Aeronautics Glossary
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To speed up. For example, when an airplane takes off it accelerates down the runway until enough lift is created by the air flowing over the wings so that it can fly.


A field of fluid dynamics that studies how gases, including air, flow and how forces act upon objects moving through air.



The study of flight and the science of building and operating an aircraft.



Control surfaces on the trailing edge of each wing that are used to make the aircraft roll. When flying straight and level, moving the control stick to the right will raise the aileron on the right wing and lower the aileron on the left wing. This will cause the aircraft to roll to the right.



A machine used for flying. Airplanes, helicopters, blimps and jets are all aircraft.



The motion of air molecules as they flow around an object, such as a wing.



An object with a special shape that is designed to produce lift efficiently when the object is moved through the air. For example, the cross-section of a wing is an airfoil.



An aircraft that uses the force of air on its wings (called lift) to fly.


air pressure

The force created by air pushing on a surface.



The height of an object, like an airplane, above sea level or above the earth's surface.



To take something apart so it can be examined and studied.


angle of attack

The angle of a wing to the oncoming airflow. A pilot pulls back on the control stick to raise the elevator. This causes the aircraft to pitch which increases the angle of attack.



The operation of aircraft. There are three types of aviation: general, commercial and military.



A straight line, through the center of gravity, around which an aircraft rotates. For example, an aircraft rolls around its longitudinal axis which is a straight line that runs through the center of the aircraft from the nose to the tail.


balanced forces

Opposing forces that are pushing or pulling against each other an equal amount. For example, if you and a friend pull on a rope, in the opposite direction with the same force, neither of you will move. This is because the forces are balanced.


Bernoulli, Daniel

Daniel Bernoulli was a Swiss mathematician. He was born on February 8, 1700 in Groningen, Netherlands. As a university student he studied philosophy and logic. His favorite subjects were mathematics and mechanics. From 1725 to 1733 he worked as a mathematician with his brother, Nikolaus, at the St. Petersburg Academy of Sciences in Russia. He then worked as a professor at the University of Basel in Switzerland until his death on March 17, 1782.


He is famous for his work in the field of fluid dynamics. In 1738 he wrote a book called Hydrodynamica. In this book he explained his theories about how gases and fluids move, and how the speed at which they move affects the pressure they exert on objects they flow around. This is the basis for the explanation of lift. His work helped to lay the foundation for aeronautics which would be developed many years later.

Bernoulli's Principle

Daniel Bernoulli explained that the faster molecules within a fluid move, the less pressure they exert on objects around them. This applies to all fluids, including water, air and gases. For example, the water in a pond will exert more pressure on the pond's bottom than a flowing stream with the same amount of water will exert on the streambed.



An airplane with two sets of wings. The first airplane ever built had two sets of wings, one on top of the other.



The curve of an airfoil.



a tail configuration (two small horizontal surfaces on either side of the aircraft) mounted toward the front of the aircraft, rather than at the rear.


center of gravity

The force of gravity acts on every individual part of an object, like an airplane. However, engineers often treat the force of gravity on all the parts of an object as a single force acting on a point in the object called the center of gravity.


chord line

A line from the front of an airfoil (the leading edge) to the trailing edge.



A compartment in the front of the airplane where the flight crew performs their job of flying the aircraft.


commercial aviation

The business of operating aircraft that carry passengers by commercial companies. Airline companies such as American Airlines, United Airlines and many others are examples of commercial aviation. A Boeing 747 is an example of an airplane that is owned by a company and operated in commercial aviation.


Computational Fluid Dynamics (CFD)

The science of using supercomputers to solve complex mathematical equations that predict how an object like an aircraft responds to the air flowing around it. CFD is a tool of aeronautics that enables engineers to "fly an aircraft in a computer."



An electronic machine that receives, processes and presents data. A computer can be programmed to perform complicated tasks, like solving complex mathematical equations or controlling a flight simulator.


control surfaces

Parts of an aircraft that are activated by the controls to change the airflow around the surfaces of the aircraft. The changes in airflow cause the aircraft to roll, pitch, or yaw. Examples of control surfaces are: ailerons, elevators and rudders.



Devices which allow the pilot to direct the movements of an aircraft. Examples of controls are: rudder pedals that control the rudders and cause the airplane to yaw; throttles that control the engines which generate thrust for the airplane; and the control stick that controls the ailerons and elevators which cause the airplane to roll and pitch.



Information that is collected from an experiment. For example, an engineer in a wind tunnel may collect data about how much lift is created by a certain wing shape.



To slow down. When an airplane comes in to land, it decelerates and rolls to a stop.


delta wing

A sweepback wing that looks like a triangle from above. The trailing edge of the wing is the base of the triangle. The XB-70A is an example of an airplane that has a delta wing. The XB-70A can fly faster than twice the speed of sound at an altitude of 70,000 feet.


dihedral angle

The upward angle of the wings that is formed where the wings connect to the fuselage.



The force that resists the motion of the aircraft through the air. One type of drag is caused by air molecules. As the aircraft flies through the molecules, they resist the motion of the aircraft. This resistance is due to friction between the air molecules and the surface of the aircraft. Airplanes are streamlined to decrease the drag force.



Control surfaces on the horizontal part of the tail that are used to make the airplane pitch. Pulling back on the control stick will raise the elevators. This causes the aircraft to pitch and increase the angle of attack.



The parts of the airplane located at the tail end. The empennage includes the horizontal stabilizer, the vertical stabilizer, and elevators.



A machine that uses combustion to create energy. An airplane will normally either have jet engines or engines that drive one or more propellers. In either case, the engines provide the thrust force that pushes the airplane through the air.



Someone who designs and builds mechanical or electrical devices. For example, an aeronautical engineer designs and builds aircraft. To do this, an aeronautical engineer must study aeronautics and understand fluid dynamics and aerodynamics.



A set of controlled procedures designed to test an idea or hypothesis. For example, a flight simulation engineer will design an experiment to test whether or not a pilot can control an airplane with a new wing design.


Federal Aviation Administration (FAA)

The FAA is a government agency, under the Department of Transportation, that oversees all aviation within the United States. The FAA controls, for example, airport safety, air traffic control, licensing of pilots, inspection of aircraft, and investigates aviation mishaps.



Another word for the vertical portion of the tail.



Moveable parts of the trailing edge of a wing that are used to increase lift at slower air speeds. Flaps increase lift by changing the shape of the airfoil. A pilot will extend the flaps when the airplane is landing. By extending the flaps, the pilot is increasing the camber of the wing, the size of the wing and the wing's angle of attack. All of these actions will cause lift to decrease so the airplane can land more slowly.


flight simulation

A tool of aeronautics in which a flight simulator on the ground is used to create an environment where a pilot sees, hears and feels like he or she is in a real aircraft. Flight simulation is used to investigate how an aircraft responds to a pilot's movement of the controls.


flight test

A tool of aeronautics in which a real aircraft is flown to gather data which will accurately describe the capabilities of that aircraft. Flight tests are used to investigate how fast, how far and how high an aircraft can go, and how it handles and performs.


fluid dynamics

The study of how fluids move. Fluids include water and gases (such as air).



A push or a pull in a certain direction that can be measured. Examples of forces are your hand pushing on a doorknob, and a propeller pulling an airplane through the air.


forward sweep wing

A wing that is swept toward the front of the airplane, unlike most fast airplanes which have wings that are swept toward the back of the airplane. The X-29 aircraft is an example of a supersonic jet that has forward sweep wings. The X-29 is capable of going over one and one-half (1 1/2) times the speed of sound.



The part of the airplane to which the empennage and wings are attached. The fuselage is where the passengers and cargo are located. It is streamlined so that it produces the least possible drag.


general aviation

The operation of aircraft that belong to the public.



The natural force that pulls an object toward the earth. We experience gravity as weight. An airplane must generate enough lift to counteract the weight of the aircraft.


horizontal stabilizer

The horizontal part of the tail. The horizontal stabilizer helps to increase the stability of the aircraft. It is also known as a tailplane.



Velocity greater than five times the speed of sound. The Hyper-X is a reusable launch vehicle that will fly into space and return. It will fly at hypersonic speeds as it re-enters the atmosphere.



A prediction which needs to be tested to tell if it is correct. An engineer can offer the hypothesis that a particular wing shape will not create enough lift to enable an airplane to fly. His or her hypothesis must then be tested using one or more of the tools of aeronautics to determine if it is correct.



Tools used to observe, measure and control . For example, pilots use instruments to measure and observe the altitude, speed and direction of an aircraft.


jet engine

An engine that works by creating a high-velocity jet of air to propel the engine forward.


landing gear

Another word for undercarriage. The landing gear is often retractable - it can be pulled into the fuselage of the aircraft to reduce drag.


lateral axis

The axis extending through the center of gravity of an aircraft, and parallel to a line connecting the tips of the wings. The lateral axis is sometimes called the "y" axis. Pitch is a motion around the lateral axis.


leading edge

The front edge of an airfoil. The leading edge is normally rounded and thicker than the trailing edge.



A force that is perpendicular to the airflow around an aircraft. In normal, forward flight, the lift force "lifts" the aircraft into the air. Engineers design airplanes so that the lift created by the wings opposes the weight force.


longitudinal axis

The axis extending through the center of the fuselage from the nose to the tail. The longitudinal axis is sometimes called the "x" axis. Roll is a motion around the longitudinal axis.


military aviation

The operation of aircraft that belong to the Armed Forces. The Air Force YF-23 is an example of an aircraft that is flown only by the military.



A copy of an object that is often times smaller than the original. Wind tunnel engineers create a model of an aircraft to put in a wind tunnel. The model is a precise replica of the outside of an aircraft.



The absolute tiniest part of something that can still be called by that name. For example, two hydrogen atoms and one oxygen atom make up one molecule of water.



An airplane with one set of wings. Most aircraft built today have only one set of wings and are classified as monoplanes.


National Advisory Committee for Aeronautics (NACA)

NACA was a government agency that was started in 1917. NACA guided research in aeronautics until 1958 when its name was changed to the National Aeronautics and Space Administration (NASA).


National Aeronautics and Space Administration (NASA)

In 1958, NASA was created as a government agency to replace NACA. NASA's charter is to expand frontiers in air and space, to inspire and serve America, and to benefit the quality of life on Earth.


opposing forces

Forces that are pushing or pulling in the opposite direction. For example, lift is perpendicular to the airflow around an aircraft. If the aircraft is flying straight and level, the lift force (which is pulling up) will be opposing the weight force (which is pulling the aircraft toward the earth).



The load carried by an aircraft that includes passengers and cargo.



A person who flies an aircraft.



A rotational motion in which an airplane turns around its lateral axis. Pushing forward on the control stick will lower the elevators, which forces the tail upward. The pilot will then see the nose of the aircraft fall or pitch.



A force being exerted on part of a surface. When you stand, your feet put pressure on the ground. Air pressure refers to air molecules pressing against a surface like the bottom of a wing.



A device that consists of blades (shaped like airfoils) that spin around a central hub, like a fan. An engine causes the blades to turn. When the blades turn, they create thrust by biting into the air and forcing it to move back. The amount of thrust can be controlled by changing the speed of the propellers.



To use force to bring something closer. The force of gravity pulls objects closer to the Earth.



To use force to move something ahead or to the side. During takeoff the thrust force, created by the engines, pushes an airplane down the runway.



In aviation, to fly over and look closely at an area below to gather information about it.



A carefully planned and performed investigation, searching for previously unknown facts.


regimes of flight

A way of placing aircraft into different categories based on their speeds. The regimes of flight are subsonic, transonic, supersonic and hypersonic.



A rotational motion in which the aircraft turns around its longitudinal axis. Pushing the control stick to the left will raise the aileron on the left wing and lower the aileron on the right wing. This will cause the airplane to roll to the left. The pilot will see the left wing tip fall and the right wing tip rise.


rotational motion

The turning of an object, like an airplane, around an axis, or a propeller around a hub. Pitch, roll and yaw are the rotational motions of an airplane around the lateral, longitudinal and vertical axes.



A control surface on the trailing edge of the vertical part of the tail that is used to make the aircraft yaw. The rudder is controlled by rudder pedals. Pushing the left rudder pedal will tilt the rudder to the left. This will cause the nose of the aircraft to turn to the left.


scientific method

A systematic way of solving a problem or answering a question using observation and measurement. The six steps of the scientific method are: state the problem, create a hypothesis, design an experiment, perform the experiment, organize and analyze the data, draw conclusions.



A device that creates an environment that is as close as possible to reality. In flight simulators, engineers create a cockpit environment identical to the one in a real airplane. In a flight simulator a pilot will see, hear and feel like he or she is in a real aircraft.



a sled-like runner used as part of the landing gear for an aircraft.


speed of sound

The speed at which sound waves travel. If you stand a distance away from a friend and say something to him, the sound waves of your voice will travel very quickly to the ear of your friend. The speed of sound is the speed at which those waves traveled.



A device, normally located on the top of the wing, for changing the airflow around a wing to reduce lift. Pilots deploy spoilers when they land so that the airplane is no longer "lifted" into the air.



The condition of being steady. A motion of an aircraft is said to have stability, or be stable, if the aircraft will return to that motion after a disturbance, without the pilot having to move the controls.



A surface that helps to provide stability for an aircraft. An airplane has two stabilizers: a vertical stabilizer and a horizontal stabilizer. Stabilizers are like the feathers on an arrow, which keep the arrow pointed in the right direction.



A breakdown of the airflow over a wing, which suddenly reduces lift. When an airplane stalls it will usually drop suddenly. Pilots know how to recover from a stall and smooth out the airflow over the wings to produce more lift again.


straight wing

A wing that sticks straight out from the fuselage - it does not slant to the front or the rear. The ER-2 is an example of an aircraft that has straight wings.



To shape an object so that it creates less drag and moves smoothly and easily through the air. Airfoils are streamlined, as is the fuselage.



Velocity less than the speed of sound. The MD-11 is a subsonic aircraft because it never flies above the speed of sound.



A computer that is especially designed to receive, process and present very large amounts of data very quickly. The Cray Y-MP is an example of a supercomputer that is resident at NASA Ames Research Center and is used for CFD.



Velocity greater than the speed of sound. The SR-71 is characterized as a supersonic aircraft because it travels from three to four times the speed of sound. A supersonic aircraft can fly from New York to London in less than two hours.


sweepback wing

A wing that is slanted toward the rear of the airplane. The F-18 aircraft is an example of a supersonic jet that has sweepback wings.



Another word for a horizontal stabilizer.



The process of using the thrust of the engines to accelerate an airplane down a runway until enough lift is generated so that the aircraft begins to fly.


test pilot

A pilot that is specially trained to test aircraft. Test pilots must be exceptional pilots, have a complete understanding of aeronautics and aerodynamics, and be able to accurately write and speak about what they see, feel and hear during the testing of an aircraft.



A force created by the engines that pushes an aircraft through the air.



A device or process that is used to do some kind of work. A hand-held calculator is a tool for doing mathematics accurately and quickly. The tools of aeronautics (CFD, Wind Tunnel Testing, Flight Simulation and Flight Test) are processes that use special devices to perform research in aeronautics.


trailing edge

The rear edge of an airfoil. The trailing edge is normally thin and sharp. The ailerons are normally located on the trailing edge of the wing.


translational motion

Motion along a straight line, such as an axis. The translational motions of an aircraft are forward and back along the longitudinal axis, side to side along the lateral axis, and up and down along the vertical axis.



Velocity between nine tenths (.9) and one and four tenths (1.4) times the speed of sound. The X-1 was the first aircraft to fly faster than the speed of sound. Several versions of the X-1 were built. One succeeded at flying twice the speed of sound at an altitude of 90,000 feet.



Air flow which is not smooth and steady. When an airplane flies through turbulent air, it can unexpectedly rise, drop, roll, pitch or yaw very abruptly.



The part of an aircraft that provides support while the aircraft is on the ground. It includes wheels, shock absorbers and support struts. There is an undercarriage unit under the nose of the aircraft as well as approximately midway back, under the fuselage. Undercarriage normally includes rubber tires, but may have skis for landing on snow or floats for landing on water.


variable sweep wing

Wings that are hinged so they can be slanted forward or backward during flight. The F-14 aircraft is an example of a supersonic jet with variable sweep wings.



The speed of an object, in a certain direction.


vertical axis

The axis extending straight up and down through the center of gravity of an aircraft. The vertical axis is perpendicular to the longitudinal and lateral axes. The vertical axis is sometimes called the "z" axis. Yaw is a motion around the vertical axis.


vertical stabilizer

The vertical part of the tail. The vertical stabilizer helps to increase the stability of the aircraft. It is also known as a fin.



The force of gravity acting on an object. The weight force pulls an aircraft toward the Earth and must be overcome by a combination of lift and thrust.


wind tunnel testing

A tool of aeronautics that involves placing a model of an aircraft or part of an aircraft into a wind tunnel and using instruments to gather data while air is blown past the model. Wind tunnel testing is used to investigate and accurately describe the effects of airflow on an aircraft or part of an aircraft.


wind tunnel

A wind tunnel is a tube or cylinder in which a model of an airplane or part of an airplane is placed. Air is blown past the model so that it experiences the same forces as it would if it were actually flying. The struts that hold the model in place measure these forces.



A part of an airplane that is attached to the fuselage. Wings are shaped like airfoils and are used to provide lift for the airplane. There are four basic types of wings: straight, sweep, delta and variable sweep.


wing warping:

a mechanism to provide lateral control of the aircraft through flexible wing tips; wires enabled the wing tips to arch so that the ends of the wings were four inches lower than the center (the concept was devised by the Wrights after observing the wing tips of a hawk in flight).



A rotational motion in which the aircraft turns around its vertical axis. This causes the aircraft's nose to move to the pilot's right or left. Pushing the right rudder pedal will tilt the rudder to the right. The pilot will see the nose of the aircraft turn to the right.