A technical instructional film that details the servicing of the Metropolitan Vickers 20 KVA alternator extensively used with mobile radar systems. Failure during aerial operations can have dire consequences, with a loss of radar contact, leaving both pilots and Air Control unaware of the developing aerial operation. The film includes manufacturing sequences at the factories of Metropolitan Vickers and Lister Diesel Engines.
The film opens with an overall view of a multi lorry mounted mobile radar system, and closes in on the lorry containing the 20 KVA alternator, supplying power to all the other lorries. Inside one lorry WAAFs and an Officer are monitoring radar equipment and recording aircraft positions. In the Area Control room Officers are scrambling aircraft in response to incoming raiders. Clip of twin engine German bomber taking off. The scramble is relayed to the mobile radar unit, which detect the bomber and the Controller orders one of the scrambled fighters to intercept the target. Cut to fighter pilot who is updated by the Controller. A telephone rings and a WAAF reports the voltage regulator of the alternator is faulty and the spare alternator will not start, putting the radar out of action. Controller advises fighter pilot that he cannot help him for the moment because of the fault. The controller expresses his frustration as all the lights fail leaving them in darkness.
In an office elsewhere, a senior officer says such events should not take place, and they rarely do. The equipment supplied is of the highest order and construction but they all need to be maintained. He bets failure is due to non adherence of STO 270, the maintenance procedure, has caused the incident just seen, and further bets that the radar itself did not fail because it is maintained by engineering mechanics who take care and pride in the complicated equipment. The power supply is simply an alternator and engine which does not demand such a high level of skill to maintain it. The senior officer knows what caused the fault – the mechanic was trying to change the voltage regulator without following correct procedure and failing to switch the engine off. The senior officer leaves his office to take a tour of the factories who supply the alternator/engine and see how they are made and maintained.
The alternator is manufactured at the Metropolitan Vickers factory in Manchester, where the senior officer meets the manager, who explains how the raw castings are machined with a vertical borer, followed by the turning and grinding of the rotor shaft, and fitting of the coils. The machinists are constantly checking their work whilst the electrical engineer checks the output waveform with an oscilloscope. Control panels are assembled on an adjacent assembly line, including the voltage regulator as we watch the progress of the alternator to completion. The senior officer and manager return to his office to discuss maintenance procedures. Meanwhile, the manufacture of the diesel engine is underway at the Dursley factory of Lister Diesel Engines and after a test run, is shipped to Metropolitan Vickers to be coupled to the alternator. The assembled unit is mounted on the lorry chassis as the senior officer and manager return to address the camera. The senior officer says we have seen the skill required during manufacture and thanks the Manager, who replies they have done their best for the Royal Air Force and hopes the Royal Air Force mechanics and engineers will correctly service and maintain the alternator in return. He offers to show a full sequence of servicing carried out by Metropolitan Vickers engineers who will do the job properly.
The Manager provides a very detailed commentary of each service item accompanied by filmed close up sequences. Engineers proceed to service the Lister engine: fuel filters, lubrication in general and of all exposed joints, greasing, air cleaner, oil pressure, and coolants. Next, the electrical part of the servicing, the alternator. The engine is stopped and covers removed from the alternator exposing the four carbon brushes and slip rings, carbon dust is brushed away and slip rings cleaned as the alternator is manually rotated. The exciter is likewise serviced and the cooling air intake filter and mount cleaned. The check of the automatic voltage regulator is one of the most important of all, as we have seen. The engine is started and the alternator set allowed to warm up, whilst a dummy load equivalent to the radar system is connected. The frequency is adjusted to 49 to 51 cycles per second and the output voltage monitored. A fault is found with the carbon pile which can only be adjusted with the alternator cold.
The output may be varied using a combination of switches inside the control panel as explained in section nine of LMV20, the Metropolitan Vickers Service manual, making the alternator a versatile and convenient set for standby use, as either a 15 KVA or a 20 KVA set also known as the Coventry Climax.
The senior officer thanks the Manager and remarks that AC Plonk failed to repair the voltage regulator and his Flight Sergeant took over. The film returns to the faulty Alternator to see the Flight Sergeant completing a repair and undertaking a visual inspection before the engine is started and the power to the radar lorry is restored. The film returns to the blacked out Control lorry of the mobile radar system just as the power is restored and the Controller says thank God, and thanks the crew who switched to the standby alternator prior to repairing the voltage regulator in the main generator. With radar contact established the Controller guides the pilot to visual contact with the Bomber, the pilot acknowledges, sees the bandit and shoots him down. The film closes as a WAAF paints a swastika representing another fallen aircraft on Control lorry wall.