Rotary Engine
The rotary engine offers many advantages over reciprocal engines, especially in aviation.
In conventional reciprocal engines a translational (up and down) movement is converted to a circular movement by a crankshaft. This means that the cylinder is constantly subjected to strong acceleration moments. The resulting forces from these speed changes are transmitted to the aircraft. The many other moving parts e.g. the crankshaft, increase the weight and overall size of the reciprocal engine.
The rotary engine works with a rotating cylinder. Imbalanced forces are almost non-existant because the center of gravity of the rotor is very close to the axis of rotation and because the rotor is dynamically balanced. Since there is no need for a crankshaft nor valves the the only moving parts in a rotary engine are the rotor and the coupled planetary gearbox.
These features mean that the rotary engine is smaller and lighter.