What is Bernoulli's principle?
Rise (fall) in pressure within a flowing fluid must always be accompanied by a decrease (increase) in the speed, and conversely, an increase (decrease) in the speed of the fluid results in a decrease (increase) in the pressure within the fluid.
Why the air going over the wing has a lower pressure
What are the four forces acting upon an aircraft in flight?
What would be condsidered stable flight?
If an aircraft in flight will tend to return to level flight of its own accord without pilot interference it is stable.
What is lift?
Lift: To overcome weight, aeroplanes generate an opposing force called Lift, which is generated by the motion of the aircraft through the air and is an aerodynamic force. Argument between Bernoulli principle and Newtons Laws of Motion. Works through the centre of pressure of the wing.
What is weight?
Weight: Force generated by the gravitational attraction of the earth on the aircraft. Acts downwards towards the earth irrespective of the aircrafts attitude. Works through the centre of gravity of the aircraft.
What is thrust?
Thrust: Mechanical force provided by the aircrafts system of propulsion. Used to overcome drag. Works through the thrust line.
What is drag?
Drag: Aerodynamic force that opposes an aircrafts motion through the air, generated by every part of the aircraft: Profile drag- consequence of shape, increases as speed increases. Induced drag- consequence of lift, decreases as speed increases. Profile + Induced= Total Drag. Works through the drag line which is the exact opposite of the thrust line.
What is laminar flow?
Laminar Flow is the smooth, uninterrupted flow of air over the contour of the wings of an aircraft in flight.
It is most often found at the front of a streamlined body and is an important factor in flight.
If the smooth flow of air is interrupted, turbulence is created which results in a loss of lift and increased drag.
An Aerofoil designed for minimum drag and a smooth flow of the boundary layer is called a laminar aerofoil.
If the angle of attack of a wing is too high the laminar flow of air will separate from the wing, becoming turbulent, this is called the critical angle of attack and is the point where the wing will begin to stall.
How does an aircraft's wing work?
The curvature of the wing forces the air going over the top to speed up and therefore decrease in pressure whilst the opposite happens underneath the wing. The pressure underneath the wing then pushes the aircraft into the air.
What is an aerofoil?
A part of an aircraft designed to produce lift.
What is the chord line of a wing?
A line that dissects a wing from the leading edge through to the trailing edge.
What is the angle of incidence of a wing?
the angle at which the wing is attached to the fuselage.
What is a stall?
An aircraft is considered to be stalled when the critical angle of attack is reached and the laminar flow over the top of the wing seperates leading to a drop in the amount of lift generated.
What is the Angle of Attack of a wing?
The angle between the chord line and the flow of air. Has a large affect on amount of lift generated by a wing- greater angle= more lift (up to stall point where lift decreases because of flow separation).
How does a Piston Engine work, and what are its advantages and disadvantages?
Based on internal combustion engine using four stroke cycle: Intake- air and vaporised fuel drawn in Compression- fuel vapour and air compressed and ignited Combustion- fuel combusts and piston driven downwards Exhaust- exhaust gasses expelled.
How does a Jet Engine work?
Discharges a fast moving jet of hot expanded gases to generate thrust in accordance with Newtons Third Law (every action...). Uses the intake, compression, combustion and exhaust process. Turbojet- Generic term for simple turbine engines (100% air in/out) Turboshaft- similar to turbojet, gas turbine optimised to produce shaft power.
How does a Turboprop Engine work?
Type of gas turbine engine where the power produced is used to drive a propeller attached to the turbine shaft.
Variable pitch propellers- angle of attack of propeller blade can be altered to change thrust and drag profile in flight.
What are the three differences between aircraft and car engines?
- Aircraft engines are air cooled- saves weight and is safer
- Dual ignition systems- independent magnetos and spark plugs
- Fuel/Air mix- manually controlled.
How many operations is there in a four stroke engine?
- Power stroke
What is a carburetor?
A device that provides a suitable mixture of air and fuel to the cylinder for ignition.
What happens to air as it enters a carburetor?
- It accelerates
- There is a drop in air pressure?
- This causes the fuel to be drawn through the main jet where is mixes with air in the venturi
How does carburetor icing occur?
Due to the venturi effect and bernoulli's principle;
- The pressure decrease of the air accompanying the deceleration also causes an instant air temperture drop
- Latent heat is absorbed by the fuel as it vaporises into vapour, further cooling the air.
Can cause temp drops of 20°C
What should pilots do to prevent carburetor icing?
- If possible avoid areas where such icing is likely to occur
- Turn on the carburetor heating system
- During descents with engine at idle power, apply engine power frequently, so as to keep the engine warm
How does a propoller work?
Propeller: Means of converting engine power into a propulsive force, rotating blade accelerates a mass of air rearwards, aircraft moves forward in reaction. Aerofoil shape (like a wing). Outer edge of disc travelling faster, therefor blade is twisted in order to alter the angle of attack and give constant lift along whole blade. More blades= solidity increasing= less radius necessary.
What is the pitch of a propeller blade?
The angle made by the chord of the blade and its plane of rotation.
Much like the angle of attack of a wing, the higher the pitch the higher the propellers angle of attack and the more air it pushes back with each revolution.
What pitch is better for taking off and climbing?
A fine pitch
Which pitch is better for cruising?
What is the term for a pitch that is a compromise between a fine and coarse pitch for a fixed propeller blade?
What is a variable pitch propeller?
A propeller that can vary its pitch dependent on need. They can even use a reverse pitch.
What are the advantages of piston engines and propellers?
-More protected and easier to access and maintain
-Lower temperatures and pressures
-RPM increases and decreases more rapidly than jet
-Cheaper to manufacture
-Shorter take off and landing runs