According to Setright’s book ‘the power to fly’, the rear airscrew was much more efficient than the front, so to balance out the power, the rear engine drove the front airscrew and the supercharger for both units, whilst the front engine drove the rear airscrew. Both airscrews were driven by hollow shafts with the power takeoff at the centre between the banks. James, however, states that one of the principle problems in setting up the engine was adjusting the pitch of each airscrew to enable them to run at the same speed, adding to the carburation problems that took three years and the loss of two planes and pilots to solve before the record in 1934
Just how independent the motors were is a matter of some confusion. James states in ‘Schenider trophy aircraft’ p. 242 that they were independent mechanically , the only common link being the connected throttles, but , crucially, that the ‘induction and ignition units were common’. If you look at the picture in Gunstons book on page 133, you can see that the magnetos were driven from the rear engine as well as the supercharger, so presumably the start sequence would have had to have been rear engine first, front engine second. If the rear motor failed….. In the photo that Mike posted the magnetos are not in place, just the mountings for them on the left under the supercharger which look like grey sugar scoops.
Edit:
Cancel some of the above! If you look carefully at photos of the complete engine at the back of James’ book, you can see the magnetos driven from the nose of the front engine – so the ignition sytems were independent
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