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CAA NZ ATPL Theory - Advanced Aerodynamics, Performance and Systems Knowledge study materials
CAA NZ ATPL Theory - Advanced Aerodynamics, Performance and Systems Knowledge study resources

CAA NZ ATPL Theory - Advanced Aerodynamics, Performance and Systems Knowledge practice questions

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Question 1Advanced Aerodynamics

In a steady level turn, the load factor n is defined as the ratio of lift to weight. If the aircraft is banked at 60 degrees and lift is increased to maintain altitude, what is the approximate load factor?

  1. 0.50
  2. 2.00 Correct answer.
  3. 1.41
  4. 1.15

Explanation

In a level turn the vertical component of lift must equal weight, so n = L/W = 1/cos(bank). For a 60 degree bank, cos 60 = 0.5, giving a load factor of 2.0.

Question 2Advanced Aerodynamics

For a propeller-driven aeroplane, induced drag is smallest when the aeroplane is flying:

  1. at low speed just above the stall
  2. at the speed for minimum power required
  3. at the speed for minimum drag Correct answer.
  4. at high speed near maximum level speed

Explanation

Induced drag varies inversely with the square of speed, so it decreases as speed increases and reaches its lowest practical value at the minimum drag speed. This speed corresponds to the maximum lift-to-drag ratio.

Question 3Advanced Aerodynamics

What is the primary purpose of positive washout (washout) in a wing design?

  1. To ensure the wing root reaches the critical angle of attack before the tip Correct answer.
  2. To move the centre of pressure forward at high angles of attack
  3. To increase the lift coefficient at the wing tip
  4. To reduce the dihedral effect at high speed

Explanation

Washout gives the tip a smaller angle of incidence than the root, so the root stalls first. This preserves aileron effectiveness and reduces the tendency to drop a wing at the stall.

Question 4Advanced Aerodynamics

The critical Mach number of an aerofoil is best described as the free-stream Mach number at which:

  1. the shock wave moves to the trailing edge
  2. the local airflow somewhere on the aerofoil first reaches Mach 1.0 Correct answer.
  3. the drag divergence Mach number is exceeded
  4. the aeroplane first encounters buffet

Explanation

The critical Mach number is reached when the accelerated local flow over the upper surface first becomes sonic while the free stream is still below Mach 1. This is the onset of transonic effects.

Question 5Advanced Aerodynamics

An aeroplane in a steady climb at a constant indicated airspeed experiences a reduction in air density as it climbs. To maintain the same indicated airspeed, the true airspeed must:

  1. stay exactly the same
  2. increase only if temperature rises
  3. increase as density decreases Correct answer.
  4. decrease in proportion to density

Explanation

Indicated airspeed depends on dynamic pressure, which is half the product of density and true airspeed squared. As density falls with altitude, true airspeed must rise to keep dynamic pressure, and therefore indicated airspeed, constant.

Question 6Advanced Aerodynamics

Which condition produces the greatest induced angle of attack at the wing tip?

  1. Low aspect ratio with high lift coefficient Correct answer.
  2. Low aspect ratio with low lift coefficient
  3. High aspect ratio with high speed
  4. High aspect ratio with low lift coefficient

Explanation

Downwash is strongest when lift coefficient is high and when the span is short relative to chord, that is, low aspect ratio. A low aspect ratio wing at high lift coefficient therefore has the largest induced angle of attack.

Question 7Advanced Aerodynamics

The centre of pressure of a cambered aerofoil at normal operating angles of attack:

  1. coincides with the centre of gravity
  2. moves forward as angle of attack increases Correct answer.
  3. remains fixed at the aerodynamic centre
  4. moves rearward as angle of attack increases

Explanation

On a cambered aerofoil the centre of pressure moves forward as angle of attack increases, because the lift distribution shifts toward the leading edge. At the aerodynamic centre the pitching moment is constant, but the centre of pressure is not fixed there.

Question 8Advanced Aerodynamics

In a steady, coordinated level turn, an increase in bank angle at constant true airspeed causes the turn radius to:

  1. increase
  2. increase then decrease
  3. remain constant
  4. decrease Correct answer.

Explanation

Turn radius equals true airspeed squared divided by g times the tangent of the bank angle. At constant speed, increasing bank angle increases tan(bank) and therefore reduces the radius.

Question 9Advanced Aerodynamics

An aeroplane is in a steady descending turn. Compared with a level turn at the same bank angle, the load factor required is:

  1. zero, because the aircraft is descending
  2. less, because the vertical component of lift need not equal full weight Correct answer.
  3. greater, because the aircraft is accelerating
  4. the same, because lift still equals weight divided by cos(bank)

Explanation

In a descent the vertical component of lift supports only part of the weight, with the remainder balanced by the vertical component of thrust or the descent path. The load factor is therefore lower than in a level turn at the same bank.

Question 10Advanced Aerodynamics

During a steady climb at a given indicated airspeed, the parasite drag compared with level flight at the same indicated airspeed will be:

  1. higher, because true airspeed is greater
  2. higher, because lift coefficient increases
  3. lower, because density is lower
  4. the same, because parasite drag depends on indicated airspeed Correct answer.

Explanation

Parasite drag depends on dynamic pressure and equivalent airspeed. At the same indicated airspeed the dynamic pressure is unchanged, so parasite drag is essentially the same regardless of altitude.

Question 11Advanced Aerodynamics

An aeroplane suffers a sudden loss of altitude and enters a strong updraught. The load factor experienced is most influenced by:

  1. the rate of change of the gust velocity relative to the aeroplane Correct answer.
  2. the absolute altitude of the aeroplane
  3. the static stability of the aeroplane
  4. the indicated airspeed only

Explanation

Gust load factor depends on the sharp-edged gust velocity and the rate at which the aeroplane encounters it, together with wing loading and lift curve slope. The rate of change of relative gust velocity determines the effective angle of attack change.

Question 12Advanced Aerodynamics

A wing with a higher aspect ratio, compared with a lower aspect ratio wing of the same area and lift coefficient, produces:

  1. less induced drag and a shallower lift curve slope
  2. more induced drag and a lower lift curve slope
  3. less induced drag and a steeper lift curve slope Correct answer.
  4. the same induced drag but a steeper lift curve slope

Explanation

Induced drag coefficient is proportional to the lift coefficient squared divided by pi times aspect ratio, so higher aspect ratio reduces induced drag. A higher aspect ratio also increases the lift curve slope because tip losses are smaller.

Question 13Advanced Aerodynamics

At the speed for maximum endurance in a propeller aeroplane, the aeroplane is flying at:

  1. minimum thrust required
  2. maximum power available
  3. maximum lift-to-drag ratio
  4. minimum power required Correct answer.

Explanation

Maximum endurance for a propeller aircraft occurs at minimum power required, which is at a lower speed than minimum drag. Maximum range occurs at maximum lift-to-drag ratio.

Question 14Advanced Aerodynamics

A swept wing is used on high-speed aeroplanes primarily because sweep:

  1. eliminates the need for washout
  2. reduces the wing area required for a given weight
  3. increases the critical Mach number by reducing the chordwise component of velocity Correct answer.
  4. increases the lift coefficient at low speed

Explanation

Sweep resolves the free-stream velocity into a component normal to the leading edge and one along it. Only the normal component governs pressure distribution, so the effective Mach number is reduced, raising the critical Mach number.

Question 15Advanced Aerodynamics

In a spin, the aeroplane is in autorotation. Which statement best describes the aerodynamic state of the inner wing during a developed spin?

  1. It is unstalled and producing more lift than the outer wing
  2. Both wings are at the same angle of attack and unstalled
  3. It is at a lower angle of attack than the outer wing and produces more lift
  4. It is at a higher angle of attack than the outer wing and is stalled Correct answer.

Explanation

Autorotation is sustained because the inner wing, moving downward, experiences a higher angle of attack and remains stalled, producing less lift and more drag. The outer wing, moving upward, is at a lower angle of attack and produces relatively more lift.

Question 16Advanced Aerodynamics

The effect of a high wing loading on the gust response of an aeroplane is that it:

  1. decreases the gust load factor for a given gust Correct answer.
  2. has no effect on gust load factor
  3. increases the gust load factor for a given gust
  4. increases the gust load factor only at low speed

Explanation

Gust load factor is proportional to gust velocity and inversely related to wing loading. A higher wing loading therefore reduces the load factor increment produced by a given gust.

Question 17Advanced Aerodynamics

Which of the following best explains why a laminar flow aerofoil has a lower minimum drag coefficient than a conventional aerofoil?

  1. It maintains laminar flow over a larger proportion of the chord Correct answer.
  2. It has a greater maximum thickness
  3. It has a larger leading edge radius
  4. It operates at higher lift coefficients

Explanation

Laminar flow aerofoils are shaped to keep the favourable pressure gradient over a large part of the chord, delaying transition. Extending the laminar region reduces skin friction and therefore the minimum drag coefficient.

Question 18Advanced Aerodynamics

An aeroplane is flying at a constant true airspeed in level flight at high altitude. As it descends to a lower altitude at the same true airspeed, the indicated airspeed will:

  1. decrease
  2. stay the same
  3. increase only if temperature falls
  4. increase Correct answer.

Explanation

Indicated airspeed reflects dynamic pressure, which equals half density times true airspeed squared. At a constant true airspeed, descending into denser air increases dynamic pressure and therefore indicated airspeed.

Question 19Advanced Aerodynamics

Aerodynamic flutter is a dangerous phenomenon primarily because it:

  1. reduces drag at high Mach numbers
  2. only occurs below the stall speed
  3. produces a divergent, self-sustaining oscillation Correct answer.
  4. causes a steady loss of lift without oscillation

Explanation

Flutter is an aeroelastic oscillation in which aerodynamic forces couple with structural stiffness to feed energy into the motion. Above the flutter speed the oscillation diverges rapidly and can destroy the structure.

Question 20Advanced Aerodynamics

For a given aerofoil, increasing the angle of attack beyond the stall angle causes the lift coefficient to:

  1. remain constant
  2. increase sharply then stabilise
  3. decrease as the flow separates Correct answer.
  4. continue increasing gradually

Explanation

Beyond the critical angle the boundary layer separates over much of the upper surface, and lift coefficient falls while drag rises sharply. The stall angle marks the peak of the lift curve.

Question 21Advanced Aerodynamics

An aeroplane is in a level turn at 60 degrees bank. If the aeroplane stalls at a load factor of 2.0 in 1g flight, at what approximate bank angle would the accelerated stall occur assuming the stall speed is unchanged in terms of load factor?

  1. 60 degrees Correct answer.
  2. 75 degrees
  3. 30 degrees
  4. 45 degrees

Explanation

The accelerated stall occurs when the load factor in the turn reaches the limiting value. A 60 degree bank produces a load factor of 2.0, matching the stated limit, so the stall occurs at that bank.

Question 22Advanced Aerodynamics

A turbojet aeroplane at high altitude experiences a reduction in thrust available as altitude increases. The principal reason is that:

  1. the turbine expands the gas to a lower pressure
  2. the exhaust gas temperature falls below ambient
  3. the compressor pressure ratio increases with altitude
  4. the mass flow of air through the engine decreases as density falls Correct answer.

Explanation

Thrust is approximately the product of mass flow and the velocity change imparted to the air. As ambient density falls with altitude, the mass flow through the engine decreases, reducing thrust for a given throttle setting.

Question 23Advanced Aerodynamics

An aeroplane with a conventional tail is trimmed for level flight. If the centre of gravity is moved aft toward the neutral point, the static longitudinal stability:

  1. becomes negative immediately
  2. increases
  3. remains unchanged
  4. decreases toward zero Correct answer.

Explanation

Static margin is the distance between the centre of gravity and the neutral point. As the centre of gravity moves aft toward the neutral point, the static margin shrinks and longitudinal stability decreases toward zero.

Question 24Advanced Aerodynamics

During a level turn at high altitude, an aeroplane approaches the buffet boundary. Which combination best describes the two limits that define this boundary?

  1. Low-speed stall buffet and high-speed Mach buffet Correct answer.
  2. Minimum control speed and maximum tyre speed
  3. Maximum take-off weight and maximum landing weight
  4. Static stability and dynamic stability limits

Explanation

The buffet boundary is bounded by the low-speed stall buffet at high angle of attack and the high-speed Mach buffet at high Mach number. Between these limits lies the usable flight envelope, which narrows at high altitude.

Question 25Advanced Aerodynamics

A propeller is operating at a constant rotational speed while the aeroplane accelerates in level flight. As forward speed increases, the angle of attack of the propeller blade sections:

  1. decreases, reducing thrust Correct answer.
  2. increases, reducing thrust
  3. remains constant because rotational speed is constant
  4. increases, increasing thrust

Explanation

The blade angle of attack is the geometric blade angle minus the helix angle of the relative airflow. As forward speed rises, the helix angle increases, so the blade angle of attack and thrust decrease.

Question 26Advanced Aerodynamics

For a finite wing, the downwash velocity behind the trailing vortices has which primary effect on the local section lift?

  1. It reduces the effective angle of attack and hence the lift generated at each section Correct answer.
  2. It converts section profile drag into induced drag along the whole span
  3. It increases the effective angle of attack and hence the lift generated at each section
  4. It eliminates the spanwise pressure difference between upper and lower surfaces

Explanation

Trailing vortices induce a downward velocity at the wing, tilting the local relative airflow downward. This reduces the effective angle of attack of each section, so the section lift is lower than the two-dimensional value at the same geometric incidence. The resulting lift vector is also tilted rearward, producing induced drag.

Question 27Advanced Aerodynamics

Compared with a straight wing of the same span and area, a wing with significant sweepback will, at high subsonic Mach number, have a critical Mach number that is:

  1. Lower, because the chordwise flow path is longer
  2. Unchanged, because critical Mach number depends only on aerofoil section
  3. Higher, because the velocity component normal to the leading edge is reduced Correct answer.
  4. Higher, because sweep increases the local chord Reynolds number

Explanation

Sweep resolves the freestream into components along and normal to the leading edge. Only the normal component governs the pressure distribution and the onset of local sonic flow, so the effective Mach number seen by the section is reduced. This raises the freestream Mach number at which shock formation begins.

Question 28Advanced Aerodynamics

An aerofoil section reaches its stall angle. Which change in the pressure distribution best explains the loss of lift?

  1. The stagnation point moves to the mid-chord, reducing the leading-edge suction peak
  2. The adverse pressure gradient on the upper surface becomes too strong and the boundary layer separates Correct answer.
  3. The transition point moves forward, thickening the boundary layer without separation
  4. The lower-surface boundary layer separates and destroys the positive pressure region

Explanation

As incidence increases, the suction peak and the adverse pressure gradient over the rear upper surface increase. When the boundary layer can no longer overcome this gradient it separates, destroying the low-pressure region and reducing lift while drag rises sharply.

Question 29Advanced Aerodynamics

In a steady, coordinated level turn, which quantity is directly determined by the bank angle alone?

  1. True airspeed
  2. Rate of turn
  3. Turn radius
  4. Load factor Correct answer.

Explanation

In a level turn the vertical component of lift must equal weight, so load factor n equals 1/cos(bank angle) regardless of speed. Turn radius and rate of turn depend on both load factor and true airspeed, so they are not fixed by bank angle alone.

Question 30Advanced Aerodynamics

Which statement correctly describes the relationship between induced drag and true airspeed in steady level flight at constant weight?

  1. Induced drag varies inversely with the square of the true airspeed Correct answer.
  2. Induced drag varies directly with the square of the true airspeed
  3. Induced drag is independent of true airspeed
  4. Induced drag varies inversely with true airspeed

Explanation

Induced drag equals the lift coefficient squared divided by pi times aspect ratio, multiplied by dynamic pressure and area. At constant weight, lift coefficient falls as the square of speed, so induced drag falls with the square of speed. Parasite drag, by contrast, rises with the square of speed.

Question 31Advanced Aerodynamics

In a propeller-driven aeroplane, thrust horsepower available is best described as:

  1. Shaft horsepower multiplied by the fuel flow
  2. Brake horsepower divided by propeller efficiency
  3. Engine rpm multiplied by propeller diameter
  4. Brake horsepower multiplied by propeller efficiency Correct answer.

Explanation

Only part of the shaft power delivered to the propeller is converted into useful thrust power. Thrust horsepower equals brake (shaft) horsepower multiplied by propeller efficiency, which is less than one. The remainder is lost in the slipstream kinetic energy and profile losses.

Question 32Advanced Aerodynamics

The centre of gravity of an aeroplane is moved forward. To maintain the same trimmed angle of attack in level flight, the tailplane must:

  1. Produce less downward force, which decreases the load carried by the wing
  2. Remain unchanged, because the wing lift is independent of the centre of gravity
  3. Produce more downward force, which increases the load carried by the wing Correct answer.
  4. Produce more upward force, which decreases the load carried by the wing

Explanation

A forward centre of gravity increases the nose-down pitching moment about the centre of gravity, so the tail must generate a greater download to balance it. This download adds to the weight that the wing must support, raising the total load factor and the stall speed.

Question 33Advanced Aerodynamics

The Mach number at which airflow somewhere on the aerofoil first reaches the local speed of sound is called the:

  1. Critical Mach number Correct answer.
  2. Maximum operating Mach number
  3. Drag divergence Mach number
  4. Never-exceed Mach number

Explanation

The critical Mach number is defined by the first appearance of sonic flow at any point on the airframe, usually the upper-surface suction peak. Drag divergence occurs later, when shock-induced separation causes a rapid drag rise.

Question 34Advanced Aerodynamics

An aeroplane of mass 4000 kg is in a steady level turn at 60 degrees bank. Taking g as 9.81 m/s², the total lift required is closest to:

  1. 45.3 kN
  2. 39.2 kN
  3. 157 kN
  4. 78.5 kN Correct answer.

Explanation

Weight is 4000 times 9.81, about 39.24 kN. In a level turn the load factor is 1/cos60, which equals 2.0, so lift must equal twice the weight, approximately 78.5 kN.

Question 35Advanced Aerodynamics

An aeroplane has a stall speed of 60 knots in 1g flight. In a steady level turn at 60 degrees bank, its stall speed is closest to:

  1. 120 knots
  2. 85 knots Correct answer.
  3. 75 knots
  4. 60 knots

Explanation

Stall speed increases with the square root of the load factor. At 60 degrees bank the load factor is 2.0, and the square root of 2 is about 1.41, so the stall speed rises to roughly 85 knots.

Question 36Advanced Aerodynamics

An aeroplane is in a steady climb at a constant calibrated airspeed. Compared with level flight at the same calibrated airspeed, the angle of attack required is:

  1. Lower, because the climb reduces the effective weight supported by the wing
  2. Higher, because the lift vector must be tilted to provide the climb and the thrust carries part of the weight Correct answer.
  3. Unchanged, because calibrated airspeed fixes the dynamic pressure and lift
  4. Higher, because the propeller efficiency is reduced in the climb

Explanation

In a climb the flight path is inclined, so only part of the thrust balances weight along the flight path and the wing lift is slightly less than weight. The wing must still generate nearly the same lift at a higher pitch attitude relative to the flight path, and the combination of reduced dynamic pressure with altitude and the tilted force balance requires a higher angle of attack than in level flight at the same indicated speed.

Question 37Advanced Aerodynamics

An aeroplane is flying at a constant indicated airspeed in a steady climb. As altitude increases, the true airspeed and the angle of attack respectively:

  1. Increase and increase
  2. Remain constant and decrease
  3. Decrease and increase
  4. Increase and remain approximately constant Correct answer.

Explanation

At a fixed indicated airspeed, equivalent dynamic pressure is constant, so the lift coefficient and hence angle of attack stay approximately the same. True airspeed rises with altitude because density falls while the indicated value is held.

Question 38Advanced Aerodynamics

An aeroplane is at the speed for minimum power required in level flight. If it accelerates slightly, the power required will initially:

  1. Remain constant, because minimum power has been passed
  2. Decrease, because induced power continues to fall
  3. Increase, because induced power rises with speed
  4. Increase, because parasite power rises faster than induced power falls Correct answer.

Explanation

Minimum power required occurs where the induced power decrease with speed is exactly offset by the parasite power increase. At speeds above this point the parasite term, which grows with the cube of speed, dominates and total power required rises.

Question 39Advanced Aerodynamics

An aeroplane in a steady glide with the engine at idle. If the glide is made at a higher true airspeed than the speed for minimum sink rate, the glide angle will:

  1. Remain unchanged, because the glide angle depends only on weight
  2. Become steeper, because the lift-to-drag ratio is lower than its maximum Correct answer.
  3. Become shallower, because the higher speed gives more distance per unit height
  4. Become steeper, because the load factor increases with speed in a glide

Explanation

Glide angle is set by the lift-to-drag ratio, with the shallowest glide occurring at maximum lift-to-drag ratio. The speed for minimum sink is below the speed for best glide ratio, so flying faster than minimum-sink speed moves toward best glide initially but beyond best glide speed the ratio falls and the glide steepens.

Question 40Advanced Aerodynamics

A wing is fitted with a leading-edge slat that is deployed. The primary aerodynamic effect is to:

  1. Move the centre of pressure rearward and increase the pitching moment
  2. Energise the boundary layer over the upper surface and delay the stall to a higher angle of attack Correct answer.
  3. Increase the camber of the trailing edge and lower the zero-lift angle
  4. Reduce the wing area and increase the wing loading

Explanation

A slat forms a slot that directs high-energy air over the upper surface of the main aerofoil. This re-energises the boundary layer and allows the section to reach a higher maximum lift coefficient before separation.

Question 41Advanced Aerodynamics

An aeroplane is descending at a constant indicated airspeed with the engine at idle. Compared with level flight at the same indicated airspeed, the load factor is:

  1. Greater than one, because the descent increases the apparent weight
  2. Less than one, because the flight path is inclined downward and lift is less than weight Correct answer.
  3. Equal to one, because the aeroplane is not accelerating
  4. Greater than one, because the wing must support the thrust component

Explanation

In a steady descent the flight path is inclined, so lift acts perpendicular to the flight path and balances only the component of weight normal to it. Lift is therefore less than weight and the load factor is slightly below one.

Question 42Advanced Aerodynamics

An aeroplane flying at high altitude encounters a sharp-edged vertical gust. The resulting change in load factor is greatest when:

  1. True airspeed is low and wing loading is low
  2. True airspeed is high and wing loading is low Correct answer.
  3. True airspeed is high and wing loading is high
  4. True airspeed is low and wing loading is high

Explanation

Gust load factor change is proportional to true airspeed and to the gust velocity, and inversely proportional to wing loading. A high true airspeed and a low wing loading therefore produce the largest load factor increment for a given gust.

Question 43Advanced Aerodynamics

An aeroplane is in a steady level turn at a constant true airspeed. If the bank angle is increased, the load factor and the stall speed respectively:

  1. Increase and decrease
  2. Remain constant and increase
  3. Decrease and increase
  4. Increase and increase Correct answer.

Explanation

Load factor in a level turn equals 1/cos(bank), so it rises as bank increases. Stall speed varies with the square root of load factor, so it also increases, raising the speed at which the wing reaches its maximum lift coefficient.

Question 44Advanced Aerodynamics

A jet aeroplane is climbing at a constant indicated airspeed. As altitude increases, the maximum rate of climb:

  1. Decreases, because thrust available falls with density while thrust required for a given lift coefficient rises Correct answer.
  2. Decreases, because the wing lift coefficient decreases with altitude
  3. Remains constant, because indicated airspeed is held constant
  4. Increases, because the lower density reduces drag

Explanation

Turbojet thrust falls approximately with density ratio, while the thrust required at a fixed lift coefficient stays roughly constant. Excess thrust therefore reduces with altitude, so the maximum rate of climb decreases and the absolute ceiling is approached.

Question 45Advanced Aerodynamics

An aeroplane is trimmed in level flight at a low speed. If it is then allowed to accelerate without any pilot input, and the aeroplane is statically stable, the resulting pitch response will:

  1. Pitch nose-up, increasing speed further
  2. Remain unchanged, because the trim setting fixes the speed
  3. Pitch nose-down, increasing speed further
  4. Pitch nose-up, reducing speed back toward the trimmed value Correct answer.

Explanation

Positive static longitudinal stability means a disturbance from the trimmed angle of attack produces a restoring pitching moment. An increase in speed reduces the angle of attack, generating a nose-up moment that slows the aeroplane back toward trim.

Question 46Advanced Aerodynamics

An aeroplane is in a fully developed spin. Which combination best describes the aerodynamic conditions on the inner wing?

  1. It is more deeply stalled with a higher angle of attack and lower lift than the outer wing Correct answer.
  2. It is less stalled with a higher angle of attack and higher lift than the outer wing
  3. It is fully attached with the same angle of attack as the outer wing
  4. It is fully attached with a lower angle of attack than the outer wing

Explanation

Autorotation is sustained because the downgoing inner wing experiences a higher angle of attack and remains more deeply stalled, producing less lift and more drag than the rising outer wing. The resulting rolling moment maintains the rotation.

Question 47Advanced Aerodynamics

An aeroplane with a swept wing is approaching the stall. Which characteristic is most typical compared with a straight wing?

  1. Root stall occurs first, producing a natural nose-down pitch
  2. The stall occurs at a lower angle of attack with no change in pitching moment
  3. Tip stall occurs first, producing a pitch-up and possible wing drop Correct answer.
  4. The stall is preceded by a strong pre-stall buffet that gives ample warning

Explanation

On a swept wing the boundary layer drifts outboard along the span, thickening the tip boundary layer so the tips stall before the root. Tip stall removes outboard lift behind the centre of gravity, giving a pitch-up, and asymmetric tip stall can produce a sharp wing drop.

Question 48Advanced Aerodynamics

A wing is operating at a lift coefficient well below the stall. Which change would most reduce the induced drag without changing lift or speed?

  1. Increasing the angle of attack and reducing the speed
  2. Increasing the wing span while keeping the same planform area Correct answer.
  3. Increasing the aerofoil thickness ratio
  4. Increasing the wing chord while keeping the same span

Explanation

Induced drag is inversely proportional to aspect ratio for a given lift coefficient. Increasing span while holding area constant raises aspect ratio, which spreads the lift over a longer span and reduces the strength of the trailing vortices.

Question 49Advanced Aerodynamics

An aeroplane is flying at high altitude near its buffet boundary. Compared with the same indicated airspeed at low altitude, the margin to the low-speed buffet is:

  1. Unchanged, because indicated airspeed fixes the lift coefficient
  2. Increased, because the lower density reduces the lift coefficient required
  3. Reduced, because the stall speed in indicated terms increases with altitude
  4. Reduced, because the higher true airspeed requires a higher angle of attack and lift coefficient Correct answer.

Explanation

At a given indicated airspeed the lift coefficient is fixed, but in a manoeuvre or at high altitude the available margin to CLmax is reduced because the true airspeed and the angle of attack needed for a given load factor are higher. The low-speed buffet boundary is reached at a higher indicated airspeed as altitude rises.

Question 50Advanced Aerodynamics

A propeller is operating at constant rotational speed while the aeroplane accelerates in level flight. As forward speed increases, the angle of attack of the blade sections and the thrust produced respectively:

  1. Decrease and decrease Correct answer.
  2. Increase and increase
  3. Decrease and increase
  4. Increase and decrease

Explanation

The blade helix angle depends on forward speed and rotational speed. As forward speed rises at constant rpm, the relative airflow meets the blade at a smaller angle of attack, so the section lift and hence thrust decrease.