Aerodynamics Flashcards by Matthew Clarke

When flying at a constant Mach number, the CAS will

Decrease

*CAS is IAS corrected for instrument error and position error due to incorrect pressure at the static port caused by airflow disruption

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When climbing at a constant Mach number, the TAS will

Decrease if temperature decreases

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The difference between leading edge slats and leading edge flaps is

Slats reenergise the boundary layer and flaps alter the effective camber of the leading edge

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As an aircraft climbs above FL300, the IAS and EAS stall speeds will

IAS and EAS stall speeds both increase

*Ie the number gets bigger and buffer between speed and stalling gets smaller

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As an aircraft accelerates from subsonic speeds through 1.0M to supersonic speeds, the C*D (coefficient of drag) will

Increase then decrease

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In a constant Mach number climb in the isothermal layer above the tropopause, TAS will

Remain constant due to the constant temperature

*Isothermal is where temp doesn’t behave normally
TAS = temp dependant

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In a constant Mach number climb in the isothermal layer above the tropopause, IAS will

Decrease due to decreasing pressure

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M-crit is

The speed above which supersonic local airflow first occurs

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The variable most affecting the speed of sound is

Temperature

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An aircraft exceeds its M-crit. Assuming no Mach Trimmer is fitted, the first thing to occur would be

Nose pitch down

*Because the CP moves rearward

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For high subsonic cruise speeds, the reason it is best to delay the formation of wing shockwaves is

To keep the drag penalty to a minimum,m

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Fast transport aircraft may have a supercritical wing section. This is to

Reduce the top wing surface acceleration

*Reduced shock induced boundary layer separaition
basically delays onset of shockwaves

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Aileron control reversal can be caused by

The wing twisting about its lateral axis due to high aerodynamic loads at high speed

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Exceeding M-crit results in a nose down pitch in the aircraft. This is because

The CP moves rearward

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An aircraft is slowly accelerating through its M-crit to transonic cruise. The coefficient of lift

Will increase then decrease

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A Mach trimmer

Ensures that with increasing speed the aircraft will tend to pitch up

*Because aircraft will pitch down when M-crit is reached because the CP moves rearward so it needs to counter the nose down trims

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At transonic speeds, the reason some aircraft use spoilers for roll control even though they have ailerons fitted is

To overcome loss of aileron effectiveness due to flow separation ahead of the aileron

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A yaw damper

Minimises the need for rudder control inputs at high altitude and high Mach number

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Wing sweep results in an increase in the stalling angle of attack. This is because

The swept wing C-lift is less than a straight wing C-life for any given body angle

*Think about fast jets to airliners - fast jets have less drag (and less lift) compared to straight airliners that have more lift and more drag

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Wing sweep is an important feature for high speed flight because

It delays the drag effects of shockwaves

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On swept wing aircraft, nose pitch up at the stall is caused by

Wing tip stall and the effective Cp moving forwards

*Cp effects the pitch

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Most swept wing aircraft are fitted with a stick pusher because

The combination of wing design and powered controls does not provide adequate stall protection and recovery may be very difficult or impossible in some cases

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Jet aircraft max rate of climb (Vy) is determined by

Excess power over weight

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Vs when related to transport category aircraft is

Minimum steady flight speed

*CHECK THIS

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You want your jet aircraft to stay airborne as long as possible. You would achieve this by flying

At an altitude where use of engine design RPM would result in a speed of V-IMD

To achieve maximum angle of climb (Vx), you would climb at

V-IMD using maximum thrust

Large jet aircraft have a large speed band where the rate of climb is fairly constant. This is because

For this band, the power available and power required curves are nearly parallel

V-A is

Manoeuvring speed

The Cp of a transport category aircraft wing should ideally have minimal movement with variations in aircraft speed because

Large trim changes would be needed with large CP movements *Think of nose pitch up and down and how you need a mach trimmer to counter the CP movement *Think of Cp as lift so as it moves back, lift of the tail goes up = nose down

You have descended to hold at 3000ft. At this altitude, your ideal holding speed would be primarily determined by

IAS considerations

Considering flap extension increases lift, they are not used for climb because

Min drag speed is higher with flap up and the extra drag cancels the lift benefit

Swept wing aircraft employ a ‘stall identification alarm system’ (stick pusher). This operates at

The speed below which controlled level flight is not sustainable

Jet aircraft overspeed warnings will operate

Slightly above Vmo/Mmo

Vmo/Mmo is

The max operating speed at which an aircraft may be intentionally flown

M-FS (free stream) is

The actual Mach number of the aircraft through the air

M-DET is

The aircraft speed above which all the local flow is supersonic

Airflow through a shockwave will experience

Increase in temp, density and pressure but decrease in velocity *Think of a shockwave as a bit like a divergent duct

An emergency climb on encountering severe low level wind shear would be achieved by

Climbing at a target 1.1Vs and using takeoff power

Jet aircraft SAR as a comparison of air distance per tonne of fuel consumed would be expr3essed in the form

100 anm / 1000 kg

To achieve maximum range at a given flight level, you would fly at

1.32 V-IMD

Optimum range is achieved by flying at

Cruise climb, 1.32V-IMD and design RPM

Climb IAS decreases with increased altitude because

Maximum excess power occurs at a lower IAS at high altitude

A jet aircraft climbs at a constant Mach number after reaching a certain altitude because

It equates with the required reducing IAS and to prevent Mach overspeed

For a given altitude and weight, the IAS variation for maximum angle of climb if flap is extended is

It decreases to maintain a lower minimum drag speed *Think of takeoff with flaps being at a lower speed

The theoretical requirement (as far as the airframe is concerned) for max range cruise is

An IAS of 1.32 V-IMD at a cruise level as high as possible

If required to cruise at a level with significant headwind when maximum range is required

You would fly faster than the nil wind max range speed because you need to achieve the best GS/drag ratio *Range is distance

In a steady climb, compared to nil headwind, a headwind will affect

Angle of climb only *Rate of climb is unchanged

V-A for an aircraft (manoeuvring speed)

Is higher at higher gross weights and lower at lower gross weights *Think of being at max weight punching through turbulence, you have to go faster because you’re heavier because the airframe gets stressed quicker because it’s got more load on it *If you’re lighter through turbulence, you get bounced around more but airframe doesn’t get as stressed because it’s not as heavy so your speed can be lower

As airflow passes through a normal (vertical) shockwave

Velocity changes from supersonic to subsonic with no changes in direction

Concerning slotted flaps and/or Fowler flaps

Slotted flaps increase the camber and preserve energy in the boundary layer of the airflow while Fowler flaps increase the camber and the chord

Flap extension at high altitude is not permitted on most aircraft because

Flap extension speed may be below the stalling speed at high altitude

The speed of the airflow through a normal shockwave changes from

Supersonic to subsonic

A nose down pitch change in an aircraft flying near M-CRIT would most likely be caused by

A rearwards CP shift

The one which is not an advantage of a swept back wing compared to a straight wing is: A. Less gust sensitivity B. Higher M-CRIT C. Less drag at high speed D. More effective trailing edge devices

More effective trailing edge devices

An internal flexible seal attached to the leading edge of a control surface is designed to

Assist control load balancing

The minimum control speed ground (V-MCG) is lower than the minimum control speed air (V-MCA) because

The main wheels are on the ground

When flying at very high altitude in a swept wing jet transport category aircraft, vibration felt through the airframe during manoeuvres would be caused by

Either high or low speed buffet

If the best lift/drag ratio for an aircraft is achieved at a speed of X, then for best angle of climb, the aircraft should fly at a speed of

Equal to X

True or false Cruising at a high FL will always increase specific air range (SAR)

False

True or false Max endurance is achieved at best L/D ratio

True *Endurance is time *Best L/D= max angle of climb, min thrust, best glide, minimum drag

True or false At all altitudes, Mach number is the ratio of TAS to LSS at MSL (local speed of sound)

False *Mach number is ratio of TAS to LSS meaning LSS at each altitude not LSS at MSL

True or false Any headwind or tailwind will reduce the distance to a PNR

True *PNR is distance based *Headwind or tail wind will mean when you turn around you have the distance to return so is shorter

True or false The Mach number required for maximum range cruise is independent of head or tail wind component

False *Range is distance so is effected by wind (think about PNR being effected by wind)

True or false Low SFC (specific fuel consumption) is best achieved at low altitude and low engine RPM

False *High altitude and design RPM

True or false The AoA required for maximum range cruise does not vary with aircraft gross weight

True *AoA always remains constant regardless of weight

True or false For a given FL and GW, induced drag will decrease with increasing IAS

True *Induced drag decreases with increasing speed *Parasite drag increases with increasing speed

True or false For a constant IAS and FL, Mach number is affected by changes in air temperature

False

True or false Maximum static thrust increases with increasing ambient temperature

False *Thrust decreases with an increase in temp

True or false During constant altitude cruise, a reduction in aircraft gross weight will require a redacting in wing angle of attack to maintain the optimum lift coefficient for subsonic cruise

False *AoA always remains constant

True or false M-CRIT is that free stream Mach number below which all airflow is subsonic

True *Mcrit is the speed at which local airflow is first supersonic so everything below Mcrit is subsonic

True or false High propulsion efficiency is typified by low mass flow and maximum possible velocity change

False *High propulsive efficiency is achieved with large mass airflow and small relative acceleration (like a turboprop)

True or false The component of Total Reaction force parallel to the remote free airstream is termed induced drag

True *Induced drag decreases with an increase in speed

True or false Engine specific fuel consumption is directly proportional to engine thrust

False *SFC = fuel flow per unit hour per thrust produced unit

True or false For a single sector flight at a constant TAS, an increased wind component will always decrease the distance from departure to PNR

True PNR is distance based so wind effects it to make it shorter EP/CTP is time based so wind will move it but headwind will make it further away and tailwind will make it closer

True or false For cruise at a constant Mach number and constant altitude, buffet boundary margins increase with increasing gross weight

False Buffet boundary margins decrease with increasing weight, the heavier you are, you get to buffet sooner (Think of being heavy, you want to make it to brekky buffet first)

True or false Wing sweep back will increase M-CRIT

True

True or false Maximum static thrust decreases with decreasing altitude

False *Thrust increases with decreasing altitude because air density increases

True or false For any flight sector, an increasing headwind component increases the distance to the CP/ETP

True *ETP/CP is time based so with a headwind, you can go further before you have to turn around *When you turn around you’ll have the tailwind choofing you home so can go further distance to start

True or false For a single stage and constant tailwind component outbound, the distance from departure to the CP increases with increasing TAS

True

True or false Maximum range is achieved at CL/CD max

False *Range is distance, happens at 1.32 Vimd *Max lift/drag = min drag -Min drag = Vx -Min drag = best endurance -Min drag = best glide range -Min drag = min fuel flow per hour

True or false Specific fuel consumption (SFC) decreases with increasing inlet air temperature

False *SFC is thrust produced per hour per unit of fuel use per hour *Thrust decreases with increasing temp *Eg 800lbs of fuel / 400lbs thrust = 2.0 800lbs of fuel / 200lbs thrust = 4.0 Because less thrust is produced with an increase in temperature

True or false Induced drag increases with increasing AoA

True *Increasing AoA = reducing speed -With increase in speed, induced drag decreases

True or false At constant cruise level, the long range cruising Mach number (M-LRC) decreases with decreasing gross weight

True

True or false The AoA for best endurance at a constant altitude decreases with decreasing gross weight

False *AoA always remains constant

True or false In the isothermal layer above the tropopause, a constant velocity (TAS) cruise climb would produce a constant Mach number

True

True or false SFC increases as engine RPM increases towards design RPM

False *SFC is unit of thrust produced per unit of fuel used per hour *Low SFC is best *SFC is best at design RPM

True or false Engine efficiency decreases rapidly past 70-75% of max RPM during engine acceleration

False *Engine efficiency is best at design RPM

True or false At constant altitude, max available engine thrust does not vary with changes in aircraft speed

False *It does change with aircraft speed

True or false At constant altitude, specific duel consumption increases with increasing engine RPM towards design RPM

False *decreases towards design RPM because design RPM is where the engine is best and low SFC is best

True or false Gas turbine engine thrust varies linearly with engine RPM

False

True or false Gas turbine engine compressor stalls are characterised by both low engine RPM and low exhaust gas temperatures

False

True or false Engine airflow undergoes the greatest pressure change through the compressor

True *Pressure increases through the compressor Pressure remains constant through combustion

True or false Wing sweep back will delay the onsets of wing compressibility effects

True

True or false Airflow behind a normal (vertical) shockwave is always subsonic

True

True or false At constant speed and altitude, induced drag is independent of bank angle

False *Induced drag is dependant on bank angle

True or false Induced drag decreases with increasing aspect ratio

True *Think of gliders having minimum drag with their huge wings

True or false Average cruise EPR require is independent of TAT

True *EPR is air intake vs outlet pressure so has nothing to do with total air temperature (temp of air outside the aeroplane)

True or false The minimum thrust and minimum angle of descent is obtained at L/D max

True

True or false At constant altitude, Mach number is the ratio of the local TAS to the MSL speed of sound

False *Mach number is the ratio between TAS and LSS

True or false At constant IAS and FL, Mach number is not affected by changes in air temperature

True

True or false The maximum range cruise Mach number is independent of head or tail wind component

False

True or false At constant cruise level, the long range cruise Mach number increases with decreasing gross weight

False

True or false Below the tropopause, a constant Mach number cruise climb would produce a constant IAS

False

True or false Specific fuel consumption increases with increasing engine RPM toward design RPM

False

True or false At constant cruise level, SGR will always increase as cruise TAS increases

False *Specific ground range is nm over the ground per fuel flow Dependant on wind as well as TAS

True or false The maximum quick turn around weight increases with increasing runway downslope

False

True or false The limiting IAS for flight with the 727 yaw damper system U/S is independent of aircraft altitude

False *Think about the king air MEL not being able to fly above FL190

True or false Both maximum endurance and maximum climb angle performance occur at L/D max

True