Steam speed records including City of Truro and Mallard

The 05002 accelerated very evenly to 200km/ where speedometers and penwriters in dyno (two of each )touched stop.
The claim of 200.4kmh mean over 5km with a top of 201 kmh came from a distance/time measurement like the one done for Mallard.
200.4 kmh is 124.52mph and very close to the mean value of Bryan Benns (Gresley?) last 4 quarter mile speeds 123.5-125-124.25-123 giving mean 124.06.
05002 train (260t) varied between ca 200 and 201 kmh over a 5 km distance.
Mallard train (400t) between 123 and 125 mph over one mile if you use LNER 1938?
A new strategy for Mallard defenders can be to prove beyond doubt that the respective clocks were not calibrated .How much to slow or fast?Try Yourself

 

I would be cautious of taking GPS figures to be quite precisely accurate.

There was the occasion in Germany when the German high speed, three cylinder Pacfic was to repeat the 100 miles an hour it had distinctly attained in Austria.
In a coach where there were a number of serious timers those with GPS on one side it got 99 mph and on the other 100 mph........

The most modern and well established way to get reliably a more accurate speed speed would be to use the doppler taking the overground speed between the rails which is standard to gain extra traction from limited slip: ie increasing the traction by running the driven wheels steadily a few percent faster than the speed along the track which the train is attaining. It seems that it is very likely that this was used when Tornado did 100 mph doing an overspeed test to be formally passed for 90 mph. Indeed this is why I have considerable confidence in the detailed speeds that were reported.

 

Nothing is precisely accurate, but GPS traces are very good indeed provided that you analyse a log rather than simply take instantaneous readouts as gospel. I agree that the instantaneous speed figures are of limited value.

 

Pure nonsense and can only be explained by age.
Holcroft in Locomotive Adventure makes the same when explaining why 05002 was more important than hectic Mallard going down a hill , but was worthless anyway due to the much higher expenses in daily,fare demanding traffic.

Power or steam per time unit (boiler size) needs to be nearly doubled for upping speed from 100 to 125.
1.25**3=1.95
Amount of coal for a given distance goes up 56% when running 125 instead of 100.
1.25**2=1.56

 

Mallards graph clearly shows a good length of 125mph. That is all.

 

I've always known you can navigate by the stars, but who'd've thought you could calculate mph from them as well…!

What were you doing? Checking against the rotational speed of the planet…?



Simon

 

Personally I wouldn't do it like that if I could avoid it. Obviously you're limited by the capabilities of whatever device you have, but if I were using a GPS phone I would use logging software that logs all the positions and analyse later. That way you can average over shorter and longer distances and compensate for the inaccuracies later.

 

Did Thomson aprove the 126mph claim?

 

Well, the dynanometer car recording says 125mph and is freely available to peruse and is a record, if that's what counts. I've seen it, if seeing is believing, freely avilable in an excellent museum at York

 

A recent post reminds us that, back in December

That confirms where the 126 figure came from but not why it was chosen for the plaque, which remains an interesting question. Worth a PM to Simon?

 

Thomson retired end of june 1946.
Took me some time to find,sorry.
My impression after reading Tim Hillier Graves description of Thompson did not really fit the 1948 happenings.