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Mcrit is the free stream mach number at which ? [ Certification weather ]

Question 225-1 : Somewhere about the airframe mach 1 is reached locally mach buffet occurs shock stall occurs the critical angle of attack is reached

.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. exemple 325 Somewhere about the airframe mach 1 is reached locally.Somewhere about the airframe mach 1 is reached locally.

Which of the following 1 aerofoils and 2 angles of attack will produce the ?

Question 225-2 : 1 thick and 2 large 1 thick and 2 small 1 thin and 2 large 1 thin and 2 small

.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 .if the aerofoil is thicker the airflow will have to travel a larger distance in a same time mach 1 will be reached earlier mcrit the speed in front of the aerofoil is reduced .if you increase angle of attack the speed of the airflow over the wing is increased during lift generation the airflow is accelerated on the upper side of the wing mach 1 over the wing will be reached earlier exemple 329 (1) thick and (2) large.(1) thick and (2) large.

The consequences of exceeding mcrit in a swept wing aeroplane may be assume no ?

Question 225-3 : Buffeting of the aeroplane and a tendency to pitch down an increase in speed and a tendency to pitch up engine unbalance and buffeting buffeting of the aeroplane and a tendency to pitch up

.we are not flying at low speed this is not a stall condition eg tendency to pitch up for a swept wing aeroplane .at high speed the center of pressure will move aft from its low transonic position at about 25% of the chord to a value at 45% of the chord this will result in a tendency to pitch down .the mach trim system will prevent this phenomenon tuck under . /com en/com080 418 jpg.mach.trim is automatically accomplished above mach 615 by adjusting the elevators with respect to the stabilizer as speed increases exemple 333 Buffeting of the aeroplane and a tendency to pitch down.Buffeting of the aeroplane and a tendency to pitch down.

A jet aeroplane cruises buffet free at constant high altitude which type of ?

Question 225-4 : Accelerated stall low speed stall shock stall deep stall

An accelerated stall is a stall that occurs while the aircraft is experiencing a load factor higher than 1 g for example while turning or pulling up from a dive in these conditions the aircraft stalls at higher speeds than the normal stall speed which always refers to straight and level flight accelerated stalls are often caused by abrupt or excessive control inputs if you're in a dive and pull back with enough suddenness and force to load the airplane to a typical design load factor of 2 5 g's you'll enter an accelerated stall if the airspeed drops below 1 58 times the stall speed at 1 g loading the square root of 2 5 is approximately 1 58 .a stall at a load factor greater than 1 even if the aircraft is decelerating is an accelerated stall exemple 337 Accelerated stall.Accelerated stall.

As the mach number increases from subsonic to supersonic the centre of pressure ?

Question 225-5 : To the mid chord position forward to a position near the leading edge to a position near the trailing edge

exemple 341 To the mid chord position.To the mid chord position.

The aft movement of the centre of pressure during the acceleration through the ?

Question 225-6 : Increase the static longitudinal stability decrease the static lateral stability decrease the longitudinal stability increase the static lateral 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 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 equilibium . 686.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 exemple 345 Increase the static longitudinal stability.Increase the static longitudinal stability.

In supersonic flight aerofoil pressure distribution is ?

Question 225-7 : Rectangular irregular triangular the same as in subsonic flight

.the pressure distribution top and bottom on a subsonic aerofoil is curved with a peak adjacent to the centre of pressure . /com en/com080 164a jpg.in supersonic flight there is no peak in the pressure distribution it being almost equal over the chord with the centre of pressure at 50% this makes it retangular . /com en/com080 164b jpg. exemple 349 Rectangular.Rectangular.

Shock stall ?

Question 225-8 : Occurs when the lift coefficient as a function of mach number reaches its maximum value results from flow separation behind the bow wave occurs as soon as mcrit is exceeded results from flow separation at the underside of the aerofoil

.when explaining the basic principles of flight we consider air to be incompressible at speedsless than 0 4 mach that is pressure is considered to have no effect on air density at speeds higher than 0 4m it is no longer practical to make that assumption because density changes in the airflow around the aircraft begin to make differences to the behaviour of the aircraft .at high altitude a large high speed jet transport aircraft will be cruising at a speed marginally above its critical mach number and will have a small shock wave on the wing if such an aircraft increases its lift by pitching up = lift coefficient increases the shock wave will rapidly grow larger causing the static pressure to increase sharply in the immediate vicinity of the shock wave the locally increased adverse pressure gradient will cause the boundary layer to separate immediately behind the shock wave this is called a 'shock stall' .'shock stall' occurs when the lift coefficient as a function of mach number reaches its maximum value exemple 353 Occurs when the lift coefficient, as a function of mach number, reaches its maximum value.Occurs when the lift coefficient, as a function of mach number, reaches its maximum value.

Which of the following flight phenomena can only occur at mach numbers above ?

Question 225-9 : Mach buffet dutch roll speed instability elevator stall

.mach buffet is a condition in which the wings begin to vibrate at supersonic speeds over the wing you will have to fly at a speed above mcrit to encounter this phenomenon exemple 357 Mach buffet.Mach buffet.

Which of the following flight phenomena can occur at mach numbers below the ?

Question 225-10 : Dutch roll tuck under mach buffet shock stall

.you have to fly at a speed above mcrit the critical mach number of an aerofoil is the free stream mach number at which sonic speed is first reached on the upper surface to encounter . tuck under the tendency to nose down when speed is increased into the transonic flight regime . mach buffet mach buffet is a condition in which the wings begin to vibrate at supersonic speeds over the wing . shock stall a shock stall is a stall caused by the airflow over an aircraft's wings being disturbed by shock waves when flying at mach numbers above the critical mach number .dutch roll may happen when static lateral stability is much more pronounced than static directional stability this can occur at mach numbers below the critical mach number exemple 361 Dutch roll.Dutch roll.

The mach trim system will ?

Question 225-11 : Adjust the stabiliser depending on the mach number keep the mach number automatically constant pump the fuel from tank to tank depending on the mach number adjust the elevator trim tab depending on the mach number

.as speed increases beyond the critical mach number mcrit shock wave formation at the root of a swept back wing will . reduce lift forward of the cg and. reduce downwash at the tailplane .together these factors will generate a nose down pitching moment at high mach numbers an aircraft will become unstable with respect to speed instead of an increasing push force being required as speed increases a pull force becomes necessary to prevent the aircraft accelerating further this is potentially dangerous .a small increase in mach number will give a nose down pitch which will further increase the mach number this in turn leads to a further increase in the nose down pitching moment this unfavourable high speed characteristic known as 'tuck under' would restrict the maximum operating speed of a modern high speed jet transport aircraft .to maintain the required stick force gradient at high mach numbers a mach trim system must be fitted this device sensitive to mach number may . deflect the elevator up. decrease the incidence of the variable incidence trimming tailplane or. move the cg rearwards by transferring fuel from the wings to a rear trim tank.by an amount greater than that required merely to compensate for the trim change this ensures the required stick force gradient is maintained in the cruise at high mach numbers exemple 365 Adjust the stabiliser, depending on the mach number.Adjust the stabiliser, depending on the mach number.

The mach trim system will prevent ?

Question 225-12 : Tuck under dutch roll buffeting shock stall

Img /com en/com080 418 jpg. mach trim system .a mach trim system provides speed stability at the higher mach numbers mach.trim is automatically accomplished above mach 615 by adjusting the elevators with respect to the stabilizer as speed increases the flight control computers use mach information from the adiru to compute a mach trim actuator position the mach trim actuator repositions the elevator feel and centering unit which adjusts the control column neutral position exemple 369 Tuck under.Tuck under.

When air has passed an expansion wave the static pressure is ?

Question 225-13 : Decreased decreased or increased depending on mach number increased unchanged

Lynx11 .expansion waves like shockwaves occur in supersonic flow only in a shockwave the flow may be reduced to subsonic but through an expansion wave the flow accelerates to a higher supersonic value and so if speed increases pressure decreases exemple 373 Decreased.Decreased.

The critical mach number of an aeroplane is the free stream mach number that ?

Question 225-14 : Local sonic flow buffet a shock wave supersonic flow

Abratinok .why shockwave is not a valid answer .thanks . jomargra .is not related the local sonic flow with the shock wave can we have local sonic flow in the wing without shock wave ..critical mach number is the free stream mach number at which local sonic flow exists on any part of the aeroplane sonic flow not supersonic therefore not more than m1 0 this is the reason why we don't have a shock wave exemple 377 Local sonic flow.Local sonic flow.

In transonic flight the ailerons will be less effective than in subsonic flight ?

Question 225-15 : Aileron deflection only partly affects the pressure distribution around the wing behind the shock wave pressure is lower aileron down deflection moves the shock wave forward aileron deflection only affects the air in front of the shock wave

.because the effect of the aileron on pressure distribution will not be felt ahead of the shockwave exemple 381 Aileron deflection only partly affects the pressure distribution around the wing.Aileron deflection only partly affects the pressure distribution around the wing.

Compressibility effects depend on ?

Question 225-16 : Mach number eas tas ias

Compressible flow is the area of fluid mechanics that deals with fluids in which the fluid density varies significantly in response to a change in pressure compressibility effects are typically considered significant if the mach number the ratio of the flow velocity to the local speed of sound of the flow exceeds 0 3 the most distinct differences between the compressible and incompressible flow models are that the compressible flow model allows for the existence of shock waves exemple 385 Mach number.Mach number.

The formula for the mach number is a= speed of sound ?

Question 225-17 : M= tas / a m= a / tas m= tas * a m= ias / a

.mach number formula is .m = tas / a.tas is true airspeed expressed in knots .'a' is 'local speed of sound' expressed in knots exemple 389 M= tas / aM= tas / a

If the altitude is increased and the tas remains constant in the troposphere ?

Question 225-18 : Increase decrease not change increase or decrease depending on the type of aeroplane

exemple 393 Increase.Increase.

Assuming isa conditions climbing at a constant mach number up the tropopause ?

Question 225-19 : Decrease first increase then decrease increase remain constant

exemple 397 Decrease.Decrease.

The speed of sound is determined only by ?

Question 225-20 : Temperature density pressure humidity

exemple 401 Temperature.Temperature.

In case of supersonic flow retarded by a normal shock wave a high efficiency ?

Question 225-21 : Small but still supersonic exactly 1 high supersonic lower than 1

.to obtain a high efficiency the mach number in front of the shock wave should remain supersonic if mach number is too slow or equal to the supersonic speed the shock wave would not appear if the mach number is too fast we will obtain a low mach number after the shock wave and a too weak efficiency exemple 405 Small but still supersonic.Small but still supersonic.

The regime of flight from the critical mach number up to approximately m = 1 3 ?

Question 225-22 : Transonic range supersonic range hypersonic range subsonic 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 exemple 409 Transonic range.Transonic range.

Just above the critical mach number the first evidence of a shock wave will ?

Question 225-23 : Upper side of the wing lower side of the wing leading edge of the wing trailing edge 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 at leading edge .the first evidence of a shock wave will appear at the upper side of the wing where sonic speed is reached exemple 413 Upper side of the wing.Upper side of the wing.

Shock induced separation results in ?

Question 225-24 : Decreasing lift constant lift increasing lift decreasing drag

.for larger mach number shock induced separation is encountered and the flow becomes unsteady with unsteady shock motions on the upper and lower surface that are out of phase with each other as the mach number is increased a steady shock reappears it is sufficiently strong to induce flow separation .the shock induced separation results in a loss of lift on the upper surface of the airfoil along with increased drag exemple 417 Decreasing lift.Decreasing lift.

In the transonic range lift will decrease at the shock stall due to the ?

Question 225-25 : Separation of the boundary layer at the shock waves attachment of the shock wave on the trailing edge of the wing first appearance of a shock wave at the upper side of the wing appearance of the bow wave

. /com en/com080 188 jpg.when shock wave interacts with boundary layer flow flow separation occurs .you will have an increase in aerodynamic drag and therefore a loss of lift exemple 421 Separation of the boundary layer at the shock waves.Separation of the boundary layer at the shock waves.

Is a transport aeroplane allowed to fly at a higher mach number than the ?

Question 225-26 : No this is not acceptable this causes no problems but only during approach if you want to fly fast at very high altitudes

exemple 425 No, this is not acceptable.No, this is not acceptable.

The mach number is the ratio between the ?

Question 225-27 : Tas of the aeroplane and the speed of sound of the undisturbed flow tas of the aeroplane and the speed of sound at sea level ias of the aeroplane and the speed of sound of the undisturbed flow ias of the aeroplane and the speed of sound at sea level

.mach number formula is .mach number = tas / lss.tas is true airspeed expressed in knots .lss is local speed of sound expressed in knots

A normal shock wave ?

Question 225-28 : Can occur at different points on the aeroplane in transonic flight is a discontinuity plane in an airflow in which the temperature drops suddenly is a discontinuity plane in an airflow in which the pressure drops suddenly is a discontinuity plane in an airflow which is always normal to the surface

exemple 433 Can occur at different points on the aeroplane in transonic flight.Can occur at different points on the aeroplane in transonic flight.

The critical mach number of an aerofoil is the free stream mach number at which ?

Question 225-29 : Sonic speed m=1 is first reached on the upper surface the maximum operating temperature is reached a shock wave appears on the upper surface a 'supersonic bell' appears on the upper surface

.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 transonic passenger jet you must flight below mcrit since if you encounter turbulence the air flow around the wing may reach mcrit on the upper surface and buffeting can appear furthermore the center of pressure will move aft from its low transonic position at about 25% of the chord to its high transonic value at 45% of the chord exemple 437 Sonic speed (m=1) is first reached on the upper surface.Sonic speed (m=1) is first reached on the upper surface.

An aeroplane is descending at a constant mach number from fl 350 what is the ?

Question 225-30 : It increases as temperature increases it decreases as pressure increases it decreases as altitude decreases it remains constant

.mach number is a dimensionless quantity representing the ratio of speed and the local speed of sound .the speed of sound is function of the temperature .speed of sound in kt = 39 x sqrt temperature in k°

A jet aeroplane is cruising at high altitude with a mach number that provides a ?

Question 225-31 : Fly at a lower altitude and the same mach number extend the flaps to the first selection fly at a higher mach number fly at a larger angle of attack

.by flying at a lower altitude with the same mach number you will decrease the low speed buffet the stall margin is increased

The critical mach number of an aeroplane is the mach number ?

Question 225-32 : Above which locally supersonic flow exists somewhere over the aeroplane at which there is subsonic flow over all parts of the aeroplane at which there is supersonic flow over a part of the aeroplane at which the aeroplane has zero buffet margin

exemple 449 Above which, locally, supersonic flow exists somewhere over the aeroplane.Above which, locally, supersonic flow exists somewhere over the aeroplane.

The mach trim function is installed on most commercial jets in order to ?

Question 225-33 : Changes in the position of centre of pressure increased drag due to shock wave formation uncontrolled changes in stabiliser setting compressibility effects on the stabiliser

.as the mach increases the centre of pressure moves aft and the nose of the aircraft will tend to drop mach tuck mach trim is automatically applied above m0 6 on most commercial jets to the elevators to counteract this and to provide speed stability exemple 453 Changes in the position of centre of pressure.Changes in the position of centre of pressure.

Which statement is correct about a normal shock wave ?

Question 225-34 : The airflow changes from supersonic to subsonic the airflow changes direction the airflow changes from subsonic to supersonic the airflow expands when passing the aerofoil

. /com en/normal and oblic shock wave jpg.

When the air is passing through a shock wave the static temperature will ?

Question 225-35 : Increase decrease stay constant decrease and beyond a certain mach number start increasing again

. /com en/normal and oblic shock wave jpg. exemple 461 Increase.Increase.

When the air is passing through a shock wave the density will ?

Question 225-36 : Increase decrease stay constant decrease and beyond a certain mach number start increasing again

. /com en/normal and oblic shock wave jpg. exemple 465 Increase.Increase.

When air has passed through a shock wave the local speed of sound is ?

Question 225-37 : Increased not affected decreased decreased and beyond a certain mach number start increasing again

. /com en/normal and oblic shock wave jpg.

If the mach number of an aeroplane in supersonic flight is increased the mach ?

Question 225-38 : Decrease increase stay constant decrease and beyond a certain mach number start increasing again

. /com en/com080 602 jpg. /com en/com080 308 jpg.the higher the mach number is the narrower the cone angle will be exemple 473 Decrease.Decrease.

The loss of total pressure in a shock wave is due to the fact that ?

Question 225-39 : Kinetic energy in the flow is converted into heat energy the speed reduction is too high the static pressure decrease is comparatively high the friction in the boundary layer is higher

exemple 477 Kinetic energy in the flow is converted into heat energy.Kinetic energy in the flow is converted into heat energy.

When the air is passing through an expansion wave the local speed of sound will ?

Question 225-40 : Decrease increase stay constant decrease and beyond a certain mach number start increasing again

.the effect on pressure temperature density and velocity is the opposite in expansion waves to oblique/normal shock waves . expansion wave .also known as a prandtl meyer expansion fan when a supersonic airflow passes over a surface that suddenly drops away or rounds corner an expansion fan of an infinite number of shock waves forms at the apex of the corner and diverts the airflow around the corner .airflowing through an expansion fan goes through the following changes .1 the airsteam accelerates and the air behind the shock wave has higher supersonic velocity.2 the airflow direction follows the surface contour.3 the static pressure behind the expansion wave decreases.4 the density behind the expansion wave decreases.5 there is no loss of energy . /com en/com080 369 jpg. oblique/normal wave . /com en/normal and oblic shock wave jpg. exemple 481 Decrease.Decrease.

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