I read somethere that the two reasons the streamlining was removed from the LMS Coronations were (a) easier maintenance and (b) it wasn't effective below 90 mph. (Perhaps a third, unstated reason was that it was bloody ugly!)
Given that the A4 streamlining was developed in the days of smoke in wind tunnels, it must have been remarkably effective at 'normal' express speeds (?70 - 80mph), as well as being aesthetically pleasing.
Does anyone know what its drag coefficiency rating might be? Would it be the same scale as for cars (eg 0.35 - though I don't know of what!)?
Drag coefficient of A4s
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Pyewipe Junction
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richard
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I don't have any drag coefficients but Roger Mannion in "The Streaks" (pg. 26) gives some hp savings: 41hp at 60mph; 97hp at 80mph; 138hp at 90mph; 190hp at 100mph; 253hp at 110mph; 639hp at 150mph.
These figures are calculated from the wind tunnel tests. The tests went up to 150mph to account for high speed running into a head wind.
Note that for the B17s (which never ran above 100mph), it is usually considered that the A4-shape body was only for show and was otherwise not 'worth the effort'.
On the other hand, the A4 shape was good at deflecting smoke from the cab at high speeds. The story goes that a thumb print was accidentally added to the wind tunnel model, just behind the chimney. On a whim it was tested, and was found to do an excellent job at deflecting smoke.
Richard
These figures are calculated from the wind tunnel tests. The tests went up to 150mph to account for high speed running into a head wind.
Note that for the B17s (which never ran above 100mph), it is usually considered that the A4-shape body was only for show and was otherwise not 'worth the effort'.
On the other hand, the A4 shape was good at deflecting smoke from the cab at high speeds. The story goes that a thumb print was accidentally added to the wind tunnel model, just behind the chimney. On a whim it was tested, and was found to do an excellent job at deflecting smoke.
Richard
Richard Marsden
LNER Encyclopedia
LNER Encyclopedia