A Basic Understanding of How Propellers Generate Thrust
While most airplanes people fly in are commercial aircraft with jet engines as their source for generating thrust, some aircraft today still rely on propellers to generate thrust. Upon first glance, a propeller aircraft might appear outdated, but in reality the technology that makes these aircraft fly is both impressive and modern.
The structure of an aircraft blade is similar to that of an aircraft wing, as their sharp curves work to displace air; however, rather than being situated on either side of the plane, propeller blades are attached to the front of the aircraft through a central hub that connects to the engine. Using the power of the engine, the blades rotate like the hands of a clock to create propulsion, moving the aircraft forward in the air. They produce a lift known as thrust that works on Newton’s third law of motion. Essentially, every action has an equal and opposite reaction; the action force of the propellers displacing air behind them generates the reaction force of a resulting pressure difference ahead and behind the aircraft causing forward propulsion, or thrust.
Depending on the efficiency needs of an aircraft, propellers may consist of one blade or upwards of six blades. The number of propeller blades is ultimately determined by the needs of the aircraft. For example, aircraft with more powerful engines will require a greater number of blades. Additionally, the angle, shape, and size of the blades all determine the strength and amount of thrust generated.
Aerodynamic forces act on all aircraft, regardless of whether they use propellers or jet engines; however, blades are subject to the additional forces of the rotational swing and the forward-acting momentum. One of these forces is known as centrifugal force, that of which is the force a propeller experiences when blades turn at a speed. As propeller blades are asymmetrical, they experience aerodynamic twisting as a result of centrifugal force. Propeller blades are also exposed to vibration as they pass close to any part of the fuselage. Moreover, propeller blades are further subject to torque bending and thrust bending, the former being the natural resistant force of the air, and the latter being the force pushing air backwards. Torque bending provides the blades with enough support to resist the propensity of the blades to bend in the opposite direction when the blades are spinning. Meanwhile, thrust bending puts the propeller blades under pressure and bends the blades forward.
