 British aero engines were normally equipped with a power take @-@ off shaft that led to the rear of the engine . In twin engine aircraft like the Anson , one of these would be used for a generator that powered the aircraft instruments at 24 V DC , the other would be left unconnected and available for use . Following a suggestion from Watt to avoid Air Ministry channels , in October Bowen flew one of the Battles to the Metropolitan @-@ Vickers ( Metrovick ) plant in Sheffield , where he pulled the DC generator off the engine , dropped it on the table , and asked for an AC alternator of similar size and shape . Arnold Tustin , Metrovick 's lead engineer , was called in to consider the problem , and after a few minutes he returned to say that he could supply an 80 V unit at 1200 to 2400 Hz and 800 W , even better than the 500 W requested . Bowen had an order for 18 pre @-@ production units placed as soon as possible , and the first units started arriving at the end of October . A second order for 400 more quickly followed . Eventually about 133 @,@ 800 of these alternators would be produced during the war . 
