u6 Flashcards
explain bernoulli and newtons principles regarding LIFT
bernoulli = curved top of wing = low P and things move from high to low P (upwards)
newton = the wing forces the air hitting it downwards, so the wing itself must rise (momentum conserved)
explain why does increasing AOA increase lift
increase AoA = increase speed of air on top = lower pressure = more lift
increasing AoA = increase surface area on bottom of wing = increase lift
how does increasing wing camber increase lift
increasing wing camber = larger pressure difference = more lift
doubling the speed of the plane will increase lift by ____ x
4x
what is induced drag?
how does AoA affect induced drag
how does wing camber affect induced drag
induced drag is a byproduct of lift - large air vortices that pushes the plane backwards
high AoA = larger pressure difference & more SA on bottom of wing = increases vortexes = more induced drag
increase wing camber = increases pressure difference = stronger vortices = more induced drag
the air vortices (induced drag) on the RIGHT wing (view from back) flow clockwise or counter clockwise
what about the LEFT wing
counter clockwise
clockwise
what are the 3 forms of parasite drag and definition
does a fast or slow plane experience more parasite drag
- form drag - aerodynamic shape of plane determines amount of drag
- skin friction - smooth skin = less friction
- interference drag - drag made by parts of the plane meeting together
fast plane = more air molecules flowing past plane = more parasite drag
slow planes have ______ induced drag and ______ parasite drag
high induced drag (high AoA)
low parasite drag
thrust is a force produced by the _______
it provides the forward motion of the plane by pushing the air _____
engine
backwards
t/f: a plane in a steady climb is in total equilibrium
true
at first when the plane pitches up it’s decelerating (not equilibrium), but as soon as it’s in steady rate of climb it’s in equilibrium again
as you increase AoA, the CoP shifts ____
once it reaches critical AoA, the CoP shifts ___
forwards
backwards
t/f: when a plane is in a steady turn, it’s in equilibrium
false
acceleration is a change in speed OR direction, and when ur turning you’re changing direction so you’re accelerating so not in equilibrium
what is the load factor equation
LF = load on the wings / weight of plane
in a turn, the plane feels heavier. why?
turn -> new centripetal force (horizontal component of lift) -> new centrifugal (outward) force
there’s now a centrifugal force
so the wings are now supporting the weight of plane + outward centrifugal force
in a 30º turn, the resultant load factor is _____ G
in a 45º turn, the resultant load factor is _____G
in a 60º turn, the resultant load factor is ___G
1.15G
1.4G
2.0G
(the load of the wings is 1.4x the weight of the plane)
high airspeed = ______ turn radius
slow airspeed = _______ turn radius
large
small
high bank angle = ______ turn radius
low bank angle = _______ turn radius
small
large
coefficient of lift depends on ________ and ________
if i want to change the amount of lift i’m getting in flight, what can i change
camber + AoA
AoA
the AoA is the angle between
the relative airflow and chord line of wing
why doesn’t a wing stall during climb
because the relative airflow changes - it’s on the same plane as your climb angle
the angle of incidence is the angle between
the chord line of wing and plane longitudinal axis (datum line)
the angle that the wing is mounted to the fuselage
why do designers pursposely mount the wing so that it has a slight AoI
slight AoI = automatic AoA
so in cruise, the pilot can now have better visibility because it’s able to pitch the nose of the plane down and still have a slight AoA to get lift
what is the stagnation point
location where the wind velocity is zero
place where the air hits the wing (now has a choice to flow above or below airfoil)
when the CoP is _____ the CoG, during stall the nose will automatically pitch down (stable)
CoP BEHIND CoG
CoG AHEAD of CoP
which planes have the strongest vortex:
- fast or slow
- clean or with gear out
- light or heavy
slow - high AoA
clean - no barriers to vortex
heavy - needs to automatically fly at higher AoA to get lift
what is the size dimension for wake turbulence
2 wingspan (width) x 1 wingspan (depth)
the vortex of a large, heavy plane settles below and behind the plane between ________ FPM
within 2 mins, the vortex levels off at ______ ft below the planes flight path
vortices trail the plane between ____NM
300-500 FPM
1000 ft
10-16 NM
how to avoid wake turbulence from a large heavy plane on takeoff:
- rotate ______ the point of the taking off plane
- rotate _______ the point of the landing plane
before
after
how to avoid wake turbulence from a large, heavy plane on landing:
- touch down _____ the point of the taking off plane
- touch down _____ the point of the landing plane
before
after
the ______ the helicopter, the stronger the vortices/wake turbulence
heavier
(not larger)
because heavy helicopters use high rotor AoA
t/f: a stalled wing generates lift
TRUE
but it’s just not enough lift to overcome the weight of the plane
ATC gives a _____ separation when a small plane departs behind a large one (when there’s no radar)
2 min
ATC gives a _________ when a small plane departs after a medium one
wake turbulence advisory
how does ground effect work
what’s the span of ground effect
what’s the limitations of ground effect - when won’t it work?
fly low to the ground, wingtip vortices get cut off (less induced drag) = accelerate faster
half a wingspan
a heavy overloaded plane might not be able to get out of ground effect (less drag within ground effect, which is good. but can’t handle normal level of drag when it tries to escape)
which wing planform (shape) has the safest stall characteristics?
rectangle because it starts to stall near fuselage first (ailerons last)
why do rectangle shaped wings have high parasite drag compared to other planform shapes
because rectangle wings have the most perpendicular airflow along the leading edge of the wing = high parasite drag c
i have a slow plane, what kind of wings would be best to reduce my induced drag
long/skinny wings
yes, there’s more parasite drag because there’s more perpendicular airflow, but since you have long wings you can have a small camber and fly at lower AoA
i have a fast plane, what kind of wings would be best to reduce my parasite drag
reduce parasite drag by getting shorter but fatter wings
shorter wings = less perpendicular airflow = less parasite drag
but the trade off is that you need a higher camber to compensate to get more lift
higher camber = higher induced drag
aspect ratio equation
aspect ratio = wingspan / wing chord (width)
high aspect ratio:
- ____ surface area
- _____ parasite drag
- _____ induced drag
high
high
low
low aspect ratio:
- ____ surface area
- _____ parasite drag
- _____ induced drag
low
low
high *because of the thicker camber
flaps increase wing
camber
as the laminar flow boundary later approaches the centre of the wing it begins to lose speed due to ________ and becomes ________
skin friction
turbulent
laminar flow wings improves the boundary layer airflow by…..
_____ lift and ____ drag
____ wing camber
for ______ planes
moving the transition point aft = delay turbulent air
low lift and low drag
high
fast
sweepback wings:
_____ planes
how does it delay shockwave formation
fast planes
airflow hits wing at an angle smaller than 90º, so it tricks the plane into thinking it’s flying slower than it actually is = delays compressibility effects = delays shockwave formation
dihedral wings have good
lateral stability
what are washed out wings? and how do they improve aileron control near stall
- AoI at the fuselage is higher than the wing tip AoI, so when the fuselage AoA reaches stall, the wingtip AoA is still low enough to not be stalled (ailerons can work)
how do stall strips improve aileron control
installed at wing root to change the boundary layer so that the wingtip AoA root stalls before the wing tips (like washed out wings)
what are wing fitness
ensures smooth airflow straight forward to back of wing by blocking span wise airflow
good for slow speeds
improves stall characteristics
slats vs slots
slats: small airfoil that opens at front of wing at low speeds to increase camber and SA = increase lift
slots: openings along leading edge that pop out at low speeds so that some air can flow in at higher AoA = extra lift
what is a spoiler
kills lift by causing airflow to separate from top of wing (deceleration)
flaps:
- how does it affect lift and drag
- ____ stall speed
- _____ visibility
- why do some flaps have slots
increases lift and increases drag
slower
better
if the curve is too big, air can’t easily bend around flaps and cause turbulent airflow
what is a vortex generator
creates turbulent but sticky air so that the boundary layer stays on the wing longer before detaching
since airflow on your wing longer, your critical AoA increases
what are winglets
blocks part of the wing tip vortices (less induced drag)
longer wingspan
also generates lift so contributes to thrust
what are canards
what happens when a canard stalls
airfoils mounted in nose that also produces lift upwards
when canard stalls = nose automatically drops = prevents main wings from stalling
increase load factor = ______ stall speed
increases
Vs in turn = equation
Vs in turn = Vs x root (LF)
the lighter the plane, the _____ the Va. why?
light plane = LOW Va
- light plane flies at lower AoA so if you were to suddenly pitch up it would take a long time (and endure more force/structural damage) before it reaches critical AoA
- by flying slower, you starting off with flying a high AoA. so when you suddenly pitch up, you’d quickly reach critical AoA (stall) before getting to the point where you would’ve reached structural damage
fly below what speed in turbulence? why?
Va to prevent excessive LF from gusts
limit load vs ultimate load
limit load = LF the pilot must fly within
ultimate load = plane designed to withstand 1.5x the load limit
normal category:
positive limit load
negative limit load
+ 3.8G
- 1.52G
utility category:
positive limit load
negative limit load
+ 4.4G
- 1.76G
aerobatic category:
positive limit load
negative limit load
more 6.0G
less - 3.0G
which category can spins be done in
utility
longitudinal stability
- stability around ____ axis
- ____ heavy plane is stable
lateral
nose
lateral stability
- around _____ axis
- how does the keel effect give more roll stability
- what type of wings give more roll stability
longitudinal
when plane is rolled, weight pulls it back to centre when the plane has a low CoG
dihedral, sweepback
directional stability
- around _____ axis
- how does the amount of fuselage behind CoG affect yaw stability
- how does sweepback wings affect yaw stability
- vertical
- more SA behind CoG = when plane yaws right, the air pushes on the large area behind the CoG and pushes it left
- yaw right, the left wing has more airflow = more drag = yaws back left
explain aileron drag
down-going aileron has more drag, so the nose will yaw in that direction so need rudder to keep coordinated turn
what two types of ailerons reduce adverse yaw from aileron drag and define each
frise ailerons - hinge offset so that the up-aileron creates an equal amount of drag to the down-aileron
differential ailerons - the up-aileron goes up MORE than the down aileron, so it creates more drag
control surfaces: dynamic balance vs mass balance vs static balance
dynamic balance: make controls easier to move (elevator down, small section of HS goes up)
mass balance: counteract flutter
static balance: entire control surface has a neutral CoG
servo tabs:
pilot moves servo down = elevator ____= pitch nose _____
pilot moves servo up = elevator ____= pitch nose _____
servo down = elevator up = nose up
servo up = elevator down = nose down
what are anti-servo tabs
- on what types of planes
- anti-servo tab up = stabilitators ____ = pitch nose ____
planes with stabilitators
anti-servo up = stabilitators up = nose up
a planes critical AoA is determined by
the design of the airfoil
in a strong headwind, you can _______ your speed from your best glide speed to improve your gliding range.
strong tailwind?
strong headwind = increase your speed by 5 KT
strong tailwind = decrease your speed by 5 KT
how does a stall pressure-sensor work? what about a vane sensor?
pressure sensor: senses pressure difference between top and bottom of wing. at high AoA = big pressure difference = warning
another pressure sensor is built at bottom of pitot tube so that air can only enter at high AoA
vane sensor: fan that rotates so that it stays on same plane as relative wind
why is CoG purposely ahead of CoP
when the wing stalls, the weight of the plane being ahead of the CoP will pitch the nose down = reduce AoA = speed up
why is thrust purposely below drag
if the engine quits (no thrust), the nose pitches down = reduce AoA and speed up
as plane speed DECREASES:
- AoA ______
- CoP moves _____
- horizontal stabilizer uses _____ downward force to maintain pitch
increases
forward
less **because CoP closer to CoG, tail doesn’t need to do as much work
as plane speed INCREASES:
- AoA ______
- CoP moves _____
- horizontal stabilizer uses _____ downward force to maintain pitch
decreases
backwards
more
t/f: mach buffet is the speed of airflow over the plane
false it’s the speed of airflow over the WING
airflow over wings can be faster than plane itself when:
- flying _____
- _____ AoA
this can form ______
what conditions increase AoA thus speed of airflow
- altitude
- weight
- loading
fast speed
high AoA
shockwaves
high altitude - need more lift so fly higher AoA
heavy weight - need more lift
more G (turns, turbulence)
