Subsonic aerodynamics Flashcards
The lift and drag forces, acting on an airfoil cross section depend on the ___ around the aerofoil cross section
pressure distribution
Hvað gerist í “convergent tube with an incrompressible sub-sonic airflow” fyrir static pressure, dynamic pressure og total pressure?
Static pressure minnkar
dynamic pressure increases
total pressure það sama
Hver er formúla dynamic pressure?
1/2 hró * v^2
Hvaða eining er notuð til að mæla thickness of aerofoil ?
% chord
Aspect ratio of a wing is the ratio between..
wingspan squared and wing area
Dihedral of the wing is the angle between the ___ and the horizontal with the aeroplane in an unbanked, level condition.
wing plane
Angle of attack is the angle between the __ vector and __ axis.
speed, longitudinal
Pressure constant and temperature increases, what happens to density?
decreases
Hvað gerist fyrir hlutfall IAS vs TAS með minnkandi flughæð?
mismunur á milli IAS og TAS minnkar með lækkun flughæðar. (Veit að TAS eykst í flughæð og því er þetta væntanlega öfugt í lækkun flugs - EAK).
Hvað kallast “the angle between the 0.25 chord line of the wing and the lateral axis”?
dihedral of the wing
Hvað kallast þetta?: Aircraft weight / wing area
wing loading
Lift acts at right angles to the ___ ____.
relative airflow
Thickness to chord ratio: __ thickness of aerofoil section to chord.
max
Taper ratio is the tip chord to ___ ___.
root chord
What is the unit of measurement for power?
a) N/m
b) N m/s
b) N m/s
The __ of an object depends on the acceleration due to gravity.
weight
kg*(m/s)^2 er í SI-unit system þekkt sem __.
Newton
Hvað gerist fyrir static- og dynamic pressure í flöskuhálsinum?
static pressure drops, dynamic pressure increases (og total pressure er sá sami).
Bergnoulli lögmálið segir: The sum of ___ energy and ___ energy is constant
pressure, dynamic
The SI system unit of measurement for weight is the __.
Newton.
The (subsonic) static pressure increases/decreases in a flow in a tube when the diameter decreases.
decreases
Það er þá væntanlega dynamic pressure sem increases.
Subsonic incompressible airflow through a venturi, the dynamic pressure in the throat is higher/lower than in the undisturbed airflow.
higher
What is the SI unit used for power?
W
What is the unit of wing loading?
N/m^2
What is the unit of dynamic pressure (q)?
N/m^2
Hvaða mælieining er notuð fyrir “rate of doing work”?
Watt (power)
Kinetic energy er mælt í..
joules
Hvað færðu ef þú segir mass(kg) * velocity(ms)
momentum
Hvaða formúla er þetta? Pstat + 1/2 rho * TAS^2 = Constant
Bernoulli
Hvernig er þríhyrningurinn með weight, mass og acceleration, hvað er efst?
weight
A line connecting the leading and trailing edge midway between the upper and lower surface of an aerofoil is called the __ line.
camber
Hvað heitir SI eining “work”?
J
What is the unit measurement for Power?
a) P
b) J/s
c) N/m
b) J/s
Hvernig breytist samspil IAS og TAS undir sjávarmáli í ISA aðstæðum?
TAS verður lægri.
Units of measurement of pressure is
a) psi
b) kg/m^3
a) psi
Hvað er rétt:
a) Drag is acting in the direction of relative wind (airflow) and lift is perpendicular to the relative wind (airflow).
b) Drag is acting in the direction of the longitudinal axis and lift is perpendicular to the longitudinal axis.
a) Drag is acting in the direction of relative wind (airflow) and lift is perpendicular to the relative wind (airflow).
If density is kept constant, the dynamic pressure increases proportionately with ____.
the square of the velocity.
Formúlan er dynamic pressure = 1/2 hró * V^2
Hvað heitir “the ratio between the wingspan and the mean geometric chord”?
aspect ratio
Hvernig væri þríhyrningurinn úr þessum (hvað væri efst)? Wingspan, mean geometric chord, wing area.
wing area væri efst, þ.e. wing area = wingspan * mean geometric chord.
A wing would be __ if the quarter chord line was inclined backwards from the lateral axis.
swept back
A wing is said to be ___ if the chord at the wing tip is less than the chord at the root.
tapered.
Hvaða SI mælieining er notuð fyrir mass?
kg
Hvaða SI mælieining er notuð fyrir weight?
N
what is the unit measurement for density?
kg/m^3
“In a streamlined flow of fluid, the sum of all energies is constant” þetta á sér rætur að rekja til hvaða kenningar?
Bernoulli
If humidity increases, what happens to density?
Density decreases
Is weight a force?
yes
Hvað er SI unit of pressure?
N / m^2
Largest distance between ___ line and camber line is called the camber of an aerofoil section.
chord
Hvað er annað orð yfir geometric washout?
wing twist
Geometric washout þýðir að the tip of the wing has higher/lower AoA than the root.
lower
Hvað kallast force: “Component of the total aerodynamic force, perpendicular to the undisturbed flow”?
lift
Profile drag is proportional to relative velocity of air/square of relative velocity of air and ___ coefficient.
square of relative velocity of air and drag coefficient.
Hvað gerist fyrir centre of pressure og magnitude of total lift ef þú eykur hraða?
CP moves aft
Total lift remains constant
When AoA decreases, what happens to the point of lowest static pressure? (Assuming no flow seperation)
It moves aft
The point where aerodynamic force acts on a wing is called the ___.
centre of pressure, CG
Where is Cl/Cd angle typically maximum? _°.
4°
Hvað gerist fyrir stagnation point ef AoA increases? (assuming no flow seperation)
stagnation point moves down
Total drag (two dimensional) comprises ___ drag and ___ drag.
pressure, skin friction
Hvernig er static pressure at stagnation point?
Static pressure reaches a maximum value
The aerodynamic centre of the wing is where pitching moment coefficient does not vary with ___.
the angle of attack.
The point where the aerodynamic force is applied is called..
the center of pressure
The point where the single resultant aerodynamic force acts on an aerofoil is called the..
Centre of pressure
With a decrease in AoA, the stagnation point moves..
up/forward (mátt segja bæði held ég).
Hvað gerist fyrir location of aerodynamic center of an airfoil section með breytingum á angle of attack?
Ekkert, independent of angle of attack.
With increasing downwash, lift generated by the airfoil ___.
increases.
Þú ert með positively cambered airfoil í straight and level flight, what happens when speed decreases to a) centre of pressure and b) magnitude of total lift force
a) centre of pressure moves forward
b) magnitude of total lift force remains constant (þar sem þú ert í straight and level flight þá hlýtur magnitude of lift að vera það sama).
Profile drag is proportional to __ density and the square of the relative __ of the air.
air, velocity
Hvað gerist fyrir center of pressure of a symmetrical aerofoil section (no flow seperation or compressibility effects) ef þú eykur AoA
ekkert, independent of AoA
At __ Cl/Cd you will find minimum drag
maximum
hró segir til um..
density
An aerofoil polar is: a graph of the relation between the lift coefficient and the drag coefficient/angle of attack.
drag coefficient
Coefficient of lift is a function of:
a) density b) pressure c) altitude d) camber of the airflow section e) angle of attack of the airflow section
d) camber of the airflow section
e) angle of attack of the airflow section
Í polvar curve graph getur þú lesið maximum __ coefficient
lift
which part of the airplane has the greatest effect on induced drag?
a) wing root junction b) wing tip c) landing gear
b) wing tip
Total drag is the sum of __ drag and __ drag.
parasite, induced
Spoilers; Hvað gerist fyrir Cd og Cl ef þú beitir spoilers með
a) Constant angle of attack
b) constant speed and load factor
Constant AoA: Cd increases, Cl decreases
Constant speed and load factor: Cd increases Cl unaffected
Hvað gerist við notkun á speed brakes?
Airplane decelerates, ROD increases, lift decreases and drag increases
Hvað gerist fyrir minimum drag speed við notkun speed brakes?
reduces
Hvað gerist við stall speed við notkun spoilers?
Increases
Spoiler surfaces on top of a wing
a) Are for use in landing only for reduction in speed
b) May be used as speed brakes in flight
b) May be used as speed brakes in flight
When roll spoilers are extended the part of the wing on which they are mounted experiences a reduction in lift, which generates the desired ___ moment. There is a local increase in drag which suppresses __ __.
rolling, adverse yaw
Which boundary layer, when considering its velocity profile perpendicular to the flow, has the greatest change in velocity close to the surface?
a) Turbulent boundary layer
b) The boundary layer in transition between turbulent and laminar.
a) Turbulent boundary layer
A turbulent boundary layer produces more __ drag than a laminar one.
friction
A laminar boundary layer turns into a turbulent one at the __ point.
transition
Er þetta lýsing á laminar eða turbulent layer?: “No velocity components exist normal to the surface”
Laminar
The boundary layer is considered to be turbulent between the transition and ___ points.
seperation
The turbulent boundary layer has the greatest/least change in velocity close to the surface.
greatest
Which resists positive pressure gradient better, laminar or turbulent layer?
Turbulent, it resists positive pressure gradient, has less tendency to separate from the surface.
What effect does ageing of an aeroplane have on the boundary layer condition?
The transition point moves forward and a larger part is turbulent
To what part of the take-off is icing most detrimental?
rotation
What does icing do to the critical angle of attack?
decreases it
The drag due to an ageing airframe is identified as
a) Parasite drag
b) Form drag
a) Parasite drag
það er nú stundum talað um skin friction drag.
Ice which is present on leading edges on wings may increase landing distances up to to%
40-50%
The most important problem of ice accretion on a transport aeroplane during flight is:
a) Increase in drag
b) Blockage of the control surfaces
c) Reduction in CLmax
d) Increase in weight
c) Reduction in CLmax
Hvaða formúlu notar þú til að finna Vs eftir því sem load factor breytist?
Vs = Vs1g * sqrt (load factor)
Hvaða formúlu notar þú þegar þú ætlar að finna stall speed í X° turn?
Vx = Vs1g * sqrt(1/cos(x))
Straight wing, hvað gerist fyrir CP við það að AoA er aukið og fer yfir critical angle of attack
CP moves back.
Þegar straight wing stallar færist CP back.
Swept back wing: CP moves ___ as angle of attack approaches and exceeds the critical angle of attack.
forward.
Þegar swept wing vængur stalar færist CP foward.
A sweep back wing has a pitch down/up effect in stall due to the ___ stalling first
Pitch up, wing tip
CP reaches it’s most forward point
a) at the stalling angle
b) just below the stalling angle
b) just below the stalling angle
Hvað gerist fyrir stagnation point á swept back wing going beyond the critical angle of attack?
stagnation point moves rearward.
Stall speeds/control speeds are determined with the CG at the forward limit.
Stall speeds. Control speeds are determined with the CG at the aft limit.
Stall speed increases/decreases when during a manoeuvre the aeroplane nose is suddenly pushed firmly downards.
decreases.
A negative tail tail stall causes an uncontrollable pitch _ moment.
down
Hver er formúla load factor?
Load factor = lift/weight
The minimum speed at which lift equals weight is
a) Vso b) Vs1 c) Vs1g
c) Vs1g
During a steady wings level climb, load factor is more/equal/less than one?
Less than one.
Skýring var að thrust væri að compenseita og því væri véli að ná að klífa.
Increase of wing loading will increase/decrease the stall speeds.
increase
Í steady wings level horizontal flight þá er load factor hver?
einn
Hvað kallast the phenomenon which could happen when sudden reduction in the downward aerodynamic force on the tailplane, happens?
Negative tail stall
Hvað færðu ef þú segir mass * acceleration due to gravity?
weight (force)
A stall that occurs while the aircraft is experiencing a load factor higher than 1g is called ___.
An accelerated stall
Hvað gerist fyrir CP vængs ef þú stallar á swept back væng?
Það færist fram.
Hvað gerist fyrir CP vængs ef þú stallar á straight wing?
CP færist aftur
When loking at the airflow over the wing, from the wing surface and up, the air is:
a) accelerated to the transition point
b) decelerated to the transition point
c) accelerated to the seperation point
a) accelerated to the transition point
Does stall speed (IAS) vary with weight?
Yes
Ef þú stallar á conventional low speed aerofoil at low subsonic speeds, flow seperation normally starts on the upper surface near the ___ edge.
trailing
Hvað gerist fyrir critical angle of attack ef þú breytir weight? En ef þú færir CG fram/aftur?
Critical angle breytist ekki. Það eykst ef þú færir CG aftur held ég.
Hvað virkjar stick pusher?
of hátt angle of attack
When pulling out of a dive the angle of attack __.
increases
Getur stall hraði breyst í turbulence?
já
hvað veldur pitch up tendency í swept wing airplanes at low airspeed?
wingtip stall
Is a stick shaker system fitted to an aeroplane to resolve deep stall problems?
No
Lowering flaps sometimes produces a pitch moment change due to movement of..
the center of pressure
When the load factor is more than 1, __ is more than ___.
lift, weight.
Þú færð gefinn stall hraða og svo load factorinn 1.5. Hvernig reiknar þú nýjan stall hraða miðað við þennan load factor?
gamli stall hraðinn * sqrt(1.5)
A stall warning vane on an aircraft wing is fitted
a) on or at the leading edge
b) just below the leading edge
b) just below the leading edge
The main purpose of a boundary layer fence on a swept wing is to:
a) improve the low speed handling characteristics
b) improve the lift coefficient of the trailing edge flaps
a) improve the low speed handling characteristics
Vs1 is:
a) stall speed in the clean configuration
b) The stall speed or the minimum steady flight speed obtained in a specific configuration
b) The stall speed or the minimum steady flight speed obtained in a specific configuration
In a steady horizontal turn, the stall speed increases with the square root of __ ___.
load factor
At 5000 ft vs sea level, the IAS will be higher or lower? How about TAS?
IAS will be the same speed at high altitude but TAS will be higher.
Airflow separation is characterised by
a) increased velocity on the surface of the body
b) airflow reversal on the surface of the body
b) airflow reversal on the surface of the body
Stall speed increases when pulling out of a ___.
dive
The sensor of a stall warning system can be activated by a change in the location of the ___ point.
stagnation
Hvað gerist fyrir critical angle of attack ef aspect ratio increases?
decreases
Hvað gerist fyrir stalling angle of a wing í beygju?
breytist ekki
The pitch up tendency of an aeroplane with swept back wings during a stall is caused by the forward/aft movement of the CG/CP
forward movement of centre of pressure (CP).
Hvað gerist fyrir stall speed (IAS) ef CG moves forward?
Eykst
Hvað gerist fyrir stall speed (IAS) ef þú lendir í icing conditions?
eykst
Hver er munurinn á Krueger flaps og slats?
a) Deploying a slat will increase critical angle of attack, deploying a Krueger flap does not.
b) Deploying a slat will form a slot, delploying a Krueger flap does not.
b) Deploying a slat will form a slot, delploying a Krueger flap does not.
As stagnation point moves downward, the flapper switch moves..
upward
Hvað er notað til að reduce spanwise airflow over swept wings?
Wing fence
Hvað gerir fixed spoiler on a leading edge root?
Ensures the root of the wing stalls before the tip.
Hvað gerist fyrir stall speed (IAS) at higher altitudes?
Initially remains constant but increases at higher altitudes.
Critical angle of attack is dependent on:
a) design of the wing
b) aircraft mass
a) design of the wing
On a forward CG airplane the Vs is lower/same/higher and the stalling angle is lower/same/higher
Vs higher (auðveldara að stalla framhlaðinni vél en létt að koma sér úr stallinu) Stalling angle er bara það sama (held að það sé bara alltaf eins).
Ef þú lendir í spinni (spinnar t.d. til left), eru vængirnir stallaðir? Báðir? Hvor?
Both wings are stalled.
Recovery úr spin: Ailerons neutral.
A super stall is most probable with
a) T-tails
b) Swept wings
b) Swept wings
Boundary layer is created by a layer on the wing in which the stream velocity is higher/lower than the free stream velocity.
lower
The purpose of a leading edge droop is? to increase ___, and delay separation of the airflow when trailing edge flaps are lowered
wing camber
When flaps are lowered the stalling angle of attack of the wing ___. Clmax ___.
decreases, increases
If the flaps are lowered in flight, with the airspeed kept constant, to maintain level flight the angle of attack..
must be decreased.
Hugsaðu þér bara þegar þú setur niður flapa og hún balloonar þá upp, verður að setja stýrin fram svo hún ballooni ekki.
When flaps are lowered the spanwise flow on the upper surface of the wing?
b. increase towards the tip
c. increases towards the root
c. increases towards the root
Lowering flaps sometimes produces a pitch moment change due to movement of..
the center of pressure
When a leading edge slot is opened, the stalling speed will?
a. increase
b. decrease
c. remain the same
b. decrease
Which type of flap would give the greatest change in pitching moment?
a. Split
b. Plain
c. Fowler
d. Plain slotted
c. Fowler
The correct definition of Vs1 is
a) the stall speed in the clean configuration
b) the stall speed or the minimum steady flight speed obtained in a specific configuration
b) the stall speed or the minimum steady flight speed obtained in a specific configuration
During a steady horizontal turn, the stall speed increases with the __ __ of the load factor.
square root
An automatic leading edge slat is operated by:
a) Aerodynamic forces acting on the leading edge.
b) Changes in the dynamic pressure acting on the stagnation point
a) Aerodynamic forces acting on the leading edge.
