BUS ROOFS AND THE PROBLEMS THEY ENTAIL,
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Some Helpful Information Upon Ventilating and Decorating, Besides the Main Consideration of Securing Watertightness.
NO part of a bus has more uses than the roof. It is the chief means for protection from the weather, and, fitted with suitable devices, it forms an important factor in the ventilation of the vehicle. The roof can be of light construction and elegantly shaped to give the bus a distinctive appearance, or made stronger so that it will carry any load, from a small quantity of luggage up to an enclosed saloon accommodating nearly forty. passengers. The roof, therefore, is a leading feature a the general design and indicates, to a large extent, the kind of work on
which the vehicle is engaged. • A typical bus roof is that which is fitted to the modern single-decker. The framework consists of a
pair of cant-rails spliced to the canopy-rails in front and to corresponding rails at the back. The canopy rails are so called because they have been used principally to support an extension of the roof projecting from the main saloon, but, with the enclosure of the driving compartment and the rear entrance, these man tend to belie their name and become only a convenient way of continuing the cant-rail where it curves Inwards and is joined to the front and back rounded corners of the roof framework.
The cant-rail must he large enough in section to take the top groove for the windows, the tenons of the side pillars and the lap joints of the hoopsticks, and have sufficient substance, so that, if necessary, the finish of the side curve of the roof may be formed in it without decreasing its strength.
The two cant-rails are connected by a series of hoopsticks curved to the roof camber, which may vary from a plain arc four inches higher at the crown
B38 than at the sides to one of pronounced D-shaped or elliptical section, having sharply curved sides and a depth of 12 inches overall. As the hoopstieks have only to hold the two cant-rails together and support the light boarding or panelling of the roof they may be of small section, but a stronger cross-rail is required at the top of any partition or bulkhead.' Even when a to load is carried the hoopsticks are seldom of greater sectional area than 1/ in. square, any extra strength required being obtained by flitch-plating them or increasing the number used.
For many years the roof of the single-decker was covered with narrow boards laid lengthwise, but now plywood is extensively employed, which can be more quickly fitted, and, being stronger, provides the opportunity for reducing the number of hoopsticks. This
is not always advisable, however, because the roof panel may vibrate if it iS not fastened at frequent intervals. When the sides of the roof are sharply ' curved, these parts are usually covered with aluminium panels. The same material is also used for covering the ends of the roof, although both plywood and thin narrow boards may be bent to the required shape. If matchboarding be bent to a comparatively, small radius it is always in a state of tension and it has been known to break a canopy-rail above an open driving seat. Bent woodwork should be properly steamed and not applied "cold." If a roof of very light construction be required it is suggested that the experiment might be tried of eliminating, say, two thirds of the usual number of hoopsticks and substituting a pair of longitudinaLs, running parallel with and spaced evenly between the cant-rails, whilst the roof could be panelled entirely, in aluminium, or with the middle flat portion in plywood.
Watertightness an Essential.
It is essential that the roof be watertight. There is little danger of any pronounced leakage, but even
a small oue can be a source of annoyance to the passengers, apart from the fact that it will set up a local discoloration of the interior finish and rot the surrounding framework. The roof boards or panels must be pierced by nails or screws in order to fasten them. Each hole so made forms a possible entry for moisture. For this reason the whole of the roof surface is first painted and then covered with a single piece of fabric. This fabric may not, in itself, be absolutely waterproof, but it forms a continuous and unbroken surface and when further coats of paint are added to the head the whole is watertight.
Any small spaces which may develop around the nail holes are effectively filled up with the combined mixture of paint and the texture of the fabric. The edges of the roof-cover are nailed to the cant and front and back roof-rails, the heads of the nails being hidden by means of a wooden or metal cornice, preferably the latter. It is generally agreed that the cornice should include a comparatively large water channel. The water can then be conducted to the ends of the vehicle into down pipes. If an inadem_ate water channel be provided the water overflows across the windows with even a slight shower.
Reducing the Possibility of Leakage.
Roof leaks are apt to be set up if anything be fastened to the roof after the fabric cover has been secured in position, such as luggage rails and wearing-slats, the latter being most likely to cause trouble owing to the number of screws required to fix them. It is, therefore, an advantage if the set of roofslats be first made into a mat by joining them together with crosspieces. Then only the cross-pieces need be fastened to the roof. Leakages may also occur around ventilators, or where the fabric has been torn owing to the movement of a loose board, or where the fabric has broken away owing to the lack of local support and the indifferent jointing of any part of the roof construction, both of which faults may cause a most serious entry of water into the body.
When framing the roof the hoopsticks are graduated to conform to the varying cross-section. of the roof. It is not advisable to make any two adjacent hoopsticks exactly the same section, in order to avoid any Eat places which may not only appear hollow, but so develop when the sides of the body spread a little in use. The roof of the lower saloon of a doubledecker is made Fin, higher in the centre than at the arch-rails at the top of the bulkheads.
Roof Ventilation in Drop-window Buses.
More attention has been paid to the use of the roof for ventilating purposes since the introduction of the drop window. This has, no doubt, been brought about owing to the adjustable main windows tending to eliminate the hitherto conventional ventilating frames. These frames were discarded because it was felt that the general appearance was thereby improved, also at first it was considered that a large drop window should easily compensate for the lack of a small hinged frame above it. When a well-cambered Tod is fitted, however, the hot air inside is not readily displaced, even when the windows are open, and some special force is required to draw out the layer of air which accumulates principally above the central gangway.
The plain roof-flap hinged on its forward edge makes a good air extractor, because a partial vacuum is created behind the open lid. A modern roof ventilator, however, is more positive in its action, because the streams of air passing above the roof are diverted into small apertures embodied in the ventilator cap, so that the air pressure is increased and a correspondingly greater amount of suction created. Such a device will function with a following wind and it is almost impossible for rain . to enter if the various parts be properly arranged. The. sliding roof has been improved so much during the past two or three years that it may be more freqUently adapted for the service bus, especially when the route concerned traverses country districts. A sliding roof panel need not interfere with the installation of air• extractors, as one or more can be fitted to it for use when the roof is closed, whilst others may be inserted in the fixed portions of the roof beyond the limit of the slides, ample room being usually available. Effective roof ventilation is also afforded if a clerestory be added. This consists of a roof with a raised central portion having ventilating frames on each side. It is a better arrangement than having small frames immediately above the main windows, because, with the clerestory roof, the small windows are closer to the central gangway, where the hot air accumulates. The clerestory is a compact design, because the roof is raised chiefly where the maximum headroom is required. Its disadvantage is that it cannot be used for carrying luggage.
If luggage be carried on the roof it is customary to enclose about a third of the area towards the rear, Where it can easily be reached by means of an iron ladder fastened at the side or in the centre of the back
panel. The lower part of the /adder is hinged, so that it can be folded up and no unauthorized person is tempted to ride -won it. If the side windows be well guarded with rails, that part of the roof which lies mid-way between the axles should be an ideal position for carrying any extra weight. Instead of a ladder steps are fastened to the body for mounting to the roof. These treads may have to be hinged if they exceed the legal limit of width when in use. The luggage space may often have a boarded surround which is used for writing display.
With the increasing amount of attention paid to the interior display of the service bus, the underside of the roof may often be decorated with some simple device. If no inside roof panels be added the boards which show between the hoopsticks may be stained alternately a dark and light colour and the edges of the hoopsticks neatly chamfered.
If an inside roof panel he used, then the decorative scheme employed is only limited by the inventiveness of the designer and the purse of the owner. A good design can, however, usually be 'achieved by simple means and without undue expense. Lincrusta, and polished wood mouldings may be combined with excel• lent effect. Any design has usually to be modified in order to leave space for the insertion of roof ventilators, or lamps, although the fixing of the latter will, as a rule, be restricted to the curved sides of the roof above the seats, where the headroom is not so valuable.