This shot of No.34081 92 Squadron, neatly demonstrates the problems of drifting exhaust obscuring the driver’s view. Bad enough in daylight, imagine what it’s like, in the dark, trying to spot that distant signal with exhaust rolling down over the cab. It wasn’t only the Bulleid Pacifics which suffered from this problem. Many classes suffered from the issue, especially under light or ‘eased’ regulator openings, and all kinds of solutions were tried and tested to try and eradicate it.
On the ‘air smoothed’ Bulleids, alterations were made in the shape of the front cowling, to the size and position of vents in the cowling, and in the shape length and curvature of the smoke deflectors, in the air smoothed casing. Various experiments were carried out on several class of LNER Pacifics; they varied from something which resembled little more than fins alongside the chimney, through smoke deflectors of varying lengths and curvatures, or not, right through to the adoption of the putative ‘German style’ currently being carried by No.60103 Flying Scotsman.
The need for smoke deflectors is created by, low exhaust speeds, large boiler diameters, and low or double chimneys. The large boiler diameter creates a larger low pressure area behind the chimney, the lower exhaust speed means it is more easily pulled down into this area, the smoke deflectors are designed to lessen or remove the low pressure area behind the chimney and thus prevent the exhaust from being drawn down. If that’s not too baffling a way of putting it!!
If you have enjoyed my blogs – I have written a book about my 60 years involvement with railways, from trainspotter, via steam age footplateman, to railway author and photographer, this is a link to it: