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paulingram
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|  | Lynton & Barnstaple
« Thread Started on Mar 16, 2012, 10:10pm » | |
I decided last year to have a go at a big 7 1/4 gauge loco. I wanted something for heavy passenger hauling.
I have spent some time starting to draw it up in 3d cad using various published source drawings. Going through it this way helps me to understand what I'm getting into and to sort out a lot of issues now rather than later.
I just thought I'd share the progress to date. Not yet ready to cut metal but getting there. I will carry on with the Cad work whilst finishing off the renovation on my 5" engine.
Paul
![[image]](http://i172.photobucket.com/albums/w23/koiboi_2007/LB1.jpg "[image]")
![[image]](http://i172.photobucket.com/albums/w23/koiboi_2007/LB2.jpg "[image]")
![[image]](http://i172.photobucket.com/albums/w23/koiboi_2007/LB3.jpg "[image]")
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Shawki Shlemon
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| | Re: Lynton & Barnstaple
« Reply #1 on Mar 17, 2012, 4:51am » | |
These pictures look good , my question is , are you building an engine of your design completely free lance ( no relationship to any full size engine )? or are you designing a free lance that look like a real engine in appearance but still a free lance and you can do whatever you like to make it meet your needs ? In my opinion the second option makes the engine mor interesting and valuable but again that is me , you may be different and I respect that .
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paulingram
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| | Re: Lynton & Barnstaple
« Reply #2 on Mar 17, 2012, 8:27am » | |
Hi Shawki
It's based on the the 2 ft gauge 2-6-2 Lynton & Barnstaple engines Yeo, Exe, Taw, Lew.
It was particularly inspired by the replica engine (Lyd) built by the Ffestiniog & Welsh Highland railway.
There are examples of these around in 7 1/4 gauge, mainly built to the Milner Engineering drawings now available from Reeves and 3 1/2" versions from the Les Warnett drawings & articles serialised in Engineering in Miniature.
I also liked a lot of the modifications and updated engineered into Lyd. I went for a combination of these sources, hence re drawing it all.
Here is an image of Lyd lifted from the internet...
![[image]](http://i172.photobucket.com/albums/w23/koiboi_2007/AT301000.jpg "[image]")
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cotswold
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| | Re: Lynton & Barnstaple
« Reply #3 on Mar 17, 2012, 8:48am » | |
'Lyd' on station pilot duties at Porthmadog.
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steamjohn248
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| | Re: Lynton & Barnstaple
« Reply #4 on Mar 17, 2012, 9:09pm » | |
Hello Paulingram,
As you say there are several of these around now. in 7 1/4". The Reeves drawings are by no means drawings to build from and are the remnants of Milners "Works Drawings".
Our was built 'Based on' but not a faithfull copy of the Land BR engines. One of our drivers is over
6' tall and yet comfortably sits IN the engine to drive.
She is now in her 3rd year of duty hauling 2 1/2 ton trains on a regular basis and seems to work well.
If we can assist feel free to get in touch.
John Dines L and B (min) R
There is (or was last time I was there), a boiler for an L and BR 2-6-2 that would be abvailable.
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Shawki Shlemon
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| | Re: Lynton & Barnstaple
« Reply #5 on Mar 18, 2012, 8:23am » | |
Hi Paulingram
Thanks for the clarification , the engine seems very interesting one , while I am in smaller engines but the large engines have a place in our hobby and very capable of hauling people , we have a few 7.25" large engines hauling passengers and giving a chance for others with small engines to play trains .For example you can see my 7.25" G Rocket next to a free lance 7.25" G on my web page , page 5 . This makes the hobby quite interesting and gives every one a chance to do what they like .I wish you all the best and hope to see some of your work here . 
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jma1009
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| | Re: Lynton & Barnstaple
« Reply #6 on Mar 18, 2012, 10:03am » | |
hi paul,
one of the most beautiful locos ever built IMHO!
the drawings you have done are very interesting.
from memory (as i dont have the relevant copies of EIM anymore) i believe Les Warnett's 3.5"g design was quite a big loco and very detailed as i believe he used the original SR works drawings. as im sure you are aware LEW differed from the original Manning Wardle locos in a number of respects, and both types allegedly suffered from a small firebox and a very long boiler leading to steaming difficulties in fullsize. i believe LYD was altered to overcome some of these difficulties at the design stage, though i bow to those much more knowledgeable than me in this respect.
my granny was very fond of these locos, travelling regularly on the L & B in the summer in the 30s till the line closed. she surprised me when i was in my teens by recognising the locos in a book i had, and still remembering their names after some 40/50 years!
cheers,
julian
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paulingram
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| | Re: Lynton & Barnstaple
« Reply #7 on Mar 18, 2012, 12:53pm » | |
Hi Julian
Lyd had a number of design changes to deal with indifferent steaming on the original. Their main changes were around re working the free gas area of the tubes and the inclusion of superheating with concentric elements.
Other changes included a steel firebox and smoothing out the steam flow to cylinders where possible.
I have gone along broadly the same path and included superheating albeit with radiant rather than concentric elements.
You can get the idea from the pic below where I have hidden the outer shell of the boiler.
Cheers
Paul
![[image]](http://i172.photobucket.com/albums/w23/koiboi_2007/boilerfrontend.jpg "[image]")
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jma1009
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| | Re: Lynton & Barnstaple
« Reply #8 on Mar 18, 2012, 1:04pm » | |
hi paul,
very interesting indeed!
i wish i could do drawings like yours! mine tend to be rather scrappy pencil or biro sketches on the inside of cereal packets that i cut up for the purpose!
i would make sure you have quite big flue tubes, and i would have a combined hot header for the superheater elements before branching off to the cylinders. have you done a free gas flow percentage calculation vis a vis the grate area and the flues/tubes? i would think you ought to aim for at least 25% on a boiler of this type, if not more.
anyone else had a granny who turned out to be a 'spotter'?!
cheers,
julian
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paulingram
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| | Re: Lynton & Barnstaple
« Reply #9 on Mar 18, 2012, 1:44pm » | |
Unfortunately, the free gas flow % is pretty low at 13% and with a boiler of these proportions, it's always going to be that way.
By the time you have reasonable sized flues and allowing for the required areas between tubes in the tube plates it cant get much higher.
The % can be a bit higher but only by dumping the larger superheater flues and thus losing the compensating efficiency gains from the superheat.
On the basis of the outside shape of the boiler being more or less fixed by the proportions of the prototype, I cant get much more free gas flow.
Paul
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jma1009
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| | Re: Lynton & Barnstaple
« Reply #10 on Mar 18, 2012, 2:34pm » | |
oh dear! 13% is pretty low 
less tubes but of bigger diameter will provide a greater free gas flow percentage... i would give it a try on the drawing board IMHO. nothing to prevent you having some of the tubes of different diameters either. they really ought to be quite big tube diameters on a boiler of this type to ensure free steaming.
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steam4ian
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| | Re: Lynton & Barnstaple
« Reply #11 on Mar 18, 2012, 8:08pm » | |
G'day Paul
Great drawings! What is your CAD programme?
Regarding tube area, why don't you try the spreadsheet in Baggo's web site?
Whilst 13% might sound low, the articles about boiler design referred to by Baggo suggest a value around to 15% as optimum. 25% is too high and would indicate inefficient heat transfer and the blast lifting the fire. Maybe your grate area is too small!
Regards
Ian
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paulingram
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| | Re: Lynton & Barnstaple
« Reply #12 on Mar 18, 2012, 11:26pm » | |
Hi Ian
I use Solidworks for the drawings. I like it and rate it.
I did have a quick look at Baggo's spreadsheets and need to have another go when I'm a bit brighter in the morning. Some of the numbers looked ok, some were multiples of the preferred ranges.
Cheers
Paul
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jma1009
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| | Re: Lynton & Barnstaple
« Reply #13 on Mar 19, 2012, 12:00am » | |
im afraid ian i dont agree at all with your comments.
i have all of jim ewins' papers on the subject, and as commented previously by me in other postings jim's research wasnt necessarily conclusive and a number of the boilers he decided would be poor steamers were in fact extremely good steamers (eg Don Young's RAILMOTOR No. 1 boiler, which i can vouch from personal experience as the first boiler and loco i made, and which others can vouch for too). therefore one is led to the inevitable conclusion that jim's quest to provide a 'be all and end all' formula is lacking.
Don Young explained his own criteria for boilers and free gas flow towards the end of his life, criteria with which i heartily agree.
furthermore, a high free gas flow percentage will not necessarily result in a higher rate of combustion in the fire. if anything the opposite is the case, or at least a much stronger blast (with higher back pressure) is required to get the grate to burn effectively through a reduced set of tubes. one also has to take into account the overall grate area and the length of the tubes. a longer boiler barrel should have proportionately bigger tubes, and in fact jim himself advocated bigger diameter tubes than the Keiller formula.
what jim was trying to do (albeit with the limitations i have attempted to describe) was to get away from the Greenly notion of huge lazy grates.
anyway that has always been my understanding of this matter.
(and i'm not an armchair theorist as one of my locos came 3rd in IMLEC)
cheers,
julian
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Nigel Bennett
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| | Re: Lynton & Barnstaple
« Reply #14 on Mar 19, 2012, 1:03pm » | |
Since you've showed me your L&B one, I'll show you my TR one....
![[image]](http://i720.photobucket.com/albums/ww203/Nigel_Bennett/TR_SW1.png "[image]")
It's not got quite that far in the metal, yet - no superstructure - but having the drawings with dimensions added as I want them for manufacture has been a real help.
Good luck with the L&B project; I did consider building one, but it's a bit of a beast in 3.1/2"g. Les Warnett did a superb job of the design, IMHO.
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jma1009
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| | Re: Lynton & Barnstaple
« Reply #15 on Mar 19, 2012, 1:42pm » | |
hi nigel,
what another fantastic drawing! excellent!
i cant offer a drawing of my narrow gauge version of ffestiniog railway LINDA in 3.5"g,
but here is a youtube clip of my eldest daughter driving her...
http://www.youtube.com/watch?v=aQ9V8Zc4p6w
there are similarities between the boiler of LINDA, and the L & B locos, and nigel's TOM ROLT. both LINDA and TOM ROLT and the L & B locos have relatively small diameter barrels but short wide (and raised) fireboxes allowing the full width of the barrel to be used for the nest of tubes, the inner firebox being as wide or wider than the barrel. this isnt possible on british standard gauge designs.
paul, your drawing doesnt show this feature but it is present in LYD and the original L & B locos, and could with advantage be reproduced in your loco (to overcome the gasflow percentage problem discussed, as well as ensuring increased inner firebox area and steam space above).
here is a pic of LYD's boiler...
http://www.whrsoc.org.uk/WHRProject/2009/pj-bl-010509-3.jpg
cheers,
julian
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paulingram
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| | Re: Lynton & Barnstaple
« Reply #16 on Mar 19, 2012, 6:51pm » | |
Nigel, that looks very nice. What did you draw it with ?
Julian, Anothe useful picture for the collection, Does this approach allow the crown of the firebox to be lifted ? I did think about baffling the inside of the boiler tube to prevent water surging away from the firebox under downslope or braking conditions.
All the best
Paul
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jma1009
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| | Re: Lynton & Barnstaple
« Reply #17 on Mar 19, 2012, 7:50pm » | |
hi paul,
the raised outer firebox isnt there to provide a higher crown but to take advantage of a nice big flat topped and wide inner firebox so providing greater heating surface in the firebox (where most of the steam is produced) and a useful area of steam space. to make use of the wider inner firebox you need a double flanged throatplate encompassing the barrel... which means the outer firebox will be higher anyway than the top of the barrel, and there is quite a lot to be said for having a large area of steam space over the top of the firebox rather like the old GWR broad gauge locos, and to some extent like a belpaire firebox.
that being said, i do think that the inner fireboxes on some miniature designs are a bit low and can be raised without any ill effects (in fact this was another of jim ewins' ideas that he advocated).
i dont think you need worry about surging or fitting baffles.
cheers,
julian
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ejparrott
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| | Re: Lynton & Barnstaple
« Reply #18 on Mar 20, 2012, 1:34pm » | |
One beauty of Paul drawing it in solidworks, is that I now understand how Joy valvegear works, never before having actually seen it in motion!
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steam4ian
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| | Re: Lynton & Barnstaple
« Reply #19 on Mar 21, 2012, 2:51am » | |
G'day Paul
I note that you have your steam dome at the front of the boiler with the raised section over the firebox at the other end (surprise, there's a certain logic in that statement).
If your water is high and you still have adequate steam space over the firebox you could get water carry over at the steam in the dome.
I disagree with Julian over the height of the crown sheet, I have come to this after bitter experience. The boiler on my loco has the crown sheet too high and is a beggar to steam on undulating track. Down hill the water can only just be over the bottom nut or else on the up hill section with the regulator open it is over the top nut and primes. The problem with having to run with the water at the bottom nut is that a moments diverted attention means you lose it. (I have no trouble steaming other locos.)
The other issue with high crown sheets and round top fire boxes is the risng water level reduces the water surface area and disproportionately reduces the steam space. anybody for an oily shower?
Regards
Ian
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