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 turns the power from an engine or another source into a spinning motion that creates a flow of air, called a slipstream, pushing the aircraft forward or backward.

A propeller is made up of a central hub connected to several blades shaped like the wings of an airplane, called airfoil sections. These blades spin around a central axis, and their angle, known as the blade pitch, can be fixed or changed to improve performance under different conditions.

Propellers can be built from different materials, including wood, metal, or modern composite materials, depending on the needs of the aircraft. They work best at speeds slower than about 480 mph (770 km/h), though special designs have managed to operate efficiently even at very high speeds, such as the McDonnell XF-88B, an experimental airplane that reached just above the speed of sound with its propeller.

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, or how well they use energy, 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 the blades to keep them working efficiently at different speeds. This helps save fuel and allows aircraft to fly faster. As an aircraft goes faster, the blades need to be adjusted to stay effective.

One famous example is the Schneider Trophy race in 1931, where a fixed-pitch propeller had to be adjusted for very high speeds. Modern planes like the Tupolev Tu-95 use special variable pitch blades to fly faster than many thought possible for propeller planes.

Main article: Thrust reversal

Some planes can turn their propellers to face backward, creating reverse thrust. This helps slow the plane down after landing, especially on wet runways, and can even let planes move backward, which is useful for boats in tight spaces.

Counter-rotation

Main article: Counter-rotating propellers

Counter-rotating propellers are used on airplanes with two or more engines placed along the wings. These propellers spin in opposite directions to balance forces that can affect the airplane’s control. Most airplanes have propellers that spin clockwise when viewed from behind, but counter-rotating propellers spin inward toward the middle of the plane—one clockwise and the other counterclockwise. There are exceptions, like the P-38 Lightning from World War II, which had propellers spinning outward away from the middle.

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 recover energy from the air and allows the propeller to use more power without growing bigger. Because it is more complex and costly, this type of propeller is only used on very fast aircraft where top performance matters more than efficiency.