Basic Aerodynamics Flashcards
Bernoulli principle
What is the basic definition of Bernoullis therom?
Air forced through a restriction speeds up
As space decreases, flow speed increases
Mass airflow remains constant but as mass flow increases, temperature and pressure decrease
What is the Dynamic Pressure equation?
q = 1/2 p V^2
q = Dynamic pressure
p = rho
V = velocity
dynamic pressure + static pressure = ?
Total Pressure
Total pressure = ? + ?
dynamic pressure + static pressure
SAME AS:
Ps + 1/2 p V^2
What type of airflow is defined below?
Successive molecules of air follow the same steady path
Streamline flow
What type of airflow is defined below?
Molecules of air do not follow a steady path
Turbulent flow
Airflow above the wing is deflected TOWARDS or AWAY from the fuselage?
TOWARDS
Airflow below the wing is deflected TOWARDS or AWAY from the fuselage?
AWAY
What is the definition of vortex wake
Spanwise flow above and below the wing meet and create a vortice
What is the definition of the boundary layer
The layer of decreasing airspeed caused by skin friction
At surface, airflow is stationary
As distance increases from aerofoil, air molecule speed increases
What is the speed of air molecule flow at the surface of an aerofoil
Stationary
What happens to airflow the further higher the molecules are in the boundary layer?
Increase until they reach the relative airflow (99%)
What direction does the Transition Point move in relation to the leading edge as speed increases
FORWARD towards the leading edge
What are the 2 flows within the boundary layer
Laminar Flow
Turbulent Flow
What is the definition of laminar flow
Air molecules sliding over each other
Thin layer
Low skin friction
What is the definition of turbulent flow
Air molecules bumping into each other
Thick layer (cm)
High skin friction
How prone are the airflows to flow seperation
Laminar flow - MORE or LESS
Turbulent flow - MORE or LESS
Laminar - MORE
Turbulent - LESS
Assume asymmetric aerofoil
What is the name of the straight line that joins the leading edge to the trailing edge
CHORD LINE
Assume asymmetric aerofoil
What is the name of the curved line that joins the leading edge to the trailing edge
CAMBER LINE
What is the equidistant line between the upper and lower surface of an aerofoil known as
MEAN CAMBER LINE
What is the maximum distance between the chord line and the mean camber line known as
MAXIMUM CAMBER
What is the following
Maximum thickness divded by chord
Thickness/Chord Ratio
What is the angle of incidence
Angle between the chord and longitudinal centre line of aircraft fuselage
Lift Factors
The amount of lift produced is influenced by which factors
Air speed
Air density
Angle of attack
Aerofoil Shape
Lift = 1/2 p V^2 S CL
The Centre of Pressure (CoP) moves FORWARD or AFT from the leading edge with an increased AoA
FORWARD
Which direction does the stagnation point move with an increase of AoA
Moves down the leading edge to the underside of the aerofoil and aft
Presents high pressure air to the stall warning device
If airspeed increases, MORE or LESS lift is produced
MORE
MORE lift means MORE or LESS drag
MORE
CLcrit is the point of what
Stalling AoA
The best glide speed is determined by what
The maximum Lift/Drag ratio
How many feet in 1nm
6080 ft = 1nm
An aircraft has a L/D ratio of 10:1
Given a height loss of 6000 ft, how far will the aircraft travel in nautical miles (nm)
9.87 nm
6000 ft x 10 = 60,000 ft travelled
6080 ft in 1nm
60,000 / 6080 = 9.87 nm
For every 1 ft of height loss, the aircraft travels 10 ft, ratio 10:1
What are the 2 types of drag represented in the drag curve
Parasite (Form) Drag (Dp)
Induced Drag (Di)
Induced drag is caused by what
LIFT
Induced drag only exists once lift is being created
Form (Zero lift) drag is made up from what
Non aerodynamic parts;
Examples;
Interference drag (i.e. wing meets the fuselage)
Fuselage rivets
Aerials
What is the Zero Lift Drag (Form) formula
Dp = 1/2 p V^2 S CD0
Drag = half x rho x V squared x surface area x Form Drag coefficient
D0 = 1/2 p V^2 S CD0
If airspeed doubles, what happens to drag?
Quadruples
Airspeed is squared. So doubling airspeed will quadruple drag
Airspeed vs Drag
1 = 1
2 = 4
3 = 9
4 = 16
As airspeed increases
Form drag INCREASES or DECREASES
Induced drag INCREASES or DECREASES
Form drag = INCREASES
Induced drag = DECREASES
As airspeed decreases
Form drag INCREASES or DECREASES
Induced drag INCREASES or DECREASES
Form drag = DECREASES
Induced drag = INCREASES
Induced Drag INCREASES or DECREASES with an increase in AoA
INCREASES
For aircrafts at same speed and altitude;
Higher weight needs MORE or LESS lift
MORE
For aircrafts at same speed and altitude;
MORE weight needs MORE lift
LESS weight needs LESS lift
For a given speed, high altitude implies MORE or LESS induced drag
MORE
Air pressure is less at high altitude. For the same aircraft with the same TAS at higher altitude, to maintain lift, an increase in AoA is required.
An increase in AoA impies MORE induced drag
What is a typical wing design type if the wing is a high aspect ratio
Long and thin
Glider
Glider AR - 30:1
MRJ AR - 10:1
Fighter Jet AR - 2:1
What is a typical wing design type if the wing is a low aspect ratio
short and thicker
Delta Wing
Fighter Jet
Glider AR - 30:1
MRJ AR - 10:1
Fighter Jet AR - 2:1
a low aspect ratio wing has MORE or LESS induced drag
MORE
The more wing tip length there is, the more air that can spill from lower to upper aerofoil surface, which means more induced drag
What is the definition and effect of washout
AoA at wing tip is lower than at the root
REDUCED vorticies
REDUCED induced drag
What is the Aspect Ratio (AR) formula
span / mean chord OR;
span^2 / area
What is ground effect
Ground “gets in the way” of upwash and downwash
Typical within 1x wing span height from the ground
What effect does ground effect have on wing tip vorticies
REDUCES their strength
What effect does ground effect have on effective air flow
REDUCES the angle
EAF becomes more like RAF
What is the relationship between airspeed and induced drag
Drag increases at a rate of the inverse square of the square of the airspeed
More speed means less AoA needed for lift
Less AoA means less vortices = Less inducted drag
As speed increases, induced drag decreases
A SEP aircraft accelerates in flight. To maintain constant lift (i.e. straight and level flight), what must the pilot do
REDUCE AoA
Refer to lift formula.
If Speed is increased, this is squared. V^2 is therefore increased
If an element is increased, lift increases.
To maintain a constant, another element must be decreased
Reduce AoA reduces the Coefficient of lift (CL) meaning lift remains constant
Which direction does aerodynamic drag act in, in relation to an aircraft in motion
OPPOSITE DIRECTION
