8.2 aerodynamics Flashcards
what is turbulent air?
air moving through a disturbance
it becomes turbulent when the air separates
what is laminar flow?
smooth regular air flow
air particles have a mass so what does this result in?
air in motion possesses a momentum
what does air exert pressure on?
on any objects in its path
what is the relationship between dynamic pressure density and velocity?
it is proportional to density and the square of velocity
what is energy due to and what is the equation for that?
due to kinetic energy
KE = 1/2 *v^2
what happens when a volume of air is completely trapped and brought in an open ended tube?
total energy remains constant and the moving air exerts pressure on the tube and kinetic energy is passed
what can and can not be done to energy and mass?
can be neither be created or destroyed
can only change states
what is streamline / free stream?
when particles of a fluid move in an orderly manner and maintain relative position in successive cross section
what is cross section represented by?
lines running parallel to one another hugging the shape of the body it is following around
in the subsonic region a flying body does not attain what?
the speeds necessary to compress the air
where is the air incompressible?
in the subsonic region
if there is no disturbance the air is what?
air is streamline and parallel
when something is streamlined it is what?
it is similar to the flow in a closed tube
what happens when the tube gets smaller in laminar flow?
the air flow remines equally spaced when it is in a tube with different diameter’s
what does the continuity equation state?
that the speed of the airflow is inversely proportional to the cross section if density remains the same
p1 = p2 so v1 * a1 = a2 * v2
when will v1 * a1 = v2 * a2 be used?
when there is a difference in volume
when is there a diffuser outlet?
when diameter increases and speed decreases
when is there a jet outlet?
when the diameter decreases and speed increases
in Bernoulli’s principle what happens when the valve is closed?
the tube is filled with fluid on the left side of the valve
when the valve is closed what pressure will there be and where?
the fluid filled on the inside of the tube has static pressure
in Bernoulli’s principle when the valve is closed where does pressure act?
acts in all directions
what is total pressure represented by in Bernoulli’s principle?
a green circle
in Bernoulli’s principle what is the relationship between total pressure and static pressure when the valve is closed?
total pressure is equal to static pressure
how is Bernoulli’s printable explained?
explained with a valve
when the vale is open what happens to static and dynamic pressure?
static pressure decreases
dynamic pressure increases
in Bernoulli’s principle what pressure is introduced?
dynamic pressure
when the valve is open what pressure remains unchanged?
total pressure
what is the equation for total pressure and constant pressure?
total Pout = p * q
constant q = 1/2 *v^2
what is the equation for dynamic pressure?
dynamic pressure = total pressure - static pressure
where is static pressure sensed?
directly at the static port
what is static and dynamic pressure indicated by?
static pressure is a red line
dynamic pressure is a blue line
what is dynamic pressures relationship to density and velocity for bodies in motion?
dynamic pressure is proportional to density and square of relative velocity
what will happen if we assume density is constant?
dynamic pressure increases 16 times and speed increases 4 times
what is dynamic pressure indicated to the pilot by?
induced air speed
what happens at the point of stagnation?
speed of the airflow falls to zero an static pressure = total pressure
if there is no dynamic pressure there is no what?
there is no air flow
in the venturi tube what is the same?
the inlet and outlet
in the venturi tube airspeed of airflow increases until what point?
until it reaches the narrowest point
what happens to speed, static pressure and dynamic pressure in a venturi tube?
speed increases
static pressure decreases
dynamic pressure increases
what happens at the narrowest point of a venturi tube?
speed decrease after the narrowest point
static pressure increases
dynamic pressure decreases
in the venturi tube it says what causes lift?
the difference in static pressure
what is a fixed boundary layer?
it is where the air stream close to the skin has a velocity of zero
what is the boundary layer?
it is a layer of fluid in the immediate surface of the skin
when air moves over the wing the fluid at the skin of the surface can be said to be what?
it can be considered stationary as monocles of the surface are brought to rest by friction
why is the surface rough on the skin?
because of imperfections but then monocles become caught there forcing them to become stationary
what happens because of the rough surface on the skin?
the second layer shears because of rough surface
when will layer begin to stop shearing?
until the layer of the air particles reach the velocity of the free stream
what is laminar flow?
smooth and undisturbed and less energetic flow
is laminar flow easy to achieve?
no
in laminar flow the layers are what?
layers are streamlined and do not cross over each other
they flow parallel to each other
what will rivets do to laminar flow?
rivets will disturb the laminar flow
when looking at laminar flow when is the pressure gradient negative?
from the thickest point of the wing to the trailing edge
what will happen if the flow is insufficient in terms of laminar flow and when will it worsen until?
it will detach from the surface and start to travel in the reserve direction #
will worsen until the wing stalls
where is laminar flow easier to obtain and why?
easier to achieve at the leading edge because there is a positive gradient
is laminar flow desirable and why?
it is desirable because it gives high lift and low skin friction and drag
what is lower drag due to in terms of laminar flow and why is it caused?
it is due to shear stress on the boundary layer
what is more likely to form turbulent floe or laminar flow and why?
turbulent flow because it is more naturally occurring
in turbulent flow what happens at the surface of the wing?
particles move at zero velocity and still cause very laminar flow
in turbulent flow where do imperfections extend?
they extend beyond the laminate layer
what does the mixture of laminar flow and free stream air cause in turbulent flow?
the mixture become chaotic and difficult to predict
what are eddies caused by?
formed when influences of the air nearby by and cause further disruption
what is difficult to maintain over a wing?
laminar flow
when does airflow naturally become turbulent?
becomes turbulent with an increase in AOA causing pressure gradient
this occurs at lower airspeeds if there are any imperfections on the wing
what is the negative of laminar flow?
this flow increases drag because layers do not slide over each other
turbulent flow causes this boundary layer to become what?
to become thicker and more energetic
what does turbulent flow allow that laminar flow does not?
for grater negative pressure
what is a positive of turbulent flow?
allows the boundary layer to remain attached to wing but laminar flow would have separated which reduces pressure drag
in free stream flow the fluid id what?
far enough away from the moving body
in free stream flow what happens as the aircraft moves through the air?
it affects the air around the aircraft causing it to change direction, heat up, change velocity and pressure
when do the effects of free stream flow decrease?
as distance increases from the aircraft
what is relative airflow?
the direction of the airflow with respect to the object moving through it
a climbing aircraft will have more what?
will have a grater nose up altitude
relative airflow is usually what?
an angle to the nose
in level flight the aircraft is doing what?
aircraft is flying directedly into the wind
in climb wind would appear to come from where?
appear to come from bellow the aircraft
in decent wind would appear to come from where?
would appear to come from above the aircraft
what is the stagnation point?
the region of space around the aircraft where the velocity of relative airflow is zero
what does the stagnation point result in?
results in static pressure compared to the surrounding fluid moving relative to the aircraft
where is the common point of stagnation?
the leading edge of the wings
the boundary layer can be what?
can be laminar or turbulent
the boundary layer is not always what?
is not always smooth or laminar
where is the laminar boundary layer located?
immediately downstream of the wing leading edge
what does turbulent boundary layer produce?
produces higher kinetic energy
where is the transition point of a wing?
at or near the maximum thickness and the lowest point of pressure
what do small disturbances inside the boundary layer do?
brig it to a turbulent boundary layer of produce floe separation
what does an increase in AOA do to the transition point?
brings the transition point further forward and an adverse pressure gradient becomes stronger
what may happen if there is not enough wing area?
not enough area so wing may stall
what causes thrust effect on the wing?
high pressure to lo pressure
wat does air movement cause?
pressure drop and following air flows from high pressure to low pressure
when flow is from low to high pressure wat happens?
the lower kinetic energy of laminar flow will lack the energy required to force it to flow against the negative pressure
wat will resulting pressure gradient on a wing cause?
air to flow from high to low pressure
in flow separation streamlines over the wing will do what?
will separate and travel over the layer of air traveling in the reverse direction
wat happens when flow is separating?
lift is reduced and pressure drag increased dramatically
wat boundary layer is more energetic?
turbulent boundary layer
wen would prevention of flow separation happen?
if the flow was laminar
where is it safer for a stall on the wing?
at the root rater than the tip
sacrificing loamier flow towards the wing tips does what?
helps control a stalling aircraft
what is the main advantage of laminar flow?
the surface has friction which saves fuel, increases range, increases sped and further glide in failure
it is easy to chive laminar flow?
no especially at high speeds and AOA
difficult to achieve in negative pressure gradient from thickest part of the wing and trailing edge
when a wing has laminar flow and stalls what does it create?
high pressure drag witch increases stall further
what is the disadvantage of laminar flow?
has lower kinetic energy so easier for flow separation to occur
what is downwash?
after passing over the airfoil it returns to its original shape
wat is upwash?
as air flows towards the wing it turns towards the low pressure region of the upper surface of te airfoil
what happens at the leading edge with the airflow?
the airflow stagnates annd seperates as it passes under the wing
what happens when air flows back over the airfoil?
4it will slow down and flow against adverse pressure gradient as high pressure bellow the wing wants to go from high pressure to low pressure
what do door gutters do?
they slope upwards to reflect upwash and downwash and reflect AFT of the wing
on finite wingspans what must be considered?
wing tip vortices must be considered
if wingspan is infinite what does the circulation around the profile cause?
upwash on LE and downwash on the TE known as bound vortex
as the vortices get stronger what happens?
enhanced drag gets grater
what i induced drag?
increase in drag
to ensure enough lift is generated what is needed?
a higher AOA is needed
wat is induced alpha?
is the angle between effect airflow and relative airflow
what is an increase in drag caused by?
the need to maintain lift
trailing vortices have a strong influence on what?
lift
drag
handling properties
wat do vortices produce?
produce downwash of flow behind the wing
which way to vortices rotate on left wing and right wing?
rotate clockwise at the wing tip
rotate anti clockwise at the wing tip
what are vortices?
circular patterns or rotating air formed behind a wing or control surface
what does an aerodynamic profile have?
leading and trailing edge
what is the chord line?
a straight line connected LE to TE the distance between the two is measured
what is the mean chord line?
a line drawn equidistant between upper and lower surface of the profile
wat is the camber of a profile?
it is the displacement of the mean camber from the chord line
wat is maximum camber?
the greatest distance between mean camber line from the chord line
expressed as a pentane of the chord line
when is there a positive and negative camber?
positive when the camber is above the chord line
negative when the camber i bellow the chord line
why is the shape of the mean camber important?
in determining aerodynamic characteristics of a profile
does a symmetrical airfoil have a camber? why?
has no camber as the chord and camber are the same
a typical low speed profile has what camber and AOA?
has a max camber of 5% at 45% AOA of the leading edge
on fineness ratio what is the maximum thickness?
depth of a section expressed as a percentage from the LE to the TE
wat is the line of maximum thickness defined as?
a percentage of the chord
what is a high aspect ratio used for?
high performance gliders
how can you change the aspect ratio in flight?
by pivoting the wings to have a large span for low speeds
where is induced drag less?
less on an aircraft with a high aspect ratio
wing tips can be designed to reduce what?
induced drag
what does high aspect ratio have?
has lower drag and slightly higher lift
wat is induced drag affected by?
aspect ratio
wing tip design
aircraft speeds
low aspect ratio looks like what?
short spans or thick chords
airfoil is the ratio between what?
ratio between length and average width of the surface
what is aspect ratio?
ratio of wing length to average chord of the wing
what is the equation for aspect ratio if chord is equal thought?
AR = length of wing / width of the wing
wat is the equation for aspect ratio if the chord line is varied thought?
AR = wing span^2 / wing area
wat does wash in refer to?
when the angle of incidence is grater towards the tip
wat does wash out refer to?
when the angle of incidence is grater towards the root
wings cam be designed so what can happen?
so they stall at the root before the tips so aircraft remains controllable
in geometrically twisted wings what does the camber look like?
constant across the span of the wing
on geometrically twisted wings where is the angle of incidence grater?
grater at the root
are the chord lines parallel in geometrically twisted wings?
no
with aerodynamically twisted wings where is the camber grater?
at the root
wat does the angle of incidence look like for aerodynamically twisted wings?
angle of incidence is constant across the wingspan
ae the chord lines parallel on aerodynamically twisted wings?
yes
what happens on a aerodynamically twisted wing at the stall speeds?
there is flow separation t he root before the twist
most aircraft wings are what?
tapered and swept and use a combination of gyrometric and aerodynamic wash out
what is the mean aerodynamic chord?
the average chord length of a tapered or swept wing
were is the angle of incidence?
between the chord line and the longitudinal axis of the aircraft
what is the angle o incidence used for?
for fixed wing but an be variable for the tailplane and horizontal stabilizer
were is the center of pressure?
point of the chord line where total sum of pressure acts on a body
what is aerodynamic force and where does it act?
it is called total reaction and acts around the center of pressure
what can the center of pressure be broken down into?
into parallel and perpendicular to relative airflow
is drag parallel or perpendicular?
drag is parallel in the same direction as relative airport
when at normal cursing speeds and small AOA where is the center of pressure of the chord line?
25% of the cord line
what happens to the center of pressure when AOA increases?
AOA increases the center of pressure moves forward
what is the max AOA before flow separation occurs?
15% to 18%
what are the 4 different types of wing shape?
elliptical wing
rectangular wing
tapered wing
swept wiing
why is there different stall characteristics of different wings?
the down wash behind the wing changes the local angle of attack
what are the characteristics of an elliptical wing?
has constant down wash behind the wing
constant down wash gives constant AOA and constant flow separation across the span of the wing
entire wing stalls at the same time
what are the characteristic of a rectangular wing?
has large wing tip vortices so larger downwash at the tip
has higher down wash and lower AOA at tip
tip sections are last to stall
what are the characteristics of the tapered wing?
down wash increases towards the root
tip stalls first
what are the characteristics of swept wings?
tends to stall at the tip first
used on most aircraft
impacts lateral and controllability because of tip stall
what is the seep angle?
between the line of 25% chord and line perpendicular to the root chord
what is positive and negative sweep?
positive sweep = backwards
negative sweep = forwards
what happens when the wing is more swept?
the more stable the aircraft is on the roll axis
what is a dihedral angle?
when the wing tips are higher thana the root
what do dihedral angles increase?
roll stability
AOA
lift what are anhedral angles?
what aircraft use dihedral angles?
commercial aircraft
what are anhedral angles?
wing tips are lower than the wing root
what is the effects of anhedral angles?
increase roll performance
reduces the amount of lift
counteract roll
provide balance and stability and maneuverability
what aircraft are anhedral wings used on?
aircraft that require high agility and memorability
what is drag?
aerodynamic force witch is parallel to the relative wind
what is the total aircraft drag the sum of?
induced drag
parasite drag
compressible drag
what is induced drag?
drag cause by lift
what is parasite drag?
caused by distribution of pressure
sum of friction
not related to lift
what is compressible drag?
caused by shockwaves when aircraft reaches the speed of sound
what is the movements of induced drag?
movements of air over wing starts at fuselage and makes way to wing tip
on induced drag where is spanwise flow the strongest?
at the wing tips so vortices at the trailing edge of the wing
with induced drag where is static pressure higher?
is lower above the wing
higher bellow the wing
what type of drag has strong vortices?
induced drag
what do induced drag vortices do to the aircraft?
contribute to drag so aircraft becomes less efficient
when is there a high lift coefficient?
when at low speeds as there is a higher AOA
when does an aircraft has a low lift coefficient?
when at low speeds and low AOA
what happens when there is a low pressure difference between the upper and lower surface of the wing?
creates small wing tip vortices so therefore lower drag
what is parasite drag cause by?
pressure distribution over a body
difference in pressure
what does form drag depend on?
friction area of a body and the speed of the airflow
when there is no friction there is no what?
drag
because the pressure before and after is the same
when there is airflow with friction is there a pattern?
there is no symmetrical pattern
is pressure the same on airflow with friction?
pressure is not the same
what types of drag have a relationship?
form and friction drag
when a profile has low foam drag and high from drag what goes along with it?
low form drag = high friction drag
high form drag = low friction drag
what is more toral drag or drag on each wing?
total drag
where is there drag felt?
wing
strut
engine
how can interference drag be reduced?
adding faring’s witch is found on wing roots, pylons, flap tracks
define interference drag?
turbulence in airflow caused by sharp corners and joints
what happens to the boundary layer as it passes through the shockwave?
it thickens
is the shockwave Infront or behind the shockwave?
Infront and behind
where does compressible drag occur?
in transonic and supersonic
in compressible drag what happens when in the transonic region?
there is a mixture of subsong and supersonic airflow and encourages shockwaves
what happens in compressible drag in supersonic flight?
vortices move faster than free stream
velocity os less than speed of sound
where does flow separation occur?
as boundary layer thickens
air sped varies due to thrust but what else must happen?
AOA must vary to maintain level flight
what must happen to maintain constant airspeed?
thrust and drag must remain equal
what must the pilot do to ensure straight and kevel flight?
coordinate AOA and thrust
what is the weight of the aircraft?
size and martials used on aircraft
fuel carried
what is the relationship between weight and lift?
definitive
what happens when lift is grater than weight or when weight is grater than lift?
when lift is less than weight vertical speed wil increase
when lift is grater than lift vertical speed will increase
why is lift required?
to counteract the weight
what is lift?
upward force on the wing perpendicular to the relative wind and lateral axis
what happens when lift force is equal to the weight force of the aircraft?
it is at a state of equilibrium and nether accelerates upwards or downwards
thrust to weight ratio is an efficacy factor for what?
total aircraft propulsion
what is the equation for force, weight, mass?
force = mass * acceleration
weight = mass * gravitational acceleration
mass = weight / gravitational acceleration
what is a resultant force?
when two or more forces act at the same time
how do 2 of the 4 fundamental forces come about?
aerodynamic loading
what happens when vertical and horizontal forces are applied?
resultant acts diognally
lift always acts in what direction to relative flow?
force of lift always acts perpendicular
drag aways acts in what direction to the relative wind?
parallel and in the same direction
as the AOA moves forward what happens to the vector?
it leans forward creating a different lift/drag ratio
what does the overall aerodynamic force acting on the wing do?
provides a resultant force on the wing
what happens when static pressure increases?
dynamic pressure decreases
what is ambient pressure?
undisturbed air at room temp
what is static pressure?
inversely proportional to dynamic pressure
what is pressure distribution caused by?
variation of local static and dynamic pressure on a surface
what relationship does Bernoulli’s printable show?
between pressure and velocity
when there is a positive AOA is used where does the upwash and downwash happen at?
upwash above the stagnation point
downwash on the trailing edge
what is pressure difference related to?
related to the difference in relative air speeds on the two surfaces
the velocity of distribution around an airfoil can be broken into two components what are they?
mean value components
circulatory components
the faster the flight speed what is needed less?
less circulation required to generate lift
what determines pressure distribution around what?
shape of profile and AOA determines pressure distribution around airfoil for coefficient of lift and drag
surface area is proportional to what?
lift generated
the surface area and its condition will influence what?
the amount of lift produced
what does the magnitude of pressure distribution on an airfoil depends on what?
energy of the airflow
aerodynamic forces can be represented by what?
dynamic pressure
surface area of profile
shape of profile
AOA
what is the equation for dynamic pressure?
= 1/2 * density * velocity^2
what is the most important variable for lift and drag?
airstream velocity which combines with airstream density determines dynamic pressure
can we calculate actual lift in flight?
no a wind tunnel is needed
what scale measures drag in actual lift?
horizontal scale
what scale measures lift in actual lift?
vertical scale
what is the equation for coefficient of lift?
measured lift / theoretical lift
what is the equation for coefficient of drag?
measured drag / theoretical drag
what happens when there is a higher angle of attack?
the higher the lift so the more drag so the more turbulent flow
what happens when there is a thick profile of the wing?
the higher the lift
what happens when there is a thick chord of the wing?
the higher the lift
what does the polar diagram show?
that lift and drag coefficients can be combined info on performance of profiles on center of lift and drag for AOA
lift drag ratio is plotted against what?
against the angle of attack
lift to drag ratio is the same as what?
as the lift coefficient to drag coefficient
what does the polar diagram show for lift and drag?
maximum lit and drag ratio
what is stall?
sudden reduction in lift when critical AOA is reached
what happens when AOA increases?
flow separation increases which reduces lift
what may a fixed wing aircraft experience during stall?
a change in altitude
what is the angle to relative wind for steady flow, stall point / maximum lift, separated flow?
6 degrease for steady flow
15 degrease for stall point / max lift
25 degrease for steady flow
where is the stall point?
25 degrease due to flow separation
where does wing root stall occur?
at the root
due to wing root stall what happens to the center of gravity?
it moves forward
during root wing stall where does the stall go?
root to tip
what happens to the nose when there is a root wing stall?
nose pitched down
what happens when the nose pitches down due to root wing stall?
aircraft loses stall rapidly
airspeed increases
AOA decreases
during wing tip stall what input is needed?
crew input required to keep aircraft under control
what happens to the pitch during wing tip stall?
aircraft pitches up
AOA increases
stall conditions increase
what happens to center of lift when wing tips stall?
it moves towards the lift and forward of the center of gravity
what stall makes flow separation more dangerous?
wing tip stall is more dangerous
what are the ways to protect wing tip stalls include side effects?
stall strips but degrease lift
use of slats
use of slots
what happens when slots open up?
the boundary layer is energized preventing flow separation at the tip
where are slats located?
on the LE at the wing tip
what aircraft are slats used on?
on lighter aircraft
slats normally do what?
extend
what happens when slots open up?
boundary layer is re energized witch prevents flow separation
what can affect the performance of an airfoil?
formation of snow and ice
accumulation of dirt and bird droppings
what can the build up of ice do?
negatively effect weight and drag cause a loss of list and frieze or imbalance of the control surfaces
when flying at temps bellow freezing point what happens?
ice can form on the tip
what flights are ice formations dangerous for?
for low speed flights
what can upper surface frost cause?
reduce the coefficient of lift and critical AOA
what will determine the type of ice formed?
the type of atmospheric conditions
what are the three types of ice?
frost, rime and clear
what happens if ice is not removed?
it can affect laminar flow flow of the aircraft over the LE and cause dangerous loss of lift during takeoff and affect control surfaces
the build up of snow and ice can do what?
increases the weight and shape on the object on which had formed
when will frost form?
when aircraft is sat overnight
when it goes from sub zero to moist walm air
when does rime ice form?
when super cold water droplets freeze on a surface that is bellow freezing temps
where can rime ice form?
engine inlet
leading edges
what is considered the most dangerous ice?
clear ice
what happens when clear ice forms?
happens in large amounts which can damage rear mounted engines
describe clear ice?
heavy coating of glossy ice
from large supercooled water droplets
