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How Aircraft Propellers Work



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What goes up must eventually come down, and without a propeller it might be sooner than you think. Actually the propeller is one of many different types of mechanics used in order to perpetuate flight in aircraft today. The propeller itself acts much like a household fan operates, converting the rotational energy into a kind of motion called "thrust". So how and what makes a propeller work to generate flight? Actually to understand the science behind the propeller one would have to take into consideration a variable degree of mathematical equations. However, to simplify the whole process I will try to break down the components of how propellers work.

Nuts and Bolts of the propeller:

-Propeller blades-
The propeller blades can come in various shapes and sizes, ranging from single double, and multiple blade types. They essentially require a motor to cause the rotation, and then air which moves through the blades causing "forward thrust". The cross-section of a majority of propeller blades is slightly or severely angled, which creates an airfoil type of shape. This angle is also known as the "pitch" or "angle of attack", which can determine the amount of thrust or the torque that can cause more or less directed airflow. The curvature in the propeller blades acts much like a corkscrew pulling inward, which is why the angle of a blade changes along the length, becoming greater toward the hub, where the air has less thrust.

Another more complex blade system known as an "adjustable pitch" can be found upon larger aircraft, and even inverted propeller systems such as in helicopters. This type of blade system can have three or more elaborate blades that pivot or adjust the angle of attack, which can be used by the pilot during flight.

-Motors and the mechanics-

Like all machines used today there has to be a mechanical component to deliver the rotation to the propeller blades. Most planes require a degree of horsepower to provide sufficient rotation, which is what drives almost any aircraft. Common motor companies include Bombardier, Rollsroyce, Bentley, De Havilland, are just a few among the many manufactures that design plane engines. They come in varying types of designs that I will list below.

* Opposed Engines have two banks of cylinders that are opposite of each other. The crankshaft is located around the center and both cylinder banks power it. The motor itself can be either liquid or air cooled, but liquid cooled engines are most common among aviation.

* In-line engine types are quite common in aviation. This engine type has cylinders that are lined up in one row. Although it is less common to have an even number of cylinders such as 4 cylinders or 8 cylinders, there are some that have had three or five cylinder engines. This engine also can be both liquid and air cooled, but since the crankshaft is located above the cylinders the motor is mounted in an inverted fashion.

* Radial engines were quite common with older planes and single prop aircraft. The radial engine has a row of cylinder heads that are arranged in a circle around the base of the crankshaft, which sits in the center of the engine.

* V-type engines can be liquid or air-cooled and they have two in-line banks of cylinders that sit apart from each other at an angle. This radial angle can be anywhere from 30-60 degrees, but still forms a notable V formation. Some of the most famous motors used in airplanes include this specific design.

-Physics and all that Science mumbo jumbo-

If you introduce a flat or rounded blade and introduce a circular motion, you will be generating a field of pressure. This may be felt as a breeze or displacement of air, which is the basic principle of a propeller. Propellers from the earliest examples of air flight by the legendary Wright brothers, to modern day aircraft, have utilized a specific design called the airfoil shape. Using steel, wood or other material, a propeller must be spun at a very high rate of speed, which creates a surmountable amount of pressure across the propeller blades. The variance of pressure upon the blades is what causes a vacuous form of wind pressure, which as it passes through the rotating blades it creates forward thrust.

Now thrust is only a component in which aircraft are dependent upon, because this continuous thrust also now requires lift. The thrust or velocity that is created by a propeller will keep an aircraft moving forward or upward, but it still requires lift to hold the aircraft aloft in the air. There are four major forces that play for or against flight.

1.) Lift is the upward force that is generated when air pushes across the wings that act like an airfoil.

2.) Drag is the opposing force, which is caused by air resistance, which actually slows a plane down. Most airplane designs are built to aerodynamically combat the drag effect, but it still requires acceleration to prevent loss of altitude.

3.) Gravity is the one of the most commonly known forces upon earth. It holds us firmly to the ground, and with flight it fights against the constant struggling between the opposing forces.

4.) Thrust is the most important component to remain in flight, it generates propulsion (forward motion), which combats both drag and gravity forces, but it also creates upward pressure which lifts the plane as it moves through the air.

-Another type of propeller driven air craft-

Helicopters require most of the same components that airplanes or other craft require, but they use a vertical propeller called a rotor blade, which is used to create vertical thrust. All helicopters harness this vertical propulsion but the rotor blades are actually acting like rotating wings due to the airfoil shape of the blades. The rotation of the blades creates a reaction torque that can actually cause the entire helicopter to spin, which is why a second rotor was added in the tail to stabilize this reaction. The helicopter also has a variable pivoting rotor blade that aids in the direction or the propulsion of any given path by inclining the axis of the main rotor in the specific direction that is trying to be achieved. I could go into great detail regarding this magnificent craft, but I will save that for another article.

The skies haven't always been cluttered with aircraft of all sizes and shapes; at one time it was only the birds that challenged man to take flight. Pioneers like Orville and Wilbur Wright tested our ability to understand our limitations, which in December of 1903 they became the first people to successfully fly a propeller powered plane which could actually carry a single passenger.

The propeller itself has a long history in the world of flight, but interestingly it was first intended to drive sea-based craft instead. The earliest examples of a propeller used to create inertia can be found in the late 1770's where James Watt proposed a screw propeller to replace steam engines. It didn't take long for the propeller to be inducted into invention designs ranging from hot-air balloons, windmills, and even energy conductors.
So where can the propeller go from here?

Most planes now are propelled by much more powerful methods such as jet engines, but yet most pilots will tell you nothing compares to flying a more simpler propeller powered plane. Honestly, the simple dynamics of the propeller have many uses in both modern and antiquated inventions, but with even the newest machines such as the military dual propeller powered OSPREY, I don't see the propeller disappearing anytime soon!

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