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Tech Exam > POF > Flashcards

POF Flashcards

1
Q
  1. What effect does a forward C of G have on stability, control effectiveness and climb performance?
A

a. Increased stability, worse RoC

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2
Q
  1. What impact does a forward CoG have on your aircraft?
A

a. Note: Forwards CoG means the tail will be producing a downwards force, acting in the same direction as weight. This means more lift is required to overcome the combine weight and tail force down vectors, which is achieved by increasing the AoA. With an increased AoA, you create more induced drag. This will increase fuel burn, and decrease climb performance.
Decrease ROC

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3
Q
  1. What is the effect of a fwd centre of gravity on RoC?
A

c. Decreased ROC

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4
Q
  1. CoG and how does it affect stall speed and its stability?
A

a. Aft CoG has increase in VS
An aft CoG will make the stall more difficult to recover from (decrease in stability).

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5
Q
  1. Factors affecting stall speed?
A

a. WILPSC

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6
Q
  1. A shock stall is the result of
A

a. The boundary layer behind the shock wave becoming turbulent and separating, spilling rearwards and striking the tail plane, creating buffet and rearward CP movement. Rear movement of the CP causes nose pitch down

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7
Q
  1. An Aft / forward C of G has what effect on the stall speed
A

a. Aft decreases the stall speed and forward increases the stall speed

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8
Q
  1. How does VMCA vary with C of G?
A

a. As the C of G moves forward, the arm to the rudder increases, increasing its effectiveness. The opposite occurs as the C of G moves rearward.
Therefore:
i. A forward C of G decreases Vmca
ii. An aft C of G increases Vmca

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9
Q
  1. Principal purpose of flaps
A

a. To increase lift at the same angle of attack and airspeed

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10
Q
  1. What is the effect of extending flap on glide angle and range?
A

a. Increases glide angle, decrease range

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11
Q
  1. Effect on flap on take-off weight and climb out weight
A

b. increase take-off weight on roll, decrease max weight on climb

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12
Q
  1. Effect on weight on Vx and cruise climb
A

a. Decrease in both

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13
Q
  1. With a headwind what happens to best AOC and ROC?
A

a. RoC will remain constant. AoC will increase.

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14
Q
  1. What happens to max range speed and Vx speed with a headwind?
A

b. Max range speed increase, Vx speed remain the same

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15
Q
  1. Do heavier aircraft have a steeper/shallower descent angle?
A

a. Shallower (is it something to do with TOD starting earlier so it will be shallower?)

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16
Q

What happens to best range speed and best angle of climb speed when flying into a headwind

A

Best range speed increase
Best Angle of Climb remains constant

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17
Q

As fuel is burnt during the cruise what affect will this have on available range speed?

A

Available speed range is increased

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18
Q

What happens to range/fuel consumption going from best range to Long range cruise?

A

a. Range increases and fuel consumption decreases as flight time is quicker due to 4% increase in speed and thus less fuel burnt less

(Long Range Cruise speed is generally about 4% faster than best range speed but has about 99% of the range for a given fuel) So flying slightly faster we get to destination quicker, less time exposed to penalty headwind and thus have more fuel to use and hence range increases. Ie; Faster for minimal fuel penalty. The reduction in the time you are exposed to the headwind, actually means that it offsets the 1% increase in fuel burn with a reduction in the amount of time in the air.

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19
Q
  1. What is the effect of flying below optimum altitude on time taken and fuel burn?
A

a. Take more time, and burn more fuel.

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20
Q

What is the formula for Gross Fuel Flow

A

GFF=Fuelflow/Groundspeed
=(kg/hr)/(nm/hr)
=kg/nm

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21
Q

What does it mean to fly for best endurance? How do we achieve this?

A

Flying for maximum amount of time for a given amount of fuel.

To use the least amount of fuel we need to use the least amount of thrust therefore we must fly at the speed for MIN DRAG. This is found at the bottom of the TOTAL DRAG vs IAS curve

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22
Q

What is the definition of range, and how do we achieve it? Factors affecting it?

A

For maximum range we need to cover the maximum distance for a given amount of fuel.

Looking at the Total Drag Curve vs IAS, best range is found at a tangent

At this speed it is the least amount of power for the a/c to achieve the highest TAS this also equates to min drag and max lift/drag ratio.

Increase in weight requires in increase in speed for a constant angle of attack
Increase in headwind results increase in mach no. Aircraft will then be subjected to the headwind for a shorter period of time.

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23
Q
  1. If you were loading an airplane to obtain max range, would you load it with a forward or aft CoG?
A

a. It would be best to load it with an aft C of G as this would require an upward force from the tailplane (or less of a downward force required from the tailplane) which acts in the same direction as lift and hence opposes some of the aircraft’s weight. Less lift from the mainplane means less drag therefore less thrust is required, less thrust means reduced fuel flow and hence more range can be obtained for the amount of fuel on board.

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24
Q
  1. Range vs Endurance
A

a. Speed for max endurance will always be lower than speed for max range

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25
Q
  1. What sort of C of G changes occur on long flights?
A

a. For a swept wing aircraft, as fuel is burnt off, the C of G moves forward. A consequence of a forward C of G is that the tailplane must then produce a compensating downwards balancing force which effectively increases the weight to be supported by the wing resulting in a higher stall speed at a constant weight.
An aft C of G is the best for fuel consumption as there is less downward push applied to the tailplane, effectively reducing weight, resulting in a lower stall speed.
A forward C of G is the most stable-stability of the aircraft is increased and the static and manoeuvre margins are large.

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26
Q

What happens to the “cruise speed” as you burn fuel?

A

a. Cruise speed reduces with gross weight due to fuel burn – less weight requires less lift resulting in less drag, therefore thrust can be reduced

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27
Q
  1. What happens to SFC as altitude is gained
A

a. It decreases

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28
Q
  1. What effect happens if the aircraft is flown past the optimum flight level
A

a. SFC increases as excessive drag results from an increased AoA which is required to create enough lift to support the aircraft

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29
Q
  1. Optimum altitude is a function of
A

a. SFC and TAS

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30
Q
  1. Does temperature affect optimum flight level
A

a. No as it has an equal effect on fuel flow and TAS

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31
Q
  1. Specific air range formula is
A

SAR=(FF (Fuel Flow))/TAS

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32
Q
  1. Long range cruise is
A

a. Flight at an optimum flight level, the airspeed is slightly higher than that at max range cruise as it is proportional to A/C weight. The range is reduced by 1 – 2 % of the max range cruise.

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33
Q
  1. What provides stability about the lateral axis?
A

a. Tailplane

34
Q
  1. What does dihedral do?
A

a. Increase lateral stability

35
Q
  1. What are the advantages of sweptback wings in terms of MCRIT and stability
A

a. Increase MCRIT, increase lateral stability in roll due change in aspect ratio of down going wing. Higher economical cruise speed

36
Q
  1. Disadvantages of sweepback
A

a. Lower Cl
Extensive use of high lift devices
High drag @ high AOA
Use of vortex generators, wing fences to reduce wingtip ‘pooling’

37
Q
  1. A swept wing aircraft pitches up / down at a stall
A

a. A nose pitch up results from the wing tips stalling first moving the CP inwards and forwards (wash out is used to try and prevent tip stalls)

38
Q
  1. What happens to the center of pressure in a stall in a swept wing aircraft
A

a. Tips will stall first so CP moves inward and forwards & nose tends to pitch up

39
Q
  1. During a turn what happens to the CP of a swept wing Aircraft
A

a. As the wing gets higher in a turn the outer portion become higher than the inner portion which creates its own form of washout resulting in a lower AOA and causing the CP to move inwards and pitch the nose upwards.

40
Q
  1. Dihedral is
A

a. The upward inclination of the wing to the lateral axis to provide lateral (roll) stability

41
Q
  1. Anhedral is
A

a. Negative dihedral – usually with high mounted swept wings to combat dynamic instability (dutch roll)

42
Q
  1. Define Mcrit
A

a. The critical Mach Number (Mcr or Mcrit) of an aircraft is the lowest Mach number at which the airflow over any part of the aircraft reaches the speed of sound, the aircraft itself has an airspeed lower then Mach 1.0.

43
Q
  1. How does weight affect MCRIT?
A

a. An increase in weight will reduce MCRIT.

44
Q
  1. Nose up pitch at the stall on a swept wing aircraft is caused by what?
A

a. Wingtip stalling first and there is more inboard lift moving the CoP moving inwards and forwards.

45
Q
  1. How does a Yaw Damper work?
A

a. It is a gyro system that is sensitive to changes in yaw which feeds a signal into the rudder controls so that rudder is applied to oppose the yaw.

46
Q
  1. How is stability affected by high speed, high altitude flight?
A

Aerodynamic damping is reduced at high altitude. There is less restoring force when a displacement happens.

Directional control can be affected. If right rudder is applied it can accelerate the left wing to it’s critical mach number which thus loses lift and has increased drag so the aircraft yaws to the left and rolls left. This means that spiral stability is increased. The aircraft won’t enter a spiral dive.

Lateral control can be affected as normally the outboard ailerons are locked due to wing twist that they cause leading to an aileron reversal. Thus only the inboard ailerons are available and possibly the differential spoilers. Oscillatory stability is reduced due to less roll control.

Longitudinal stability is reduced.

47
Q
  1. What is Mach Tuck?
A

a. Is a nose down pitching tendency due to a change in the position of the COP resulting from a rearward movement of the shock wave which occurs as an aircraft in transonic flight accelerates beyond its limiting mach number (Mmo).

48
Q
  1. Mach tuck
A

a. Is when the aircraft is accelerated through the transonic range causing the CP to move rearwards and increasing the lift generated by the tail plane due to modified airflow from the wing causing a nose pitch down.

49
Q
  1. If Mach tuck is not corrected the result will be
A

a. The nose pitch down causes further speed increase which causes further movement rearwards of the CP which causes further nose pitch down…..etc

50
Q
  1. How do designers increase the Critical Mach Number of an aircraft?
A

Swept Wing
Thinner wing

51
Q
  1. Oscillatory instability is
A

a. A combined yawing and rolling movement

52
Q
  1. Dutch roll is
A

a. Oscillatory instability when the rolling motion is predominant

53
Q
  1. Dutch roll is a result of
A

a. A yaw to the left or right which makes the outside wing speed up producing more lift resulting in a roll, after which because of the greater exposed area of the faster wing it has a higher drag component therefore causes a yaw in the opposite direction, resulting in a roll in the direction of the yaw

54
Q
  1. A stabilizing device to prevent Dutch roll is
A

a. A yaw damper (gyroscopically operated stabilisers)

55
Q
  1. Snaking is
A

a. Oscillatory instability when the yawing motion is predominant

56
Q
  1. Oscillatory instability is worse when
A

a. At high altitudes
sweep back a/c @ low IAS

57
Q
  1. Purpose of winglet
A

a. Reduced induced drag

58
Q
  1. When is total drag a minimum?
A

d. When parasite drag and induced drag are equal

59
Q
  1. What causes induced drag?
A

b. Wingtip vortices

60
Q
  1. What is ground effect?
A

a. The cushioning effect when flying close to the ground, due to reduced wingtip vortices

61
Q
  1. Wave drag is
A

a. The separation of the airflow behind the shock wave

62
Q
  1. Wash out is
A

a. A decrease in incidence from root to tip – to prevent wing tip stall

63
Q
  1. What devices are used to prevent wing tip stall (spanwise flow)
A

a. Wing fence
Saw tooth leading edge
Vortex generators

64
Q
  1. Area Rule
A

a. This is a design function to ‘blend’ areas where wings, tail, join the fuselage to minimise the increasing and decreasing cross section, minimizing the amount of drag formed by shockwaves

65
Q
  1. When are inboard ailerons used?
A

a. High speed

66
Q
  1. What are differential ailerons?
A

a. The upwards deflecting ailerons deflects further into the airflow, increasing profile drag to help reduce adverse yaw

67
Q
  1. In an aircraft with spoilers for roll control, to roll the aircraft right
A

a. Right spoilers deploy, right aileron goes up

68
Q
  1. To counter a nose heavy aircraft with a variable incidence tail plane you should
A

c. Increase incidence by raising leading edge

69
Q
  1. What is the reason for using a variable incidence tail plane
A

a. To counteract large trim changes through use of fuel and large speed changes allowing the elevator to remain fully effective under all conditions of longitudinal trim
Less drag at high speed
Provides control when a shockwave forms on the tail plane

70
Q
  1. Benefit of an all moving tailplane?
A

a. Less trim drag, full range of elevator movement

71
Q
  1. Aileron size is limited by?
A

a. Flap size

72
Q
  1. What are the functions of spoilers
A

a. Lift dumping in flight – increase the rate of descent
Speed brakes in flight – to quickly decrease speed in flight
Ground spoilers to destroy lift – to achieve shorter landing distances
Assist lateral (roll) control - allows smaller aileron size, avoids aileron reversal
Direct lift control

73
Q
  1. What is Direct Lift Control?
A

a. Use of aerodynamic surfaces (spoilers) to provide control of rate of descent without need to change body angle on approach

74
Q
  1. Differential spoilers provide
A

a. Roll control when flight spoilers are in use and aileron input is given

75
Q
  1. What are the limitations of spoilers?
A

a. At high speed spoilers can blow back

76
Q
  1. Power assisted controls provide what
A

a. Pilot force which is assisted by power units which inturn provides “Feel”

77
Q
  1. Power operated controls provide what
A

a. Provide all the force necessary to operate a control surface, control column feel is provided artificially

78
Q
  1. ‘Q’ feel is
A

a. An artificial method of providing the pilot with control column loading using either springs or hydraulics which provide variable loading proportional to airspeed

79
Q
  1. Large aircraft are usually fitted with what type of flap
A

a. Slotted fowler (moves down and rearwards)

80
Q
  1. When does aileron droop occur
A

a. When flaps are extended (usually the inboard ailerons)

Tech Exam (8 decks)

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