Challenger Smokebox Design

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k36no4862002
Posts: 151
Joined: Sun Feb 08, 2009 4:27 pm
Location: Surrey, UK

Challenger Smokebox Design

Post by k36no4862002 »

Hello,
A quick question for the more experienced out there. I'm building a1/6th model of 3985.
Scaled down the chimney's come out at 4" in diameter with a smokebox diameter of 14".
I was working on a 5/8" blast pipe nozzel. I have recently been doing some research into locomotive drafting and came accross the 1 in 6 and 1 in 3 calcs.
Applying these cals to my smokebox shows that the blast nozzel would need to be 24" away from the chimney.

So I assume this is not going to work on a single central nozzel. Therefore I'm assuming I need to model my model based on a lempor or multiple nozzel design so the the exhaust gasses completley fill the chimney at the top?

Is my basic assumption correct?

If so I'll have to do more reading as I dont really want a smaller than scale chimney but I also want this thing to make steam too

Thanks
Paul
Paul Edmonds,
Surrey, United Kingdom.
2.5" Scale D&RGW K36, 1/6" Scale Challenger 4-6-6-4 (nearly done!!)
Steve Goodbody
Posts: 219
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Re: Challenger Smokebox Design

Post by Steve Goodbody »

Hi Paul,
Doesn't the Challenger have two chimneys? 5/8" certainly sounds like a very large bore nozzle for each one if so, but the grate is probably huge.

By way of reference, I've found the following guidelines to be reliable to get you in the right ballpark for a single-chimney design for burning coal.

- Blast nozzle diameter (in inches) = 0.005 x grate area (in square inches)
- Choke diameter (in inches) = 0.06 x grate area (in square inches)
- Height of petticoat choke = 1:3 cone (with the tip of the cone below the blast nozzle, such that the cone touches the inside diameter of the nozzle)
- Top of chimney = 1:6 cone (with the tip of the cone below the blast nozzle top as above)

For two chimneys, I would start by assuming the combined nozzle area and combined choke area want to be the same as for the single-chimney guideline based on the above, but others may have direct experience for two-chimney engines and I would certainly bow to that experience.

I can send you a simple Excel spreadsheet that calculates the above based on your grate area, if that's of help. PM me if so.

Best regards
Steve
Marty_Knox
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Re: Challenger Smokebox Design

Post by Marty_Knox »

The Challenger does indeed have two chimneys - with four blast nozzles under each!
I believe that drawings are available from the UP Historical Society.
RET
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Re: Challenger Smokebox Design

Post by RET »

Hi Paul,

Big Boys and Challengers are quite similar; basically, a Big Boy is a stretched Challenger so there are quite a few similarities. You can get ALL of the full size drawings for either one from the Union Pacific Historical Society. All you have to do is visit their website. A CD with all of the drawings for one or the other locomotive is available for about $35.00 U.S. plus shipping. For the Big Boy CD, there are over 2,900 drawings. For either locomotive, this is one of the best bargains you will ever get in your entire life!

Even although the Chaski thread is for a Big Boy, you should find that the "Union Pacific Big Boy in 3/4 Inch Scale" thread on chaski.org under "Live Steam" should be a big help. Some of the pictures show how the smokebox is constructed. The thread will give the history of our locomotive up to the present. What's in the model is the same as full size; that's the way Gerhardt built it.

I've put air pressure on the blower connection to the smokebox and at a little over 5 psi., the blower nozzles fill the stacks completely so if you duplicate what Gerhardt did, it should work just fine. One sixth full size is a bit unusual, but it works out to 10" gauge. Is that what you are building? If you get it finished, that's going to be both a big and a heavy beast. Even at 3 1/2" gauge, our locomotive will weigh something over 250 pounds (without the tender) and engine and tender together are eight feet long (and that is in 3 1/2" gauge!).

Hope this helps. Building one of these things is not something you knock off in an afternoon or two, literally it takes years even if you know what you are doing and are taking over a project that someone else has started. Its not that expensive in money, but it IS expensive in time. I wish you all the luck in the world. When we get ours to the stage where it runs under its own power, I'm sure we will both have smiles that go from one ear to the other.

Richard Trounce.
k36no4862002
Posts: 151
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Location: Surrey, UK

Re: Challenger Smokebox Design

Post by k36no4862002 »

All,
Thanks for your help, I have the CD drawing which is where I got the chimney diameter from. I tend to build these engines using works drawings to get the overall look but I then try to use calculations and other workings to make sure the model will operate from a drivers and engineered point of view.
So it looks like I have to go back to the drawing board and go for the 4 exhaust nozzle per chimney idea per the original, which is fine, it gives me a design to get on with, whilst I could just copy the works drawings it does not hurt to check these things out as from experience not everything scales every time.

The loco will when finished (not long now I hope been on it 15 years) will be the same scale the the Big Boy that was in the UK back in the 80's and is now in Australia. Pic for reference, whilst it's over-
BB.jpg
scale for 7 1/4 tracks it still looks about right and means the driver can sit in the tender and not on it.
Paul Edmonds,
Surrey, United Kingdom.
2.5" Scale D&RGW K36, 1/6" Scale Challenger 4-6-6-4 (nearly done!!)
Glenn Brooks
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Re: Challenger Smokebox Design

Post by Glenn Brooks »

Paul,

Sounds like the original front end design was based on Engineer Porta’s Lempor evacuator front end. Porta designed use of multi port Kyychap blast nozzles for the Argentine Railway system coal fired locomotives in the mid ‘50’s. The Lempor front end is proven to be up to 40% more efficient than the older turn of the century single blast nozzle, standardized by the US based Master Mechanics Association in the 1890’s.

With a 14” diameter boiler you will have room to spare to build a Lempor front end. There are many differences between the multi port blast nozzle ejector system and the single port- chiefly the multi-port exhaust surface area is over twice as large as single port versions. Also exhaust tube placement does not depend on the 1:6 and 1:3 formulas, rather the length and diameter are related to heating surface area and cylinder area. Also the petticoat stack is tapered to maximize exhaust efficiency and the individual nozzles are machined at 6* offset to more perfectly direct each exhaust stream up into the stack outlet.it basically sits right on top of the multi port nozzles. The body of the nozzle is machined with a mixing area on top and separate intake chambers below, to further create vacuum to exhaust each opposing cylinder, as they cycle thru to exhaust.

A rule of thumb with the Lempor, is you will be able to reduce back pressure in your cylinders to the point where you will have almost no stack talk. And thereby realize a corresponding increase in horsepower!

I think you would regret building the old school single stack nozzle for this locomotive. Your loco wasn’t designed for such a low level of efficiency and may well suffer performance issues if so outfitted. Rather, may I say you will likely be very pleased if you do build a Lempor front end!

Plus building two multi port blast nozzles, per the prototype, would be absolutely amazing achievement to see and run!

Just as an example, here is the Lempor blast nozzle I refitted to my 12” gauge Ottaway last winter. The nozzle is about 3” tall and has removable ports so I could experiment with different port diameters - to maximize the exhaust stream. The difference in steam generation and power output with the Lempor is very, very substantial in my loco. My loco is now quick and responsive to the throttle, and I have virtually no problem maintaining operating pressure - it wants to run!

I documented details in my build in this thread: viewtopic.php?f=45&t=108988&hilit=Lempor

Jass Koopmans in the Netherlands wrote a fairly complete discussion of the Lempor in his doctoral thesis on front end locomotive development around 20 years ago. His book “The Fire Burns Brighter” is out of print, but still around on line. It’s a fascinating read...

Also, Nigel Day, in UK, is the leading expert on Lempor design these days. Nigel has refined Koopmans’s work and built and operated Lempor front ends on a variety of sizes from full size and 1/8th scale. If you like, I could send you his email.

Regards,
Glenn
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JJG Koopmans
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Re: Challenger Smokebox Design

Post by JJG Koopmans »

Before fabricating anything one should realize why this works at all. Basically a double chimney with 8 orifices is to be regarded as a bundle of 8 scale models of a single large chimney. The original explanation was already given by Mr Buckingham in 1913 and is covered by many pages in modern textbooks on fluid dynamics. The socalled Lempor theory does not make this connection and is flawed for a number of reasons. I would like to mention (in passing) that the 1:1 Challenger 3985 had a Lempor system for a very short disappointing time. My explanation of a multiple orifice front-end can be found here:
https://www.researchgate.net/publicatio ... st_orifice
It covers 1:1 cases, but I have working systems from small Tich and Rob Roy, WCR #9 to the GWR King 6023.
To get a working system, the orifices should be distanced properly from the chimney throat, fancy de Laval orifices are not needed since you do not want supersonic exhaust flows and these orifices are only slightly inclined, remember, they are part of a bundle of scaled chimneys!
As for the last sentence in the foregoing, Mr Day is certainly not refining my work, he is in total disagreement!
Kind regards
Jos Koopmans
Berkman
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Re: Challenger Smokebox Design

Post by Berkman »

Wasn't the further work called "lemprex" or something?
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Chris Hollands
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Re: Challenger Smokebox Design

Post by Chris Hollands »

One thing people have to remember is the front end of an articulated engine often has the exhaust ball joints attached to the smokebox and blast

pipe arrangement this complicates things quite a bit and also limits space available for 1:6 / 1:3 theory's especially in a model .

A successful ball joint design requires quite a bit of space and a place for a spring to tension the ball and seal area not so simple .
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Chris Hollands
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Re: Challenger Smokebox Design

Post by Chris Hollands »

FYI - This is what I have done regards the blast nozzle arrangement on my Challenger, will it work I hope so I'm sure I will have to make some adjustments but its the best I could do to come close to the various principles I have read or seen .
I was unable to do the 1:6 setup it just was not going to work with what I had , the nozzle is 1/2" at the moment I will be running on propane .
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Chris Hollands
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Re: Challenger Smokebox Design

Post by Chris Hollands »

One more
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NP317
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Re: Challenger Smokebox Design

Post by NP317 »

Impressive!
RussN
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