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Imaginary Locomotives

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brack

brack

Posted
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Thought that had con-rods?

 

I know the earlier Swiss electrics used bigger drive wheels and smaller unpowered wheels in some cases (Ae4/7 etc), wondered if there was a benefit to it.

The Ae3/6 and Ae4/7 (amongst others) used a buchli drive to allow the heavy motors some independent movement to the axles (to allow them to be sprung - Raven's passenger electric had quill drive for the same reason, as did several of the pennsy electrics). I don't know if the big driving wheels are necessary for the drive system, but the gears on the driven side are pretty much almost as big as the wheel. The smaller wheels on the unpowered axles are just carrying wheels for steering and weight distribution like on a steam loco (the driving wheels are effectively like a rigid framed loco). High speed electrics of that time often had large wheels in a rigid frame and carrying wheels yet slower freight locos of the same period had 3' ish wheeled bogies and bogie mounted (unsprung?) Traction motors directly geared to the axles like we see in modern locos, so I'd assume it's due to the drive/springing arrangements of the relatively large and heavy traction motors available that could operate at high speed/power (Raven's EE1 had 2 motors per axle) - they'd need to be body mounted and sprung. A larger diameter driving wheel would give more axle clearance to fit a drive mechanism, or perhaps there's a carryover from steam loco design?

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Mr_Tilt

Mr_Tilt

Posted
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and looked like a tube train on stilts.

 

On which subject, have you ever noticed how much a Class 66 looks like the Leader from the front?

 

That 'pointed head' look to the upper part of both cabs is very similar. 

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Joseph_Pestell

Joseph_Pestell

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French railways had several classes of 2D2 electric locos which have been modelled by Jouef, Roco and others. I would have to look up the driving wheel diameter but it was about 5'6", I think. (Edit: 1.75m according to Wikipedia which is same height as me, 5'9").

Edited by Joseph_Pestell
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melmerby

melmerby

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Can you call it 4-8-4 if it didn't have con-rods. When the rods joining the middle two drivers were removed it became a 4-4-4-4.

Officially any axle that is driven by a common power source with another is coupled, whether an outside coupling rod is attached or not

As all the wheels could be driven through gears from just one engine the Fell was always a 4-8-4 (or 2-D-2 as it was a diesel?)

 

Keith

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Bloodnok

Bloodnok

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Question: is there any mechanical advantage to having the largest driving wheels possible?

There's a marginal benefit in an elongated contact patch -- having larger wheels can result in a slightly more sure-footed loco. It's not a particularly big difference though -- other factors (the weight of the wheels themselves) will be more significant.

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Clive Mortimore

Clive Mortimore

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Question: is there any mechanical advantage to having the largest driving wheels possible? I don't mean on express steam as I understand it there, I mean modern diesel/electric locomotives. If a fictitious express locomotive had jackshaft drive then it makes sense for similar reasons to a steam locomotive. But what about the more common individual traction motor axle driven locomotives? Any advantage to doubling the 'standard' wheel diameter there?

 

Ta

No. Larger the wheel the less mechanical efficiency. 

 

Steam locos do not have a gear box so the amount of power supplied to the wheels is regulated by emission of steam into the cylinders.

 

The amount of torque applied to the crank on the driving wheel is the same for two locos of differing wheel diameter if boiler pressure, cylinder size and stroke are the same. Take GWR Saint class with 6 ft 8 1/2 ins wheels, Grange class with 5 ft 8 ins wheels and 28xx class with 4 ft 7 1/2 ins wheels. The larger a wheel is the faster it will go on the edge compared to a smaller wheel revolving at the same time. The smaller wheel has a greater torque than the larger one.  That is why freight locos have small wheels for the additional torque but can not manage high speeds. Express locos have larger diameter wheels for speed, a large diameter wheel covers more rail per revolution of the driving wheel crank but has less torque than a freight loco. The Grange class being mixed traffic has a wheel diameter that allows for reasonable speed on passenger duties and reasonable torque on slow heavy freights, as the Fat Controller would say " A really useful engine".

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Gibbo675

Gibbo675

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There's a marginal benefit in an elongated contact patch -- having larger wheels can result in a slightly more sure-footed loco. It's not a particularly big difference though -- other factors (the weight of the wheels themselves) will be more significant.

Hi Bloodnok,

 

The greatest variables affecting the contact patch are tyre profile and tyre wear. Certain profiles are formed into what are classed as adhesion profiles which do not have the flat 1:20 angle across the tread but are hollowed to give greater wheel rail contact.

 

Here is some light reading;

 

https://static1.squarespace.com/static/59f1c5ec51a58457c01eaed0/t/5a3918280d9297467018eae6/1513691413356/MT288+wheelset+tread+standards+and+gauging.pdf

 

https://www.rssb.co.uk/rgs/standards/GMRT2466%20Iss%203.pdf

 

Gibbo.

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AlfaZagato

AlfaZagato

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I've had a couple of ideas knocking around in my head pertinent to this thread.  Before I get too much into the details, I am a massive GWR fan.

 

Firstly, I've long had a concept for a 2'6" gauge Shay, mildly Swindonized for use on the Welshpool & Llanfair.   I honestly can't give any reason why this could have happened, other than wanting a Swindon-Lima monstrosity grinding about a layout.  Something like a class B with a cut-down Collet cab, No. 2 boiler, and chopper couplings.

 

Next, what if Nationalization hadn't happened?   Maybe a diesel or electric Cathedral?  I know such an idea has been posted before, but my thought was the GWR used the same jigs and tooling for the cabs on a Metro-Vick diesel-electric prototype, similar to how Bulleid used the same or similar ends on his three EE's as to the EMU fleet.

 

Finally, I had discovered that the W&L and the Vale of Rheidol were more-or-less in alignment with each other, and thought it unlikely but possible that they reached out across the 40 miles of intervening Welsh countryside to connect.   Given the distance, I figured Swindon may have tried downsizing the Hawksworth Ten-Wheeler County, rendering it outside-framed.

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melmerby

melmerby

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Posted (edited)

 

Finally, I had discovered that the W&L and the Vale of Rheidol were more-or-less in alignment with each other, and thought it unlikely but possible that they reached out across the 40 miles of intervening Welsh countryside to connect.   Given the distance, I figured Swindon may have tried downsizing the Hawksworth Ten-Wheeler County, rendering it outside-framed.

And the gauge slowly narrowed as you travelled from the W&L to the VoR. :jester:

 

Keith

Edited by melmerby
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Gibbo675

Gibbo675

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Steam locos do not have a gear box so the amount of power supplied to the wheels is regulated by emission of steam into the cylinders.

 

 

Hi Clive,

 

They do however have fully reversible variable valve timing and depending on the type, some have variable advance (lead steam) and others are just fixed.

 

Gibbo.

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Michael Edge

Michael Edge

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Good point, I hadn't thought of it like that. The centre coupling rods were removed because the axles were already coupled by gearing.

 

Officially any axle that is driven by a common power source with another is coupled, whether an outside coupling rod is attached or not

As all the wheels could be driven through gears from just one engine the Fell was always a 4-8-4 (or 2-D-2 as it was a diesel?)

 

Keith

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Mr_Tilt

Mr_Tilt

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Shane and I had talked about what we planned to do with 832 quite a few times as I'd signed it in to the R&D fleet by pure fluke. We were working late on POP-Train when 832 arrived at the RTC and I was the 'senior rank' present.  :D The way Shane built the model is how it was intended to be, but they decided that the APT-P Power Car tilt system needed to be tested as well as the transmission for the BP17 bogies and the anti-tilt pantograph so we built the 'Trestrol' instead, the real world Lab 24.

 

Shane said he'd like to build 832 as it was originally planned, but I never thought he'd actually do it until one day he said 'What do you think of this?' and showed it to me! As usual with his work it's an amazing model.

 

I'll try and persuade him to bring it to Warley this year as he and I are both on the DEMU stand there on the Sunday.

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LNWR18901910

LNWR18901910

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What a great selection of models! Suppose we made an electric locomotive with both back ends of the Class 91?

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