Chapter 1 Basic terminology Chapter 2 How an aircraft generates lift Chapter 3 Stability and control Chapter 4 Operation of an aeroplane Chapter 5 Aeroplane performance considerations Chapter 6 Take-off techniques Chapter 7 Landing techniques Chapter 8 Legal requirements Chapter 9 Emergency procedures Contents
Contents Chapter 10 Terminology for direction of flight Chapter 11 Distance, Speed and Velocity Chapter 12 Time and units of time Chapter 13 Basic physics Chapter 14 Power plants and systems - the basics Chapter 15 BAK Navigation principles Chapter 16 BAK Meteorology principles Chapter 17 Miscellaneous
Aerofoil An aerofoil is a cross sectional shape of an aircraft wing. Angle of Incidence The angle of incidence is the angle between the chord line of the aerofoil and a reference axis or a nominated straight line from the front to the back of the aircraft. Angle of attack The angle of attack is the angle between the chord line and the relative airflow. Chord line The chord line is a line joining the leading and trailing edge in a straight line. Camber Camber is the curve of an aerofoil from the leading edge to the trailing edge. Centre of gravity The centre of gravity is the average location of the weight of an aircraft. It is the point on the aircraft that if it were fixed to a cable and hung from a crane it would balance perfectly. Centre of pressure The centre of pressure is the point where the total sum of all the pressure fields act on the aircraft wing. Basic Terminology Chapter 1
An Aerofoil is the cross section shape of a wing designed to generate lift when moving through the air. The centre of pressure is the point where the total sum of all the pressure fields act on the aircraft wing. The Center of Gravity is the average location of the weight of an aircraft.
Mean Camber line The mean camber line is the halfway point between the upper and lower surface of the aerofoil. Relative airflow The relative airflow is the airflow, that has both speed and direction, that moves over our aerofoil we call the relative airflow. Thickness to Chord or Chord Ratio Compares the thickness of the wing compared to its chord. Maximum point of thickness The point of maximum thickness that is the thickest part of the wing Trailing edge The trailing edge is the rear of the aerofoil. Total reaction force Lift is a force that acts at right-angles to the relative airflow while drag acts in the opposite direction of the relative airflow; the resultant force between the lift, and the drag, is the ‘total reaction force’. Washout Washout refers to the wing being designed so that the angle of incidence reduces from the wing root to the wing tip. This causes a lower angle of attack at the wing tips. This is to ensure the wing root stalls before the wing tip and makes the stall less severe. Leading edge The leading edge is the front of the aerofoil. Ch.1 - Basic Terminology Drag Drag is the force that opposes the movement of an aircraft through the air.
The leading edge is the front of the wing or aerofoil The resultant force between lift and drag is the total reaction force. The Trailing edge is the rear of the aerofoil.
How an aircraft generates lift is very complex. There is not a single mathematical explanation of why lift occurs, and it is the result of many complex factors. It is very easy to oversimplify how an aircraft produces lift or just pick and choose the easiest explanations as to why it occurs. We will look in detail at the major reasons an aircraft - and in particular a wing - produces lift. An aircraft flies because the aircraft is able to generate a force known as ‘lift’. This lift is generated by the shape of the wing, and this shape is called an ‘aerofoil’. There are numerous reasons why lift is created. We will look at three of the main reasons. In simple terms, an aerofoil produces lift by creating a lower pressure above the wing than below the wing, which produces a net upward force. To create this pressure difference, two things need to happen. We either need the top of the wing to be curved, or we require the wing to be inclined (angled) towards the relative airflow, or both. So how does a curved surface or an inclined (angled) wing cause a drop in pressure on top of the wing? To understand life, we first need to look at the ‘Coanda effect’. The Coanda effect causes the airflow to follow the curvature of the wing. This means that when the relative airflow hits the front of the wing, it is deflected up and over the wing and below the wing. Due to the coanda effect and the shape (or angle) of the wing in relation to the airflow, it deflects and curves this airflow over the wing. Lift and the Coanda effect How an aircraft generates lift Chapter 2
More curvature on the top of the wing the greater the lift force. The ‘Coanda Effect’ causes the airflow to follow the curvature of the wing. Greater angle of attack in relation to the relative airflow more lift force.
As we have already seen due to the Coanda effect, as the airflow hits the front of the wing due to the curvature of the aerofoil - or angle of the wing- in relation to the airflow, it causes a drop in pressure that produces lift and also sucks or accelerates more airflow over the top of the wing, which accelerates the airflow over the top of the wing. Bernoulli's principle states that ‘when a fluid increases its speed, there is a reduction in pressure’. This curvature of the airflow over the wing is actually what causes the drop in pressure. Lift and Bernoulli's principle There is also another reason why the aerofoil produces lift and this is due to Newton's third law of motion. Newton's 3rd law states: ‘For every action, there is an equal and opposite reaction’. Due to the Coanda effect the airflow is deflected down at the back of the aerofoil. This creates a force deflecting down at the rear of the wing. Due to Newton's third law, an opposite force must result from this downward force and this upward force is lift. Lift and Newton's laws This deflection of the airflow causes a drop in static pressure above the wing. Even if we had a straight non-curved wing, if we angle the straight wing in relation to the relative airflow, a drop in static pressure will occur. This is one reason why paper aeroplanes can produce lift even though they have no curved upper surface. Ch.2 - How an aircraft generates lift
An increase in angle of attack causes a drop in static pressure over the wing and an increase in the lift force. Newton's Law - For every action there is an equal and opposite reaction. An increase in the relative airflow over the wing causes a drop in static pressure and an increase in the lift force.
The amount of lift an aircraft wing produces is determined by the shape of the wing, the density of the air, the viscosity or compressibility of the air, the velocity of the air over the wing and the inclination of the wing in relation to the airflow. This is very complex. So the lift equation is: Lift = Coefficient x Density x Velocity2 x Wing Area divided by 2. For pilots we basically have control over three variables when it comes to lift. Firstly, on most aircraft we can control the flaps that change the camber (shape) and sometimes even the surface area of our wing. We can change the velocity of the airflow over the wing, and we can change the angle of attack of the wing in relation to the relative airflow. The Lift equation Ch.2 - How an aircraft generates lift
Flaps change the camber (or shape) of the wing and create more lift! Pilot can increase the angle of attack and create more lift. Pilot can increase velocity of airflow over the wing and create more lift.
The wing dihedral is the upward angle of the aircraft’s wings from the wing root to the wing tip. Having the wings designed to have an upward angle makes the aircraft more stable. If the wings had no dihedral then the aircraft would continue in this direction unless the pilot corrected the bank. Dihedral Aspect ratio refers to the length and width of an aircraft wing. A short wide wing has a ‘low aspect’ ratio, while a long thin wing has a ‘high aspect’ ratio. Aspect ratio Camber is the amount of curve from the leading edge to the trailing edge. More camber normally results in a thicker wing. The more camber the more lift the aerofoil produces. More camber also results in more drag. This is one reason why high performance aircraft do not have much camber, so they can minimise drag. Camber Sweepback is the angle of the wing that slopes back from the aircraft fuselage. Usually higher performance aircraft have swept wings, this is due to reduced drag at higher speed with a swept wing. Sweepback Design features Ch.2 - How an aircraft generates lift
The Upward angle of the aircraft wings from from the wing root to the wing tip! Sweepback is the angle of the aircraft's wings that slopes back from the fuselage. Aspect ratio is the length and width of a wing!
A slot normally located on the trailing edge is used to deflect air from below the aircraft to the upper wing to reduce the stall speed and allow the aircraft to fly at lower speeds for shorter takeoff and landings. Slats - like flaps - are a lift-generating device, however they are found on the leading edge of a wing and, like flaps, they extend to increase the camber of the wing and produce more lift, allowing the aircraft to takeoff and land at a slower airspeed. Slats and slots A trim tab is a small control surface attached to the main primary control surfaces. Trim tabs can be located on ailerons, rudders and the elevator. Most training aircraft only have trim tabs on the elevator. A trim tab is basically a secondary flight control surface which allows the pilot to reduce the pressure on the control column. As an example of how they work, let’s look at an elevator trim tab. During a climb the elevator is angled down and the elevator is now experiencing a lot more airflow pushing (dynamic pressure) against the entire surface of the elevator. This airflow forces the elevator back to the neutral position. The trim tab acts like a small wing, when the pilot chooses the desired elevator position, the trim tab can be set to create an opposite lift force to maintain the position of the elevator. The elevator will not stay in this position without any input from the pilot. Trim tabs Flaps are a lift-generating device which allows the aircraft to produce more lift by changing the camber, or shape, of the wing. The use of flap lowers the aircraft stall speed. By creating more lift the aircraft can takeoff and land at a lower speed, and the result is less runway is required for both takeoff and landing. Flaps Ch.2 - How an aircraft generates lift
Flaps are a lift generating device which allows aircraft to produce more lift by changing the Camber, or shape, of the wing. Trim reduces the control column and rudder pressure on some aircraft to make flying easier for the pilot. Slats and slots are a lift generating device located on the front of a wing, normally large jet aircraft.
The higher the density of the air, the more lift that is produced by the wing. The higher the altitude, the less dense the air. As a very general rule, if we halve the air density we halve the amount of lift the wing can produce. The higher an aircraft flies, the less dense the air is and therefore the less lift the wing can produce. Air density Angle of attack is the angle between the wing chord and the relative airflow. As we increase the angle of the attack of the wing, the lift will also increase until it reaches its maximum at the critical angle of attack. Drag created by lift is called ‘induced drag’. As the angle of attack of the wing increases so does the induced drag. Angle of attack The larger the surface area of the wing, the more lift that can be produced. As a general rule, if we double the size of the wing, we double the amount of lift available. The same can be said for drag, as the surface area of the wing increases so does the drag; so as a general rule if we double the size of the wing, we double the drag. Surface area of the wing The angle of incidence is the angle between the Chord line and a reference axis that runs along the fuselage. The angle of incidence cannot be changed on an aircraft and has no effect on the production of lift. Angle of incidence Lift and Drag Ch.2 - How an aircraft generates lift
The higher the altitude, the less dense the air. Drag created by lift is called INDUCED DRAG! Double the size of the wing, double the amount of lift.
The higher the velocity and airspeed of the aircraft the higher airflow over the wing, therefore the higher the lift being produced. Velocity affects the total aerodynamic force, both lift and parasite drag increase with an increase of the velocity of the airflow over the wing. Interestingly, in relation to lift and drag forces, if we double the velocity of the airflow we quadruple the lift and parasite drag being produced. Velocity Changing the flap setting effectively changes the camber and shape of the wing. More flap creates more lift and also creates more drag. Flap setting Drag is the force that acts in the opposite direction of thrust. Drag is caused by friction of a solid object against the airflow, differences in air pressure, and the creation of lift. Drag As we increase the camber of a wing the lift will increase and so will the drag. Whenever lift increases so does the induced drag. Shape Even slight damage to a wing and the propeller can create changes to the lift and drag for the aerofoil and affect the performance. For instance, if a wing hits a bird and part of the wing has been damaged, this can disturb the airflow over the wing and decrease the total lift. Slight damage to the propeller can have serious implications. Even a small stone chip can cause structural cracks that could lead to vibrations and eventually total blade failure, so this is why a good inspection of the propeller is vital before every flight. Damage Ch.2 - How an aircraft generates lift
Airflow over the wing creates lift and drag called the total aerodynamic force. More flap creates more lift and more drag. Whenever lift increases so does induced drag.
Parasite drag is caused by the aircraft itself and its components being exposed to the relative airflow. We can break parasite drag down even further. (1 Form Drag is drag due to the shape of the aircraft1 $1 Interference Drag is created when different types of surfaces meet or join such as where the wing meets the aircraft fuselage1 1 Skin Friction Drag is due to the smoothness or roughness of the aircraft’s skin. Parasite drag Induced drag is drag caused by the lift being produced by the wing. Induced drag Drag acts rearward in the opposite direction of the aircraft and in the same direction as the relative airflow. The total drag force on the aircraft changes depending on weight, aircraft configuration, airspeed, temperature and pressure. Drag opposes thrust Total drag is a mixture of both induced and parasite drag. Induced drag reduces as speed increases and parasite drag increases as speed increases. Total drag versus airspeed In level flight there is a small relationship between attitude and angle attack. Most small training aircraft do not have an angle of attack indicator. In level flight at normal operating speeds the attitude is closely related to the angle of attack. Relationship between attitude and angle of attack Ch.2 - How an aircraft generates lift
Parasite Drag is caused by the aircraft and its components being exposed to the relative airflow. Induced drag reduces with airspeed and parasite drag increases with airspeed. Induced drag is a direct result of lift being produced by the wing.
Ch.2 - How an aircraft generates lift The attitude is also closely related to the aircraft airspeed. Let's look at what happens when an aircraft slows down in level flight. We know that lift is a factor of velocity, so as the aircraft slows down, the lift starts to reduce. If nothing changes the aircraft will start to descend. The only way for the aircraft to stay level is to create more lift by increasing the angle of attack. The pilot controls the angle of attack by altering the aircraft’s attitude by pitching the nose up or down with elevator control. An aircraft wing stalls when its angle of attack exceeds the critical angle. In most training aircraft this is about 16 degrees angle of attack. Now we will look in detail at the forces that act on the wing as it approaches the stall. Let's assume the aircraft is slowing down and trying to maintain level flight. As the relative airflow starts decreasing so too the lift decreases. To maintain level flight, the angle of attack will need to be increased. On top of the wing we have the centre of pressure. The centre of pressure is the average point where all the different pressure forces are applied on the wing. As the wing's angle of attack starts to increase, so does the lift and drag, and the centre of pressure starts to move forward. While the wing is still producing lift the airflow remains ‘laminar’, which means the airflow flows smoothly over the wing. As the wing approaches the critical angle of attack the airflow starts to become turbulent towards the back of the wing. The part of the wing where the laminar airflow starts to separate and become turbulent, is called the ‘separation point’. Angle of attack and stalling
An aircraft's wing stalls when its angle of attack exceeds the critical angle. The aircraft will stall at any airspeed if it exceeds its critical angle of attack. Lift increases right up to the critical angle.
Ch.2 - How an aircraft generates lift This effectively means lift is reduced from the back of the wing first, and both the separation point and centre of pressure move forward as the wing reaches its critical angle of attack, which is normally around 16 degrees. As the angle of attack reaches the critical angle the separation point and centre of pressure move drastically forward, at this point the air becomes very turbulent on top of the wing. The airflow under the wing is generally still laminar. At the critical angle of attack there is a huge increase in turbulent air, and a large loss of lift. At this point the force of weight will be more than lift, and the aircraft will descend. The wing is producing the most amount of lift just prior to the critical angle of attack (16 degrees angle of attack). It is important to note that an aircraft can stall at any airspeed. The stall is caused by the aircraft exceeding the critical angle of attack. In relation to stalling, as an aerofoil increases its angle of attack the lift increases and so does the induced drag. There is an angle of attack that represents the maximum lift for the least amount of drag for the aircraft. This maximum lift for the least amount of drag is known as ‘best lift to drag ratio’ and is used to determine the aircraft’s best glide ratio. We do not use angle of attack indicators in most light aircraft. The pilot operating handbook will advise on the aircraft’s best glide speed which is the best glide ratio. If this speed (and corresponding angle of attack) is maintained, the aircraft will fly the longest range with no engine power (in a glide). Any speed either side of this number will increase the total drag and reduce the aircraft range. Best lift to drag and glide speed
The centre of pressure is the resultant force point on the wing of where lift and drag acts. The maximum lift for the least amount of drag is known as the best lift to drag ratio. As the aircraft reaches the stall the center of pressure moves forward then at the stall it moves rearward rapidly!
A fixed wing aircraft is known as a ‘three axis’ aircraft. A three axis aircraft in flight is able to rotate in three different dimensions or axes: yaw (when the nose moves left or right about an axis running up and down); pitch (when the nose moves up or down about an axis running from wing to wing); and roll (when the aircraft rotates about an axis running from nose to tail). These axes are also known as the lateral axis, longitudinal axis and the normal (or vertical) axis. The aircraft yaws around the vertical axis, pitches around the lateral axis, and rolls around the longitudinal axis. Aircraft axes The elevator controls pitch, the ailerons control roll, and the rudder controls yaw. We also have ‘secondary’ or ‘support’ control surfaces; these are the flaps and the trim tab. Flaps are a lift-generating device attached to the wing. Trim tabs can be attached to the ailerons, rudder and elevator. The trim reduces the control column pressure for the pilot. The elevator and ailerons are controlled with our control column (or control stick) and the rudder is controlled by our rudder pedals Flaps are normally controlled with an electric flap switch or manual lever, while trim is controlled by an electric switch or manual control wheel (depending on aircraft type). Control surfaces Stability and Control Chapter 3 Planes of movement: pitch, roll and yaw
The aircraft yaws around the vertical axis, pitches around the lateral axis, and rolls around the longitudinal axis. Flaps are normally controlled with an electric flap switch or manual lever, while trim is controlled by an electric switch or manual control wheel. The elevator controls pitch, the ailerons control roll, and the rudder controls yaw.
The centre of gravity is affected by the weight distribution of the aircraft. The pilot, the fuel, the number of passengers and baggage all affect the position of the centre of gravity position. This change in weight can affect both the longitudinal and lateral stability of the aircraft. Centre of gravity The centre of pressure is the point where the total sum of all the pressure fields act on the aircraft wing. The centre of pressure moves and is dependent on the amount of lift being produced from the wing. The centre of pressure does affect the aircraft lateral stability. The most obvious effect is at the critical angle when the aircraft stalls. Most light training aircraft have been designed so the centre of gravity is located in front of the centre of pressure - for added lateral stability. When an aircraft stalls, because the centre of gravity is in front of the centre of pressure, the nose will pitch down due to the weight being forward of the centre of pressure. With enough height, in most instances the aircraft will recover itself. Too much weight distributed on one side of the aircraft can affect the longitudinal stability of an aircraft. For example if the right-hand fuel tank is full and the left-hand wing tank is empty, this can cause the aircraft to become unstable in roll. Likewise, too much weight placed in the back of the aircraft may make the aircraft unstable in the lateral axis in pitch. The vertical axis can also be affected by the centre of gravity or pressure. Centre of pressure Effect on planes of movement Ch.3 - Stability and Control
The centre of gravity is affected by the weight distribution of the Aircraft. When an aircraft stalls, because the centre of gravity is located in front of the centre of pressure, the nose will pitch down due to the weight being forward of the centre of pressure The Centre of pressure is the point where the total sum of all the pressure fields act on the aircraft wing.
Recreational Aviation Australia also has an online form for lodging incident reports at www.raa.asn.au
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