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CAA NZ CPL Aircraft Technical Knowledge study materials
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CAA NZ CPL Aircraft Technical Knowledge practice questions

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Question 1Basic aerodynamics and flight controls

For a wing at constant weight in straight and level flight, how does induced drag change as airspeed increases?

  1. It increases in proportion to the square of the airspeed
  2. It increases linearly as airspeed increases
  3. It remains constant as airspeed increases in level flight
  4. It is inversely proportional to the square of the airspeed Correct answer.

Explanation

For a given weight in level flight, lift is constant, so induced drag is proportional to 1/V squared. As speed rises, the wing meets the same lift requirement with a smaller angle of attack and a weaker wingtip vortex system. Parasite drag, by contrast, rises with V squared, and total drag is minimum where the two are equal.

Question 2Basic aerodynamics and flight controls

A light aeroplane stalls when:

  1. the wing exceeds its critical angle of attack Correct answer.
  2. the engine is throttled to idle in a glide
  3. the airspeed falls below the published stall speed for the current weight
  4. the elevator reaches its full upward deflection

Explanation

A stall is an aerodynamic phenomenon defined by the critical angle of attack, not by a particular airspeed. Any combination of weight, load factor and speed that pushes the wing past that angle will stall it, and the published stall speed applies only to stated conditions such as maximum weight and 1g.

Question 3Basic aerodynamics and flight controls

In a level turn at 60° bank, the load factor is approximately:

  1. 2.0 Correct answer.
  2. 2.5
  3. 1.41
  4. 1.15

Explanation

In a level turn the load factor is n = 1/cos(bank angle). At 60° bank, cos 60° = 0.5, so n = 2.0, meaning the wings must produce twice the aeroplane's weight in lift.

Question 4Basic aerodynamics and flight controls

During a roll to the left, the aeroplane yaws to the right. Which control input best corrects this adverse yaw?

  1. Apply opposite aileron to stop the roll
  2. Apply back pressure to increase the angle of attack
  3. Apply left rudder to coordinate the roll Correct answer.
  4. Apply right rudder to oppose the yaw

Explanation

Adverse yaw occurs because the down-going aileron increases camber and induced drag on that wing, pulling the nose toward the rising wing. In a left roll the right aileron is down, so the nose yaws right and left rudder is needed to coordinate. Using opposite aileron would fight the intended roll rather than correct yaw.

Question 5Basic aerodynamics and flight controls

What is the main purpose of positive wing dihedral?

  1. To increase the critical angle of attack at high speed
  2. To give lateral stability by rolling away from a sideslip Correct answer.
  3. To improve longitudinal stability during a climb
  4. To reduce induced drag when the wing is at high lift

Explanation

Positive dihedral means the wings are angled upward from root to tip. In a sideslip, the lower wing meets the relative airflow at a higher angle of attack than the upper wing, so it produces more lift and rolls the aircraft away from the slip. This provides lateral static stability.

Question 6Basic aerodynamics and flight controls

Moving the centre of gravity forward within the approved range will generally:

  1. decrease longitudinal static stability and decrease the stall speed
  2. decrease longitudinal static stability and increase the stall speed
  3. increase longitudinal static stability with no change in stall speed
  4. increase longitudinal static stability and increase the stall speed Correct answer.

Explanation

A forward CG increases the nose-down moment, so the tailplane must produce more downforce and the wing must carry more load. This increases longitudinal static stability but also raises the angle of attack needed for a given speed, so stall speed increases. The aircraft also needs a longer take-off run and has less elevator authority for flare.

Question 7Basic aerodynamics and flight controls

Selecting take-off flap on a typical light aeroplane primarily:

  1. decreases the lift coefficient and requires a higher approach speed
  2. increases the lift coefficient without changing drag
  3. raises the lift coefficient and drag, lowering the stall speed Correct answer.
  4. reduces the critical angle of attack and raises the stall speed

Explanation

Take-off flap increases wing camber, raising the maximum lift coefficient and allowing the aeroplane to fly at a lower speed. It also increases drag, which is why take-off flap is less than landing flap. The stall speed is reduced because CLmax is higher.

Question 8Basic aerodynamics and flight controls

Wingtip vortices from a fixed-wing aeroplane are strongest when it is:

  1. light, clean and fast
  2. heavy, clean and slow Correct answer.
  3. heavy, with flaps selected and fast
  4. light, with flaps selected and slow

Explanation

Wingtip vortices are a product of the pressure difference between the lower and upper surfaces and are strongest when the wing is working hardest. High weight, low speed and a clean configuration all require a high lift coefficient, which strengthens the circulation and the vortices. Flaps spread lift inboard and can reduce the peak tip loading somewhat.

Question 9Basic aerodynamics and flight controls

In high-speed aerodynamics, the critical Mach number is:

  1. the free-stream Mach number at which local airflow first reaches Mach 1 Correct answer.
  2. the airspeed at which the wing first stalls in a level turn
  3. the maximum speed at which the aeroplane can safely fly in smooth air
  4. the speed at which propeller tip speed first exceeds the speed of sound

Explanation

The critical Mach number is the aircraft Mach number at which the airflow at some point on the airframe, usually the upper wing surface, first reaches Mach 1. Beyond it, shock waves begin to form, causing drag rise, buffet and possible control changes. It is a local-flow limit, not the aircraft's maximum operating speed.

Question 10Basic aerodynamics and flight controls

During a high-power, high-angle-of-attack climb, P-factor tends to:

  1. yaw right because the ascending blade has a greater angle of attack
  2. roll right and pitch nose-down because the ascending blade produces more thrust
  3. have no effect once the aeroplane is established in a steady climb
  4. yaw left because the descending blade has a greater angle of attack Correct answer.

Explanation

P-factor arises because the propeller disc is inclined to the relative airflow in a high-angle-of-attack climb. The descending blade meets the air at a larger angle of attack than the ascending blade and therefore produces more thrust. With a clockwise propeller seen by the pilot, that extra thrust on the right side yaws the nose left.

Question 11Basic aerodynamics and flight controls

In fixed-wing aerodynamics, the angle of attack is the angle between the wing chord line and:

  1. the flight path after landing
  2. the longitudinal axis of the fuselage
  3. the relative airflow Correct answer.
  4. the horizontal datum

Explanation

Angle of attack is measured between the wing chord line and the relative airflow, not between the wing and the horizon. Pitch attitude and the longitudinal axis describe the aeroplane's orientation, while relative airflow depends on the flight path and speed.

Question 12Basic aerodynamics and flight controls

Which primary flight control surface is used to control an aeroplane about its longitudinal axis?

  1. Aileron Correct answer.
  2. Flap
  3. Rudder
  4. Elevator

Explanation

Ailerons are the primary roll control and therefore control rotation about the longitudinal axis. The elevator controls pitch about the lateral axis, the rudder controls yaw about the normal axis, and flaps are high-lift devices.

Question 13Basic aerodynamics and flight controls

In unaccelerated straight and level flight, the load factor acting on the aeroplane is:

  1. 2.0
  2. 0.5
  3. 0.0
  4. 1.0 Correct answer.

Explanation

Load factor is lift divided by weight. In unaccelerated straight and level flight, lift equals weight, so the load factor is 1.0; it rises above one only when the wings must produce more lift, such as in a turn or pull-up.

Question 14Basic aerodynamics and flight controls

For a given weight and speed in straight and level flight, increasing the wing aspect ratio will generally:

  1. have no effect on induced drag but increase parasite drag at all speeds
  2. increase induced drag because the larger span produces more vortex energy
  3. reduce induced drag by weakening the wingtip vortices Correct answer.
  4. reduce parasite drag because the wing has less surface area

Explanation

A higher aspect ratio produces a longer, narrower wing, which weakens wingtip vortices and reduces downwash. For the same weight and speed, the induced drag coefficient is lower, so induced drag falls; parasite drag is not necessarily reduced.

Question 15Basic aerodynamics and flight controls

Longitudinal static stability in a conventional aeroplane is primarily provided by:

  1. the vertical fin, which provides directional stability about the normal axis
  2. a centre of gravity located well behind the neutral point
  3. wing dihedral, which provides lateral stability in a sideslip
  4. the tailplane, with the CG ahead of the neutral point Correct answer.

Explanation

Longitudinal static stability requires a nose-down pitching moment as angle of attack increases, normally from the tailplane, with the CG ahead of the neutral point. The fin provides directional stability, and dihedral provides lateral stability.

Question 16Basic aerodynamics and flight controls

Compared with a flapless approach at the same airspeed, using full landing flap on a light aeroplane generally allows:

  1. a shallower approach path at a lower power setting and higher speed
  2. a lower stalling speed with no change in total drag
  3. a steeper approach path without an increase in airspeed Correct answer.
  4. a shorter landing roll only if the approach is flown faster

Explanation

Full landing flap increases both lift coefficient and drag, so the aeroplane can fly a steeper approach at the same airspeed without gaining speed. The stalling speed is reduced, but total drag at a given speed is higher, not unchanged.

Question 17Basic aerodynamics and flight controls

As bank angle is increased in a level turn, to maintain level flight the pilot must:

  1. increase angle of attack to produce more lift Correct answer.
  2. keep angle of attack constant and accept a gradual descent
  3. increase airspeed only, with no change in angle of attack
  4. reduce angle of attack and increase airspeed to maintain lift

Explanation

In a level turn the wings must support both weight and the increased load factor, so the vertical component of lift must stay equal to weight. The pilot increases angle of attack to produce that extra lift, which also raises induced drag.

Question 18Basic aerodynamics and flight controls

Differential ailerons are rigged so that the up-going aileron deflects through a larger angle than the down-going aileron. This reduces adverse yaw because it:

  1. increases lift on the up-going wing so that the roll rate is maintained
  2. moves the centre of pressure forward on the rising wing to reduce yaw
  3. reduces the angle of attack on the down-going wing and delays its stall
  4. adds drag on the descending wing to balance the extra drag on the rising wing Correct answer.

Explanation

Differential ailerons deflect the up-going aileron more than the down-going aileron. The extra parasite drag on the descending wing opposes the extra induced drag on the rising wing, reducing the yaw that accompanies roll.

Question 19Basic aerodynamics and flight controls

Wing sweep is used on high-speed aeroplanes mainly to:

  1. increase the aspect ratio so that induced drag is lower at high altitude
  2. reduce the stalling speed by keeping the airflow attached at high angles
  3. raise the critical Mach number by reducing chordwise flow velocity Correct answer.
  4. move the centre of pressure aft to improve longitudinal stability

Explanation

Sweepback makes the airflow meet the wing at an angle, so only the chordwise component of velocity affects the effective Mach number. This delays the onset of local sonic flow and raises the critical Mach number.

Question 20Basic aerodynamics and flight controls

When an aeroplane flies just above the runway surface, the most significant aerodynamic effect is that:

  1. elevator effectiveness is reduced by the ground surface
  2. the stalling angle of attack is increased significantly
  3. parasite drag increases sharply and the aeroplane decelerates
  4. induced drag decreases and the aeroplane tends to float Correct answer.

Explanation

Near the ground, the surface restricts downwash and weakens wingtip vortices, so induced drag falls for a given lift coefficient. The reduced drag can make the aeroplane float during landing or refuse to settle.

Question 21Basic aerodynamics and flight controls

Which primary flight control surface controls the aeroplane about its lateral axis?

  1. The aileron
  2. The rudder
  3. The flap
  4. The elevator Correct answer.

Explanation

The elevator is mounted on the tailplane and changes pitch by altering the tail downforce; pitch rotation is about the lateral axis. Ailerons control roll about the longitudinal axis, the rudder controls yaw about the normal axis, and flaps are secondary lift/drag devices.

Question 22Basic aerodynamics and flight controls

The rudder of a conventional aeroplane controls rotation about which axis?

  1. The wing chord axis
  2. The lateral axis
  3. The normal (vertical) axis Correct answer.
  4. The longitudinal axis

Explanation

The rudder is mounted on the fin and deflects the tail left or right, producing yaw about the normal (vertical) axis. Roll about the longitudinal axis is controlled by ailerons, and pitch about the lateral axis by the elevator.

Question 23Basic aerodynamics and flight controls

Which of these is classified as a secondary flight control?

  1. Aileron
  2. Flap Correct answer.
  3. Rudder
  4. Elevator

Explanation

Flaps are secondary flight controls because they modify the wing's lift and drag characteristics rather than directly controlling the aeroplane's attitude. Elevator, aileron and rudder are primary flight controls.

Question 24Basic aerodynamics and flight controls

In level flight at constant altitude, as true airspeed increases, parasite drag:

  1. decreases in proportion to airspeed
  2. increases only when flap is extended
  3. increases approximately with the square of airspeed Correct answer.
  4. remains constant until the speed of sound is reached

Explanation

Parasite drag is proportional to dynamic pressure, so at constant altitude it rises approximately with the square of true airspeed. Induced drag behaves differently and decreases as airspeed increases.

Question 25Basic aerodynamics and flight controls

Moving the centre of gravity aft within the approved range will generally:

  1. have no effect on longitudinal static stability
  2. decrease longitudinal static stability Correct answer.
  3. increase longitudinal static stability
  4. increase the nose-down pitching moment required from the tailplane

Explanation

An aft centre of gravity shortens the effective moment arm between the centre of gravity and the tailplane, reducing the restoring pitch moment. This lowers longitudinal static stability and can make stall or spin recovery more difficult.

Question 26Basic aerodynamics and flight controls

Vortex generators are fitted to a wing primarily to:

  1. delay boundary-layer separation by energising the airflow Correct answer.
  2. reduce the critical Mach number
  3. increase the wing's aspect ratio
  4. provide a direct indication of the stall angle

Explanation

Vortex generators are small vanes that create vortices which mix higher-energy air into the boundary layer. This delays separation and helps maintain aileron or elevator effectiveness at high angles of attack.

Question 27Basic aerodynamics and flight controls

If an aeroplane's gross weight is increased while all other factors remain unchanged, the stalling angle of attack and the stall speed will respectively:

  1. increase; remain the same
  2. increase; increase
  3. remain the same; remain the same
  4. remain the same; increase Correct answer.

Explanation

The critical angle of attack at which the wing stalls is a fixed aerodynamic characteristic for a given wing, so weight does not change it. Increasing weight requires a higher lift coefficient at any given speed, so the aeroplane must stall at a higher speed.

Question 28Basic aerodynamics and flight controls

Extending spoilers on a wing in flight primarily:

  1. decreases lift without affecting drag
  2. increases lift and increases drag
  3. decreases lift and increases drag Correct answer.
  4. increases lift and decreases drag

Explanation

Spoilers disrupt the smooth airflow over the upper wing surface, reducing lift and adding drag. They are used for descent, speed control and, on some aeroplanes, roll control.

Question 29Basic aerodynamics and flight controls

A wing with positive camber can produce lift at zero angle of attack because:

  1. the centre of pressure is always located at the centre of gravity
  2. positive camber gives a positive lift coefficient even at zero chord-line angle Correct answer.
  3. the stagnation point remains fixed exactly at the leading edge at all speeds
  4. the boundary layer remains laminar over the entire upper surface

Explanation

Positive camber means the mean line is curved upward, so the upper surface accelerates the airflow more than the lower surface even when the chord line is parallel to the relative airflow. This pressure difference produces a positive lift coefficient at zero angle of attack.

Question 30Basic aerodynamics and flight controls

Mach tuck is best described as:

  1. a transonic nose-down pitch from aft centre-of-pressure movement Correct answer.
  2. a yaw oscillation caused by asymmetric shock waves at high angle of attack
  3. a nose-up pitch caused by flap deployment at high Mach number
  4. a loss of elevator effectiveness caused only by ice contamination

Explanation

In the transonic range, shock waves form and the centre of pressure moves aft, creating a nose-down pitching moment known as Mach tuck. The effect can reduce elevator authority and requires care during high-speed descent or recovery.

Question 31Basic aerodynamics and flight controls

In a light aeroplane, the purpose of the elevator trim tab is to:

  1. Provide a backup pitch control if the elevator becomes jammed
  2. Relieve the steady control force needed to hold a selected pitch attitude Correct answer.
  3. Control the aeroplane about its longitudinal axis
  4. Increase the maximum elevator deflection available from the control column

Explanation

A trim tab is a small hinged surface at the trailing edge of the elevator that deflects in the opposite direction to the elevator, changing the aerodynamic force on that surface. This allows the aeroplane to be held in the chosen attitude without the pilot maintaining a continuous push or pull. It is an aid to relieving stick force, not a substitute for the primary control.

Question 32Basic aerodynamics and flight controls

Dihedral angle is built into the wings of a conventional aeroplane in order to:

  1. Increase the lift coefficient of the wing at a given angle of attack
  2. Increase the critical angle of attack of the wing
  3. Produce a restoring rolling moment when a wing drops and the aeroplane sideslips Correct answer.
  4. Reduce the induced drag produced at the wingtips at high speed

Explanation

When a wing drops, the aeroplane slides sideways, so the relative airflow meets the down-going wing at a smaller effective angle of attack than the rising wing. The rising wing therefore generates more lift, producing a rolling moment that tends to level the wings. This is a form of lateral static stability.

Question 33Basic aerodynamics and flight controls

An aeroplane is maintained in level flight at constant weight while it is slowed from cruise speed. In these conditions the induced drag:

  1. Remains unchanged, because the weight being supported has not altered
  2. Decreases, because the wings are meeting the air at a reduced speed
  3. Decreases, because the airflow over the wing is smoother at low speed
  4. Increases, because the wing must operate at a higher lift coefficient Correct answer.

Explanation

In level flight the lift must equal the weight, so as speed falls the lift coefficient must rise. A higher lift coefficient means a stronger pressure difference between the lower and upper surfaces, which strengthens the wingtip vortices and increases induced drag, roughly in proportion to the square of the lift coefficient.

Question 34Basic aerodynamics and flight controls

For a cambered wing, as the angle of attack is increased towards the stalling angle, the centre of pressure generally:

  1. Moves aft towards the trailing edge
  2. Moves forward towards the leading edge Correct answer.
  3. Stays at the same chordwise position while the lift simply increases
  4. Reaches the trailing edge at the stalling angle of attack

Explanation

As a cambered wing is brought to a higher angle of attack, the suction peak on the upper surface becomes stronger and moves forward, and the total lift acts at a point closer to the leading edge. The centre of pressure therefore travels forward up to the stall. Beyond the stall the flow separates and the centre of pressure moves sharply aft again.

Question 35Basic aerodynamics and flight controls

In flight, the elevator is deflected upward. As a result, the tailplane generates:

  1. An upward force, which pitches the nose down
  2. A downward force, which pitches the nose down
  3. An upward force, which pitches the nose up
  4. A downward force, which pitches the nose up Correct answer.

Explanation

An elevator deflected upward increases the downward aerodynamic force produced by the tailplane. Acting behind the centre of gravity, this downforce rotates the aeroplane nose-up about the lateral axis. This is why the control column is moved backwards to raise the nose.

Question 36Basic aerodynamics and flight controls

Wingtip vortices generated by a large aeroplane are strongest when that aeroplane is:

  1. Heavy, slow and in a clean configuration Correct answer.
  2. Light, fast and with flaps extended
  3. Light, slow and with flaps extended
  4. Heavy, fast and with flaps extended

Explanation

Vortex strength depends on the weight carried and on how hard the wing is working, which rises as speed falls; it is roughly proportional to weight divided by speed and span. A heavy aeroplane flying slowly with no flap extended therefore leaves the most hazardous wake. Flap extension reduces vortex strength by spreading the lift distribution outboard.

Question 37Basic aerodynamics and flight controls

Which change would most directly reduce interference drag on a light aeroplane?

  1. Fairing the junctions between the wing, fuselage and strut ends Correct answer.
  2. Increasing the dihedral angle of the wings
  3. Moving the centre of gravity rearward within the permitted range
  4. Polishing the wing surfaces to a high gloss

Explanation

Interference drag arises where two components meet and their local airflow patterns disturb one another, such as at the wing root or where struts join the wing. Smooth fairings at those junctions blend the flows and reduce the extra drag created there. It is a separate component from skin friction and from induced drag.

Question 38Basic aerodynamics and flight controls

A horn balance, in which part of the control surface projects ahead of the hinge line, is fitted to a rudder or elevator primarily to:

  1. Increase the maximum deflection available from the surface
  2. Reduce the hinge moment required to hold the surface deflected Correct answer.
  3. Prevent the surface from fluttering at high indicated airspeed
  4. Improve the static stability of the aeroplane about that axis

Explanation

The projecting area ahead of the hinge line produces a moment about the hinge that opposes the moment from the main part of the surface. The pilot therefore needs less force on the controls to deflect or hold the surface. This is aerodynamic balancing, and it has no effect on the stability of the aeroplane as a whole.

Question 39Basic aerodynamics and flight controls

Two wings have the same area and are producing the same lift coefficient, but one has a much higher aspect ratio. That wing produces less induced drag because:

  1. It weakens the tip vortices and downwash, so less of the lift is tilted rearward Correct answer.
  2. It raises the critical angle of attack, which lowers the stalling speed
  3. It delays the onset of wave drag at high subsonic Mach numbers
  4. It increases the total lifting area, which spreads the load over a larger surface

Explanation

The pressure difference between the lower and upper surfaces spills around the tips, creating vortices and a downwash field behind the wing. A long, narrow wing has less of its span affected relative to its chord, so the vortices are weaker and the downwash angle is smaller, which means the lift vector is tilted rearward less. Induced drag falls as a result.

Question 40Basic aerodynamics and flight controls

An aeroplane stalls at 50 knots in straight and level flight at 1g. At the same weight and configuration, its stalling speed in a level 60 degree banked turn will be closest to:

  1. 65 knots
  2. 58 knots
  3. 71 knots Correct answer.
  4. 50 knots

Explanation

A level 60 degree banked turn requires a load factor of 1 divided by the cosine of 60 degrees, which is 2. Stall speed rises with the square root of the load factor, so the 1g stall speed is multiplied by about 1.41. Applying that to 50 knots gives approximately 70 to 71 knots.

Question 41Airframe construction and structural components

On a semi-monocoque fuselage, what is the primary function of the circumferential frames?

  1. They carry the main bending loads along the length of the fuselage.
  2. They form the outer aerodynamic surface and carry all shear loads.
  3. They provide attachment points for the wing spar only.
  4. They maintain the cross-sectional shape and support the skin against buckling. Correct answer.

Explanation

Frames, called bulkheads when they form a complete ring, are circumferential members that hold the fuselage cross-section to shape and stabilise the skin against buckling. They also distribute concentrated loads, but longitudinal bending is carried mainly by the longerons and the skin.

Question 42Airframe construction and structural components

On a metal wing, what is the main structural role of the ribs?

  1. They provide the main bending strength along the span.
  2. They carry the torsional load from the leading edge to the trailing edge.
  3. They maintain the aerofoil shape and transfer skin and spar loads. Correct answer.
  4. They attach the wing to the fuselage.

Explanation

Ribs are chordwise members that preserve the aerofoil contour and support the skin between the spars. They also transfer loads from the skin and from concentrated fittings into the spars.

Question 43Airframe construction and structural components

In a truss-type fuselage, which members carry the primary flight and landing loads?

  1. The longitudinal longerons alone.
  2. Triangulated tubes acting in tension and compression. Correct answer.
  3. The fabric or thin non-structural covering.
  4. The circumferential frames, which act mainly in bending and torsion.

Explanation

A truss fuselage is a framework of tubes arranged in triangles, so members are loaded mainly in tension or compression rather than bending. The covering is normally non-structural and only provides the aerodynamic shape.

Question 44Airframe construction and structural components

Why are longitudinal stringers fitted to a stressed-skin fuselage in addition to the frames?

  1. To stiffen the skin against buckling and carry longitudinal load. Correct answer.
  2. To seal the pressurised cabin at every frame joint.
  3. To provide a continuous electrical bonding path along the fuselage.
  4. To allow large skin panels to be removed without disturbing the frames.

Explanation

Stringers are longitudinal members riveted to the skin between frames. They stabilise the skin against buckling and share longitudinal bending and shear loads with the skin and longerons.

Question 45Airframe construction and structural components

What is a box-beam spar in a metal wing?

  1. A single tubular spar running continuously from root to tip without a web.
  2. Two caps joined by two webs to form a closed box. Correct answer.
  3. A single deep web with flanges formed by the skin.
  4. A solid rectangular bar machined from a single billet.

Explanation

A box-beam spar uses upper and lower caps to take bending and two webs to take shear, forming a closed box that is efficient in both bending and torsion. It is common in modern metal wings.

Question 46Airframe construction and structural components

When riveting an aluminium alloy skin repair, what does the edge distance of a rivet refer to?

  1. The total thickness of the sheets being joined by the rivet.
  2. The diameter of the rivet head measured after the rivet is set.
  3. The distance from the rivet centre to the sheet edge. Correct answer.
  4. The distance between adjacent rivets measured along the same row.

Explanation

Edge distance is measured from the centre of the rivet hole to the edge of the sheet. It must be at least about twice the rivet diameter; too little allows the rivet to tear out under load.

Question 47Airframe construction and structural components

Why is 2024 aluminium alloy sheet often supplied as Alclad for aircraft skins?

  1. The cladding makes the sheet easier to heat-treat after it has been formed.
  2. The pure aluminium cladding significantly increases the sheet's tensile strength.
  3. The cladding provides a corrosion-resistant surface over a stronger core. Correct answer.
  4. The cladding allows the skin to be welded instead of riveted.

Explanation

Alclad sheet has a thin layer of commercially pure aluminium bonded to each side of a stronger 2024 core. The pure aluminium corrodes preferentially and protects the core, while the core provides the strength.

Question 48Airframe construction and structural components

In a composite sandwich panel used for aircraft structure, what is the main function of the core?

  1. To provide the aerodynamic finish and resist rain erosion.
  2. To separate the skins and carry shear between them. Correct answer.
  3. To carry most of the tensile and compressive loads in the panel.
  4. To act as a lightning strike protection layer.

Explanation

The core separates the two skins and carries shear, so the skins act like the flanges of an I-beam. This gives high bending stiffness for low weight.

Question 49Airframe construction and structural components

An aircraft structure is designed so that a crack in one load path can be tolerated until it is found at scheduled inspection. Which design philosophy does this describe?

  1. Safe-life design, in which the component is retired at a fixed life.
  2. Fatigue-life design, in which life is predicted from load spectra.
  3. Fail-safe (damage-tolerant) design Correct answer.
  4. Monocoque design, in which the skin carries all the loads.

Explanation

Fail-safe or damage-tolerant design provides multiple load paths or crack stoppers so that a detectable crack does not cause immediate failure. Safe-life design instead retires the part before the predicted fatigue life is reached.

Question 50Airframe construction and structural components

Why should abrupt changes in cross-section and sharp internal corners be avoided in aircraft structural members?

  1. They prevent the use of rivets in the surrounding structure.
  2. They reduce the stiffness of the member in torsion only.
  3. They make the part more difficult to paint and inspect during manufacture.
  4. They increase stress concentration and can initiate fatigue cracks. Correct answer.

Explanation

Sharp changes in section raise the local stress well above the nominal stress, and repeated loading can start a fatigue crack at that point. Generous fillets and gradual section changes reduce the stress concentration.