P2 Locomotive Company and related matters

I'm guessing the cartazzi wheelset is not yet at its ride height in the photo, the clearance under the inner frame plate looks minute!

Well done to the P2 team, it's another major step forward. Good Luck to Daniela in her new role too, a great addition to the team...

Richard.

 

Its not on its springs yet...

 

I was trying to work out where abouts in the hornguides the axlebox will sit once the springs are on... Interesting to see the assembly stages in photos, I wonder if Haynes will do another book along the same lines as Tornado? That would be nice!

Richard.

 

I always wanted to know how these wheels swivel in their bearings when they slide from side to side. I know that the axleboxes move at an angle but I don't understand the geometry.. Any takers?

Sent from my Nexus 7 using Tapatalk

 

Underneath the spring there is a fixed Slide, on top of the cartazzi axle box there is another slide, the slides have a series of matching wedges which, with the wheels/ axles/ boxes horizontal to the frames, are interfaced neutrally , with both wheels taking (say) 15% of the locomotive weight.
The cartazzi axle box and its guides are not arranged perpendicular to the frames in the horizontal plane as is normal but angle backwards from the inside of the frames to the outside. this means the whole axle can slide from side to side and in so doing turns to follow any curve in the rail.

When the locomotive goes into a left ( say) curve the cartazzi axle is pushed to the left relative to the frames by the action of the rail, ( it can do this because its on slides), it also angles to follow the curve of the track, ( because the hornguides are angled to allow this). However because the slides are 'wedged' this action pushes the whole axle in the vertical plane down relative to the locomotive as it is moving up the wedges on the slides.
This transfers more of the locomotive weight to it ... on leaving the curve this weight acts to restore the cartazzi and therefore the whole locomotive back to its central/ neutral position... I think.

 

I thought a quick Google would have brought up some good informative pictures of a Cartazzi but I have failed to find one so here's my attempt.
The first drawing shows one side of a Gresley Cartazzi axle in plan. You will see that the hornguides are at an angle to the axle centreline. The guides are actually curved so that, as the axle assembly moves from side to side it rotates about a virtual pivot point. This is exactly the same arrangement as with a radial truck. The difference between a radial truck and a Cartazzi is shown in the second drawing, which is an elevation of the axlebox. You will see that the top of the axlebox is inclined slightly and, on top of this is a matching piece onto which the spring bears. The opposite axlebox is a mirror image. The axlebox is mechanically free to move sideways relative to the loco frame when the loco is on a curve. However, as it move sideways the inclined top of the axlebox increases the load on the spring, creating a resistance to that movement. Because the two axlebox tops are oppositely inclined the action of the springs is always to try and centralise the wheelset.

I've crudely coloured the drawings to try and better explain things.

 

Got it! I didn't realise the axleboxes were curved as the curvature is hard to see in various photos..

Thanx

Sent from my Nexus 7 using Tapatalk

 

Perhaps I should have said that a Cartazzi doesn't have to have a radial axle with its curved guides as part of its construction. This arrangement applies to the LNER pacifics, though. The Hudswell Clarke built Manchester Ship Canal tanks had Cartazzi axleboxes on the leading coupled wheels to give flexibility but there were no curved hornguides and the axles simply floated across. There was a vertical knuckle pin in the coupling rods to allow this to happen. However, with these tanks, the centre driving wheels were flangeless so I have always been at a loss to understand how the Cartazzi axlebox could ever have worked as intended in practice!

 

Are the horn guides actually curved? It would seem to be a tricky machining job.

 

I can't be positive but I can't see how it would work without them being. Radial trucks are. That's the principle behind them.

 

From memory, in a Cartazzi box the bearing crown is a separate component with a spherical (or equivalent) top, so it can rotate about the vertical axis within the axlebox. This allows the horn block surfaces to be straight (at an angle) with the rotation of the crown in the box avoiding any binding.

 

Very interesting. Thanks for this. I would have thought that machining a curve on the hornguide faces would not have been a difficult task for a major loco works, though.

 

A few posts ago, I thought I had Cartazzi trucks 'sussed'. That feeling has now totally evaporated. Am I the only one who would find an animation or 3D rendering of the motion of a Cartazzi truck helpful at this point?

Do we have anyone who both understands the principles and is a whizz with 3D or animation software ...... pretty please!

 

'Bearing' in mind that in the case of the new P2 (and A1 60163) they have roller bearing. So maybe these are self-aligning, thereby allowing the degree 'twist' required. I really ought to know, but if I did I've since forgotten.

 

And I see that also the P2 web-site has imagined that "slogan": https://www.facebook.com/photo.php?fbid=1420590144716477&set=gm.1988530891363864&type=3&ifg=1

To see pictures like this makes me happy.
A new generation of young people interested and involved in th railway heritage.
Please continue to recrute more females into this industry. They are well as qualified as boys!

kind regards

Knut

 

Today the Trust announced that the Cylinder Club, launched at last year's Convention to finance the cylinder fabrication, is now full, 100 members and £100,000 raised or pledged.


Foxy

 

What is the cylinder diameters and distance to midplane?

 

Interesting looking on the P2 web site. It remarks that they are making welded fabrication Finite Element Analysis (FEA) to check for structural integrity rather than a mono-bloc casting. That set me thinking, considering that the V2 Green Arrow has been [for the moment st least] permanently withdrawn as it's mono-bloc casting is worn out. Could/would the N.R.M. consider using a similar procedure if successful for Green Arrow.........

 

I think the only way to find out would be to offer them a BIG cheque up front to fund a "feasibility study".