1 Principles Of Flight Flashcards
What is the air density in an ISA?
1.225 kg/m^3
What is the standard pressure in an ISA?
1013.25 hPa
1 hPa = ? ft at low level
30 ft
What occurs with temperature at the Tropopause
It remains constant
What is the Tropopause height in an ISA?
36,090 ft
What is the temp lapse rate in the troposphere?
-1.98C / 1000ft
What occurs with density as height increases?
It decreases
What factors affect density?
Pressure
Temp
Altitude
Water Vapour
How is density affected by temperature?
As temperature increases density decreases
What is Newton’s 1st Law?
Law of Inertia
A body remains in a state of rest or uniform motion unless acted on by an external force
What is momentum?
Mass x Velocity
What is Newton’s 2nd Law?
Law of Force
The rate of change of momentum (acceleration) experienced by a body of mass is proportional to the force applied to it
What is Newton’s 3rd Law?
Law of Action/Reaction
For every action there is an equal and opposite reaction
A gas in steady motion has what properties? (in term of energies)
Potential Energy
Heat Energy
Pressure Energy
Kinetic Energy
Total Pressure = ? + ?
Static Pressure + Dynamic Pressure = Total Pressure
Write Bernoulli’s Theorem
Total Pressure = P + (1/2 x ρ x V^2)
In Bernoulli’s what is ρ?
Density
What happens to pressure with an increase in velocity of a fluid?
Pressure decreases
What is an Aerofoil?
Surface designed to generate lift from airflow over it’s surface.
What is the Leading Edge Radius?
The shape of the leading edge.
What is the Chord Line?
Infinite line through the leading and trailing edge of an aerofoil section.
What is the Chord?
Distance between the leading and trailing edge of an aerofoil section
What is the Camber?
The curvature of the aerofoil. (Upper surface camber/Lower surface camber)
What is the Mean Camber Line?
A line equidistant from the upper and lower surfaces of an aerofoil.
What is the Angle of Incidence?
Angle between the chord line and the longitudinal fuselage datum.
What is the Relative Airflow (RAF)?
Direction of airflow that is remote from the aircraft/ unaffected by its presence. Also known as Freestream flow
What is the Angle of Attack (AoA)?
The angle between the chord line and the relative airflow.
Streamline is?
The path that a particle of air would/will take
Freestream Flow is?
A region of air where P, T and relative vel. are unaffected by the passage of an aerofoil
Define Aspect Ratio
AR = Span/Mean Chord or (Span^2)/Mean Chord
Describe a wing with High Aspect Ratio
Long and Thin (Glider)
Describe a wing with Low Aspect Ratio
Short and Stubby (F35)
What is Laminar Flow (steady flow)?
Steady flow lines with no mixing
What is Separated Flow?
Halfway between steady and unsteady flow
What is Turbulent Flow (unsteady flow)?
Large amount of mixing and not represented with streamlines
What 4 factors impact the pressure distribution on an aerofoil?
Shape of the aerofoil
Aerofoil attitude to RAF
Air Density
Velocity
True or False. Changing the AoA changes the Centre of Pressure?
True
Centre of Pressure is optimal at what AoA?
Normal
At a LOW AoA the Centre of Pressure moves to the …. of the aerofoil
Rear
At a HIGH AoA the Centre of Pressure moves to the …. of the aerofoil
Front
Lift acts perpendicular to what?
Relative Airflow
Drag acts perpendicular to what upwards force?
Lift
Combining Lift and Drag gives what?
Total Aerodynamic Reaction
What is the Lift equation and define each term?
L = C(L) 0.5 rho V^2 S
L=Lift C(L)= Coefficient of Lift rho=density V=Free Stream Velocity S= Wing Area
What is the Critical Angle of Attack?
15 or 16 deg
Coefficient of lift is made up of what 3 components?
AoA
Wing Planform
Wing Surface Condition
What happens to the critical AoA as the camber of the aerofoil increases?
Critical AoA reduces with increasing camber
Describe the C(L) vs AoA graph with changing cambers
The steepness of the performance line does not change but shifts to the left as camber is increased, with the max C(L) increasing slightly.
How does Aspect Ratio (AR) affect the C(L) vs AoA graph?
AR alters the gradient of the performance line. High AR steeper gradient, lower AR shallower gradient.
Lower AR tend to have higher critical AoA.
How does the planform affect the C(L) vs AoA graph?
Straight wing has a more gentle change of C(L) around critical angle.
Swept wing has a more abrupt change to the C(L) around the critical angle.
How does wing surface condition affect the C(L) vs AoA graph?
Smoother surface gives max performance.
As the surface roughens, the gradient of the performance curve remains the same but the critical angle is lower.
What factors affect lift?
RAF
AoA
Downwash. Increasing AoA will increase downwash Increase downwash will reduce the effective AoA. Reduced AoA tilts the lift component backwards therefore reducing lift.
What vector opposes thrust?
Drag
What are the 2 types of drag?
Zero Lift Drag (ZLD)
Lift Dependant Drag (LDD)
What is the Drag equation?
D =C(D) x 0.5 x rho x V^2 x S
D=Drag C(D)= Coefficient of Drag rho=density V=Free Stream Velocity S= Wing Area
Zero Lift Drag is made up of what 3 components?
Surface Friction - Aero resistance from contact of RAF with surface of aircraft.
Form drag - The shape ‘shown’ to the airflow.
Interference - Caused by external tanks, pods, weapons etc
How can we reduce interference drag?
Better aero shapes, internal stowage
Lift dependant drag comprises of
Induced Drag
Elements of Zero Lift Drag (ZLD)
Induced drag predominantly comes from what behaviour associated with spanwise flow?
Vortex formation
5 factors that effect vortex formation are:
Wing Planform Aspect Ratio Lift and Weight Speed AoA
How can we minimise Induced Drag?
Winglet Tip Tank/Missile Taper High AR Washout Change of Aerofoil Section
What is the ‘Taper’ of a wing?
The changing of the chord between the base to the tip of the wing
What is washout?
The ‘twist’ of the wing along its length?
Zero Lift Drag (ZLD) …… as speed increases.
increases
Zero Lift Drag (ZLD) is dominant at ….. speeds
higher
Lift Dependant Drag (LDD) …… as speed increases.
decreases
Lift Dependant Drag (LDD) is dominant at …… speeds
lower
Total drag is the combination of …… + ……
Zero Lift Drag (ZLD)
+
Lift Dependant Drag (LDD)
What does V(IMD) stand for?
Velocity (Indicated Minimum Drag)
With respect to fuel, why is V(IMD) of interest?
Lowest fuel consumption required to overcome drag of aircraft.
Optimal lift/drag ratio occurs at about what velocity? (name of velocity)
V(IMD)
Max lift occurs at AoA of ….
16 deg
Min drag occurs at AoA of ….
2 deg
Most efficient lift/drag performance our aerofoil of interest occurs at …. (AoA)
4 deg
What is the lift/drag ratio defined as?
C(L) / C(D)
The LATERAL axis passes….
through the wings
The LONGITUDINAL axis passes….
along the length of the fuselage
The NORMAL axis passes…
vertically through the a/c
What action is performed around the LONG, LAT and NORMAL axis’
LONG - Roll
LAT - Pitch
NORMAL - Yaw
Name the 3 PRIMARY flight control surfaces
Elevator
Aileron
Rudder
What action do each of the the Primary Flight Control Surfaces control?
Elevator - Pitch
Aileron - Roll
Rudder - Yaw
A ‘heavy’ stick can make the a/c …. to control
Difficult
A ‘light’ stick may cause the a/c to be ….. easily.
Overstressed
Control movements should be …… to the given a/c
Proportional
What PFCS is most responsive?
Aileron
What are the PRIMARY and further effects of the PFCS?
Elevator - (P) Pitch + (Furth) Height/Speed Interchange
Aileron - (P) Roll + (Furth) Yaw
Rudder - (P) Yaw + (Furth) Roll
Name the SECONDARY flight control surfaces
Flaps
Spoilers
Air Brakes
Trim Tabs
Flaps provide extra l… and d…
Lift and drag
What happens to the Lift vs Drag ratio when the form drag is increased?
The Lift vs Drag ratio will decrease.
With flaps extended. What happens to the critical angle?
Critical angle will decrease
Flaps have 3 effects. 2 increasing, 1 decreasing. What are these?
Increase Lift
Increase Drag
Decrease Lift/Drag ratio
What are the 2 types of trim surfaces?
Fixed Trim
Trim Tabs
If you want to trim the nose up. What direction should the trim tabs in the elevator be pointing?
Upwards
Rate of climb is determined by what?
Airspeed
Angle of Climb
If we want to climb and maintain the same speed. We need to add ….
POWER
To maintain a climb at a given airspeed (more accurately EAS) ____ power is required than in level flight.
MORE
The angle of climb is determined by the amount of _____ left after ______ drag.
THRUST
OPPOSING
For a piston a/c, the max angle of climb speed will be just above what speed? Denoted as V(MU)
Unstick speed
The lowest calibrated airspeed at and above an a/c can safely lift off and continue take-off is …..
Unstick speed
V(MU)
At higher altitudes the “power available” curve of the engine is _____
LOWER
Glide descent is defined as ______ travel per altitude ____.
FORWARD travel per altitude LOST
When descending. To maintain airspeed, energy must be _____ to overcome drag.
EXPENDED
Endurance gliding is about ….
flying for as LONG (time) as possible.
Range gliding is about ….
flying as FAR as possible.
Max glide distance is achieved at …. lift/drag ratio.
OPTIMUM
A tailwind will ____ ground distance travelled while gliding.
DECREASE
A headwind will ____ ground distance travelled while gliding.
INCREASE
Weight does what to glide angle? (also impact on range vs endurance gliding)
- Not effect the gliding angle.
- Range gliding is unchanged in still air.
- Endurance gliding decreases with increased weight.
What control surface do we use to ROLL the aircraft?
Aileron
T or F? When turning, without other inputs you will lose altitude.
TRUE
The vertical lift component will be reduced in a turn.
To maintain altitude when turning you are required to increase lift by increasing what?
And what is the secondary effect of this?
Angle of Attack
Therefore will begin to introduce a centripetal force and therefore g.
Progressive increase in lift and loading in a turn can be continued until:
A/c stall when AoA reaches critical angle
g threshold of pilot is reached
g threshold of the a/c is reached
When making a level turn the _____ component of ____ must be equal to the ____ to maintain altitude.
VERTICAL component of LIFT
equal to
WEIGHT
When an a/c turns, lift acts towards the ____ of the turn as well as _____.
CENTRE of the turn as well as UPWARDS
In a level turn, if weight increases;
What is also required to increase?
What else will increase to maintain the same radius turn?
Vertical component of lift required to increase.
Therefore, the centripetal force will also increase (‘g’)
To achieve a max rate turn, the following should be satisfied…
- Wing loading (weight of a/c) to be as low as possible.
- Air as dense as possible.
- Max value of the product of C(L) and Angle of Bank.
In a minimum radius or max rate turn, thrust _____ the lift needed from the wing and can help ____ turn radius.
thrust REDUCES the lift needed
help IMPROVE/MINIMISE
Describe a standard rate turn
3 deg per second
180 in a minute
A clean a/c will always stall at the ____ AoA, regardless of weight
SAME AoA
Basic stall speed is denoted by ….
V(B)
In level flight and at low speeds, the AoA will be _____
HIGH
As the wing works ‘hard’ to maintain lift in the reduced airflow.
During the stalling process, describe what happens to the centre of pressure.
As the AoA increases towards the critical angle the CoP will move towards the leading edge.
When it passes the critical angle it will quickly move back towards the trailing edge.
At what point does the air over the wing become turbulent?
Transition Point
As speed reduces, what must the AoA do to keep lift constant?
The AoA must INCREASE.
Key factors that change stalling speed are:
- Changing weight
- Manoeuvring (Load factor(n))
- Configuration (changes in C(L)max)
- Power and slipstream
Changing the weight of the a/c impacts; the stall SPEED or stall ANGLE?
SPEED
If the weight is increased, the AoA required to maintain level flight ______ for the same speed.
INCREASES
Stability describes the motion of a body after __________________________
after AN EXTERNAL FORCE HAS BEEN REMOVED/APPLIED.
The two types of stability are:
Static - Immediate Reaction
Dynamic - Subsequent Reaction
What happens to a POSITIVELY Stable body?
A body returns to original position
What happens to a NEUTRALLY Stable body?
A body that takes up a new position
What happens to a NEGATIVELY Stable body?
A body continues to move away from original position
STATIC stability describes …
The immediate reaction of the body after disturbance.
DYNAMIC stability describes …
The subsequent reaction of the body after disturbance.
Factors that will affect the long term response of an a/c are:
Momentum (Vel x Mass) Static stabilities (pitch, roll, yaw) Angular velocities about the 3 axes Angular momentum Aerodynamic damping methods
Dynamic stability can be described in 5 ways. These are:
Negative Dynamic Stability Negative Dynamic Stability (Divergence) Neutral Dynamic Stability Positive Dynamic Stability (Damped Phugoid) Positive Dynamic Stability (Convergence)
What design features will enhance
DIRECTIONAL STABILITY?
- Large Fin
- Long Moment Arm
Example: TORNADO
What design features will enhance
LONGITUDINAL STABILITY?
- Long Horizontal Tailplane
- Long Moment Arm
Example: A400
What design features will enhance
LATERAL STABILITY?
- Large Fin
- Dihedral
- Sweep Back
- High Wing
Example: C17
The range of an a/c is determined by
Airframe Consideration - Flaps, Gear etc Temperature - Colder=More Dens + Increase engine efficiency High Altitude IAS vs Drag IAS vs TAS
Considering range, V(IMD) is important because …
It is the speed that provides the least amount of drag on the airframe.
In a turboprop maximum range is achieved at:
- Cruise Climb
- Max Continuous RPM
- IAS at V(IMD)
Lift Dependent Drag curves moves to the _____ when you lose weight
LEFT
In a turbojet a/c when flying for range we should:
- Fly at Max TAS/drag
- At low altitudes at 1.32xV(IMD)
- As weight reduces (burning fuel) a/c should cruise climb at constant mach
What RPM do we want to operate at in a TURBOPROP and TURBOJET?
TURBOPROP - Max CONTINUOUS
TURBOJET - OPTIMUM
TURBOJET engines are designed to operate in the _____ rpm band.
OPTIMUM rpm band
What speeds do we want to operate at in a TURBOPROP and TURBOJET?
TURBOPROP - V(IMD)
TURBOJET - 1.32xV(IMD)
What is a C of A?
Certificate of Airworthiness
The maximum permissible T/O weight is the least after considering:
- C of A limit
- WAT (Weight-Alt-Temp) limit for T/O and LANDING
- Field Length
- T/O net flight path
- En-route terrain clearance
Define Wing Loading
Weight/Area
Name 3 lift augmentation devices
Slats - delay stall until higher angle of attack
Flaps - increase lift by increasing the camber
Boundary layer control
Lift augmentation devices are used to increase ______ ______ ____________
MAX LIFT COEFFICIENT
The airflow caused by slats does what to the boundary layer?
RE-ENERGISES it
The use of slats does provides what?
- Improved control at low speeds
- Augments lift
Flaps vary the ______ ____ of the wing section
CAMBER LINE
The GREATER the mean camber the _____ the lift capability of the wing.
GREATER
Name the 3 types of propeller
- Fixed Pitch
- Variable Pitch - Piston
- Variable Pitch - Gas turbine
TRUE or FALSE? - Propellers have washout?
TRUE - Propellers do have washout (twist) along their length
At what speed does drag increase significantly?
Near the speed of sound
The PREFECT propeller rotates _____ from the pilots perspective
CLOCKWISE
Propeller blade washout is used to _____ an ______ angle of attack along its length
MAINTAIN an EFFICIENT
____ Pitch is used to maintain maximum efficiency at LOW AIRSPEEDS
FINE Pitch
____ Pitch is used to maintain maximum efficiency at HIGHER AIRSPEEDS
COARSE Pitch
Define Windmilling
Loss of positive torque on the propellers
Propellers will spin due to air movement over their surface. Spinning the drive shaft and the gearbox
Propellers are _________ following engine failure, to prevent them inducing significant drag
FEATHERED
How can you increase the ‘SOLIDITY’ of the propeller
- Increase the number of blades
- Increase the chord of each blade
Swing on take-off can be caused by:
- Slipstream effect
- Torque Reaction
The slipstream effect of a CLOCKWISE rotating propeller (pilot’s view) will induced asymmetric flow over the fin and rudder.
Resulting in the a/c yawing to the ____
LEFT
The torque reaction of a CLOCKWISE rotating propeller (pilot’s view) will induce a counter torque on the a/c frame.
There will be an increased load on the ____ side undercarriage causing the a/c to swing ____ on travel down the runway during takeoff.
Increased load on LEFT undercarriage
Swing to the LEFT on travel
What does Vx represent?
Max angle climb speed
What does Vy represent?
Max rate climb
V(mu) is known as the ______ speed.
UNSTICK
What a/c will try and operate at OPTIMUM RPM?
Jet Engine A/C
What a/c will try and operate at MAX CONTINUOUS RPM?
TurboProp
Lowering slats does what to the critical angle?
INCREASES CRITICAL ANGLE
