Aerodynamics Flashcards
Vector
a quantity that represents magnitude and direction. It is commonly used to represent displacement, velocity, acceleration, and force
Displacement
the distance and direction of a body’s movement
Velocity
speed and direction of a body’s motion (the rate of change of position)
Acceleration
rate of a body’s change of velocity
Force
How is calculated?
push or pull exerted on a body
Force is mass X acceleration
A vector is represented by a(n)?
arrow. The length of the arrow represents the magnitude and the heading of the arrow represents the direction.
Can vectors be added together?
Vectors may be added by placing the head of the first vector on the tail of the second and drawing a third vector from the tail of the first to the head of the second. This new vector is the resulting magnitude and direction of the original two vectors working together.
Mass (m)
quantity of molecular material that comprises an object.
Volume (v)
amount of space occupied by an object
Density (ρ)
mass per unit of volume (Mass divided by Volume)
Work (W)
How is calculated?
when a force acts upon a body and moves it
a scalar quantity equal to the Force (F) times the distance of displacement (s), or W = F × s
Power (P)
rate of doing work or work done per unit of time (t)
or P = W / time
Horsepower
a unit of measurement used to express the amount of power being produced. Horsepower is calculated by dividing the results of either power formula above by 550 (this is a unit conversion using the units of pounds, feet, and seconds)
Weight (W)
force with which a mass is attracted toward the center of Earth by gravity
Moment (M)
How is it calculated?
what is created when a force is applied at some distance from an axis or fulcrum, producing rotation about that point.
The distance from the axis or fulcrum to the point of force is called the Moment Arm
Moment = Force x Distance
Energy
What are the two forms?
a scalar measure of a body’s capacity to do work. There are two forms of energy: potential energy (P.E.) and kinetic energy (K.E.). Total energy (T.E.) is the sum of potential energy and kinetic energy
Energy is required for work (W)
Potential Energy (P.E)
the ability of a body to do work because of its position or state of being. Potential energy is a function of mass, gravity, and height (MGH)
Kinetic Energy (K.E.)
the ability of a body to do work because of its motion. It is a function of mass and velocity
Energy cannot be created nor destroyed but may be ____ from one form (potential or kinetic) to the other. This principle is called ____ of energy.
For example, if a T-6A is in level, unaccelerated flight at a constant altitude and airspeed, both kinetic and potential energy are ____ .If you were to push the nose over you would lose altitude (____ energy) but “transform” that altitude loss into increased airspeed (____ energy) (Figure 1-10).
transformed
conservation
constant
potential
kinetic
What is Newton’s First Law called? What does it say?
The first law is the “Law of Equilibrium.”
“A body at rest tends to remain at rest and a body in motion tends to remain in motion in a straight line at a constant velocity unless acted upon by some unbalanced force.”
Describes inertia
What is Newton’s Second Law? What does it say?
Newton’s second law is the “Law of Acceleration”:
“An unbalanced force acting upon a body produces an acceleration in the direction of the force that is directly proportional to the force and inversely proportional to the mass of the body.”
When the thrust of an aircraft is greater than its drag, the excess thrust will cause the aircraft to accelerate until the increasing drag equals thrust.
What is Newton’s Third Law? What does it say?
Newton stated a third law, the “Law of Interaction.”
“For every action, there is an equal and opposite reaction.”
This law is demonstrated when the rearward force from an aircraft propeller’s prop wash causes an aircraft to thrust forward with an equal amount of force
What are the three characteristics of air?
Pressure, Temperature, and Density
Ambient static pressure
How does it change with altitude?
a measurement of the weight of an air column over a specific area.
As altitude increases, there are fewer particles in a given column of air, thus ambient static pressure is less because the column of air above you weighs less
Air density
How does it change with altitude?
the total mass of air particles for a given volume.
As altitude increases, the distance between particles is greater (fewer particles of air for a given volume). This means that as altitude increases, air density decreases.
Temperature
How does it change with altitude?
Temperature is the measure of the average kinetic energy of the air particles.
Air temperature decreases at a rate of 2 °C for every 1000 feet. This is called the average, or standard, lapse rate.
What does the General Gas Law describe?
relationship between four basic atmospheric properties
(P) Pressure
(ρ) Density
(T) Temperature
(R) Universal Gas Constant
Fluid
any substance, liquid or gaseous, that has the ability to flow. Our atmosphere is a “gaseous fluid,” which means “airflow” is subject to the laws of fluid motion.
What are the three types of pressure?
Static pressure, dynamic pressure, and total pressure
Static Pressure (Ps)
the force that molecules of air exert on each other by their random movement
Dynamic Pressure (PD)
a measure of impact pressure of a large group of air molecules moving together
Total Pressure (PT)
sum of static and dynamic pressure
What 3 things must remain constant in a streamtube?
Mass, Total Energy, and Total Pressure
If the cross-sectional area on one side of streamtube decreases, what must increase so that mass flow remains constant?
Velocity
What are the 3 types of altitudes?
True altitude, Pressure altitude, and Density altitude
True altitude
actual height above mean sea level (MSL)
Pressure altitude
a height measured above a standard datum plane.
The standard datum plane is the actual elevation at which the barometric pressure is equal to 29.92 inHg which means on a standard day: pressure altitude = true altitude
Density altitude
pressure altitude corrected for temperature deviations from the standard atmosphere. Density altitude is not used as an actual “height reference” but rather as an index for gauging aircraft performance
On a standard day, what altitudes are equal?
All of them
True = Pressure = Density
What happens to aircraft performance as Density Altitude is increased? Why does this happen?
Performance will decrease
because less engine power is produced when fewer air molecules are available to burn and because a propeller creates less thrust when it has fewer air molecules to push aft.
A high DA requires ___ true airspeeds for takeoff and landing resulting in ___ takeoff and landing distances
higher and longer
True Airspeed (TAS)
the actual speed at which an aircraft moves through an airmass
Groundspeed (GS)
How does it compare to TAS?
the speed at which an aircraft moves relative to the ground.
It is true airspeed corrected for winds
Indicated Airspeed (IAS)
the speed that the pilot reads off the airspeed indicator
How does the airspeed indicator work?
The airspeed indicator shows dynamic pressure. It takes the total pressure of the air through the pitot tube and subtracts the static pressure from the static port to obtain dynamic pressure or IAS
The airspeed indicator is calibrated at the factory for standard day at sea level, where IAS equals TAS. What happens to TAS if IAS is held constant while climbing to a higher altitude?
Since air density decreases with an increase in altitude, TAS increases if IAS is held constant while climbing to a higher altitude.
at a constant IAS, TAS increases approximately 3 knots for each 1,000 foot increase in altitude
Calibrated airspeed (CAS)
indicated airspeed corrected for either indicator error or for minor sensing errors caused by the location of the pitot-static system on an airplane (can be mostly ignored for subsonic airspeeds)
Equivalent airspeed (EAS)
calibrated airspeed corrected for errors caused by compressibility effects (can be mostly ignored for subsonic airspeeds)
Airfoil
a streamlined shape designed to produce lift as it moves through the air
Mean Camber Line
the major design feature of an airfoil. It is a line drawn from the leading edge to the trailing edge, halfway between the upper and lower surface of the airfoil
Chordline
an infinitely long straight line drawn through the leading and trailing edges of the airfoil
Chord
the segment of the chordline measured from the leading edge to the trailing edge
Root chord, Tip chord, and Average chord
The root chord is the chord at the wing root, and the tip chord is the chord measured at the wingtip. Average chord is the average of all chords from the wing root to the wingtip.
Camber
the curvature of the mean camber line of an airfoil. Camber is measured by finding the maximum distance between the mean camber line and the chord line.
Symmetric Airfoil
A symmetric airfoil has zero camber. The MCL and chord are the same. There is as much cross-section above the chord as below the chord, hence the term symmetric
Positively cambered Airfoil
A positively cambered airfoil has the MCL above the chord. There is more cross-section above the chord than below the chord. This cambered airfoil produces lift at zero angle of attack.
Negatively cambered Airfoil
A negatively cambered airfoil has the MCL below the chord. There is more cross-section below the chord than above the chord. You have probably seen negatively cambered airfoils on high-performance race cars.
Spanwise Flow
airflow that travels along the span of the wing, parallel to the leading edge
This airflow does not accelerate over the wing and therefore does not create liftC
Chordwise Flow
air that flows at right angles to the leading edge of the airfoil
Since it is the only flow that accelerates over a wing, it is the only airflow that produces lift
Pitch Attitude
the angle between the longitudinal axis of an airplane and the horizon
Flightpath
an aircraft’s apparent motion through an airmass
Relative wind
the apparent motion of the air with respect to the motion of the aircraft. The relative wind is in the direction opposite the flightpath.
Angle of Attack (AoA)
the angle between the chordline of the airfoil and the relative wind
Do NOT confuse this with pitch attitude.
Angle of Incidence
the angle between the airplane’s longitudinal axis and the chordline of its wing
Dihedral Angle
The angle of the upslope or downslope of the wings when viewed from head on.
Upslope is considered dihedral, and a downslope or negative dihedral is called anhedral.
Wingspan
What is the T-6A’s wingspan?
he distance from wingtip to wingtip
The T-6A wingspan is 33 feet 5 inches.
Wing area (S)
How is it calculated?
he apparent surface area of a wing within an outline of the wing on the plane of its chord. It is approximated by multiplying the wingspan (b) by the average chord (c)
Wing loading (WL)
the ratio of an aircraft’s weight to the surface area of the wings or WL = Weight / S.
Wing Taper
reduction in the chord for a given airfoil from the root to the tip, and is measured by dividing the tip chord by the root chord
What is the benefit of tapered wings?
Tapered wings provide reduced weight and increased structural stiffness compared to a rectangular wing.
Sweep Angle?
the angle between the quarter chord line (a line that is 25% of the chord and not parallel to the leading edge) and a line parallel to the lateral axis of the aircraft
The T-6A wing is both?
tapered and swept
Aspect Ratio (AR)
ratio of the wingspan (b) to the average chord (c)
What is an example of an aircraft with a high aspect ratio and an example of a low aspect ratio?
An aircraft with a high aspect ratio (35:1), such as a glider, would have a long slender wing
A low aspect ratio (3:1) indicates a short stubby wing such as an F-22
What 3 things define an airplane’s Center of Gravity (CG)?
-where the 3 axes intersect
-where all weight is concentrated
-point which movements are measured
3 axis of rotation
Longitudinal/Roll/Ailerons
Lateral/Pitch/Elevator
Vertical/Yaw/Rudder
Aerodynamic center (AC)
the point where all aerodynamic forces are acting (also known as center of lift)
How is the aerodynamic center typically positioned compared to the center of gravity?
The aerodynamic center (AC) point is typically aft of the aircraft’s CG to provide improved longitudinal stability around the lateral or pitch axis.
Weight and balance is concerned with the position of the CG in reference to the?
mean aerodynamic chord (MAC)
if the aircraft CG is too far aft, there will not be enough elevator authority to maintain level flight (the airplane will want to continue to pitch up into an eventual stall). If it is too far forward the opposite happens
Mass/Volume represents?
Density
What is done when a force acts upon a body and moves it?
Work
Which of Newton’s Laws state that “a body at rest tends to remain at rest and a body in motion tends to remain in motion…unless acted upon by some unbalanced force”?
Law of Equilibrium
The measurement of the average kinetic energy of air particles is called
Temperature
**(True/False) Dynamic pressure is the measurement of force that molecules exert on each other in a still fluid.**
True (need clarification for this one)
In a streamtube, where is the greatest total pressure?
The total pressure is the same everywhere
As the area of the streamtube decreases?
Velocity increases
A higher than standard day density altitude will do what to the takeoff roll?
increase takeoff roll (and decrease climb performance)
(T/F) Groundspeed is indicated airspeed corrected for winds.
False. Groundspeed is TRUE AIRSPEED corrected for winds
True Airspeed (TAS) must ____ as you climb in altitude with a constant indicated airspeed (IAS)
increase by ~3 knots per 1000 feet
The apparent motion of the air with respect to the motion of the aircraft is defined as the
Relative wind
Angle of Attack is the angle between the
relative wind and chordline
What is the benefit of a tapered wing?
Structural stiffness
What kind of aircraft have a very high aspect ratio?
Gliders
Having a CG that is too far aft causes the aircraft to exhibit
a tendency to pitch up into a stall
What is the point from which movements in roll, yaw, and pitch axes are measured
Center of gravity
The axis about which the airplane’s nose moves up and down is the
lateral or pitch axis
What is created when a force is applied some distance from an axis, producing rotation
Moment
Mass per unit volume defines?
Density
The ability of a body to do work due to its position or state of being
Potential energy
“For every action there is an equal and opposite reaction.”
The Law of Interaction
True airspeed will be ____ indicated airspeed at 10,000 feet altitude.
greater than
What is a measure of the wing along the chordline, from the leading edge to the trailing edge?
the chord
Air density is ____ at 10,000 feet compared to 5,000 feet
lower
Altimeter setting for a standard day? What altitudes are equal?
29.92; pressure altitude = true altitude (and DA if temp is standard)
What is the point at which all weight is concentrated?
Center of Gravity
What axis is where the aircraft nose moves left or right about the Cg?
Yaw
What are the four primary forces acting on an aircraft in flight?
Weight, Lift, Thrust, and Drag
Equilibrium
Absence of acceleration (an aircraft in SLUF)
Does an aircraft have to be in straight and level flight to be in equilibrium?
No. An aircraft can be climbing but not accelerating or decelerating. In a climb or descent, equilibrium occurs when lift equals the “perpendicular” component of weight and thrust is equal to the sum of drag plus the “parallel” component of weight.
This means that for equilibrium flight in a climb or descent, the thrust component must be greater in a climb or less in a descent than it is for unaccelerated level flight.
During the takeoff ground run, ___ exceeds ___ (and friction) and ___ exceeds ___
thrust exceeds drag (and friction) and weight exceeds lift
At liftoff, ___ exceeds ___. ____ still exceeds ____ as the aircraft accelerates.
lift exceeds weight; thrust still exceeds drag
Aerodynamic force
a force that is the result of pressure and friction distribution over an airfoil (Lift and Drag)
The aerodynamic force acting perpendicular to the relative wind
Lift
The aerodynamic force acting parallel and in the same direction as the relative wind
Drag
The pressures acting on an airfoil are the result of
dynamic pressure (the air is being accelerated around the airfoil which decreases static pressure both above and below it)
On a positively cambered airfoil, the static pressure above the airfoil is
less than the static pressure below the airfoil. This differential pressure causes lift in the upward direction
What is the Lift equation?
Lift = Cl 1/2 p V^2 S
What three lift equation factors can a pilot control?
Velocity, Angle of Attack, and Shape (or camber)
What is the relationship between CL and AOA?
CL increases with increasing AOA until reaching CLMAX
The AOA that corresponds to CLMAX point is called the critical angle of attack
What happens if you increase aircraft AOA beyond the critical angle of attack?
a decrease in coefficient of lift due to boundary layer separation. This loss of lift is called a stall.
In straight-and-level flight, as angle of attack is increased, the pilot has to
decrease velocity to maintain level flight
Does a symmetric airfoil produce lift at 0 AoA? Why or why not?
No. Airflow over the top of a symmetric airfoil at zero degrees AOA travels the same distance as airflow over the bottom surface. This results in identical changes in static pressure both above and below the airfoil. Since no differential in pressure exists, no lift is produced.
Does a cambered airfoil produce lift at 0 AoA? Why or why not?
Yes. At zero degrees AOA, airflow over the upper surface of a positively cambered airfoil must travel a greater distance as compared to the bottom surface. This increased dynamic pressure results in a lower static pressure on the upper surface compared to the lower surface. The static pressure differential pulls the wing upward, creating a lift force
Aerodynamic twist
What does it do for an airfoil?
a decrease in camber from the wing root to the wingtip
Since a positively cambered airfoil stalls at a lower angle of attack, the wing root will stall before the wingtip.
Geometric twist
What does it do for an airfoil?
a decrease in the angle of incidence from wing root to wingtip. The root is mounted at some angle to the longitudinal axis, and the leading edge of the remainder of the wing is gradually twisted downward so that the angle of incidence at the wingtip is less.
Wing root is always at a greater AoA than the wingtip, thus stalling first
Does the T-6A have aerodynamic twist or geometric twist?
The T-6A has both aerodynamic twist and geometric twist.
Can drag ever be zero?
Because there is always some resistance to motion, drag can never be zero.
What are the two types of drag that combine to create total drag?
Parasite drag and Induced drag
Parasite drag
drag that is not associated with the production of lift
composed: Form, Friction, and Interference
increases as velocity increases
Form drag
What is it dependent on?
the separation of airflow from a surface and the wake that is created by that separation
The amount of form drag produced by an object is dependent upon the object’s shape and size of its frontal area exposed to the relative wind
Friction drag
How can it be reduced?
caused by turbulent airflow in the boundary layer
Friction drag can be reduced by smoothing the exposed surfaces of the airplane through painting, cleaning, waxing, etc
How does keeping airflow in the boundary layer turbulent impact form and friction drag?
Keeping the airflow in the boundary layer turbulent makes it adhere to the surface better, reducing form drag with only a slight penalty in friction drag.
If the boundary layer were all laminar (smooth) airflow, it would easily separate from the surface creating a large wake behind the airfoil and increasing form drag.
Interference drag
How can it be reduced?
generated by mixing airstreams between aircraft components, such as the wing and fuselage
can be reduced by proper fairing and filleting to smooth out the point where the airstreams meet.
Induced drag
What is its relationship with velocity?
Induced drag is that component of drag that is associated with the production of lift.
As velocity increases, induced drag decreases. This is generally due to a lower angle of attack and the aircraft becoming more streamlined.
Why does induced drag happen?
Although the upwash and downwash created by chordwise flow are equal and counteract each other, some of the higher pressure air below the finite wing flows spanwise to the wingtip to try to equalize the pressure around the wing.
After the air flows up and around the wingtip, it mixes with the chordwise flow and creates additional downwash at the trailing edge.
Downwash is 2x greater than upwash
What factors increase induced drag?
Increased weight, decreased velocity, decreased wingspan, or decreased air density
What is a way to reduce induced drag?
Install devices to impede spanwise flow around the wingtip, such as winglets
Total drag curve is the combination of the parasite drag and induced drag curves. Is the total drag curve dependent on factors such as weight, altitude, or configuration?
Yes. These curves are plotted for a given weight, altitude, and configuration. Should any of these change, the curves would shift.
What is used to determine the efficiency of a wing?
The ratio of lift vs. drag (L/D)
At what point is L/D greatest? What is true at this point?
L/D Max
-Minimum total drag
-Parasite drag and induced drag are equal!!
-Greatest ratio of lift to drag (not maximum lift)
-The most efficient angle of attack for the wing
What is ground effect, when does it happen, and why?
Ground effect is a phenomenon that significantly reduces induced drag (Di) and increases effective lift when the airplane is within one wingspan of the ground. When the airplane is close to the ground, the downwash at the trailing edge of the wing is blocked by the ground and creates more effective lift and a “floating” sensation
What is Thrust Horsepower describing?
Propeller output
What is Shaft Horsepower describing?
Engine output
Propeller efficiency (p.e.)
The ability of a propeller to convert engine output (SHP) into thrust (THP)
p.e. = THP / SHP
Why is propeller efficiency never 100%?
friction in the reduction gearbox and drag from the propeller
What happens to all propellers as altitude or temperature increases?
They become less efficient because there is less air for the blades to bite and produce thrust
(a variable pitch propeller like the T-6A will increase blade angle to help minimize lost thrust)
In equilibrium flight, total thrust must equal total drag. Therefore, the thrust required graph is just?
an overlay of the total drag curve (where L/D Max is the same)
If you accelerate past L/D Max, what drag will increase at a greater rate? What if you decelerate?
Accelerate -> Parasite
Decelerate -> Induced
What is Thrust Available and why does it decrease with velocity?
Thrust available (TA) is the amount of thrust that is produced by an engine at a given PCL setting, velocity, and density.
A propeller can only accelerate air to a maximum velocity, so as the velocity of the incoming air increases, it is accelerated less by the propeller, resulting in a decrease in thrust available
What is thrust excess?
Thrust excess occurs if thrust available is greater than thrust required at a particular velocity
At maximum power, equilibrium flight is maintained when thrust available equals thrust required (where the 2 curves cross on the graph). What does this represent and what is it in the T-6A?
This is the maximum velocity in level flight that an airplane can achieve. It is 255 KIAS at sea level for the T-6A
What does a positive thrust excess cause? What about a lack of thrust excess?
A positive thrust excess causes a climb, acceleration or both depending on the angle of attack. A lack of excess thrust causes a descent, deceleration, or both depending on angle of attack.
Where is maximum excess thrust depicted on the graph and where does max excess thrust occur in a propeller-driven aircraft?
Maximum excess thrust is depicted on the graph where the distance between the TA and TR curves are the greatest.
For a propeller-driven aircraft, max excess thrust occurs at a velocity LESS THAN L/d max!!!
Power available (Pa)
the amount of power that an engine is producing at a given PCL setting, velocity, and density.
Maximum power available is produced at full PCL.
A propeller’s PA initially increases but then decreases due to a loss of thrust available as velocity increases
How is Power Available calculated?
To obtain power (work/time), multiply thrust available by velocity and then divide by 325 to obtain horsepower.
Power Required (Pr)
the amount of power required to produce thrust required
Minimum power required for level flight
is at a SLOWER velocity than L/Dmax
Where does maximum excess power occur in a propeller-driven aircraft?
At L/DMAX!!!
How does weight change Pr and Tr?
Increased weight now means more lift is required to overcome that extra weight. To increase lift you either have to increase velocity or AoA. Either way, Pr and Tr increases with increased weight
How does altitude change Tr?
If the weight of an airplane remains constant, the lift required is the same at 20,000 feet as it is at sea level. But, to produce that same lift at 20,000 feet the velocity (TAS) must increase due to the decrease in air density. Therefore, TR must increase
How does altitude change Ta and Pa?
Maximum engine output decreases with decreased air density. So, both Thrust Available (TA) and Power Available (PA) decrease at higher altitudes
What happens when a pilot moves the stick to the right?
The right aileron raises to change the camber of that portion of the wing to that of a more symmetric airfoil – producing less lift.
The left aileron lowers, increasing camber on that portion of the left wing – producing more lift.
With less lift on the right wing and more lift on the left wing, the aircraft now rotates about the longitudinal axis to the right.
What happens when a pilot pulls the stick aft?
the trailing edge of the elevator goes up (making the tail go down) and the aircraft pitches up
What happens when a pilot steps on the left rudder pedal?
The rudder deflects to the left (making the tail move right) and the nose of the aircraft moves left
What happens when the camber of the wing is increased (via flaps or ailerons)?
The coefficient of lift increases, but the stall angle of attack decreases
What kind of flap does the T-6A use?
A split flap
Differentiate between the 4 different types of trailing edge flaps
Plain flap: increases camber of wing
Split flap: creates more drag than plain
Slotted flap: creates more lift and less drag than plain
Fowler: creates more lift and surface area
How do leading edge flaps differ to trailing edge flaps?
Both change the wing camber, but leading edge flaps create excessive drag at low angles of attack. However, at high angles of attack the air flow separation is delayed and stall speed is lowered
What advantage do flaps have on takeoff and landing?
Slower speeds and better visibility
Lowering the flaps increases lift allowing the aircraft to be flown at slower speeds for takeoff, approach, and landing. Also, a flatter pitch angle can be used during takeoff and landing, making it easier to see what is ahead.
50% flap setting
you gain more lift than drag (which is why its typically used for takeoff)
Lowering the landing gear causes an increase in what? What tendency does this give the aircraft?
Lowering the landing gear causes an increase in parasite drag from the gear and the gear doors. The aircraft has a tendency to pitch slightly down as the gear is lowered, and slightly up as the gear is raised.
Lift is defined as
component of aerodynamic force that acts perpendicular to the relative wind.
In straight-and-level flight (constant lift), angle of attack and velocity have __________ relationship.
an inverse
Which airfoil produces no lift at zero degrees angle of attack?
Symmetric
What is the benefit of geometric and aerodynamic twist on a wing?
The wing root stalls before the wingtip
Parasite drag is defined as drag
caused by anything other than the creation of lift.
