Principles of flight Flashcards
Kts to Ms-1 conversion ?
x 0.5144
Kg to Lbs
x 2.2
G (Acceleration due to gravity) value ?
9.81 M/s2
Density units
Kg M3
Acceleration units
M/S2
Pressure Equation
Pressure = Force / Area
Pressure units (in PoF)
N/M2
Work done equation
Work done = Force x distance
Power is defined as ?
Rate of energy use
P= Force x Speed
Newtons 1st law
A body at rest or moving at a constant rate will remain so until acted upon by an external force.
Newtons 2nd law
The acceleration experienced by an object id proportional to the force applied and inversely proportional to the mass. (F=MA)
Newtons 3rd law
For every action there is an equal and opposite reaction
What is Air density affected by ? (Decrease)
Humidity increase
Temperature increase
Pressure decrease
Static pressure relationship with (pressure) altitude ?
Static pressure reduces as altitude increases
Density relationship with (density) altitude ?
Density increases as altitude decreases
What is static pressure ?
The pressure felt by an object due to the mass of the column of air the object is in.
Kinetic energy formulae
1/2 M V2
1/2 (rHo) V2
Dynamic pressure equation
1/2 (rHo) V2 (Where V is the TAS of the airflow)
IAS is a measure of what ?
Dynamic pressure
How is dynamic pressure measured?
Pitot-static system
(Takes static pressure away from total pressure)
Bernoulli’s theorem .. ?
In a flow of ideal fluid, the sum of pressure and kinetic energy remains constant
Pressure difference around an aero foil (Static pressures, so opposite to dynamic)
Relatively Low pressure above
Intense low pressure at the front on the surface above
Relatively High pressure below
Angle of attack is ? (2D flow)
Angle between the aero foils chord line and the direction of the airflow
A positively cambered aerofoil is when …
The mean camber line is above the chord line
Negatively cambered aerofoil is when …
The mean camber line is below the chord line
How to get the thickness ratio
Max thickness / Chord length
Stagnation point is ?
Point where no air moves at the front of the leading edge
Drag is …
The component of the total reaction which is parallel to the free stream flow, acting in the same direction
Lift is… ?
The component acting perpendicular to the free stream flow
The Centre or pressure is ? (CP)
The average point from where the aerodynamic forces act
What happens to CP on a cambered aerofoil when you increase AoA
Moves forward
What happens to CP on a symmetrical aerofoil when you increase AoA
The CP does not move
What happens to Flow velocity over the upper surface when AoA is increased
Increases, produces a greater pressure drop
Three main factors affecting the lift coefficient ?
AoA
Thickness
Camber
What is alpha Crit ? (ClMAX)
The AoA at which the wing stalls
Lift Co-efficient formula
L = 1/2 x p (rho) x V2 x S x Cl
IAS2 can be substituted in for (1/2 x p x V2) as IAS is already adjusted for density
Skin friction drag is ?
The result of shearing forces (moving) between layers of air within the boundary layer. Small and occurs all over A/C. (Below 99% of free stream)
Laminar boundary layer summary ?
Layers of air flow parallel with each other.
A few MM thick
Low energy- Separates more easily
Has low drag
Requires a smooth polished surface
Turbulent layer summary ?
Motion is random
A few Cm thick
High energy- delays separation
High drag
Likely on rough, unpolished aircraft
How can skin friction drag be minimised ?
Having a clean smooth surface. Repainting the A/C can help reduce it, but adds weight.
Transition point ?
Where boundary layer changes from laminar to turbulent
Separation point ?
Where boundary layer separates from the A/C surface, creating wake.
(Moves forward as AoA increases)
Taper ratio
Ratio of Wing tip chord / Root chord
Wing planform ?
The outline shape of the wings seem from above
Aspect ratio
Ratio of Wingspan / Average wing chord
Angle of incidence ?
Angle between chord line and longitudinal axis
Washout
The wing is twisted along its span to reduce angle of incidence from root to tip. Reduces chance of tip stall on swept wings.
Where is the most lift produced ?
Wing root
Sweep back is ?
Angle between lateral axis and where the wings are set back too
Longitudinal axis ?
Nose to tail
Rolls, controlled by ailerons on the wing
Lateral axis
Across the wings
Pitching, controlled by elevator on rear stabiliser
Normal axis
Top to bottom
Yaws, controlled by rudder
What is induced drag ?
The result of the lift vector being tipped backwards because the effective AoA is greater than the AoA
Tip vortices are strongest when the A/C is
Slow and heavy
How do tip vortices rotate ?
Towards the A/C
What happens to vortices as AoA increases
Difference in pressure between upper and lower surfaces increases, thus increasing the strength and size of the vortices
Flow direction below and above the wing (Spanwise flow)
Under - Towards the wing tip
Upper - Towards the fuselage
How is wake turbulence somewhat reduced ?
Lowering a trailing edge flap
What is effective air flow ?
Is the effect of the wing modifying the direction of air flow. Creating a flow at an angle to the relative airflow.
What is ⍶ i
Induced AoA
What is ⍶ e
Effective AoA
How is form drag reduced ?
Streamlining
How is skin frication drag reduced ?
Ensuring a smooth polished surface
What is fitted to some A/C with no natural buffet to notify of a potential stall
Stick shaker
Tapered planform P + N
Decreases vortex strength
Good efficiency / used on high perf light A/C
Air will miss the horizontal stabiliser so no natural buffet.
Elliptical wing P + N
Chord length is mathematically varied to counter and increase is vortex strength.
Most efficient wing planform.
Whole wing will stall at once, causing a sudden and more severe stall
Swept wing P + N
Good at high speed
No natural buffet
Stalls first at wing tip, so high chance of a wing drop stall
Low efficiency at low speed
How is form drag reduced ?
Streamlining
Separation of Total drag
Induced drag + parasite drag
PD-
skin friction
Interference
Form
Induced drag is ?
A bi product of lift
Factors affecting induced drag ?
(Anything that makes the wing work hard)
Low speed
Banking
Pitching up
Increased load factor
A/C weight
Drag Equation
Drag = 1/2 x p x V2 x S x Cd
Induced drag is proportional to
ID ∝ 1/V2
Cdi & Cdp ?
Co-efficient of induced drag
Co-efficient of parasite drag
How to reduce induced drag ?
Tip modification -
Spilt
Blended
Tip tank
Wing modifications -
Wing fence
Vortilon
Strake
Notched leading edge
What do Tip and wing modifications do ?
Improve low speed characteristics
What does a vortex generator do ?
Draws in air from free stream flow and re-energises the boundary layer delaying separation, and delays the low speed stall
( It is not used for reducing induced drag)
Parasite drag is proportional to ?
Pd ∝ V2
How is parasite drag effected
Same as interference, skin friction and form drag
Total drag is ?
Induced and parasite drag combined
What happens if an A/C is speed stable after a speed disturbance ?
The A/C will tend to return to it’s original speed
Drag Vs mass
As the A/C gets heavier induced drag will increase
Vmd is ?
Minimum speed drag
Speed stable regions impact on drag in a gust ?
Drag increases
Speed unstable region impact on drag after a gust ?
Drag reduces
What has no effect on total drag curve ?
Dynamic pressure
A general purpose aerofoil is most efficient at ?
4° alpha
On Drag/TAS plot curve bottom inditcates ?
VMD
On Drag/IAS plot, bottom of the curve indicates what ?
VIMD
An increase in mass causes the drag curve to move ?
Up and right
On a Drag/TAS graph, how does the curve shift with altitude ?
The curve shifts to the right with increasing altitude.
Lift drag ratio ?
L : D
On a Drag/IAS graph how does the curve move with altitude?
All altitudes are the same with IAS, so it doesn’t move. (Drag and IAS are both based on dynamic pressure)
Only ignoring compressibility effects !!
What happens to drag curve with extension of flaps ?
Curve goes up and left
Vmd gets slower
Would also happen with landing gear and spoilers
Dirty and clean descriptors (wing)
Dirty- with flaps
Clean- without flaps
How does stalling occur ?
Airflow on the upper surface of the wing stops following and separates. This occurs when the A/C exceeds its critical AoA
Adverse pressure gradient is ?
A pressure gradient trying to make flow reverse direction (under the wings to upper surface)
As AoA increases it gets stronger.
Separation point moves forward
Stalling consequences
Reduced lift
Increased drag
CP moves aft (fwd on swept)
Nose pitches down (up on swept)
Struggle to maintain control (sluggish)
I commanded roll
Vs is ?
Current stall speed
Vs1g is ?
Stall speed when flying at 1g
Vs1 is ?
Stall speed in the given configuration
Vs0 is ?
Stall reference speed, used by low aspect ratio A/C
Load factor Vs stall relationship
n ∝ V2
High aspect ratio Vs stalling ?
If ⍶ crit is exceeded Cl drops fast, high rate of descent.
High AR gives better lift and lower alpha crit
Low AR Vs Stalling
Exceeding ⍶ crit only gives of small Cl reduction so you may not notice, risking a deep stall
Vsr is ?
A ‘pretend’ stall speed set by the manufacturer that warning and recovery systems are set too
Deep stall is when ?
The horizontal stabiliser is stalled, making it much harder to recover.
T-tail and swept wing A/C are more prone to deep stall
Deep stall protection ?
Stick pusher
Ailerons Vs stalling
Using ailerons close to the stall could cause a wing drop stall. Which causes the plane to roll opposite to the attempted roll direction
Landing gear Vs stall
Lowering landing gear increases stall speed
Flaps Vs stalling
Leading and trailing edge devices reduces stall speeds
Thrust Vs stalling
The power on stall speed, is less then the power off stall speed
(Thrust reduces stall speed)
Altitude Vs stall speed
Above 0.4 Mach TAS stall speed increases
Stall speed Vs weight formula
Vs ∝ √m (can be mass or weight)
Stalling in a turn, effects on load factor and stalling speed ?
Load factor increases and thus stalling sped increases
Alpha crit is ?
The highest achievable AoA before the wing stalls
The aeroplane develops strong buffeting, this means it has ?
Stalled
Direction of pitching moment after swept wing stall ?
Pitch up
Direction of pitching moment after straight wing stall ?
Pitch down
Wing drop stall is ?
When the wing tip stalls first, so drops
Why does a swept wing pitch up after stall ?
Because the CP moves forwards and inwards, closer to the CG creating a shorter arm and reducing pitch down moment.
Purpose of T-Tail
To keep stabiliser/elevator out of engine wash and make it more efficient
Natural stall warnings ?
Pre-stall buffeting
Sluggish controls
Hard to keep nose up
Alt drop
Artificial stall warnings ?
Buzzer
Synthetic voice
Stick shaker
Common stall prevention ?
Stick pusher-
Automatically pushes the stick forward to lower the nose at a certain AoA
Flapper switch is for ?
Role + Location
AoA sensing (Light AC)
A spring loaded switch located in the leading edge, Ince AoA is high enough, switch will become below the stagnation point and this will activate a buzzer.
Null seeking probe is for ?
Role + location
AoA sensing (Large AC)
Cone shaped and stuck on outside of the fuselage. 2 pressure ports sense different pressures which trigger a motor to rotate the cone until pressure in each port is equal, probe now point into RAF, Air data computer (ADC) then converts this to AoA
AoA vane is for ?
AOA sensing
A mini aerofoil attached to a rotating plate. It rotates to align itself with the RAF, the rotation is then converted to an electrical signal and is then converted to AoA by the ADC
When does the stall Warner activate ?
5% of 5kts before stall speed (whichever is greater)
First indication recovery ?
Lower nose with elevator
Add power to accelerate
Avoid aileron use
Once stalled process -> Unstalled ?
Lower nose using elevator
Reduce power to idle
Once unstalled
Roll wings level if needed
Smoothly Re-apply power and level off
Spin phases ?
Incipient spin
Fully developed spin
Recovery
Incipient spin stage is ?
The first few rotations before the aerodynamic forces and fully balanced
Fully developed spin is when ?
The aerodynamic forces are fully balanced
(Lift, Yaw, Drag)
Spin recovery steps ?
Neutral control stick-
Identify spin direction using turn indicator needle
-Apply full opposite rudder
-Push nose down into a dive once the spin has stopped
-Roll wings level and gently pull out the dive
What happens if you pull too hard when coming out of a dive after stalling ?
Load will increase and you will Re-stall (an accelerated stall)
At low speed a … camber aerofoil is better ?
Thick high
At low speed … camber aerofoil is better ?
Thin low
2 types of lift augmentation devices are ?
Leading edge devices
Trailing edge devices
TE Devices are ?
Plain flap
Spilt flap
Slotted flap
Fowler flap
What is a plain flap ?
A hinged TE that increases wing camber, but does not effect surface area.
Cl max increases
⍶ grit reduces
What eventually happens to Cl on an A/C in straight and level flight that extends plain flaps while at a constant speed ? (SF)
Cl remains the same
(as no other vectors changed and using the principal of the formula is has to remain equal)
Any flap impact on Cl max and ⍶ grit graph ?
Curve moves up and Left (with the exception of split which only minorly moves left)
Flap types going from smallest Cl to largest on Cl, ⍶ crit graph ?
Clean
plain
split
slotted
fowler
What is the purpose of flaps ?
To allow/generate the same lift production but at lower speeds. (not for increasing lift)
Initial flap effect ?
-Increases downwash angle
-creates a negative ⍶ on the stabiliser helping produce more downwash
-this results in more downforce from stabiliser creating a pitch up moment
- A/C tries to balloon above its intended flight path and the pilot must counter that action by pushing the stick forwards
Split flaps ?
The lower surface of the aerofoil is hinged.
The upper surface camber is unchanged so ⍶ grit reduction is smaller
More drag and wake turbulence is created
Slotted flap ?
Leaves behind a gap after being extended, which high energy air from the lower surface flows through to the upper surface.
The air then Re-energises the boundary Layer to resist against the APG and delaying the stall.
Fowler flap ?
Is stored inside initially and extends out and aft and down increasing wing surface area.
Could be slotted
Leading edge devices are ?
Slats
Variable leading edge
Kruger flap
Slat ?
The leading edge moves forward leaving a slot
The upper boundary layer is re-energised which delays the stall. No change in camber.
LE devices impact on graph curves and order ?
Causes the curves to move up
(Low –> High)
Clean
Slats
Kruger flaps
Variable camber flaps
Variable leading edge camber flaps ?
The leading edge is drooped to increase the leading edge radius and camber
Kruger flap ?
Hinged flap on LE
similar purpose to camber device but does not increase ⍶ crit or Cl as much. Kruger flaps stall before LE camber flaps
Is mostly used near the wing root on swept A/C so the Rott stalls first preventing wing drop stalling.
on a Flaps graph the steepness of the dotted line represents ?
The lift to drag ratio.
-The steeper the line the higher the L:D ratio
-Highest in a clean configuration
Flaps impact ?
Climb performance and glide distance get worse.
Which devices are deployed first and why ?
leading edge devices are deployed first and retracted last as they give the largest benefits for the least drag
Flap setting used on takeoff ?
A small flap setting is normally used because it allows for sufficient lift to be produced at a slower speed which allows for a shorter takeoff distance
Immediately after takeoff a crew member retracts the flaps by mistake what will happen ?
The A/C will sink and you could stall
impact of flaps stuck clean ?
This effects approaching and landing speeds
- Faster approach and landing speeds
- Longer landing distance
- Shallower descent angle
- increase change of tail strike
Impact of flaps stuck extended ?
-Increased fuel burn
-Worse climb performance (due to more drag)
-Lower ceiling
Same landing conditions as stuck clean
What does asymmetric fleas mean ?
Flaps are extended on one side but not another creating asymmetrical lift and drag therefore a roll and yaw moment.
Could cause an uncontrollable roll
On large A/C how is asymmetric flaps prevented ?
Wing tip brakes
How far off does ground effect occur ?
It may occur within 1 wingspan of the ground
it will occur within 1/2 a wingspan of the ground
Effects when leaving ground effect ? (T/O)
Smaller ⍶e
Less lift
Bigger ⍶I
More drag
Further from stalling
Effects when entering ground effects ? (LDG)
Bigger ⍶e
More lift
Smaller ⍶I
Less drag (up to 50%)
Closer to stalling
Ground effect impact on landing ?
It will happen when A/C is flaring this will cause the A/C to balloon.
The balloon on landing will be worse on really hot days due to thermals rising from hot tarmac.
Which type of A/C will experience the largest loss of lift ?
Low wing A/C on take off
(Wings are closer to the ground do more effected by ground effect, and you gain lift when landing and lose lift when taking off.
Elevator primary and secondary effects ?
Primary = Pitch
Secondary = Speed control
Aileron primary and secondary effects ?
Primary = Roll
secondary = Yaw
Rudder primary and secondary effects ?
Primary = Yaw
Secondary = Roll
Ruddervator
Elevon
Taileron
makeups ?
Ruddervator = Elevator + Rudder
Elevon = Elevator + Aileron
Taileron = Rudder + Aileron
Desired control characteristics ?
Not too heavy or light
Harmonised pitch and roll control
Forces to vary with IAS
Movements required not too small or big
Must be responsive
How is control force magnitude controlled ?
aerodynamic balances
7 types of aerodynamic balance ?
Inset valve
Horn balance
Internal balance
Balance tab
Anti-balance tab
Servo tab
Spring tab
What is control surface flutter ?
In turbulent air conditions the control surfaces can move back and forth.
How is control surface flutter controlled ?
It can be eliminated by moving the CG forwards this can be done by installing mass balances in the region forwards of the hinge
Conventional control surface ?
When there is a mechanical connection between the pilot control column and the control surfaces. The pilot provides 100% of the force required to move the controls
Partially powered control surface ?
When the pilot provides some of the force needed to move the control surfaces. the rest is powered bye hydraulics. the pilot still gets a natural feel for the controls
Fully powered control surface ?
The hydraulics provide all of the force needed to move the control surfaces. Mechanical connection is no longer needed, the pilot no longer has a natural feel for the controls
Why is no natural feel a bad things with regards to control surfaces ?
It makes it too easy to over stress the aircraft
Methods of creating artificial feel ?
Bob weight
Spring system
Fly by wire
Roll control
Uses a roll rate command and deflects the ailerons needed to achieve it
Hard protections definition ?
(examples)
Control protections that cannot be overridden by by pilot.
-G protection
-Pitch alt protection
-Roll alt protection
-Low speed protection
-High speed protection
Soft protections definition ?
(examples)
Control protections that can be overridden by the pilot
-Low speed stability
-High speed stability
Downgrades in control law cause ?
At least hard protections to be lost.
-Significant failure cause control law downgrades
FBW relationship with CG ?
FBW can be a lot more accurate when guessing how much control deflection needed when it knows the CG. Fortunately it can self determine this and does not use the pilot entered value.
A down aileron impacts ?
Increases camber
Increases lift
Increases AoA
An up aileron impacts ?
Decreased camber
Decreased lift
How is adverse aileron yaw prevented ?
Can be done by giving the dampening wing (Wing with up-going aileron) more drag
How do differential ailerons work ?
The more an aileron deflects the more drag it produces, differential ailerons are rigged so that the aileron on the down going wing (the wing with the up going aileron) deflects more.
How do frise ailerons work ?
The going up rise ailerons creates more drag as there is a component that protrudes below the wing.
What are roll spoilers ?
Spoilers used on large A/C to increase the drag on the down going wing.
They deflect up on the down going wing
They deflect down on the up going wing
What is used at high speed instead of high speed ailerons ?
Inboard ailerons or Roll spoilers
Alternative uses of roll spoilers ?
Prevent adverse aileron yaw
Slow down the a/c
To increase the descent rate
To lift dump after landing
Aerodynamic damping is ?
When an a/c manoeuvres it creates a change in airflow direction, the impact of this is to resist the manoeuvre.
Stronger Aerodynamic damping the Lowe the rate of pitch, yaw and roll
What reduces aerodynamic damping ?
Shorter wingspan
Faster TAS
High altitude
High temperature
When will a “Takeoff feel normal”
When trim counters the position of the CG
Eg - A full forward CG and a full nose up trim
- A full aft CG and a full nose down trim
In order to yaw right …?
Turn the rudder right using the left pedal
How does the rudder produce its secondary effect, roll ?
When the a/c is yawing to the right the left wing would be moving faster causing it to produce more lift, which would cause the a/c to roll to the right.
The pitch angle is between ?
Longitudinal axis and horizontal
Climb angle is between ?
Horizontal and Flight path/RAF
⍶ Is between ?
Chord line and Flight path/RAF
L in a climb = ?
L=W x cosɣ
Lift compared with weight in a climb ?
Lift is less than weight during a climb
Thrust formula in a climb ?
(+ Re-arranged for the angle)
T = D + Wsinɣ
or
Sinɣ= (T-D)/W - Useful to know
Excess thrust is ?
The difference in thrust and drag at a given weight determines the climb angle, this is known as excessive thrust
How is excess thrust viewed on a thrust drag graph ?
Its the gap between the a/c speed line and the thrust drag curve
What is Vx ?
The speed for the largest angle of climb
(bottom of thrust/drag curve)
What is a climb gradient ?
A climb gradient describes your vertical change as a percentage of your horizontal change.
Eg- A 5% climb gradient would mean for every 100m forward you move you climb 5m
Climb gradient formulas ?
Climb% = (Tan or sin) ɣ x 100
Climb% = (Vertical D/ Horizontal D) x 100
Climb% = (T-D)/W x 100
What are the two things forward speed is controlled by ?
Thrust
Pitch
What must a pilot do if a larger rate of climb is desired ?
Pitch up more, which causes speed to drop, therefore more thrust must be added to prevent speed drop.
If Thrust is not great enough speed will drop and a/c will decelerate towards a stall.
What is the L:D ratio ?
A measure of the a/c performance, high L:D ratio gives better performance
Drag formula ?
D = Weight / L:D ratio
Angle of descent formula ?
Sinɣ= D-T / W
What determines range ?
Descent angle ɣ only
What effects endurance ?
Rate of descent only
How is maximum range achieved ?
Minimum ɣ (closest to 0)
How is maximum Endurance achieved ?
Minimum Rate of descent (RoD)
Where is L/D Max on a curve ?
VMD
Impact of mass on L : D ratio and glide angle and range ?
Mass has no effects on L:D ratio, hence it has no effect on glide angle or glide range
As long as -
The a/c flies at VMD
There is no wind
Impacts of head and tail winds on glide range ?
Headwind decreases ground range
- Heavy a/c will travel further
Tailwind increases ground range
-Lighter a/c will glide further
What configuration does max L/D ratio occur in ?
It occurs in the clean configuration
Impacts of flaps, spoilers and gear on the L/D ratio ?
They all decrease it, and therefore they reduce glide range and increase glide angle (Bad)
How is rate of descent determined ?
Power deficit, Minimum power deficit is a speed of VMP
Max glide endurance happens at what speed ?
VMP
Still air glide range formula ? (No wind)
= a/c height x L/D ratio
Ground range formula ?
= Still air range x GS / TAS
(GS = TAS adjusted for wind)
Headwind = -
Tailwing = +
Radius formula ?
= V2 / g x tanᵠ
(V is in m/s)
Radius measured in meters (m)
Impact of mass on turn radius ?
Mass has no effect on turn radius
Why is turn radius relevant ?
To ensure turns are tight enough to avoid proximity to terrain/airspace etc
Rate of turn is ?
The change in direction in degrees per second. standard turn rates are:
Rate 1: 3º per second (360º in 2 mins)
Rate 2 6º per second
Rate of turn formula ?
= TAS/r x 57.3
TAS is in M/s
What happens to rate of turn if TAS doubles ?
Rate of turn halves, as its in inverse squared relationship
How does underbank and overbank arise ?
Underbank is when in a descending turn the inboard wing produces more lift.
Overbank is when in an ascending turn the outboard wing produces more lift.
Turning impact on thrust ?
When turning at any altitude an increase in thrust is required to compensate for the extra drag
Extreme skid - ?
A skid occurs when we turning using too much rudder or too little bank.
A/C occupants feel like they are being thrown to the outside of the turn.
The nose is inside the turn, the tail is outside the turn
Extreme slip - ?
A slip occurs when we use too little rudder or too much bank.
A/C occupants feel like they are falling into the turn.
The nose is outside the turn the tail is inside
Negative of unbalanced turns ?
Uncomfortable
they are also inefficient causing more drag and higher fuel burn.
Skid indication and fix ?
The needle and ball are on opposite sides of the gauge.
-More bank in direction of turn
-Less rudder in direction of turn
-More rudder opposite to turn
Slip indication and fix ?
Needle and ball or on the same side of the gauge
-More rudder in the direction of turn
-Less bank in the direction of turn
A/C design is a balance of ?
Stability
Manoeuvrability
they are inversely proportional (S decrease = M increase)
What is static stability ?
The initial response to a disturbance in equilibrium
What is dynamic instability ?
The a/c’s subsequent response over time
What is positive static stability ?
The initial response after a disturbance is in the direction of the equilibrium position
What is negative static stability ?
The initial response after a disturbance is to move away from the point of equilibrium
What is neutral static stability ?
There is no response to disturbance
Positive and negative beta angle ?
A positive beta angle is when the RAF the to the right of the longitudinal axis.
A negative beta angle is when the RAF is to the left of the longitudinal axis
How much force is required to pull 1g ?
0 N
What is a moment ?
Moment = force x arm (Distance between datum and force)
Cl and and anti Cl moments ?
Anti clockwise = (-) moment
Clockwise = (+) moment
If value is 0 object wont rotate
Aerodynamic center is ?
A point on the aerofoil where the moment created by the force of the aerofoil produced remains constant with changes in the AoA.
AC is similar to the CP, but it is in a fixed location.
(AC does not move)
Point of zero lift for a cambered aerofoil ?
-4º ∝
Zero-lift line is ?
A line which when parallel to the RAF results in the aerofoil producing zero lift.
What is absolute AoA ?
The angle between the RAF and the zero lift line.
Zero lift line on a symmetrical and cambered aerofoil ?
Chord line is the zero lift line on a symmetrical aerofoil.
whereas its above the Cl for a cambered aerofoil
Longitudinal stability moment, moment co-efficient, alt change and positive ?
Moment = M
Moment co-efficient = Cm
Altitude change = Pitch
Positive = up
lateral stability moment, moment co-efficient, alt change and positive ?
Moment = L’
Moment co-efficient = Cl’
Alt change = Roll
Positive = Right
Directional stability moment, moment co-efficient, alt change and positive ?
Moment = N
Moment co-efficient = Cn
Alt change = Roll
Positive = Right
Longitudinal stability ?
An increase in AoA should create a negative Cm if the a/c is stable
Lateral stability ?
A positive B angel should create negative Cl’ id the a/c is stable-
A stable a/c will roll away from the RAF
Directional stability ?
A positive B angle should create a positive Cn-
A stable a/c will yaw towards the the RAF
An a/c with positive lateral stability and negative directional stability what will happen if a disturbance causes a the RAF to come from the left of the nose ?
Roll : Right
Roll : Right
Trimming impact on stability ?
Trimming does not change how stable the a/c is. but it does change the equilibrium ∝a
Stick free stability ?
The pilot is not (or lightly) holding the control column.
Stick fixed stability ?
The pilot is firmly holding the control column into position
How is stick position stability lost ?
If an a/c becomes longitudinally unstable.
(most likely due to CG being too far aft)
What happens when the a/c slows down in relation to stick force stability ?
Downforce reduces, causing a pitch down moment- which is prevented by pilot pulling back
How can a pilot recognise stick force stability during flight ?
To retain speed below trim speed requires a pull force
To retain speed above trim speed requires a push force
Effect of altitude on stick force per g ?
Stick force per G is less a t high altitude due to reduced aerodynamic damping
What is the neutral point ?
