ROTARY ENGINE. A type of steam engine in which the use of reciprocating parts is avoided with the object of saving the energy wasted in converting reciprocal or to-and-fro move ment into rotary movement. The rotary principle has never had any practical success in competing with the smaller recipro cating engines, but steam turbines (which are really a class of rotary engine) have furnished the solution of the problem for moderate and large size installations. Many rotary mechanisms have been tried in the past. Some have comprised a flap piston rotating within a cylinder, the pressure of the steam causing rotation. Sometimes the flap has a sliding action within the piston, the shaft of the latter being mounted eccentrically in relation to the bore. More or less complicated arrangements of levers and of gears have also been patented, with multiple pistons. Watt's
famous attempt was really a semi-rotary engine, with a radial piston which swung to and fro and actuated a pinion and rack device for working the rods of pit pumps.
In the earlier periods of aeroplane construction rotary engines were much employed, notably the Gnome and the Le Rhone, but the radial engine forms the equivalent of these types now. Yet the rotary principle finds great success in certain other directions, such as pumps, blowers and gas-exhausters. The latter are in principle blowers reversed. In a well-known type the piston or drum is set with its axis eccentrically in the cylinder, and radial blades slide in its slots, making a gas-tight fit against the bore. The drum rotates and pumps the gas from the inlet which is at one side of the cylinder to the outlet at the other side. (See