Question 258-1 : On a large transport aeroplane the auto slat system ? [ Explanation maintenance ]

Question 258-2 : How does the total drag change in straight and level flight at constant mass as speed is increased from the stall speed vs to maximum ias vne or vmo ?

Initially decreases then increases.

Img com encom032 209jpg

Question 258-3 : How is stall warning presented to the pilots of a large transport aeroplane ?

Stick shaker andor aerodynamic buffet.

Artificial stall warning on small aircraft is usually given by a buzzer or horn the artificial stall warning device used on modern large aircraft is a stick shaker in conjunction with lights and a noise makerseparated airflow prior to a low speed stall can cause airframe buffet aerodynamic buffet is a valuable stall warningif the pilots do not react you can find an 'alpha floor protection' system'alpha floor protection' is a system designed to prevent an aircraft from reaching very near its critical angle of attack because of slowing down too much the system automatically increases the thrust of the aircraft when speed is predicted to reach or exceed the critical angle of attack often found on newer generations of commercial aircraft such as the airbus 320 330 340 380 and boeing 777

Question 258-4 : Load factor is ?

Liftweight.

Question 258-5 : In order to perform a steady level turn at constant speed in an aeroplane the pilot must ?

Increase thrustpower and angle of attack.

In order to perform a steady level turn at constant speed in an aeroplane the pilot must increase thrustpower and angle of attack there is a constant rate of change of direction and the force acting on the machine are equilibrium some of the lift force is applied to the turn so the lift vector is reduced com encom080 590jpgas you make turn the original lift vector has to be split as a side element is added to pull you into turnthe side element is centripetal force acting towards the center of the turn total lift is the resultant of them both the diagonal line and you can see that the vertical lift vector has reduced and needs some compensation to maintain the lift or the aircraft will descendyou must increase the angle of attack to increase lift it will cost some speed if you not increase thrustpower

Question 258-6 : Minimum drag of an aeroplane in straight and level flight occurs at the ?

Maximum clcd ratio.

We are in level flight not in descent we must produce liftwith the higher clcd ratio we will produce the minimum drag in level flight

Question 258-7 : Lift is the ?

Component of the total aerodynamic force perpendicular to the local flow.

com encom080 604jpglift is the upward force created by the wings moving through the air that sustains the airplane in flight lift operates to overcome weight it must be equal to or greater than the weight of the object in flight and acting in the opposite directionlift can be increased by increasing the forward speed of the aircraft or by increasing the angle of attack

Question 258-8 : The stick shaker stalling is taken from ?

Ias.

Question 258-9 : Low speed pitch up is caused by the ?

Outward drift of the boundary layer on a swept back wing.

Flying at low speed means flying at high angle of attack there is a tendency for the swept wing to develop a strong spanwise flow towards the wingtip when thewing is at high angles of attack com encom080 27jpgstall occurs at the wingtips first resulting in a shift of the center of lift of the wing in a forward direction relative to the center of gravity of the airplane causing the nose to pitch up

Question 258-10 : Which statement is correct i stall speeds are determined with the cg at the aft limitii minimum control speeds are determined with the cg at the forward limit ?

I is incorrect ii is incorrect.

Vso and vs1 are the stalling speeds or the minimum steady flight speed cas at which the aeroplane is controllable with 1 for reciprocating engine powered aeroplanes engine s idling the throttle s closed or at not more than the power necessary for zero thrust at a speed not more than 110% of the stalling speed and 2 for turbine engine powered aeroplanes the propulsive thrust may not be greater than zero at the stalling speed or if the resultant thrust has no appreciable effect on the stalling speed with engine s idling and throttle s closed 3 propeller s in the take off position 4 the aeroplane in the condition existing in the test in which vso and vs1 are being used 5 centre of gravity in the position which results in the highest value of vso and vs1 and 6 weight used when vso or vs1 are being used as a factor to determine compliance with a required performance standardvmc must be established with 1 the aeroplane in each take off configuration or at the option of the applicant in the most critical take off configuration 2 maximum available take off power or thrust on the operating engines 3 the most unfavourable centre of gravity 4 the aeroplane trimmed for takeoff and 5 the most unfavourable weight in the range of take off weights

Question 258-11 : In a steady co ordinated horizontal turn lift is ?

Greater than in straight and level flight because it must balance the weight and generate the centripetal force.

com encom080 623gifcentripetal force is the force in the direction of the center of the turn

Question 258-12 : The span wise flow is caused by the difference between the air pressure on top and beneath the wing and its direction of movement goes from ?

Beneath to the top of the wing via the wing tip.

com encom080 459jpgthe spanwise flow goes from beneath to the top of the wing via the wing tip

Question 258-13 : Amongst the following factors which will decrease the ground distance covered during a glide assume zero powerthrust ?

Headwind.

com encom080 642jpgthe wind and liftdrag ratio determine the distance travelled over the ground of an aeroplane in a glide liftdrag ratio changes with angle of attack not with the mass

Question 258-14 : When speed is increased in straight and level flight on a positively cambered aerofoil what happens to the 1 centre of pressure and 2 the magnitude of the total lift force ?

1 moves aft and 2 remains constant.

The pressure created by an aerofoil at any point may be represented by a vector at right angles to its surface whose length is proportional to the difference between absolute pressure at the point and the free stream static pressureall of them can be represented by a single vector acting at a particular point called the centre of pressure com encom080 686jpgthe centre of pressure is a theoretical point on the chord line through which the resultant of all forces the total reaction is said to actits position is usually around 25% of the way from the leading edge simply because more lift is generated there but it moves steadily forward as the angle of attack is increased until just before the stalling angle when it moves rapidly backwards the centre of pressure's most forward point is just before the stalling angle this is why an aeroplane's nose drops when the wings stall and the centre of pressure moves behind the cgthus when speed is increased in straight and level flight on a positively cambered aerofoil you have to decrease the angle of attack to keep the the total lift force constant and the point where the resultant of all forces are acting the centre of pressure moves aft

Question 258-15 : The lift coefficient cl versus angle of attack curve of a symmetrical aerofoil section intersects the vertical axis of the graph ?

At the origin.

com encom080 687ajpg com encom080 687jpga symmetrical aerofoil section produces lift at positive angle of attack the lift coefficient cl versus angle of attack curve intersects the vertical axis of the graph at the origin

Question 258-16 : The lift coefficient cl versus angle of attack curve of a negatively cambered aerofoil section intersects the vertical axis of the graph ?

Below the origin.

com encom080 688jpga negatively cambered aerofoil section produces lift at positive angle of attack only in our example at approximately 3° angle of attack the lift coefficient cl versus angle of attack curve intersects the vertical axis of the graph below the origin

Question 258-17 : The lift coefficient cl versus angle of attack curve of a positively cambered aerofoil section intersects the horizontal axis of the graph ?

To the left of the origin.

com encom080 689jpgfor a positively cambered aerofoil section the curve intersects the horizontal axis of the graph to the left of the origin because for a positively cambered aerofoil section the angle of attack has a negative value when the lift coefficient equals zero

Question 258-18 : Which statement is correct i a stick pusher activates at a higher angle of attack than a stick shakerii a stick pusher prevents the pilot from increasing the angle of attack further ?

I is correct ii is correct.

A stick pusher activates at a higher angle of attack than a stick shakera stick pusher prevents the pilot from increasing the angle of attack furthera stick pusher is a device installed in some fixed wing aircraft to prevent the aircraft from entering an aerodynamic stall some large fixed wing aircraft display poor post stall handling characteristics or are vulnerable to deep stall to prevent such an aircraft approaching the stall the aircraft designer may install a hydraulic or electro mechanical device that pushes forward on the elevator control system whenever the aircraft's angle of attack reaches the pre determined value and then ceases to push when the angle of attack falls sufficientlyvdo927you can see that first the stick shaker is activated and if the pilot do not reacts and the angle of attack continues to increase the stick pusher is activateda stick shaker is a mechanical device to rapidly and noisily vibrate the control yoke the 'stick' of an aircraft to warn the pilot that the speed is close to the stall speed a stick shaker do not prevent the pilot from increasing the angle of attack further it just warns the pilot

Question 258-19 : Wing sweep angle is the angle between ?

The quarter chord line of the wing and the lateral axis.

com encom080 692jpg

Question 258-20 : 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.

Vso and vs1 are the stalling speeds or the minimum steady flight speed cas at which the aeroplane is controllable with 1 for reciprocating engine powered aeroplanes engine s idling the throttle s closed or at not more than the power necessary for zero thrust at a speed not more than 110% of the stalling speed and 2 for turbine engine powered aeroplanes the propulsive thrust may not be greater than zero at the stalling speed or if the resultant thrust has no appreciable effect on the stalling speed with engine s idling and throttle s closed 3 propeller s in the take off position 4 the aeroplane in the condition existing in the test in which vso and vs1 are being used 5 centre of gravity in the position which results in the highest value of vso and vs1 and 6 weight used when vso or vs1 are being used as a factor to determine compliance with a required performance standardvmc must be established with 1 the aeroplane in each take off configuration or at the option of the applicant in the most critical take off configuration 2 maximum available take off power or thrust on the operating engines 3 the most unfavourable centre of gravity 4 the aeroplane trimmed for takeoff and 5 the most unfavourable weight in the range of take off weights

Question 258-21 : An aeroplane's sideslip angle is defined as the angle between the ?

Speed vector and the plane of symmetry.

com encom080 717jpga sideslip is defined as the angle between the speed vector and the plane of symmetry it not only produces a rolling moment but also a yawing moment the strength of which is dependent on the magnitude of the directional static stability

Question 258-22 : Which of these statements about boundary layers is correct ?

A laminar boundary layer is thinner than a turbulent one.

Question 258-23 : Which of these statements about boundary layers is correct ?

A turbulent boundary layer produces more friction drag than a laminar one.

Question 258-24 : Which of these statements about weight or mass is correct ?

The weight of an object depends on the acceleration due to gravity.

Question 258-25 : Which of these statements about weight or mass is correct ?

The mass of an object is independent of the acceleration due to gravity.

Question 258-26 : Which of these statements about weight or mass is correct ?

In the si system the unit of measurement for mass is the kilogram.

Question 258-27 : The total drag of a three dimensional wing consists of ?

Induced drag and parasite drag.

Bcg160 induced drag is the drag caused by lift generating specially due to the wing tip vortex created due to the tipwhise flow component of lower wing airflow this is why induced drag appers when talking about a 3d wingparasite drag includes 1 skin frinction drag 2 form pressure drag 3 interference dragby ansewering induced drag + parasite drag you are including inside skin friction drag form drag interference drag so it is the only answer that is completed

Question 258-28 : Which statement about the effects on drag of fitting external tip tanks to the wings of an aeroplane is correct i parasite drag increasesii induced drag increases ?

I is correct ii is incorrect.

The external wing tip tanks act like winglets they reduce the wing tip vortices induced drag decreases but they increase the parasite drag form drag + skin friction drag 2759 siai marchetti sf 260 with tip tanks

Question 258-29 : Which statement about the effects on drag of removing external tip tanks from the wings of an aeroplane is correct i parasite drag increases ii induced drag increases ?

Question 258-30 : Which statement about an aeroplane entering ground effect at constant angle of attack is correct i the lift coefficient cl increases ii the induced drag coefficient cdi decreases ?

I is correct ii is correct.

Ground effect changes airflow com encom080 821jpgwhen entering the ground effect it requires a decrease in angle of attack to maintain the same cl thus if the angle of attack is maintain constant the lift coefficient cl increases on entering ground effect induce flow reduces and the induced angle of attack decreases thus the induced drag coefficient cdi decreases

Question 258-31 : The mean geometric chord of a wing is the ?

Wing area divided by the wing span.

Mean geometric chord this is the average chord length through a wind found by wing areawing span com encom080 737pngthe mean geometric chord location is the same for two extreme positions of the root chord

Question 258-32 : Taper ratio of a wing is the ratio between ?

Tip chord and root chord.

com encom080 738jpg

Question 258-33 : Given an aeroplane in steady straight and level flight at low speed and considering the effects of cg location and thrust the lowest value of wing lift occurs at ?

Aft cg and take off thrust.

Img684with an aft cg the lift on the tail is at a maximum the horizontal stabiliser produces positive lift at low speed the nose is pointing upward and there will be a significant upward thrust to take some of the weight off the wingsthis question also appears with the opposite statement at the exam 'the highest value of wing lift occurs at forward cg and idle thrust' 683

Question 258-34 : Assuming isa conditions and no compressibility effects if an aeroplane maintains straight and level flight at the same angle of attack at two different altitudes the ?

Ias at both altitudes is the same.

Level flight at the same angle of attack means the same iaslift formula = cl x 12 rho v² x scl = lift coefficientrho = densityv = tas in ms s = surfacelift at altitude 1 = lift at altitude 2they say same angle of attack thus cl is the same surface does not change and there is no compressibility effectssince rho decreases with altitude tas must increase in order to keep rho x v² unchanged

Question 258-35 : Which of these statements about stall speed is correct ?

Decreasing sweepback decreases stall speed.

Anhedral is incorporated into high wing sweptback designs to decrease the lateral stability nothing to do with stall high wing aircraft have powerful stabilising results in sideslip due to fuselage shielding now swept wings are prone to tip stall which moves the centre of pressure sharply forward combine this with the changing downwash over the tail causes a sharp nose up change of trim so the stall speed is higher if you decrease the sweepback you decrease the stall speed

Question 258-36 : Which of these statements about induced drag are correct or incorrect i an elliptical spanwise lift distribution generates less induced drag than a rectangular lift distributionii induced drag increases with decreasing aspect ratio ?

I is correct ii is correct.

The correct statement is an elliptical spanwise lift distribution generates less induced drag than a rectangular lift distribution both lift distribution and load distribution are of great importance in the wing design processto give minimum induced drag the span wise efficiency factor e should be as close to 1 as possible this is the case of an elliptic span wise lift distribution a number of methods are available to modify the span wise distribution of lift they include 1 planform taper to obtain an elliptic planform used for the spitfire wing which was remarkably elliptic 2 a geometric twist andor aerodynamic twist to obtain elliptic lift distribution or 3 a combination of all of these methodsin the past 1930s it was thought that for an elliptic lift distribution the chord must vary elliptically along the span the direct result of such logic was that the wing planform must be elliptical for this reason several aircraft wing planforms such as supermarine spitfire a famous british world war ii fighter were made elliptic but today we know that there are various parameters that make the lift distribution elliptic thus there is no need for the wing planform to be planform an elliptical planform is hard to manufacture and is costly from the point of view of construction the best type of wing is the un tapered untwisted wingthe correct statement is induced drag increases with decreasing aspect ratio aspect ratio is defined as the square of the wingspan divided by the area of the wing planform com encom080 38jpginduced drag varies with lift speed and aspect ratio is inversely proportional to aspect ratio and v² so multiply by 1v² and directly proportional to lift²cl²weight²

Question 258-37 : Assuming no flow separation which of these statements about the flow around an aerofoil as the angle of attack increases are correct or incorrect i the stagnation point moves downii the point of lowest static pressure moves aft ?

I is correct ii is incorrect.

com encom080 23jpgin red the stagnation point will move downin blue the point of lowest pressure will move forward

Question 258-38 : For a subsonic flow the continuity equation states that if the cross sectional area of a tube decreases the speed of the flow ?

Increases.

Question 258-39 : Which of these statements about wing sweepback are correct or incorrect i increasing wing sweepback decreases mcritii increasing wing sweepback decreases the drag divergence mach number ?

I is incorrect ii is incorrect.

what is mcrit critical mach number com encom080 1049ajpgthe critical mach number of an aeroplane is the highest speed possible without supersonic flow over the wing what is sweepback most of the difficulties of transonic flight are associated with shock wave induced flow separation therefore any means of delaying or alleviating the shock induced separation improves aerodynamic performance one method is wing sweepback sweepback theory is based upon the concept that it is only the component of the airflow perpendicular to the leading edge of the wing that affects pressure distribution and formation of shock waveson a straight wing aircraft the airflow strikes the wing leading edge at 90° and its full impact produces pressure and lift a wing with sweepback is struck by the same airflow at an angle smaller than 90° this airflow on the swept wing has the effect of persuading the wing into believing that it is flying slower than it really is thus the formation of shock waves is delayed advantages of wing sweep include an increase in critical mach number force divergence mach number and the mach number at which drag rises peaks in other words sweep delays the onset of compressibility effects what is drag divergence mach number the drag divergence mach number not to be confused with critical mach number is the mach number at which the aerodynamic drag on an airfoil or airframe begins to increase rapidly as the mach number continues to increase this increase can cause the drag coefficient to rise to more than ten times its low speed valueincreasing wing sweepback increases the drag divergence mach number com encom080 1049bjpgthe effect of increasing angle of sweep is an increase in the critical mach number and an increase in the drag divergence mach number

Question 258-40 : Which of these statements about wing sweepback are correct or incorrect i decreasing wing sweepback increases mcritii decreasing wing sweepback increases the drag divergence mach number ?

I is incorrect ii is incorrect.

what is mcrit critical mach number com encom080 1049ajpgthe critical mach number of an aeroplane is the highest speed possible without supersonic flow over the wing what is sweepback most of the difficulties of transonic flight are associated with shock wave induced flow separation therefore any means of delaying or alleviating the shock induced separation improves aerodynamic performance one method is wing sweepback sweepback theory is based upon the concept that it is only the component of the airflow perpendicular to the leading edge of the wing that affects pressure distribution and formation of shock waveson a straight wing aircraft the airflow strikes the wing leading edge at 90° and its full impact produces pressure and lift a wing with sweepback is struck by the same airflow at an angle smaller than 90° this airflow on the swept wing has the effect of persuading the wing into believing that it is flying slower than it really is thus the formation of shock waves is delayed advantages of wing sweep include an increase in critical mach number force divergence mach number and the mach number at which drag rises peaks in other words sweep delays the onset of compressibility effects what is drag divergence mach number the drag divergence mach number not to be confused with critical mach number is the mach number at which the aerodynamic drag on an airfoil or airframe begins to increase rapidly as the mach number continues to increase this increase can cause the drag coefficient to rise to more than ten times its low speed valuedecreasing wing sweepback decreases the drag divergence mach number com encom080 1049bjpgthe effect of decreasing angle of sweep is a decrease in the critical mach number and a decrease in the drag divergence mach number