Question 254-1 : What is the effect of high aspect ratio of an aeroplane's wing on induced drag ? [ Explanation maintenance ]

Question 254-2 : The most important problem of ice accretion on a transport aeroplane during flight is ?

Reduction in clmax.

For a transport aeroplane increasing in weight is not the most important problem only frontal areas are covered by ice not all of the airplane surfaces increase in drag can be one of the most important problem but you can counteract drag by increasing the angle of attack until you reach clmax which will be reduces because the airflow separation will occur earlierclmax reduction is the most important problem com encom080 51jpg

Question 254-3 : The effects of very heavy rain tropical rain on the aerodynamic characteristics of an aeroplane are ?

Decrease of clmax and increase of drag.

Question 254-4 : In what way do 1 induced drag and 2 parasite drag alter with increasing speed in straight and level flight ?

1 decreases and 2 increases.

Parasite drag only varies with speed and is directly proportional to v² com encom032 209jpgthe induced drag decreases as the lift coefficient decreases if you increase speed in straight and level flight you must reduce the angle of attack it means a reduction of cl coefficient of lift

Question 254-5 : Which of the following wing planforms produces the lowest induced drag all other relevant factors constant ?

Elliptical.

Both lift distribution and load distribution are of great importance in the wing design processto give minimum induced drag the span wise efficiency factor e should be as close to 1 as possible this is the case of an elliptic span wise lift distribution a number of methods are available to modify the span wise distribution of lift they include 1 planform taper to obtain an elliptic planform used for the spitfire wing which was remarkably elliptic 2 a geometric twist andor aerodynamic twist to obtain elliptic lift distribution or 3 a combination of all of these methodsin the past 1930s it was thought that for an elliptic lift distribution the chord must vary elliptically along the span the direct result of such logic was that the wing planform must be elliptical for this reason several aircraft wing planforms such as supermarine spitfire a famous british world war ii fighter were made elliptic but today we know that there are various parameters that make the lift distribution elliptic thus there is no need for the wing planform to be planform an elliptical planform is hard to manufacture and is costly from the point of view of construction the best type of wing is the un tapered untwisted wing

Question 254-6 : If flaps are deployed at constant ias in straight and level flight the magnitude of tip vortices will eventually flap span less than wing span ?

Decrease.

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 pressureif flaps are deployed at constant ias we must reduce the aoa to stay in a level flight thus pressure difference between the top and the bottome of the airfoil is reduced the magnitude of tip vortices will decrease

Question 254-7 : Induced drag at constant ias is affected by ?

Aeroplane weight.

Question 254-8 : Induced drag is created by the ?

Spanwise flow pattern resulting in the tip vortices.

Question 254-9 : Vortex generators ?

Transfer energy from the free airflow into the boundary layer.

Vortex generators are rows of small thin blades which project vertically about 25 cm into the airstream they each generate a small vortex which causes the free stream flow of high energy air to mix with and add kinetic energy to the boundary layer this re energises the boundary layer and delays separation com encom080 162jpg

Question 254-10 : Compared with level flight prior to the stall the lift 1 and drag 2 in the stall change as follows ?

1 decreases 2 increases.

At the stall the lift coefficient begins to fall but it is still high the angle of attack is still high and therefore induced drag is still high profile drag is rising as the airflow separates and breaks down overall there is a small drop in lift coefficient and a continuing rapid rise in drag coefficient

Question 254-11 : Entering the stall the centre of pressure of a straight 1 wing and of a strongly swept back wing 2 will ?

1 move aft 2 move forward.

Straight wing the centre of pressure moves forward when the angle of attack increases until it approaches and exceeds the critical angle of attack then it moves aft at the stallswept back wing there is a tendency for the swept wing to develop a strong spanwise flow towards the wingtip when the wing is at high angles of attack com encom080 27jpgstall occurs at the wingtips first resulting in a shift of the center of lift of the wing in a forward direction relative to the center of gravity of the airplane causing the nose to pitch up

Question 254-12 : Which of the following statements about the spin is correct ?

During spin recovery the ailerons should be kept in the neutral position.

Question 254-13 : During an normal spin recovery ?

The ailerons are held in the neutral position.

Question 254-14 : Which of the following statements about the stall of a straight wing aeroplane is correct ?

Just before the stall the aeroplane will be have an increased nose down tendency.

Straight wing the centre of pressure moves forward when the angle of attack increases until it approaches and exceeds the critical angle of attack then it moves aft just before the stall or at the stall com encom080 111pngloss of lift is felt ahead of the centre of gravity of the aircraft and the centre of pressure moves rearwards so the nose drops and angle of attack is reduced

Question 254-15 : Which of the following are used as stall warning devices ?

Stick shaker and stallstrip.

We are talking about warning devices so angle of attack sensor or angle of attack indicator are not regarded as stall warning devices as they dont give you a warningif you dont have an eye on the angle of attack indicator you won't know that you are approaching the stallstallstrips example com encom080 112jpg

Question 254-16 : Which combination of design features is known to be responsible for deep stall ?

Swept back wings and a t tail.

There is a tendency for the swept wing to develop a strong spanwise flow towards the wingtip when the wing is at high angles of attack com encom080 27jpgstall occurs at the wingtips first resulting in a shift of the center of lift of the wing in a forward direction relative to the center of gravity of the airplane causing the nose to pitch up com encom080 810jpgit is a characteristic of t tail aircraft to pitch up viciously when stalled in extreme nose high attitudes making recovery difficult or violentthe tailplane and elevator are in the path of the separated airflow from the wingit must be emphasised that pitch up is the primary cause of deep stall and a t tail is a contributory factor

Question 254-17 : When a strongly swept back wing stalls and the wake of the wing contacts the horizontal tail the effect on the stall behaviour can be a n ?

Nose up tendency andor lack of elevator response.

There is a tendency for the swept wing to develop a strong spanwise flow towards the wingtip when the wing is at high angles of attack com encom080 27jpgstall occurs at the wingtips first resulting in a shift of the center of lift of the wing in a forward direction relative to the center of gravity of the airplane causing the nose to pitch up com encom080 810jpgit is a characteristic of t tail aircraft to pitch up viciously when stalled in extreme nose high attitudes making recovery difficult or violentthe tailplane and elevator are in the path of the separated airflow from the wingit must be emphasised that pitch up is the primary cause of deep stall and a t tail is a contributory factor

Question 254-18 : The function of the stick pusher is ?

To activate and push the stick forward at or beyond a certain value of angle of attack.

A stick pusher prevents the pilot from increasing the angle of attack furthera stick pusher is a device installed in some fixed wing aircraft to prevent the aircraft from entering an aerodynamic stall some large fixed wing aircraft display poor post stall handling characteristics or are vulnerable to deep stall to prevent such an aircraft approaching the stall the aircraft designer may install a hydraulic or electro mechanical device that pushes forward on the elevator control system whenever the aircraft's angle of attack reaches the pre determined value and then ceases to push when the angle of attack falls sufficiently

Question 254-19 : On a wing fitted with a fowler type trailing edge flap the full extended position will produce ?

An increase in wing area and camber.

Question 254-20 : When flaps are extended whilst maintaining straight and level flight at constant ias the lift coefficient will eventually ?

Remain the same.

Lift coefficient can be changed either by changing angle of attack or by changing the camber as the question states maintaining straight and level flight at constant ias then you have to generate the same lift so lift coefficient must stay constantlowering the flaps will increase the camber and for fowler flaps the wing area as well so the lift coefficient will increase to maintain lift coefficient constant you will have to reduce the angle of attack

Question 254-21 : When flaps are deployed at constant angle of attack the lift coefficient will ?

Increase.

The angle of attack is the angle between the relative airflow and the wing chord when you deploy flaps it will increase camber and the local angle of attack both of which would increase the lift for the same value of dynamic pressure cl will increase

Question 254-22 : Trailing edge flap extension will ?

Decrease the critical angle of attack and increase the value of clmax.

Trailing edge flap extension increases the camber of a wing and increases the coefficient of lift air flow on the upper surface must follow this increased cambered profil thus airflow separation on the upper surface of the wing will occur earlier the airflow separation will start at a lower angle of attack than for a clean wing example when the critical angle of attack was 15° for the wing without trailing edge flaps deployed it is now at 10°and as the coefficient of lift is increased you can fly at a lower speed by producing the same lift since s wing surface increases in the lift formula = 12 rho s v² cl

Question 254-23 : Which of the following statements about the difference between krueger flaps and slats is correct ?

Deploying a slat will form a slot deploying a krueger flap does not.

com encom080 123jpg

Question 254-24 : What is the most effective flap system ?

Fowler flap.

com encom080 124jpga fowler flap move aft then turn down it significantly increases the camber and the wing area

Question 254-25 : Deploying a fowler flap the flap will ?

Move aft then turn down.

com encom080 125gif

Question 254-26 : A slotted flap will increase the clmax by ?

Increasing the camber of the aerofoil and re energising the airflow.

Question 254-27 : In order to maintain straight and level flight at a constant airspeed whilst the flaps are being retracted the angle of attack must be ?

Increased.

When you retract the flaps surface wing is reducedin order to maintain straight and level flight at a constant airspeed you must increase the coefficient of lift cl in the lift formula lift = cl x 12 rho v² x scl = lift coefficientrho = densityv = tas in ms s = surfaceto increase cl you must increase the angle of attack

Question 254-28 : The function of the slot between an extended slat and the leading edge of the wing is to ?

Cause a venturi effect which energizes the boundary layer.

The function of the slot is to accelerate the flow close to the upper skin retarding the de attachment along the chord com encom080 993jpgit is kind of a nozzle that works with the rest of the wing when deployed

Question 254-29 : An aeroplane has the following flap settings 0° 15° 30° and 45° slats can also be selectedwhich of the following selections will most adversely affect the clcd ratio ?

Flaps from 30° to 45°.

Lowering flap increases both the lift and the drag but not in the same proportion although the lift is the larger force the proportional increase in the drag is greater and so the maximum obtainable liftdrag ratio decreasesthe flaps angle from 30° to 45° regarding to the free airflow offers a larger surface thus the parasite drag will be more increased

Question 254-30 : After take off the slats when installed are always retracted later than the flaps why ?

Question 254-31 : Upon extension of a spoiler on a wing ?

Cd is increased and cl is decreased.

Spoilers creates a burbling flow over the wing to destroy lift when you extend a spoiler the coefficient of drag cd is increased and the coefficient of lift cl is decreasedtake care if the question states speed and load factor remain constant and the aircraft remains in straight and level flight it means that the reduction in lift is recovered by increasing the angle of attack and thrust thus in this case cl remains unaffected

Question 254-32 : When spoilers are used as speed brakes ?

At same angle of attack cd is increased and cl is decreased.

Question 254-33 : How does stall speed ias vary with altitude ?

It remains constant at lower altitudes but increases at higher altitudes due to 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 amounthowever at higuer altitudes we consider another factor the compresibility that affects the anemometer and hence increases the reading of iasresuming the ias stall speed is considered constant at lower altitudes below 10000 ft and increases with altitude at higuer altitudes due to compresibility effects

Question 254-34 : The type of stall that has the largest associated angle of attack is ?

A deep stall.

As an aircraft enters a deep stall the pitch up tendency increases the angle of attack to a very high value and the aircraft also starts to sink which further increases the angle of attack com encom080 810jpgthe tailplane and elevator are in the path of the separated airflow from the wingit must be emphasised that pitch up is the primary cause of deep stall and a t tail is a contributory factor

Question 254-35 : Vortex generators on the upper side of the wing ?

Decrease wave drag.

Vortex generators decrease shock wave induced flow separation by transfer energy from the free airflow into the boundary layerthe advantage of wing devices that create vortices is that a vortex adds energy to the airflow and increases its forward momentum this momentum encourages the airflow to remain attached to the surface of the wing at higher angles of attack than it would otherwise as a result the wing is able to continue generating lift in conditions where it would have stalled this behavior is particularly advantageous on high performance military aircraft that need to be extremely maneuverable at high angles of attack in combat the advantage for commercial airliners is increased safety since the plane is less likely to experience a wing stall during critical stages of flight like takeoff and landing com encom080 162jpg

Question 254-36 : The high lift device shown in the figure is a err a 081 181 ?

Slat.

com encom080 182jpg

Question 254-37 : The high lift device shown in the figure below is a err a 081 182 ?

Krueger flap.

com encom080 182jpg

Question 254-38 : A plain flap will increase clmax by ?

Increasing the camber of the aerofoil.

Question 254-39 : The frontal area of a body placed in a certain airstream is increased by a factor 3 the shape will not alter the aerodynamic drag will increase with a factor ?

3.

drag formula d = 12 x rho x v² x s x cdif s frontal area = surface is increased by a factor 3 drag d will increase with a factor 3

Question 254-40 : The aerodynamic drag of a body placed in a certain airstream depends amongst others on ?

The airstream velocity.

The drag formula is drag = cd 12 rho v² swhere cd = drag coefficientrho = densityv = tas airstream velocity in ms s = surfacethere is no reference to the cg location the weight or the specific mass of the body