Aerodynamics 1 Flashcards
Define Scalar
A quantity expressing only magnitude (e.g. Time, amount of money, volume of a body)
Define Vector
A quantity the expresses both magnitude and direction. A vector quantity is represented by an arrow that displays direction and has a length proportional to magnitude.
Define Mass
(m) The quantity of molecular material that comprises an object
Define Volume
The size of the mass, or the amount of space occupied by an object
Define Density
(ρ) Mass per unit volume
Define Force
Mass times Acceleration; A vector quantity equal to the push or pull exerted on a body. By Newton’s second law, a force is a function of an acceleration and the mass of the body.
Define Weight
The force at which a mass is attracted toward the center of the earth by gravity
Define Moment
A tendency to cause rotation around a point or axis, as a control surface around its hinge or an airplane around its center of gravity; the measure of this tendency, equal to the product of the force and perpendicular distance between the point of rotation and the direction of the force., expressed as a vector. Also called torque.
Define Work
(W) Work is done when a force acts on a body and it moves. Work is a scalar quantity measured in ft.-lbs. W=F x s
Define Power
(P) The rate of doing work, or work per unit time. Measured in ft.-lbs./sec or horsepower.
Define Energy
The ability or capacity to do work. Expressed in ft.-lbs.
Define Potential Energy
(PE) The ability of a body to do work because of its position or physical state.
Define Kinetic Energy
(KE) The ability of a body to do work because of its motion.
Explain Newton’s Law of Equilibrium
Newton’s First Law. “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.”
State the requirements for an airplane to be in equilibrium flight
Equilibrium flight exists when the sum of all forces and the sum of all moments around the center of gravity are equal to zero. This may occur during straight and level, climbing, or descending flight so long as there is no change in flight path.
State the requirements for an airplane to be in trimmed flight
Trimmed flight exists when the sum of all moments around the center of gravity is equal to zero. The sum of all forces around the center of gravity may not be equal to zero. This may occur in a constant rate turn.
Explain Newton’s Law of Acceleration
Newton’s Second Law. “An unbalanced force (F) acting on a body produces an acceleration (a) in the direction of the force that is directly proportional to the force and inversely proportional to the mass (m) of the body.” equation: a=F/m. (e.g. when the airplanes thrust is greater than its drag, the excess thrust will accelerate the airplane until drag increases to equal thrust)
Explain Newton’s Law of Interaction
Newton’s Third Law. “For every action there is an equal and opposite reaction; the forces of two bodies on each other are always equal and are directed in opposite directions.” (e.g. The rearward force from a propeller’s propwash causes an aircraft to move forward with an equal amount of force)
Define Static Pressure
(Ps) The weight of a column of air over a given area; the pressure each air particle exerts on another due to the weight of all the particles above; the potential energy per unit volume.
Define Air Density
(ρ) The total mass of air particles per unit volume
Define Temperature
A measure of the average kinetic energy of air particles, expressed in degrees (°C), Fahrenheit (°F), or Kelvin (K).
Define Lapse Rate
The rate that temperature decreases as you increase in altitude. (usually 2 °C per 1000 ft until about 36,000 ft) From about 36,000 ft through 66,000 feet the air remains at a constant -56.5 °C. This is called the isothermal layer.
Define Humidity
The amount of water vapor in the air
Describe the relationship between humidity and air density
As humidity increases, density decreases. This is because water molecules have less mass but displace the same number of air molecules.
Define Viscosity
(µ) A measure of a fluid’s resistance to flow and shearing.
Describe the relationship between temperature and viscosity
Air viscosity increases when temperature increases.
Define local speed of sound
The rate at which sound waves travel through a particular air mass.
Describe the relationship between temperature and local speed of sound
As air temperature increases, the speed of sound increases.
State the values for standard atmosphere
- Static Pressure (Ps0) = 29.92 in. Hg. (1013.25 mbar)
- Temperature (T0) = 59 °F (15 °C)
- Average Lapse Rate = 3.57 °F / 1000 ft. (2°C / 1000 ft)
Describe the General Gas Law, given static pressure, air density, temperature, and altitude
The standard gas law sets the relationship between the three properties of air: pressure (P), density (ρ), and temperature (T). R is the constant for any given gas. P=ρRT (e.g. if density remains constant and temperature increases, then pressure will increase)
Explain Bernoulli’s Equation, given dynamic pressure, static pressure, and total pressure
Bernoulli’s equation explains the variation of pressure exerted by a moving mass of fluid. His equation shows that the total energy of a fluid can be separated into potential energy (static pressure) and kinetic energy (dynamic pressure). Total pressure (H or Pt) = static pressure (Ps) + dynamic pressure (q). (Dynamic pressure = 1/2 density (ρ) x velocity (V) squared.)
Define Steady Airflow
Airflow in which at every point in the moving air mass, the pressure, density, temperature and velocity are constant.
Define Streamline
The path traced by a particle of air while in steady flow
Define Streamtube
An impenetrable tube formed by many streamlines. Streamtubes are closed systems.
Explain the continuity equation given density, cross-sectional area, and velocity
The amount of mass passing any point in the streamtube may be found by multiplying area by velocity to give volume/unit time and then multiplying by density to give mass/unit time. This is called Mass flow rate (Ṁ) and is expressed as Ṁ=ρAV. In subsonic airflow we can ignore changes in density due to compressibility. The mount of mass flowing through any given section of the streamtube must be equal, therefore if area decreases, velocity increase. A1V1=A2V2.
Define Indicated Altitude
The indication on a pressure altimeter when the Kollsman window is set to the current local altimeter setting.
Define Above Ground Level (AGL) altitude
The height of a point measured from the earth’s surface directly below it.
Define Mean Sea Level (MSL) altitude
The height of a point measured from mean sea level. (Also known as True Altitude)
Define Pressure Altitude
The height above the standard datum plane. The standard datum plane is the actual elevation at which the barometric pressure is 29.92 in.Hg. (In a standard atmosphere, Pressure altitude equals true altitude)
Define Density Altitude
Pressure altitude corrected for nonstandard temperature. DA is the pressure altitude on a standard day that has the same density as the ambient air.
Describe the pitot-static system given the system components and Bernoulli’s equation
Using Bernoulli’s equation, dynamic pressure (q), relating to airspeed, can be calculated by measuring the total and static pressure acting on the aircraft. The pitot-static system consists of a pitot tube that sense total pressure (H or Pt), and a static port that senses static pressure (Ps). H=Ps+1/2ρV^2, By rearranging this equation, we may find velocity.
Define Indicated Airspeed
Indicated airspeed is the actual instrument indication of the dynamic pressure the airplane is exposed to during flight. This may be significantly different then actual flight speed due to altitude, and installation or instrument error.f
Define Calibrated Airspeed
Indicated airspeed corrected for instrument error.
Define Equivalent Airspeed
The true airspeed at sea level on a standard day that produces the same dynamic pressure as the actual flight condition. It is found by correcting calibrated air speed for compressibility error.
Define True Airspeed
The actual velocity at which an airplane moves through an air mass. It is found by correcting equivalent airspeed for the difference between the local air density and the density of the air at sea level on a standard day.
Define Ground Speed
The airplane’s actual speed over the ground. If we correct true airspeed for wind, we get ground speed.
Describe the factors affecting the different types of airspeed
- Indicated airspeed (IAS) is affected by altitude, compressibility effects, instrument error, and installation error.
- Calibrated airspeed (CAS) Is affected by altitude and compressibility effects.
- Equivalent Airspeed (EAS) is affected by altitude.
- True Airspeed (TAS) is the actual speed of the aircraft moving through an air mass.
- Ground speed (GS) is affected by wind.
Define an aircraft
Any device used or intended to be used for flight in the air.
Define an airplane
An engine driven, heavier-than-air, fixed wing aircraft that is supported by the dynamic reaction of airflow over its wings.
Describe the five components of an airplane
- Fuselage: basic structure of the airplane to which all other components are attached
- Wing: an airfoil attached to the fuselage designed to produce lift
- Empennage: the assembly of the stabilizing and control surfaces on the tail of the airplane
- Landing Gear: permits ground taxi operations and absorbs the shock encountered during takeoff and landing
- Engine: provides thrust necessary for powered flight
State the advantages of the semi-monocoque fuselage construction
The semi-monocoque fuselage is lightweight and is easier to repair than a monocoque fuselage. The T-6B uses a semi-monocoque fuselage
Define full cantilever wing construction
All bracing is internal to the wing. T-6B wings are full cantilever.
Describe the airplane three-axis reference system
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longitudinal axis: passes from nose to tail;
- movement about this axis is called roll.
- control surface: Ailerons
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lateral axis: passes from wingtip to wingtip;
- movement about this axis is called pitch.
- control surface: Elevator
-
vertical axis: passes vertically through the center of gravity;
- movement about this axis is called yaw.
- control surface: Rudder
Define chord line
An infinitely long straight line that passes through the leading and trailing edges.
Define chord
The precise measurement between the leading and trailing edges along the chord line.
Define root chord
The chord measured at the wing centerline.
Define tip chord
The chord measured at the wingtip.
Define average chord
The average of every chord from the wing root to the wing tip.
Define mean camber line
The locus of points halfway between the upper and lower surfaces, measured perpendicular to the mean chamber line itself.
State the effects of up wash and down wash on a finite wing.
Some of the high pressure air in the leading edge stagnation point flows spanwise to the wingtips and up to the upper surface of the wing. It combines with the other down wash when it flows over the trailing edge, therefore reducing effective lift and increasing induced drag.
State the cause of induced drag on a finite wing
Since there is twice as much down wash as up wash near the wingtips of a finite wing, the average relative wind is slanted downward, thus the total lift vector will be inclined aft. The horizontal component of total lift is induced drag.
Describe factors affecting induced drag, given the induced drag equation, and changes in lift, weight, density velocity, and wingspan
Increasing lift or weight will increase induced drag. Increasing density (ρ), velocity (V), or wingspan (b) will reduce induced drag.
Describe effects of angle of attack changes on coefficient of lift and coefficient of drag.
As AOA increases, lift increases up to a maximum value (Clmax). The coefficient of drag is low and nearly constant at low AOA, but increases rapidly at higher angles of attack.
Explain the lift to drag ratio, using the lift and drag equations.
A high L/D ratio indicates a more efficient airfoil. It is calculated by dividing lift by drag.
Define total drag.
Parasite drag and Induced drag added together.
Describe the effects of changes in velocity on total drag
Total drag will be lowest where induced drag and parasite drag are equal. It will increase rapidly at lower airspeed and increase gradually at higher airspeeds.
Describe the effects of throttle setting on thrust available.
- Full throttle will result in greatest thrust available.
- As throttle is retarded, thrust available decreases.
Describe the effects of velocity on thrust available.
- For turbo-prop aircraft, thrust available decreases with an increase in velocity.
- For turbojets, thrust available remains the same regardless of velocity.
Describe the effects of density on thrust available.
As air density decreases thrust available decreases.
Describe the effects of throttle setting on power available.
- Full throttle will result in greatest power available.
- As throttle is retarded, power available decreases.
Describe the effects of velocity on power available.
- For turbo-prop aircraft, As velocity increases, power available will initially increase, but will then decrease due to a decrease in thrust available.
- For turbojets, power available will increase linearly
Describe the effects of density on power available.
As air density decreases power available decreases.
State the location of L/D MAX on the thrust required curve.
L/D Max is at the bottom of the thrust required curve.
State the location of L/DMAX on the power required curve.
L/DMAX is to the right of the bottom of the power required curve (where a line drawn from the origin is tangent to the Pr curve)
Describe how thrust required and power required vary with velocity
Thrust required is lowest at L/D max, increases rapidly at lower velocities, and increases gradually at higher velocities. Power required follows a similar pattern, but curves back up at a lower velocity than L/D max.
Describe the effects of changes in weight on thrust and power components: thrust required, power required, excess thrust, and excess power
- An increase in weight will require an increase in thrust required and a corresponding increase in power required.
- Weight changes have no effect on thrust available and power available,
- thus thrust excess and power excess will decrease.
Describe the effects of changes in altitude on thrust and power components: thrust required, power required, thrust available, power available, excess thrust, and excess power
- As altitude increase, the thrust required curve shifts to the right, but not up.
- Since power required is a function of thrust required and velocity, the Pr curve will shift up and to the right.
- Both thrust available and power available will decrease as altitude increases.
- Thrust excess and Power excess will also decrease with an increase in altitude.
Describe the effects of changes in configuration on thrust and power components: thrust required, power required, excess thrust, and excess power
- Lowering the landing gear will increase drag, thus causing thrust required and power required to increase.
- Lowering the flaps increases the coefficient of lift, but also greatly increase parasite drag, thus the thrust required and power required curves shift up and to the left.
- Configuration changes have no effect on Thrust available and Power available, therefore if landing gear or flaps are lowered, excess thrust and excess power will decrease.
Describe the aerodynamic effects of raising or lowering the flaps
Lowering the flaps increases the coefficient of lift, allowing the aircraft to fly at lower velocity, but also significantly increases drag.
Describe the aerodynamic effects of raising and lowering the landing gear
Lowering the landing gear has no effect on lift, but does dramatically increase parasite drag.
Describe how the trim tab system holds an airplane in trimmed flight
A trim tab at the trailing edge of a control surface creates a force that moves the control surface opposite the direction the tab is oriented. For example a trim tab on the elevator that is deflected down, will create a force that will cause the elevator to deflect up. The total force from the elevator will cause the airplane to pitch nose up. The pilot trims to relieve pressure on the controls so that they stay in the desired position without being held there by the pilot.
State how trim tabs can be used to generate artificial feel on a control surface
- Servo tabs move in the opposite direction of the surface, making it easier for the pilot to deflect the control surface.
- Anti-servo tabs move in the same direction, requiring more force to deflect the control surface.
Describe the purpose of bobweights and downsprings
The bobweight increases the force required to pull the stick aft during maneuvering flight, while the downsprings increase the force required to pull the stick aft at low airspeeds.
