Chapter 1 - Basic Aerodynamic Principles of Flight Flashcards
What factors affect density in the atmosphere?
Temperature
Altitude
Water vapour
Pressure
What is Newton’s First Law?
Inertia
What is Newton’s Second Law?
Force
What is Newton’s Third Law?
Action/Reaction
What is momentum?
Mass x Velocity
The property a moving object has due to its mass and velocity.
What is Bernoulli’s Theorem?
p + 1/2rhoV^2 = Constant
Static Pressure + Dynamic Pressure = Total Pressure
I.e.: Pressure Energy + Kinetic Energy = Constant
What energy does a gas in steady state motion have?
Potential energy
Heat energy
Kinetic energy
Pressure energy
What is the chord line?
A line joining the leading and trailing edges of an aerofoil section.
What is the chord?
Distance between the leading and trailing edge, measured along the chord line.
What is camber?
The curvature of the aerofoil (above and below the chord line?)
What is the mean camber line?
A line equidistant from the upper and lower surfaces of an aerofoil section.
What is the angle of incidence?
What is another name for this?
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 (RAF)?
Direction of the airflow remote from the aircraft and UNAFFECTED by its presence.
Aka freestream flow
OR
Air in the region where pressure, temperature and relative velocity is unaffected by the passage of the aerofoil through it.
What is Angle of Attack (AoA)?
The angle between the chord line and the relative air flow (RAF).
What is wing span?
The max lateral dimension of a wing.
What is aspect ratio?
Wing span divided by mean chord.
AR = Span/Mean Chord
What is wing area?
The PLANFORM area of the wing.
Describe a high AR wing and a low AR wing?
High = Long and thin (thin chord)
Low = Short and stubby
What is taper?
The change of the chord of the wing from the wing root to wing tip.
Helps reduce LDD at the wingtip (less vortex drag) and improves lateral stability.
What is the transition point?
The point on the aerofoil where the boundary layer becomes turbulent and thickens.
What direction is the force of Lift?
Perpendicular to the relative air flow
What direction is the force of Drag?
Perpendicular to the force of lift OPPOSING MOTION
Where do lift and drag appear to act from?
The centre of pressure (CP)
Moves rearwards with decreasing AoA and forwards with increasing AoA.
What is the Total Aerodynamic Reaction?
The result of the combination of lift and drag into a single component.
What does pressure distribution depend on?
The shape of an aerofoil
Aerofoil attitude to relative airflow
Air density
Velocity
What is the amount of lift generated dependant on?
Free stream velocity
Air density
AoA
Wing shape (S)
Wing shape and planform
Speed of sound
How does wing sweep affect CL?
Swept wings produce less CL at a given AoA, but they stall at a higher critical angle.
How does AR affect CL?
High aspect ratio produces more CL for a given AoA but stalls at a lower AoA, i.e. crit AoA is lower.
How does wing surface affect CL?
A smooth wing and rough wing will produce the same CL at a set AoA, but a rough wing will stall at a much lower AoA, whereas the smooth wing can continue to fly at higher and higher AoAs, continuing to increase CL.
How does AoA affect the amount of downwash?
Higher AoA increases the amount of downwash.
how does downwash affect the RAF.
Changes the angle such that the effective AoA is reduced. This tilts the lift component rearwards, reducing the amount of lift (acting vertically upwards).
What are the two types of drag?
Zero Lift Drag
Lift Dependent Drag
What comprises ZLD?
Surface friction drag
Form drag
Inference drag
How can we reduce form drag?
Streamlining
What causes interference drag?
Flow inference at:
Wing/fuselage
Wing/nacelle
Wing/external weapons/fuel tanks/pods
How can we reduce interference drag?
Fairings, aerodynamic shapes, internal stowages
What causes form drag?
Separation of the airflow from a surface
Forms eddies which disrupt the streamline flow, these create a turbulent wake which increases drag.
What factors affect vortex formation?
Wing planform Aspect ratio Lift and Weight (more weight needs more lift, higher CL = stronger vortices produced) Speed (increases lift) AoA (increases CL)
Note - Quickly check up on the downwash notes, being produced by trailing vortices, reduces effective AoA, therefore need to increase AoA, which increases lift and causes more Lift Induced Drag
Check now
What methods can be used to reduce induced drag?
Winglet Tip tank/missile Taper High AR Washout Change of aerofoil section
Which type of drag is dominant at high speeds and which is dominant at low speeds?
LDD = Low speeds
ZLD = High speeds
What is Vimd?
Speed for best Lift/Drag ratio
What is Vmp?
Minimum power setting
What is speed for the max speed/drag ratio?
Vimd x 1.32
What is adverse aileron yaw?
When rolling, the upgoing wing (aileron down) will be producing more lift. This increases Lift Induced Drag, causing the aircraft to yaw up towards this wing.
Therefore, when banking right, apply a bit of right rudder during the bank and vice versa.
What is the main purpose of slats?
Prolong the lift curve
Delay the stall until a higher AoA
By re-energising the boundary layer at higher AoAs
What is the affect of flaps?
Increase CL generated at a set AoA
Stall at a lower AoA, however can fly at a lower AoA for a set lift a lower speeds, allows lower speeds to be reached and a steeper approach to be made at a set speed (better vis is an added bonus)
Extra drag due to extra lift being produced
How do flaps increase Lift?
Increased camber
Change of chord and subsequent increase in AoA
Increase in wing surface area
Why does the nose pitch up when flaps are deployed?
Low horizontal tail = Increase in downwash over the horizontal plane/elevator
High horizontal tail = Rearward movement of the CP due to more lift being produced
What are the types of spoilers?
Flight spoilers - Can be used as speed brakes
Roll spoilers - Asymmetric deployment to enhance roll response
Ground spoilers - All spoilers extended to max angle during landing, dump lift generated by the wing and so help force the full weight of the aircraft onto the landing gear, improving wheel brake efficiency. Also cause aerodynamic drag.
What are the two types of trim tab?
Fixed tab - set on the ground prior to flight
Trim tab - Operated from the cockpit in flight
Trim tabs deflect in the opposite direction to the control surface they are holding.
