What are aircraft?
Aircraft are best described as machines or vehicles that can fly. They achieve this by using a variety of techniques to overcome the force of gravity. Planes, helicopters, and other typically fly using a combination of specially-designed wings or rotor blades, and engine power. The pair work in unison to achieve flight: The engine creates thrust, propelling the body, and the wings manipulate air pressure to create lift. This allows the plane to fly.
Flight would be impossible without both of these things, but the shape of the wings, known as airfoil or aerofoil in the United Kingdom, is particularly critical for a successful flight. Wings are designed with a curved top and flat bottom; the curved top lowers air pressure above the wing, creating lift.
If you study flight, you are a student of aviation. Aviation encompasses everything from the crewed option, which are often, but not always, commercial airplanes. It also includes helicopters, small planes, and unmanned objects such as drones.
A brief history
When one pictures an aircraft, they typically imagine a commercial airline. However, the first vehicles to achieve manned flight were not two-winged planes, but hot-air balloons. These were developed in the 18th century, and are still in use today.
Hot-air balloons are now rarely used for travel, due to their slow speed and difficult operation, but helped inspire five eras of aviation: pioneers of flight, from the first airborne experiments until the beginning of World War I; the First World War, from 1914 to 1918, which was the first major war to largely depend on flight; aviation between the world wars, from 1918 to 1939; World War II, from 1939 to 1945, and the postwar era, from 1945 to present.
The world wars were utterly pivotal in the development of the modern aircraft, as nations increasingly leaned upon them to engage enemies. That said, today’s designs are in many ways unrecognisable from the machines and vehicles used in flight during the mid-20th century, and continue to be transformed by innovation.
How Aircraft fly
Aerostats: Hot-air balloons, blimps, and similar, are known in the industry as aerostats, because they are lighter than air, and float like an empty bottle floats in a sea of water. In order to achieve flight, an aerostat employs gasses that are lighter than regular air, such as helium, hydrogen, or simply heated air, inside of a large bag. This makes the body lighter than the surrounding air, so it floats.
The first hot-air balloons were, in fact, sky lanterns, invented and popularized in China before the 3rd century, B.C. They followed kites, also invented in ancient China, as the first ever objects to achieve flight.
Aerodynes: Most are much heavier than air, and are known as aerodynes. These planes, which includes commercial planes, private jets, and most aircraft with wings, achieve flight by manipulating air pressure using both propulsion, created with an engine, and a specific wing shape, called an aerofoil.
Most of this list type use aerodynamic lift; which keeps it airborne because the wings constantly move forward, propelled by an engine. The wings have a curved top and flat bottom, creating lower wind pressure on the top of the wing, thus lifting the aircraft upward. The aerodynamic lift can also be achieved by using an engine to spin the wings around in a circular motion, creating the same effect. Helicopters and drones typically use this particular technique.
Another type of lift is powered lift. This technique often has two wings, but use engines that can create downward thrust, meaning it can lift straight off the ground. This technique is rarely seen in much of the aviation industry, but is popular in the military, as it allows aircraft to take off and land without requiring a large runway.
The two major types of aerodynes are fixed-wing and rotorcraft. Fixed-wing airplanes were invented by the Wright brothers, who achieved the first-ever manned flight on December 17, 1903 in North Carolina. Rotorcraft are helicopters and their various hybrids, and use an engine to spin rotor blades, which force air downward to create lift. There are other ways to create lift and achieve flight: via a lifting body, wherein the body of the plane itself is shaped in a way to produce lift; the Flettner airplane, which employs the Magnus effect to fly using a spinning cylinder; and an ornithopter, which flaps its wings to fly, much like a bird.
Size and speed
Aircraft range from a few pounds, such as a consumer drone, through to massive commercial airplanes such as the Boeing 747 and the Airbus A380, two of the world’s biggest passenger planes. The A380 can hold 525 passengers, and fly up to 15,700 kilometres, or the distance from New York to Hong Kong.
As of 2016, the largest ever built is the Airlander 10, a British hybrid blimp measuring 95 meters. However, if one considers weight as the best measure of the largest aircraft, the award goes to the Antonov An-225, a fixed-wing cargo aeroplane that has transported a record 200 tons of goods. The weight is between 550 and 700 tons.
When it comes to speed, NASA’s X-43A Pegasus, a hypersonic research project, holds the record for the fastest recorded flight by an aircraft ever, at Mach 9.6, or 11,850 kilometers per hour. The Boeing 747 is significantly slower, but is still the fastest major commercial jet in operation today, with top speeds of 920 kilometers per hour.
Unpowered: While most aircraft use power for propulsion, typically in the form of an engine, some use no power. So how do they fly? Take gliders. They can take off by using wheels to roll down from a height, using gravity for propulsion before taking flight. Some gliders are propelled by a tow line attached to a vehicle on the ground, or from another aeroplane. As gliders fly without power, they can only fly downward once left to their own devices, so their usage is severely limited.
Other examples of unpowered planes include kites, which fly while attached to a string or strings on the ground, and kytoons, which are balloon-kite hybrids.
Powered: For the most part, usage consists of either piston engines or gas turbines in order to achieve and maintain flight. There are numerous types: propeller aircraft spin their propellers to create lift; jet have no propellers but burn fuel with air in a combustion chamber to accelerate and create that all-important thrust. Rotorcraft, such as helicopters, can tilt a powered rotor blade in order to fly in certain directions.
Design and construction
There are many constraints on the design of the typical aircraft. Designers must consider safety standards, the constraints of the current economy, and even the specific needs of the consumer and manufacturer when producing a finished article. That said, most designs can be divided into three distinct groups: structure, including the load-bearing elements of the machine; the propulsion system, including how the aircraft is powered; and avionics, which are the parts responsible for control, navigation and communication.
Flight envelope: It is unsafe to fly an aircraft outside the envelope. This is another way of saying that they come with certain capabilities, and it is dangerous to try to push it beyond them. In the strictest sense, an aircraft’s flight envelope refers to its airspeed, load, manoeuvrability, and other factors, in which it is most stable.
Range: If you can fly you from New York to New Zealand before it needs to stop and refuel, then its range is over 14,000 kilometers, or the distance between New York and New Zealand. For powered aircraft, range is usually decided by how much fuel it can carry; if the aircraft is unpowered, range is more susceptible to environmental factors, such as weather conditions.
Flight dynamics: While a car’s orientation is usually limited to two dimensions, airborne vehicles can move in three dimensions. Roll is the rotation of an aircraft on the longitudinal axis (think of a small plane rolling over and over during an air show); pitch is the rotation of an aircraft on the sideways horizontal axis, and is decided by whether the plane is pitched upward or downward (think takeoff and landing); and finally, yaw is the rotation of an aircraft on the vertical axis (imagine the aircraft shaking its head). It is important to have names for all three orientations because flight dynamics is the practice of controlling an aircraft around each of them.
Stability: In order to fly, a plane must be stable. If an aircraft is unstable, it may be unable to fly to its destination, or worse, it may crash. The more stable an aircraft it is, the more difficult it is to manoeuvre, which means it is more likely to remain on its flight path and reach its destination. An aircraft can overcome instability in the orientations mentioned earlier by using stabilisers; these are the trio of small fins on the back of most aircraft.
Control: Flight control surfaces, otherwise known as the long, narrow flaps on the back end of fixed wings, are used to control altitude. Aircraft are also usually controlled by control systems featuring actuators, used to rotate the machine across its three orientations.
Impacts of use
The invention of the aircraft, and most notably the commercial aspect, heralded a great change for travel and has transformed the global economy for governments, companies, and consumers alike. However, while often more fuel efficient than other modes of transport are known to affect the environment. For example, they produce contrails, or trails of engine exhaust, that some scientists suggest can alter the weather. They are also incredibly loud, and a common nuisance for people who live near airports.
Military: Military aircraft are manufactured for, and used in, war and other military operations. Combat usage for fighters, to shoot ammunition at other aircraft, and bombers, to drop explosives on foreign lands. Much military aircraft, however, is non-combative, and used to transport soldiers and cargo between countries, and perform rescues.
Civil: Civil aircraft is broadly considered to include both commercial and general types. Commercial-type are major airliners that carry passengers, and VIP’s, among others, while generally can include anything from private jets to hot-air balloons.
Experimental: Used to test new aerospace technology, or where that the Federal Aviation Administration (FAA) has assigned “Experimental” for airworthiness, typically fall within this category.
Model: Models are small, unmanned popular among aerodynamic researchers testing new innovations, and hobbyists.