The Kings' bogies

The reason that is usually cited for the Kings' odd bogies, with outside frames at the front and inside frames at the rear, is that it was necessary to allow room for the cylinders. However the nominal cylinder diameter of the Kings is only a quarter inch more than that of the Castles, and the first series of Stanier Pacifics had the same cylinder size as the Kings, and more or less the same De Glehn layout. So why did the Kings need that feature when the Castles and Princesses didn't?

 

Worth remembering that the Kings were designed against a tight deadline. If you don't find a better solution within a tight deadline you're stuck with the one you first thought of... FWIW Nock says that they wanted a plate frame bogie, unlike the Castles and it was fitting the plate frames in that in that proved difficult.

 

Perhaps that extra 1/4 of an inch means the inside cylinders have to sit lower down in the frames in order to keep the valves at the same height. They are also 2 inches longer than a Castle.

 

The King's Bogies? what a subject to pick...s'not funny.

 

The driving wheel diameter on the Kings is 2.5" less than the Castles, so the cylinder centreline is 1.25" lower. The GWR bar frame bogie may simply not have fitted, it has a cross member up front at the top of the frame. The Princesses seem to have a plate-framed bogie with equaliser beams, whereas the King bogie has separate springs. I think the Modified Hall bogie is also separately sprung. All things being equal, I reckon you can get away with less height inboard of the wheels using equaliser beams than without. If Collet's team wanted to do away with the equaliser beams, what they did may have been the only viable solution.

 

What Nock says is that they'd been experiencing breaking rivets with the bar frame bogie, and that was the reason for moving to plate frames. Later on, however, they found a cure for the Castle bogie issues, although its interesting to note that the Modified Halls also had a plate frame bogie.

 

The Princesses (and Duchesses) had a bar frame bogie very similar to the GWR version which was itself a copy of American practice. There is a drawing of one on the last page of www.railwaysarchive.co.uk/documents/MoT_Weedon1951.pdf, the faulty assembly of the bogie wheelsets being the cause of the accident.

 

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I stand corrected. That drawing does show an interesting difference between the LMS and GWR bogies, in that the LMS version has a cast or fabricated end stretcher, which is depressed in the centre, whereas the Castle bogie has a flat top bar at the end and bar braces below (this is a Manor bogie, but pictures of Castles indicate the same). The depressed centre on the LMS bogie stretcher would almost certainly have been to get clearance relative to something.

 

I wonder if the longer coupled wheelbase of the Kings was also a factor, necessitating more clearance for curves?

 

If this thread about Bogies is anything like the other threads on Nat pres it will keep running and running......