Propeller (aeronautics)

In aeronautics, an aircraft propeller, also called an airscrew, is an important part that helps airplanes and other flying machines move through the air. It uses power from an engine to spin and create a flow of air, called a slipstream, which pushes the aircraft forward or backward.

A propeller is made of a central hub with several blades shaped like airplane wings, called airfoil sections. These blades spin around a center point, and their angle, known as the blade pitch, can be fixed or changed for better performance.

Propellers can be made from different materials, such as wood, metal, or modern composite materials, depending on the aircraft's needs. They work best at speeds slower than about 480 mph (770 km/h), but special designs have flown very fast, like the McDonnell XF-88B, an experimental airplane.

History

See also: Early flying machines

Long ago, around 400 BC, children in China played with a fun toy made of bamboo. When you spun this toy by rolling a stick attached to it, the toy would fly into the air. This simple idea inspired many inventors over the years.

Later, in the late 1400s, a famous inventor named Leonardo da Vinci sketched plans for a machine that could fly straight up, like a screw in the air. In the 1700s, scientists in Russia and France made small models that copied the spinning bamboo toy. These models helped people learn more about flying. By the 1800s, inventors began attaching propellers to balloons and other early flying machines. Two brothers named the Wright brothers made a big advance by shaping their propeller blades like wings, which made their airplane fly better than ever before.

Theory and design

Propellers help aircraft fly by turning engine power into a swirling motion that pushes the plane forward. Their efficiency depends on angles like the angle of attack. When these angles are just right, the propeller works best, creating more push without extra resistance.

Propellers are shaped like wings and work best at certain angles. To stay efficient as speeds change, many propellers can adjust their angles. The number and shape of the blades matter too. More blades can reduce strain on each one but may make the propeller larger. Special designs help propellers work at higher speeds by changing blade shapes and arrangements.

Variable pitch

Main article: Variable-pitch propeller (aeronautics)

Variable pitch propellers change the angle of their blades. This helps planes fly better at different speeds. It saves fuel and lets planes go faster. When a plane goes faster, the blades adjust to keep working well.

A famous example is the Schneider Trophy race in 1931. Back then, a fixed-pitch propeller had to be changed for very high speeds. Today, planes like the Tupolev Tu-95 use special variable pitch blades. These let them fly faster than many thought possible for propeller planes.

Main article: Thrust reversal

Some planes can turn their propellers backward. This makes reverse thrust. It helps slow the plane after landing, especially on wet runways. It can also let planes move backward, which is useful in tight spaces.

Counter-rotation

Main article: Counter-rotating propellers

Counter-rotating propellers are used on airplanes with two or more engines along the wings. These propellers spin in opposite directions to help the airplane stay balanced. Most airplanes have propellers that spin clockwise from behind, but counter-rotating propellers spin toward the middle—one clockwise and the other counterclockwise. There are exceptions, like the P-38 Lightning from World War II, which had propellers spinning outward.

Contra-rotation

Main article: Contra-rotating propellers

A contra-rotating propeller has two propellers stacked on top of each other that spin in opposite directions. This design helps the propeller use more power. Because it is more complex and costly, this type of propeller is only used on very fast aircraft.