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Question 241-1 : 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 ? [ Question security ]

The elevator must be deflected downward

Img /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 . 885. exemple 341 The elevator must be deflected downward.

Question 241-2 : 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

Img681. exemple 345 Fully down and the cg is fully forward.

Question 241-3 : Rotation about the lateral axis is called ?

Pitching

Rotation about the lateral axis is called pitching . 686 exemple 349 Pitching.

Question 241-4 : Rolling is the rotation of the aeroplane about the ?

Longitudinal axis

.rolling is the rotation of the aeroplane about the longitudinal axis . 684 exemple 353 Longitudinal axis.

Question 241-5 : 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 intial 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 exemple 357 Nose of the aeroplane tends to move to the right.

Question 241-6 : The cg of an aeroplane is in a fixed position forward of the neutral point speed changes cause a departure from the trimmed position which of these statements about the stick force stability is correct ?

Stick force stability is not affected by trim

.stick force gradient stick force stability is one measure of longitudinal stability if the stability does not change then neither does the stick force gradient changing the trim setting changes the total stick force and the 'in trim' point but not the gradient stick force stability is not affected by trim .it can be seen from this figure . /com en/com080 75 jpg.the slope of the curve is much smaller at low speed than at high speed indicating that answer 'an increase of 10 kt from the trimmed position at low speed has more effect on the stick force than an increase of 10 kt from the trimmed position at high speed' is incorrect .an increase in speed must generate a pull force .answer 'aeroplane nose up trim decreases the stick force stability' is incorrect because aeroplane nose up trim decreases stick force stability exemple 361 Stick force stability is not affected by trim.

Question 241-7 : The 1 stick force stability and the 2 manoeuvre stability are positively affected by ?

1 forward cg movement 2 forward cg movement

.positive is more stick force and more manoeuvre stability .negative is less stick force and less manoeuvre stability .cs 25 requires a minimum stick force stability of 1 lb per 6 kt change in speed .if you move the cg too far back towards the neutral point then it gets lighter on the stick and you will not satisfy the regulation so if the cg is forward your aircraft is more stable and a change in pitch requires a positive 'force' on the stick or on the control column exemple 365 (1) forward cg movement (2) forward cg movement.

Question 241-8 : The value of the manoeuvre stability of an aeroplane is 150 n/g the stick force required to achieve a load factor of 2 5 from steady level flight is ?

225 n

.the question states steady level flight so we are at 1g ..we only require +1 5g to reach a load factor of 2 5g..1 5 x 150 n/g = 225 n exemple 369 225 n.

Question 241-9 : For a normal stable aeroplane the centre of gravity is located ?

With a sufficient minimum margin ahead of the neutral point of the aeroplane

exemple 373 With a sufficient minimum margin ahead of the neutral point of the aeroplane.

Question 241-10 : The maximum aft position of the centre of gravity is amongst others limited by the ?

Required minimum value of the stick force per g

.the magnitude of the stick force required to pitch for an aircraft with manual controls is determined by the distance the cg is forward of the neutral point .when the centre of gravity moves forward the stick force per g increases but you need a minimum value of the stick force per g and if the position of the centre of gravity is too aft a small input from the tail will generate a large unstable wing moment and you will get a rapid attitude change with little tailplane deflection moving the cg aft reduces longitudinal static stability and hence the degree of stick force the maximum aft position of the centre of gravity is amongst others limited by the required minimum value of the stick force per g exemple 377 Required minimum value of the stick force per g.

Question 241-11 : Longitudinal static stability is created by the fact that the ?

Centre of gravity is located in front of the neutral point of the aeroplane

exemple 381 Centre of gravity is located in front of the neutral point of the aeroplane.

Question 241-12 : Following a disturbance an aeroplane oscillates about the lateral axis at a constant amplitude the aeroplane is ?

Statically stable dynamically neutral

. static stability .static stability refers to the initial tendency or direction of movement back to equilibrium in aviation it refers to the aircraft's initial response when disturbed from a given aoa slip or bank .positive static stability is the initial tendency of the aircraft to return to the original state of equilibrium after being disturbed . dynamic stability .dynamic stability refers to the aircraft response over time when disturbed from a given aoa slip or bank .neutral dynamic stability means once displaced the displaced object neither decreases nor increases in amplitude a worn automobile shock absorber exhibits this tendency .for information . positive dynamic stability means over time the motion of the displaced object decreases in amplitude and because it is positive the object displaced returns toward the equilibrium state . negative dynamic stability means over time the motion of the displaced object increases and becomes more divergent exemple 385 Statically stable - dynamically neutral

Question 241-13 : Which statement on dynamic longitudinal stability of a conventional aeroplane is correct ?

Damping of the phugoid is normally very weak

. /com en/com080 483a jpg.since the pitch rate is quite low and only negligible changes in angle of attack take place damping of the phugoid is weak however such weak damping does not necessarily have any great consequence since the period of oscillation is so great long period oscillation is easily controlled by the pilot exemple 389 Damping of the phugoid is normally very weak.

Question 241-14 : The 'short period mode' is an ?

Oscillation about the lateral axis

.oscillation about the lateral axis 'short period mode' is movement in the longitudinal axis . 686.the short period mode is a usually heavily damped oscillation with a period of only a few seconds the motion is a rapid pitching of the aircraft about the center of gravity the period is so short that the speed does not have time to change so the oscillation is essentially an angle of attack variation the change could be caused by a sudden gust or by a longitudinal displacement of the stick . short period mode . /com en/com080 84 jpg.for information the longer period mode is called the 'phugoid' exemple 393 Oscillation about the lateral axis.

Question 241-15 : An aeroplane that has positive static stability ?

Can be dynamically stable neutral or unstable

exemple 397 Can be dynamically stable, neutral or unstable.

Question 241-16 : A statically unstable aeroplane is ?

Never dynamically stable

exemple 401 Never dynamically stable.

Question 241-17 : One of the requirements for positive dynamic stability is ?

Positive static stability

exemple 405 Positive static stability.

Question 241-18 : Which of the following statements about dihedral is correct ?

The 'effective dihedral' of an aeroplane component means the contribution of that component to the static lateral stability

.the dihedral is the angle between the wings and the horizontal looked at from the front where the wingtips are higher than the roots .it is an angle that raises the centerline of the wing tip above the centreline of the root . /com en/com080 208 jpg.effective dihedral is pretty much what it sounds like effective dihedral is the effect of other aspects of the aircraft configuration that produce an effect similar to geometric dihedral many aspects of an aircraft's configuration can effect its effective dihedral but two major components are wing sweep and the wing location with respect to the fuselage such as a low wing or high wing .as a rough estimation 10° of sweepback on a wing provides about 1° of effective dihedral while a high wing configuration can provide about 5° of effective dihedral over a low wing configuration .when a wing goes down dihedral effect will tend to decrease bank angle and roll the wing back up this is a positive contribution to the static lateral stability exemple 409 The 'effective dihedral' of an aeroplane component means the contribution of that component to the static lateral stability.

Question 241-19 : Which design features improve static lateral stability .1 high wing.2 low wing.3 large and high vertical fin.4 ventral fin.the combination that regroups all of the correct statements is ?

1 3

.for static lateral stability to be present an aircraft must have stopped rolling and be side slipping .the design features that provide static lateral stability are . the dihedral effect increase in angle of attack on the lower wing compared to the upper wing . high wing and low cg pendulous affect . keel effect the keel/side surface above the centre of gravity will be presented to the relative airflow which will give a force to help in correcting the roll and a low cg .an aircraft can have one or a combination of the above to provide the required amount of static lateral stability although some aircraft may be too stable and methods such as anhedral wings are used to reduce static lateral stability .more information on vertical and ventral fin .dorsal and ventral fins contribute in exactly the same way to directional static stability a dorsal fin contributes positively to lateral static stability . /com en/com080 618a jpg.if the aircraft is yawed to the left the dorsal and ventral fins will create a side force to the left the line of action of this force is well aft of the aircraft cg giving a yawing moment to the right a stabilising effect . /com en/com080 618b jpg.the ventral fin being below the aircraft cg has a negative influence on lateral static stability . /com en/com080 618c jpg. exemple 413 1, 3.

Question 241-20 : Which wing design feature decreases the static lateral stability of an aeroplane ?

Anhedral

. first static stability .static stability refers to the initial tendency or direction of movement back to equilibrium in aviation it refers to the aircraft's initial response when disturbed from a given aoa slip or bank . second static lateral stability of an aeroplane .an aircraft that tends to return to wings level flight after it has been disturbed is considered to be laterally stable . now what is anhedral and dihedral wing design features .this is the upward and outward slope of the wing if the wing tip is higher than the wing root relative to the horizontal plane the aircraft has positive dihedral negative dihedral is termed anhedral . /com en/com080 94 jpg.when an aircraft rolls the aircraft will begin to sideslip the lower wing presents a larger span as seen from the direction of the approaching air the effect is to roll the aircraft back towards the horizontal .this will always be a restoring moment for a dihedral wing but it's the opposite for an anhedral wing . what about high wing .mounting the wings above the centre of gravity aids lateral stability because the weight of the aircraft will act as a pendulum to restore level flight . and why increased wing span do not decrease the static lateral stability .without dihedral if the restoring moment is insufficient to restore level flight the aircraft will begin to sideslip .in a sideslip the lower wing has in increased angle of attack while the upper wing has a reduced angle of attack the greater lift on the lowered wing will restore level flight and this effect is increase with an increased wing span exemple 417 Anhedral.

Question 241-21 : The manoeuvrability of an aeroplane is best when the ?

Cg is on the aft cg limit

.manoeuvrability is the ability of a pilot to increase the load factor of the aircraft which is of course accomplished through turning climbing or descending .however manoeuvre stability is the aircrafts ability to resist such a change .thus a forward cg will increase the stability but reduce controllability manoeuvrability where as an aft cg will be just the opposite exemple 421 Cg is on the aft cg limit.

Question 241-22 : The effect of a ventral fin on the static stability of an aeroplane is as follows . 1=longitudinal 2=lateral 3=directional ?

1 no effect 2 negative 3 positive

. static stability .static stability refers to the initial tendency or direction of movement back to equilibrium in aviation it refers to the aircraft's initial response when disturbed from a given aoa slip or bank .a dorsal or ventral fine will increase directional stability the fin acts like a weathercock to keep the aircraft straight if it yaws the surface is struck more from the side to force the nose back while decreasing lateral stability the ventral fin makes you roll when hit by a gust from the side .ventral fin has no effect on pitching longitudinal axis exemple 425 1 : no effect, 2 : negative, 3 : positive

Question 241-23 : Which of the following statements about static lateral and directional stability is correct ?

An aeroplane with an excessive static directional stability in relation to its static lateral stability will be prone to spiral dive spiral instability

.spiral divergence will exist when static directional stability is very large when compared to the static lateral stability dihedral effect when a wing goes down dihedral effect will tend to decrease bank angle and roll the wing back up .the character of spiral divergence is not violent the aeroplane when disturbed from the equilibrium of level flight begins a slow spiral which gradually increases to a spiral dive when a small sideslip is introduced the strong directional stability tends to restore the nose into the wind while the relatively weak 'dihedral effect' lags in restoring the aeroplane laterally the rate of divergence in the spiral motion is usually so gradual that the pilot can control the tendency without difficulty

Question 241-24 : Which moments or motions interact in a dutch roll ?

Rolling and yawing

exemple 433 Rolling and yawing.

Question 241-25 : Ignoring downwash effects on the tailplane extension of fowler flaps will produce ?

A nose down pitching moment

exemple 437 A nose-down pitching moment.

Question 241-26 : Which one of the following systems suppresses the tendency to 'dutch roll' ?

Yaw damper


Question 241-27 : Which aeroplane behaviour will be corrected by a yaw damper ?

Dutch roll


Question 241-28 : If the sum of all the moments in flight is not zero the aeroplane will rotate about the ?

Centre of gravity

exemple 449 Centre of gravity.

Question 241-29 : Wing dihedral ?

Contributes to static lateral stability

.when a wing goes down dihedral effect will tend to decrease bank angle and roll the wing back up this is a positive contribution to the static lateral stability the dihedral effect is an increase in angle of attack on the lower wing compared to the upper wing exemple 453 Contributes to static lateral stability.

Question 241-30 : A c g location beyond the aft limit leads to ?

An unacceptable low value of the manoeuvre stability stick force per g fe/g


Question 241-31 : What should be usually done to perform a landing with the stabiliser jammed in the cruise flight position ?

Choose a higher landing speed than normal and/or use a lower flapsetting for landing

exemple 461 Choose a higher landing speed than normal and/or use a lower flapsetting for landing.

Question 241-32 : The pitch up effect of an aeroplane with swept back wing in a stall is due to the ?

Wing tip stalling first

exemple 465 Wing tip stalling first.

Question 241-33 : How does positive camber of an aerofoil affect static longitudinal stability it has ?

No effect because camber of the aerofoil produces a constant pitch down moment coefficient independent of angle of attack

The aerofoil will always pitch about the aerodynamic center and it depends where the average forces of the top surface are acting through compared to where the average forces of the bottom surfaces are acting through .with a symmetrical aerofoil the forces of the top and bottom surfaces act through the same position so it has no pitching moment .a cambered aerofoil will have the top surface forces acting through a point further back along the chord than the bottom forces so it will pitch nose down

Question 241-34 : Which statement about a primary control surface controlled by a servo tab is correct ?

The position is undetermined during taxiing in particular with tailwind

.the function of a servo tab is to assist in moving large control surfaces rather than holding them in one position servo tabs move in the opposite direction to the surfaces they are attached to trough a mechanism on the port elevator torque tube .the system requires airflow from leading edge to trailing edge when taxiing in a tailwind a servo tab is ineffective so the control surface just flops around throw in a tailwind and it can end up anywhere .servo tab . /com en/com080 350a jpg.anti servo tab . /com en/com080 350b jpg.the control column is directly connected to the control surface but a tab is geared to the movement of the control surface so that it either assists the movement of the control or counters the movement of the control thus the controls can be made to feel heavier anti servo tab or lighter servo tab than they would otherwise exemple 473 The position is undetermined during taxiing, in particular with tailwind.

Question 241-35 : Sensitivity for spiral dive will occur when ?

The static directional stability is positive and the static lateral stability is relatively weak

.the effects of static lateral stability and static directional stability do interact if an aeroplane is in a sideslip to the right for example static directional stability will generate a yawing moment to the right but static lateral stability will generate a rolling moment to the left the net result on the aeroplane can be decided by which type of static stability is dominant .if the yawing moment from static directional stability is larger than the rolling moment from static lateral stability the aeroplane would roll further to the right and sideslip more the aeroplane will enter a spiral dive to the right spiral instability .on the other hand if the rolling moment from static lateral stability is larger than the yawing moment from static directional stability the lower wing will have more lift and more induced drag and the aeroplane will not only initially roll to the left but will then yaw to the right and so on this is known as dutch roll .the way to remember which type of dynamic stability will result if the aeroplane has a dominance of static directional stability it will tend to suffer spiral instability whereas if the aeroplane has a dominance of static lateral stability it will tend to suffer from dutch roll exemple 477 The static directional stability is positive and the static lateral stability is relatively weak.

Question 241-36 : Which part of an aeroplane provides the greatest positive contribution to static longitudinal stability ?

The horizontal tailplane

exemple 481 The horizontal tailplane.

Question 241-37 : An advantage of locating the engines at the rear of the fuselage in comparison to a location beneath the wing is ?

Less influence of thrust changes on longitudinal control

exemple 485 Less influence of thrust changes on longitudinal control.

Question 241-38 : The tendency to dutch roll increases when ?

The static lateral stability increases

exemple 489 The static lateral stability increases.

Question 241-39 : Which statement is correct ?

Dynamic stability is possible only when the aeroplane is statically stable about the relevant axis

.static and dynamic stability .static stability refers to the initial response of the aeroplane to displacement example if the aircraft pitches up due to a gust of wind then without any input from the pilot it returns back to where it was it has displayed positive static stability since this was in pitch it would be longitudinal stability if after pitching up the aircraft stayed pitched up that would be neutral static stability if the aircraft were to pitch up further away from where it was that would be negative static stability .dynamic stability refers to what the aircraft does over time using the example above the aircraft pitches up then pitches back down .positive static stability as the aircraft pitches down it is subjected to a angular velocity it has mass and its momentum might make it swing past its initial position but since it has positive static stability it will then pitch back up and after a few oscillations settle back to where it was initially that is positive dynamic stability if after say 2 minutes the aircraft is still pitching up and down at the same rate that would be an example of neutral dynamic stability if the aircraft swings further and further away over time that would be an example of negative dynamic stability .you cannot have an aircraft which is dynamic stable on an axis if it is not stable statically on this axis exemple 493 Dynamic stability is possible only when the aeroplane is statically stable about the relevant axis.

Question 241-40 : Positive static lateral stability is the tendency of an aeroplane to ?

Roll to the left in the case of a sideslip with the aeroplane nose pointing to the left of the incoming flow

.rolling is the rotation of the aeroplane about the longitudinal axis . 684.a side slip to the right is the slip of the tail to the right the nose goes left .when a sideslip occurs the lower wing presents a larger span as seen from the direction of the approaching air and as with dihedral the effect is to roll the aircraft back towards the horizontal exemple 497 Roll to the left in the case of a sideslip (with the aeroplane nose pointing to the left of the incoming flow).


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