Central SMT

As a keen and youthful enthusiast always on the lookout for something unusual in/on the buses I spotted, I quickly realised  differences, subtle or otherwise, among vehicles of the same make or class : shape of destination screen, position of traffic indicators, type of internal lighting, white or black rubbers on window surrounds, etc. In similar fashion, a batch of Central’s Bristols always intrigued me with their black slatted rectangles on the front bulkheads. At the time, I was informed they were simply part of a heating system, known as Cave-Brown-Cave. Not being of a technical or mechanical mind, my curiosity was duly satisfied, but decades on, the story behind this concept deserves some further explanation.

Cave-Brown-Cave may sound like a firm of lawyers or accountants, or even the forwards line-up in some old football 4-3-3 formation, but that would be mocking the man in question. Wing-Commander T.R. Cave-Brown-Cave was Professor of Engineering at Southampton University. He contested that it should be possible to deliver more heat with a greater air-flow than would appear possible via a conventional fan-drive system as used on buses and coaches.

Initially, the good Professor experimented with a Guy Arab from the local Corporation fleet, with no mean degree of success; later, a Hants & Dorset Bristol K5 of 1940 was also fitted with C-B-C equipment and sent forth to demonstrate the new heating and ventilation system. Suitably impressed, Bristol Commercial Vehicles agreed to install Cave-Brown-Cave gear on the nine prototype Bristol FSs. The frontal appearance of the vehicles was considerably altered. Two radiators, one on each side of the destination box and mounted at upper-deck floor level were used. The normal air-intake grille, radiator and fan were effectively made redundant as engine cooling was eliminated. However, through operating experience, it was found that some degree of engine cooling was necessary, especially in warm weather, and a radiator grille was fitted retrospectively.

Subsequently, C-B-C heating and demisting equipment was offered to other BTC companies. A quick look through records shows that the Scottish Bus Group didn’t exactly lead from the front, as it were. Western SMT and SOL did place orders for the system on some late-model LDs, FSs and early FLFs. Central SMT’s contribution to the Professor’s financial well-being was their 1961 new double-deck order:

7 Bristol FSF6Gs   B 116 – 122       (CGM 116 – 122)

7 Bristol LD6Gs     B 123 – 129       (CGM 123 – 129)

These were the only vehicles delivered new with C-B-C equipment, and remained unique until the 1973 Bristol ‘Swap Shop’ which saw Central off-load their VRs in exchange for second-hand FLFs from NBC companies.