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Questions and Answers
What happens to the location of the aerodynamic centre as the angle of attack changes?
What happens to the location of the aerodynamic centre as the angle of attack changes?
In a positively cambered aerofoil section, what occurs to the centre of pressure as the angle of attack approaches the critical angle?
In a positively cambered aerofoil section, what occurs to the centre of pressure as the angle of attack approaches the critical angle?
Which statement correctly describes the relationship between speed and the centre of pressure during straight and level flight?
Which statement correctly describes the relationship between speed and the centre of pressure during straight and level flight?
What is the significance of the stagnation point on an aerofoil's profile?
What is the significance of the stagnation point on an aerofoil's profile?
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When the angle of attack increases, how does the centre of pressure respond?
When the angle of attack increases, how does the centre of pressure respond?
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What does the term 'aerodynamic centre' refer to in relation to the pitching moment?
What does the term 'aerodynamic centre' refer to in relation to the pitching moment?
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Which statement is true regarding the speed of airflow over the aerofoil's surface?
Which statement is true regarding the speed of airflow over the aerofoil's surface?
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What happens to the magnitude of total lift force when speed increases while maintaining level flight?
What happens to the magnitude of total lift force when speed increases while maintaining level flight?
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What effect does increasing the wing area have on lift?
What effect does increasing the wing area have on lift?
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What happens to the static pressure and velocity as streamlines converge?
What happens to the static pressure and velocity as streamlines converge?
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Which body among B, C, A, and D has the lowest form drag?
Which body among B, C, A, and D has the lowest form drag?
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If the drag coefficient (CD) and velocity are constant, what is the impact of increasing air density (ρ) on the drag force?
If the drag coefficient (CD) and velocity are constant, what is the impact of increasing air density (ρ) on the drag force?
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At a given angle of attack, how does the lift/drag ratio change with varying air density?
At a given angle of attack, how does the lift/drag ratio change with varying air density?
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In terms of normal operating conditions for conventional airplanes, how does the lift coefficient (CL) compare to the drag coefficient (CD)?
In terms of normal operating conditions for conventional airplanes, how does the lift coefficient (CL) compare to the drag coefficient (CD)?
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If the frontal area of a body in the airstream is increased by a factor of 3, what is the impact on form drag?
If the frontal area of a body in the airstream is increased by a factor of 3, what is the impact on form drag?
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What is the relationship between lift and drag for a given angle of attack if air density changes?
What is the relationship between lift and drag for a given angle of attack if air density changes?
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What does the thickness to chord ratio of an aerofoil represent?
What does the thickness to chord ratio of an aerofoil represent?
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How is camber of an aerofoil defined?
How is camber of an aerofoil defined?
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Which of the following statements regarding true airspeed (TAS) is correct?
Which of the following statements regarding true airspeed (TAS) is correct?
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What is the significance of the mean aerodynamic chord in aircraft design?
What is the significance of the mean aerodynamic chord in aircraft design?
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In the context of aerofoil design, which term refers to the angle formed between the chord line and the relative wind?
In the context of aerofoil design, which term refers to the angle formed between the chord line and the relative wind?
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Which statement accurately differentiates between indicated airspeed (IAS) and calibrated airspeed (CAS)?
Which statement accurately differentiates between indicated airspeed (IAS) and calibrated airspeed (CAS)?
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What does a higher aspect ratio in an aerofoil generally imply?
What does a higher aspect ratio in an aerofoil generally imply?
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Which aerofoil characteristic is directly impacted by the taper ratio?
Which aerofoil characteristic is directly impacted by the taper ratio?
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Study Notes
Subsonic Aerodynamics - Basics
- Mass Conservation: Mass remains constant over time; it cannot be created or destroyed, only rearranged in space.
- Bernoulli's Theorem: In streamlined fluid flow, the sum of all energies (static and dynamic pressure) is constant. Static pressure + dynamic pressure = constant.
- Total Pressure Constant: Dynamic pressure (1/2ρV²) + Static pressure = constant.
- Bernoulli's Equation: PT = PS + 1/2ρV² (Total pressure = Static pressure + Dynamic pressure)
- Dynamic Pressure: Is equal to 1/2 ρV². It's zero when velocity is zero. It increases proportionally with the square of velocity.
- Static Pressure and Density: If temperature is constant and pressure increases, density increases. If density is constant, dynamic pressure increases with velocity squared.
- Venturi Effect: Static pressure in a venturi throat is lower than in undisturbed airflow, while dynamic pressure is higher. Total pressure remains the same.
- Incompressible Flow: Density does not change.
- Temperature and Humidity: Density of the atmosphere decreases with an increase in humidity
Aerodynamic Center and Centre of Pressure
- Aerodynamic center: The point where the pitching moment coefficient doesn't change with varying angles of attack. Located at approximately 25% chord.
- Centre of Pressure (CP): The point where the single resultant aerodynamic force on the airfoil acts. Its position varies with the angle of attack.
Wing Loading and Forces
- Wing Loading: Ratio of aircraft weight to wing area (W/S).
- Drag: Acts in the direction of relative wind (airflow).
- Lift: Perpendicular to relative wind (airflow).
- Angle of Attack: Angle between wing chord line and direction of relative airflow.
- Angle of Incidence: Angle between wing chord line and relative undisturbed airflow.
Lift and Drag Coefficients (CL and CD)
- CL vs AoA (Angle of Attack): CL is max at critical AoA and decreases after that point (stalling angle)
- CD vs AoA: CD is lower at lower AoA, generally decreasing gradually up to stall.
- Lift related to velocity: Lift is proportional to the square of velocity (V^2) and air density (1/2ρV²)
- Aerodynamic Center location: Is at 25% chord location.
Aerodynamic Concepts:
- Aspect Ratio: wingspan / mean chord
- Taper Ratio: ratio of tip chord to root chord
- Sweep Angle: Angle between the quarter-chord line and the lateral axis.
- Thickness to Chord Ratio: Ratio of maximum thickness to chord length of an airfoil section.
- Camber: The difference between the upper and lower surfaces' curves of an airfoil.
- Mean Camber Line: Line midway between upper and lower surfaces.
Aerodynamic Coefficients
- CL: Lift Coefficient (lift/qS)
- CD: Drag Coefficient (drag/qS)
- CL/CD Max: Optimum lift-to-drag ratio important for aircraft performance, efficiency and stability.
Subsonic and Supersonic Flow
- Mach number (M): Ratio of the speed of an object to the local speed of sound (TAS / local speed of sound)
- Transonic Range: Speeds just above and below the speed of sound.
- Critical Mach Number (M_crit): The Mach number at which the airflow over a part of the aircraft reaches sonic speed.
- Drag Divergence Mach Number (M_drag): The Mach number where the drag starts to increase rapidly.
Three-Dimensional Flow
- Induced Drag: Drag caused by the downwash of air from the wings. It is proportional to (CL^2 / AR).
- Aspect ration: Increasing aspect ratio decreases induced drag, because of the effect of tip vortices. Higher aspect ratios = high lift and low drag, as in an eliptical shaped wing compared to a rectangular one. Generally increasing aspect ration is beneficial for the aero plane's efficiency.
Stall Angle of Attack
- Stall: The speed and/or angle of attack at which an aeroplane is no longer able to generate enough lift to maintain its altitude
- Critical AoA: The minimum angle needed to cause a stall.
- Effect of Wing Shape: A wing shape can be more effective to increase the critical/stall angle of attack by using flaps, slats, spoiler and winglets.
Control Surface Deflections (+ or -)
- Aerodynamic Forces: Vary with respect to the speed, and angle of attack, of the moving air.
- Adverse Yaw: A yawing moment that acts in opposite direction to the turn, it requires differential ailerons to counteract the moment.
Engine and Propeller Considerations
- Static Stability: The tendency of an aircraft to return to its original trim condition after a disturbance. (e.g., a gust).
- Dynamic Stability: The aeroplanes response to a disturbance over time. (e.g. a gust)
- Inertia: An important effect of engine location regarding propeller gyroscopic effect, and sensitivity to Dutch roll and yaw.
- Propeller efficiency effects propeller twisting from the root to the tips, blade pitch, and blade radius.
Summary of High and Low Speed Flight
- High Speed: Primarily concerned with supersonic airflow and the formation of shock waves, leading to drag increase and potentially stability loss (exceeding critical conditions).
- Low Speed: Primarily concerned with angle of attack and stalling, control surfaces, adverse yaw, and potential stability issues when using flaps or at stall speed.
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Description
This quiz covers fundamental concepts in subsonic aerodynamics, including mass conservation, Bernoulli's theorem, and the Venturi effect. It explains how dynamic and static pressures interact in fluid flow. Test your understanding of these essential principles in aerodynamics.
