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Question 79-1 : In order to provide an adequate stall margin in level flight, a speed of 1.3vs is used. at a mass of 120000 kg this is a cas of 180 kt. if the mass of the aeroplane is increased to 135000 kg, the value of 1.3vs will be ? [ Attainment AIM ]
Increased to 191 kt, drag will increase and air distance per kg of fuel will decrease.
135000/120000 = 1.125.180 x square root of 1.125 = 191 kt..if speed increases, drag increases. thus, for a same unit of fuel, the air distance will be lesser.
Question 79-2 : What are the effects of a cg in front of the forward limit.range... ?
And absolute ceiling decrease.
A forward cg means that the pitch down moment is high. the elevator must provide a moment opposing this pitch down moment, adding a high downward force to the weight of the aircraft, which is then increased. therefore the climb performance and ceiling will be decreased. the increased drag of the elevator will cause a higher fuel consumption for a given airspeed, thus decreasing range and endurance.
Question 79-3 : The centre of gravity of an aircraft ?
Can be allowed to move between defined limits.
Centre of gravity cg is that point through which the force of gravity is said to act on a mass and always acts parallel to the gravity vector.
Question 79-4 : Which statement regarding the relationship between traffic load and range is correct ?
The traffic load can be limited by the desired range.
Traffic load might be exchanged for fuel to extend range.
Question 79-5 : The term useful load as applied to an aircraft includes ?
Traffic load and usable fuel only.
Question 79-6 : If other factors are unchanged, the fuel mileage nautical miles per kg is ?
Lower with a forward centre of gravity position.
With a forward cg, the aircraft is nose heavy , it has a nose down moment, thus, the downforce on the tail on a steady flight, must be increased..the total aircraft weight increases and therefore more weight = more drag = more power...the fuel mileage nautical miles per kg is lower with a forward centre of gravity position...example. with a aft cg, fuel mileage = 10 nm for 100 kg.. with a forward cg, fuel mileage = only 8 nm for 100 kg.
Question 79-7 : The stalling speed of an aeroplane will be highest when it is loaded with a ?
High gross mass and forward centre of gravity.
A forward cg requires more lift and generates more drag, the stalling speed will be greater than with an aft cg...also, for a higher gross mass it is mandatory to generates more lift... which generates more induced drag... the stalling speed increases.
Question 79-8 : With the centre of gravity on the forward limit which of the following is to be expected ?
A decrease in range.
The most forward the cg is, the more down force the tail needs to generate to compensate and keep the airplane from pitching down. this increased down force must be counteracted by increased lift from the wing. that, of course, means an increase in angle of attack or airspeed = the stall speed increases = consumption increases = range decreases.
Question 79-9 : If the centre of gravity of an aeroplane moves forward during flight the elevator control will become ?
Heavier making the aeroplane more difficult to manoeuvre in pitch.
When the centre of gravity moves forward during flight, the aeroplane will be more stable but requires more forces to change pitch elevator control will become heavier.
Question 79-10 : The determination of the centre of gravity in relation to the mean aerodynamic chord consists of defining the centre of gravity longitudinally in relation to the ?
Length of the mean aerodynamic chord and the leading edge.
Longitudinal cg location is normally expressed as a percentage of the mean aerodynamic chord mac from its leading edge.
Question 79-11 : The maximum zero fuel mass ?
Is calculated for a maximum load factor of +2.5 g.
Question 79-12 : When has the centre of gravity to be computed ?
Prior to every flight.
Question 79-13 : What is a possible consequence of loading an aircraft incorrectly so that the centre of gravity is positioned ahead of the forward limit ?
The aircraft becomes excessively stable and requires larger control inputs.
This question is asking about the effect on performance with a forward cg position. with the increase in trim drag and the extra main wing lift required, as shown in the figure, the effects include... higher stalling speed. increased fuel consumption. reduced range and endurance. reduced climb performance. increased stability. increase in take off and landing speeds...looking at the answers.. the aircraft may become excessively manoeuvrable and beyond control > incorrect. with a forward cg the aircraft becomes very stable, as the tail plane has a long arm to the cg. this makes the aircraft hard to control and manoeuvre... the aircraft becomes excessively stable and requires larger control inputs > correct. the tail plane has a long arm to the cg and becomes very stable and heavy on the controls... there may be insufficient forward pitch control available to keep the aircraft level > incorrect. with a forward cg, the pilot will need to hold the nose up by applying back pressure to the control column and trimming. forward pitch control will not be a problem... there may be a tendency to over pitch the aircraft during the flare just before landing > incorrect. with a forward cg, the aircraft becomes nose heavy and the tendency would be to under pitch during the flare
Question 79-14 : What happens when the centre of gravity cg is moved in a forward direction ?
A reduction in rate of climb capability.
When the center of gravity is moved to forward limit, this gives us a pitch down moment, this pitch down moment has to be corrected by an up deflection of the elevator to keep straight and level flight, this up deflection increases the drag, increasing drag reduces the endurance.the up deflection of the elevator which is used to compensate for the nose heavy moment, is the same deflection we use to pitch up to increase the rate of climb, when part of it is used already for compensation, this result in reduction of climb capability.
Question 79-15 : What are the effects of a cg in front of the forward limit range… ?
And absolute ceiling decrease.
When the center of gravity is outside the forward limit, this gives a pitch down moment, this pitch down moment has to be corrected by an up deflection of the elevator to keep straight and level flight. this increases the aircraft's weight by adding a high downward force.as a consequence climb performance and ceiling will be decreased.
Question 79-16 : Which cg position is used when determining minimum control speeds in performance a cg… ?
At the aft limit.
Aft cg provides the shortest moment arm relative to the rudder, this gives the least restoring moments with regard to maintaining directional control, that make it favourable in determination of minimum control speeds.
Question 79-17 : Why is it important to have accurate information about the airplane mass and cg position during flight ?
Allow selection of the real, optimum cruising flight level.
Looking at the answers 'allow airlines to better compute navigation and route charges' > incorrect. knowledge of the aircraft's mass and cg position allows for performance planning in the vertical, rather than horizontal.'allow selection of the real, optimum cruising flight level' > correct. this will depend on the aircraft's weight, cg position & air temperature and will vary as fuel is burnt.'are only required for take off and landing, to comply with load sheet requirements' > incorrect. knowledge of the mass and cg of the aircraft are essential in flight for a number of reasons, including selection of optimum flight levels, diversion planning, fuel management think a380 moving fuel from the tail tank in flight to control the cg position etc.'are unimportant since all performance decisions are based on expected masses on the operational flight plan' > incorrect. expected masses are used for planning only. in flight, any operational decision will be based on actual conditions.
Question 79-18 : What is the effect if the centre of gravity is behind the aft limit in level and forward flight ?
The stability is decreased.
This question is asking about the effect on performance with a rearwards cg position...with the decrease in trim drag and also less main wing lift being required, the effects include... lower stalling speed. decreased fuel consumption. increased range and endurance. increased climb performance. decreased stability. increased controllability. decrease in take off and landing speeds...looking at the answers.. the stability is increased > incorrect. with an aft cg, the tail has a shorter arm and so the aircraft is left stable... the controllability is decreased > incorrect. with an aft cg, the short arm to the tail means less stability and so the aircraft is easier to control, ie manoeuvre... the control forces are increased > incorrect. with an aft cg, the short arm to the tail means less stability and so the control forces required reduce and the aircraft is easier to manouvre... the stability is decreased > correct. with an aft cg, the tail has a shorter arm and is less effective. stability reduces in all aspects, as the tailplane and fin / rudder act around the cg.
Question 79-19 : If the centre of gravity is outside the forward limit in level and forward flight, the drag… ?
Increases, and endurance decreases.
When the center of gravity is outside the forward limit, this gives us a pitch down moment,.this pitch down moment has to be corrected by up deflection of elevator to keep straight and level flight,.this down deflection increase the drag, increasing drag reduce the endurance.correct answer drag increases, endurance decreases.
Question 79-20 : A pilot has finished the pre planning. shortly before departure an additional container with a mass of 3000 kg of traffic load is accepted. the pilot forgets to calculate the new performance values of the aircraft. take off and climb is accomplished without any problems. how will the performance of ?
Rate of climb and range will be decreased.
In this scenario the aircraft weighs 3000 kg more than planned. despite a safe take off and climb, the performance of the aircraft will be affected, compared to the expected situation at the lighter weight. the effects of a heavier aircraft include higher stalling speedincreased fuel consumptionreduced range and endurancereduced climb performance, both rate & gradient of climblooking at the answers 'angle of climb and obstacle clearance will be improved' > incorrect. both of these will reduce with the extra weight on board.'fuel flow and endurance will be reduced' > incorrect. endurance will reduce but the fuel flow will increase. the extra weight will require more lift, which creates more drag = more thrust = more fuel burn...'rate of climb and range will be decreased' > correct. as shown above.'fuel flow and specific range will be increased' > incorrect. fuel flow will increase but the range will reduce due to the extra weight being carried on board.
Question 79-21 : An additional baggage container is loaded into the aft cargo compartment but is not entered into the load and trim sheet.the aeroplane will be heavier than expected and calculated take off safety speeds… ?
Will give reduced safety margin
Increasing the aircraft mass also affects most of the factors associated with the cg, particularly fuel consumptiona and stalling speed. an increase in weight requires increased lift, more lift equals more drag and more drag means higher fuel consumption. increasing mass also affects the stall speed, vs, which is roughly proportional to the square root of weight...many speeds used in performance calculations, such as the rotate speed, vr and the safety spped, v2, are extracted through graphs and tables and are based on the stalling speed from which they differ by a standard safety margin according to the rules and regulations. so, they also increase as the aircraft weight increases, so as to keep the safety margin constant...in case an additional baggage container is loaded into the aft cargo compartment without being entered into the load and trim sheet, then the vs will increase, but the take off safety speeds will remain the same, thus reducing their difference from the vs and as a result the safety margin will also reduce.
Question 79-22 : What are the effects on stability and controllability of a cg behind the aft limit longitudinal stability… ?
Is reduced and controllability is increased.
This question is asking about the effect on performance with a rearwards cg position. the cg is behind the aft limit which could lead to various issues, but easa only want to know about the general effects of a rear cg...with the decrease in trim drag and also less main wing lift being required, the effects include... lower stalling speed. decreased fuel consumption. increased range and endurance. increased climb performance. decreased stability. increased manoeuvrability. decrease in take off and landing speeds
Question 79-23 : If the aircraft was loaded with the centre of gravity in front of the forward cg limit, counteracting the nose pitching down moment will lead to… ?
Increased drag.
When the center of gravity is outside the forward limit, this gives us a pitch down moment,.this pitch down moment has to be corrected by down deflection of elevator to keep straight and level flight,.this down deflection increase the drag, increasing drag reduce the endurance.correct answer increased drag.
Question 79-24 : If the centre of gravity is further forward than the forward limit is, the aircraft's horizontal surfaces have a… ?
Longer than usual moment arm and the fuel consumption is increased.
When the center of gravity is outside the forward limit, this gives us a pitch down moment,.this pitch down moment has to be corrected by up deflection of elevator to keep straight and level flight,.this up deflection increase the drag, increasing drag reduce the endurance increase fuel consumption.correct answer longer than usual moment arm and the fuel consumption is increased.
Question 79-25 : Comparing a forward cg position with an aft one, the forward cg position will cause a… ?
Decrease in range.
In the normal flight condition, the main wing creates lift and the elevator creates drag. due to a forward cg position, more downward force drag is necessary at the elevator. drag increases = range decreases = rate of climb capability decreases.
Question 79-26 : Prior to departure an aircraft is loaded with 16 500 litres of fuel at a fuel density of 780 kg/m3. this is entered into the load sheet as 16 500 kg and calculations are carried out accordingly. as a result of this error, the aircraft is… ?
Lighter than anticipated and the calculated safety speeds will be too high.
Fuel volume 16 500.fuel density 780 kg/m3.fuel mass = 16 500 x 0.78 = 12 870 kg..load entered in load sheet is higher than actual load of airplane, airplane is lighter than anticipated and calculated safety speeds is too high.
Question 79-27 : If during flight a considerable amount of fuel was transferred from a fuel tank located in the forward fuselage section to a fuel tank located at the rear section of the fuselage, what effect would this have on the aircraft ?
Increase in range and decrease in stall speed.
The total mass of the aircraft can be said to act through one point, called the centre of gravity cg and the total lift acts through the centre of pressure cp...the position of the cp changes with speed and as alpha changes, whilst the position of cg changes as load and fuel change. when this happens, new balancing forces and trim changes will be needed...the relative positions of the cg and cp affect the longitudinal stability of the aircraft. in practice, the cg is usually forward of the cp, thus, the more forward the cg, the more stable the aircraft in pitch. some stability in pitch is desirable, but not too much, because the extra down force on the elevator effectively adds to the aircraft weight and requires the lift to be increased to counter it. more lift means more drag created by the trim trim drag and more drag means higher fuel consumption...aircraft manufacturers determine a safe range for the cg. the aft limit is usually just in front of the centre of pressure, but it provides less stability than that provided by the forward limit, but a smaller balancing tail moment will be required...for this question, if during flight a considerable amount of fuel was transferred from a fuel tank located in the forward fuselage section to a fuel tank located at the rear section of the fuselage, the aircraft's cg will be repositioned aft...to sum up, an aft cg... increases the rate of climb and the climb gradient. decreases torr, todr, asdr, thus mtom can be increased. the stick forces required will be less. rotation will be easier. stall speed decreases, which permits a higher ceiling altitude. makes flare easier during landing, thus decreasing ldr and increasing mlm. range and endurance increase due to the decreased fuel consumption
Question 79-28 : Which one of the following describes a possible handling and performance problem encountered with a cg too far aft ?
Degradation or loss of nose wheel steering.
The efficiency of the nose wheel steering will decrease for an aft centre of gravity because the weight on the nose wheel is also decreased. it results in degradation or even loss of nose wheel steering.
Question 79-29 : Which statement is correct..i. stall speeds are determined with the cg at the forward limit..ii. minimum control speeds are determined with the cg at the aft limit ?
I is correct, ii is correct.
In a question borrowed heavily from pof, the main thing to remember is that we test these values in the worst case scenario. in short... stalls cg forward = aircraft is effectively heavier as the tailplane is generating down force to balance the aircraft.. minimum control speed cg aft = shortest arm for the rudder to work with....in more detail..1. stall speeds are determined with the least favourable cg position. for an aircraft, this is the most forward point because then the main wing will be producing the most lift. with the cg furthest ahead of the centre of pressure, the horizontal stabiliser will be producing a downwards force, which the main wings will have to compensate for by producing more lift. the main wings will therefore have to be at a higher angle of attack and therefore be closer to the stall. hence the stall will occur at higher speeds with a forward cg then with a rearward cg...2. minimum control speeds are also determined with the least favourable conditions. when considering an engine failure, we know that the aircraft will rotate around its cg, but the distance of the moment doesn't change when it moves fore or aft, the engines moment would only change when we move it along the lateral axis of the aircraft. however, the position of the cg will influence the rudder arm, and hence the rudder moment. a cg on the af limit will provide a small arm and therefore the least ability to oppose the yawing moment of the engine failure.
Question 79-30 : What are the possible consequences when loading an aircraft incorrectly so that its cg is positioned behind the aft limit ?
There may be insufficient forward pitch control available to keep the aircraft level in straight flight.
The relative positions of the centre of gravity cg and centre of pressure cp affect the longitudinal stability of the aircraft. most transport aircraft will usually have their aft cg limit just forward of the cp, because that provides to an aircraft pitch stability...if the cp is aft of the cg, the increased lift vector will tip the aircraft nose down, which is a stable result as it tends to restore the original pitch attitude. in this case, the aircraft has positive longitudinal static stability...if the cg is aft of the cp, thus positioned behind the aft limit, the increased lift will tip the aircraft nose up, leading to higher angles of attack and even more lift until the aircraft stalls. this is an unstable result, a negative longitudinal static stability, where... the control forces will be light.. the aircraft will be excessively manoeuvrable, leading to a possible over rotation on take off and a possible tail scrape and during landing over pitching may occur during the flare.. insufficient forward pitch control will be available to keep the aircraft level in straight flight.
Question 79-31 : Some aircraft are equipped with fuel trim tanks located in the aeroplane's fin or horizontal stabiliser to actively manage cg position. which of the following is an advantage of having a trim tank in the horizontal stabiliser ?
It allows the crew to keep the cg at an aft position.
The fuel tanks will generally be located in the wings outer and inner and in a central position in the fuselage. but, they may also be found in the fin and the horizontal stabiliser...the centre of gravity cg position does change as fuel is burnt off, but within defined limits. if it is burnt from a tank aft of the aircraft's cg, then the cg will move forward. conversely, if the fuel is burnt from a tank positioned forward of the cg, then it will move aft...over the years, fuel tanks in the tail fin and horizontal stabiliser, called as trim tanks , have been employed by different manufacturers for two main reasons... to provide extra fuel capacity.. to maintain the aircraft cg position at the optimum aft position for minimum drag, improved manoeuvrability and, as a consequence, for maximum fuel economy, as less downforce on the horizontal stabiliser is required...the fuel in these tanks may automatically drain as fuel is used from the centre and wing tanks or may be actively controlled by the crew through transfer systems.
Question 79-32 : What will be the effect on the longitudinal static stability, if the centre of gravity cg is located behind the aft cg limit ?
Stability decreases beyond acceptable limits.
The relative positions of the centre of gravity cg and centre of pressure cp affect the longitudinal stability of the aircraft. most transport aircraft will usually have their aft cg limit just forward of the cp, because that provides to an aircraft pitch stability...if the cp is aft of the cg, the increased lift vector will tip the aircraft nose down, which is a stable result as it tends to restore the original pitch attitude. in this case, the aircraft has positive longitudinal static stability...if the cg is aft of the cp, thus positioned behind the aft limit, the increased lift will tip the aircraft nose up, leading to higher angles of attack and even more lift until the aircraft stalls. this is an unstable result, a negative longitudinal static stability, where... the control forces will be light.. the aircraft will be excessively controllable, leading to a possible over rotation on take off and a possible tail scrape and during landing over pitching may occur during the flare.. insufficient forward longitudinal control will be available to keep the aircraft level in straight flight....if the cg is too far aft, the moment arm between it and the cp diminishes, reducing the inherent stability of the airplane beyond acceptable limits and in the extreme going negative and rendering the airplane longitudinally unstable...generally, the less stable the aircraft, the more controllable and vice versa.
Question 79-33 : On an aeroplane with a mass just below mzfm, when is the wing load at its maximum ?
On landing.
The main loads on a wing are bending loads, incorporating tension and compression, both in flight and on the ground.in flight, the weight of the aircraft is supported by the lift of the wings, on the ground by the landing gear.although the normal loads tend to bend the wing upwards, on landing and in turbulence, the wing flexes downwards, so the spar has to take bending loads in both directions.therefore, the wing load is at a maximum at the wing root on landing and in turbulence.
Question 79-34 : What is a possible consequence of loading an aircraft incorrectly so that the centre of gravity is positioned ahead of the forward limit ?
There may be insufficient aft pitch control available to keep the aircraft level.
The aircraft can be considered to be nose heavy with a forward cg. the pilot will need to pull the control column to keep the nose up. if the cg moves too far forward, the pilot can run out of aft pitch control and the nose will drop...this question is asking about the effect on performance with a forward cg position. with the increase in trim drag and the extra main wing lift required, as shown in the figure, the effects include... higher stalling speed. increased fuel consumption. reduced range and endurance. reduced climb performance. increased stability. increase in take off and landing speeds
Question 79-35 : The performance limited take off mass pltom is defined as the... ?
Take off mass subject to departure aerodrome limitations.
As quoted from cap 696..performance limited take off mass pltom is the take off mass subject to departure aerodrome limitations...such factors include... runway length. terrain around the airport. climb out requirements. ambient conditions, such as humidity and temperature etc....note do not confuse structural limits with performance limits in these definition questions.
Question 79-36 : The performance limited landing mass is defined as… ?
The landing mass subjected to airport normal conditions.
The performance limited landing mass pllm is the mass subject to the landing aerodrome limitations also taking the current metrological conditions into account. this limit is not a set figure and needs to be calculated for each sector. if the pllm is exceeded the aircraft may overrun the landing distance available, tyre temperature limits could be exceeded and a go around might not be achievable.the regulated landing mass rlm is the is the lowest of the performance limited landing mass and maximum structural limited landing mass. the actual landing mass must not exceed this limit.the maximum structural landing mass mslm is the maximum permissible total aeroplane mass on landing in normal circumstances and given the most favourable conditions anywhere in the world. it is a set structural limitation and does not change for a particular aircraft. if the mslm is exceeded structural damage can occur to the aircraft.
Question 79-37 : Given.dry operating mass= 29 800 kg.maximum take off mass= 52 400 kg.maximum zero fuel mass= 43 100 kg.maximum landing mass= 46 700 kg.trip fuel= 4 000 kg.fuel quantity at brakes release= 8 000 kg.the maximum traffic load is ?
12 900 kg.
Traffic load is the total mass of passengers, baggage and cargo, including any non revenue load... 127.the lowest mass is our limitation.
Question 79-38 : The take off mass of an aircraft is 117 000 kg, comprising a traffic load of 18 000 kg and fuel of 46 000 kg..what is the dry operating mass ?
53 000 kg.
Dry operating mass = the total mass of an aircraft ready for a specific type of operation excluding all usable fuel and traffic load..this mass includes items such.as.+ crew and crew baggage..+ catering and removable passenger service equipment food, beverages, potable water, lavatory chemicals etc..+ special operational equipment e.g. stretchers, rescue hoist, cargo sling...dry operating mass = take off mass traffic load fuel.dry operating mass = 117000 18000 46000 = 53000 kg.
Question 79-39 : The dry operating mass includes ?
Crew and crew baggage, catering, removable passenger service equipment, potable water and lavatory chemicals.
Please download the following document used as a reference at the exam../pdf/031 mass definitions.pdf
Question 79-40 : The maximum load per running metre of an aircraft is 350 kg/m. the width of the floor area is 2 metres. the floor strength limitation is 300 kg per square metre..which one of the following crates length x width x height can be loaded directly on the floor ?
A load of 400 kg in a crate with dimensions 1.2 m x 1.2 m x 1.2 m.
Maximum load per running metre 400 / 1.2 = 333 kg/m..floor strength limitation 400 / 1.2 x 1.2 = 277,77 kg/m²..both limitations are respected.
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