ATPL(A) 081 Principles of FlightRevision notes and practice questions

081 Principles of FlightFree sample, 10 questions

1. 1As an aircraft climbs out of ground effect after lift-off, the wing tip vortices (1) ______ and the induced angle of attack (2) ______.

   1. (1) decrease; (2) decrease
   2. (1) increase; (2) increase
   3. (1) increase; (2) decrease
   4. (1) decrease; (2) increase
   Show the answer

   Answer B. Close to the runway, the ground blocks the full development of the tip vortices and of the downwash behind the wing. Once the aircraft climbs away, that restriction disappears: the vortices grow, the downwash increases and the induced angle of attack increases with it. Induced drag rises, and a higher angle of attack is needed to keep the same lift. The two quantities always change in the same direction.

2. 2A large turbojet aeroplane is flying at its optimum altitude and the crew aim for the most efficient flight performance. If the speed were increased slightly above the critical Mach number, the lift coefficient would (1) ____, requiring a/an (2) ____ in the angle of attack.

   1. (1) increase;
      (2) decrease
   2. (1) decrease;
      (2) decrease
   3. (1) decrease;
      (2) increase
   4. (1) increase;
      (2) increase
   Show the answer

   Answer A. Just above the critical Mach number the lift curve becomes steeper: compressibility increases the lift coefficient obtained at a given angle of attack, as the flow over the upper surface accelerates to supersonic speed ahead of the shock. The lift required is unchanged, so the angle of attack must be reduced to keep the lift coefficient at the value the flight needs.

3. 3An aeroplane has a stall speed of 100 kt. At what speed will it stall in a level, co-ordinated turn with a load factor of 1.5?

   1. 141 kt.
   2. 82 kt.
   3. 122 kt.
   4. 150 kt.
   Show the answer

   Answer C. The stall speed increases with the square root of the load factor. In a co-ordinated turn at a load factor of 1.5, the aeroplane stalls at 100 × √1.5 = 100 × 1.225 = 122 kt. Multiplying by the load factor itself (150 kt) or by √2 (141 kt) are the classic mistakes.

4. 4Flying a multi-engine aeroplane with the flaps down, you suffer a failure of the right engine. Which way will the aeroplane roll, and how do the flaps affect it?

   1. Right roll, flaps reduce roll
   2. Left roll, flaps increase roll
   3. Right roll, flaps increase roll
   4. Left roll, flaps reduce roll
   Show the answer

   Answer C. When the right engine fails the aircraft yaws right, the left wing moves faster and gains lift, and the right wing loses the lift from its propeller slipstream, so the aircraft rolls right. With flaps down, a larger share of the lift comes from the slipstream over the flapped sections, so the lift difference between the wings, and the roll, is greater. The roll is always towards the dead engine, never away from it.

5. 5During a go-around, the crew forget to retract the trailing-edge flaps. What could be the consequence?

   1. Degraded climb performance and possible Vfe exceedance.
   2. An increased rate of climb and a reduced angle of climb.
   3. Decreases rate of climb and increases angle of climb.
   4. Increase of climb performance and decrease angle of climb.
   Show the answer

   Answer A. Flaps left at the landing setting keep their high drag, so both the climb gradient and the rate of climb are poorer than planned. As the aircraft accelerates in the climb, the speed can also reach the flap limit speed VFE for that setting, with a risk of structural damage. Flaps at go-around never improve climb performance, which rules out every other option.

6. 6Which flight control loses the most effectiveness once MCRIT is exceeded?

   1. Spoilers
   2. Elevator
   3. Flaps
   4. Ailerons
   Show the answer

   Answer D. Above MCRIT, shock waves form on the upper surface of the wing. The ailerons sit at the wing trailing edge, behind the shock, where the flow can separate; deflecting them also moves the shock, so their effectiveness drops sharply and aileron buzz can occur. The tail surfaces are thinner and have a higher critical Mach number, so the elevator and rudder are less affected, and flaps are not used at high speed.

7. 7A jet aeroplane cruising close to its maximum altitude suffers an engine failure. While the pilots concentrate on the checklist, they do not notice that the speed is decreasing. Buffet develops and eventually becomes strong enough to act as a deterrent. This means that the aircraft is...

   1. stalled.
   2. becoming over-stressed.
   3. below VMC.
   4. speed unstable.
   Show the answer

   Answer A. As the speed decreases the angle of attack rises and, at high altitude, the low-speed buffet appears early because of compressibility effects. Under the certification definition, buffet strong enough to deter the pilot from slowing further is treated as the stall, even if the classic critical angle of attack has not been reached. VMC concerns directional control at low speed near the ground, not buffet at cruise altitude.

8. 8An aircraft is flying a 3° approach path with the engines at idle. Using the data below, calculate the drag.
   Weight: 650 000 N
   Thrust: 30 000 N

   1. 4 000 N
   2. 150 000 N
   3. 34 000 N
   4. 64 000 N
   Show the answer

   Answer D. On a 3° descent a component of the weight acts forward along the flight path: 650 000 × sin 3° = 650 000 × 0.0523 = 34 000 N. In a steady descent the drag balances that component plus the thrust: D = 30 000 + 34 000 = 64 000 N. Taking only the weight component (34 000 N) forgets the thrust, and subtracting the thrust gives 4 000 N.

9. 9Skin friction drag is caused by the...

   1. air's viscosity producing shear forces within the boundary layer.
   2. loss of momentum within an airflow caused by the aerofoil changing the flow direction.
   3. friction between the surface and the air molecules in direct contact with the surface.
   4. difference in pressure acting on the aerofoil's surface in the direction of flight.
   Show the answer

   Answer A. Skin friction drag comes from the viscosity of the air: the layer touching the surface is brought to rest, and shear between adjacent layers moving at different speeds inside the boundary layer produces a force on the surface along the flow. The tempting answer is wrong because the air in contact with the skin does not slide over it at all. A turbulent boundary layer produces more skin friction than a laminar one.

10. 10(1) ____ the mass of an aircraft will lead to a/an (2) ____ in MCRIT.

    1. (1) Decreasing;
       (2) decrease
    2. (1) Increasing;
       (2) no change
    3. (1) Increasing;
       (2) increase
    4. (1) Increasing;
       (2) decrease
    Show the answer

    Answer D. A heavier aircraft needs a higher lift coefficient at a given speed and altitude, which means a higher angle of attack and a faster flow over the upper surface. The local flow reaches the speed of sound at a lower flight Mach number, so the critical Mach number decreases with increasing mass.