The Canopied Electrobus.
Page 9
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A "Commercial Motor" Report on Its Stability in Service.
In accordance with instructions received from the Eloctrobus Company, Limited, of Whitehall House, Charing Cross, WO have examined and measured the covered-in, double-deck bus which that company proposes lo run in public service in London : we have carefully looked into the question of the stability of that %chicle, and have compared it with a wellknown and largely-used petrol motorbus now in London service. We are of opinion that no danger, so far as lateral stability is concerned, would attend the operation of such a bus. The low position of the heavy battery brings down the centre of gravity of the covered electrobus to a point much below that of a petrol vehicle.
Taking the worst conditions under which a bus may be operated, namely, with a full load of passengers and the conductor on the top deck, and no passengers inside of the bus, and comparing the covered-in Electrobus with an ordinary petrol bus under precisely similar conditions, we find that, whereas the centre of gravity of a particular petrol bus is live feet eight inches above the ground line, the similar point on the Electrobus is only five feet three inches above the level of the ground. Not only is the centre of gravity lower in the latter case, but the wheel gauge is wider than the normal one, and it would be perfectly safe to tilt such a machine through an angle of about eight degrees more than the particular petrol bus which we have examined.
So far as the new vehicle's ability to stand up to a strong
id is concerned, we have satisfied ourselves on that point, and, after careful measurements and calculations, we find that, with the maximum of exposed area (i.e., assuming that the whole area between the facia board and the top of the canopy were filled in with curtains or glass), the righting effort of the vehicle is sufficient to stand up to a wind pressure of 29 lb. per square foot, which pressure is equivalent to a wind velocity of about 75 miles an hour. Without closed sides, the wind pressure would have to be increased to 37 lb. per square foot in order to overthrow the bus; this pressure zersesF a wind velocity of 85 miles an hour. Such veloci
ties are rarely—if ever—experienced, except at sea. The petrol bus which we have quoted would require a pressure of 37 lb. per square foot to bring about its downfall. The Electrobus, with its canopy and open sides, as shown on the drawing, and the particular petrol bus without a canopy, are equally stable so far as their capability for resisting the pressure of the wind is concerned. The spot " A " on the drawing indicates the centre of the minimum area, and the spot " B " shows the centre of the maximum area exposed to the wind.
Turning, now, to the small diagram, this shows the bus being driven round a sharp turning, the radius of which, is, for the purpose of example, say, 30 feet. The vehicle (G) might safely proceed along the path marked " H. J." at a
speed of 12 miles an hour, even if a 70-mile-an-hour gale were blowing up the street in the direction of the arrow K, thus striking the bus " broadside on." In all our calculations, we have assumed that the machines were standing on a cross-fall slope of iin so (camber), as is shown in the end view of the bus. In this view, the centres of gravity of the principal constituent parts of the load which make up the total weight are indicated as follow :—C, the top-deck passengers; D, the body and its fittings; E, the chassis and battery; and F, the centre of gravity of the combined mass. Were the full complement of passengers inside the bus, the righting effort and, consequently, the stability of the vehicle would be greatly increased. In our opinion, the very small additional weight due to the canopy is by no means conducive to instability, and, taking into account all the necessary factors, an electrobus would be perfectly safe with such an addition.
For THE EDITOR.
(Signed) Cssoace W. WATSON, A.M.I.Mec.h.E., M.I.A.E.
(Nlember of the Editorial Staff.)