As further illustrations, it may be noted that Voisin brothers adopted the Farman _ailerons_ and abandoned the cellular type of sustaining surface introduced by Hargrave, finding the vertical surfaces strongly frictional and unnecessary for lateral equilibrium, in presence of the _ailerons_. They also abandoned the forward horizontal rudder, seeing that it could very well be omitted. On the other hand, it must be observed that the Farmans, Sommer and Curtiss still retained the combined fore and aft rudder. Curtiss and Farman also tried their hands at monoplane construction, though without abandoning the biplane. The most famous monoplanists, however, held firmly to their first love. In this they were emulated by many new designers, Nieuport, Hanriot, Déperdussin, etc. These show a marked tendency to employ smoothly covered hulls shaped after the fish or torpedo. To drive the little aëroplanes so far developed, especially the racers, there was a general preference for a single-screw propeller mounted directly on the engine shaft, though doubtless for machines weighing many tons a multiplicity of such propellers would be used. Theoretically the advantage of twin screws was conceded, but in practice they were employed by very few constructors. The Chauvière wooden propeller was the favorite in France, and was approved by the constructors of propellers elsewhere, at least in its general features. The Voisin firm, indeed, still adhered to the metal propeller, and occasionally some experimentalist employed the more venerable French screw consisting of radial sticks covered with fabric. But the great records in the sporting world were achieved with solid wooden propellers. A special chapter would be required to describe the various motors, even cursorily. Their relative values, however, may be summarized in the following brief words by Réné Gasnier, in the _Aërophile_ for November, 1910: