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Several attempts have been made to mount two or more engines in such a way that they can drive one or two propellers. During the latter part of the War the Germans attempted to make aeroplanes of this type with a variety of arrangements. They were extremely clumsy and heavy and of little practice use. We ourselves have designed and constructed gearing to connect four Puma engines to two propellers for the Bristol Aeroplane Company which they are now fitting into a large triplane.

This gearing was designed with a great deal of care and the weight of the transmission gear proved to be 1 1/2 pounds per horse power. It is possible that this could be improved slightly by using higher speed engines, but we do not think that it is likely to be done for less than one pound per horse power at best. There is also the inefficiency of the two bevel reduction gears to consider. When it is remembered that the average commercial aeroplane takes as revenue load about three and one half pounds per horse power, the loss of one to one and one half pounds and the decrease of efficiency would seem to make the use of this type of gear impossible.

The German four-engines aeroplane which we have had the

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