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Question 260-1 : The increase in stall speed ias with increasing altitude is due to ? [ Theoretical lift off ]
Compressibility effects.
.the ias stall speed is considered constant at low altitudes because of the tas stall speed increases due to the decreasing altitude, but the ias is almost constant. this is because the factor increasing the tas stall speed density also affects the ias speed, in the same amount..however, at higuer altitudes we consider another factor, the compresibility, that affects the anemometer and hence increases the reading of ias..resuming, the ias stall speed is considered constant at lower altitudes below 10000 ft and increases with altitude at higuer altitudes, due to compresibility effects...higher altitude > lower air density + lower air viscosity because of lower temperatures > lower reynolds number > less kinematic energy in the boundary layer to oppose adverse pressure gradients > earlier flow separation > lower clmax and aoacrit > higher stall speed.
Question 260-2 : An large jet transport aeroplane has the following four flap positions up, take off, approach and landing and two slat positions retracted and extended. generally speaking, the selection that provides the highest positive contribution to clmax is ?
Slats from retracted to extended.
.when trailing edge flaps are deployed from up to take off, there will be a comparatively large increase in cl and a small increase in cd, but with each successive increase in flap angle, the increase in cl coefficient of lift will be less, whereas the increase in cd coefficient of drag will be greater.....when considering just trailing edge flaps in isolation, it could be said that the greatest increase in clmax will be when the flaps move from up to take off.....data shows that the most efficient trailing edge flap triple slotted fowler flap increases clmax by about 100% but only when fully deployed. we can only speculate on the increment in clmax from up to take off.....however, when considering just slats in isolation, the same data shows the increase in clmax for the slat from retracted to extended is about 60%.....of the four answers offered it can be said that the slats moving from retracted to extended would be the selection that will provide the highest positive contribution to clmax.
Question 260-3 : In a straight, steady climb the thrust must be ?
Greater than the drag because it must also balance a component of weight.
Question 260-4 : Regarding a positively cambered aerofoil section, which statement is correct..i. the angle of attack has a negative value when the lift coefficient equals zero..ii. a nose down pitching moment exists when the lift coefficient equals zero. ?
I is correct and ii is correct.
. /com en/com080 1030a.jpg. /com en/com080 1030b.jpg.for a positively cambered aerofoil section, the angle of attack has a negative value when the lift coefficient equals zero...example a positively cambered aerofoil section. /com en/com080 909.jpg.in this example, lift coefficient = 0 when angle of attack = 4° the angle of attack is negative and the pitching moment is nose down.
Question 260-5 : Regarding a symmetric aerofoil section, which statement is correct.i. the angle of attack is zero when the lift coefficient equals zero..ii. the pitching moment is zero when the lift coefficient equals zero. ?
I is correct and ii is correct.
. /com en/com080 687a.jpg.a symmetrical aerofoil needs to have a positive pitch to produce lift. if the pitching moment is zero, the lift is zero.
Question 260-6 : Regarding a symmetric aerofoil section, which statement is correct.i. the angle of attack has a positive value when the lift coefficient equals zero..ii. a nose down pitching moment exists when the lift coefficient equals zero. ?
I is incorrect and ii is incorrect.
. /com en/com080 687a.jpg.a symmetrical aerofoil needs to have a positive pitch to produce lift. if the pitching moment is zero, the lift is zero.
Question 260-7 : Which of these statements about wing sweepback are correct or incorrect.i. increasing wing sweepback increases mcrit..ii. increasing wing sweepback increases the drag divergence mach number. ?
I is correct, ii is correct.
What is mcrit critical mach number .. /com en/com080 1049a.jpg..the 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 waves...on 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 value..increasing wing sweepback increases the drag divergence mach number... /com en/com080 1049b.jpg..the effect of increasing angle of sweep is an increase in the critical mach number and an increase in the drag divergence mach number.
Question 260-8 : Considering subsonic incompressible airflow through a venturi, which statement is correct.i. the dynamic pressure in the throat is higher than in the undisturbed airflow..ii. the total pressure in the throat is the same as in the undisturbed airflow. ?
I is correct, ii is correct.
Img /com en/com080 815.jpg..static pressure decreases in a venturi, and airflow speed increases.
Question 260-9 : Which of these statements about the strength of wing tip vortices are correct or incorrect.i. assuming no flow separation, the strength of wing tip vortices decreases as the angle of attack decreases..ii. the strength of wing tip vortices increases as the aspect ratio decreases. ?
I is correct, ii is correct.
.formation of vortices.the action of the airfoil that gives an aircraft lift also causes induced drag. when an airfoil is flown at a positive aoa, a pressure differential exists between the upper and lower surfaces of the airfoil. the pressure above the wing is less than atmospheric pressure and the pressure below the wing is equal to or greater than atmospheric pressure. since air always moves from high pressure toward low pressure, and the path of least resistance is toward the airfoil's tips, there is a spanwise movement of air from the bottom of the airfoil outward from the fuselage around the tips. this flow of air results in 'spillage' over the tips, thereby setting up a whirlpool of air called a 'vortex'...just as lift increases with an increase in aoa, induced drag also increases. this occurs because as the aoa is increased , there is a greater pressure difference between the top and bottom of the airfoil, and a greater lateral flow of air consequently, this causes more violent vortices to be set up, resulting in more turbulence and more induced drag...the strength of the wingtip vortices is determined by the magnitude of the pressure difference between the upper and lower wing surfaces, and by the time during which this pressure difference acts to drive the air into the vortices. the greater the pressure difference or the longer the time available, the stronger the vortices will be...the time during which the pressure difference acts upon the air is proportional to the time it takes the air to pass from the leading edge to the trailing edge of the wing. so for any given airspeed, the length of the wing chord determines the time taken. this means that decreasing the chord length will decrease the vortex strength, which will decrease the stalling angle and the drag...the intensity or strength of the vortices is directly proportional to the weight of the aircraft and inversely proportional to the wingspan and speed of the aircraft...good answers for this kind of questions.assuming no flow separation, the strength of wing tip vortices increases as the angle of attack increases..assuming no flow separation, the strength of wing tip vortices decreases as the angle of attack decreases..the strength of wing tip vortices decreases as the aspect ratio increases..the strength of wing tip vortices increases as the aspect ratio decreases.
Question 260-10 : Considering subsonic incompressible airflow through a venturi, which statement is correct.i. the dynamic pressure in the undisturbed airflow is higher than in the throat..ii. the total pressure in the undisturbed airflow is lower than in the throat. ?
I is incorrect, ii is incorrect.
Img /com en/com080 815.jpg..static pressure decreases in a venturi, and airflow speed increases.
Question 260-11 : Assuming no flow separation, which of these statements about the flow around an aerofoil as the angle of attack decreases are correct or incorrect.i. the stagnation point moves up..ii. the point of lowest static pressure moves aft. ?
I is correct, ii is correct.
Question 260-12 : Considering subsonic incompressible airflow through a venturi, which statement is correct.i. the dynamic pressure in the undisturbed airflow is lower than in the throat..ii. the total pressure in the undisturbed airflow is higher than in the throat. ?
I is correct, ii is incorrect.
Img /com en/com080 815.jpg..static pressure decreases in a venturi, and airflow speed increases.
Question 260-13 : 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 ?
Tas is lower at the lower altitude.
.in straight and level flight, lift does not change as it is only balancing against weight.....aircraft is maintaining level flight and therefore lift cannot change....lift = cl 1/2rho v² s....cl = lift coefficient..rho = density..v = tas in m/s..s = surface....at the same angle of attack same cl , with 'rho' increasing with decreasing altitude, since surface 's' does not change, only tas can be must be reduced.
Question 260-14 : The main purpose of a boundary layer fence on a swept wing is to ?
Improve the low speed handling characteristics.
.the spanwise flow encountered with swept wings may be reduced by the use of stall fences, which are thin plates parallel to the axis of symmetry of the airplane.. /com en/com080 1207.jpg.in this manner a strong boundary layer buildup over the ailerons is prevented...notice recent aircrafts do not use boundary layer fence anymore.
Question 260-15 : The stall speed decreases. all other relevant factors are constant ?
When, during a manoeuvre, the aeroplane nose is suddenly pushed firmly downwards e.g. as in a push over.
.when flaps are retracted the stall speed increases you will stall at a higher speed than the speed with flaps deployed..stall speed is based on 1g flight, when you do a push over, load factor decreases..stall speed changes at the square root of the load factor..vs at 1g = 100 kt..if load factor is 0.5g, now stall speed is square root 0.5 = 0.7 x 100 kt = 70 kt.
Question 260-16 : The load factor is greater than 1 one ?
When lift is greater than weight.
.dividing lift by weight gives load factor..load factor increases in a turn and in a pull up manoeuvre. those actions require more lift.
Question 260-17 : Which of these statements about weight or mass is correct ?
In the si system the unit of measurement for weight is the newton.
The si unit of weight is the newton n = kg.m/s².
Question 260-18 : What is the effect of winglets on the drag of the wing ?
Increase parasite drag, decrease induced drag.
Question 260-19 : If the wing area is increased, lift will ?
Increase because it is directly proportional to wing area.
Question 260-20 : Which of these statements about stall speed is correct ?
Increasing forward sweep increases stall speed.
.the effect of increasing wing sweep angle is to decrease the lift curve slope and clmax as depicted below. /com en/com080 999.jpg.while the swept wing offers a strong transonic drag reduction, the lift penalty at high angle of attack is substantial. as a wing is swept, clmax decreases... /com en/com080 1226.jpg.spanwise airflow over a forward swept wing is the reverse of a conventional swept wing, but the stall speed increases or decreases in a same way.
Question 260-21 : The lift formula can be written as. rho = density ?
L = cl * 1/2rho * v² * s.
.where. 1/2 rho is dynamic pressure.. cl is coefficient of lift.. v is speed in m/s.. s is wing area.
Question 260-22 : During a straight, steady climb and with the thrust force parallel to the flight path ?
Lift is the same as during a descent at the same angle and mass.
During climb and descent, lift is lower than weight..lift is a vertical vector..lift in climb or descent = weight x cos climb angle.
Question 260-23 : Assuming no compressibility effects, induced drag at constant ias is affected by ?
Aeroplane mass.
Question 260-24 : Given that.pstat = static pressure..rho = density..pdyn = dynamic pressure..ptot = total pressure..bernoulli's equation reads as follows ?
Pstat + 1/2rho * tas² = constant.
.dynamic pressure is '1/2 rho tas²'...bernoulli's theorem is.pt = ps + pd.then, if pd inscreases, ps decreases, as pt always remains constant.
Question 260-25 : The point in the diagram giving the lowest speed in unaccelerated flight is.. err a 081 1265 ?
Point 4.
Img /com en/com080 1264.jpg..
Question 260-26 : The point in the annex showing zero lift is.. err a 081 1269 ?
Point a.
Question 260-27 : If the airspeed reduces in level flight below the speed for maximum l/d, the total drag of an aeroplane will ?
Increase because of increased induced drag.
.total drag is lowest when parasite drag is equal to the induced drag. /com en/com032 209.jpg..if the airspeed reduces below the speed for maximum lift/drag ratio, then induced drag increases, thus total drag increases...notice if the airspeed increases above the speed for maximum l/d, total drag also increases, due to increase of the parasite drag...parasite drag only varies with speed and is directly proportional to v²..induced drag varies with lift, speed and aspect ratio, is inversely proportional to aspect ratio and v² so multiply by 1/v².
Question 260-28 : Slat or flap asymmetry occurring after either extension or retraction, may have an effect on controllability since ?
Slat asymmetry causes a yawing moment, whereas flap asymmetry causes a large rolling moment.
At high speed the angle of attack will be small and with an asymmetric leading edge slat deployment, there will be little change in cl but cd would increase on the deployed slat turbulent boundary layer. this causes yaw which can be controlled by rudder...however at lower speeds and high angle of attack, a large change in clmax will occur between the wings with a flap asymmetry. this would then lead to a strong rolling moment.
Question 260-29 : Which of the following variables are required to calculate lift from the lift formula ?
Dynamic pressure, lift coefficient and wing area.
.lift formula = 1/2 rho cl x v² x s...where..'1/2 rho v²' is dynamic pressure rho = density, v = speed in m/s...'cl' is coefficient of lift...'s' is wing area.
Question 260-30 : Which of these statements about weight or mass is correct ?
Weight is a force.
Question 260-31 : The induced angle of attack is ?
The angle by which the relative airflow is deflected due to downwash.
.the angle between the chord line and effective airflow is the effective angle of attack the angle between effective airflow and the horizontal flow that was the relative airflow is called the induced angle of attack, which is equal to the downwash angle.
Question 260-32 : When an aeroplane enters ground effect ?
The lift is increased and the drag is decreased.
Question 260-33 : Which of these statements about weight or mass is correct ?
The mass of a body can be determined by dividing its weight by the acceleration due to gravity.
Question 260-34 : Which of these statements about weight or mass is correct ?
The weight of a body can be determined by multiplying its mass by the acceleration due to gravity.
Question 260-35 : From a polar curve of the entire aeroplane one can read ?
The maximum cl/cd ratio and maximum lift coefficient.
Question 260-36 : The diagram shows the parameter x versus tas. if a horizontal flight is considered the axis x shows.. err a 081 1319 ?
The coefficient of lift.
New question cqb 15 august 2011...this question already exists in the database with answer 'induced drag'...'lift formula.lift = 1/2 rho cl x v² x s...where..'1/2 rho' is dynamic pressure...'cl' is coefficient of lift...'v' is speed in m/s...'s' is wing area...if the speed is increase, angle of attack has to be reduced to maintain lift contant coefficient of lift will reduce as the speed increases.
Question 260-37 : The additional increase in drag at mach numbers above the critical mach number is due to ?
Wave drag.
Question 260-38 : Air passes a normal shock wave. which of the following statements is correct ?
The static temperature increases.
Img /com en/normal and oblic shock wave.jpg..
Question 260-39 : The bow wave will first appear at ?
A mach number just above m = 1.
.a bow wave is a shock wave that forms when the aircraft is flying at a speed just faster than the speed of sound..the bow wave is so named because it is similar to a wave inwater off the bow of a boat.. /com en/com080 41.jpg.the wave is in front of the body.
Question 260-40 : Two methods to increase the critical mach number are ?
Thin aerofoils and sweepback of the wing.
.the critical mach number of an aerofoil is the free stream mach number at which sonic speed m=1 is first reached on the upper surface. /com en/com080 152.jpg. in this example, mcrit = 0.72...on 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. /com en/com080 1049b.jpg..the effect of increasing angle of sweep is an increase in the critical mach number...furthermore, if the aerofoil is thinner, the airflow will have to travel less distance over the upper wing surface than on a thicker aerofoil, in a same time period. the mcrit can be increased since mach 1 will be reached later locally.
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