Why do I love Articulated Locomotives? This is a question that I have asked myself on numerous occasions and still come up with the same answer -because of the work required to design and build them... I have a love of the strange and weird and it has been rightly said nothing is stranger than my collection of DIY monsters.

I can appreciate the Art Deco beauty that is a New York Central Hudson or a Norfolk and Western Y class, the sheer power that is a Challenger. But to my mind there is nothing as wonderful as a Rhodesian Railways class 15A or the Algerian PLM Garrett .

On the mainline UK rails you would be lucky to see an LMS Garrett or the mighty LNER U1....

They were answers to problems -some of them were successful -some may never have been answered by that particular locomotive. But most of all they were design statements, and in my small way I applaud their designers!!!

What follows here is a small series of thoughts on what types there were...

The Single Fairlie is characterised by the pivoting steam bogie at the front and a simple bogie at the back. In the USA these are known as Mason Bogies, as Fairlie's Patent was not applicable in the USA at that time.

The Double Fairlie is characterised by the obvious double ended boiler on the two steam bogies. The firebox is central and there is a divider in it to prevent the blast from one funnel pulling the flames from the water tubes in the other side -which was an early problem. They reached enormous size on the Mexico Central railway -but always suffered from the fact that as the boiler got larger the more it intruded into the loading gauge -until there was not enough room for the crew.

The Modified Fairlie looks remarkably like a Garratt -this is not a mistake... The North British Locomotive Company (NBL) designed this to look like a Garratt but not infringe any of the Beyer Peacock Patents. The main problem with a Modified Fairlie is the fact that the water and coal bunkers are on the same frame as the boiler. This gives VERY large overhangs plus the inertial stress on cornering puts extreme side thrusts on the pivots. They were chiefly used by the SAR and supplied by NBL and Henschel und Sohn.

The Meyer can claim to be the most common form of articulated locomotive. They are compact and easy to maintain. The main features of a Meyer are the central cylinders. The front Low Pressure  and the rear High Pressure. The main problem with the standard Meyer is the fact that the fire box cannot be very large. The Royal Saxony Railway were great lovers of these although they can be found from Fiji to South Africa it is perhaps these locos that come to mind when they think of Meyers...

Messrs Kitsons of Leeds solved this problem and (of course) patented it. The solution was to move the bogies further apart thus leaving room for the firebox. I have shown the most common layout of cylinders for a Kitson Meyer with the cylinders at the rear of the bogies. The last implementation of the Kitson Meyer design can be said to be the 'Leader' locomotive. They were very popular in South America -reaching huge sizes. The main problem with this design is the fact that the frame can make the loco far too rigid for poor quality trackwork.

What exactly constitutes the true definition of a Mallett is open to question... It is normally agreed that the front bogie is free to swing under the boiler and the rear bogie is fixed. In the original the front bogie is the Low Pressure cylinder and the rear is the High Pressure. Several experimental designs have produced variations on this with triple expansion -or a second set of low pressure cylinders on a trailing bogie. Confusion has arisen as it is quite common in the USA to call a simple articulated (using straight boiler steam) to all cylinders as a Mallett.

The Garratt is the most famous of all the articulated locomotives and its advantages are well known. However it does have one very bad characteristic -its length... This leads to very long steam pipes and other things having to be stretched to vast distances. There are only two known examples of compounded Garratts, these being K1 and the Burma Railways loco. Possibly it could have been compounded in the classic von Borres manner -a central high pressure and two external low pressure cylinders. But the fitting of receiver vessels and such like would involve far too much long plumbing and rod work...

The Union Garratt was an attempted dodge like the Modified Fairlie (see above) to bypass the Beyer Peacock Patents on it. The rear tender is fixed to the cab and imposes additional strains on the rear pivot point.

The Golwe is a unique design, (some would say thankfully!) However technically speaking it was very advanced. It had the compactness of a Mallett with the articulated cornering ability of a Garratt, it could have the deep fire box of a Kitson Meyer. So, why isn't it very well known?

It was only produced by one small Belgian company for The French Colonial Railways. So, your chances of seeing one were pretty rare. In total there may have been only 48 of these...

The du Bousquet was a design that may be classed as a Meyer...  It has the Meyer central cylinders and the front water tender of a Garratt. Topologically it can be seen to be the exact reverse of the Golwe. These were made in quite large numbers for the Paris commuter railways. Examples existed in Spain and China as well.

It is normally thought that Geared Locomotives are a small subset of the articulated type -however the reverse is quite true...

The very first locomotive made by Trevithick was a geared one!

The Shay type of locomotive is characterised by a single drive shaft on right hand side (with the exception of three made for English owners). There are two or three vertical cylinders driving a crankshaft. Power is then transferred via two sets of Universal Joints to the bogie and thence to the drive wheels by external bevel gears. The chief problem with this design is the vibration and so the design is strictly low speed. There was a Shay at The Peacock Iron Works in Bilston Staffs. As far as I know this was the only Shay in England.

The Heisler type of locomotive has two cylinders under the boiler at right angles and power is transferred to a central drive shaft thence to the power bogies via a Universal Joint. Each of the UJs then transfers power to the wheels via bevel gear at the ends of the bogie. The remaining wheels are driven by conrods. The fact that the cylinders are underneath the boiler limits the size of the boiler. But, Heisler type locomotives are the fastest of the genus -capable of 12mph.

The later Climax 'B' type of locomotive had two cylinders at a raised angle driving a transverse shaft on which there were central bevel gears. On central longitudinal shafts were the two power take off bevels leading to two power bogies. The final drive to the wheels is similar to that of the Heisler. The reason why the final bevel gear is at the end of the bogie is to lessen the angle change taken by the drive shaft

Of all the types of locomotives Chain driven ones are perhaps the rarest... However this has not stopped enlightened design in this field. The chief problem of any chain design is cornering -chains are notoriously inflexible but this can be overcome. The main advantage of a chain drive loco is the smoothness of the power delivery and there is no hammer blow to the track. Whereas rods work by pushing and pulling, chains only pull -this leads to some interesting design problems...

The Davidson Company of New Zealand patented a type of chain that had shoulders machined into the links -thus the force was taken on these rather than on the ends of the links. They produced a series of locomotives based on this system. The drive from two horizontal cylinders being transferred to the front and rear chain driven bogies in a similar manner to that of the Climax -except it drove a central tranfer box to the chain sprockets. On each axle there was a drive sprocket which took every other link in the chain. In the drawing below I have simplified things by only having one drive chain per bogie whereas in practice there were two. The pitch of the chain was 4 inches. The Davidson design tackled the problem of cornering by having long lengths of chain.

Possibly the most (in)famous locomotive to be driven via chains was LEADER. The loco had an 'unbalanced' drive system that some theorise may have lead to its major problems with the central crankshaft breakages. BUT, all who used it did remark that it was very smooth running with a high tractive ability. The LEADER design tackled the cornering problem by pivoting the entire assembly as a bogie -thus in effect everything remained in place with no torsional problems.

Lever articulation is an extinct technology. There are, as far as I know, no existing examples of this type. There have been several and here are just two of the more successful.

The system as proposed by Johnstone was in two forms -the type shown below was for his Double Fairlie type locomotives. It is mechanically incorrect -or rather it is only correct in the 0 and 180 degree positions. The later type as proposed for his 4-6-0+4-6-0 IS mechanically correct as everything is centred on the axis of the driving wheel -however this was never built... I am grateful for Mr C.J.Walas who provided me with the actual Patent drawings for the Double Fairlie type.

The system as proposed by Hagans is perhaps the most successful -as witnessed by the fact that they built quite a few of them!!!

The piston pushes on the first green lever and moves it backwards transmitting power through the red lever to the wheels and conrods. Power is also taken off the blue push rod to the second green lever and thence to the wheels and conrods via the red lever. Thus power is sent to both bogies from one set of pistons. The rear bogie swivels in the manner of a mallet. How the power is transmitted to the rear bogie during cornering is done by the pivot point of the rear green lever moving forwards or backwards... This is done by taking the position of the rear bogie from a measuring bar and moving the pivot with it.