BR 2-8-2

[kgbw49]

Thank you, Juniatha! Impeccable analysis as always! Much appreciated! :-)

[Juniatha]

No ------!

kgbw49

An engine with but eight drive wheels normally can never have the same effective or wheel rim t.e as one with ten drive wheels.

In the case of the BR designs, the Mikado (==> I suppose the third coupled axle was to be the main drive axle) could be helped by the 9's low axle load if the Mike instead had been given full admissible load. Something of this kind happened on German DR / DB were a 41 class 2-8-2 was built to an adjustable axle load of 18 / 20 tons (metric) and then the 50 class light Decapod was built for secondary roads to 16 tons. So, they both had 80 tons adhesion mass and consequently both should have had the same effective tractive effort. As it turned out, the 41 proved to be a temperamental engine while the 50 was a reliable lugger mainly because the ten coupled wheels were less susceptible to slip spots and the like - both engines types had the same frame work principal design and also the same was valve gear, the 41 class even had the smaller relative cylinder volume when worked with b.p. reduced to the standard 228 psi. That shows how much piston force or more exactly p·s:D=c¹ matters - as long as it is ample enough to reach adhesion limit. At Rheine, then about to become the last steam depot, the shop delivered a strong expression of what they thought about that adjustable axle load: on a number of 41 engines they had the front set to 18 tons and the back to 20 tons on driven axles.

Jesus ...!

https://www.youtube.com/watch?v=FoGhN9r1L9o

Juniatha

 

[Overmod]

kgbw49

Might a 2-8-2 with slightly higher drivers such as 63-64 inches have essentially the same tractive effort but maybe slightly more speed potential?

Keep in mind that there is a dirty little secret about the 9F design: it did not need "taller" drivers.  It is not a wives' tale that the locomotive was stable up to 90mph, in balancing (which is what the driver size would affect) -- this is a consequence of care in both cross- and overbalance provision.  The longer rigid wheelbase might have assisted guiding on British 'permanent way' capable of appropriate axle load, too (and contemporary German and Japanese practice showed how the lead tender truck could be used for effective chassis stabilization equivalent to what a Delta truck or Cartazzi axle could provide.

 

[kgbw49]

Yes, very much so! Thank you so very much and a grand holiday season to you and yours!

[M636C]

kgbw49

Thanks for that compelling info about the genesis of the 9F. Based on that new knowledge (for me) about the 9F having somewhat of a genesis in a 2-8-2 design, it prompted a question.

The 9F had a relatively small tractive effort for a 2-10-0 and small 60" drive wheels. Might a 2-8-2 with slightly higher drivers such as 63-64 inches have essentially the same tractive effort but maybe slightly more speed potential?

Then again, maybe the light and tight loading gauge and dimensions, and short yard and passing tracks in the UK made that a moot point which is why they ended up with the 9F, I suppose. The 

Any insight would be greatly appreciated!

 

Check out British Railways Standard Steam Locomotives by E.S. Cox (who led the design team for these locomotives). A diagram appears on page 50.

The 2-8-2 used the Britannia boiler on 5'3" driving wheels. For some reason, the smaller Clan class cylinders, 19.5" x 28" rather than the Britannia cylinders, 20" x 28". The final 9F had a smaller boiler but the Britannia cylinders. Thus the 2-8-2 was rated 8F, not 9F , with a tractive effort of 35912 lbf rather than 39687 lbf.

There may have been a concern that four axles with just under 20 long tons axle load (19t 18cwt = 19.9 t) did not have enough adhesion for the higher tractive effort. The 9F had only 15.5 long tons on each axle, so could run on lighter track. The factor of adhesion (adhesive weight divided by tractive effort) was 4.22 for the 2-8-2 and 4.38 for the 2-10-0.

If you want any other details just ask...

Remember, apart from being light by USA standards, the 2-10-0 was only 13' 1" high overall and the 2-8-2 half an inch lower. The 9F was the first major locomotive designed for use in the UK with a wide firebox over the trailing coupled axles, and the wheels were reduced to 5'0" to allow this. Riddles had built a 2-10-0 during the war intended for use in Eastern Europe which had a wide fiorebox over 4' 8.5" driving wheels and a number of these were also used by BR.

Does this help?

Peter

[kgbw49]

Thanks for that compelling info about the genesis of the 9F. Based on that new knowledge (for me) about the 9F having somewhat of a genesis in a 2-8-2 design, it prompted a question.

The 9F had a relatively small tractive effort for a 2-10-0 and small 60" drive wheels. Might a 2-8-2 with slightly higher drivers such as 63-64 inches have essentially the same tractive effort but maybe slightly more speed potential?

Then again, maybe the light and tight loading gauge and dimensions, and short yard and passing tracks in the UK made that a moot point which is why they ended up with the 9F, I suppose.

Any insight would be greatly appreciated!

[Overmod]

cx500

The 2-8-2 that is presently under construction is a new build to a Gresley design passenger engine.

Those designs from the early '30s have utterly nothing to do with BR, which was started in the late '40s under the Labour government.  If he were concerned with Pacific rebuilds in I believe the Peppercorn era -- still not "BR" designs -- I think he'd have said that. 

[cx500]

The 2-8-2 that is presently under construction is a new build to a Gresley design passenger engine.  The small group was built in the 1930s.  Post-war they were converted into Pacifics, so this is a reincarnation of an extinct class.  Nothing to do with the Riddles standard designs.

[Overmod]

About the only locomotive this could be is the locomotive Riddles proposed, with a Britannia standard boiler -- it became the 9F 2-10-0.

I don't have access to the stats of the proposed locomotive, but at least some of the references on the 9F class should have them ...

https://www.watercressline.co.uk/archive/The-Works/Locos/5.html

[IA and eastern]

What was the TE and axle loading of the proposed BR 2-8-2. Gary