4 Primary Forces Flashcards
During unaccelerated flight, the four main forces are said to be
in a state of equilibrium
The product of mass and gravitational force is called
Weight
What is the centre of gravity?
The point through which the weight of a body acts
Wing loading is calculated how?
Weight of aircraft / Wing area
Wing loading is simply the
Weight supported per unit area of wing
The Bernoulli Principle
High flow gives low pressure
What term is given to layer of air closest to an aerofoil’s surface?
Boundary layer
What term is given to the point at which air within the boundary layer becomes turbulent and thickens significantly?
Transition point
When an airflow no longer follows a streamlined flow pattern, it has become..?
Turbulent
What term is given to the point at which the boundary layer separates from the aerofoil and becomes turbulent?
Separation point
The separation point is where what leaves the aerofoil?
Boundary layer
Describe the venturi effect in terms of pressure?
Pressure energy decreases, kinetic energy increases
Dynamic pressure equation
1/2 x rho x V-squared
Bernoulli’s principle states that increased velocity means
Decreased static pressure
The angle-of-attack is simply the,..
The angle at which the aerofoil is presented to the airflow
Camber is a term for what?
Curvature
Increasing the camber does what to airflow?
Airflow accelerates and generates greater lift
What causes the air to accelerate as it flows over an aerofoil?
An upwash is created and the air flows through a more constricted area
What term is given to the straight line between the ends of the camber line?
Chord line
The chord line connects the ends of what?
Mean camber line
What is the name of the measurement of a chord line’s length?
Chord
The distance between the mean camber line and chord lines called the?
Camber
The camber is the distance between what?
Mean camber line and chord line
What is the camber of a symmetrical aerofoil?
Zero
Lift’s equivalent of CoG is called what?
Centre of Pressure
The centre of pressure is…
The point at which the total reaction of the aerodynamic forces of an aerofoil act through
Total reaction has which two components?
Lift and drag
Lift and drag combine to form what force that acts through the centre of pressure?
Total reaction
Lift acts at what relation to the relative airflow?
Perpendicular
Drag acts at what relation to the relative airflow?
Parallel
What angle of the wing is AoA measured from?
Chord line
What is the angle of incidence?
Angle at which the wing is fixed to the airframe relative to longitudinal axis
What is the term given to the angle at which the wing is fixed to the airframe relative to longitudinal axis?
Angle of incidence
What term is given to the point at which the airflow comes to rest relative to the wing?
Stagnation point
If the Centre of Pressure moves forward, what is occurring?
AoA is increasing
AoA increasing has what effect on the Centre of Pressure’s position?
It moves forward
Air density is given what Greek letter?
Rho
The coefficient of lift is considered what?
Lifting ability of a wing at a given AoA
Equation of lift
Coefficient of Lift x 1/2 x Rho x V-Squared x Wing Surface Area
As wing shape is fixed, any change in Coefficient of Lift only occurs when what changes?
AoA
When is the Centre of Pressure at its furthest point forward?
Stalling AoA
The lift curve for a symmetrical aerofoil will give a Coefficient of Lift of 0 at what AoA?
0 degrees Angle of Attack
For a symmetrical aerofoil, 0 degrees AoA equattes to what Coefficient of Lift?
0
A laminar flow wing has what properties?
Low curvature that allows air to retain laminar flow over more of its surface than a cambered aerofoil
Laminar essentially means what in terms of airflow?
Streamlined
Laminar flow wing’s advantages over cambered aerofoil?
Same lift produced for less drag at cruise speed
The higher stalling speed of a laminar flow wing can be explained how?
The Maximum Coefficient of Lift is a lower value than the C-Lift Max for a well-cambered aerofoil
Longitudinal axis of the aircraft is important for what angle?
Angle of incidence
Air resistance is commonly known as what?
Drag
Types of drag can be split into what two categories?
Induced drag
Parasite drag
Induced drag is…
Drag associated with production of lift
Drag associated with production of lift is known as..?
Induced drag
Parasite drag consists of what 3 sub-categories?
Skin friction
Form
Inteference
For skin friction drag, what occurs within an increase in airspeed?
Increase of skin friction drag
For skin friction drag, what occurs within an increase in AoA?
Increase of skin friction drag
Form drag is created how?
Airflow separates from the surface
Eddies are formed
Streamline flow distrubed and thus increases drag
Skin friction drag is essentially the…
Friction forces between an object and air
How do designers reduce form drag?
Delay separation of the boundary layer from the surface
How does form drag result in stalling on a wing at high AoAs?
Pressure gradient on upper surface is too severe
Boundary layer no longer adheres to the surface
Separation occurs well forward near the leading edge
If you streamline a surface and decrease its curvature, what effect is had on the boundary layer?
Delaying separation of the boundary layer and reducing eddying
Interference drag can be thought of as drag occuring from..
Combined parts of an aircraft as a whole
Parasite drag’s relationship with airspeed
An increase in airspeed will increase parasite drag
Parasite drag increases in what manner with increased airspeed
As a square rule (V-squared)
Spanwise flow of induced drag on lower surface of wing?
Outwards from fuselage
Spanwise flow of induced drag on upper surface of wing?
Inwards towards fuselage
Why are wingtip vortices greatest at high values of C-Lift?
The pressure difference between upper and lower wing surfaces are greatest
Aspect ratio equation (span, chord)
Span / Chord
Aspect ratio equation (wing arrea, chord)
Area / Chord-squared
Why do tapered wings have weaker wingtip vortices?
Relatively, there is less wingtip so the induced drag is less
A wing whose AoA differs at the wingtip and wing root possesses what?
Washout
How does inbuilt washout reduce induced drag?
Wingtip AoA is lower than wing root AoA
Inbuilt washout means lift is produced where on a wing?
Predominantly by the inner part of the wing
WInglets or wing fences can reduced induced drag how?
Spanwise flow is reduced so induced drag is less
Why is induced drag greater at lower airspeeds?
AoA must increase to maintain given lift
Slower passage of air rearwards forms greater vortices and greater downwash
Greater downwash inclines local airflow downwards further
Lift force tilted further back
Stronger component of lift force is in the drag direction
Relationship between lift and induced drag
The greater the lift produced, the greater the induced drag
What occurs in a total drag graph
As airspeed increases:
Induced drag reduces
Parasite drag increases
Total drag initially decreases then increases
What drag predominates at low speeds?
Induced drag
What drag predominates at high speeds?
Parasite drag
Total drag is least when what is equal?
Parasite and induced drag
Minimum drag speed is where on a total drag graph?
Where the parasite drag and induced drag lines intersect
The point at which parasite drag and induced drag intersect on a total drag graph (and equal zero) is known as what?
Minimum drag speed
Minimum drag speed is considered the speed at which…
The wings produce lift to balance weighht but with minimum amount of drag possible
Drag equation
Coefficient of Drag x 1/2 x rho x V-Squared x S
The only difference between the equations for drag and lift are the presence of?
The respective coefficients (of lift or drag)
Lift/Drag Ratio is calculated how?
C-Lift / C-Drag
The AoA at the highest point of a Lift/Drag ratio curve can be described as
The most efficient angle of attack
With decreasing weight and flying at the same IAS, what happens to the AoA?
It decreases
With decreasing weight and flying at the same AoA, what happens to the airspeed?
It decreases
Using the AoA and C-lift equation, explain how IAS remains constant but TAS changes at different airspeeds?
Rho is less at higher altitudes, so V (in V-squared) must increase to maintain IAS
What type of airspeed is most important for AoA and lift considerations?
IAS
Why is IAS the most significant airspeed for AoA and lift considerations?
IAS is related to dynamic pressure, thus impacting aerodynamics
What does S denote in drag calculations?
Wing area
Wing area is denoted by what term in drag equations?
S
The axis upon which a propeller rotates is called the…?
Plane of rotation
Static pressure situation surrounding a propeller blade?
The static pressure ahead of the blade is less than that behind
Name of angle between chord line of a propeller and the plane of rotation?
Blade angle
The blade angle is the angle between what?
Propeller chord line and plane of rotation
Name of cambered side of propeller blade?
Blade back
Name of flat side of propeller bade?
Blade face
Name of angle between the resultant veolicty of the propeller blade and the plane of rotation?
Helix angle
The Helix angle is the angle between what?
Resultant velocity of the propeller blade and the plane of rotation
What two angles combine to form the blade angle of a propeller?
AoA + Helix angle
The AoA + Helix angle forms what angle for a propeller?
Blade angle
How does blade angle change from the hub of a propeller to its tip?
It decreases
Why does blade change decrease from the hub to tip of a propeller?
Greater velocity meeans less AoA needed
Approximately where on the propeller blade is thrust produced effectively?
Between 60% and 90% of the tip radius
Why is the direction of the relative airflow on a propeller and the direction of flight not parallel?
Rotational velocity offsets the forward motion of the aircraft
In theory, it is assumed that the direction of flight is what relation to the plane of propeller rotation?
Perpendicular
In theory, it is assumed that the direction of flight is perpendicular to what?
Plane of propeller rotation
Propeller torque is…?
Resistance to motion in the plane of rotation
For propellers, total reaction is divided into what two components?
Propeller torque force
Thrust
For the components of propeller torque force and thrust, which is related to the plane of rotation?
Propeller torque force
For the components of propeller torque force and thrust, which is related to the direction of flight?
Thurst
What is the angle between propeller torque force and thrust?
Perpendicular
Lift/drag comparative forces for propellers?
Lift is enngine torque and drag is propelller torque
Why does RPM increase in a dive with constant throttle position?
Relative airflow is changed
Forward speed increases
Propeller torque is reduced
Why does a propeller blade’s AoA decrease as speed increases at constant RPM?
Forward motion component is greater so the relative airflow hits the blade at a shallower angle
Why does a propeller blade’s AoA increase as speed decreases at constant RPM?
Forward motion component is less so the relative airflow hits the blade at a higher angle
At constant speed, why does a propeller blade’s AoA increase as the RPM increases?
Rotational motion component is greater so the relative airflow hits the blade at a higher angle
At constant speed, why does a propeller blade’s AoA decrease as the RPM decreases?
Rotational motion component is less so the relative airflow hits the blade at a shallower angle
For variable-pitch propellers, what pitch is optimum for lower airspeeds?
Fine pitch
For variable-pitch propellers, what pitch is optimum for higher airspeeds?
Coarse pitch
Fine pitch means what kind of pitch for a propeller?
Low pitch
Coarse pitch means what kind of pitch for a propeller?
High pitch
What happens to the AoA as RPM remains constant in a variable-pitch propeller?
It remain constant
Variable-pitch propellers are also known by what other name?
Constant-speed propellers
What kind of speed is referred to in the term ‘constant-speed’ for variable-pitch propellers?
RPM
Feathering a propeller does what?
Aligns the blades with the airflow
Slipstream effect causes an AoA to be created where?
Between the tailfin and slipstream airflow
Name of effect that occurs with propellers under high power conditions?
Slipstream effect
A clockwise-rotating propeller will possess effects that will yaw an aircraft in what direction?
Left
When discussing fine and coarse pitch, these terms are described relative to what?
Plane of rotation
For a propeller diagram, what is represented by the x-axis?
Forward motion of a propeller blade
For a propeller diagram, what is represented by the y-axis?
Rotational motion of a propeller blade
For a propeller diagram, a higher airspeed does what to the ‘triangle’?
Lengthens its base
Hypotenuse strikes blade at reduced angle
For a propeller diagram, a higher RPM does what to the ‘triangle’?
Lengthens its height
Hoptenuse strikes blade at greater angle
For a propeller diagram, what two ‘triangle’ transformations will increase the AoA?
Reducing the base (reducing the forward speed)
Increasing the height (increasing the RPM)
For a propeller diagram, what is the hypotenuse?
Resultant velocity of propeller blade through the air
What is the influence of wing aspect ratio on induced drag?
High aspect ratio (long thin wing) = less induced drag
Relationship between wake vortices and induced drag
The smaller the vortices, the lower the drag
Why does smaller width of a wing reduce induced drag?
There is less spillage of high pressure beneath the wing onto the lower pressure above the wing
Name the two types of boundary layer associated with an aerofoil?
Laminar and Turbulent
As speed increases, what happens to the Transition Point?
It moves forward towards the leading edge
The transition point moving forward (as speed increases) has what effect?
More turbulent flow and increased drag
What are the key differences between the laminar boundary layer and turbulent boundary layer?
The turbulent layer is thicker
The turbulent layer has high skin friction drag
The turbulent layer is more resistant to separation whereas the laminar layer is very unstable
What three effects are experienced by the aircraft in ground effect?
Aerofoil produces more lift since the Total Lift Vector is more perpendicular to the ground
Induced drag vector is reduced
Wingtip vortices are reduced
Why does an aerofoil produce more lift during ground effect?
Relative airflow becomes flatter and the Total Lift Vector maintans its perpendicular angle by angling forward
