Draughting of Jubilees

Since Bahamas is the double chimney one, the concerns expressed in post #1 probably don't apply.

 

Just a comment I meant to make on the double ascent of Shap when 5699 had twelve on. My view was that she was being over fired driver should have thrown the shovel in the tender. I think with a thinner fire she would have made a better fist of things.

 

Maybe at that degree of working the thin fire had already gone up the chimney....

 

Based on what evidence? If you were not on the engine how can you know the the quality of coat used, the state of the fire or a dozen of other variables that come into play? I have no idea which trip you are referring to, but if the crew were having a rough trip that day I'm sure they found it educational and character building - there's nothing like a bit of a challenge.

Peter James

 

That sounds more the root of a poor ascent to me, 12 is on the heavy side for Jube.

 

Yes, heavy - but not beyond what the class was capable of doing. But despite the accolades from enthusiasts and the work put into them by he LMS to make them steam, they were never right. If the engine was in good nick with good coal, the driver knew his business, and the fireman had the right skills they were capable of astounding performances. But if any one of those four was below par, it was almost guaranteed to be a rough trip.

 

Apparently they got one right 5677 had a 28 element boiler which it kept, but whatever they did not seem to have a consistent approach to sorting out problems, 5684apparently ran well with a double kylschap.
As to the Shap run you can easily see what the fireman is doing by watching the chimney black smoke is unburned hydrocarbons there was not much wrong with the coal she was videoed later with a clear exhaust going like the clappers

 

An identical remark was made by a former LMS fireman at the time of the posting of the Shap ascent.
As for the black smoke, just lack of oxygen from a substandard front-end.
Kind regards
Jos Koopmans

 

Would it make sense to continue this discussion?
Kind regards
Jos

 

I think so -- as 2968 says if all was good they were a great engine . they should have been better than a Castle (much) but a lot of the time , they were not .

as regards speed , one could say the same thing about the Scots .massive power but I don't recall any Scot log where 90 mph featured . maybe they were too rough for high speed .

come to that I have never seen anything from a Jub that a Claughton didn't do 20 years before

lets sort out the LMS 3 cyl. engines . posterity will thank us !

 

I think it does. Your blast pipe in 6023 has (short of a main line test run) been proven to be a resounding success. Now is the time for a similar device to be fitted to a Jubilee or possibly a Bulleid pacific to enhance performance. It appears to be a fairly straight forward procedure of unbolting the present blast pipe and replacing it with a Jos Koopmans multiple jet design. I think it's fantastic that steam locomotive development can be continued in the 21st century. I'd like to see and hear a Jos Koopmans blast pipe on a single chimney Castle.

 

@JJG Koopmans would you foresee any issues in designing an exhaust system for a 3 cyl loco as opposed to a 2/4 cyl (as 99% of 4 cyl locos behave as large 2 cyl locos for exhaust purposes).

I think there is plenty of scope for improvement on many 3 cyl machines for sure (as suggested in posts above).

 

I do not see any issues with a 2, 3 or 4 cylinder system. In general the blast orifice of a 3-cylinder version is smaller due to the smaller peakflows.
It is a pity that Ell did not separate his data between 2/4 and 3 cylinder locomotives, his orifice size formula is one outcome fits all! I wish I
had his original list of sizes!
As for a revised design on an existing locomotive, I regard the present single orifice as optimal for that situation. For the multiple version the
possible improvement is based on that size, since the jets behave identical in the chimney the 2/3/4 difference disappears.
Apart from the Rugby test data, the only information I have on the Jubilee front-end is the original layout as in Rowledge/Reed p. 19 fig 8.
If the present single orifice Jubilees still have that arrangement with a 1:7 tapered chimney, the improvement could be spectacular.
Kind regards
Jos

 

if the relative low cost of the new blast cap results in an more economic engine , i'm very surprised that one if Carnforth's jubilees hasn't been trailed with one, or are the people at Carnforth quietly watching the results on 6023 before deciding so see if joss's system is worth fitting, but as ever I don't expect that what would be an commercially sensitive subject will be openly discussed between anyone other than those who may possibly be involved.

 

According to Cox they worked out improved drafting for the Jubilees which gave about a 25% improvement in max steam output. The changes included 1:14 taper. But Cox also says the tube sizes were wrong.

 

It is unclear to me whether all Jubilees received a changed front-end, it may be restricted to a few. As for the tubes sizes, I hope that
the existing Jubilees have been restored with proper sizes as the later series of boilers had that problem ironed out.
Kind regards
Jos

 

Reading between Cox' lines that may well have been the case.

 

I lived on the Midland main line where the 5X s worked most of the express .My mother house was next to the line ,family ,mates ,next door neighbours drove and fired them. I never heard a bad word about then .Trains ran to time. A number of non stop trains were booked 71 mins from Kettering to St Pancras for 72 miles ,a not to easy route. Even so there was no need to blaze away at high speeds.Drivers who liked to thrash along weren't liked by most fireman ,and were known as gowers ,after all who waned to go work at all hours to shovel more coal .

 

With a better front end, you should be able to go faster without shovelling more coal.
For now, I'd just be happy to wait and see what the difference in performance is between Bahamas and the SC Jubilees.

 

Rowledge and Reed supply the numbers of the modified sc Jubilees, there were only 9 of them. In practice they were disappointing.
Looking at the original front-end drawing, it shows a chimney with an L/D ratio of about 1.8 and a orifice to chimney distance ratio
of 7.66 meaning that the jet entrains some 75% of the smokegases before entering the chimney which has to do very little to suck
the remainder. A new blastcap with 4 orifices of 3 inch each, higher in the smokebox, will give the present chimney an L/'D' of
3.6 which surpasses both the equivalent orifice diameter of 5.83 in. and the L/D of 2.92 of Bahamas.
Since the present 1:7 tapered chimney can be seen as a bundle of 4 1:14 tapered chimneys they act together as a scaled version of a 1:14
tapered sc of double length which enhances performance.
Kind regards
Jos