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Prof. Robert W. Wood.

eed. The third is the helicopter, which supports itself in the air by its revolving screw. At first sight the aeroplane appears to have the advantage, for the reason that the motion which causes the lift is also used for progression. That is, the  force that lifts it also propels it through the air. So it seems that we are killing two birds with one stone.

Aeroplane and Helicopter
In the helicopter the motion of the screw is round and round in a circle, and simply designed to lift the machine off the ground. You do not get any motion forward from that screw. Its advantage is that it will remain stationary in the
, will rise or descend slowly and doesn't have to be going forward to remain suspended. This is the line along which many of the investigators of today are working.

Santos-Dumont's Troubles.
To get the forward motion on the helicopter, another screw has to be added. Or a screw of greater power than is necessary to lift the machine is used, and machine inclined. Then it glides upward. The helicopter seems to possess greater stability than the aeroplane. Santos-Dumont's aeroplanes have behaved very badly recently. I notice he had an accident the other day. The Wrights claim to have done better.
Up to the present time nobody has built a machine which will raise itself in the air and carry a man with it simply by the lifting power of the propeller. A number of models have been constructed which lift their own weights, but the man-carrying machine has not been made.
As you may have read in the papers, I am interested in the construction of a machine at the present time. This of the helicopter type."
Professor Wood then discussed some of the mathematical formulae which guide experimenter in aerial flight. The reason no bird-wing machine operated a man's own power can be successful, said, is because a man's strength is
y about one-eighth horse-power and a propeller operated by an engine of that horsepower would have to be about 100 feet in diameter.