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Question 264-1 : 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 ? [ Theoretical lift off ]
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.
Question 264-2 : 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.
Question 264-3 : 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.
Question 264-4 : For a normal stable aeroplane, the centre of gravity is located ?
With a sufficient minimum margin ahead of the neutral point of the aeroplane.
Question 264-5 : 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.
Question 264-6 : Longitudinal static stability is created by the fact that the ?
Centre of gravity is located in front of the neutral point of the aeroplane.
Question 264-7 : 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.
Question 264-8 : 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.
Question 264-9 : 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.
Question 264-10 : An aeroplane that has positive static stability ?
Can be dynamically stable, neutral or unstable.
Question 264-11 : A statically unstable aeroplane is ?
Never dynamically stable.
Question 264-12 : One of the requirements for positive dynamic stability is ?
Positive static stability.
Question 264-13 : 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.
Question 264-14 : 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..
Question 264-15 : 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.
Question 264-16 : 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.
Question 264-17 : 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.
Question 264-18 : 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 264-19 : Which moments or motions interact in a dutch roll ?
Rolling and yawing.
Question 264-20 : Ignoring downwash effects on the tailplane, extension of fowler flaps, will produce ?
A nose down pitching moment.
Question 264-21 : Which one of the following systems suppresses the tendency to 'dutch roll' ?
Yaw damper.
Question 264-22 : Which aeroplane behaviour will be corrected by a yaw damper ?
Dutch roll.
Question 264-23 : If the sum of all the moments in flight is not zero, the aeroplane will rotate about the ?
Centre of gravity.
Question 264-24 : 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.
Question 264-25 : 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 264-26 : 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.
Question 264-27 : The pitch up effect of an aeroplane with swept back wing in a stall is due to the ?
Wing tip stalling first.
Question 264-28 : 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 264-29 : 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.
Question 264-30 : 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.
Question 264-31 : Which part of an aeroplane provides the greatest positive contribution to static longitudinal stability ?
The horizontal tailplane.
Question 264-32 : 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.
Question 264-33 : The tendency to dutch roll increases when ?
The static lateral stability increases.
Question 264-34 : 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.
Question 264-35 : 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.. 2389.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.
Question 264-36 : What is the effect of an aft shift of the centre of gravity on 1 static longitudinal stability and 2 the required control deflection for a given pitch change ?
1 reduces 2 reduces.
.you will have less static stability and less control deflection for a given response.
Question 264-37 : When an aeroplane has zero static longitudinal stability, the cm versus angle of attack line ?
Is horizontal.
.pitching moment coefficient cm versus angle of attack diagram. /com en/com080 426.jpg.by 'zero', they mean 'neutral'. the response after encountering an up gust will always be same regardless of the angle of attack.
Question 264-38 : What is the effect of elevator trim tab adjustment on the static longitudinal stability of an aeroplane ?
No effect.
.the elevator trim tab adjustment is take out stick forces at one particular attitude. none of the basic factors that determine stability has changed.
Question 264-39 : Which statement concerning sweepback is correct ?
Sweepback provides a positive contribution to static lateral stability.
.sweepback angle is the angle at which the wing points backwards from the root to the tip.. /com en/com080 467.png.sweepback is used mainly on high speed aircraft and its primary purpose is to delay the formation of sonic shock waves which are produced at high speeds and cause a large increase in drag..the secondary effect of sweepback is to improve lateral stability. when a side slip 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...in general, as the sweepback angle is increased the dihedral angle will be reduced.
Question 264-40 : Which three aerodynamic means decrease manoeuvring stick forces ?
Servo tab horn balance spring tab.
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