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Exam > pilot : The location of the centre of pressure of a positively cambered aerofoil ?

Question 206-1 : Shift forward not shift shift aft shift in spanwise direction

.the pressure created by an aerofoil at any point may be represented by a vector at right angles to its surface whose length is proportional to the difference between absolute pressure at the point and the free stream static pressure .all of them can be represented by a single vector acting at a particular point called the centre of pressure. 669..the centre of pressure is a theoretical point on the chord line through which the resultant of all forces the total reaction is said to act .its position is usually around 25% of the way from the leading edge simply because more lift is generated there but it moves steadily forward as the angle of attack is increased until just before the stalling angle when it moves rapidly backwards the centre of pressure's most forward point is just before the stalling angle this is why an aeroplane's nose drops when the wings stall and the centre of pressure moves behind the cg.thus when speed is increased in straight and level flight on a positively cambered aerofoil you have to decrease the angle of attack to keep the the total lift force constant and the point where the resultant of all forces are acting the centre of pressure moves aft exemple 306 shift forward.shift forward.

The si unit of measurement for density is ?

Question 206-2 : Kg/m³ psi kg/cm² bar

exemple 310 kg/m³.kg/m³.

The unit of measurement of pressure is ?

Question 206-3 : Psi kg/dm² kg/m³ lb/gal

exemple 314 psipsi

A laminar boundary layer is a layer in which ?

Question 206-4 : No velocity components exist normal to the surface the vortices are weak the velocity is constant the temperature varies constantly

.'vertical axis' is also call 'normal axis' by 'normal' they mean 'perpendicular to the wing surface' .the airflow in the laminar boundary layer is parallel to the wing surface in a horizontal direction and hence there are no flows perpendicular to the surface exemple 318 no velocity components exist, normal to the surface.no velocity components exist, normal to the surface.

The subsonic static pressure ?

Question 206-5 : Decreases in a flow in a tube when the diameter decreases is the total pressure plus the dynamic pressure is the pressure in a point at which the velocity has become zero increases in a flow in a tube when the diameter decreases

exemple 322 decreases in a flow in a tube when the diameter decreases.decreases in a flow in a tube when the diameter decreases.

The lift and drag forces acting on a wing cross section ?

Question 206-6 : Depend on the pressure distribution about the wing cross section are normal to each other at just one angle of attack are proportional to each other independent of angle of attack vary linearly with the angle of attack

.the distribution of velocities with resulting pressure distribution is determined by the shape or profile of the surface and the angle of attack cl or cd .the aerodynamic force of lift results from the pressure differential between the top and bottom surfaces of the wing .drag is the product of dynamic pressure drag coefficient and surface area exemple 326 depend on the pressure distribution about the wing cross section.depend on the pressure distribution about the wing cross section.

The lift force acting on an aerofoil no flow separation ?

Question 206-7 : Is mainly caused by suction on the upperside of the aerofoil increases proportional to the angle of attack until 40 degrees is mainly caused by overpressure at the underside of the aerofoil is maximum at an angle of attack of 2 degrees

exemple 330 is mainly caused by suction on the upperside of the aerofoil.is mainly caused by suction on the upperside of the aerofoil.

The relative thickness of an aerofoil is expressed in ?

Question 206-8 : % chord camber meters degrees cross section tail angle

exemple 334 % chord.% chord.

The aerofoil polar is ?

Question 206-9 : A graph of the relation between the lift coefficient and the drag coefficient a graph of the relation between the lift coefficient and the angle of attack the relation between the horizontal and the vertical speed a graph in which the thickness of the wing aerofoil is given as a function of the chord

. /com en/com080 1264 jpg.airfoil and aircraft polars have been used for a long time in aeronautics the correct german term is lilienthal'sches polardiagramm indicating that this method of graphing results of airfoil tests has been used first by otto lilienthal he plotted the lift and drag forces of his experimental results as lift versus drag as we still use it today using coefficients instead of the actual forces exemple 338 a graph of the relation between the lift coefficient and the drag coefficient.a graph of the relation between the lift coefficient and the drag coefficient.

Aspect ratio of a wing is the ratio between ?

Question 206-10 : Wing span squared and wing area wing span and dihedral angle wing root chord line and wing tip chord line wing span and wing root chord

.aspect ratio is the ratio of the square of the wing span to the total wing.planform area .you could have two aerofoils of equal surface area but different aspect ratios depending on what they were designed for the higher the aspect ratio of length to width the more lift you get with less induced drag at the tips .a wing with higher aspect ratio with long wingspan and small chord reaches higher lift coefficient but stalls at a lower angle of attack than the wing with low aspect ratio exemple 342 wing span squared and wing area.wing span squared and wing area.

Dihedral of the wing is ?

Question 206-11 : The angle between the 0 25 chord line of the wing and the lateral axis the angle between the leading edge of the wing and the lateral axis the angle between the 0 25 chord line of the wing and the vertical axis the angle between the 0 25 chord line of the wing and the horizon

.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..notice horizon isn't a plane neither an axis.the angle between the 0 25 chord line of the wing and the lateral axis is the correct answer exemple 346 the angle between the 0.25 chord line of the wing and the lateral axis.the angle between the 0.25 chord line of the wing and the lateral axis.

The induced drag ?

Question 206-12 : Increases as the lift coefficient increases increases as the aspect ratio increases has no relation to the lift coefficient increases as the magnitude of the tip vortices decreases

exemple 350 increases as the lift coefficient increases.increases as the lift coefficient increases.

Flap extension at constant ias whilst maintaining straight and level flight ?

Question 206-13 : Maximum lift coefficient clmax and the drag lift coefficient and the drag stall speed lift and the drag

.lift = cl x 1/2 rho v² x s..cl = lift coefficient.rho = density.v = tas in m/s .s = surface..clmax available increases with all types of flap so will drag the pilot adjusts attitude and power to maintain speed and straight and level flight exemple 354 maximum lift coefficient (clmax) and the drag.maximum lift coefficient (clmax) and the drag.

When trailing edge flaps are extended whilst maintaining straight and level ?

Question 206-14 : The centre of pressure moves aft the lift coefficient and the drag coefficient increase the stall speed increases the total boundary layer becomes laminar

.to maintain straight and level flight at constant ias while deploying trailing edge flaps you have to lower the nose decreasing angle of attack so your lift coefficient will remain constant .the centre of pressure moves backward when the angle of attack decreases exemple 358 the centre of pressure moves aft.the centre of pressure moves aft.

Which of the following situations leads to a decreasing stall speed ias ?

Question 206-15 : Decreasing weight increasing altitude increasing air density increasing load factor

exemple 362 decreasing weight.decreasing weight.

The difference between ias and tas will ?

Question 206-16 : Decrease with decreasing altitude increase with decreasing temperature increase with increasing air density decrease with increasing speed

.true air speed tas is obtained from indicated air speed ias by correcting for instrument position compressibility and density errors.use the very simple 'ertm' diagram ertm for e as/ r as rectified air speed or cas / t as/ m ach. /com en/com080 103a jpg..if altitude increases difference between ias and tas increases inversely if altitude decreases difference between ias and tas decreases.for rapid calculation .tas = ias + 2% per 1000 ft altitude exemple 366 decrease with decreasing altitude.decrease with decreasing altitude.

Compared with stalling airspeed vs in a given configuration the airspeed at ?

Question 206-17 : Greater than vs 1 30 vs 1 12 vs 1 20 vs

.a stick shaker is a mechanical device to rapidly and noisily vibrate the control yoke the 'stick' of an aircraft to warn the pilot of an imminent stall it is connected to the control column of most business jets airliners and military aircraft .when the angle of attack alpha approaches a critical value the stick is made to shake as a warning.example stalling airspeed vs is 100 kt stick shaker activation is at 110 kt the airspeed at which stick shaker will be triggered is greater than vs to give enough time to the pilot to react by increasing speed and/or reducing the angle of attack exemple 370 greater than vs.greater than vs.

The term angle of attack in a two dimensional flow is defined as ?

Question 206-18 : The angle between the wing chord line and the direction of the relative wind/airflow the angle between the aeroplane climb path and the horizon the angle formed by the longitudinal axis of the aeroplane and the chord line of the wing the angle for maximum lift/drag ratio

exemple 374 the angle between the wing chord line and the direction of the relative wind/airflow.the angle between the wing chord line and the direction of the relative wind/airflow.

The critical angle of attack ?

Question 206-19 : Remains unchanged regardless of gross weight increases if the cg is moved forward decreases if the cg is moved aft changes with an increase in gross weight

.the angle at which the stall occurs is called the critical angle of attack . a fixed wing aircraft by definition is stalled at or above the critical angle of attack rather than at or below a particular airspeed the airspeed at which the aircraft stalls varies with the weight of the aircraft the load factor bank angle the center of gravity of the aircraft and other factors however the aircraft always stalls at the same critical angle of attack exemple 378 remains unchanged regardless of gross weight.remains unchanged regardless of gross weight.

Comparing the lift coefficient and drag coefficient at normal angle of attack ?

Question 206-20 : Cl is much greater than cd cl is much lower than cd cl has approximately the same value as cd cl is lower than cd

.for maximum aerodyamic efficiency it is necessary to generate enough lift to balance the weight while at the same time generate as little drag as possible the higher the lift/drag ratio the greater the aerodyamic efficiency therefore at normal angles of attack cl is much higher than cd between 10 and 20 times greater exemple 382 cl is much greater than cd.cl is much greater than cd.

Which statement is correct regarding cl angle of attack ?

Question 206-21 : For a symmetrical aerofoil section if the alpha is zero cl is zero for a symmetrical aerofoil section if the alpha is zero cl is not zero for an asymmetrical aerofoil section if the alpha is zero cl is zero for an asymmetrical aerofoil section with positive camber if alpha is greater than zero cl is zero

. /com en/com080 878 jpg..a symmetrical aerofoil need to have a positive angle of attack to produce lift it the pitching moment is zero the lift is zero .a positively cambered aerofoil produces lift with a zero angle of attack exemple 386 for a symmetrical aerofoil section, if the alpha is zero, cl is zero.for a symmetrical aerofoil section, if the alpha is zero, cl is zero.

The mean aerodynamic chord mac for a given wing of any planform is ?

Question 206-22 : The chord of a rectangular wing with same moment and lift the chord of a large rectangular wing the average chord of the actual aeroplane the wing area divided by the wing span

.for a rectangular wing of constant aerofoil dimensions and constant chord the mac is just the chord .'same moment and lift' means equilibrium on a rectangular wing mac permits to define a point where the lift forces acting this single point is about half way out along the wing and at about 25% back from the leading edge exemple 390 the chord of a rectangular wing with same moment and lift.the chord of a rectangular wing with same moment and lift.

Induced drag may be reduced by ?

Question 206-23 : An increase in aspect ratio the use of a wing tip with a much thinner aerofoil a decrease of the aspect ratio an increase in the taper ratio of the wing

.induced drag varies with lift speed and aspect ratio is inversely proportional to aspect ratio and v² so multiply by 1/v² and directly proportional to lift²/cl²/weight² . /com en/com080 38 jpg.aspect ratio is defined as the square of the wingspan divided by the area of the wing planform exemple 394 an increase in aspect ratio.an increase in aspect ratio.

The relationship between induced drag and the aspect ratio is ?

Question 206-24 : A decrease in the aspect ratio increases the induced drag there is no relationship induced drag = 1 3 aspect ratio value an increase in the aspect ratio increases the induced drag

.it is reduced because the effect of wing tip vortices is reduced.coefficient of induced drag cdi = cl² / pi x aspect ratio .aspect ratio is defined as the square of the wingspan divided by the area of the wing planform . /com en/com080 38 jpg.induced drag varies with lift speed and aspect ratio is inversely proportional to aspect ratio and v² so multiply by 1/v² and directly proportional to lift²/cl²/weight² exemple 398 a decrease in the aspect ratio increases the induced drag.a decrease in the aspect ratio increases the induced drag.

A high aspect ratio wing produces ?

Question 206-25 : A decrease in induced drag an increase in induced drag less sensitivity to gust effects a decrease in stall speed

.it is reduced because the effect of wing tip vortices is reduced.coefficient of induced drag cdi = cl² / pi x aspect ratio .aspect ratio is defined as the square of the wingspan divided by the area of the wing planform . /com en/com080 38 jpg.induced drag varies with lift speed and aspect ratio is inversely proportional to aspect ratio and v² so multiply by 1/v² and directly proportional to lift²/cl²/weight² exemple 402 a decrease in induced drag.a decrease in induced drag.

What will happen in ground effect ?

Question 206-26 : The induced angle of attack and induced drag decreases an increase in strength of the wing tip vortices a significant increase in thrust required the wing downwash on the tail surfaces increases

.ground effect changes airflow. /com en/com080 821 jpg..when entering the ground effect it requires a decrease in angle of attack to maintain the same cl the induced angle decreases exemple 406 the induced angle of attack and induced drag decreases.the induced angle of attack and induced drag decreases.

Which statement is correct about the laminar and turbulent boundary layer ?

Question 206-27 : Friction drag is lower in the laminar layer friction drag will be equal in both types of layers friction drag is lower in the turbulent layer separation point will occur earlier in the turbulent layer

exemple 410 friction drag is lower in the laminar layerfriction drag is lower in the laminar layer

Behind the transition point in a boundary layer ?

Question 206-28 : The mean speed and friction drag increases the boundary layer gets thinner and the speed increases the mean speed increases and the friction drag decreases the boundary layer gets thicker and the speed decreases

. /com en/com080 247 jpg..the laminar boundary layer the one at the front of the wing is smooth and thin inside it the speed of the air reduces smoothly from the free stream value to near zero at the surface because of this regular reduction in speed the average speed inside the layer is about half the free stream value and this fact and the fact that the layer is very thin mean that the total kinetic energy inside the layer is relatively small.the turbulent layer is thicker and the turbulence pulls down free stream air deep into the layer this has two results one is that the turbulent layer has more kinetic energy and the other is that near the surface the airflow slows down very rapidly causing more drag drag is bad but kinetic energy is good for the turbulent layer punches through problems and keeps the airflow attached to the wing as you get nearer the stall.in summary the turbulent layer is thicker has a higher mean speed within the layer more drag but more internal energy exemple 414 the mean speed and friction drag increases.the mean speed and friction drag increases.

When trailing edge flaps are extended in level flight the change in pitching ?

Question 206-29 : Nose down nose up zero dependent on cg location

.pitch behavior depends on flap type wing position and horizontal tail location the increased camber from flap deflection produces lift primarily on the rear portion of the wing this produces a nosedown pitching moment. /com en/com080 253 jpg. exemple 418 nose down.nose down.

Extension of leading edge flaps will ?

Question 206-30 : Increase critical angle of attack decrease clmax decrease drag not affect critical angle of attack

exemple 422 increase critical angle of attack.increase critical angle of attack.

Slat extension will ?

Question 206-31 : Increase the critical angle of attack reduce tip vortices create gaps between leading edge and engine nacelles decrease the energy in the boundary layer on the upperside of the wing

exemple 426 increase the critical angle of attack.increase the critical angle of attack.

What factors determine the distance travelled over the ground of an aeroplane ?

Question 206-32 : The wind and the lift/drag ratio which changes with angle of attack the wind and the aeroplane's mass the wind and clmax the wind and weight together with power loading which is the ratio of power output to the weight

.a headwind will decrease the distance travelled over the ground .a tailwind will increase the distance travelled over the ground.the angle of attack for the best ratio varies with the design of the wing but is around a third to a quarter of the size of the stalling angle flying at the best lift/drag ratio is flying at the maximum range speed most lift for the least drag for the most economy and the most distance for altitude lost .the wind and lift/drag ratio determine the distance travelled over the ground of an aeroplane in a glide exemple 430 the wind and the lift/drag ratio, which changes with angle of attack.the wind and the lift/drag ratio, which changes with angle of attack.

The following unit of measurement kgm/s² is expressed in the si system as ?

Question 206-33 : Newton pascal joule watt

Chikarelly .the correct answer is watt..what.could you please give more explanation if you are sure an answer is wrong.watt = kgm²/s3. patorules .si unit kg = mass and m/s² = acceleration .mass x acceleration = force and si unit for force is newton exemple 434 newton.newton.

Excluding constants the coefficient of induced drag cdi is the ratio of ?

Question 206-34 : Cl² and ar aspect ratio cl²and s wing surface cl and cd cl and b wing span

.coefficient of induced drag cdi = cl² / pi x aspect ratio.the constant is pi 3 14159 so excluding the constant the coefficient of induced drag cdi is the ratio of cl² and ar aspect ratio exemple 438 cl² and ar (aspect ratio).cl² and ar (aspect ratio).

One important advantage the turbulent boundary layer has over the laminar type ?

Question 206-35 : It has less tendency to separate from the surface it is thinner skin friction drag is less energy is less

.the laminar boundary layer is a very smooth flow while the turbulent boundary layer contains swirls the laminar flow creates less skin friction drag than the turbulent flow but is less stable boundary layer flow over a wing surface begins as a smooth laminar flow as the flow continues back from the leading edge the laminar boundary layer increases in thickness at some distance back from the leading edge the smooth laminar flow breaks down and transitions to a turbulent flow from a drag standpoint it is advisable to have the transition from laminar to turbulent flow as far aft on the wing as possible or have a large amount of the wing surface within the laminar portion of the boundary layer the low energy laminar flow however tends to break down more suddenly than the turbulent layer . /com en/com080 266 jpg. exemple 442 it has less tendency to separate from the surface.it has less tendency to separate from the surface.

When comparing a rectangular wing and a swept back wing of the same wing area ?

Question 206-36 : Higher critical mach number greater strength increased longitudinal stability lower stall speed

exemple 446 higher critical mach number.higher critical mach number.

High aspect ratio as compared with low aspect ratio has the effect of ?

Question 206-37 : Decreasing induced drag and critical angle of attack increasing lift and critical angle of attack increasing lift and drag increasing induced drag and decreasing critical angle of attack

.high aspect ratio little downwash low aspect ratio great downwash that means that at the same angle of attack the low aspect ratio wing flies at a lower effective angle of attack than the high aspect ratio wing..suppose..low aspect ratio wing.angle of attack 10..effective angle of attack 5...high aspect ratio wing.angle of attack 10..effective angle of attack 8...at any given angle of attack the high aspect ratio wing will have a higher effective angle of attack and therefore be closer to stall critical alpha than low aspect ratio wing..the effective airflow phenomena explains why high aspect ratio is favorable at low speeds why elliptical wing is superior drag wise/horrible stall wise and why ground effect wont let you down exemple 450 decreasing induced drag and critical angle of attack.decreasing induced drag and critical angle of attack.

What wing shape or wing characteristic is the least sensitive to turbulence ?

Question 206-38 : Swept wings straight wings wing dihedral elliptical wing

.turbulence up and down gusts produce transient changes in the angle of attack different wing planforms give different increases in lift coefficient for each degree of angle of attack the swept wing is the least sensitive to turbulence exemple 454 swept wings.swept wings.

What is the si unit of measurement for power ?

Question 206-39 : Nm/s kgm/s² pa/m² n/m

.icao annex 5 units of measurement attachment b . 2 mass force and weight .2 1 the principal departure of si from the gravimetric system of metric engineering units is the use of explicitly distinct units from mass and force in si the name kilogram is restricted to the unit of mass and the kilogram force from which the suffix force was in practice often erroneously dropped is not to be used in its place the si unit of force the newton is used likewise the newton rather than the kilogram force is used to form derived units which include force for example pressure or stress n/m² = pa energy nm = j and power nm/s = w exemple 458 nm/s.nm/s.

The use of a slot in the leading edge of the wing enables the aeroplane to fly ?

Question 206-40 : It delays the stall to a higher angle of attack the laminar part of the boundary layer gets thicker it decelerates the upper surface boundary layer air it changes the camber of the wing

exemple 462 it delays the stall to a higher angle of attack.it delays the stall to a higher angle of attack.

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