Flight and Airplanes

Flight

Forces involved in flying

A force may be thought of as a push or pull in a specific direction. This slide shows the forces that act on the Wright 1900 aircraft when flown as a kite. You can compare these forces to the forces on the aircraft when flown as a piloted glider and you will note only a few differences. There are also a few differences from the forces on a powered aircraft, but the similarities are so great that the Wrights were able to use kite experiments to determine the aerodynamic performance of their unpowered aircraft from 1900 to 1902. They also used kite experiments to learn the basics of flight control. You can also learn the basics of aerodynamics by flying a kite. The forces on your kite are exactly the same as the forces on the Wright brothers' kite.

Weight

Weight is a force that is always directed toward the center of the earth. The magnitude of the force depends on the mass of all the parts of the aircraft. The weight is distributed throughout the aircraft, but we can often think of it as collected and acting through a single point called the center of gravity. In flight, an airplane rotates about the center of gravity, but a kite rotates about the connection point of the control wires. A kite's motion is confined or pinned like a door which rotates on its hinges. The kite's weight is always directed toward the center of the earth.

Lift

To make a kite fly, we must generate a force to overcome the weight. This force is called the lift and is generated by the motion of the air over the kite. Lift is an aerodynamic force ("aero" stands for the air, and "dynamic" denotes motion). Lift is directed perpendicular (at right angle) to the wind direction. As with weight, each part of the kite contributes to a single lift force. Most of the lift of the Wright 1900 kite was generated by the wings. The lift acts through a single point called the center of pressure. The center of pressure is defined just like the center of gravity, but using the pressure distribution around the body instead of the weight distribution.

Drag

As the air moves past the kite, the kite resists the motion of the air. This resistance force is called the drag of the kite. The direction of the drag force is always in the direction of the wind. Drag acts through the center of pressure in the same way that lift acts through the center of pressure. (In reality, there is only one aerodynamic force on the kite. Engineers break this force into lift and drag to more easily explain the motion of an object along its flight path.)

Tension

To keep the kite at a fixed location, a pair of control lines are attached to the kite. The control lines generate a force called tension which is used to overcome the drag. Without the control lines, the kite would move in the direction of the wind and there would be no relative velocity between the wind and the kite. The lift would go to zero and the kite would fall to the ground because of gravity. For convenience, the tension force is often broken into two components, one vertical and one horizontal.

When the kite is in stable flight, the lift is equal to and opposes the combination of the weight and the vertical pull of tension. The drag is equal to and opposes the horizontal tension. Compared to the forces on an airplane, the horizontal pull on a kite plays the roll of the thrust. The vertical pull of the line tension is mainly the weight of the line; the kite must lift its own weight and the weight of the line.

The relative strength of the forces determines the motion of the kite as described by Newton's laws of motion. If the wind velocity increases, the lift increases and exceeds the weight of the kite. The kite then moves vertically and the tension force increases because of increased drag. The vertical component of tension increases because of the change in angle that the tension force makes with the vertical. A new balance point is established and the kite achieves a different stable condition.

The Wright Brothers aircraft without an engine

The Wright Brothers Airplane (with engine)

Engine used in the wright brothers plane

Paper airplanes are really examples of gliders. Gliders are aircraft without engines. Here is a website that will offer use a lot of different types of paper airplanes. I want each student to choose a different style of paper airplane. Once everyone has chosen their plane you need to make three of them. Later we will be flying them in competition.

Fold N Fly

Printable Paper Airplanes

As we started to understand the forces acting on aircraft we began to gain more control. Here is an example of a more modern plane

Parts of a Plane

The body of the plane is called the fuselage. It is generally a long tube shape. The wheels of a plane are called the landing gear. There are two main wheels on either side of the plane fuselage. Then there is one more wheel near the front of the plane. The brakes for the wheels are like the brakes for cars. They are operated by pedals, one for each wheel. Most landing gear can be folded into the fuselage during the flight and opened for landing.

All planes have wings. The wings are shaped with smooth surfaces. The smooth surfaces are slightly curved from the front or leading edge, to the back or trailing edge. Air moving around the wing produces the upward lift for the airplane. The shape of the wings determines how fast and high the plane can fly. A cut through the wing from front to back is called an airfoil.

The hinged control surfaces are used to steer and control the airplane. The flaps and ailerons are connected to the backside of the wings. The flaps slide back and down to increase the surface of the wing area. They also tilt down to increase the curve of the wing. The slats move out from the front of the wings to make the wing space larger. This helps to increase the lifting force of the wing at slower speeds like takeoff and landing. The ailerons are hinged on the wings and move downward to push the air down and make the wing tilt up. This moves the plane to the side and helps it turn during flight. After landing, the spoilers are used like air brakes to reduce any remaining lift and slow down the airplane.

The tail at the rear of the plane provides stability. The fin is the vertical part of the tail. The rudder at the back of the plane moves left and right to control the left or right movement of the plane. The elevators are found at the rear of the plane. They can be raised or lowered to change the direction of the plane's nose. The plane will go up or down depending on the direction of that the elevators are moved.

We are now going to enter Nasa's future flight design

Flight Lab Map

aeronautics Lab

Propulsion Lab

Fuselage Lab

Lift Lab

Design Center

CFD Lab

Wind tunnel

Flight Test

What is Air?

Air is a physical substance which has weight. It has molecules which are constantly moving. Air pressure is created by the molecules moving around. Moving air has a force that will lift kites and balloons up and down. Air is a mixture of different gases; oxygen, carbon dioxide and nitrogen. All things that fly need air. Air has power to push and pull on the birds, balloons, kites and planes.

In 1640, Evagelista Torricelli discovered that air has weight. When experimenting with measuring mercury, he discovered that air put pressure on the mercury.

Francesco Lana used this discovery to begin to plan for an airship in the late 1600s. He drew an airship on paper that used the idea that air has weight. The ship was a hollow sphere which would have the air taken out of it. Once the air was removed, the sphere would have less weight and would be able to float up into the air. Each of four spheres would be attached to a boat-like structure and then the whole machine would float. The actual design was never tried.

Hot air expands and spreads out and it becomes lighter than cool air. When a balloon is full of hot air it rises up because the hot air expands inside the balloon. When the hot air cools and is let out of the balloon the balloon comes back down.

How Wings Lift the Plane

Airplane wings are shaped to make air move faster over the top of the wing. When air moves faster, the pressure of the air decreases. So the pressure on the top of the wing is less than the pressure on the bottom of the wing. The difference in pressure creates a force on the wing that lifts the wing up into the air.

Here is a simple computer simulation that you can use to explore how wings make lift.

Laws of Motion

Sir Isaac Newton proposed three laws of motion in 1665. These Laws of Motion help to explain how a planes flies.

1. If an object is not moving, it will not start moving by itself. If an object is moving, it will not stop or change direction unless something pushes it.

2. Objects will move farther and faster when they are pushed harder.

3. When an object is pushed in one direction, there is always a resistance of the same size in the opposite direction.

Forces of Flight

Controlling the Flight of a Plane

How does a plane fly? Let's pretend that our arms are wings. If we place one wing down and one wing up we can use the roll to change the direction of the plane. We are helping to turn the plane by yawing toward one side. If we raise our nose, like a pilot can raise the nose of the plane, we are raising the pitch of the plane. All these dimensions together combine to control the flight of the plane. A pilot of a plane has special controls that can be used to fly the plane. There are levers and buttons that the pilot can push to change the yaw, pitch and roll of the plane.

To roll the plane to the right or left, the ailerons are raised on one wing and lowered on the other. The wing with the lowered aileron rises while the wing with the raised aileron drops.

Pitch makes a plane descend or climb. The pilot adjusts the elevators on the tail to make a plane descend or climb. Lowering the elevators caused the airplane's nose to drop, sending the plane into a down. Raising the elevators causes the airplane to climb.

Yaw is the turning of a plane. When the rudder is turned to one side, the airplane moves left or right. The airplane's nose is pointed in the same direction as the direction of the rudder. The rudder and the ailerons are used together to make a turn

How does a Pilot Control the Plane?

Click on the Radar Display, the Direction Finder, the Altitude Indicator and the Throttle Console parts of the cockpit for a more detailed view.

To control a plane a pilot uses several instruments...

The pilot controls the engine power using the throttle. Pushing the throttle increases power, and pulling it decreases power.

The ailerons raise and lower the wings. The pilot controls the roll of the plane by raising one aileron or the other with a control wheel. Turning the control wheel clockwise raises the right aileron and lowers the left aileron, which rolls the aircraft to the right.

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Picture of plane in roll

The rudder works to control the yaw of the plane. The pilot moves rudder left and right, with left and right pedals. Pressing the right rudder pedal moves the rudder to the right. This yaws the aircraft to the right. Used together, the rudder and the ailerons are used to turn the plane.

Picture of plane Yaw

The elevators which are on the tail section are used to control the pitch of the plane. A pilot uses a control wheel to raise and lower the elevators, by moving it forward to back ward. Lowering the elevators makes the plane nose go down and allows the plane to go down. By raising the elevators the pilot can make the plane go up.

Picture of Plane Pitch

The pilot of the plane pushes the top of the rudder pedals to use the brakes. The brakes are used when the plane is on the ground to slow down the plane and get ready for stopping it. The top of the left rudder controls the left brake and the top of the right pedal controls the right brake.

If you look at these motions together you can see that each type of motion helps control the direction and level of the plane when it is flying.

Sound Barrier

Sound is made up of molecules of air that move. They push together and gather together to form sound waves . Sound waves travel at the speed of about 750 mph at sea level. When a plane travels the speed of sound the air waves gather together and compress the air in front of the plane to keep it from moving forward. This compression causes a shockwave to form in front of the plane.

In order to travel faster than the speed of sound the plane needs to be able to break through the shock wave. When the airplane moves through the waves, it is makes the sound waves spread out and this creates a loud noise or sonic boom . The sonic boom is caused by a sudden change in the air pressure. When the plane travels faster than sound it is traveling at supersonic speed. A plane traveling at the speed of sound is traveling at Mach 1 or about 760 MPH. Mach 2 is twice the speed of sound.

Regimes of Flight

Sometimes called speeds of flight, each regime is a different level of flight speed.

Jet engines move the airplane forward with a great force that is produced by a tremendous thrust and causes the plane to fly very fast.

All jet engines, which are also called gas turbines, work on the same principle. The engine sucks air in at the front with a fan. A compressor raises the pressure of the air. The compressor is made with many blades attached to a shaft. The blades spin at high speed and compress or squeeze the air. The compressed air is then sprayed with fuel and an electric spark lights the mixture. The burning gases expand and blast out through the nozzle, at the back of the engine. As the jets of gas shoot backward, the engine and the aircraft are thrust forward. As the hot air is going to the nozzle, it passes through another group of blades called the turbine. The turbine is attached to the same shaft as the compressor. Spinning the turbine causes the compressor to spin.

The image below shows how the air flows through the engine. The air goes through the core of the engine as well as around the core. This causes some of the air to be very hot and some to be cooler. The cooler air then mixes with the hot air at the engine exit area.

This is a picture of how the air flows through an engine

What is Thrust?

Thrust is the forward force that pushes the engine and, therefore, the airplane forward. Sir Isaac Newton discovered that for "every action there is an equal and opposite reaction." An engine uses this principle. The engine takes in a large volume of air. The air is heated and compressed and slowed down. The air is forced through many spinning blades. By mixing this air with jet fuel, the temperature of the air can be as high as three thousand degrees. The power of the air is used to turn the turbine. Finally, when the air leaves, it pushes backward out of the engine. This causes the plane to move forward.

Parts of a Jet Engine

Fan - The fan is the first component in a turbofan. The large spinning fan sucks in large quantities of air. Most blades of the fan are made of titanium. It then speeds this air up and splits it into two parts. One part continues through the "core" or center of the engine, where it is acted upon by the other engine components.

The second part "bypasses" the core of the engine. It goes through a duct that surrounds the core to the back of the engine where it produces much of the force that propels the airplane forward. This cooler air helps to quiet the engine as well as adding thrust to the engine.

Compressor - The compressor is the first component in the engine core. The compressor is made up of fans with many blades and attached to a shaft. The compressor squeezes the air that enters it into progressively smaller areas, resulting in an increase in the air pressure. This results in an increase in the energy potential of the air. The squashed air is forced into the combustion chamber.

Combustor - In the combustor the air is mixed with fuel and then ignited. There are as many as 20 nozzles to spray fuel into the airstream. The mixture of air and fuel catches fire. This provides a high temperature, high-energy airflow. The fuel burns with the oxygen in the compressed air, producing hot expanding gases. The inside of the combustor is often made of ceramic materials to provide a heat-resistant chamber. The heat can reach 2700°.

Turbine - The high-energy airflow coming out of the combustor goes into the turbine, causing the turbine blades to rotate. The turbines are linked by a shaft to turn the blades in the compressor and to spin the intake fan at the front. This rotation takes some energy from the high-energy flow that is used to drive the fan and the compressor. The gases produced in the combustion chamber move through the turbine and spin its blades. The turbines of the jet spin around thousands of times. They are fixed on shafts which have several sets of ball-bearing in between them.

Nozzle - The nozzle is the exhaust duct of the engine. This is the engine part which actually produces the thrust for the plane. The energy depleted airflow that passed the turbine, in addition to the colder air that bypassed the engine core, produces a force when exiting the nozzle that acts to propel the engine, and therefore the airplane, forward. The combination of the hot air and cold air are expelled and produce an exhaust, which causes a forward thrust. The nozzle may be preceded by a mixer, which combines the high temperature air coming from the engine core with the lower temperature air that was bypassed in the fan. The mixer helps to make the engine quieter.

The First Jet Engine - A Short History of Early Engines

Sir Isaac Newton in the 18th century was the first to theorize that a rearward-channeled explosion could propel a machine forward at a great rate of speed. This theory was based on his third law of motion. As the hot air blasts backwards through the nozzle the plane moves forward.

Henri Giffard built an airship which was powered by the first aircraft engine, a three-horse power steam engine. It was very heavy, too heavy to fly.

In 1874, Felix de Temple, built a monoplane that flew just a short hop down a hill with the help of a coal fired steam engine.

Otto Daimler, in the late 1800's invented the first gasoline engine.

In 1894, American Hiram Maxim tried to power his triple biplane with two coal fired steam engines. It only flew for a few seconds.

The early steam engines were powered by heated coal and were generally much too heavy for flight.

American Samuel Langley made a model airplanes that were powered by steam engines. In 1896, he was successful in flying an unmanned airplane with a steam-powered engine, called the Aerodrome. It flew about 1 mile before it ran out of steam. He then tried to build a full sized plane, the Aerodrome A, with a gas powered engine. In 1903, it crashed immediately after being launched from a house boat.

In 1903, the Wright Brothers flew, The Flyer, with a 12 horse power gas powered engine.

From 1903, the year of the Wright Brothers first flight, to the late 1930s the gas powered reciprocating internal-combustion engine with a propeller was the sole means used to propel aircraft.

It was Frank Whittle, a British pilot, who designed and patented the first turbo jet engine in 1930. The Whittle engine first flew successfully in May, 1941. This engine featured a multistage compressor, and a combustion chamber, a single stage turbine and a nozzle.

At the same time that Whittle was working in England, Hans von Ohain was working on a similar design in Germany. The first airplane to successfully use a gas turbine engine was the German Heinkel He 178, in August, 1939. It was the world's first turbojet powered flight.

General Electric built the first American jet engine for the US Army Air Force jet plane . It was the XP-59A experimental aircraft that first flew in October, 1942.

Types of Jet Engines

Turbojets

The basic idea of the turbojet engine is simple. Air taken in from an opening in the front of the engine is compressed to 3 to 12 times its original pressure in compressor. Fuel is added to the air and burned in a combustion chamber to raise the temperature of the fluid mixture to about 1,100°F to 1,300° F. The resulting hot air is passed through a turbine, which drives the compressor. If the turbine and compressor are efficient, the pressure at the turbine discharge will be nearly twice the atmospheric pressure, and this excess pressure is sent to the nozzle to produce a high-velocity stream of gas which produces a thrust. Substantial increases in thrust can be obtained by employing an afterburner. It is a second combustion chamber positioned after the turbine and before the nozzle. The afterburner increases the temperature of the gas ahead of the nozzle. The result of this increase in temperature is an increase of about 40 percent in thrust at takeoff and a much larger percentage at high speeds once the plane is in the air.

The turbojet engine is a reaction engine. In a reaction engine, expanding gases push hard against the front of the engine. The turbojet sucks in air and compresses or squeezes it. The gases flow through the turbine and make it spin. These gases bounce back and shoot out of the rear of the exhaust, pushing the plane forward.

Picture of Turbojet Engine

Turboprops

A turboprop engine is a jet engine attached to a propeller. The turbine at the back is turned by the hot gases, and this turns a shaft that drives the propeller. Some small airliners and transport aircraft are powered by turboprops.

Like the turbojet, the turboprop engine consists of a compressor, combustion chamber, and turbine, the air and gas pressure is used to run the turbine, which then creates power to drive the compressor. Compared with a turbojet engine, the turboprop has better propulsion efficiency at flight speeds below about 500 miles per hour. Modern turboprop engines are equipped with propellers that have a smaller diameter but a larger number of blades for efficient operation at much higher flight speeds. To accommodate the higher flight speeds, the blades are scimitar-shaped with swept-back leading edges at the blade tips. Engines featuring such propellers are called propfans.

Picture of turboprop engine

Turbofans

A turbofan engine has a large fan at the front, which sucks in air. Most of the air flows around the outside of the engine, making it quieter and giving more thrust at low speeds. Most of today's airliners are powered by turbofans. In a turbojet all the air entering the intake passes through the gas generator, which is composed of the compressor, combustion chamber, and turbine. In a turbofan engine only a portion of the incoming air goes into the combustion chamber. The remainder passes through a fan, or low-pressure compressor, and is ejected directly as a "cold" jet or mixed with the gas-generator exhaust to produce a "hot" jet. The objective of this sort of bypass system is to increase thrust without increasing fuel consumption. It achieves this by increasing the total air-mass flow and reducing the velocity within the same total energy supply.

Picture of Turbofan Engine

Turboshafts

This is another form of gas-turbine engine that operates much like a turboprop system. It does not drive a propellor. Instead, it provides power for a helicopter rotor. The turboshaft engine is designed so that the speed of the helicopter rotor is independent of the rotating speed of the gas generator. This permits the rotor speed to be kept constant even when the speed of the generator is varied to modulate the amount of power produced.

Picture of Turboshaft Engine

Ramjets

The ramjet is the most simple jet engine and has no moving parts. The speed of the jet "rams" or forces air into the engine. It is essentially a turbojet in which rotating machinery has been omitted. Its application is restricted by the fact that its compression ratio depends wholly on forward speed. The ramjet develops no static thrust and very little thrust in general below the speed of sound. As a consequence, a ramjet vehicle requires some form of assisted takeoff, such as another aircraft. It has been used primarily in guided-missile systems. Space vehicles use this type of jet.

Picture of Ramjet Engine

Design your own 747