upper-saloon waist panels, which incorporate the route-indicator boxes. No. 4850 was the double-decker provided for this exclusive road test, and its kerb weight was 8 tons 1+ cwt. Some 41 tons of iron weights had been distributed over the floors, of the .lower and upper saloons and various cans of fuel and so forth brought the imposed load to 4 tons 151 cwt., Jim Pearson and Bob Richards, of the B.M.M.O. experimental department, and myself .accounting for a further I ton. The running weight of 13 tons 2+ cwt., therefore, represented the weight of a bus with driver, conductor and 72 seated and six standing passengers-genuine rush-hour conditions.
Most of the test work was carried out on the Coleshill side of Birmingham. Braking performance was tackled first and was good. Only relatively light pressure was 9126 required to bring the bus to a standstill in 23 ft. from 20 m.p.h. and in 47 ft. from 30 m.p.h. Good as these retardation figures are, they were marred slightly by squeal from the disc brakes, a noise that appeared worst under light pedal-pressure conditions.
Average maximum deceleration indicated by the Tapley meter was 63 per cent, and, when braking from 30 m.p.h. both rear wheels locked, leaving 30-ft.-long skid marks. The wheels were locking within 17 ft. of the brake pedal having been applied, indicating that full braking pressure was available within less than + second of pressing the pedal. Hand-brake efficiency was correspondingly high, applications from 20 m.p.h. giving meter readings of
26 per cent and causing the rear tyre S ti mark the road surface heavily.
A 'five-mile out-and-return fuel-consumption test course Was employed and three runs were made with the vehicle carrying its full load and repeated with half the iron weights (equivalent to 36 passengers) removed.
Study of the fuel-consumption analysis would suggest that possibly the consumption rates,. when making stops, were inclined to be high, but the adjacent column shows that the average speeds based on the total time that the bus was moving were much aboVe average for this type of test.
This accentuates the lively acceleration, which was being used to the full during these tests. Had the bus been driven in a more leisurely manner, more than 7 mpg; would probably have been obtained-with, full load. Indeed. I understand that D.9 buses already in, service have been returning averages of more than 10 ra.p.g..-in.city operation, which is commendable
for 72-seaters. . .
Accelerationruns showed particular liveliness up to 30 m.p.h. from a standstill when starting" in bottom gear. The time recorded between 30 m.p.h. and 40 mph. was also most satisfactory: The direct-drive times appear slightly sluggish by comparison, but this is because of the high• degree of coupling slip at up to 15 m.p.h., a feature illustrated by the faster acceleration between .20 m.p.h. and 30 m.p.h.. compared with that between 10 m.p.h. and 26 m.p.h. Gear speeds observed showed that 18 m.p.h. could be reached in second gear, 30 mph. in third gear and about 47 m.p.h. in top.
For the hill-climbing test, the fully laden D.9 was driven to Mucklow.
Halesawen, which is on a Midland "Red" bus route, This climb is 0.9 mile long, with, an average gradient of 1 in 16.7. and sections of up to 1 in 11. The ascent was made in an ambient temperature of 42° F. and the 31-minute climb causedthe engine-coolant temperature to rise; by only 14° F. from 147° F. to 161° F.,
The lowest gear employed—second —was engaged three times for a total .
period of 1 minute 30 seconds. The mini:mum road spezdt observed was 13 m.p.h., underlining the spiiited capabilities of the bus. Indeed, we were ir baulked during the ascent by an almost empt bus of earlier vintage. danger of being Midland " Red "
Severe Test for Brake Fade
To check for fade resistance, I coasted the double-decker down the hill at 20„ m.p.h. in neutral for 21 minutes. At the bottom a full-pressure stop produced a meter reading of 50 per cent. This figure is deceptive, because the road surface was wet and the rear wheels locked immediately, despite which the bus remained stable.
The test was severe, however, and shows the brakes to be relatively fade-free. An earlier check for fade resistance had been made at the completion of the fully-laden six-stops-permile fuel test, the thirtieth stop in this series being a "crash" halt, which produced 61 per cent. efficiency—only 2 per cent. lower than 'normal.
Gipsy Hill, Oldbury (maximum gradient 1 in 7) was the scene of the gradient stop-start tests. When facing both up and down hill, the hand brake held the vehicle easily and, although a first-gear restart revealed somewhat slow pick-up tendencies, a reverse restart was made comfortably. The general hill performance was entirely suitable for normal operation, particularly as the bus was running at about maximum weight.
So far as passengers are concerned, travellers in both saloons will find the D.9 to have good riding characteristics. Most noticeable of these is the marked lack of roll, even when twisting round small roundabouts at fairly hi :h speeds. Engine noise is practically inaudible in the upper -aloon and by no
means. pronounced downstairs, although slight gearbox noise can be heard when sitting adjacent to the gearbox trap.
The seating layout of the lower saloon is of assistance to the conductor, in that, to clear the front wheels, the foremost seats face inwards, thereby giving him a clear floor space in which to collect fares at that end of the saloon.
Midland "Red" drivers are among the best in Britain and are highly critical .of, the handling characteristics of their charges. They say the D.9 is the best double-decker they have ever driven.
Excellent Driving' Conditions
Driving conditions can hardly be faulted. This holds true for the range of vision, the position of the controls and their lightness, access into the cab, the lack of engine noise and the thoughtful provision of an effective heating and demisting system, the demister nozzles of which are directed towards the front quarter light as well as the main windscreen panel.
A detail point worthy of note is that the heater and demister' unit is connected directly to the engine dynamo circuit so that it cannot be left on when the driver stops his engine and leaves the cab. Another .point is that the gear-change control has a master switch, which, when open,prevents accidental gear engage.ment.
Brief maintenance tasks showed the high degree of engine accessibility to be matched by the accessibility of most of the other major components. I was able to check the water level in six seconds, the engine oil level in 20 seconds (including the time to lift. and close the bonnet),. the gearbox oil level iii '1 minute 24 seconds (including rernoval and replacement of the floor traP; which is -Seemed by four budget locks), and tie Tad in the-brake-fluid reservoir in -16 seconds. This reservoir
is' convenientlyplaced beneath the near-side front seat cushion.
Two 6v. batteries are mounted beneath each of the rearmost seat cushions, and it was possible to,verify a.11 the. cell 'levels in two minutes. The fluid reservoir for the .steering-Servo circuit is adjacent to the gearbox. and its level an easily be checked when examining the gearbox oil level. Rothcorn-. portents have dipsticks.
I verified the rear-axle oil level hi .24 seconds, including climbing into and out of thepit. --The. filler .neck ,ie• covered by a hinged flap, which is secured by a wing nut. With the bonnet raised (11 'Seconds) I removed the felt element of the main fuel filter in 28 ;seconds and 'replaced it.
in 441 seconds, the filter accessibility making a pleasant change from that normally encountered on 'heavy vehicle's. I then removed the copper gauze of the dry air cleaner in' 1 minute 16 seconds and reassembled the filter in 1 minute .27 seconds.
My next job-was to remove a fuel injector. I chose No. 2 and withdrew it in 1 minute 57 .seconds without any difficulty, replacement occupying 2 minutes 47 seconds. The fuel system was bled in half a minute by running the engine, there being
no priming lever on the lift pump. . •
I did not adjust' the brakes, but Checked them all visually in minute. The front:brake pads were looked at to see how much friction material was left and the back-lash at the rearbrake cam levers was checked, judgment of clearance 'being a
matter of experience. '
The Midland "Red D.9 is 'an outstanding. vehicle in all respects and reflects the -imagination of its designers and the skill of its builders. Despite such features as disc brakes and rubber suspension (both .of which reduce maintenance), it is essentially simple and straightforward in conception.