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CAA NZ CPL Theory - Principles of Flight & Aircraft Performance study materials
CAA NZ CPL Theory - Principles of Flight & Aircraft Performance study resources

CAA NZ CPL Theory - Principles of Flight & Aircraft Performance practice questions

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Question 1Principles of Flight

In straight-and-level flight at constant airspeed, the four forces acting on an aeroplane are in equilibrium. Which statement correctly describes this condition?

  1. Thrust exceeds drag to overcome induced drag at low speed
  2. Lift exceeds weight so that the aircraft maintains altitude
  3. Weight acts forward of lift, producing a nose-up pitching moment
  4. Lift equals weight and thrust equals drag, with no net force or moment acting on the aircraft Correct answer.

Explanation

In unaccelerated straight-and-level flight the sum of all forces and moments is zero, so lift balances weight and thrust balances drag. Any imbalance would produce acceleration or a flight-path change rather than steady flight.

Question 2Principles of Flight

An aeroplane is flying at a constant indicated airspeed while maintaining level flight. As fuel is burned and gross weight decreases, what happens to the angle of attack required?

  1. It increases because the wing must work harder
  2. It decreases only if the centre of gravity moves aft
  3. It stays the same because airspeed is unchanged
  4. It decreases because less lift is needed at the same speed Correct answer.

Explanation

Lift must equal weight in level flight, so a lighter aircraft needs less lift. Since lift depends on angle of attack at a given speed, the angle of attack required reduces as weight falls.

Question 3Principles of Flight

What is the primary reason a wing produces lift according to Newtonian principles?

  1. Air is compressed under the wing, creating a high-pressure cushion
  2. The wing deflects air downward, and the air exerts an equal and opposite upward reaction Correct answer.
  3. The upper surface is always longer than the lower surface
  4. The boundary layer separates at the trailing edge

Explanation

Newton's third law explains lift as the reaction to the downward momentum given to the air by the wing. This is consistent with the pressure difference described by Bernoulli's theorem; both describe the same physical effect.

Question 4Principles of Flight

For a given wing, what happens to the coefficient of lift as angle of attack increases from zero up to the critical angle?

  1. It increases approximately linearly until the critical angle is reached Correct answer.
  2. It increases only after the critical angle is exceeded
  3. It remains constant until the critical angle
  4. It decreases steadily as angle of attack rises

Explanation

Within the normal operating range the lift coefficient rises almost linearly with angle of attack. At the critical angle the flow separates and the lift coefficient reaches a maximum before dropping sharply.

Question 5Principles of Flight

An aircraft stalls at a higher indicated airspeed when it is heavily loaded. What is the underlying reason?

  1. Indicated airspeed under-reads when the aircraft is heavy
  2. Heavier aircraft always have a higher critical angle of attack
  3. The higher weight requires a greater lift coefficient, so the critical angle of attack is reached at a higher speed Correct answer.
  4. The wing's camber increases with weight

Explanation

Stall occurs at the critical angle of attack regardless of weight, but a heavier aircraft needs more lift and therefore a higher angle of attack at any given speed. It reaches the critical angle at a higher speed.

Question 6Principles of Flight

What effect does increasing the load factor have on the stall speed of an aircraft?

  1. Stall speed increases in direct proportion to the load factor
  2. Stall speed is unaffected by load factor
  3. Stall speed decreases because the wing is more heavily loaded
  4. Stall speed increases in proportion to the square root of the load factor Correct answer.

Explanation

Stall speed varies with the square root of the load factor, so doubling the load factor increases stall speed by about 41 percent. The critical angle of attack is unchanged, but more lift is needed at any speed.

Question 7Principles of Flight

During a level, coordinated turn, why must the aircraft bank?

  1. To tilt the lift vector so its horizontal component provides the centripetal force for the turn Correct answer.
  2. To increase the vertical component of lift above weight
  3. To move the centre of gravity laterally
  4. To reduce the angle of attack and so reduce drag

Explanation

In a turn the lift vector tilts, and its horizontal component supplies the centripetal force that curves the flight path. The vertical component must still balance weight, so total lift must increase.

Question 8Principles of Flight

In a level constant-altitude turn at 60 degrees of bank, the load factor is approximately:

  1. 1.0
  2. 1.15
  3. 2.0 Correct answer.
  4. 4.0

Explanation

Load factor in a level turn equals 1 divided by the cosine of the bank angle. The cosine of 60 degrees is 0.5, so the load factor is 2.0.

Question 9Principles of Flight

What causes a wing to stall?

  1. Flying at too high an altitude
  2. Exceeding the critical angle of attack Correct answer.
  3. Flying below a fixed airspeed
  4. Exceeding the never-exceed speed

Explanation

A stall is caused by the angle of attack exceeding the critical value, at which point the airflow separates from the upper surface. It can occur at any speed, altitude or attitude.

Question 10Principles of Flight

How does extending flaps affect the stall speed and the stall angle of attack of a wing?

  1. Both stall speed and stall angle of attack increase
  2. Stall speed increases and the stall angle of attack is increased
  3. Neither stall speed nor stall angle of attack changes
  4. Stall speed decreases and the stall angle of attack is generally reduced Correct answer.

Explanation

Flaps increase camber and hence the maximum lift coefficient, lowering the stall speed. However, the increased camber means the critical angle of attack is reached at a lower angle than for the clean wing.

Question 11Principles of Flight

What is the primary purpose of washout in wing design?

  1. To increase the dihedral effect at high speed
  2. To increase the maximum lift coefficient at the root
  3. To delay tip stall by giving the wingtip a lower angle of attack than the root Correct answer.
  4. To reduce the wing's induced drag at low speed

Explanation

Washout twists the wing so that the tip has a smaller angle of incidence than the root. The root therefore stalls first, preserving aileron effectiveness and reducing the tendency to drop a wingtip.

Question 12Principles of Flight

Which type of drag is most significant at low airspeed and high angle of attack?

  1. Interference drag
  2. Induced drag Correct answer.
  3. Form drag
  4. Parasite drag

Explanation

Induced drag arises from the generation of lift and increases as the square of the lift coefficient, so it dominates at low speed and high angle of attack. Parasite drag rises with the square of airspeed and dominates at high speed.

Question 13Principles of Flight

An aircraft is flying at the speed for minimum total drag. If it slows below this speed, what happens to total drag?

  1. Total drag continues to decrease because parasite drag falls
  2. Total drag increases because induced drag rises faster than parasite drag falls Correct answer.
  3. Total drag decreases until the stall speed is reached
  4. Total drag remains constant because lift equals weight

Explanation

At the minimum-drag speed induced drag equals parasite drag. Below this speed the angle of attack must rise, so induced drag increases faster than parasite drag reduces, and total drag rises.

Question 14Principles of Flight

What is the effect of ground effect on an aircraft shortly after take-off?

  1. The critical angle of attack is reduced
  2. Parasite drag increases and the aircraft accelerates more slowly
  3. The stall speed increases significantly
  4. Induced drag is reduced and the aircraft may appear to float above the runway Correct answer.

Explanation

Close to the ground the wingtip vortices are suppressed, reducing downwash and induced drag. Lift increases for a given angle of attack, so the aircraft may float and climb sluggishly after lift-off.

Question 15Principles of Flight

What is the purpose of dihedral in a wing?

  1. To increase longitudinal stability
  2. To reduce induced drag at high angles of attack
  3. To provide lateral stability by creating a restoring rolling moment after a sideslip Correct answer.
  4. To increase the rate of roll for a given aileron deflection

Explanation

With dihedral, a sideslip causes the lower wing to meet the airflow at a greater angle of attack than the higher wing. The resulting rolling moment tends to level the wings, providing lateral stability.

Question 16Principles of Flight

An aircraft with positive static longitudinal stability, if disturbed nose-up, will:

  1. Continue to pitch up until it stalls
  2. Maintain the new attitude without further change
  3. Develop a nose-down pitching moment tending to restore the original attitude Correct answer.
  4. Develop a nose-up moment that increases the disturbance

Explanation

Positive static stability means the aircraft generates a restoring moment opposing the disturbance. A nose-up disturbance produces a nose-down moment, tending to return it to trim.

Question 17Principles of Flight

Moving the centre of gravity aft toward the neutral point has what effect on longitudinal stability?

  1. The aircraft becomes more stable in yaw
  2. The stall speed decreases significantly
  3. Static stability increases and the aircraft becomes harder to pitch
  4. Static stability decreases and the aircraft becomes more easily disturbed in pitch Correct answer.

Explanation

As the CG moves aft toward the neutral point, the restoring moment from the tail reduces. Static stability decreases, control sensitivity increases and the aircraft becomes more prone to pitch upset.

Question 18Principles of Flight

What is the function of the horizontal tailplane in conventional aircraft?

  1. To provide a trimming and restoring pitching moment for longitudinal stability Correct answer.
  2. To provide lateral stability in sideslip
  3. To generate most of the aircraft's lift
  4. To counteract adverse yaw from the ailerons

Explanation

The tailplane produces a downward or upward force that balances the pitching moment of the wing and provides a restoring moment when the aircraft is disturbed in pitch.

Question 19Principles of Flight

What is adverse yaw?

  1. A pitch-up tendency when flaps are extended
  2. A yawing moment in the same direction as the turn caused by rudder input
  3. A yawing moment opposite to the intended turn caused by increased induced drag on the down-going aileron wing Correct answer.
  4. A tendency for the aircraft to yaw into wind during a crosswind landing

Explanation

When aileron is applied, the down-going aileron increases lift and induced drag on the rising wing. This drag pulls that wing back, yawing the nose away from the intended turn direction.

Question 20Principles of Flight

What is the purpose of a differential aileron system?

  1. To increase the total aileron deflection available
  2. To provide pitch trim
  3. To increase the roll rate at high speed
  4. To give the up-going aileron more deflection than the down-going one, reducing adverse yaw Correct answer.

Explanation

Differential ailerons deflect the up-going aileron more than the down-going one, reducing the induced drag on the rising wing. This reduces the adverse yaw produced during a roll.

Question 21Principles of Flight

During a steady climb at constant indicated airspeed, how does the thrust required compare with total drag?

  1. Thrust equals weight minus lift
  2. Thrust must equal drag plus the component of weight acting along the flight path Correct answer.
  3. Thrust is less than drag because lift is reduced
  4. Thrust equals drag only

Explanation

In a climb the thrust must overcome both drag and the rearward component of weight along the flight path. In a steady climb at constant speed, thrust equals drag plus that weight component.

Question 22Principles of Flight

What happens to the best angle of climb speed (Vx) and best rate of climb speed (Vy) as altitude increases?

  1. Vx decreases while Vy increases
  2. Vx and Vy remain constant at all altitudes
  3. Vx increases toward Vy, and both decrease in true airspeed Correct answer.
  4. Both Vx and Vy increase in indicated airspeed

Explanation

As altitude increases, excess power available falls, so Vy in true airspeed decreases. Vx increases toward Vy because the thrust available diminishes, reducing the benefit of climbing steeply, and the two converge at the absolute ceiling.

Question 23Principles of Flight

An aircraft is descending at a constant airspeed with the engine at idle. What is the relationship between thrust and drag in a steady glide?

  1. Thrust exceeds drag
  2. Drag and thrust are both zero
  3. Drag exceeds thrust, and the difference is balanced by the forward component of weight Correct answer.
  4. Thrust equals drag

Explanation

In a steady glide the forward component of weight along the flight path supplies most of the force balancing drag. With idle thrust, drag exceeds thrust and the weight component makes up the difference.

Question 24Principles of Flight

Which factor most increases the take-off ground roll distance?

  1. A lower aircraft weight and a headwind
  2. A headwind, a lower density altitude and a downhill slope
  3. A lower temperature and a higher pressure
  4. A tailwind, a higher density altitude and an uphill slope Correct answer.

Explanation

Tailwind reduces the airspeed relative to the ground, high density altitude reduces thrust and lift, and an uphill slope adds a rearward weight component. All three increase the ground roll.

Question 25Principles of Flight

What is the effect of a crosswind on the landing distance compared with a still-air landing?

  1. Landing distance decreases because crosswind increases lift
  2. Landing distance generally increases because the headwind component is reduced and directional control demands are higher Correct answer.
  3. Landing distance is unchanged because only the total wind speed matters
  4. Landing distance depends only on the runway surface

Explanation

Only the headwind component reduces landing distance, so a crosswind with little or no headwind component gives less deceleration benefit. The pilot must also manage drift and directional control, which can extend the landing roll.

Question 26Principles of Flight

In a steady, unaccelerated glide with the engine at idle, which statement correctly describes the force balance along and perpendicular to the flight path?

  1. Thrust equals drag and lift equals weight
  2. Lift equals weight and there is no force along the flight path
  3. Drag acts along the flight path in the direction of motion and is balanced by thrust
  4. Weight has a component along the path balanced by a component of drag, and lift balances the component of weight perpendicular to the path Correct answer.

Explanation

In a steady glide the aircraft is in equilibrium, so the forces must resolve to zero in both axes. The component of weight acting forward along the flight path is balanced by drag, while lift balances the component of weight perpendicular to the flight path. Because the flight path is inclined, lift is slightly less than the total weight.

Question 27Principles of Flight

An aircraft is in a steady level turn at 45 degrees of bank. What is the approximate load factor?

  1. 1.19
  2. 0.71
  3. 2.00
  4. 1.41 Correct answer.

Explanation

Load factor in a level turn is n = 1/cos(bank angle). For 45 degrees, cos 45 is about 0.707, so n is approximately 1.41. This means the wing must produce about 41 percent more lift than in level flight.

Question 28Principles of Flight

What is the primary reason an aircraft's induced drag decreases as it accelerates from just above the stall to a higher airspeed in level flight?

  1. The angle of attack increases, reducing the spanwise pressure differential
  2. Parasite drag coefficient decreases because the Reynolds number falls
  3. The coefficient of lift required falls, so the wing produces less lift-dependent drag Correct answer.
  4. The wingtip vortices become stronger and spread the lift over a wider span

Explanation

Induced drag depends on the square of the lift coefficient, and in level flight the lift coefficient must fall as airspeed rises. A lower lift coefficient means a smaller pressure differential and weaker tip vortices, so induced drag reduces. This is why induced drag dominates at low speed and high angle of attack.

Question 29Principles of Flight

What is the significance of the critical angle of attack?

  1. It is the angle at which parasite drag first exceeds induced drag
  2. It is the angle at which the wing produces maximum lift coefficient, beyond which the airflow separates and lift decreases Correct answer.
  3. It is the angle of attack at which the wing produces zero lift
  4. It is the angle at which the aircraft reaches its never-exceed speed

Explanation

The critical angle of attack is where the lift coefficient reaches its maximum. Exceeding it causes the airflow to separate from the upper surface, lift falls and the wing stalls. The stall angle is essentially fixed for a given wing, so a stall can occur at any airspeed if the critical angle is reached.

Question 30Principles of Flight

How does the boundary layer behave over the upper surface of a wing as the angle of attack approaches the stall?

  1. The adverse pressure gradient strengthens, causing the boundary layer to separate and lift to decrease Correct answer.
  2. It remains laminar and attached to the trailing edge
  3. The transition point moves forward and separation is delayed indefinitely
  4. The boundary layer becomes thinner, increasing the pressure differential

Explanation

As angle of attack rises, the adverse pressure gradient over the rear of the upper surface becomes stronger. The boundary layer eventually cannot overcome it and separates, causing a loss of lift and a large increase in pressure drag. This separation is the physical mechanism of the stall.

Question 31Principles of Flight

An aircraft at maximum take-off mass is compared with the same aircraft at a lighter mass. How do the speeds for best angle of climb and best rate of climb change with the heavier mass?

  1. Vx decreases and Vy increases
  2. Both Vx and Vy increase Correct answer.
  3. Both Vx and Vy decrease
  4. Vx increases and Vy decreases

Explanation

A heavier aircraft needs more excess thrust and excess power for the same climb performance. To achieve the best angle of climb, a higher speed is needed because excess thrust is the limiting factor, and the best rate of climb speed also increases because the aircraft must fly faster to generate the excess power required.

Question 32Principles of Flight

What is the effect of a headwind on the maximum range of an aircraft in a powered cruise?

  1. Range is reduced because the same air distance covers less ground distance Correct answer.
  2. Range is unchanged in still air but reduced only during climb
  3. Range is increased because the aircraft spends more time in the air
  4. Range is unaffected because range depends only on fuel flow

Explanation

Maximum range is a ground distance, so a headwind means each unit of air distance corresponds to less ground distance covered. Fuel is consumed per unit of air distance, so the headwind reduces the ground range achieved for a given fuel load. A tailwind has the opposite effect.

Question 33Principles of Flight

What is the effect of extending landing flaps on the approach speed and the approach angle?

  1. A higher approach speed is required and the approach path becomes shallower
  2. A lower approach speed is possible and the approach path becomes steeper for a given power setting Correct answer.
  3. A lower approach speed is possible and the approach path becomes shallower for a given power setting
  4. The approach speed is unchanged but the approach angle becomes steeper

Explanation

Flaps increase the maximum lift coefficient, so a lower approach speed is possible. They also increase drag, so for a given power setting the aircraft descends more steeply, allowing a steeper approach path. This combination is why flaps are used for landing.

Question 34Principles of Flight

What is the effect of a rearward movement of the centre of gravity on the elevator force required to hold a given angle of attack?

  1. The elevator force reverses direction immediately at the centre of gravity
  2. The elevator downforce required increases
  3. The elevator force is unchanged because it depends only on airspeed
  4. The elevator downforce required decreases and may become an upforce Correct answer.

Explanation

A rearward centre of gravity reduces the moment arm of the tailplane about the centre of gravity and reduces the nose-down pitching moment that must be trimmed out. The tailplane therefore needs less downforce, and if the centre of gravity moves behind the aerodynamic centre the tail may need to produce an upforce.

Question 35Principles of Flight

What happens to the static margin when the centre of gravity is moved forward?

  1. The static margin becomes negative and the aircraft becomes unstable
  2. The static margin increases and the aircraft becomes more stable but less manoeuvrable Correct answer.
  3. The static margin decreases and the aircraft becomes less stable
  4. The static margin is unchanged because it depends only on the tail volume

Explanation

Static margin is the distance between the centre of gravity and the neutral point expressed as a fraction of mean aerodynamic chord. Moving the centre of gravity forward increases this distance, giving greater longitudinal static stability at the cost of increased stick force and reduced manoeuvrability.

Question 36Principles of Flight

What is the purpose of a ventral fin or strake fitted below the rear fuselage of some aircraft?

  1. To provide additional lift during the take-off run
  2. To increase longitudinal stability at low airspeed
  3. To increase directional stability at high angles of attack and sideslip Correct answer.
  4. To reduce induced drag at high lift coefficients

Explanation

A ventral fin adds side area aft of the centre of gravity, increasing directional stability, particularly at high angles of attack where the vertical fin may be blanked by the fuselage. It helps resist sideslip and spin entry. It does not add meaningful lift or reduce induced drag.

Question 37Principles of Flight

In a spin, what is the relationship between the two wings?

  1. Both wings are unstalled and the aircraft is in a spiral dive
  2. One wing is stalled and the other is not, and the aircraft is rotating only in yaw
  3. Both wings are fully stalled and the aircraft is rotating about all three axes Correct answer.
  4. One wing is stalled and the aircraft is rotating only in pitch

Explanation

A spin is an aggravated stall in which both wings are stalled but one is more deeply stalled than the other, producing autorotation. The aircraft rotates about all three axes, predominantly in yaw and roll, while descending. This distinguishes a spin from a spiral dive, in which the wings are not stalled.

Question 38Principles of Flight

What is the effect of a forward slip on the aircraft's flight path?

  1. The aircraft maintains its heading while the nose is yawed away from the flight path to increase drag Correct answer.
  2. The aircraft tracks along its longitudinal axis while the nose is pointed into wind
  3. The aircraft increases its airspeed while descending vertically
  4. The aircraft reduces its rate of descent by pointing the nose into wind

Explanation

In a forward slip the aircraft is banked one way and yawed the other, so the nose points away from the flight path. This presents the fuselage side to the relative airflow, increasing drag and allowing a steeper descent without an increase in airspeed. It is used for losing height on approach.

Question 39Principles of Flight

What is the cause of the downwash behind a wing, and what is its effect on the effective angle of attack?

  1. Downwash is caused by engine slipstream and has no effect on the effective angle of attack
  2. Downwash is caused by the tailplane and reduces the effective angle of attack
  3. Downwash is caused by tip vortices and reduces the effective angle of attack Correct answer.
  4. Downwash is caused by the fuselage and increases the effective angle of attack

Explanation

The pressure differential between the lower and upper surfaces produces tip vortices and a downward velocity component behind the wing. This downwash tilts the relative airflow downward at the wing, reducing the effective angle of attack and creating induced drag.

Question 40Principles of Flight

What is the effect of increasing aspect ratio on induced drag for the same lift coefficient and wing area?

  1. Induced drag is unchanged because it depends only on lift coefficient
  2. Induced drag decreases because the tip vortices are spread over a larger span Correct answer.
  3. Induced drag increases in proportion to aspect ratio
  4. Induced drag decreases because parasite drag increases

Explanation

Induced drag is inversely proportional to aspect ratio for a given lift coefficient and wing area. A higher aspect ratio spreads the same lift over a longer span, weakening the tip vortices and reducing the downwash angle. This is why gliders use long, slender wings.

Question 41Principles of Flight

What is the effect of extending leading-edge slats on the stall angle of attack and the maximum lift coefficient?

  1. Both the stall angle and the maximum lift coefficient increase Correct answer.
  2. The stall angle increases but the maximum lift coefficient decreases
  3. The stall angle decreases and the maximum lift coefficient increases
  4. Both the stall angle and the maximum lift coefficient decrease

Explanation

Leading-edge slats re-energise the boundary layer over the upper surface, delaying separation to a higher angle of attack. This raises both the stall angle and the maximum lift coefficient, which is why slats are used on aircraft that need high lift at low speed.

Question 42Principles of Flight

What is the effect of deploying a speed brake on the glide performance of an aircraft?

  1. The glide angle becomes shallower and the glide range increases
  2. The glide angle becomes steeper and the glide range decreases Correct answer.
  3. The glide angle is unchanged but the glide speed increases
  4. The glide angle becomes steeper but the glide range is unchanged

Explanation

A speed brake adds parasite drag, which increases the total drag for any given lift coefficient. In a glide this steepens the glide angle and reduces the glide range, which is why speed brakes are used on approach to lose height without increasing airspeed.

Question 43Principles of Flight

What is the effect of an increase in air density on the true airspeed required to achieve a given indicated airspeed?

  1. True airspeed is lower than indicated airspeed at high altitude
  2. True airspeed is higher than indicated airspeed at high altitude Correct answer.
  3. True airspeed equals indicated airspeed at all altitudes
  4. True airspeed is unaffected by density and depends only on temperature

Explanation

Indicated airspeed depends on dynamic pressure, which is a function of density and true airspeed squared. At high altitude, where density is lower, a higher true airspeed is needed to produce the same dynamic pressure and therefore the same indicated airspeed. This is why true airspeed exceeds indicated airspeed at altitude.

Question 44Principles of Flight

What is the effect of a tailwind on the take-off ground roll compared with a still-air take-off?

  1. The ground roll is unchanged because lift depends only on airspeed
  2. The ground roll is longer because the aircraft must accelerate to a higher ground speed for the same airspeed Correct answer.
  3. The ground roll is shorter because the aircraft reaches lift-off speed sooner
  4. The ground roll is shorter because the tailwind increases lift

Explanation

Lift-off depends on airspeed, which is measured relative to the air mass. With a tailwind the aircraft must reach a higher ground speed to achieve the same airspeed, so it accelerates for longer and the ground roll increases. A headwind has the opposite effect.

Question 45Principles of Flight

What is the effect of a lower air density on the power required for a given true airspeed in level flight?

  1. Power required decreases because the propeller becomes more efficient
  2. Power required is unchanged because lift and weight are unchanged
  3. Power required increases because the engine produces less power and the aircraft needs a higher true airspeed for the same lift Correct answer.
  4. Power required decreases because drag decreases

Explanation

In lower density the engine and propeller produce less power, and the aircraft must fly at a higher true airspeed to generate the same lift at a given angle of attack. Both effects increase the power required for a given true airspeed, which is why climb and take-off performance degrade at altitude.

Question 46Principles of Flight

What is the significance of the manoeuvring speed, Va?

  1. It is the speed at which the aircraft achieves its best rate of climb
  2. It is the speed at which the aircraft reaches its never-exceed speed
  3. It is the speed above which the aircraft can be stalled without exceeding the limit load factor
  4. It is the speed below which full control deflection will not overstress the airframe Correct answer.

Explanation

At or below the manoeuvring speed the wing stalls before the limit load factor is reached, even with full control deflection. This protects the structure from overstress. Above Va, a full deflection could produce a load factor greater than the limit before the stall occurs.

Question 47Principles of Flight

What is the effect of a reduction in air density on the true airspeed at which the aircraft stalls?

  1. The true airspeed at which the aircraft stalls depends only on the aircraft mass
  2. The true airspeed at which the aircraft stalls is unchanged
  3. The true airspeed at which the aircraft stalls decreases
  4. The true airspeed at which the aircraft stalls increases Correct answer.

Explanation

The stall occurs at a fixed angle of attack and therefore a fixed lift coefficient. Because lift depends on density and the square of true airspeed, a lower density requires a higher true airspeed to produce the same lift. The indicated stall speed stays roughly constant, but the true stall speed rises with altitude.

Question 48Principles of Flight

What is the effect of ground effect on induced drag and on the power required to maintain level flight?

  1. Induced drag decreases and the power required decreases Correct answer.
  2. Induced drag increases and the power required increases
  3. Induced drag is unchanged and the power required decreases
  4. Induced drag decreases and the power required increases

Explanation

Close to the ground the vertical component of the airflow around the wing is restricted, reducing downwash and tip vortex strength. This lowers induced drag, so less thrust and power are needed to maintain level flight, which is why the aircraft tends to float during the landing flare.

Question 49Principles of Flight

What is the effect of a rearward movement of the centre of gravity on the spin recovery characteristics of an aircraft?

  1. Spin recovery becomes more difficult and the spin may flatten Correct answer.
  2. Spin recovery is unaffected because the centre of gravity affects only longitudinal stability
  3. Spin recovery becomes easier because the aircraft becomes less stable
  4. Spin recovery becomes easier because the tailplane is more effective

Explanation

A rearward centre of gravity reduces the moment arm of the tailplane and reduces longitudinal stability, making the aircraft more prone to a deep stall and flattening the spin. Recovery becomes more difficult because the antispin moment available from the tailplane is reduced.

Question 50Principles of Flight

What is the effect of a constant-speed propeller in coarse pitch on the thrust produced at low airspeed compared with fine pitch?

  1. Both pitches produce the same thrust at low airspeed
  2. Fine pitch produces more thrust at low airspeed Correct answer.
  3. Coarse pitch produces more thrust at low airspeed
  4. Coarse pitch produces more thrust at all airspeeds

Explanation

Fine pitch presents a smaller blade angle, allowing the engine to develop high rpm and producing high thrust at low airspeed, which is desirable for take-off. Coarse pitch is more efficient at high airspeed and cruise, where a larger blade angle matches the higher forward speed.