Trolleybus Tower Wagon
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Notes About This Vehicle

There is also video of this vehicle >
From the days of electric tramways, special vehicles with extending towers were used to assist with the installation and maintenance of the overhead wires and suspension fittings; the earliest were horse drawn. Later, these towers were placed on motor chassis and the practice grew of converting former buses with life-expired bodies into tower wagons, by re-using the chassis and running units.
Trolleybuses started to replace trams in London from 1931 and additional tower wagons converted from buses were delivered in 1935. In the same year the first batch of eight new purpose-built vehicles arrived, fleet numbered 150 to 157, with a further eight in 1937, numbered 195 to 202. All 16 vehicles were re-classified in 1939 as 75Q to 90Q and the vehicle in this drawing changed from 201 to become 89Q.
These new wagons were based on AEC’s ‘Mercury’ chassis with a spacious cab and a wooden 3-section telescopic tower manufactured by Eagle Engineering Co. Ltd. of Warwick (they also made 4-piece towers). With the Mercury chassis no longer in regular production in 1938, further tower wagons from AEC were built on the ‘Matador’ and ‘Monarch’ chassis. The practice also continued of using ex-bus chassis as service vehicles where their bodies were beyond economical overhaul. Some STLs, the fleet of which were being replaced by new RTs, served this purpose. In later years further ‘Mercury’ chassis (not the same as the earlier type) also received towers.
It can be seen in this drawing that the unladen weight labelled on the nearside is surprisingly perhaps under four tons. The towers were regarded as part of the vehicle’s load carried, thus making a useful tax saving.
When no longer needed by London Transport 89Q became a recovery vehicle in Worcester and a crane replaced the tower. After having several owners it was then bought by the London Transport Museum for preservation in 1992/93 and completely restored. Parts for the tower made by Eagle Engineering were recovered from other vehicles.
The tower could be raised powered by the engine, with a safety lock disengaging the gearbox; the tower could also be raised manually by a crank handle at the rear. The tower in itself was a clever piece of design. The outer (lower) section was permanently fixed to the rear of the vehicle. The middle and upper sections were necessarily each smaller in plan, fitting neatly one within the other, with greased metal runners on the outer vertical corners, and rebated equivalents on the inner vertical edges, to act as slides.
In order to keep the three sections in close contact, the outer (lower) section had all its fixing bolts with their nuts protruding on the outside. The innermost (upper) section had the reverse, with the nuts on the inside. The middle section could of course not have nuts protruding either inwards or outwards in proximity to the corner uprights and so the wooden cross pieces and other structural aspects were crafted with cross-halving and other woodwork joinery. In some places stout dowels held components in place, as well as fishplates.
On the nearside was a 3-piece extension ladder, each part of which was attached to its appropriate section of the tower, and thus raising and lowering with it. Horizontal metal rods acted as guides to stop the sections jamming.
Not being an engineer, I cannot explain why the two-piece central jacking screw had the lesser diameter one at the bottom and the wider at the top.
A technical description issued by AEC in1937 explained men could conveniently work on overhead equipment under low bridges when the tower was in its lowest position and that a 3-section tower reaches a height of 30 feet (35 feet for a 4-section tower). In reality the towers were seldom (if ever) raised to the maximum in London, with trolleybus overhead equipment having a regulation height of 21 feet from the ground. Workmen would of course mostly be below the wires and with their heads notably higher than the platform handrail. That said, there was the need to service the traction poles on occasions and some tall ones had finials 34 feet or more from the ground.
A tool box was fitted to the offside of the tower with another at the rear of the upper platform for the workmen. At the top of the upper section of the tower, below the platform, was a large metal cog, bolted to it. At the rear was another, much smaller diameter cog. With the aid of a crank handle this could be turned and so, working its way around the large cog, the whole platform could be rotated to suit the task in hand.
In its lowered position the platform had shallow sides and a three handrail supports each on the nearside and offside, collapsed when not in use. When the tower was raised for use and the platform in its erected position, these supports were moved to vertical, raising the handrail, which was then secured by a pair of metal rods on each side to provide stability. On both nearside and offside, a vertical right-angled plate stopped the uprights from going beyond 90 degrees. On the nearside a horizontal angled plate acted as a small step for workers transferring from the ladder onto the platform.
These vehicles were in effect mobile workshops and as part of their repair kit carried spare overhead traction and suspension wires and also a spare wheel. A large vice was provided on a small workbench at the rear.
When trolleybuses started to disappear from London’s streets in 1959, somewhat ironically this very same fleet’s maintenance vehicles was used to dismantle the overhead equipment it had helped install in the 1930s. The last of London’s trolleybuses ran in service in the early hours of 9th May 1962.

Notes About This Drawing

The drawing is based on a very few indistinct black & white period images of other tower wagons in service, but largely from over 400 general and close-up detail colour photographs of 89Q in its current state of preservation at the London Transport Museum’s store at Acton. In the absence of any construction drawings the vehicle was also measured extensively. With the kind assistance of the staff at Acton, the tower was raised for further photography and for a video to be made.
In 1956 89Q was loaned to a film company and featured in a few scenes of a B-thriller called The Hostage. In this film 89Q reveals some details not quite the same as in its present restored state. For example, the ‘Autovac’ fuel tank is black, where often they were red. These details have been incorporated in the present drawings. Some close-up scenes in the film may show another vehicle, where differences are apparent in the position of the lettering transfers. None of the detail in this drawing can be regarded as definitive of when the vehicle was in service.
It should be understood that all four elevations are seen here as one would see each part of the vehicle at a truly perpendicular angle. In real life this is of course impossible.
 
drawing copyright Douglas Rose September 2018
 
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