8.2 Flashcards
Dynamic pressure
The pressure on the surface of a body, which causes moving air to stop.
Depends of density and velocity.
Flow continuity
When water flows through a duct, mass flow is the same at any point.
Convergent duct
Velocity increases
Pressure and temperature decreases
Divergent duct
Velocity decreases
Pressure and temperature increases
Bernoullis principle
Total pressure is constant if no work is done to it
Stagnation point
Point where the air separates over and below the wing
Airspeed indicator
Uses pitot pressure inside capsule and static pressure outside capsule to measure dynamic pressure.
Indicated airspeed
Speed of aircraft measured by its pitot static system and displayed on the airspeed indicator.
Calibrated airspeed
Indicated airspeed corrected for instrument and position error
Equivalent airspeed
Calibrated airspeed corrected for compressibility
True airspeeed
Equivalent airspeed corrected for density
Ground speed
Airspeed minus windspeed
What displays display what airspeeds?
PFD displays IAS and Mach number
ND displays GS and TAS
Mean camber line
Line joining leading and trailing edge curving at the very middle.
Fineness ratio
Ratio of the chord to the thickness
Camber
Different between mean camber line and chord line
Relative airflow
Vector sum of aircraft forward speed and airflow resulting from any vertical of the aerofoil.
Angle of attack
Angle between chord line and relative airflow.
If aerofoil is descending, relative airflow will flow upward increasing the angle of attack.
Newton’s third law
Every action has an equal and opposite reaction
Drag
Parallel with relative airflow.
If thrust is greater than drag, aircraft will accelerate to where they equal again causing a steady state.
Aerodynamic resultant
Sum of lift and drag
Dorsal fin
Vertical stabiliser is above the fuselage
Wash out
Decrease in wing angle of incidence from root to tip.
Improves stability.
Wash in
Increase angle of incidence from root to tip.
Decrease stability of wing.
Mean Aerodynamic chord (MAC)
Wing area over wing span
Aspect ratio
Span over chord
Dihedral
Upward angle of wing increasing stability
Wing loading
Weight of aircraft divided by wing area
Angle of incidence
Angle between chord line and a reference axis along fuselage.
If aircraft is flying straight and level, the AOI will equal the AOA.
Two types of Boundary layers
Laminar flow: layers move smoothly in parallel
Turbulent flow: irregular pattern of flow
Laminar vs Turbulent
Laminar is thinner and smoother producing less drag.
Turbulent contains more energy as turbulent molecules interact with free stream air and gain energy.
Upwash
Air flows upwards just before leading edge due to the boundary layer.
Downwash
Downward movement of air over wing.
Decreases angle of attack.
Vortices
Formed when air flows from higher pressure (under) to low pressure (upper).
Any two flows of air meet at an angle forms a vortex.
Reynolds number
Determines wether a flow is laminar or turbulent.
When does boundary layer separation occur?
High speeds - turbulent separation close to trailing edge.
Low speeds - separation is moved forward, causing stall.
3 types of Profile drag (parasite)?
Skin Friction drag
Form drag
Interference drag
Skin friction drag
Caused by friction of fluid against the surface of an object.
Reduced by smoothing the surfaces and polishing.
Transition point
Point where laminar turns to turbulent
Form drag
Also known as pressure drag.
Separation of the boundary layer from a surface and the wake created by the separation.
Reduced by streamlining (fairings).
50% of total drag.
Interference drag
Caused by the mixing of airflow streams between airframe components e.g. wing and fuselage.
Reduced by using fairings and fillets.
Drag coefficient
Lower drag coefficient means less drag
Induced drag
Where high pressure below and low pressure above meets at the wing tip causing vortexes producing drag.
Larger the lift, larger the pressure difference meaning greater vertexes.
Proportional to lift, inversely proportional to the square of speed.
Induced downwash
Effect of vortex deflects air downwards creating additional downwash.
Increased downwash at trailing edge reduces angle of attack reducing lift.
Span effect
Higher the aspect ratio, less induced drag.
Greater the cord length at wing tip the more intense the vortex becomes.
Induced drag and lift
As angle of attack increases the induced drag increases
Profile drag and induced drag in relation to speed
Profile drag increase with speed.
Induced drag decreases with speed.
Wave drag
Retards forward movement of the plane.
Caused by the formation of shock waves.
Does an aerofoil produce more lift or drag
Produces more lift many times greater than drag.
Angle of attack will cause…
Centre of pressure to move forward
Transition point to move forward
Separation point to move forward
Stagnation point to move down and aft
When does windspeed move quicker? (Pressure)
Low pressure
Symmetrical vs cambered (centre of pressure?
Symmetrical remains constant
Cambered varies with angle of attack
Centre of pressure in terms on location?
Small angles of attack 40-50% of chord, doesn’t exceed 25%.
Moves forward as angle of attack increase but rapidly moves back when stalling.
Stalling angle?
16 degrees
Dynamic pressure formula?
1/2 pV^2
At zero angle of attack (Cambered vs Symmetrical), lift?
Cambered produces some lift and some drag.
Symmetrical produces no lift but some drag. (Stalls at a higher angle of attack)
How to maintain altitude with decreasing air density?
Increase angle of attack
Increase airspeed
What happens to the camber and AOA when flaps are deployed?
They’re both increased
What happens to camber and AOA when leading edge slats are deployed?
Camber is increased
AOA is decreased
But when the slats are deployed with the flaps they increase AOA
Lift/drag ratio
Steady increase up until 4 degrees
(Most amount of lift with least amount of drag also known as the optimum angle of attack).
Deteriorates up until 15 degrees then it stalls.
Polar curves
Coefficient of lift vs coefficient of drag
Can vortexes generate lift?
Yes, the energy in a vortex’s can be extremely high
How does a stall happen?
When airflow has broken away from most of the upper surface.
Where does the separation point move as AOA increases?
Starts at trailing edge and progressively moves forward.
What does stall depend on?
Only on AOA
How to maintain level flight with heavy aircraft?
Amount of lift must be equal to weight.
Increase AOA.
It will therefore stall at a higher airspeed.
Load factor
Total lift over aircraft weight.
Ratio of load acting on aircraft during a manoeuvre vs straight and level flight.
Stalls during manoeuvres due to an increased load factor?
Accelerated stall
How to maintain altitude on low density?
AOA is increased.
Higher airspeed.
What happens if speed increases past mach number?
Cause a stall due to shockwaves
Coffin corner
Altitude where stall speed is equal to critical Mach number
