Tom Anderson wrote:
On Mon, 2 Jan 2006, Bob wrote:

Does anybody know if humps are still built into station tracks on new
tube lines.

The CTRL seems to do it:

http://www.ctrl.co.uk/route/tile1.asp?L=8

Although i don't know if that's really about playing tricks with
energy, or wanting to keep the tunnel nice and deep where possible.

When done by the CRL I don't think it was about "playing tricks with
energy". Electricity was still a very new form of energy and such
considerations hadn't arisen, it was simply a way of using a natural
phenomenon (gravity) to improve the performance of the trains. However good
the braking and acceleration of a vehicle on the level it will be enhanced
by going up/down hill at the appropriate moment.

On Tue, 3 Jan 2006, Brimstone wrote:

Tom Anderson wrote:
On Mon, 2 Jan 2006, Bob wrote:

Does anybody know if humps are still built into station tracks on new
tube lines.

The CTRL seems to do it:

http://www.ctrl.co.uk/route/tile1.asp?L=8

Although i don't know if that's really about playing tricks with
energy, or wanting to keep the tunnel nice and deep where possible.

When done by the CRL I don't think it was about "playing tricks with
energy". Electricity was still a very new form of energy and such
considerations hadn't arisen, it was simply a way of using a natural
phenomenon (gravity) to improve the performance of the trains. However
good the braking and acceleration of a vehicle on the level it will be
enhanced by going up/down hill at the appropriate moment.

Er, that *is* playing tricks with energy - the uphill slope of the hump is
a machine which converts the train's kinetic energy into gravitational
potential energy, thereby assisting the brakes, and the downhill slope is
a machine which does the inverse, delivering energy into the acceleration
process, and so assisting the motor.

It's exactly like using regenerative braking to turn a train's kinetic
energy into electrical energy during braking, which can then be
reconverted into kinetic energy during acceleration - only the hump does
it rather more reliably and efficiently!

A third equivalent would be a colossal spring lining the tunnel, which the
train would compress during braking, and whose expansion would assist
departure. Far less efficient (ISTR that you lose at least half the energy
to heat when you do that), and probably not the most reliable or safe
approach, either.

tom

--
Plus, you gotta understand I can now type far, far faster than I can
think. This is not boasting - its admitting a personal tragedy. -- D

Tom Anderson wrote:
On Tue, 3 Jan 2006, Brimstone wrote:

Tom Anderson wrote:
On Mon, 2 Jan 2006, Bob wrote:

Does anybody know if humps are still built into station tracks on
new tube lines.

The CTRL seems to do it:

http://www.ctrl.co.uk/route/tile1.asp?L=8

Although i don't know if that's really about playing tricks with
energy, or wanting to keep the tunnel nice and deep where possible.

When done by the CRL I don't think it was about "playing tricks with
energy". Electricity was still a very new form of energy and such
considerations hadn't arisen, it was simply a way of using a natural
phenomenon (gravity) to improve the performance of the trains.
However good the braking and acceleration of a vehicle on the level
it will be enhanced by going up/down hill at the appropriate moment.

Er, that *is* playing tricks with energy - the uphill slope of the
hump is a machine which converts the train's kinetic energy into
gravitational potential energy, thereby assisting the brakes, and the
downhill slope is a machine which does the inverse, delivering energy
into the acceleration process, and so assisting the motor.

It's exactly like using regenerative braking to turn a train's kinetic
energy into electrical energy during braking, which can then be
reconverted into kinetic energy during acceleration - only the hump
does it rather more reliably and efficiently!

A third equivalent would be a colossal spring lining the tunnel,
which the train would compress during braking, and whose expansion
would assist departure. Far less efficient (ISTR that you lose at
least half the energy to heat when you do that), and probably not the
most reliable or safe approach, either.

If you want to take "energy" in the widest sense, rather than the limited
term meaning that which powers the train OK.

When done by the [CLR] I don't think it was about "playing tricks with
energy". Electricity was still a very new form of energy and such
considerations hadn't arisen, it was simply a way of using a natural
phenomenon (gravity) to improve the performance of the trains. ...

As already pointed out, that amounts to the same thing.

I'd just like to note that when the C&SLR decided to do it, they
were expecting their trains to be cable-hauled, not electric.

The energy and performance issues are of course essentially the same
either way. But with cable haulage, a hump gives a special benefit.
The train is accelerated from rest up to cable speed by tightening the
grip until it clamps firmly onto the cable; and while that's going
on, the cable is rubbing against the grip as it slides through it.
So a gravity-assisted start could significantly reduce wear and tear
on the cable.
--
Mark Brader, Toronto | "If gravity stops working, a power cut is
| the least of your problems." -- David Bell

My text in this article is in the public domain.