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Transcript of Aviation
which create its air pressure. Air is an important
substance such that all things that fly need air. Forces of Flight The four forces that act on an airplane are
Thrust (forward motion)
Drag (backward motion)
Gravity (downward) Thrust Thrust is a force directed in a forward motion and is
produced by the engine.
This force is generated by the engines of an aircraft through
a propulsion system In aircrafts, engines are used to create propulsion.
An airplane's main thrust comes from the propeller and the propeller is turned on by the turbine engine. In this turbine engine, the airfoil-shaped fans suck in air and compress it and then it is forced into the combustian chamber where the air is heated by the burning fuel. The air then rushes out at a great force spinning the turbine fans.
Newton's third law applies to the thrust such that the action force is the air being pushed backwards and reaction force is the forward motion of the airplane. Lift Lift is a force perpendicular to thrust opposing the force of gravity
Two examples of 'types of lift'
Aerodynamic lift THRUST HOW IS LIFT GENERATED
There are currently three theories showing on NASA's website.
"Equal transit" or "longer path" theory.
Now we will be showing a short video which explains how thrust is generated and how the turbine engines work L
T Weight and Gravity Weight is distributed evenly throughout the airplane and that weight is always changing due to the constant usage of fuel. Center of gravity
It is a point at which the weight of an object appears to be concentrated
There are two problems associated with the object’s weight and location of the center of gravity
Overcoming the force of gravity
Controlling the object in flight How to control flight parameters There are three parameters - Roll, Pitch and Yaw
There is a rotation about the longitudinal axis which gives and up-down movement of the wing tips.
Ailerons - are located on the trailing edge of both wings.
These ailerons raise and lower the wings. -> Pitch
It is the movement of airplane’s nose either up or down.
Elevator - is located on the rear of aircraft on the tail.
It helps an aircraft pitch up to climb and down to dive. -> Yaw
It is the rotation about the vertical axis giving side-to-side movement of the nose
Rudder - is located in the rear of the aircraft on the tail.
It allows the airplane to move towards left or right while in flight It is important to balance the weight evenly in an airplane, or else the airplane will tilt either towards the nose or towards the tail. Drag
For this force to be generated, a solid object must be in contact with a fluid.
There must be motion and difference in velocity between the object and fluid.
Like lift, drag ∝ area of the object. Doubling the area doubles the drag. There are many factors that affect the magnitude of the drag. For example:
- When and airplane with smooth waxed surface is airborne, there will be less “skin friction” than an airplane with rough surface.
- Viscosity depends on the temperature such that the higher the temperature, the higher the viscosity. And the higher the viscosity, the thicker the air, therefore, there is a greater drag. There are different types of drag:
form drag and induced drag
--Form Drag - this source of drag arises because of the object’s form and shape
This drag can be reduced by restructuring the aircraft to a curved shape which allows the air to flow smoothly around the object (like the airfoil shape ) --Induced Drag - is created by the vortices at the tip of the aircraft’s wing.
The trailing vortex is created due to the high pressure from underneath the wing which causes the air to curl in a circular motion
The induced drag depends upon the angle of attack. The critical the angle of attack, the greater the induced drag. wing flaps Nacelle Drop tanks Vortices A situation in which all four forces acting on an airplane produce no net external force is a cruising airliner. Weight is always decreasing but the change is too small compared to the weight of the plane.
If the pilot changes the setting, the forces will become unbalanced and as Newton’s second law says, the aircraft will move in the direction of greater force. Sound barrier Sound barrier is the point at
which a plane moves from transonic
to supersonic speed. Aerodynamicists have designated the speed ratio with a special parameter called the Mach number after the physicist, Ernst Mach.
Mach number = object speed / Speed of sound
Plane travelling slower than the speed of sound is travelling below Mach 1.
Plane travelling at the speed of sound is travelling at Mach 1.
A plane travelling at twice the speed of sound is travelling at Mach 2. When a plane travels slower than the speed of sound (subsonic), pressure waves move out around the plane When a plane travels at the speed of sound (transonic), pressure waves at nose form a shock wave. Elevators Rudder When a plane travels at speed faster than the speed of sound (supersonic), shockwaves form a cone resulting in a sonic boom G-Force G-Force is a gravitational force acting on a body as a result of acceleration.
Acceleration is described in units of the force called “Gs”
1G is the force of gravity on Earth Types of acceleration
Angular You experience positive g-force when the aircraft pitches upward
You experience negative g-force when the aircraft pitches downward
redout However, according to NASA...
airfoils are designed to produce lift <- this statement is not accurate
the air molecules do not meet up at the trailing edge
Bernoilli's principle is absolutely correct Factors that affect lift
size - Lift ∝ surface area.
-air A propeller is a type of fan with multiple airfoils. These propellers are now fitted in the turbine engines which are named turbine fans. Turbine fans THE END "skipping stone" theory NASA's argument
this theory is concerned with only the interaction of the lower surface of the moving object and the air
this theory neglects the action <--> reaction of molecules striking the upper surface NASA's arguments...
airfoil is not a Venturi nozzle
this theory deals with only the pressure and velocity along the upper surface of the airfoil Inclination affect of lift
--As the nose of the airplane rises, the angle of attack increases. Lift ∝ angle of attack only for small angles.
The stall shown in the graph happens when the angle of attack is too high and airplanes suddenly loose lift. Downwash affects on lift
--As an aircraft moves lower, the vortex lines form from the edge of the wings. This vortex forms due to the mix of high pressure and low pressure air at the end of the wing tips.
As you will learn after, these vertices are the cause of induced drag (aerodynamic friction). This drag is the cause of the reduction of the lift magnitude of the entire wing. Bernoulli's principle states that as the velocity of a fluid increases, the pressure exerted by that fluid decreases. "venturi" theory Birds in flight
These forces can also be applied to birds in flight. For example,
In order to overcome gravity, a bird must create lift and thrust by flaping its wings.
Birds can obtain lift because of the structure of their wings. Their wings are shaped very similarly to the shape of an airfoil. wing flaps