Theory of Flight Flashcards
What is the air density in an ISA?
1.225 kg / m^3
What is the standard pressure in an ISA?
1013.2 hPa
1 Pascal = ? ft at low level
30 ft
What occurs with temperature at the Tropopause?
It remains constant.
What is the average Tropopause height over the UK?
36 090 ft
What is the rate of temperature decrease in the troposphere?
1.98 C per 1000 ft (lapse rate)
What occurs with density as height is increased?
It reduces.
What factors affect density?
Pressure, temperature, altitude, water vapour
How is density affected by temperature?
Density decreases with temperature.
What is Newton’s First Law?
A body remains in a state of rest or in a uniform motion in a straight line unless acted upon by an external force.
What is momentum?
The property a moving object has due to its mass and velocity.
What is Newton’s Second Law?
The rate of change in momentum is proportional to the applied force and change in momentum takes place in the direction of the applied force.
What is Newton’s Third Law?
Every action is opposed by an equal and opposite reaction.
What one word summarises Newton’s First Law?
Inertia
What one word summarises Newton’s Second Law?
Force
What one word summarises Newton’s Third Law?
Action/Reaction
A gas in steady motion has what properties?
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 speed?
Pressure decreases.
What are the four forces acting on an aircraft in flight?
Weight
Lift
Thrust
Drag
What is an Aerofoil?
An aerofoil is a surface designed to gain lift from the airflow that moves over it.
What is the Chord Line?
A straight line drawn from the leading edge to the trailing edge.
What is the Chord?
The Chord is the physically distance between the leading and trailing edge.
What is Camber?
The curvature of the aerofoil above and below the chord line.
What is the Mean Camber Line?
A line, equidistant between the upper and lower surfaces of an aerofoil section.
What types of camber are there?
Positive and Negative Camber, providing upwards and downwards force.
What is Angle of Incidence?
The angle at which the aerofoil is attached to the fuselage.
It is defined as the angle between the chord line and the longitudinal fuselage datum.
What is Relative Air Flow?
Direction of the airflow remote from the aircraft and unaffected by its presence.
What is the Angle of Attack?
The angle between the chord line and the relative air flow.
What is Laminar Flow?
The point where the airflow is smooth with no disruption.
What is the Transition Point?
The point on the aerofoil where the boundary layer becomes turbulent and thickens.
What is Wingspan?
The maximum lateral dimension of a wing.
What is Wing Area?
The planform area of the wing.
What is Wing Aspect Ratio?
Aspect Ratio = Span / Mean Chord
What is the Mean Chord?
The average length of the chord is known as the mean aerodynamic chord (MAC).
What shape would a high aspect ratio wing be?
Thin Narrow Wing.
What shape would a low aspect ratio wing be?
Short and Stubby.
What are the three types of steady streamline flow?
Classical Linear Flow
Controlled Separated Flow
Unsteady Flow
Describe Linear Flow
Low AoA
Streamlines follow the contour of the aerofoil
No separation of the flow from the surface
What is the Boundary Layer?
The layer of airflow close to the aerofoil surface. In this layer the velocity of flow is reduced from the free stream flow by the action of viscosity.
What is the Transition Point?
Where laminar flow transitions to turbulent flow.
What is the equation for lift?
L = .5 * Cl * r * V^2 * A
The lift equation states that lift is equal to the lift coefficient (Cl) times the density of the air (r) times half of thesquare of the velocity (V) times the wing area (A).
What is Drag?
Drag is the resistance to the aircraft’s movement in flight.
What is relative air flow?
The direction of the airflow remote from the aerofoil and unaffected by its presence.
What is CL?
The Coefficient of Lift
What is α?
Angle of Attack
What is Rho (ρ) ?
Density
What is CD?
Coefficient of Drag
What is P?
Pressure.
What direction is lift in relation to RAF?
Lift is perpendicular to the Relative Air Flow.
What is the Critical Angle for the Prefect?
15-16°
How does Camber affect the critical angle?
If camber is increased the stalling/critical angle is reduced
What variables are used to calculate the Coefficient of Lift?
Camber
Aspect Ratio
Alpha
Surface condition
What types of drag are there?
Zero Lift Drag (ZLD)
Lift Dependent Drag (LDD) or ‘induced’
What is drag?
Drag is the resistance to the aircraft’s movement in flight. Total drag is the sum of the aerodynamic forces which act parallel and opposite to the direction of flight.
ZLD comprises?
Surface Friction Drag
Form Drag
Interference Drag
Zero Lift Drag occurs when an aircraft is flying at a zero lift angle of attack. All drag forces act parallel and opposite to the direction of flight.
What causes interference drag?
Interference drag is created by the result of flow interference at the wing/fuselage, wing/nacelle, external fuel and weapons.
This can be reduced with internal storage, aerodynamic shapes.
What is form drag?
Form drag is created by the separation of the airflow from the surface. This forms eddies which disrupt the streamline flow.
What is Form Drag?
Form drag or pressure drag arises because of the shape of the object. The general size and shape of the body are the most important factors in form drag; bodies with a larger presented cross-section will have a higher drag than thinner bodies; sleek (“streamlined”) objects have lower form drag.
What factors affect vortex formation?
Wing Planform
Aspect Ratio
Lift and Weight
Speed
AoA
What methods can be use to reduce induced drag?
Winglets
Tip Tanks
Taper
High Aspect Ratio
Washout
Change of the aerofoil section
What is V IMD?
Indicated Minimum Drag Speed
The best Lift/Drag Ratio
Describe the relationship between ZLD and LDD
Zero Lift Drag (ZLD) is dominant at high speed and increases as speed increases.
Lift Dependent Drag (LDD) is predominant at low speeds and decreases as speed increases.
Total drag is the sum total of all the drag forces.
What is the purpose of the Lift/Drag Ratio?
Lift/Drag ratio allows the performance of and aerofoil at a given AoA and airspeed to be determined.
At what AoA is the Lift/Drag Ratio greatest?
4 degrees
The angle of attack at which we obtain the best lift/drag ratio is called the Most Efficient Angle of Attack.
(For the Prefect in the example)
What is the further effect of Ailerons?
Yaw
What is the further effect of elevator?
Height gain or loss/speed interchange
What is the further/secondary effect of rudder?
Roll
What is the purpose of flaps?
Flaps give the aircraft increased lift at lower airspeeds.
Increased drag as lift increases.
Decreased lift/drag ratio.
What types of Flap are there?
Plain/Camber
Split
Zap
Slotted
Double-slotted
Fowler
What is the purpose of the Air Brakes?
Air Brakes will increased drag at will, enabling the speed to be decreased more rapidly, or regulated during descent.
What is the purpose of Spoilers?
Spoilers are flat plates located on the wing, at right angles to air flow. They can be used to increase the drag on a wing to induce roll.
What types of tab are there?
Fixed tab and Trim tab
What is the definition of Lift?
The force acting perpendicular to the relative airflow
What is VMU?
VMU is the Minimum Unstuck Speed.
It is the calibrated airspeed at and above which the aircraft can safely lift off the ground and continue to take off.
What is Vy?
Vy is the Best Rate of Climb Speed.
This occurs where there is the greatest difference between power available and power required.
What is VMD?
VMD is the Minimum Drag Speed
What is the difference between VX and VY?
VX is the Max Angle of Climb Speed
VY is the Max Rate of Climb
What criteria must be met to achieve a minimum radius turn?
Wing loading as low as possible
Air as dense as possible
Max value of the product of CL and angle of bank
The higher the TAS the higher the angle of bank, the tighter the turn.
What components make up the coefficient of lift?
Camber
Aspect Ratio
Angle of Attack - (Alpha)
Surface condition
What is the difference between IAS/TAS
IAS
Indicated airspeed is the airspeed read directly from the ASI on an aircraft, driven by the pitot-static system. It uses the difference between total pressure and static pressure. The IAS.
TAS
True airspeed is the relative velocity between the aircraft and the surrounding air mass.
What is the boundary layer on a wing?
Boundary Layer
The layer of airflow close to the aerofoil surface. In this layer the velocity of the flow is reduced from the free stream flow by the action of velocity
What are the pressure changes over the wing approaching a stall?
The negative pressure over the wing moves forward with increasing angle of attack until the pressure distribution collapses creating a large pressure bubble underneath the wing.
In what direction across does the wing stall?
Root to tip of wing.
An aerodynamic twist can be introduced to the wing with the leading edge near the wing tip twisted downward. This is called washout and causes the wing root to stall before the wing tip. This makes the stall gentle and progressive. Since the stall is delayed at the wing tips, where the ailerons are, roll control is maintained when the stall begins.
How does weight affect the stalling speed?
Stall speed increases, as the weight increases; and decreases as the weight decreases.
What factors can change the stall speed?
Change in weight
Load factor (n) from maneourvre
Configuration (change to CLmax)
Power and slipstream
How do flaps affect stall speed?
Increased wing area from flap reduces the stall speed.
What types of Aircraft Stability are there?
Static - Immediate reaction
Dynamic - Subsequent reaction
What is positive stability?
Positive Stability
When a body returns to the original position after disturbance has been removed.
What is neutral stability?
Neutral stability
When a body takes up a new position in relationship to the original position after the disturbance has been removed.
What is Negative stability?
Negative stability
When a body continues to move away from its original position after the disturbance has been removed.
What design features enhance stability?
Directional stability
Large Fin
Long Moment Arm
Longitudinal stability
Large horizontal tailplane
Long moment arm
Lateral stability
Large Fin
Dihedral
Sweep Back
High Wing
What is positive dynamic stability?
Two types
Dead Beat Convergence/Subsidence
Damped Phugoid
At what speed does best range occur for jet aircraft at low altitude?
1.32 * VIMD
What is the difference between range and endurance?
Range - converting fuel into distance
Endurance - converting fuel into time
What factors must be considered for maximum permissible take-off weight?
CofA Limit
WAT (Weight-Altitude-Temperature) limit
Field Length Requirement
Take-off net flight path
En-route terrain clearance
Landing distance requirement
What is BLC?
Boundary Layer Control
What is the purpose of slats?
Slats are a lift augmentation device that delay the stall until a high angle of attack. They can increase the CLmax by as much as 70% and increase the stalling angle by 10°.
The slats change the pressure distribution, the air flow re-energises the boundary layer.
What are the advantages of slats?
Improved control at low speed
Augmenting lift
Why do propeller blades twist towards their ends?
This is to maintain a constant angle of attack (often 4°)
What is windmilling?
Allowing the propeller to find its optimal angle of attack.
What is feathering?
Feathering turns the blade so the aggregate effect of the blade section produces zero torque, the propeller is stopped and drag reduced to a minimum.
This option may be selected if windmilling of the propeller may lead to eventual seizure or fire.
What direction will swing, torque and slipstream cause the aircraft to turn? (With CW rotating engine)
To the left.
Therefore require right rudder correction.
What is Newton’s first law?
Inertia
A body remains in a state of rest of in a uniform motion in a straight line unless acted upon by an external force
What is Newton’s Second Law?
Force
The rate of change in momentum is proportional to the applied force and the change in momentum takes place in the direction of the applied force.
What is Newton’s Third Law?
Action/Reaction
Every action is opposed by an equal and opposite reaction.
What properties does a gas in steady motion possess?
Potential Energy
Heat Energy
Pressure Energy
Kinetic Energy
What is the equation for Total Pressure?
Total Pressure = Static Pressure + Dynamic Pressure
What are the four forces acting on an aircraft in steady flight?
Thrust
Lift
Weight
Drag
What is the Chord and Chord Line?
Chord - the distance measured along the chord line. A line joining the leading and trailing edge of an aerofoil section.
Chord Line - The chord is the distance between the leading and trailing edge measured along the chord line.
What is camber?
Camber
The curvature of the aerofoil and below the chord line.
What is the Angle of Incidence?
Angle of Incidence
The angle at which the aerofoil is attached to the fuselage. Defined as the angle between the chord line and the longitudinal fuselage datum.
What is Relative Airflow?
Relative Airflow (RAF)
Direction of the airflow remote from the aircraft and unaffected by its presence.
What is the Steamline?
If air particles follow a same steady path this is represented by a streamline.
There is no flow across the streamline, only along it.
What is Freestream Flow?
Air in the region where pressure, temperature and relative velocity is unaffected by the passage of the aerfoil through it.
What is the Boundary Layer?
The layer of airflow close to the aerofoil surface. In this layer, the velocity of flow is reduced from the free stream flow by the action of viscosity
What is the Transition Point?
The point on the aerofoil where the boundary layer becomes turbulent and thickens.
What is Laminar Flow?
The point where airflow is smooth with no disruption.
What is Turbulent Flow?
The region where the airflow is rough and the movement of air particles is unpredictable.
What is the Total Aerodynamic Reaction?
The resultant of the combination of both lift and drag into a single component.
Lift - The force is perpendicular or right angles to the RAF.
Drag - The perpendicular force to lift opposing motion.
What is Aspect Ratio?
Aspect Ratio = Span/Mean Chord
What shape will a High and Low Aspect Ratio wing be?
High Aspect Ratio - Thin narrow wing.
Low Aspect Ratio - Short and stubby wing.
What is Classical Linear Flow?
Low AoA
Streamlines follow the contour of the aerofoil.
No separation of flow from the surface.
What is Controlled Separated Flow?
Halfway stage between the steady streamline and unsteady flow.
What is the critical angle when referring to an aerofoil?
The critical angle is the Angle of Attack of the aerofoil that generates the greatest CL value, beyond this the low pressure bubble above the wing collapses and the CoG moves from the front to the rear of the aerofoil.
What is the lift equation?
L = CL * 1/2 * ρ * V2 * S
Air Density = ρ
Wing Area = S
Coefficient of Lift = CL
What variables are used to calculate the Coefficient of Lift (CL)?
AoA - Lift Curve
Aerfoil Sections (Symmetrical, Positive, Standard)
Aspect Ratio (High/Low)
Planform (Straight/Swept)
Wing Surface Condition (Lift Curve)
Speed of Sound
What is the Drag Formula?
D = CD * 1/2 * ρ * V2 * S
What is Zero Lift Drag?
An aircraft flying at a zero lift angle of attack, all the drag forces act parallel and opposite to the direction of flight.
ZLD comprises Surface Friction Drag, Form Drag, Interference Drag.
What is Surface Friction Drag?
The aerodynamic resistance due to the contact of relative airflow with the surface of the aircraft.
What factors affect the degree of Surface Friction Drag?
Total surface area of the aircraft.
Viscosity of the air.
Change in velocity of the airflow.
Surface texture/condition.
What is Form Drag?
The difference between surface friction and form drag can be easily appreciated if a flat plate is considered in two attitudes.
First at a zero angle of attack, when all drag is friction drag and second at 90 degrees angle of attack when all drag is form drag due to the separation.
What is Interference Drag?
Created by the result of flow interference at wing/fuselage, wing/nacelle, wing/external weapons.
Can be reduced by the addition of fairings, aerodynamic shapes, internal stowages.
What is Lift Dependent Drag?
Created whenever an aerofoil is producing lift.
Comprises:
Induced drag
Elements of ZLD.
What factors affect Vortex Formation?
Wing Planform
Aspect Ratio
Lift and Weight
Speed
AoA
What is Induced Downwash?
Trailing vortices modify the flow pattern and has the effect of drawing the airflow downwards behind the wing.
The amount of downwash produced is directly related to the size and strength of the vortices being generated.
Increased downwash alters the RAF and the effective AoA.
What methods can be used to reduced drag?
Winglets
Tip Tanks
Taper
High Aspect Ratio
Washout
Change of Aerofoil Section
At what angle is lift greatest in the Lift/Drag ratio?
16°
At what angle is the most efficient lift/drag performance produced?
4°
What is the symbol for Best Lift/Drag Ratio?
VIMD
At what VIMD is the max speed/drag ratio achieved?
1.32 * VIMD
What is Total Drag?
The sum total of all drag forces.
What axis does the elevator work around?
The lateral axis through pitch.
What axis does the Aileron work around?
The Longitudinal axis through roll.
What axis does the Rudder work around?
The Normal axis via Yaw.
What is the further effect of elevators?
Height/speed change
What is the further effect of ailerons?
Yaw
What is the further effect of the Rudder?
Roll
What is the purpose of Flaps?
Flaps give the aircraft the required lift at a lower airspeed. They therefore increase drag.
What is the difference between slats and flaps?
Flaps are located on the trailing edge of the wing.
Slats are located on the leading edge of the wing.
What is the purpose of Spoilers?
Spoilers are flat plates located on the wing at right angles to the airflow. They can be used to increase drag on the wing or induce roll.
What is the purpose of Air Brakes?
Air brakes can be extended to increase the drag on an aircraft at will, enabling the speed to be decreased more rapidly or regulated in descent.
What is the purpose of the trim tab?
The trim tab alleviates unnecessary control forces on the pilot.
There are fixed tabs, adjusted on the ground and trim tabs controlled by the Pilot.
What factors can increase glide performance?
Tailwind will increase the ground distance travelled.
Reduced weight will increase gide endurance
What is the boundary layer?
The layer extending from the surface to the point where no drag effect is discernible.
What is Boundary Layer Separation?
Airflow hits the stagnation point of the wing.
Passes smoothly over the laminar flow area.
Transition Point - airflow becomes turbulent.
Separation Point - airflow is separated.
How are load factor and stalling speed linked?
The load factor (n) is squared as the stalling speed doubles
What is the difference between postive, neutral and negative stability?
Positive - A body returns to its original position after disturbance.
Neutral - A body takes up a new position after disturbance.
Negative - A body continues to move away from its original position after disturbance.
What is the difference between static and dynamic stability?
Static stability describes the immediate reaction of the body after disturbance, while dynamic stability describes the subsequent reaction.
What is Negative Dynamic Stability?
The body oscillates around the equilibrium with increasing amplitude.
What is Negative Dynamic Stability (Divergence)?
Divergence is when the body returns to the equilibrium then diverges.
What is Neutral Dynamic Stability?
The body oscillates about the equilibrium with constant amplitude.
What is Positive Dynamic Stability (Damped Phugoid)?
The body oscillates about the equilibrium with decreasing amplitude (damped)
What is Positive Dynamic Stability (Dead beat convergence/subsistence)?
Motion heavily damped - oscillations cease and the motion becomes dead beat positive stability
Briefly desribe Bernoulli’s theory
As fluid speed Increases
Pressure Decreases
What is the Lift Formula in words?
Lift is equal to the coefficient of lift multiplied by half the density times velocity squared multiplied by surface area.
What components comprise the coefficient of lift
Camber (the asymmetry between the two acting surfaces of an aerofoil, with the top surface of a wing)
Aspect Ratio
Surface Condition
Alpha
What are the four forces in straight and level flight?
Lift
Weight
Thrust
Drag
What direction is lift relative the the relative air flow?
Perpendicular
90
What are the two drag curves?
Zero Lift Drag (increase with speed), comprises surface friction drag, form and interference.
Lift Dependent Drag (decreases as speed increases)
What are the benefits of flying at high altitude?
Jet engines are designed for optimum performance at colder temperatures.
Thermal efficiency.
Less drag.
IAS vs TAS
What is a cruise climb?
A climb technique employed by aircraft, usually at a constant power setting, resulting in an increase of altitude as the aircraft weight decreases
What is V2 speed?
V2 is the speed at which the airplane will climb in the event of an engine failure. It is known as the takeoff safety speed
