In article , Richard J.
wrote:
Michael Bell wrote:
This may not be the right forum for this question, but what the
hell!

Standing at Hitchin station and wistfully watching the fast trains
going through, the wheel-on-rail noise of class 91 + Mark IV
coaches seemed much louder than the Eurostars. (Comparisons with
HSTs are difficult because of their noisy diesel engines - at full
chat as they pick up speed going North). This was just a casual
observation. Is this generally accepted? Are the reasons known?

It may be because Eurostars (Class 373) are articulated, with one bogie
shared between two carriages except at the ends of each unit. Thus at
any instant while one is passing you, there are fewer bogies in contact
with the rails within x metres of your position than with a rake of Mark
IVs.

I got the feeling that the difference was greater than could be accounted for
by that factor - and is it true anyway that there are significantly fewer
bogies per length of train? The body sections of TGVs are noticeably shorter
than British Mark IV coaches.

Being analytical, what might the reasons be?

* Steadier running by TGV wheels.

* TGV wheels less resonant. The resonance of solid metal objects such as
wheels can be damped by coating part or all of them with a viscous
material such as bitumen or polyurethane, and then fitting another rigid
sheet on top of that, it can be as thin as foil or even paper. The damping
force is then the non-elastic distortion of the viscous layer, and it is VERY
effective, it is called "constrained layer damping" and it used in sheet
metal structres such as cars and fridges, but it can also be used for
thicker metal objects.

* Greater enclosure of TGV wheels? I suggest that only to dismiss it. I
can't think it is significant.

I can't think of any other reasons.

Michael Bell

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