BR Standard class 6 No. 72010 'Hengist' and Clan Discussion Thread

Fair comment, including the point about the offset thrusts, though I would expect that factor to be more relevant to racking forces on the frames than to balancing. I seem to recall that the Counties were one class that qualified as "boat race" engines. Maybe Gresley wasn't so far wrong in choosing three cylinder designs for almost every duty.

 

Do you not count the GWR Saints as large in this context?

 

Must admit, I hadn't thought of those. But all GWR 4-6-0s look alike anyway!

However, they still didn't have the frames over the axlebox centres, one of the points in the 72010 report.

 

Had many a run back in the day behind an 8F pressed into passenger service, especially at peak holiday times. 48151 of course carried on this tradition.

 

Not express and in that context no different from a class 5 but interestingly balanced to suit the task better. Saint isnt really a big engine either.
Always makes me laugh when people refer to 'the Massive' 9F when its smaller in every respect ( apart from cylinder bore) to Light Pacifics

 

Which class are you referring to?

 

That report is not the only instance of concern being expressed about the off-set forces brought about by having the frames over the axlebox centres. Solutions to one perceived problem frequently give rise to another problem. I rather like the French solution which was a welded equivalent of the cast steel bed which offered other advantages in that it was not only lighter but offered the chance to include air reservoirs, large lubrication tanks and sand boxes within the construction. Too much of a leap for BR to make at the time though.

 

Had managed to to gain the impression that only few of the French welded frame construction were built, what might be known from any experience in service?

 

Their were a number of designs produced which used this system. The 152P was close to completion but fell victim to the French politics being played out (blame steam traction for the need to import coal, no mention of the fact that this coal was imported in order to produce the type coke type needed by the French steel industry). The French engineers were very good at predicting the performance of the locomotives that they were producing. They also had much experience at producing modified frame designs to withstand the impact of much improved performance brought about by scientifically driven design improvements. They produced designs for fully welded plate frames but although these were cheaper to produce than the welded steel bed frames they did not offer the range of valuable options available with the bed type.

From what I can gather, these frames were designed to be an improvement on the cast type. The careful design of an alternative to the plate type with all its bolts and rivets to say nothing of its lack of rigidity has much to recommend it. The French were looking for locomotives with a sustained power output far in excess of that required in the UK. They had achieved 5,500 hp but needed more hence the design of a frame type suitable to meet the needs of the power output. A maintained output of 6,000 hp is very different to the outputs seen as adequate for the UK. If you are designing for this level of output you need to design accordingly and hence the attention to the frame design. Much to learn here.

 

The crank pins are some distance outside the frames anyway, whether the axle boxes are centered in the frames or just outside, so it makes some difference to the racking forces, but not the difference between large forces and none. Anyway why does it have a major effect on the longitudinal unbalance forces?

 

Power class. Typically less than 30sq ft grate. 225psi 18.5 inch cylinders.

 

No, I was asking which kind of loco you were describing as "Not express and in that context no different from a class 5 but interestingly balanced to suit the task better".

 

As I read it mr Mikado means the 9Fs that was timed to do 90 timed by thrustworthy timers many times.
The 9F proud parents was Riddles WD 2-8-0 and 2-10-0
Due to the small wheels and heavy pistons there was no much space for balance mass in wheels and only the rotary parts were balanced.
Mr Steve has once stated that cab conditions became intolerable over 25mph due to fore and aft shutling.
When Riddles ordered Jarvis to make a postwar 2-10-0 this was a no go way.
In rest of Europe post 1940 there was made alot of fast passenger locomotives as three or fourcylinder compounds but none as two cylinder simples.
Only UK tried with Britanias and Clans and got a lot of drag box and frame breakage problems..
To accomodate the balancing masses for 40% of the reciprocating masses Jarvis selected to spread all this extra evenly in all driving wheels.
The WDs and 9Fs had nearly same wheel diameter and same reciprocatary masses.WDs became uncomfortable at 25mph and 9Fs thus at 40mph due to 40%balancing.
Uncomfort grows squarely with rpm so a 9F at 90 must have been uncomfortable indeed.
The way to get a fast,non frame-breaking Clan is to have more solid(heavy )track and balance more tha 40% if the Civils will allow.

 

Given the official BR response, that really ought to read "were caught doing 90mph several times".

 

The WD 2-8-0s were certainly rough riders above 25 mph with coal coming out of the tender to spread over the footplate; I don't know about the WD 2-10-0s having no experience or heard anything expressing an opinion. But the 9Fs were excellent riders; it was the only good thing many enginemen in my neck of the woods had to say about them (well, there were a few other good points too!). But the general opinion was that the 9F rode as well as most coaches.

 

Interesting discussion but wouldn't the 9F have suffered less sideways "racking" due to its longer fixed wheelbase, especially compared to a 4-6-2?

 

The WD 2-8-0s were certainly rough riders above 25 mph with coal coming out of the tender to spread over the footplate; I don't know about the WD 2-10-0s having no experience or heard anything expressing an opinion. But the 9Fs were excellent riders; it was the only good thing many enginemen in my neck of the woods had to say about them (well, there were a few other good points too!). But the general opinion was that the 9F rode as well as most coaches.[/QUOTE]

Having ridden on 600 Gordon between York and Sheffield coming back from the S&D 150 event I can confirm that they most definitely end up with the footplate full of coal. The ride at 45/50 mph is most uncomfortable on the footplate.

 

It was not wanted to let the drivers control these Yawing movements for wear reasons.
The outcome of Cox/Stanier journey to India preWW2 was to increese the stifness of boggie/pony truck sideway springs
Fixed wheelbase is not so important as guided length and spring rate.
Pre WW2 quite some of the allowable reciprocating balance was dedicated for neutralising yawing until Bulleid eliminated it after trying on a Schools class.
On a 15feet wheelbase Lady of the Lake it was essential but on a 27-32feet long modern not so much

 

Hi Mr M, I Had in mind Std 5/ Black 5/ hall / B1. An 8f has similar sized Cylinders and boiler pressure to these and so its piston thrusts are of a similar magnitude. A Brit or County is a fair step up in Piston thrust. Hadnt thought much about the 9f which were not primarily passenger locos but from the passenger work performed there doesnt seem to be anecdotals about being rock and rolled by a 9f starting a train. Presumably the tender draw bar arrangement was pretty 'standard' on a 9F but the approach to balancing iirc quite different.
i Still have a few qualms about the plan to up the boiler pressure on 72010, in itself its not a problem but feel a reduction in cylinder size should be there at the outset to limit the piston thrust to values closer to the original, here is another reason for that.
Having a damping arrangement on the Tender to train drawbar as well as the loco to tender one worth looking at or do we just end up with a cab floor full of coal ?

 

Hermod has mentioned smallish-wheeled locos running at high speeds in other countries. How have they been balanced to avoid causing longitudinal oscillation of their trains? Was it at the expense of more hammer-blow?