Hi Jim
On (17 Sep 97) Jim Dunmyer wrote to Alec Cameron...
 JD>  >JD> There was an experimental subway train in New York City that was 
 JD> propelled by vacuum also.
 > Wow. I wonder what sort of a draft that caused. Subways get to be 
 JD> Probably NO draft, as there'd be no relative difference in airspeed.
 JD> Think about it. :-)
Thinking is a health hazard!
Imagine a north bound train in tunnel. The duct would be opened behind the
piston ie at the south end of the lead car. Duct vacuum would be maintained
ahead of the piston ie at the north end of the lead car.
Atmsopheric air from the south end of the tunnel would enter the duct behind
the piston ie at the south end [back] of the lead car. The tunnel air 
ressure
would be diminished near the train rear [being sucked into the duct] but the
tunnel air pressure would be increased in front of the train due to its
forward motion.
Conclusion- little or no reduction in the tunnel draft ahead of the train. 
nd
some reduction in the induced tunnel draft in back of the train.
In theory, the air admitted by the driver into the duct, should have been
collected from in front of the lead car.  Cheers....ALEC
... ........When I contemplate the moon, my head aches [Galileo]
--- PPoint 1.92
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