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Theory of Flight, an introduction. It touches some fundamentals of aerodynamics before the thorough course.
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UEE 306 Uçuş Teorisi
Ahmet AĞIRMAN
Erciyes Üniversitesi Sivil Havacılık Yüksek Okulu
Preliminaries
Lecture 1
UEE306-2013/2014
Overview and Definitions
The Atmospher
Basic Aerodynamics
Subsonic Airflow
Overview and Definitions
The Atmospher
Basic Aerodynamics
Subsonic Airflow
Flight
• Ability to hover in as well as navigate through the air
• Not all but some living beings like eagles besides human-made systems like aircrafts
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
Primary req’s of an a/c
• Wing: Generates a lift force
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
Primary req’s of an a/c
• Wing: Generates a lift force
• Fuselage: Accomodates the payload
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
Primary req’s of an a/c
• Wing: Generates a lift force
• Fuselage: Accomodates the payload
• Tail surfaces: Adds stability
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
Primary req’s of an a/c
• Wing: Generates a lift force
• Fuselage: Accomodates the payload
• Tail surfaces: Adds stability
• Control surfaces: Change direction of flight
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
Primary req’s of an a/c
• Wing: Generates a lift force
• Fuselage: Accomodates the payload
• Tail surfaces: Adds stability
• Control surfaces: Change direction of flight
• Engines: Make a/c go forward
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
The axis system
• x, y, z lines
• +x, -x, +y, -y, +z, –z directions
• A/c flight: combination of +x, y, z
• +x: due to engines
• -z: due to weight
• +z: due to ?
• y: due to ?
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
The four forces
• Stationary a/c: Only weight force at –z direction acts on it
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
The four forces
• Stationary a/c: Only weight force at –z direction acts on it
• In order to fly, a force ≥ W at +z direction needed, which is Lift, L
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
The four forces
• Stationary a/c: Only weight force at –z direction acts on it
• In order to fly, a force ≥ W at +z direction needed, which is Lift, L
• In order to get L, a force moves a/c at +x direction needed, which is Trust, T
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
The four forces
• Stationary a/c: Only weight force at –z direction acts on it
• In order to fly, a force ≥ W at +z direction needed, which is Lift, L
• In order to get L, a force moves a/c at +x direction needed, which is Trust, T
• Due to moving forward at +x direction, a force at –x direction created, which is Drag, D
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
Lift vs buoyancy
• Lift occurs due to motion
• Buoyancy does not occur due to motion
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
Mass, Force & Weight
• Mass – SI Unit: kilogram (kg) – Amount of a material – Can exist witout weight – A measure of effort putting an object in motion or rest
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
Mass, Force & Weight
• Mass – SI Unit: kilogram (kg) – Amount of a material – Can exist witout weight – A measure of effort putting an object in motion or rest
• Force & Weight – SI Unit: Newton (N) – Force: Universal reason for any physical change, i.e. in motion, in appereance, etc. – Weight: Gravitational force that objects apply to each other
– Force vs mass: 𝐹 = 𝑚. 𝑔 where 𝑔 = 9,81𝑚𝑠2 : gravitational acceleration, m: mass
• An aircarft with 60 tonnes of weight needs a minimum of lift:
𝐹 = 𝑚.𝑔 = 60000𝑥9,81 = 585600 𝑁 – Cannot exist without mass
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
Center of Gravity (CG)
• A location on aircraft through which the weight of a/c assumed to act
• A flying a/c assumed to rotate around its CG
• The CG of an a/c should remain in certain physical limits due to stability and controllability of the a/c
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
Work, Power, Energy
Work o SI Unit: Joule (J) o A net force does work if
the object moves in the direction of the force
o Work=Force x Distance, Nm or J
o Example: when 10 N force moves a body 2 metres away in the direction of it the work done is 20 J
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
Work, Power, Energy
Work o SI Unit: Joule (J) o A net force does work if
the object moves in the direction of the force
o Work=Force x Distance, Nm or J
o Example: when 10 N force moves a body 2 metres away in the direction of it the work done is 20 J
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
Power
o SI Unit: Watt (W)
o The work has been done in unit time
o Power=ForcexDistance/Time, Nm/s or J/s or Watt
o Example: when 10 N force moves a body 2 metres away in the direction of it in 4 seconds, the power of that force is 5 W
Work, Power, Energy
Work o SI Unit: Joule (J) o A net force does work if
the object moves in the direction of the force
o Work=Force x Distance, Nm or J
o Example: when 10 N force moves a body 2 metres away in the direction of it the work done is 20 J
o Imagine that work is the energy consumed, precisely the kinetic energy consumed.
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
Power
o SI Unit: Watt (W)
o The work has been done in unit time
o Power=ForcexDistance/Time, Nm/s or J/s or Watt
o Example: when 10 N force moves a body 2 metres away in the direction of it in 4 seconds, the power of that force is 5 W
Energy
o SI Unit: Joule (J)
o Ability to do work
Kinetic Energy
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
Kinetic Energy
o SI Unit: Joule (J)
o Energy possesed due to motion
o 𝐸𝑘 =1
2𝑚𝜗 2
o Example: 1 kg of air with 52 m/s (100 knots) velocity has 1352 J of (kinetic) energy
Newton’s first law of motion & Inertia
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
The law o Unless an external force applied,
o a body will rest if it was on rest OR o will keep its linear movement if was doing so.
Inertia o Resistance of a body against a change in its motion o Inertia is measured by mass of the body o The reason a body needs an external force to
experience a change in motion is inertia.
Newton’s second law of motion & Velocity, Acceleration
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
The law
o In order to change acceleration of a body, there needs to be a force proportional to mass of the body
𝐹 = 𝑚𝑎
o Velocity: The amount of distance the body takes in a unit of time. (m/s)
o Acceleration: The rate of change of velocity (m/s²)
Momentum
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
Which one requires a bigger force to get stopped in 1 sec?
10 kg of body with 3 m/s velocity vs 5 kg of body with 3 m/s velocity
10 kg of body with 5 m/s velocity vs 10 kg of body with 3 m/s velocity
1 tonnes of body with 1 m/s velocity vs 15 kg of body with 100 m/s velocity?
o Momentum: the amount of motion a body posseses: 𝑀=𝑚𝑣, kg-m/s
o Velocity: The amount of distance the body takes in a unit of time. (m/s) o Acceleration: The rate of change of velocity (m/s²)
Newton’s third law of motion
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
Every action has an equal and opposite reaction
UEE306-2013/2014
Overview and Definitions
The Atmospher
Basic Aerodynamics
Subsonic Airflow
The atmosphere and air
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
• Envelope of the Earth • Has a mass and weight • Has an undetermined shape • Most important parameter is air density • If air density over airfoil decreases, then mass flow per
second decreases thus for the required lift force, speed should increase
• Air is compressible • Air flows from high pressure region to low pressure region • Air has a viscosity which is relatively very small
Static Pressure
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
• SI Unit: N/m², symbol: ‘p’ • 1 N/m² = 1 Pa, 100 Pa = 1 hPa = 1
milibar • 1013,25 milibar = 1.01325 bar = 1 atm • Result of weight of atmosphere • For a given altitude, all locations of
a/c have same static pressure • Static pressure decrases
exponentially by increase of altitude • Static pressure is always in precense
upon aircaft
Temperature
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
• SI Unit: C° or K°
• 1 K° = -273 C°
• Between 0 to 36000 ft, decreases almost linearly by increase of altitude as 6,4 C° for every 1000 meter
• After 36000 ft, it is constant at -56 C° for a while
Air Density
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
• SI Unit: kg/m³, symbol: ro (ρ)
• Depends on temperature, static pressure and humidity
• Ideal gas formula: 𝑝𝑉 = 𝑛𝑅𝑇
or
𝑝𝑉 =𝑚
𝑀𝑅𝑇
where M: molar mass in kg/mol
then
𝑝 =𝑚
𝑀
𝑅
𝑉𝑇
𝑝 = 𝜌𝑅𝑠𝑇
where ρ=m/M, density of dry air; 𝑅𝑠: Spesific dry air constant
hence
𝑝𝜌𝑇 = constant
Air Density
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
• SI Unit: kg/m³, symbol: ro (ρ) • Depends on temperature, static pressure and humidity • Ideal gas formula:
𝑝𝑉 = 𝑛𝑅𝑇 or
𝑝𝑉 =𝑚
𝑀𝑅𝑇
where M: molar mass in kg/mol then
𝑝 =𝑚
𝑀
𝑅
𝑉𝑇
𝑝 = 𝜌𝑅𝑠𝑇
where ρ=m/M, density of dry air; 𝑅𝑠: Spesific dry air constant hence
𝑝𝜌𝑇 = constant
• Note: When altitude increases;
Air Density
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
• SI Unit: kg/m³, symbol: ro (ρ) • Depends on temperature, static pressure and humidity • Ideal gas formula:
𝑝𝑉 = 𝑛𝑅𝑇 or
𝑝𝑉 =𝑚
𝑀𝑅𝑇
where M: molar mass in kg/mol then
𝑝 =𝑚
𝑀
𝑅
𝑉𝑇
𝑝 = 𝜌𝑅𝑠𝑇
where ρ=m/M, density of dry air; 𝑅𝑠: Spesific dry air constant hence
𝑝𝜌𝑇 = constant
• Note: When altitude increases;
Air Density
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
• SI Unit: kg/m³, symbol: ro (ρ) • Depends on temperature, static pressure and humidity • Ideal gas formula:
𝑝𝑉 = 𝑛𝑅𝑇 or
𝑝𝑉 =𝑚
𝑀𝑅𝑇
where M: molar mass in kg/mol then
𝑝 =𝑚
𝑀
𝑅
𝑉𝑇
𝑝 = 𝜌𝑅𝑠𝑇
where ρ=m/M, density of dry air; 𝑅𝑠: Spesific dry air constant hence
𝑝𝜌𝑇 = constant
• Note: When altitude increases;
International Standard Atmosphere (ISA)
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
• Sea level values: – Temperature (𝑇0): 15 C°
– Static Air Pressure (𝑝0): 1013,25 hPa or 1 atm
– Dry air density (𝜌0): 1,225 kg/m³
• Temperature change is – 2 C° for each 1000 ft or
– 6,4 C° for each 1000 m untill 36000 ft
• Relative air density (𝜌𝑎𝑙𝑡𝑖𝑡𝑢𝑑𝑒/𝜌0) decreases: For example, at 40000 ft altitude relative air density is 0,25
Dynamic Air Pressure
Overview & Definitions The atmospher Basic Aerodynamics Subsonic Airflow
• Kinetic energy of incompressible air in unit volume, symbol is ‘q’ • Kinetic energy of air with mass m:
𝐸𝑘 =1
2𝑚𝜗2;
J or Nm • Kinetic energy of air in unit volume:
(𝐸𝑘)𝑉 = (
1
2𝑚𝜗2)/𝑉;
Nm/m³=N/m²=F/A=p≜Pressure
𝐸𝑘−𝑢𝑛𝑖𝑡 𝑣𝑜𝑙𝑢𝑚𝑒 =1
2𝜌𝜗2, N/m²
• Example: An aircrafts flies with 100 m/s velocity at sea level. Then the dynamic pressure over the body is
𝑞 =1
2𝜌𝜗2 =
1
21,225𝑥1002 = 61,25ℎ𝑃𝑎
• If you know the total surface A the dynamic pressure applies, then the total force the a/c under will be
𝐹 = 𝑝𝐴
Measurement of Dynamic Air Pressure
Overview & Definitions The Atmospher Basic Aerodynamics Subsonic Airflow
• Pitot tube receives the total pressure:
𝑝𝑡𝑜𝑡𝑎𝑙 = 𝑝𝑠𝑡𝑎𝑡𝑖𝑐 +1
2𝜌𝜗2
• Static port receives only the static pressure • Air Speed Indicator (ASI) substracts the static pressure from the total:
𝑞 = 𝑝𝑡𝑜𝑡𝑎𝑙 − 𝑝𝑠𝑡𝑎𝑡𝑖𝑐 then
𝜗 =2(𝑝𝑡𝑜𝑡𝑎𝑙 − 𝑝𝑠𝑡𝑎𝑡𝑖𝑐)
𝜌
Problem: ASI is calibrated to sea level conditions: 𝜌 = 𝜌0 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 for all altitudes
Air speed you read from ASI at altitudes other then sea level is not REAL air spead and so called Indicated Air Speed (IAS)
Good news: The speed change you read from ASI is accurate at all altitudes! If you see from ASI you twiced your speed, then a/c really twiced its speed.
Indicated Air Speed (IAS)
Overview & Definitions The Atmospher Basic Aerodynamics Subsonic Airflow
• The speed you directly read from ASI.
• Assume that
– you are at a non-sea-level altitude
– with air density 𝜌𝑎𝑙𝑡𝑖𝑡𝑢𝑑𝑒,
– then dynamic pressure at that altitude be 𝑞𝑎𝑙𝑡𝑖𝑡𝑢𝑑𝑒,
– and sea level air density be 𝜌0.
• The aircraft should have a true air speed or TAS.
• Then, the dynamic pressure can be expressed as
𝑞𝑎𝑙𝑡𝑖𝑡𝑢𝑑𝑒 =1
2𝜌0𝐼𝐴𝑆
2 =1
2𝜌𝑎𝑙𝑡𝑖𝑡𝑢𝑑𝑒𝑇𝐴𝑆
2
Calibrated Air Speed (CAS)
Overview & Definitions The Atmospher Basic Aerodynamics Subsonic Airflow
• The air speed when position or pressure errors eliminated from IAS at low speed flights (<320m/s)
• Sometimes you cannot read true pressure levels at pitot tube and static port due to: – Positions of pitot tube and static vents on aircraft
– Effects of flaps and landing gears, or even a/c, etc.
– Manevours and angle of attact
– Incorrect alignment of pitot tube according to air stream
• After elimination of pressure or positin errors we get CAS
CAS=IAS−𝐸𝑟𝑟𝑜𝑟𝑃𝑜𝑠𝑖𝑡𝑖𝑜𝑛
Equivalent Air Speed (EAS)
Overview & Definitions The Atmospher Basic Aerodynamics Subsonic Airflow
• The air speed when position and compressibility errors eliminated from IAS at high speed flights (>320m/s)
• If a/c flies at high speeds, then compressibility effects are the case
• The dynamic pressure ASI measures (𝑞𝑐) is not the actual 𝑞 but a higher value:
𝑞𝑐 = 𝑞(1 +𝑀2
4+
𝑀4
40 +
𝑀6
1600+⋯) > 𝑞
• After elimination of pressure and compressibility errors we get EAS
EAS=IAS−𝐸𝑟𝑟𝑜𝑟𝑃𝑜𝑠𝑖𝑡𝑖𝑜𝑛 −𝐸𝑟𝑟𝑜𝑟𝐶𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑖𝑏𝑖𝑙𝑖𝑡𝑦
True Air Speed (TAS)
Overview & Definitions The Atmospher Basic Aerodynamics Subsonic Airflow
• The air speed when position and compressibility errors eliminated and sea-level
calibration fixed • Assume that
– you are at a non-sea-level altitude – with air density 𝜌𝑎𝑙𝑡𝑖𝑡𝑢𝑑𝑒 , – then dynamic pressure at that altitude be 𝑞𝑎𝑙𝑡𝑖𝑡𝑢𝑑𝑒 , – and sea level air density be 𝜌0 – You read EAS from ASI at that altitude
• After elimination of pressure and compressibility errors we get EAS
TAS=𝑓(IAS−𝐸𝑟𝑟𝑜𝑟𝑃𝑜𝑠𝑖𝑡𝑖𝑜𝑛−𝐸𝑟𝑟𝑜𝑟𝐶𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑖𝑏𝑖𝑙𝑖𝑡𝑦) = 𝑓(𝐸𝐴𝑆)
or
𝑞𝑎𝑙𝑡𝑖𝑡𝑢𝑑𝑒 =1
2𝜌0𝐸𝐴𝑆
2 =1
2𝜌𝑎𝑙𝑡𝑖𝑡𝑢𝑑𝑒𝑇𝐴𝑆
2
thus 𝑻𝑨𝑺 = 𝑬𝑨𝑺/ 𝝈, where 𝜎 = 𝜌𝑎𝑙𝑡𝑖𝑡𝑢𝑑𝑒/𝜌0
• EAS=TAS only at sea levels since 𝜎 = 1 at sea level. • Remember: at 40000 ft 𝜎 = 0,25. That implies
– if at sea level you read EAS=100 knots, TAS is 100 knots – if at 40000 ft you read EAS=100 knots, TAS is 200 knots!
Speed of Sound (a)
Overview & Definitions The Atmospher Basic Aerodynamics Subsonic Airflow
• Sound is a mechanical wave emiting through air spherically • Speed of sound is function of temperature:
𝑎 = 𝛾𝑅∗𝑇
• When air temperature is low, then sound is slow • Mach number is a simple ratio of
𝑀 =𝑇𝐴𝑆
𝑎
• Critical Mach number, (𝑀𝑐𝑟𝑖𝑡), is the number before an a/c
reaches speed of sound; at some areas of the a/c, air speed reaches the speed of sound.
How to Fix These Errors?
Overview & Definitions The Atmospher Basic Aerodynamics Subsonic Airflow
• Read the notes
UEE306-2013/2014
Overview and Definitions
The Atmospher
Basic Aerodynamics
Subsonic Airflow
The Principle of Continuity
Overview & Definitions The Atmospher Basic Aerodynamics Subsonic Airflow
From a given cross area (A), at a given velocity (v), with air density ρ, mass of air flowing at a unit of time is constant at all cross areas of the system:
𝐴1𝑥𝜗1𝑥𝜌 = 𝐴2𝑥𝜗2𝑥𝜌 = ⋯ = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 (𝑘𝑔
𝑠)
Bernoulli's Theorem
Overview & Definitions The Atmospher Basic Aerodynamics Subsonic Airflow
An ideal incompressible fluid with zero viscosity satisfies the following:
𝑝 +1
2𝜌𝜗2 = 𝑝𝑡𝑜𝑡𝑎𝑙 = 𝑝𝑝𝑖𝑡𝑜𝑡 = 𝑝𝑠𝑡𝑎𝑔𝑛𝑎𝑡𝑖𝑜𝑛 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
Streamlines and the Streamtube
Overview & Definitions The Atmospher Basic Aerodynamics Subsonic Airflow
• Streamline : the path traced by a particle of air in a steady airflow • Streamlines cannot cross • Close together streamlines: increased velocity • Diverging streamlines: decelerating airflow and resultant increasing pressure • Converging streamlines: accelerating airflow, with resultant decreasing
pressure
• Streamtube: an imaginary tube made of streamlines • No flow into or out of the streamtube through the
"walls", only a flow along the tube
UEE306-2013/2014
Overview and Definitions
The Atmospher
Basic Aerodynamics
Subsonic Airflow
Wing Geometry
Overview & Definitions The Atmospher Basic Aerodynamics Subsonic Airflow
Wing Geometry
Overview & Definitions The Atmospher Basic Aerodynamics Subsonic Airflow
• Airfoil: A shape capable of producing lift with relatively high efficiency • Chord Line: A straight line joining the centers of curvature of the leading and
trailing edges of an aerofoil • Chord: The distance between the leading and trailing edges measured along
the chord line • Angle of Incidence: The angle between the chord line and the horizontal
datum of the aircraft • Mean Line or Camber Line: A line joining the leading and trailing edges of an
aerofoil, equidistant from the upper and lower surfaces • Maximum Camber: The maximum distance of the mean line from the chord
line. • Thickness/Chord ratio: The maximum thickness or depth of an aerofoil section
expressed as a percentage of the chord, with its location as a percentages of the chord aft of the leading edge
• Leading edge radius: The radius of curvature of the leading edge
Air Flow Terminology
Overview & Definitions The Atmospher Basic Aerodynamics Subsonic Airflow
• Total Reaction: The resultant of all the aerodynamic forces acting on the aero foil section
• Centre of Pressure (CP): The point on the chord line, through which Lift is considered to act
• Lift: The aerodynamic force which acts at 90o,to the Relative Air Flow. • Drag: The aerodynamic force which acts parallel to and in the same direction
as the Relative Air Flow (or opposite to the aircraft flight path) • Angle of Attack (𝛼 or alpha) (can also be referred to as Aerodynamic
Incidence): The angle between the chord line and the Relative Air Flow
Air Flow around an Airfoil
Overview & Definitions The Atmospher Basic Aerodynamics Subsonic Airflow
Influence of Dynamic Pressure
Overview & Definitions The Atmospher Basic Aerodynamics Subsonic Airflow
• "If the static pressure on one side of a body is reduced more than on the other side, a pressure differential will exist «
• "If the dynamic pressure is increased, the pressure differential will increase« • "If the dynamic pressure (lAS) is increased, the upward force will increase"
Influence of Angle of Attack
Overview & Definitions The Atmospher Basic Aerodynamics Subsonic Airflow
How to create an airfoil? (For geeks)
End of
Lecture 1
UEE306-2013/2014