How does an Airplane Fly?How does an Airplane Fly?

Forces on an Airplane in FlightThe four aerodynamic forces that act upon an airplane in flight are lift (the upward acting force), weight (or gravity, the downward acting force), thrust (the forward acting force), and drag (the air resistance or backward acting force). These four forces are continuously battling each other while an airplane is in flight.

 

 

Gravity opposes lift, thrust opposes drag. In order to take off, the aircraft's thrust and lift must be suffucient to overcome its weight and drag. In level flight at constant speed, thrust exactly equals drag and lift exactly equals the pull of gravity. To land, an aircraft's thrust must be reduced safely below its drag, as its lift is reduced to levels less than its weight.

Control Surfaces andControl Surfaces and

An airplane in flight moves around three axes of rotation: longitudinal axis, lateral axis, and vertical axis. These axes are imaginary lines that run perpendicularly to each other through the center of gravity of the airplane. Rotation around the longitudinal axis (the line from the nose of the plane to the tail) is called roll. Rotation around the lateral axis (the line from wingtip to wingtip) is called pitch. Rotation around the vertical axis (the line from beneath to above the plane) is called yaw. The pilot guides and controls the aircraft by controlling its pitch, roll, and yaw via the control surfaces. These include the ailerons, elevators, and rudder.

How an Airplane Generates LiftHow an Airplane Generates Lift

 

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Since lift is dependant on the motion of the air, it increases as the speed of the air increases. Lift also increases (to a point) as the angle that the wing makes with the airflow (known as the angle of attack) increases. Past a certain point, however, increased angle of attack will cause the wing to suddenly lose its lifting ability, or stall.

AileronsAilerons

The ailerons on an airplane's wings control roll around the longitudinal axis. They work together, simultaneously, tied to the control wheel, or stick, in the cockpit. When the control wheel is turned left, the aileron on the left wing goes up and the one on the right wing goes down.

The ailerons alter the lifting ability of the wings slightly. When an aileron is lowered, the lift on the outer portion of that wing increases, causing that wing to rise a little. When an aileron is raised, the lift on the outer portion of that wing is decreased slightly, causing that wing to drop a little. Since the ailerons on an airplane work together, their action causes the airplane to roll.

RudderRudder

The rudder on the rear edge of the vertical fin on the airplane's tail controls yaw around the vertical axis. It is connected to the pedals at the pilot's feet. Pushing the right pedal causes the rudder to deflect to the right. This makes the tail of the airplane move toward the left, causing the nose to move to the right. Pushing the left pedal makes the rudder deflect to the left, the tail moves to the right, and the nose points to the left.

rudder left, tail right

rudder neutral (centered)

rudder right, tail left

Rudder Position(As viewed from above)

Although the rudder pedals and control wheel in the cockpit are not linked together, they must be used simultaneously to control the plane. The pilot guides the airplane by careful and precise movements of the control wheel and rudder pedals, as well as adjusting the thrust of the aircraft.

How Does an Airplane Produce How Does an Airplane Produce Thrust?Thrust?

Thrust is the force created by a power source that overcomes the airplane's aerodynamic drag (its resistance to passing through the air) and gives it forward motion. This force can either "pull" or "push" the aircraft forward, depending on the type of power source used. Common types include reciprocating (piston-powered) engines driving propellers, and jet engines.

Reciprocating Engines with PropellersReciprocating Engines with Propellers

A reciprocating engine is an internal-combustion engine in which pistons moving back and forth act upon a crankshaft to create rotational movement. (This is the same type of engine that powers most family cars.) A mixture of fuel and air is compressed by the pistons, an electric spark causes the mixture to explode, driving the pistons downward. This motion is transferred to the crankshaft by connecting rods. The rotating crankshaft turns the propeller.

. Thus, the propeller creates a propulsive force perpendicular to its plane of rotation that moves the aircraft forward as a reaction. Props can either "pull" the aircraft from their position on the front of the wings or fuselage, or "push" it from behind, or both.After you are finished reading this article, you many wish to view an expanded discussion on Piston Engines. Read our two article set "How Engine Make Power".

Jet EnginesJet Engines

A jet engine is any engine that ejects a jet or stream of gas or fluid, thereby obtaining thrust in reaction to the ejection force. A jet aircraft engine obtains oxygen from the atmosphere for the combustion of its fuel, creating thrust in reaction to the rapid exhaust of the combustion products. There are several types of jet engines. Some are briefly described below.

TurbojetTurbojetA turbojet engine is a jet engine that incorporates a turbine-driven compressor to take in and compress air for the combustion of fuel. The exhaust from the combustion drives the turbine and creates the thrust-producing jet.

Basic Turbojet Engine

aileron neutral, normal lift

aileron lowered, increased lift

aileron raised, decreased lift

Aileron Position(As

from the end of the wing) 

TurbopropTurbopropA turboprop engine is a turbojet engine in which a portion of the exhaust energy is used to drive a propeller. The engine's thrust is therefore generated by a combination of the propeller's thrust and the jet exhaust from the engine.

Basic Turboprop Engine

RamjetRamjet

A ramjet engine is the simplest type of jet engine since it has no moving parts. The engine is basically a specially-shaped duct open at both ends, with the air necessary for combustion being compressed by the forward motion of the engine. Fuel is sprayed into the airstream and the mixture is ignited. The high-pressure air coming into the combustion chamber keeps the reaction from going back toward the inlet.

   

   

Basic Ramjet Engine

Ramjet engines cannot operate under static conditions. In order to function, they have to already be traveling through the air at slightly over the speed of sound. (The speed of sound is somewhat over 740 miles per hour at sea level.) This means that the aircraft using them must first get up to the required speed using some other type of propulsion, then start the ramjets. They can operate at up to five times the speed of sound.