Just as British aircraft production was not just about huge production lines, British fighters could not operate without other aircraft operating in more lowly roles such as target tugs for gunnery practice.
The opinion of many production engineers that line- and track-assembly methods were only economical for large-scale production and could only be applied in workshops of considerable area was shown to be incorrect by the ingenious, but simple, track system installed by Metalair Ltd., for the assembly of Martinet cabin tops. The track installed fitted an area that measured only 68ft. by 26ft., the track equipment being of the most simple and practical nature, and the operations had been carefully planned and timed to ensure balanced production. To overcome lack of floorspace use was made of light overhead racks for storage and drying purposes.
There were two short tracks, each carrying three trucks: on one line were assembled the main details and the other was for final assembly and inspection. Joining the ends of the tracks were cross rails which, by means of a movable switch, allowed the trucks to be transferred to a central rail for return to the other end of their respective lines. By this simple method the trucks progressed with a circular movement, returning to the beginning of their track for loading.
One of the detail assembly trucks. It can be seen that the sliding hood fixture on the right is arranged to tilt to enable the drilling from the underside.
A final assembly truck. Part of the rear windscreen is on the right and the crash pylon in the centre were already in position. Note the truck is running in simple angle-iron rails.
Overhead racks, operated by light winches on which the detail components were suspended for drying after spraying and for short-term storage.
For ease of assembly the cabin top was divided into five main components, i.e., front windscreen, front sliding hood, centre fixed hood, rear sliding hood, and rear windscreen. Each truck on the detail assembly line was arranged to accommodate two different components, one windscreen and a hood : in the case of the front windscreen, which required twice the assembly time of any of the other four items, the fixture was duplicated and the windscreen passed twice around the track before completion. By this means one front windscreen was completed in the same period as the other four components, thus maintaining balanced production.
Each truck was simply designed from light steel angles and strip, and incorporated the fixtures required for the particular component. Where necessary, the fixtures were arranged to swivel or turn over to provide access to the rear or underneath, and each incorporated its own drilling jig and locations. All screws and nuts were run up to a predetermined tension with portable electric equipment carried on each truck. There were three stations on each line, where three sets of operations were performed at each by four workers.
To maintain the workers’ interest in the programme, special indicators and stage clocks were erected at the end of each line. From these the starting (left) and finishing (right) times of the current stage were shown, and every operator was able to see at a glance if the work was progressing according to schedule. As the trucks moved to new stages the clocks were reset by the foreman. On the same boards was given also the following information : (i) number of complete stages finished during the day and during the week up to date, and, below these, the total completed on the contract up to date. From this data the operators were always able to compute their piecework earnings, and were instantly aware if they were behind on their programme. Between the two pairs of indicating clocks was a board showing (top) the total number of stages which should be completed up to the end of the day to maintain the weekly target and the number actually completed up to date, during the current working week. This provided a quick comparison of target figures and actual output.
Instruction boards installed above each work station They carried the operators’ names, jig or station number, and a red light came on to call the attention of the inspector when the work was completed.
A finished Miles Martinet cabin top, ready for removal from this sub-assembly line.
Over each workstation was a board bearing the workers’ name, the stage number and the operations to be performed at that station. This provided a ready guide for any new personnel. The portion bearing the name was easily detachable should the operator leave or move to another station. Many of the staff had not undergone anything like a full apprenticeship and therefore trained to be capable of working in any department. Instead, given the pressure of war, many workers had been taken on and trained for one specific task.
Adjacent to each board was a red lamp which was switched on when the operations on the component were completed, this attracting the attention of the floor inspector who then examined the work. When all lights were illuminated the trucks moved on to the next station, the lights were switched off, and the end truck unloaded and returned, via the central rails, to the commencement of the track. At the side of the tracks were benches to which the parts were transferred from the trucks for certain operations, such as trimming, glazing, etc. The benches were fitted with racks for tools, details, and jigs for small sub-assemblies.
As the finished parts were removed at the end of the detail line they passed on to a spray booth for masking and painting, and were then dried and stored on overhead racks until required for final assembly. There were five of these racks made from light angle iron, each raised and lowered separately on steel cables by light winches. Drying was facilitated by warm air at rack level, which was fed through a duct from a furnace outside the building.
Miles Martinet target tug HN861 in flight.
