Tornado's rimless chimney

[David C]

Tornado had a conventional lipped chimney but after its naming the rimless version appeared. Does anyone know why?

I've heard the lipped version is coming back on in the future

[Flamingo]

That's an easy one or is it a trick question?

Tornado's 'rimless' chimney is right for an A1 painted in LNER Green. Probably the only type of chimney the class carried while in that livery. The 'lipped' type of chimney did not appear until several years later by which time the A1s were in BR green. Before that though we can look forward to seeing 60163 in BR blue.

Actually the chimney is not completely rimless - look at it carefully and notice that the top edge is slightly rounded over to form a small rim.

[brsince78]

I'd always thought that the rimless chimney was an austerity measure until I read somewhere that it was designed to present a smooth surface area for the airflow around the chimney top to aid in smoke clearance. Clearly this was not necessary given the later replacement with the lipped design.

[stembok]

brsince78: The addition of the lip to the chimneys on the A1s/A2s was done for aesthetic reasons and was a decided improvement from that point of view, but it was pointed out at the time that the original chimney had been designed that way to make smoke lifting more efficient and that the lip would have the opposite effect. I'm not sure whether any tests were done to clarify the matter, though one or two Thompsons retained their original chimneys to withdrawal, A2/2 60506 and A2/3s 60514/19.

[Flamingo]

Odd that those A2s managed to keep their so-called rimless chimneys. They each must have been through works several times in that state, so did they always keep the same boilers (unlikely) or exchange with each other (also rather unlikely)?

As to the effect on smoke lifting ability, the only engine of those three on which the type of chimney might have made any difference was 60506. The other 2 had large conventional smoke deflectors fitted.

[Solario]

Here is confirmation of the chimney on one of the locos - Honeyway, taken at Doncaster shed circa 1960.