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Question 263-1 : In the transonic range the aeroplane characteristics are strongly determined by the ? [ Theoretical lift off ]
Mach number.
.transonic flight regime between sonic and supersonic speeds, only part of the airflow over the wing is above the speed of sound..the mach number is the speed used in transonic range.
Question 263-2 : Which statement is correct about an expansion wave in supersonic flow.1. the static temperature in front of an expansion wave is higher than the static temperature behind it..2. the speed in front of an expansion wave is higher than the speed behind it. ?
1 is correct and 2 is incorrect.
The effect on pressure, temperature density and velocity is the opposite in expansion waves to oblique/normal shock waves... chrism.supersonic flight is no longer part of the learning objectives i believe....learning objectives 081 02 01 05 subdivision of aerodynamic flow. list the subdivision of aerodynamic flow. subsonic flow.. transonic flow.. supersonic flow.. describe the characteristics of the flow regimes listed above.
Question 263-3 : What is the relation between the mach angle mu and the corresponding mach number ?
Sin mu = 1/m
. /com en/com080 602.jpg..
Question 263-4 : Which type of buffet will occur if a jet aeroplane slowly accelerates in level flight from its cruise speed in still air at high altitude ?
Mach buffet.
Question 263-5 : Which speeds are used and in which sequence if an emergency descent is carried out from the normal cruise altitude of a large jet transport aeroplane ?
Mmo, vmo.
.vmo/mmo is defined as the maximum operating limit speed. vmo is expressed in knots calibrated airspeed kcas , while mmo is expressed in mach number. the vmo limit is usually associated with operations at lower altitudes and deals with structural loads and flutter. the mmo limit is associated with operations at higher altitudes and is usually more concerned with compressibility effects and flutter. at lower altitudes, structural loads and flutter are of concern at higher altitudes, compressibility effects and flutter are of concern...in descent and at low altitude vmo..in climb and at high altitude mmo...at first, at high altitude, mmo must be taken in consideration, and after passing the 'crossosver altitude' the altitude at which a specified cas and mach value represent the same tas value , vmo must be used.
Question 263-6 : Aileron flutter can be caused by ?
Cyclic deformations generated by aerodynamic, inertial and elastic loads on the wing.
Question 263-7 : Regarding the transonic speed range ?
Both subsonic and supersonic speeds exist in the flow around the aeroplane.
.subsonic range is from 0 and ends at mcrit..transonic range starts at mcrit up to mach 1.3..supersonic range is from mach 1.3 to approximately mach 5..above mach 5 the hypersonic speed range.
Question 263-8 : The subsonic speed range ?
Ends at mcrit.
.subsonic range is from 0 and ends at mcrit..transonic range starts at mcrit up to mach 1.3..supersonic range is from mach 1.3 to approximately mach 5..above mach 5 the hypersonic speed range.
Question 263-9 : Which of these statements about the supersonic speed range is correct ?
The airflow everywhere around the aeroplane is supersonic.
.subsonic range is from 0 and ends at mcrit..transonic range starts at mcrit up to mach 1.3..supersonic range is from mach 1.3 airflow everywhere around the aeroplane is supersonic to approximately mach 5..above mach 5 the hypersonic speed range.
Question 263-10 : Which of these statements about an oblique shock wave are correct or incorrect. i. the static temperature in front of an oblique shock wave is lower than behind it.. ii. the static pressure in front of an oblique shock wave is lower than behind it. ?
I is correct, ii is correct.
Question 263-11 : Which of these statements about an oblique shock wave are correct or incorrect. i. the density in front of an oblique shock wave is lower than behind it.. ii. the total pressure in front of an oblique shock wave is higher than behind it. ?
I is correct, ii is correct.
Question 263-12 : Which of these statements about an oblique shock wave are correct or incorrect.i. the density behind an oblique shock wave is higher than in front of it..ii. the local speed of sound behind an oblique shock wave is higher than in front of it. ?
I is correct, ii is correct.
. /com en/normal and oblic shock wave.jpg.air is warmer behind the shock wave, thus local speed of sound is higher lss is directly proportional to air temperature.
Question 263-13 : Which of these statements about 'tuck under' are correct or incorrect.i. a contributing factor to 'tuck under' is a forward movement of the centre of pressure of the wing..ii. a contributing factor to 'tuck under' is an increase in the downwash angle at the location of the horizontal stabiliser. ?
I is incorrect, ii is incorrect.
.'tuck under' is the tendency to nose down when speed is increased into the transonic flight regime. as the mach number inscreases in the transonic range, the centre of pressure will move aft.. /com en/com080 418.jpg.'tuck under' is caused by a reduction in the downwash angle at the location of the horizontal stabiliser.
Question 263-14 : Which of these statements about an oblique shock wave are correct or incorrect.i. the local speed of sound in front of an oblique shock wave is lower than behind it..ii. the mach number in front of an oblique shock wave is higher than behind it. ?
I is correct, ii is correct.
. oblique/normal wave.. /com en/normal and oblic shock wave.jpg..
Question 263-15 : The speed range from approximately m=1.3 to approximately m=5 is called the ?
Supersonic range.
.subsonic range is from 0 and ends at mcrit..transonic range starts at mcrit up to mach 1.3..supersonic range is from mach 1.3 to approximately mach 5..above mach 5 the hypersonic speed range.
Question 263-16 : What is the highest speed possible without supersonic flow over the wing ?
Critical mach number.
.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..
Question 263-17 : When the speed over an aerofoil section increases from subsonic to supersonic, its aerodynamic centre ?
Moves from approximately 25% to about 50% of the chord.
The aerodynamic center is a point somewhere between the leading edge and the trailing edge where there will be no change in the pitching moment of the aerofoil as the pressure pattern on the aerofoil changes. this point on the aerofoil does not move as you change angle of attack and the pitching moment of a wing is always constant about it....in the transonic region, the formation of shock waves on the wing surface and the resulting separated flow causes movement of the wing aerodynamic center..the magnitude of the aerodynamic center movement depends on the design parameters of the wing. the aft shift of the aerodynamic center results in an increase in longitudinal stability at a constant mach number or an increase in angle of attack stability the aft shift of the aerodynamic center is analogous to moving the airplane center of gravity forward.
Question 263-18 : What is the value of the mach number if the mach angle equals 45° ?
1.4
.the formula is.mach angle = sin^ 1 x 1/machnumber.45° = sin^ 1 x 1/m.sin 45° = 1/m.m = 1.41.
Question 263-19 : If the mach number is 0.8 and the tas is 480 kt, what is the speed of sound ?
600 kt.
Jamacof .m = tas lss..0,8 = 480 lss.lss = 600.
Question 263-20 : One advantage of a supercritical wing aerofoil over a conventional one is ?
It allows a wing of increased relative thickness to be used for approximately the same cruise mach number.
Question 263-21 : The sonic boom of an aeroplane flying at supersonic speed is created by ?
Shock waves around the aeroplane.
Question 263-22 : A supercritical wing ?
Will develop no noticeable shock waves when flying just above mcrit.
Celsohernandez.what is a supercritical wing...when the speed of an aircraft approaches the speed of sound, the local airflow about the airplane, particularly above the upper surface of the wing, may exceed the speed of sound. such a condition is called supercritical flow. on previous aircraft, this supercritical flow resulted in the onset of a strong local shock wave above the upper surface of the wing illustration 'a'. this local wave caused an abrupt increase in the pressure on the surface of the wing, which may cause the surface boundary layer flow to separate from the surface, with a resulting severe increase in the turbulence of the flow. the increased turbulence leads to a severe increase in drag and loss in lift, with a resulting decrease in flight efficiency.. /com en/com080 969.jpg.supercritical airfoils are shaped to substantially reduce the strength of the shock wave and to delay the associated boundary layer separation illustration 'b'. since the airfoil shape allows efficient flight at supercritical flight speeds, a wing of such design is called a supercritical wing...just above mcrit, a supercritical wing will develop no noticeable shock waves.
Question 263-23 : The aft movement of the centre of pressure during the acceleration through the transonic flight regime will ?
Increase in static longitudinal stability.
Transonic flight regime between sonic and supersonic speeds, only part of the airflow over the wing is above the speed of sound...the aft movement of the centre of pressure during the acceleration through the transonic flight regime will increase the static longitudinal stability...as the mach number increases in the transonic range, the centre of pressure will move aft..a corrective pitch up input on the stabiliser is required. 685.to maintain equilibrium, an increase in downward force is required. the blue arrow, vector of the total aerodynamic lift, vertical to the centre of pressure, moves aft. red point is the centre of gravity..transonic range starts at mcrit up to mach 1.3...the aft movement of the centre of pressure will increase the initial tendency to return to the original state of equilibrium after being disturbed on the lateral axis longitudinal stability because more down force on the tail is required to maintain level flight thus a more important force will be necessary for disturbing this equilibrium the static longitudinal stability is increased.. 686.an aeroplane exhibits static longitudinal stability, if, when the angle of attack changes the change in total aeroplane lift acts aft of the centre of gravity...notice lateral stability decreases in the transonic range but it is not caused by the centre of pressure shift. it is caused by asymmetric shock wave generation on either wing.
Question 263-24 : What is the effect of aeroplane mass on shock wave intensity at constant mach number ?
Increasing mass increases shock wave intensity.
Shock wave intensity is determined by the aircraft design, the altitude, the size and weight of the aircraft. the power, or volume, of the shock wave is dependent on the quantity of air that is being accelerated, thus, increasing aeroplane mass will increase the quantity of air that is being accelerated at constant mach number.
Question 263-25 : The position of the centre of pressure on an aerofoil of an aeroplane cruising at supersonic speed when compared with that at subsonic speed is ?
Further aft.
Question 263-26 : Which of these statements about an oblique shock wave are correct or incorrect.i. the density in front of an oblique shock wave is higher than behind it..ii. the total pressure in front of an oblique shock wave is higher than behind it. ?
I is incorrect, ii is correct.
.. /com en/normal and oblic shock wave.jpg..behind a shock wave static pressure rises but speed, and therefore dynamic presure, falls. some energy is lost in the temperature rise, so total pressure static + dynamic has fallen..total pressure in front of an oblique shock wave is higher than behind it.
Question 263-27 : Assuming isa conditions and a descent below the tropopause at constant mach number and aeroplane mass, the ?
Lift coefficient decreases.
. descent at constant mach number means the tas will increase...if the tas increase at a constant mach number descent, we must reduce the angle of attack, to maintain lift at the same level during descent lift = 1/2 rho s v² cl , thus the lift coefficient cl will be decreased.
Question 263-28 : Which statement with respect to the speed of sound is correct ?
Varies with the square root of the absolute temperature.
Babar350.why the answer ' is independent of altitude' is wrong..since the right answer is ' varies with sqr root of kelvin temp' , it is indeed independent of altitude, isn't it...the speed of sound is dependent of altitude since temperature normally changes with altitude..speed of sound in kt = 39 x sqrt temperature in k°.
Question 263-29 : For most jet transport aeroplanes, the maximum operating limit speed, vmo ?
Is replaced by mmo at higher altitudes.
Question 263-30 : Behind a normal shock wave on an aerofoil section the local mach number is ?
Less than 1.
Img /com en/normal and oblic shock wave.jpg..
Question 263-31 : When shock stall occurs, lift will decrease because ?
Flow separation occurs behind the shock wave.
Question 263-32 : If ias remains constant, the effect of decreasing aeroplane mass is that mcrit ?
Increases.
Question 263-33 : Which of these statements on shock stall is correct ?
Shock stall is a stall due to flow separation caused by a shock wave.
Question 263-34 : Which of these statements about the transonic speed range is correct ?
The transonic speed range starts at mcrit and extends to mach numbers above m = 1.
Question 263-35 : When an aeroplane with the centre of gravity forward of the centre of pressure of the combined wing / fuselage is in straight and level flight, the vertical load on the tailplane will be ?
Downwards.
. /com en/com080 65.jpg
Question 263-36 : On a jet aeroplane engines mounted below the low wing the thrust is suddenly increased. which of these statements is correct about the elevator deflection required to maintain zero pitching moment ?
The elevator must be deflected downward.
. /com en/com080 526.jpg.thrust line is below the center of gravity if thrust is suddenly increased, it creates a pitching moment..to counteract, you must push the stick or control column forward. the elevator is deflected downward, the tail will be pushed upward. 2775
Question 263-37 : During landing of a low winged jet aeroplane, the greatest elevator up deflection is normally required when the flaps are ?
Fully down and the cg is fully forward.
. 2776
Question 263-38 : Rotation about the lateral axis is called ?
Pitching.
Rotation about the lateral axis is called pitching.. 686
Question 263-39 : Rolling is the rotation of the aeroplane about the ?
Longitudinal axis.
Rolling is the rotation of the aeroplane about the longitudinal axis. 2389
Question 263-40 : An aeroplane has static directional stability, in a side slip to the right, initially the ?
Nose of the aeroplane tends to move to the right.
.a side slip to the right is the slip of the tail to the right. the nose goes left..if an aeroplane has static directional stability, the initial tendency is to come back in the flight pattern of the aircraft through the air.. /com en/com080 74.jpg.directional stability is accomplished by placing a vertical stabilizer or fin to the rear of the centre of gravity on the upper portion of the tail section.
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