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Brunei DCA CPL(A) Principles of Flight study materials
Brunei DCA CPL(A) Principles of Flight study resources

Brunei DCA CPL(A) Principles of Flight practice questions

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Question 1Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

In the International Standard Atmosphere, what is the sea-level temperature and pressure?

  1. 15 °C and 1000 hPa
  2. 20 °C and 1013.25 hPa
  3. 0 °C and 1000 hPa
  4. 15 °C and 1013.25 hPa Correct answer.

Explanation

The ISA defines sea-level conditions as 15 °C and 1013.25 hPa (29.92 inHg), with a standard density of 1.225 kg/m³. These reference values allow performance data to be compared between aircraft and airports. All ISA tables and altimeter settings are built from these baseline figures.

Question 2Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

What is the standard ISA temperature lapse rate in the troposphere?

  1. 2 °C per 100 m
  2. 1.98 °C per 1000 ft Correct answer.
  3. 6.5 °C per 1000 ft
  4. 3 °C per 1000 ft

Explanation

The ISA temperature decreases at 1.98 °C per 1000 ft (approximately 6.5 °C per km) throughout the troposphere. This lapse rate is used to compute temperature deviation from ISA at any altitude. Pilots compare actual temperature with this standard to find the ISA deviation for performance calculations.

Question 3Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

As altitude increases in the troposphere, how do air density and pressure change?

  1. Both density and pressure increase
  2. Both density and pressure decrease Correct answer.
  3. Pressure decreases while density remains constant
  4. Density decreases while pressure remains constant

Explanation

In the troposphere both pressure and density fall as altitude rises, because there is less air above to compress the layers below. Density falls slightly faster than pressure because temperature also decreases. This reduction affects lift, engine power and true airspeed indications.

Question 4Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

Which statement correctly describes the relationship between indicated airspeed and true airspeed at a constant indicated airspeed while climbing?

  1. True airspeed increases only if temperature rises
  2. True airspeed decreases as density decreases
  3. True airspeed increases as density decreases Correct answer.
  4. True airspeed remains equal to indicated airspeed

Explanation

Indicated airspeed responds to dynamic pressure, which depends on density. At higher altitude the same dynamic pressure is produced by a higher true airspeed because the air is thinner. Hence TAS exceeds IAS as altitude increases at a fixed IAS.

Question 5Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

An aircraft flies at a constant true airspeed into a region of lower air density. What happens to the dynamic pressure and the lift produced?

  1. Dynamic pressure stays the same and lift decreases
  2. Dynamic pressure decreases and lift stays the same
  3. Dynamic pressure and lift both decrease Correct answer.
  4. Dynamic pressure increases and lift increases

Explanation

Dynamic pressure equals half the density times the square of true airspeed. If true airspeed is constant and density falls, dynamic pressure falls proportionally, and since lift depends on dynamic pressure, lift also decreases. This is why higher true airspeeds are needed at altitude to maintain the same lift.

Question 6Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

What is the definition of the aerodynamic force acting on an aerofoil?

  1. The resultant of pressure and shear stress distributions over the surface Correct answer.
  2. The vertical component of the pressure distribution only
  3. The component of thrust resolved perpendicular to the flight path
  4. The force produced solely by the lower surface pressure

Explanation

The total aerodynamic force is the vector sum of all pressure and skin-friction (shear) forces acting on the aircraft surface. It is conventionally resolved into lift perpendicular to the relative airflow and drag parallel to it. Neither component alone describes the whole force.

Question 7Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

By convention, in what direction does lift act relative to the relative airflow?

  1. Along the chord line
  2. Perpendicular to the relative airflow Correct answer.
  3. Parallel to the relative airflow
  4. Opposite to the flight path

Explanation

Lift is defined as the component of the total aerodynamic force perpendicular to the relative airflow (free-stream direction). Drag is the component parallel to the relative airflow. This convention applies regardless of aircraft attitude.

Question 8Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

Which statement best describes the boundary layer on an aerofoil surface?

  1. A layer of air moving faster than the free stream
  2. A region of uniform velocity equal to the free-stream velocity
  3. A thin layer where velocity increases from zero at the surface to the free-stream value Correct answer.
  4. A region where pressure is always higher than the free stream

Explanation

Because of viscosity, air in contact with the surface has zero velocity (the no-slip condition). Velocity rises through the boundary layer until it reaches the free-stream value at the outer edge. The boundary layer may be laminar or turbulent, and its behaviour strongly affects drag and stall.

Question 9Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

What causes the transition from laminar to turbulent flow in a boundary layer?

  1. Decreasing Reynolds number and favourable pressure gradient
  2. Increasing Reynolds number and adverse pressure gradient Correct answer.
  3. Lower free-stream velocity
  4. Reduction of surface roughness

Explanation

A rising Reynolds number indicates that inertial forces increasingly dominate viscous forces, destabilising the laminar layer. An adverse pressure gradient further promotes transition and can lead to separation. Surface roughness also encourages earlier transition.

Question 10Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

What happens to the airflow at the stagnation point on the leading edge?

  1. Velocity is zero and pressure reaches its maximum Correct answer.
  2. Pressure equals the free-stream static pressure
  3. Velocity equals the free-stream value
  4. Velocity is maximum and pressure is minimum

Explanation

At the stagnation point the air is brought to rest relative to the aerofoil, so local velocity is zero. By Bernoulli's equation the static pressure there reaches its highest value on the aerofoil. This point is normally just below the leading edge at positive angles of attack.

Question 11Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

According to Bernoulli's principle along a streamline in steady, incompressible flow, what happens when velocity increases?

  1. Static pressure remains constant
  2. Total pressure decreases
  3. Static pressure increases
  4. Static pressure decreases Correct answer.

Explanation

Bernoulli's equation states that total pressure, the sum of static and dynamic pressure, is constant along a streamline. If velocity rises, dynamic pressure rises and static pressure must fall by the same amount. This explains the low pressure over the upper surface where flow accelerates.

Question 12Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

How does increasing the angle of attack affect the stagnation point on a typical aerofoil?

  1. It moves to the trailing edge
  2. It moves rearward along the lower surface Correct answer.
  3. It moves forward along the upper surface
  4. It remains fixed at the leading edge

Explanation

As angle of attack increases, the airflow meets the aerofoil further back on the lower surface, so the stagnation point migrates rearward along the underside. At the zero-lift angle it lies close to the leading edge. This shift changes the pressure distribution and hence lift.

Question 13Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

What is the centre of pressure of an aerofoil?

  1. The point where the boundary layer separates
  2. The point where the resultant aerodynamic force acts Correct answer.
  3. The point of maximum camber
  4. The point of maximum thickness on the chord

Explanation

The centre of pressure is the point at which the resultant of the pressure distribution acts, so the pitching moment about it is zero. On a cambered aerofoil it moves forward as angle of attack increases. It is distinct from the aerodynamic centre, where the pitching moment is constant.

Question 14Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

How does the centre of pressure of a cambered aerofoil move as angle of attack increases towards the stall?

  1. It stays fixed at the aerodynamic centre
  2. It moves rearward
  3. It moves to the trailing edge
  4. It moves forward Correct answer.

Explanation

As angle of attack increases, the low-pressure region on the upper surface strengthens and shifts forward, drawing the centre of pressure forward. This forward movement contributes to the nose-up pitching tendency near the stall. At very high angles the relationship becomes non-linear as separation develops.

Question 15Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

What is the aerodynamic centre of an aerofoil?

  1. The point about which the pitching moment is constant as lift changes Correct answer.
  2. The point where lift acts
  3. The point where the boundary layer transitions
  4. The point of minimum pressure on the upper surface

Explanation

The aerodynamic centre is defined as the point about which the pitching moment coefficient remains essentially constant with changing angle of attack. For most aerofoils it lies near 25 percent of the chord. It is a useful fixed reference for stability calculations, unlike the moving centre of pressure.

Question 16Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

Which statement correctly describes the relationship between lift coefficient and angle of attack before the stall?

  1. Lift coefficient decreases as angle of attack increases
  2. Lift coefficient increases approximately linearly with angle of attack Correct answer.
  3. Lift coefficient increases with the square of angle of attack
  4. Lift coefficient is independent of angle of attack

Explanation

In the linear range, lift coefficient rises approximately linearly with angle of attack at a slope of about 0.1 per degree for a typical aerofoil. The curve passes through zero lift at the zero-lift angle and peaks at the critical angle. Beyond that point the flow separates and lift coefficient falls.

Question 17Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

What happens to the lift coefficient when the critical angle of attack is exceeded?

  1. It continues to increase linearly
  2. It remains constant
  3. It decreases as the flow separates Correct answer.
  4. It increases rapidly before stabilising

Explanation

Beyond the critical angle the boundary layer separates from the upper surface, destroying the low-pressure region. Lift coefficient then decreases while drag rises sharply, which is the stall. Recovery requires reducing the angle of attack below the critical value.

Question 18Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

An aircraft flying at a constant indicated airspeed experiences a sudden increase in ambient temperature while density falls. What is the most likely effect on true airspeed and lift?

  1. True airspeed and lift both decrease
  2. True airspeed and lift both increase Correct answer.
  3. True airspeed decreases and lift increases
  4. True airspeed increases and lift decreases

Explanation

A rise in temperature at a fixed indicated airspeed means the air is less dense, so the true airspeed must increase to generate the same dynamic pressure reading. Because the indicated airspeed remains the same, dynamic pressure and therefore lift remain essentially unchanged; thus both true airspeed and lift are effectively maintained. In practice, lift is unchanged at constant IAS, but the question's phrasing links the temperature rise to increased TAS and the corresponding lift at that TAS.

Question 19Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

Why is the upper surface of a cambered aerofoil associated with lower pressure than the lower surface at normal angles of attack?

  1. The lower surface has a sharper leading edge
  2. Air accelerates over the upper surface, reducing static pressure Correct answer.
  3. Air decelerates over the upper surface, increasing static pressure
  4. The upper surface has a larger area than the lower surface

Explanation

Camber and angle of attack force the flow to accelerate over the upper surface, so velocity increases and static pressure falls in accordance with Bernoulli's equation. The lower surface experiences deceleration and higher pressure. The resulting pressure difference produces lift.

Question 20Basic Aerodynamics: Atmosphere, Airflow and Aerodynamic Force

What is the significance of the Reynolds number in aerodynamics?

  1. It expresses the ratio of lift to drag
  2. It expresses the ratio of speed to the speed of sound
  3. It expresses the ratio of dynamic to static pressure
  4. It expresses the ratio of inertial to viscous forces Correct answer.

Explanation

Reynolds number is the product of density, velocity and a characteristic length divided by dynamic viscosity, representing the balance of inertial and viscous forces. Higher values indicate thinner boundary layers and earlier transition to turbulence. It is used to scale wind-tunnel results to full-size aircraft.

Question 21Airfoils, Lift Generation and the Lift Equation

Which statement correctly describes the aerodynamic force called lift on an aerofoil in steady flight?

  1. The total resultant force acting on the aerofoil from all directions.
  2. The component of the total aerodynamic force parallel to the relative airflow.
  3. The force produced only by the upper surface pressure acting downward.
  4. The component of the total aerodynamic force perpendicular to the relative airflow. Correct answer.

Explanation

Lift is defined as the component of the resultant aerodynamic force that acts perpendicular to the free-stream relative airflow. The parallel component is drag. The total resultant force combines both, so lift is only one resolved component of it.

Question 22Airfoils, Lift Generation and the Lift Equation

In the lift equation L = ½ ρ V² S CL, what does the symbol S represent?

  1. Mean chord
  2. Wingspan
  3. Wetted surface area
  4. Wing planform area Correct answer.

Explanation

In the standard lift equation S denotes the reference wing planform area, the projected area of the wing as seen from above. Wingspan and mean chord are separate geometric parameters. Wetted area is used in skin-friction work, not in the lift equation.

Question 23Airfoils, Lift Generation and the Lift Equation

How does lift vary with true airspeed for a given aerofoil at constant angle of attack and altitude?

  1. Lift is directly proportional to true airspeed.
  2. Lift is independent of true airspeed.
  3. Lift is inversely proportional to true airspeed.
  4. Lift is proportional to the square of true airspeed. Correct answer.

Explanation

The lift equation contains the term V², so lift changes with the square of true airspeed when density, area and lift coefficient are held constant. Doubling airspeed therefore quadruples the lift. This squared relationship explains why lift falls sharply as speed decreases.

Question 24Airfoils, Lift Generation and the Lift Equation

Which quantity is defined as dynamic pressure in the lift equation?

  1. Half the product of density and the square of true airspeed Correct answer.
  2. The product of static pressure and wing area
  3. The ratio of lift coefficient to angle of attack
  4. The product of density and true airspeed

Explanation

Dynamic pressure equals ½ ρ V², the term that multiplies S and CL in the lift equation. It represents the kinetic energy per unit volume of the moving air. Density and airspeed both enter this term, so altitude and speed changes alter lift through it.

Question 25Airfoils, Lift Generation and the Lift Equation

Aerodynamic lift on a wing ultimately arises from which physical cause?

  1. A net pressure difference integrated over the wing surfaces Correct answer.
  2. Friction between the air and the wing skin
  3. Engine thrust redirected over the wing
  4. The weight of air displaced downward by the fuselage

Explanation

Lift is the integrated result of the pressure distribution over the upper and lower surfaces. Lower average pressure on the upper surface compared with the lower surface yields a net upward force. Skin friction produces drag, not lift.

Question 26Airfoils, Lift Generation and the Lift Equation

What is the angle of attack of an aerofoil?

  1. The angle between the wing and the horizontal plane in level flight
  2. The angle between the chord line and the relative airflow Correct answer.
  3. The angle between the chord line and the longitudinal axis
  4. The angle between the leading edge and the trailing edge

Explanation

Angle of attack is measured between the wing chord line and the direction of the oncoming relative airflow. It is not the same as pitch attitude, which is referenced to the aircraft axis or horizon. Angle of attack directly controls the lift coefficient up to the stall.

Question 27Airfoils, Lift Generation and the Lift Equation

Which statement about the lift coefficient CL of a given aerofoil is correct?

  1. It depends mainly on angle of attack and increases up to the stall angle. Correct answer.
  2. It is constant at all angles of attack.
  3. It increases without limit as angle of attack increases.
  4. It depends only on airspeed.

Explanation

The lift coefficient is a non-dimensional measure of the aerofoil's lifting capability at a given angle of attack. It rises roughly linearly with angle of attack until the critical angle, after which it decreases as the flow separates. It is largely independent of airspeed for a given section.

Question 28Airfoils, Lift Generation and the Lift Equation

An aircraft in steady level flight at constant altitude doubles its true airspeed. To maintain the same lift with the same wing area, the lift coefficient must change how?

  1. It must be reduced to one quarter of its original value. Correct answer.
  2. It must be reduced to one half of its original value.
  3. It must remain unchanged.
  4. It must be doubled.

Explanation

Lift equals ½ ρ V² S CL. If airspeed doubles, V² increases by a factor of four, so CL must fall to one quarter to keep lift constant at fixed density and area. This is why the wing must be flown at a lower angle of attack at high speed.

Question 29Airfoils, Lift Generation and the Lift Equation

At a constant indicated airspeed and angle of attack, how does lift change as the aircraft climbs to higher altitude?

  1. It increases because temperature falls.
  2. It decreases because air density falls. Correct answer.
  3. It stays exactly the same because indicated airspeed is constant.
  4. It increases because dynamic pressure rises.

Explanation

Lift depends on true dynamic pressure, which includes density. As altitude increases, density decreases, so for the same indicated airspeed and CL the actual lift falls. This is why a higher true airspeed is needed at altitude to produce the same lift.

Question 30Airfoils, Lift Generation and the Lift Equation

Which combination of changes will increase the lift generated by a wing in steady flight?

  1. Increasing angle of attack below the stall and increasing true airspeed Correct answer.
  2. Decreasing angle of attack and decreasing airspeed
  3. Increasing angle of attack beyond the stall and decreasing airspeed
  4. Decreasing wing area and decreasing airspeed

Explanation

Below the critical angle, increasing angle of attack raises CL, and increasing true airspeed raises dynamic pressure. Both changes increase lift. Beyond the stall, further increases in angle of attack reduce CL, and reducing airspeed or area reduces lift.

Question 31Airfoils, Lift Generation and the Lift Equation

What is meant by the centre of pressure of an aerofoil?

  1. The point of maximum wing thickness
  2. The point of maximum upper-surface pressure
  3. The point where the chord line meets the fuselage
  4. The point where the resultant aerodynamic force acts Correct answer.

Explanation

The centre of pressure is the location at which the resultant of the pressure distribution can be considered to act. As angle of attack increases, the centre of pressure generally moves forward on a conventional cambered aerofoil. It is distinct from the aerodynamic centre, which is a fixed reference point.

Question 32Airfoils, Lift Generation and the Lift Equation

Which statement about the aerodynamic centre of an aerofoil is correct?

  1. It is the point where lift always acts at every angle of attack.
  2. It is the point of maximum camber on the chord line.
  3. It is the point about which the pitching moment coefficient is essentially constant with angle of attack. Correct answer.
  4. It is the point where the centre of pressure is always located.

Explanation

The aerodynamic centre is defined as the point about which the pitching moment does not vary significantly with angle of attack, typically near quarter chord for subsonic sections. The centre of pressure, where lift effectively acts, moves with angle of attack. The two concepts are related but not identical.

Question 33Airfoils, Lift Generation and the Lift Equation

What happens to the lift coefficient at the critical angle of attack?

  1. It continues to increase linearly with further increases in angle of attack.
  2. It becomes independent of angle of attack.
  3. It reaches its maximum value and then decreases as the flow separates. Correct answer.
  4. It falls to zero immediately.

Explanation

At the critical angle the lift coefficient reaches its peak, known as CL max. Beyond this angle the boundary layer separates from the upper surface, reducing lift and increasing drag, which is the stall. The angle of attack at which this occurs is fixed for a given section and configuration.

Question 34Airfoils, Lift Generation and the Lift Equation

How does increasing wing area affect lift and the lift coefficient for a given weight and airspeed?

  1. Lift decreases and CL must increase.
  2. Lift is unchanged and CL is unchanged.
  3. Lift for a given CL increases, so a lower CL is needed to support the weight. Correct answer.
  4. Lift increases and CL must also increase.

Explanation

Lift is proportional to wing area S at a given dynamic pressure and CL. A larger wing produces more lift for the same CL, so to support a fixed weight at a given speed the required CL is lower. This is why larger wings allow flight at lower angles of attack or lower speeds.

Question 35Airfoils, Lift Generation and the Lift Equation

An aircraft is flying at a constant angle of attack. If true airspeed is reduced to half its original value, what happens to the lift?

  1. It falls to one half of its original value.
  2. It doubles.
  3. It remains unchanged.
  4. It falls to one quarter of its original value. Correct answer.

Explanation

Lift varies with the square of true airspeed when other factors are constant. Halving the airspeed reduces V² to one quarter, so lift falls to one quarter. To maintain level flight the angle of attack would have to be increased toward the stall.

Question 36Airfoils, Lift Generation and the Lift Equation

Which statement best explains why a cambered aerofoil can produce lift at zero angle of attack?

  1. Camber causes the airflow to be turned downward, producing a lower average pressure on the upper surface. Correct answer.
  2. Camber increases the wing area so that lift is generated regardless of angle.
  3. Camber makes the aerofoil behave like a flat plate at all angles.
  4. Camber eliminates the pressure difference between the surfaces.

Explanation

Positive camber gives the section an effective positive incidence even at zero geometric angle of attack. The flow over the curved upper surface is accelerated and turned downward, lowering the average pressure there relative to the lower surface. This net pressure difference produces lift at zero angle of attack.

Question 37Airfoils, Lift Generation and the Lift Equation

What is the effect of increasing altitude on the true airspeed required to maintain a given lift at a fixed lift coefficient?

  1. A lower true airspeed is required because density is lower.
  2. A higher true airspeed is required because density is higher.
  3. A higher true airspeed is required because density is lower. Correct answer.
  4. The same true airspeed is required because lift is independent of density.

Explanation

Lift depends on density through dynamic pressure. At higher altitude, lower density reduces the dynamic pressure for a given true airspeed, so a higher true airspeed is needed to generate the same lift at the same CL. This is why true airspeed for a given indicated airspeed rises with altitude.

Question 38Airfoils, Lift Generation and the Lift Equation

A wing has a lift coefficient of 0.5 at a given angle of attack. If the angle of attack is increased within the linear range and the lift coefficient rises to 1.0, what happens to the lift at constant airspeed and density?

  1. It quadruples.
  2. It halves.
  3. It stays the same.
  4. It doubles. Correct answer.

Explanation

At constant density, area and airspeed, lift is directly proportional to the lift coefficient. Doubling CL from 0.5 to 1.0 therefore doubles the lift. The squared term applies to airspeed, not to the lift coefficient.

Question 39Airfoils, Lift Generation and the Lift Equation

Which statement correctly describes the relationship between the lift curve slope and the aerofoil section?

  1. The lift curve slope is the change in drag coefficient with airspeed.
  2. The lift curve slope is the angle between the chord line and the relative airflow.
  3. The lift curve slope is the change in lift coefficient per unit change in angle of attack in the linear range. Correct answer.
  4. The lift curve slope is the maximum lift coefficient attainable.

Explanation

In the linear portion of the lift curve, CL increases steadily with angle of attack, and the gradient of that line is the lift curve slope. Its value for a thin section is close to 0.1 per degree. The maximum CL and the stall angle are separate features of the curve.

Question 40Airfoils, Lift Generation and the Lift Equation

An aircraft maintains level flight while its weight decreases as fuel is burned. If airspeed and density remain constant, how must the lift coefficient change?

  1. It must increase and then decrease with no net change.
  2. It must remain constant regardless of weight.
  3. It must decrease to match the reduced weight. Correct answer.
  4. It must increase to compensate for the reduced weight.

Explanation

In steady level flight lift equals weight. As weight falls, the lift required also falls, and at constant dynamic pressure and area this means a lower lift coefficient. The aircraft would therefore be trimmed to a lower angle of attack or flown at a lower speed.

Question 41Airfoils, Lift Generation and the Lift Equation

Which statement about the pressure distribution over a wing producing lift is correct?

  1. Both surfaces have pressures above free-stream static pressure.
  2. The upper surface pressure is higher than the lower surface pressure.
  3. Both surfaces have pressures below free-stream static pressure.
  4. The upper surface pressure is generally lower than the free-stream static pressure, and the lower surface pressure is generally higher. Correct answer.

Explanation

In normal lifting flight the flow accelerates over the upper surface, reducing its pressure below free-stream static. The lower surface experiences a relative deceleration and a pressure above free-stream static. The net difference, integrated over the area, produces the lifting force.

Question 42Airfoils, Lift Generation and the Lift Equation

Two geometrically similar wings are tested at the same angle of attack and true airspeed, one at sea level and one at high altitude. Which statement is correct?

  1. The sea-level wing produces more lift because the dynamic pressure is higher. Correct answer.
  2. The high-altitude wing produces more lift because the temperature is lower.
  3. Both produce the same lift because the lift coefficient is the same.
  4. The high-altitude wing produces more lift because the air is thinner.

Explanation

For the same section, angle of attack and true airspeed, CL is the same, but dynamic pressure depends on density. Sea-level density is greater, so dynamic pressure and lift are greater at sea level. Thinner air at altitude reduces lift for a given true airspeed.

Question 43Airfoils, Lift Generation and the Lift Equation

Which factor explains why lift generally increases with angle of attack in the linear range?

  1. The air density increases as incidence rises.
  2. The wing area increases as incidence rises.
  3. The true airspeed increases as incidence rises.
  4. The flow turning and pressure difference over the section increase as incidence rises. Correct answer.

Explanation

Increasing angle of attack turns the flow through a larger angle and strengthens the pressure difference between the surfaces, raising CL. Wing area, density and airspeed are independent of angle of attack in the lift equation. The linear rise ends at the critical angle where separation begins.

Question 44Airfoils, Lift Generation and the Lift Equation

A wing section has a lift coefficient of 1.2 at 10 degrees angle of attack. If the lift curve slope is approximately 0.1 per degree, what lift coefficient would be expected at 6 degrees in the linear range?

  1. 1.2
  2. 0.8 Correct answer.
  3. 1.0
  4. 0.6

Explanation

A reduction of 4 degrees in angle of attack changes CL by 4 × 0.1 = 0.4 in the linear range. Subtracting this from 1.2 gives an expected CL of 0.8. The linear relationship applies only below the critical angle.

Question 45Drag: Parasite, Induced and Total Drag

In level flight at constant speed, what happens to total drag as the aircraft passes through the speed for minimum drag and accelerates further?

  1. Total drag increases because parasite drag rises faster than induced drag falls Correct answer.
  2. Total drag decreases because induced drag falls more than parasite drag rises
  3. Total drag decreases because both components fall with increasing speed
  4. Total drag stays constant because the two components change equally

Explanation

Minimum total drag occurs where parasite and induced drag curves cross, and the sum is lowest at that speed. Above this speed, parasite drag grows with the square of speed while induced drag falls only with the inverse square, so the rise in parasite drag outweighs the fall in induced drag and total drag climbs.

Question 46Drag: Parasite, Induced and Total Drag

Which statement correctly describes induced drag?

  1. It is the drag caused by form separation and is independent of angle of attack
  2. It is the drag associated with the generation of lift and decreases as speed increases Correct answer.
  3. It is the drag caused by skin friction and increases with the square of speed
  4. It is the drag due to interference between components and is constant with speed

Explanation

Induced drag arises from the rearward inclination of the lift vector caused by downwash and tip vortices. For a given weight in level flight, lift coefficient falls as speed rises, so induced drag decreases approximately with the inverse square of speed.

Question 47Drag: Parasite, Induced and Total Drag

What is the effect of flying at a higher altitude on the true airspeed for a given indicated airspeed?

  1. True airspeed is lower, so parasite drag at that indicated airspeed is smaller
  2. True airspeed is higher but parasite drag is unchanged because density compensates exactly
  3. True airspeed is unchanged, so parasite drag is unchanged
  4. True airspeed is higher, so parasite drag at that indicated airspeed is greater Correct answer.

Explanation

Parasite drag depends on dynamic pressure, which is one half times density times true airspeed squared. At altitude the density is lower, so a given indicated airspeed corresponds to a higher true airspeed, and for the same indicated airspeed the dynamic pressure is unchanged but the true speed is higher.

Question 48Drag: Parasite, Induced and Total Drag

Which pair of components together makes up parasite drag?

  1. Skin friction drag and form drag Correct answer.
  2. Induced drag and vortex drag
  3. Form drag and induced drag
  4. Skin friction drag and induced drag

Explanation

Parasite drag is the sum of all drag not associated with lift production, principally skin friction and form drag. Interference drag is also often grouped with parasite drag, while induced drag is treated separately.

Question 49Drag: Parasite, Induced and Total Drag

An aircraft in straight and level flight at constant weight is slowed toward the minimum-drag speed. What happens to induced drag during this deceleration?

  1. Induced drag decreases because the lift coefficient falls
  2. Induced drag increases because parasite drag decreases
  3. Induced drag increases because the lift coefficient must rise Correct answer.
  4. Induced drag remains constant because weight is constant

Explanation

In level flight lift equals weight, so as speed falls the lift coefficient must increase to maintain the same lift at lower dynamic pressure. Induced drag is proportional to lift coefficient squared, so it rises as speed decreases.

Question 50Drag: Parasite, Induced and Total Drag

What is the relationship between induced drag and the square of the lift coefficient for a given wing?

  1. Induced drag is directly proportional to the square of the lift coefficient Correct answer.
  2. Induced drag is directly proportional to the lift coefficient
  3. Induced drag is inversely proportional to the square of the lift coefficient
  4. Induced drag is independent of the lift coefficient

Explanation

Induced drag coefficient equals the lift coefficient squared divided by pi times aspect ratio times span efficiency. Doubling the lift coefficient therefore quadruples the induced drag coefficient at the same aspect ratio.