AERODYNAMICS ONE Flashcards
1
Q
Why do we have ISA?
A
Allows for accurate comparisons of a/c performance due to pressure, temp and density variations.
2
Q
ISA Figures? (Incl tropopause)
A
- MSL Temp: 15deg C
- MSL Pressure: 1013.25hpa
- MSL Density: 1.225kg/m3
- Temp Lapse rate: 1.98deg C/1000ft
- Pressure lapse rate: 1hPa/30ft (blw 10,000ft)
- Tropopause: 36,090ft ave
- Tropopause temp: -56.5 deg C
3
Q
Effect of altitude on density?
A
In the atmosphere, the rapid drop in px as altitude increases has the dominant effect on density (in comparison to increase in px due to temp decrease).
Therefore, density reduces with increasing alt.
4
Q
Airspeeds?
A
IAS: Indicated (ASI reading)
CAS: Calibrated (IAS corrected for px & instrument errors)
EAS: Equivalent (CAS corrected for compressibility of air)
TAS: True (EAS corrected for density)
G/S: Ground speed, TAS corrected for HWC/TWC.
5
Q
Why is TAS & EAS important?
A
TAS: sig bc it gives a measure of the speed of a body relative to the undisturbed air.
EAS: sig bc the aerodynamic forces acting on the a/c are directly proportional to the dynamic px (and thus EAS)
6
Q
Describe Bernoulli’s Theorem?
A
In an ideal fluid with a steady streamline flow, the sum of the energies present remains constant.
Potential energy & heat energy are insig, therefore;
Px energy + Kinetic energy = constant.
Theorem can be used to describe changes in velocity & px of air as it flows over an aerofoil resulting in lift.
7
Q
Describe the px distribution over the aerofoil using Bernoulli’s theorem?
Diagram?
A
Bernoulli’s: As speed of flow (KE) increases, static px decreases.
Airflow is accelerated over upper SFC of the aerofoil, as it has to travel further in the same amount of time to reach the trailing edge.
Increase in velocity = decrease in px. Results in px differential b/t upper & lower SFC (low above, high below), results in lift.
8
Q
Define free stream flow/relative airflow
A
Air in a region where px, temp and relative velocity are unaffected by the passage of the a/c through it.
9
Q
Define total reaction
A
The resultant of all the aerodynamic forces acting on the wing or the aerofoil section
10
Q
Define Lift
A
The component of TR which is perpendicular to the RAF/flight path
11
Q
Define Total drag
A
The sum of all components of the aerodynamic forces, which act parallel and opposite to the direction of flight
12
Q
Define Centre of Pressure
A
The point, usually on the chord line through which the TR is considered to act
(Lift & Drag vectors act through CoP)
13
Q
Define chord line
A
A straight line joining the centers of curvature of LE & TEs of an aerofoil
14
Q
Define Chord
A
Dist b/t LE & TEs, measured along the chord line
15
Q
Define angle of attack
A
The angle b/t the chord line and the flight path (or RAF)
16
Q
Define camber line
A
Line joining LE & TEs of an aerofoil, equidistant from upper & lower SFCs
17
Q
Angle of incidence?
A
The angle at which an aerofoil is attached to the fuselage. Angle b/t the mean chord line and the longitudinal fuselage datum
18
Q
Washout?
A
The decrease of Angle of incidence b/t wing root and wingtip
19
Q
Thickness/chord ratio?
A
The maximum thickness or depth of a wing section expressed as a percentage of the chord length
20
Q
Wing area?
A
The area of a wing projected on a plane perpendicular to the normal axis
21
Q
Wing loading?
A
The weight per unit of area of the wing = weight/wing area
22
Q
Streamline?
A
The path traced by a particle in a steady fluid flow
23
Q
Draw an aerofoil diagram;
- LE & TE
- LE radius
- Chord line
- Mean Camber line
- Max camber location
- Location of max thickness
A
24
Q
Draw a diagram of an aerofoil with;
- AoA
- Chordline
- RAF
- CoP
- Lift/Drag/TR
A
25
Lift equation? (Drag?)
What has the largest effect of Lift/drag?
CL: Coefficient of lift
p: Air density
V2: Free stream velocity (TAS)
S: WIng area
(Drag is same, but Cd)
Velocity, as it is squared
26
Factors affecting lift? (8)
- Free stream velocity
- Air density
- Wing area
- Wing shape in section & planform
- AoA
- Condition of SFC (esp LE as this affects the sep pt)
- Viscosity of air
- Speed of sound
27
Factors affecting coefficient of lift/drag (5)
- AoA
- Shape of wing section & planform
- Condition of wing SFC
- Reynolds #
- Speed of sound
28
Axes of rotation through CoG?
- Vertical (normal) axis through CoG: Yaw (nose L/R)
- Lateral axis wingtip-wingtip: Pitch (nose up/down)
- Longitudinal axis nose to tail: Roll
29
Define aspect ratio?
The ratio of span/chord OR span2/wing area.
Affects the degree to which induced downwash influences the wings characteristics.
High AR - gliders: less affect
Low AR - Fighter: more effect (reduces wings 'effective' AoA)
30
Describe how T6 ailerons work
Differential ailerons.
Up going aileron deflects at a larger angle compared to down-going aileron.
This reduces the differences in drag & helps eliminate adverse yaw.
(e.g. 20deg up - 11deg down)
31
Define the boundary layer?
- The layer of air extending from SFC to the point where no dragging effect is discernible. (wing drags air particles with it)
- The nature of the boundary layer is a controlling factor in drag, maximum lift & stall characteristics of the wing.
- The region of flow in which the speed is less than 99% of the RAF. And usually exists in two forms; laminar & turbulent.
32
Transition point?
Point on the aerofoil at which laminar flow changes to turbulent flow.
33
What is adverse px gradient?
Over the wing SFC, the px reaches a minimum at the point of maximum thickness (has to move fastest at this point). Px increases from here towards the TE.
Px always flows high to low, due to this the px gradient actually opposes the airflow over the wing = Adverse px gradient
34
How does adverse px gradient affect the separation pt?
APG opposes the flow & therefore decreases kinetic energy of the boundary layer until it reaches zero velocity (relative to the wing). Detachment of the airflow at a particular point due to this is known as the separation pt.
35
What occurs beyond the separation pt?
Separation of the airflow from the aerofoil & resultant Turbulent wake
36
What is the stagnation pt?
The point on the wing where the velocity of the air particles is said to be zero. (Creates an area of relatively higher px on LE)
This will lie somewhere on the LE where the flow divides to go over upper & lower SFCs.
Will move with changes in AoA (down as AoA increases & vice versa).
37
Effect of zero camber on lift & CoP movement?
Where is the separation point?
A symmetrical aerofoil produces no lift at zero AoA because it has no px differential above & below.
With a symmetrical section there is virtually no CoP movement at subsonic speeds.
At higher AoA the sep pt moves down, effectively creating camber.
38
Effect of positive camber on lift & CoP movement?
Positively cambered aerofoil will produce lift at zero AoA b/c the airflow attains higher velocity over the upper SFC creating px differential & lift.
With a cambered aerofoil the CoP movement over the normal working range of angles of attack is b/t 20-30% of the chord aft of the leading edge.
39
How does a higher T/C ratio affect movement of the CoP?
There will be greater movement of the CoP over the working ranges of AoA, by effectively creating camber as upper flow has to go further than lower flow.
40
Caveat wrt Bernoulli's theorem?
Assumes fluid is ideal & only applies to an incompressible fluid with no viscosity
We can assume air is ideal below 0.4M (subsonic)
41
What is adverse yaw?
Undesirable yaw that causes the nose of the a/c to yaw out of the turn due to the drag created by the up-going wing.
42
Four methods of reducing adverse yaw?
- Differential ailerons
- Frieze Ailerons
- Coupling of ctrls (E.g. yaw dampner - rudder auto-applied in direction of turn)
- Spoilers (deployed on downgoing wing to increase drag)
43
Why does TAS increase with altitude?
Density decreases as alt increases, (less air molecules)
Therefore a higher speed is required to obtain the same dynamic pressure in comparison to lower alts
44
Max angle climb? (OCS)
Graph?
A/C gains most alt in shortest dist.
Flown at the speed which gives the max excess of thrust after opposing drag.
Piston: usually as slow as is safe above rotate.
45
Max rate climb?
Excess power/weight (is the fastest time to climb to a height)
46
How to decrease wing loading?
By decreasing the overall weight and by increasing wing area.
47
Define zero lift drag?
When an a/c is flying at zero lift angle of attack, the resultant of all the aerodynamic forces acts parallel and opposite to the direction of flight, as there is no lift.
Composed of;
- SFC friction drag
- Form drag
- Interference drag
48
SFC friction drag - 3 causes?
Caused by: SFC area of the a/c, coefficient of the viscosity of the air, rate of change of velocity across the airflow (laminar = slower, turbulent = faster).
All proportional (i.e. increase in above = increase in SFD)
49
Form drag
Drag caused by separation of the boundary layer from a SFC and the wake created by the separation.
Dependent on the shape of the object
50
Interference drag
Results due to flow interference b/t the boundary layers of parts of the a/c that join together. (e.g. wing & fuselage)
51
Lift dependent drag?
In producing lift, the a/c will produce additional drag known as LDD.
Composed of induced drag & increments of ZLD (only noticeable at high AoA)
52
Induced drag?
Extra drag caused by increasing AoA to maintain original climb AoA, after downwash caused by vortices reduced effective AoA.
53
**Draw a diagram of the drag curve
Label & describe: Vimd, Vmp, 1.32 Vimd
Vimd: Max L/D ratio (drag is min)
Vmp: Min pwr rqd for S&L flight (min product of drag/velocity) - best endurance speed.
1.32 Vimd: Best range speed (tangent to total drag curve)
54
Effect of alt on power required?
At constant wgt and EAS, drag does not change with changes in Altitude.
However Power rqd is a function of drag x TAS.
And TAS DOES change with altitude at a constant EAS.
Therefore: ^ in Alt, means ^ in PWR is rqd to fly S&L at constant EAS.
55
Power available?
Defined as the rate of doing work;
Power = thrust x velocity.
(If throttles are up, but you are stationary, you have no power output).
56
What does the minimum S&L speed require?
Requires high AoA to create appropriate amount of lift. Majority of engine power is used to overcome drag.
57
What two speeds does the minimum S&L power setting correspond to?
Lower airspeed: on the back of the drag curve
Higher airspeed: Above Vmp
58
Why is lower airspeed of the min S&L power setting undesireable?
Speed stability at the lower speed is poor, any small reduction of power will cause a decrease in airspeed due to the rapid rise in drag below that pt.
Large increases in pwr & therefore fuel will be needed to increase speed back to min S&L speed
59
Minimum power speed? (Vmp)
Caveat
The speed at which the smallest qty of drag is incurred for that weight, config & altitude.
Best endurance. (rqrs smallest power output & therefore fuel burn)
Speed stability also poor
60
Max S&L speed?
Point where PWR required is equal to the max power avlble from the engine
61
Min Drag speed?
Vimd
Speed which is tangential to the power rqd curve.
Best range speed.
Operating below this speed means the effect of rising induced drag offsets the TAS advantages.
62
Best rate of climb speed?
Determined by amount of excess POWER.
The point of greatest distance b/t pwr avlble & pwr required.
63
**Draw a graph of power rqd/available - Piston vs jet
Label the speeds
64
**Draw a diagram of the lift/drag curve, with effect of increasing weight
How does Vimd change?
Wgt ^ = LDD ^ (due increase in AoA)
65
What 4 factors is induced drag affected by?
- Planform (wing shape) - winglets reduce Induced drag.
- Aspect ratio (low AR = higher induced drag)
- Lift & weight (^W = ^ L -= ^ D)
- Speed: Decrease = increase in ID. (As AoA increase rqd to maintain CL)
66
Two ways to climb the a/c
- Use of thrust above that rqd to maintain level flight
- Zoom climb: gain in height by loss in airspeed
67
How does velocity of air within the boundary layer change?
It is greater at the SFC of the turbulent flow than the laminar, due to the effect of mixing with the faster moving air above the boundary layer. Indicates higher level of KE.
68
Draw a diagram depicting the boundary layer.
69
How does ASI determine a/c speed?
Measures the speed of the a/c by comparing total px (static plus dynamic) with static px.
70
Define dynamic px?
A volume of air moving at speed possesses KE, and therefore exerts px on any object in its path = dynamic px.
71
Aerodynamic force eqn?
Break it down?
AF = 1/2pv2S
(Force = pressure x area)
Dynamic px = 1/2pv2
Where p = density of airmass (kg/m3)
v = TAS in m/s
72
Equation of continuity?
Mass can neither be created nor destroyed, therefore airmass flow is constant.
Decrease in cross sectional area = increase in velocity of airmass (venturi)
73
How does a pitot tube work
Mass of air enters tube, must decelerate to zero, force therefore exerted at end of tube.
Px is a measure of force per unit area (Work = Fd)
Moveable diaphragm in tube detects work done & converts it to airspeed
74
In what direction is lift said to act?
Perpendicular to the SFC of the aerofoil
(arrows away = -ive px,
arrows towards = +ive px)
75
How does increase in AoA affect CL & movement of CoP?
CL increases
CoP shifts forward
76
What 3 things affect position of CoP?
1. Changes in AoA
2. Camber variation
3. Change to symmetrical section (T/C ratio)
77
Laminar sub-layer
A very thin layer that exists immediately adjacent to the SFC within the turbulent boundary layer
78
How does an increase in AoA affect the separation point?
Sep pt moves forward, detached flow causes large reductions in lift
79
Where do the greatest positive pressures (lift producing vectors) occur?
At stagnation points when the flow is brought to rest (LE & TE)
80
What occurs at the stall angle?
The low px area on top of the wing suddenly reduces, any remaining lift is due to px increase on lower SFC (due amount of aerofoil exposed to the flow)
81
What 3 factors incrementally increase ZLD?
- Effect of lift (transition pt/adverse px gradient)
- Form drag (increase AoA = increase in frontal area)
- Interference drag
82
Aircraft forces act through?
Location of CoP vs. CoG ?
Force couples cause what moments?
Resultant?
Lift & Drag act through CoP
Weight & Thrust though CoG.
Most a/c, CoP is behind the CoG
Lift & Weight couple causes nose Down moment
Thrust & drag couple causes nose up moment
These do NOT neutralize each other - tailplane rqd
83
What does the amount of force up/down of the tailplane rely on?
Speed
Weight
84
How are tailplane forces impacted by prop wash?
Tailplane is in the wake of the prop, causes the RAF over the tailplane to be sig higher speed.
Reduce PWR = reduce tailplane force produced.
Trim must be adjusted.
85
What is trim drag?
- Tailplane produces a downward force
- This combines with the wgt force to induce an apparent increase in the wgt of the a/c.
- ^ Wgt = ^ lift rqd
- ^ lift = ^ AoA
= Increase in drag (trim drag)
86
Effect of weight on power required?
- Decrease in weight = decrease in amount of lift rqd (otherwise a/c will climb)
- Decrease of AoA = reduction of LDD
- Drag reduction means power reduction also rqd to rebalance drag/thrust couple.
Overall: Decrease wgt = Decrease in power.
87
Describe the power avlble graph for a turboprop
Thrust is constant straight line for sig portion of speed range, however at the point where prop tips reach very high speed, the efficiency of the prop causes thrust to reduce rapidly.
88
Describe the forces acting on the a/c in a steady climb?
If a/c is tilted up, but not accelerating, the force vectors are still balanced.
LIFT ACTS 90DEG to flt path
WGT STILL ACTS STRAIGHT DOWN.
Therefore:
- Lift balances portion of wgt vector acting on the same line (perpendicular).
- Thrust must balance both the rearwards component of weight & the aerodynamic drag component.
89
What is rqd to maintain a clb at a given EAS?
More power has to be used than in level flight to;
- Overcome drag
- Lift weight at vertical speed (ROC)
- Accelerate a/c slowly as TAS increases with alt.
90
What is RoC determined by?
What is angle of climb determined by?
The amount of excess POWER (thrust - drag)
The amount of thrust left after opposing drag.
91
What is the reason for the difference b/t curves for jet vs. piston on power avlble/power rqd graphs?
Thrust of jet engine remains virtually constant at a given alt, regardless of speed = straight line.
Piston engine suffers loss of THP at both ends of speed range due reduced prop efficiency
92
How does an increase in altitude effect the speed for best ROC?
Service ceiling?
Speed for best ROC reduces with alt.
The altitude where the power avlble curve only just touches the power required curve gives the point where a sustained ROC is no longer possible = service ceiling.
93
Describe the force vectors in a steady non-accelerating glide descent
How do we maintain a given speed in the glide?
T=D & L=W
Since there is nil thrust force, then the nose attitude must be adjusted
to ensure the component of the W force acting parallel with the flt path balances the drag.
94
How does weight affect range?
Variation in weight has nil impact on glide angle so long as speed is adjusted to fit.
(^ wgt = increase in speed & vice versa)
95
Speed to fly for minimum ROD? (Endurance)
Speed to fly for maximum distance? (range)
ROD is least when power rqd is least (Vmp) (MIN PWR)
For dist to be min, glide angle must be min (Vimd) (best L:D ratio) (MIN DRAG)
96
6 Factors affecting glide range?
- Power
- Weight
- Wind
- Airspeed
- Config
- Manoeuvre
97
**Effect of increase in alt on turn radius?
Turn radius also increases, turn rate decreases (with constant IAS)
Due to higher TAS at higher alt (for a constant EAS), momentum of a/c will be higher which results in greater turn radius/lesser turn rate.
98
**Max rate of turn?
60deg AoB = 2G
99
Factors affecting turn performance?
- Lift
- Drag
- Power
- Load factor
- TAS
100
Effects of banking on lift?
What must we do to prevent descent?
For a/c to turn, centripetal force is rqd to pull a/c towards centre of turn.
A/C banked (lift vector inclined) > AoA kept constant > Vertical component of lift becomes too small to balance wgt > a/c starts to descend.
Therefore the higher the AoB, the higher the AoA rqd to keep a/c level in the turn. (vertical component of lift is then large enough to maintain lvl flt, horizontal component is large enough to produce CF rqd to turn a/c)
101
Why does stall speed increase with increase in load factor (G)
Because to maintain altitude in a turn or maneuver, an aircraft needs to generate more lift, requiring a higher angle of attack, which in turn means the aircraft will stall at a higher airspeed
102
In what way does weight affect range with changes to HWC/TWC?
The higher TAS for a heavier weight allows less time for the wind to affect the a/c, therefore it is better to have a heavier a/c gliding for range to be in to wind.
103
How does power affect glide range?
^ power = descend at same speed but at shallower angle. Means we can go further
104
How does wind
affect glide range?
(range only, NOT endurance) - HWC will reduce total distance you are able to cover.
(endurance doesn't care about distance, just time A/B)
105
How does airspeed
affect glide range?
Any departure from Vimd/Vmp speeds will reduce performance.
106
How does config
affect glide range?
Any config that causes less lift/more drag will decrease range & any config that results in reduction of TR will increase RoD & therefore reduce RoD.
107
How does maneuvering
affect glide range?
Lift vector in turn means less against W and D, penalties for both range & endurance
108
Effect of turn on power?
Increase in lift required in turn,
subsequent increase in drag
More power rqd in turn to maintain constant airspeed
109
Formula for load factor?
How does it vary?
Numbers?
G = Lift/weight
Varies with AoB due to angular acceleration in the direction of the turn (^ AoB = ^ in G & ^ in lift)
AoB/Load:
0deg/1G
15deg/1.04G
30deg/1.15G
45deg/1.41G
60deg/2G
75deg/3.86G
80deg/5.76G
85deg/11.47G
90deg/infinity.
110
Drag Tree?
111
Factors affecting flight ctrl effectiveness?
- Size & shape of ctrl
- Deflection angle (variable depending on pilot input)
- EAS^2
- Moment arm (dist from CoG)
112
Min radius turns?
At what AoB do we theoretically achieve min radius?
How do we actually achieve min radius (tightest) turns?
Tightest turn possible (smallest space taken up)
90deg AoB
- Max product of CL & AoB
- Minimise wing loading (W/S)
- Maximum density (Sea lvl)
113
Maximum rate of turn?
Max # of degrees/sec (e.g. how fast we can turn 360deg)
Quickest turn vs. smallest radius.
114
How do we achieve max rate of turn generally?
Comparison to min radius?
3 components?
Generally, If we increase V and/or decrease radius, rate of turn will increase.
Max rate occurs at a higher speed than min radius
- Max product of CL, AoB and SPEED. (can't all be max at the same time)
- Minimise wing loading
- Maximum density (Sea lvl)
115
How does SFC area of the wing impact Min radius & max rate turns?
Increasing wing SFC for same wgt a/c will decrease wing loading - minimise radius turns & maximising rate turns.
116
Define Va?
Velocity Application
the speed above which full ctrl deflection will overstress the a/c. (without stall warning from the light buffet.
Below this speed you can apply full ctrl deflection & stall the a/c.
117
Nose wheel a/c?
Most common today,
two main units slightly aft of CoG & smaller nose wheel to balance remaining load.
118
Why are nose wheel a/c more stable than taildraggers?
Due to pstn on CoG in relation to the axis of the main wheels and the moment that is created
119
6 Advantages of tricycle undercarriage a/c?
- Positively stable during its ground roll
- Lookout ahead is good
- Good grd ctrl using NWS
- Nil tendency to nose over under hard braking
- Jet efflux is clear of the ground
- Tail brake-chutes easily deployed
120
What 2 factors can effect max rate/min radius turns?
- Thrust: can we achieve the speeds rqd?
- Flap: Produces more lift but also more drag but can assist with tightening turn radius (so long as within flap limiting speed/G limit)
121
What is Vne & Vd
Never exceed speed (max permissible speed to be flown)
Destruction speed (beyond which a/c will begin to self-destruct.
122
Rolling G limit?
G limit when rolling the a/c
Due to the fact that the wing structure has to provide the strength to absorb twisting moments caused by aileron deflection
123
What does the manoeuvre envelope display?
7 things you can derive?
(Vg/Vn diagram): A/C aerodynamic limits & structural limits.
Vb: basic stall spd
Va
G at any speed/height
Max EAS
Stall speed
Max G factor
Rolling G limits
124
8 factors affecting takeoff distance
- Wind
- SFC Condxn
- Slope
- Altitude
- Temp
- A/C weight
- Config
- Engine power
125
What are the 4 induced effects on T/O?
Prop/engine TQ
Slipstream
Gyroscopic precession (Taildraggers only)
Asymmetric blade effect
126
Describe How prop/engine TQ effect occurs?
With prop & eng turning in the same direction, a reaction is created in the opposite direction (Newtons law).
This tends to rotate the a/c body around the longitudinal axis & applies more apparent weight on one wheel than the other.
(LH wheel on T6)
= Yaw to the left for T6 (CW rotation)
127
Describe How slipstream effect occurs?
Prop rotation causes slipstream to have a corkscrew effect, causing it to strike a side of the aft fuselage & vertical fin (LH side for T6 = LH yaw)
128
Describe How gyroscopic precession effect on T/O occurs?
Taildraggers only
Prop acts as gyro, when tail is raised, this has effect of applying force to top of prop disc.
precession results in yaw away from direction of rotation (LH for CW rotation)
129
Describe How asymmetric blade effect occurs?
- A/C in tail down attitude (increase in AoA)
- Downgoing blade has higher AoA to RAF & therefore "bites" more air in comparison to up going blade.
- Downgoing therefore produces more thrust
- Thrustline shifts right (for CW rotation)
- A/C yaws left
130
Aquaplaning?
Formula?
Tyres are lifted hydrodynamically off the SFC.
V(ap) = 9(square root of P)
p = tyre px in psi
v = speed in kts
131
What increases our chances of aquaplaning?
- Greater water depth
- Less tyre tread
- Smoother SFC
- lower tyre px
132
Disadvantages of tricycle undercarriage?
- Longer carriage rqd for prop clearance
- Nose wheel must be stronger/cushioned/ retractable = weight
- less A/D braking
- Often rqrs tail bumper
133
Taildragger vs tricycle ground stability?
TDs are unstable due CG aft of main wheels.
When a/c isn't aligned w direction of travel, the couple formed by CG and wheel drag tend to increase misalignment
NW a/c are stable (increases w movement of CG fwd) couple formed by CG & wheel drag aligns a/c to direction of travel.
134
Define Stall
An a/c stalls when the sep point in the boundary layer moves forward and the flow over the upper SFC of the wing breaks down with associated loss of lift.
135
Why does the separation point move forward as AoA increases?
^ in AoA results in the difference b/t the point of minimum px (usually thickest part), and the stagnation px at the TE increases
(Adv px gradient increases, causing sep pt to move fwd)
136
Critical angle?
The AOA at which the CL of an aerofoil is at maximum.
Beyond this = stall (due sep of airflow over wing)
137
Basic stall speed?
The airspeed below which a clean a/c of maximum weight, with the throttles closed, can no longer maintain S&L flight due to exceedance of the critical angle
138
**Incipient stall symptoms? (4)
- Low & decreasing airspeed
- High nose attitude
- Reduced ctrl response & feel
- Light buffet (caused by turbulent separated flow buffeting tailplane)
139
Stick shaker in T6?
felt 5kts prior to stall
Buffet 3kts prior to stall
140
**Fully developed stall symptoms (4)
- Heavy buffet (caused by airflow over wing collapsing & flowing back over tailplane)
- Nose down pitch (caused by CoP moving rapidly aft & abrupt loss of lift at the stall)
- (Often high) Rate of descent developing
- Poss wing drop (caused by one wind stalling before the other).
141
Effect of weight on stall speed?
If weight is increased, lift rqd to maintain S&L also increases.
If AoA already at crit angle, the additional lift rqd can only be produced by flying faster
^W = ^Vs
142
4 ways to reduce stall speed?
- Deploy flaps
- Increase power
- Decrease weight
- Slipstream
143
How does deploying flaps reduce stall speed?
CL max is increased with use of flaps/slats due increase in wing area.
Stall speed is lowered.
144
How does increasing power reduce stall speed?
If power is applied at the stall, the nose high attitude gives a vertical component of thrust, which assists in supporting the weight, hence less lift is rqd from the wings, reducing Vs
145
How does slipstream reduce stall speed?
Local increase in dynamic px from the slipstream will give more lift in comparison to power off case.
Lower airspeed is therefore able to support a/c wgt.
Decreasing Vs
146
How do flaps assist with lift?
Vary the camber of a wing section. Greater the camber, the greater the lift for a given AoA
147
How do slats/slots assist with lift?
Slat prolongs lift curve by delaying stall until a higher AoA, does this by;
- Flattening marked peak at the low px envelope, therefore reducing adverse px gradient & therefore delays sep pt.
Slot:
- Air that passes through slot is accelerated by venturi effect which re-energises the boundary layer (assisting against adv px grad)
148
What are slats/slots?
Small auxiliary aerofoil of highly cambered section, attached to part of LE
(slot b/t slat & wing)
149
What is boundary layer control?
Three methods?
Control of boundary layer so that it remains attached to aerofoil SFC for as long as poss.
Achieved by adding KE to lower layers;
- Suckling
- BLowing
- Vortex generators
150
Flt Ctrl SFCs: Rate controls?
Ailerons
When aileron is applied, the rolling moment is opposed by aerodynamic damping in roll.
Due to this, for a given roll deflection, a given 'rate' of roll results.
151
Flt Ctrl SFCs: displacement controls?
Elevators & rudders
When rudder or elevator is applied, the yaw or pitch change is opposed by both aerodynamic damping & the a/c's inherent stability
152
Damping in roll effect?
When a/c rolls, down going wing AoA increases, up going decreases.
Lift is therefore increased on down going & decreased on up going.
New rolling moment produced opposes the initial disturbance & the direction of the initial roll (stable)
153
How does altitude affect damping in roll effect?
^ alt = increase in roll rate, due to decrease in roll damping (caused by increase in TAS with alt)
