Looking for a six-coupled locomotive

[Steven.T]

Surely you must get more tractive effort from a loco with more driving wheels? Take 9F for example, all those wheels must be there for a reason!

[dougrail]

Can we get a full scale engineer in, por favor...

[Stuvon]

Surely you must get more tractive effort from a loco with more driving wheels? Take 9F for example, all those wheels must be there for a reason!

Yes they are! But it all comes down to axle loadings. A 9F is so heavy that even with 10 drivers it still has an axle load of 15 Tons, this is very similar to a J15 0-6-0 which supports 13 tons per axle. - In this case the greater number of wheels on the 9F mean it will will have a higher tractive effort.

Transfer this to models... An 0-6-0 Lawley (3.8kg) has a similar total weight to an 0-4-0 Ragleth (4.1kg), therefore the Ragleth will have a higher axle load (Lawley = 1.27kg per axle vs Ragleth = 2.05kg per axle) and thus a Ragleth should have a higher tractive effort.

[IrishPeter]

It is a balancing act between the locomotive engineers requirements and the civil engineers requirements, with the cost factor in there somewhere.  However, a high axle loading should mean good adhesion, but might get the civil engineer after you.  It is noticeable that certain lines with low rail weights - e.g. the Barsi Light Railway at 35lbs/yard which adopted 0-8-4Ts to spread the weight of a 30 ton locomotive - or the Saxon NG lines with the 0-8-0, 0-10-0 and 2-10-2 built powerful locomotives with low axle loads.  The Barsi 0-8-4T, built to a five ton axle load, had a tractive effort (11,000lbs, IIRC) spread over all those driving axles the locos were not prone to slipping and could haul 280T at 15mph up a 1% grade whilst rounding a 3 chain curve.  On the other hand, the Ballycastle Railway Kitsons were only slightly heavier but as 4-4-2Ts with roughly 10.5T on each driving axle and a tractive effort of 13,800lbs, they slipped and slipped and slipped, and strggled with the usual 70 to 100T trains on the BRCo. Predictably, they were exiled to the Ballymena and Larne section in 1925 and replace with the old Beyer 0-6-0Ts with an 8T axle loading which gripped far better and could lug four loaded bogies plus tail traffic over the line with little difficulty!  

Somewhere buried in my book collection I have the formular for working out 'factor of adhesion' which depends on tractive effort, axle loading, and summat else, as I recall it.

Peter in AZ

[TonyW]

I assume (I know Ass you and me....) that the VoR and the Silver Lady centre drivers sit on the track due to the sprung chassis?

Ah yes, I should have inserted the word "unsprung" before "Roundhouse".

Non touching centre drivers should actually increase tractive effort, as the weight of the engine is shared over only 4 wheels rather then 6 and this will increase the friction

I can think of a full-size example which tends to suggest otherwise. The General Electric ES44C4 diesels used by BNSF in the USA have A1A-A1A wheel arrangement, i.e. the centre axle on each bogie is unpowered. They also have a linkage arrangement that lifts the unpowered axle off the rail head when rail conditions are poor and the powered axles lose traction. http://www.youtube.com/watch?v=g-4ZlqODyo8

[Keith S]

Peter, it sounds as if you could use a Garratt, or start running double-headers. I guess that would be quite challenging with your very different types of locomotives and manual control.

The Roundhouse engines all use the same cylinders, so unless the six-coupled engines are quite a bit heavier than the four-coupled engines, I can't picture adhesion or pulling power being much different. Especially if the middle wheels don't even touch! I would be tempted to get a Lady Anne or something and order flanged middle wheels, then pile on a lot of extra weight (maybe lead weights in the dummy tanks?) and see what happens. I think Roundhouse engines could benefit traction-wise from extra weight: mine is quite capable of spinning its wheels if you try to hold it back, I suppose that means the limit to its pulling ability is lack of adhesion, rather than lack of power.

[IrishPeter]

I have a 'Millie' which I tend to think of as the mighty brick - she looks like a brick, she weighs about the same as a brick, and could pull a brick!  With a rolling start she can pull five bogie coaches and five four wheel wagons (about 12lbs tare) up a 1 in 24 gradient, which is the sort of performanace needed on the Ross and Cromarty Light.  However, she is a small locomotive - only 9.75 inches over buffer beams, so she looks like a bit dropped off with a couple of 26" bogie carriage in tow.  I am going to build some smaller bogie coaches (allegedly 'the original stock' as opposed to the long ones 'the Calthrops') but they will still be 20-22 inches long!

Peter in AZ

[Dr. Bond of the DVLR]

Could someone please tell me what "Tare" means?

[IrishPeter]

Basically its the empty weight of the vehicle, so that when something was run on to the weighbridge you knew how much to subtract.

Peter in AZ

[Stuvon]

I can think of a full-size example which tends to suggest otherwise. The General Electric ES44C4 diesels used by BNSF in the USA have A1A-A1A wheel arrangement, i.e. the centre axle on each bogie is unpowered. They also have a linkage arrangement that lifts the unpowered axle off the rail head when rail conditions are poor and the powered axles lose traction. http://www.youtube.com/watch?v=g-4ZlqODyo8

I'm with you on this and it's simply a way of making the driving wheels take more weight and increase the friction.

Thinking about 0-6-0 vs 0-4-0, in model form the extra contact area of 2 more wheels probably adds about the amount that the lower axle weight takes away. Therefore the weight of the loco probably has the biggest effect on pulling power.

[INJIN]

Multiple driving wheels can do two things.

Increse the adhesion factor by putting a larger footprint onto the rails. For instance an 0-4-0 has only four points of contact with the rails but an 0-10-0 has ten points of contact & therfore although asuming the two are the same weight the 0-10-0 will pull much more.

The other thing is more wheels have he effect of lowering the axle load for a given weight of locomotive.

So..........generaly freight locomotives have lots of small wheels which give good traction & a lower speed at which peak power is delivered. Faster locomotives tend to have larger but fewer driving wheels which develop maximum horsepower at a higher speed.

We are talking narrow gauge here of course but the rules still apply.

[Narrow Minded]

Extract from my copy of the "LOCOMOTIVE ENGINEERS POCKETBOOK" (dated 1926)
Adhesion and Number of Coupled Axles

[Sylvian Tennant]

I've put an order down for a lady anne, just waiting for roundhouse to contact me back for confirmation.

I made my choice from what I saw on here and what I saw in the flesh.

[Stuvon]

Extract from my copy of the "LOCOMOTIVE ENGINEERS POCKETBOOK" (dated 1926)

Right...  N = Number of coupled axles, T = Tractive Force, L = Load on coupled Axles.

Taken from the above book:

N= 5T
    2240L

for those that don't like algebra, (sorry if I have over simplified this) this means:

N = (5xT)
    (2240xL)

By multiplying both sides by (2240xL) this can be rewritten as:

N x 2240 x L = 5 xT

Dividing both sides by 5 gives:

N x 448 x L = T

or

N x L x 448 = T

Now assuming no leading or trailing axles ie 0-?-0
NxL (number of coupled axles x Load on coupled axles) = Loco Weight.

Therefore:

(Loco Weight in Tons) x448 = Tractive force in Tons     (assuming the coefficient of friction is 0.2)((taken from book above))

Therefore assmuing the weight of the loco does not change it does not matter if the centre drivers of a Lady Ann touch or not the Tractive force is the same  ;)

[Narrow Minded]

Therefore assmuing the weight of the loco does not change

Which of course it does as the water in the boiler is used

[Stuvon]

[INJIN]

Looks like this is where my theory falls to the ground!

I'm gonna make my next loco an 0-2-0!!

[dougrail]

Looks like this is where my theory falls to the ground!

I'm gonna make my next loco an 0-2-0!!

[Stuvon]

[INJIN]

I could follow Marcs example though..............

http://www.sidestreet.info/locos/loco96.html