Aircraft piston engines are internal combustion engines that power many general aviation aircraft. The main components include cylinders where fuel and air mix and combust, pistons that move up and down within the cylinders, connecting rods that transfer piston motion to the crankshaft, and spark plugs that ignite the fuel-air mixture. The crankshaft converts the linear motion of pistons into rotational motion that drives the propeller.
The four-stroke cycle consists of intake, compression, power, and exhaust strokes. During intake, the piston moves down while the intake valve opens, drawing in the fuel-air mixture. In compression, both valves close and the piston moves up, compressing the mixture. The power stroke begins when the spark plug ignites the compressed mixture, forcing the piston down. Finally, during exhaust, the exhaust valve opens and the piston moves up, expelling burnt gases.
The propeller is a twisted airfoil that converts rotational motion into forward thrust. Each blade has a specific angle of attack that varies along its length to account for different rotational speeds at different radii. As the propeller rotates, it accelerates air backward, creating an equal and opposite reaction force that propels the aircraft forward. The blade angle, or pitch, determines how much air is moved with each revolution.
Engine-propeller matching involves selecting a propeller that allows the engine to operate at its most efficient power setting. The engine power curve shows available power at different RPM, while the propeller load curve represents the power required to turn the propeller. The intersection of these curves determines the operating point. Proper matching ensures the engine runs at optimal RPM and power output, maximizing fuel efficiency and performance while preventing engine overload or underutilization.
Variable pitch propellers use a hydraulic or electric control system to adjust blade angle during flight. At takeoff, a fine pitch setting provides maximum thrust at low airspeeds. During cruise, a coarse pitch setting maintains engine efficiency at higher airspeeds. The pilot can adjust propeller pitch through cockpit controls, allowing the engine to operate at optimal RPM while the propeller adapts to changing flight conditions. This system significantly improves fuel efficiency and aircraft performance across the entire flight envelope.