Tech Questions 3

  1. q26
    • State the critical engine on a jet during take off?
    • Nil in head wind
    • The most upwind engine in crosswind due to increased yaw if engine fails (weather cocking).
    • In the cruise the outboard engines of a 4 engine aircraft are critical.
    • Beech 1900d Left engine
    • q27
    • What effect does a balanced field have on take off performance?
    • A balanced field means that it is critical that an abort is carried out immediately on engine failure recognition.
    • Also that the take off on one engine could be marginal if continued as a balance field is a take off right on performance limits for the given aircraft weight - not favourable.
    • q28
    • Definition of second segment of take off path?
    • From gear retraction to level acceleration altitude, which is normally a minimum of 400 ft above take off surface. In this segment the gear is retracted, the flaps are in take off position and the aircraft is set in take off power. The speed is equal to V2 (initial climb out speed) and the required minimum gross gradient of climb, in a two engined aircraft, is 2.4%. The net flight path gradient is the gross flight path gradient reduced by 0.8%, i.e 1.6%.
    • Conditions are
    • Landing gear is retracted
    • Flaps are still in take off position
    • Speed is V2
    • The minimum gross climb gradient in a twin engined aircraft is 2.4%
    • The minimum net climb gradient in a twin engined aircraft is 1.6% and
    • take off power is still set.
    • q29
    • Definition if ISA
    • 1013.25 hPa (29.92"hg)
    • 15 degrees Celcius
    • Lapse rate is 1.98 degrees celcius per 1000' up to 36,090' then -56.5 degrees celcius
    • Density is 1.225 kg/m3
    • q30
    • Temperature at 39,000ft?
    • -56.5 degrees celcius
    • q31
    • Aircraft maintains a constant IAS in climb, what happens to TAS & LSS & Mach?
    • Constant IAS
    • TAS will increase
    • LSS will decrease
    • Mach will increase
    • q32
    • How does temperature affect the speed of sound?
    • The speed of sound is directly proportional to the square root of the absolute temperature (the speed of sound will increase with an increase in temperature)
    • LSS =38.94^K
    • At sea level ISA LSS=661kts
    • At 35,000' ISA LSS=575kts
    • q33
    • Airspeed in a climb at a constant TAS/IAS/Mach No. What do each other do?
    • Constant IAS = Both TAS & Mach No INCREASE
    • Constant Mach No = Both IAS & TAS DECREASE
    • Constant TAS = Mach No INCREASE, IAS DECREASE
    • q34
    • Cruise Mach No is more limiting when?
    • In warm temperatures
    • The higher the aircraft flies
    • *When Mach number is reduced (high altitudes) and when TAS is reduced (warm temperatures)*
  2. Mach No = TAS
  3. q35
    • What happens to the speed of sound with altitude / temperature?
    • LSS reduces with altitude and with cooling temperatures
    • q36
    • Formula for True Altitude?
    • TA = Actual temp (K) x Indicated altitude
    • . ISA temperature (K)
  4. True altitude is your actual altitude above mean sea level, no errors.
  5. Absolute altitude is your height above ground.
  6. q37
    • Formula for Mach No?
    • M = TAS / LSS
    • q38
    • Explain airspeed errors?
    • IAS - Position error - CAS - Compressibility error - EAS - Density error - TAS
    • q39
    • What errors does a Mach meter NOT suffer from?
    • Density error and compressibility error
    • q40
    • The two capsules in a Mach meter are what?
    • Airspeed
    • Altitude calibration
    • q41
    • Mfs is...
    • Free stream Mach Number - airflow unaffected by the aircraft
    • q42
    • Ml is...
    • Local Mach number - is the speed of air relative to the local speed of sound measured at a point on the aircraft.
    • q43
    • Mcrit is...
    • The lowest free stream Mach number at which Mach 1 is reached on any part of the aircraft.
    • MCRIT is the critical Mach number. This is the speed at which the airflow over certain parts of the airframe (most likely the point of maximum camber of the aerofoil) reaches M1.0. MCRIT is increased through slimness and through the use of sweepback.
    • q44
    • How does weight affect Mcrit?
    • An increase in weight will reduce Mcrit
  7. Vortex generators (re-energise the flow)
    • q57
    • What happens to the center of pressure in a stall in a swept wing aircraft?
    • Tips will stall first so CP moves inward and forwards & nose tends to pitch up
    • q58
    • During a turn what happens to the CP of a swept wing aircraft?
    • 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.
    • Downgoing wing has a relative airflow more from below, upgoing wing has a relative airflow more from above.
    • q59
    • Dihedral is...
    • The upward inclination of the wing to the lateral axis to provide lateral (roll) stability
    • q60
    • Anhedral is...
    • Negative dihedral – usually with high mounted swept wings to combat dynamic instability (dutch roll)
    • q61
    • Area Rule
    • 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. The area of cross section should increase gradually to a maximum, then decrease gradually. Giving more streamline shape. Max cross-section area should be approx half-way.
    • q62
    • Formula for Aspect Ratio is...
    • AR = Span (width) / Chord (length)
    • q63
    • High Aspect ratio (subsonic speeds) gives...
    • Better lift
    • Better lift/drag ratio
    • Less induced drag due reduced wing tip vortices
    • q64
    • What is Mach tuck?
    • 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.
    • q65
    • What happens if Mach tuck is not corrected?
    • The nose pitch down causes further speed increase which causes further movement rearwards of the CP which causes further nose pitch down…..etc
    • q66
    • Oscillatory instability is...
    • A combined yawing and rolling movement
    • q67
    • What is dutch roll and what causes it?
    • It is oscillatory instability when the rolling motion is predominant and,
    • It is 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.
    • A yaw damper is a gyro system sensitive to changes in yaw which feeds a signal into the rudder which then applies rudder to oppose the yaw. With this device, a Dutch roll will not develop because the yaw which triggers it all off is not allowed to develop. It applies the rudder in the correct direction and in the correct amount, thus preventing the slip starting or building up and stopping all rolling tendency Apart from the swept wing, the basic cause of Dutch rolling tendency is lack of effective fin and rudder area.
    • q68
    • What is a stabilising device to prevent dutch roll?
    • Yaw Damper
    • q69
    • What is snaking?
    • Oscillatory instability when the yawing motion is predominant
    • q70
    • Oscillatory instability is worse when...
    • At high altitudes
    • On sweepback aircraft at low IAS
  8. High altitude = High angle of attack = High dihedral effect = High chance of dutch roll.
  9. Approach at slow speeds = High angle of attack = High dihedral effect = High chance of dutch roll.
  10. q71
    • The aircrafts aerodynamic ceiling is...
    • The point at which the high airspeed mach buffet and low speed stall buffet merge, called coffin corner.
    • q72
    • The manoeuvre envelope must be...
    • At an altitude and airspeed sufficient to avoid stalling and slow enough to avoid structural damage
    • q73
    • Gliding angle depends on...
    • Ratio of lift to drag ratio – greater weight does not effect gliding angle or range, does effect speed.
    • q74
    • Rate of vertical descent depends on...
    • Angle of glide and airspeed
    • q75
    • Aircraft in constant descent at 300kts, how does weight affect glide angle.
    • The heavier the aircraft, the earlier descent must commence. So the more shallow the glide angle.
    • Conversely, the lighter the aircraft, the steeper the descent glide angle, for the same speed as the heavier aircraft.
    • q76
    • Define rolling, pitching and yawing movement. About what axis, called what stability?
    • Rolling is about longitudinal axis and is lateral stability
    • Pitching is about lateral axis and is longitudinal stability
    • Yawing is about normal axis and is directional stability
    • q77
    • What is the resultant of using ailerons for turning / rolling, and how is it corrected?
    • Adverse aileron yaw which is caused by the lowering of one aileron (down going aileron, up-going wing)
    • Lowered aileron causes additional drag which produces a yawing moment in the opposite direction. By increasing the angle of attack too much causing more drag and by aileron pushing into airflow.
  11. Corrected by use of spoilers and differential or frise ailerons. Or slot-cum-aileron control (Kermode p302)
    • q78
    • What is the difference between differential and frise ailerons?
    • Differential ailerons: Up going aileron moves through large rangle to increase drag
    • Frise ailerons: Up going aileron projects below as well to cause excessive drag
    • q79
    • Aileron size is limited by...
    • Flap size
    • q80
    • The effect of wing twist from operating ailerons at height speed is...
    • It will minimise the effect of the ailerons / reverse the effect all together. Turning at high speeds can increase lifting forces on the upgoing wing so much that it twists the wing and reduces the effective AoA. Use inboard ailerons or spoilers at high speeds.
    • q81
    • How do ailerons prevent wing twist at high speeds?
    • They are locked out to prevent wing twisting, inboard ailerons are employed to provide roll as well as spoilers.
    • q82
    • How do spoilers produce roll?
    • The spoilers are raised on the down going wing reducing the lift on that wing
    • q83
    • What are the function of spoilers?
    • 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
    • q84
    • What is direct lift control?
    • Use of aerodynamic surfaces (spoilers) to provide control of rate of descent without need to change body angle on approach
    • q85
    • What are differential spoilers?
    • They provide roll control when flight spoilers are in use and aileron input is given
    • q86
    • What is the limitation of spoilers?
    • At high speed they can blow back
    • q87
    • What is the reason for using a variable incidence tail plane?
    • 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
    • q88
    • Power assisted controls provide what?
    • Pilot force which is assisted by power units which in turn provides “Feel"
    • Provide all the force necessary to operate a control surface, control column feel is provided artificially
    • q89
    • What is Q feel?
    • An artificial method of providing the pilot with control column loading using either springs or hydraulics which provide variable loading proportional to airspeed
    • q90
    • Extending flaps increases what?
    • Wing camber
    • Wing area and CL
  12. q91
    • Slotted flaps allow...
    • The airflow to be re-energised avoiding separation
    • q92
    • Large aircraft are usually fitted with what type of flap?
    • Slotted fowler (moves down and rearward)
    • q93
    • When does aileron droop occur?
    • When flaps are extended (usually the inboard ailerons)
    • q94
    • A Krueger flap does what?
    • Extends forward of the leading edge providing an increase camber
    • q95
    • Leading edges slats extend...
    • Outwards providing a slot to delay boundary layer separation
    • q96
    • An aft / forward C of G has what effect on the stall speed?
    • Aft decreases the stall speed and forward increases the stall speed
    • q97
    • What are the purposes of vortex generators?
    • To re-energise the boundary layer & delay separation or air from wing
    • q98
    • What is hydroplaning and what does it depend on?
    • When a tyre is lifted clear of the runway due to a build up of fluid pressure beneath the tyre
    • Tyre pressure
    • Runway surface
    • Tread depth
    • Tyre speed
    • Water depth
    • Runway grooving
    • q99
    • What is the formula for the Hydroplaning Speed?
    • Rotating and Non-rotating.
    • Rotating = 9.0 x square root of tyre pressure
    • Non-Rotating = 7.7 x square root of tyre pressure
    • Beech Nose wheel 60psi, Main gear 97psi +/- 5psi
    • = 88kts rotating, 75kts non-rotating
    • q100
    • When are reduced thrust take off's used?
    • There is a long runway available
    • MTOW is low
    • q101
    • What are the 2 methods for reduced take offs?
    • Fixed derate (i.e 10%-20%) - For a given ambient condition, the thrust reduction achieved by selecting another certified takeoff rating that is lower than the maximum takeoff rating.
  13. Assumed temperature - Based on a certified takeoff rating and ambient condition, the thrust reduction achieved by selecting the rated thrust for a temperature that is higher than the outside air temperature.
  14. q102
    • Using an assumed temperature reduced thrust take off, what speed corrections are there?
    • V1 is reduced to allow for slower acceleration but other speeds are the same for the actual TOW
    • q103
    • Factors that affect the engine thrust...
    • Mass airflow increases...Thrust increases
    • Temp increases...Thrust decreases
    • Humidity increases...Thrust decreases
    • Altitude increases..Pressure decreases...Thrust decreases
    • q104
    • What is ram effect?
    • As the aircraft increases speed the increase in density and mass flow through the engine results in an increase in thrust
  15. q105
    • An increase in engine RPM results in...
    • Higher mass air flow
    • SFC decreases
    • Higher temps
    • Thrust output increases
    • q106
    • Two ways of measuring thrust are:
    • EPR (the ratio of inlet pressure and turbine exit pressure)
    • N1 (low pressure rotor speed)
    • q107
    • Engine bleed air has what effect:
    • EPR decreases (engine pressure ratio)
    • EGT increases
    • Thrust decreases
    • q108
    • What is a compressor stall / surge?
    • A reverse flow of air through the engine caused by unstable air
  16. To prescribe the certification requirements for operators to perform Air Operations and the operating requirements for the continuation of this certification. Air Operations include Air Transport Operations (ATO) and Commercial Transport Operations (CTO).
    • q118
    • What is the purpose of Part 121?
    • To prescribe the operating requirements for air operations of aeroplanes that have a passenger seating configuration of more than 30 seats, excluding any required crew member seat, or a payload capacity of more than 3410 kg, carried out by the holder of an Airline Air Operator Certificate issued under Part 119 of the Rules.
    • q119
    • What is the purpose of Part 61?
    • Prescribes the requirements to hold pilot licences and ratings; the prerequisites for those qualifications; and their privileges and limitations.
    • q120
    • What is the purpose of Part 91?
    • Part 91 is an important rule as it forms the basis of general operating and flight rules for the New Zealand aviation environment. The requirements ensure that the safe operation of aircraft is possible with the minimum endangerment to persons and property.
    • q121
    • What is the critical engine on a propeller aircraft?
    • On a propeller aircraft with conventionally rotating propellers, the critical engine is the left outboard engine, conversely with propellers rotating anti-clockwise, the outboard right engine would be critical. Counta/contra-rotating propellers do not have a critical engine.
    • With conventionally rotating propellers, the down-going blade on each engine has a greater angle of attack producing more lift (thrust) thus offsetting the thrust line on each engine to the right. The right engine (on conventionally rotating propellers) has a greater arm to the C of G causing greater yaw, making the left engine critical.
    • q122
    • How does crosswind affect the critical engine?
    • On a propeller driven aircraft, a crosswind from the opposite side to the critical engine will assist the situation because the yaw required to offset that which is produced by the failure of the critical engine will be assisted by the effect of the crosswind (weathercocking).
    • The reverse situation will make matters worse. Crosswind from the same side as the critical engine will require even more demand from the rudder. The yaw produced by the failure of the critical engine will be compounded by the effect of the aircraft weathercocking.
    • q123
    • What are the approach speeds for Cat B?
    • CAT B
    • Vat (1.3Vs) 91 - 120
    • Initial App...120 - 180 (140 Reversal turn)
    • Final App...75 - 130
    • Circling...135
    • MAP...150
    • 45/180 degree turn...1 min
  17. q124
    • What is ETP and what is the formula?
    • Equi time point – a point enroute where it will take the same time to go back as it will to carry on
    • Dist to ETP = Distance x GS home G/S onward + G/S home
    • With a tailwind out ETP will move closer to departure.
    • ETP moves into wind
    • q125
    • What is PNR and what is the formula?
    • Point of no return – a point which is based on fuel (endurance) at which you have the fuel to return if req’d
    • PNR Formula
  18. Time to PNR (min.s) =
  19. Endurance (min.s) x G/S home
    G/S out + G/S home
  20. Dist to PNR =
    • Endurance (hrs(decimals)) x G/S out x G/S home
    • G/S out + G/S home
  21. q126
    • What is the formula for Equivalent Still Air Distance?
    • ESAD = Dist x TAS
    • G/S
  22. The distance the aircraft has flown through the air.
  23. q127
    • What is the formula for Gross fuel flow?
    • GFF = Fuel Flow (kg/hr)
    • G/S (nm/hr) = kg/gnm
  24. q128
    • What is endurance?
    • With endurance we need to fly as long as possible 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.
    • Since the thrust, and hence the consumption, should be the same at the same indicated speed at any height, it should not matter at what height we fly for endurance. Actually, when engine efficiency is taken into account, there are advantages in flying high (engine operating at design speeds and also the thermal efficiency, compressor efficiency, and the pressure ratio is better at higher altitudes).
    • Fuel Consumption with increase in Alt remains Constant, However in practise fuel consumption decreases with altitude.
    • In summary, for Endurance fly at speed for min drag as high as possible.
    • q129
    • Explain Range?
    • For maximum range we need to cover the maximum distance for a given amount of fuel. If we look at the TOTAL DRAG vs IAS curve once again then it can be seen that a very large increase in IAS can be achieved with a comparably small increase in total drag by drawing a line at a tangent to the curve. This is the speed for Maximum Range.
  25. 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.
  26. The effect, on range, of an 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.
    • q130
    • If you were loading an airplane to obtain max range, would you load it with a forward or aft CoG?
    • 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.
    • q131
    • Compare speed for Range Vs Endurance?
    • Speed for max endurance will always be lower than speed for max range.
  27. Max range is greatest distance covered for the amount of fuel used.
    • SAR = TAS / GFC (gross fuel consumption)
    • Tangent to the power req curve. Best range TAS INCREASES with altitude not IAS. Reduce weight to increase range.
  28. Max endurance is to remain in the air for the greatest amount of time for least amount of fuel. Min drag speed.
    Best at SL (less power) for piston engine. High for turbines. Increase in weight, reduces endurance.
  29. q132
    • What sort of C of G changes occur on long flights?
    • 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.
    • q133
    • How does cruise speed vary with fuel burn?
    • Cruise speed reduces with gross weight due to fuel burn – less weight requires less lift resulting in less drag, therefore thrust can be reduced.
    • q134
    • What happens to SFC as altitude is gained?
    • It decreases
    • q135
    • What effect happens if the aircraft is flown past the optimum flight level?
    • SFC increases as excessive drag results from an increased AoA which is required to create enough lift to support the aircraft.
    • (The optimum altitude occurs at the optimum angle of attack for least thrust greatest TAS)
    • q136
    • Optimum altitude is a function of...
    • SFC and TAS
    • q137
    • Does temperature affect optimum flight level?
    • No as it has an equal effect on fuel flow and TAS
    • q138
    • Specific air range formula is...
    • SAR = TAS
    • GFC (gross fuel comsumption)
    • q139
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