Principles Of Flight Flashcards
What are newtons 3 laws of motion?
1: Law of inertia - A body will remain in a state of rest or uniform motion unless it experiences an external force
2: Law of acceleration - The rate of change of momentum is proportional to the force applied and takes place in the direction of the force applies
3: Every action has an equal and opposite reaction
What is Bernoullis principle?
As the speed of fluid increases over a curved surface (When the fluid passes through a constricted section of the pipe) the static pressure of the fluid decreases.
Pressure in inversely proportional to velocity
Fast moving air = Low pressure zone/lift
Slow moving air = High pressure zone
What is the adverse pressure gradient?
Airflow over the wing: Pressure decreases and velocity increases
Airflow leaving the wing = pressure increase and velocity decrease
How is Air speed measured?
Through a Pitot tube by Total pressure - Static Pressure = Dynamic pressure (Gives IAS)
What is the Chord line?
A straight line from the Leading edge to the trailing edge.
What is meant by “Chord”
The length of the chord line
What is the Leading edge radius?
A measure of the sharpness of the leading edge as a percentage ratio of the chord
What is the thickness/chord ratio?
The thickest section of the wing, expressed as a percentage of the chord length.
What is wing taper?
A wing platform in which the wing of the chord changes continuously between the root and the tip
What is a swept wing?
A wing that is angled backward or forwards from the fuselage
What is the Mean Camber Line?
An imaginary line drawn through the centre of an aerofoil section, halfway between the upper and lower surfaces showing the camber.
Maximum Camber?
The maximum distance between the chord line and the mean camber line
What is the Camber?
The distance of the curve above or below the chord line.
Explain Positive Camber
The top of the wing surface is curved
Explain zero camber
The wing is cured on both sides
Explain negative camber
The wing is curved on the bottom only - providing a downward pressure
What does the Camber of the wing determine?
The characteristics and boundary layer
What is free stream flow?
A region of air that remains unaffected by the aircraft.
What is relative airflow?
The flow relative to the aircraft thrust direction not to be confused with free stream flow
Explain upwash and down wash.
Upwash - Air that moves towards the low pressure area of the wing
Downwash - The equal and opposite reaction at the trailing edge
What is span wise flow?
Air flowing sideways or backwards over the wing. It’s effect is greatest at the wing tip.
Explain the air movement on top of the wing.
A low pressure zone is created, the flow of air rushes over and flows towards the fuselage from the leading edge
Explain the movement of air under the wing.
A high pressure zone is created, the air flow moves past and curves outwards from the fuselage
Explain a vortex sheet.
A vortex sheet is the result of the airflow curving over and towards the fuselage and under and away from the fuselage creating multiple vortex “sheet”
How does aircraft speed and weight alter vortices?
High speed/weight = Slow vortices
Low speed/weight = Fast vortices
Explain the rams horn vortex
The Rams horn vortex is a controlled airflow separation of a vortex running along the fuselage down to the Leading edge and finally to the wingtip. Relative airflow moves over the Rams Horn reattaches itself behind the vortex. With the Rams Horn effect and dogs teeth on the LE, the boundary layer will remain on the LE
What are the three forces acting on a wing?
Lift - The force produced by an aerofoil, perpendicular to the RAF
Drag - The force from an aerofoil, parallel to and in the same direction as the RAF
Total Reaction (TR) - The combination of lift and drag. The direction the wing would move when subjected to both lift and drag.
Describe Angle of Attack AoA
The angle of the chord line in the wing and RAF. The Greek symbol alpha is used to represent this.
What are positive, negative and neutral AoA?
Positive - Chord line points up
Neutral - Chord line is S&L
Negative - Chord line points down
What is the critical point angle?
The point in which the angle of attack is too great and the RAF separates from the wing causing a stall
What is meant by best lift and least drag?
Aerofoil that produces the best lift with the least drag.
Practical applications would be Max endurance speed flown at the minimum amount of power to maintain S&L flight.
What is the Leading edge stagnation point?
Collated air molecules resulting in an envelope/bubble of high pressure air. It consists of both static air pressure and dynamic air pressure
What are low pressure bubbles?
Pending angle of attack are areas of Low pressure above and below the aerofoil. Lower angle of attack = larger Low pressure bubble. Higher angle of attack = smaller low pressure bubble
What is the high pressure bubble?
A high pressure zone/bubble on bottom of a positive cambered aerofoil. The downwash and change of direction causes a higher than free stream pressure on the lower surface similar to flat plate lift.
What type of aerofoil is this and what is its characteristic?
Low speed aerofoil - Well/positive cambered (The top of the wing is curved)
Typical for high lift
What type of aerofoil is this and what is its characteristics?
Symmetrical aerofoil (typical vertical stabiliser) - Zero Camber (the wing is curved on both sides)
Centre pressure doesn’t move forward
Typical of rotor blades on older helicopters
Typical for aerobatic aircraft for inverted flight
What type of aerofoil is this and what is its characteristic?
High speed aerofoil - (typical subsonic) - Positive Camber
Super critical aerofoil
Low drag
Subsonic speeds for range and fuel efficiency
Accommodates shockwaves
What type of aerofoil is this and what is its characteristic?
Wedge shaped aerofoil
Typical for super sonic
What type of aerofoil is this and what is its characteristic?
Negative aerofoil and Negative camber
Typical horizontal stabiliser
What is meant by the Boundary layer effect?
A parcel of air that is dragged on the leading edge with the wing. If this parcel of air moves, it is effectively a stall
What is the transition point?
The point at which laminar airflow transits to turbulent flow. The airflow gains kinetic energy at the point of maximum camber.
What is the turbulent flow over the wing?
Air that has both horizontal and vertical components, that has gained more kinetic energy to penetrate the adverse pressure gradient. The air can stick to the wing for longer and has thickened in the vertical axis.
What is the separation point on the wings?
Where turbulent flow separates from the wing surface.
What is the separated airflow from the wing?
The airflow that starts to move in relation to normal flow of pressure (High to low) and produces a REVERSE flow on the surface of the wing.
In relation to aircraft wings, what is meant by aspect ratio?
It is the ratio between the wingspan and length of chord.
What types of aspect ratio are there (In relation to aircraft wings)?
High aspect ratio
Medium aspect ratio
Low aspect ratio
What are the characteristics of high aspect ratio?
Long wings, short cord (C130, TPT planes, gliders)
Slower high lift aircraft
Small wing tip vortices
Very little induced drag
Span wise pressure gradient flow has less time to develop
Single wing spar
What are the characteristics of Medium aspect ratio?
Built for medium speed aircraft (PC21)
Medium chord
What are the characteristics of a low aspect ratio wing?
Short stubby wings Massive wing tip vortices Lots of induced drag Wings are built for strength and manoeuvre Typical of fighters and aerobatic planes Multiple wing spars
What are the two considerations for wing aspect ratio?
Lift-dependant drag (Downwash)
Structural considerations
What are the characteristics of a High aspect ratio wings downwash?
Smaller wingtip vortices
Shorter span wise pressure gradient flow
What are the characteristics of a low spect ratio wings downwash?
Larger wingtip vortices
Larger Span-wise pressure gradient flow
What are the four forces acting on an aircraft?
Lift
Weight
Thrust
Drag
Define the lift force
Lift is the aerodynamic force that acts perpendicular to Relative Air Flow (RAF).
Lift is the product of the pressure differential between the upper and lower wing surfaces.
How is lift generated?
Through use of an aerofoil camber thus creating a low pressure bubble on the top of the wing and a high pressure bubble on the surface of the wing. Bernoulli’s principle states with Increased density or velocity, lift will increase.
What is the Lift formula?
CL = Coefficient of lift V = Velocity (EAS^2) (true airspeed) S = Size and shape of surface area of the wing P = Air density
The lift coefficient or lift generated is dependant on?
Aerofoil size and shape Viscosity (internal friction) of the airflow Density of the airflow Angle of Attack Speed of the airflow
What can the Pilot change in relation to lift?
Altering the CL (Coefficient of lift) by changing the AoA Altering velocity by increasing or decreasing thrust Altering S (Size and surface area of the wing) by use of flaps
What do the flaps allow the aircraft to do?
Allow adequate lift at slower speeds by increased lift and drag
List some common Flaps for wings
Plain flap Split flat Slotted flap Fowler flap Double slotted Fowler flap Gouge flap Krueger flap
At a High Angle of Attack (AoA) Where is the separation point?
The separation point moves forward towards the leading edge and separates of the surface of the wing at an earlier point
If your wings have stalled, how do you get out of it?
Decrease the angle of attack
What do the flaps do?
Changes the Chord, increases camber, AoA, increasing lift and drag.
What are slats and what do they do on a wing?
Slats are narrow chord aerofoil that attach to and extend along the front of the leading edge.
When extended they create a small aerofoil section, re-energising the airflow and delay separation at lower airspeeds
What is drag force?
Drag is the total air resistance to an object moving through it. The force is the “equal and opposite” to thrust
What is the drag formula?
Cd = Shape and AoA of the aerofoil S = frontal area of the aerofoil
Note = As lift did, drag increases as the square of the speed
What is zero lift drag?
Zero lift drag is all drag that is not related to the generation of lift.
It is a combination of:
Skin friction
Form drag - Size shape speed of the aircraft
Interference drag - Junctional areas of the aircraft wing root
At what angle is the general purpose wing AoA set at?
4deg AoA
What is the angle of incidence?
The angle at which the wing is bolted to the aircraft. 4deg - known as the riggers angle
What two factors make up total drag?
Lift dependant drag + Zero lift drag
What is the vector for Minimum total drag speed?
Vimd
Slow flight is conducted at a large AoA? T/F
True
In a turn, the centripetal force is a result of using what control surface?
Elevator
In a steady climb, lift is greater than weight? T/F
True
What does Rate of Climb performance depend on?
Excess thrust available
When a spin occurs, the RAF has separated and IAS is low? T/F
True
The total pressure in an airflow is?
The sum of its static pressure and dynamic pressure
Bernoullis equation states that
Total energy (Pitot) = Potential energy (static) + Kinetic energy (airspeed)
Lift acts opposite to?
But not aligned with, weight
Adding a fairing to streamline the flow will?
Decrease interference drag
Rolling is motion around what axis?
Longitudinal
What is a moment arm?
It’s the distance from the force to the axis
Rolling to the right requires
RH Aileron up
LH aileron down
