Steam Speed Record

[matacaster]

As we all know Mallard hit 126mph briefly to claim this record. The reciprocating nature of the piston engine would likely place a barrier to much higher speeds and the hammer blow would likely be significant.

The Stanier turbomotive would seem to overcome this issue, but, as far as I am aware, its potential (ie via turbine drive) for faster speeds was never really realised.

1- What prevented the turbomotive from exceeding 126mph? (lack of horsepower?, turbine durability?, poor reliability? etc

2- Had another one been built would a double-header have been able to claim the speed record?

 

[Spartacus]

The trouble with a turbine is you have a speed, or more specifically an RPM, sweet spot at which you produce the most power, with it dropping of after that, sometimes quite dramatically, and if you want that to be at a high speed that's going to reduce performance at lower speeds, so you'll end up going uphill and accelerating much slower. The Turbomotive's sweet spot was around 60mph; it was set to give it's best performance while still accelerating and climbing hills.

 

[John Webb]

According to the chapter on the 'Turbomotive' in J W P Rowledge's book 'The L.M.S. Pacifics' (David and Charles, 1987) the design parameters of the loco were a 2,600hp turbine giving an estimated tractive effort on starting of 40,000lb; 12,000lb at 70mph and a maximum speed of 90mph, the parameters being chosen as suitable to haul a 500ton train between Euston and Glasgow. Unlike previous manufacturers' attempts at turbine power in the UK, the LMS pacific had no condensing system which simplified matters.