Flashcards
The Flying Environment
Cards in this deck (70)
- 1Examples of aircraft performance metrics (at least 5)Range, cruise speed, service ceiling, specific range (distance per unit fuel), maneuvering (climb rate, turn rate, turn radius, time to climb, load factor), top speed, absolute ceiling, stall speed, operating cost, takeoff/ landing distance, flight envelope, endurance
- 2What is the standard atmosphere model?A status atmospheric model of how the pressure, temperature, density, viscosity of the Earth's atmosphere change over a wide range of altitudes
- 33 critical quantitiesPressure, temperature, density
- 4Equation of statep = ρRT (where R = 287.1 Nm/ kg K)
- 5Layers of the atmosphere in order to lowest altitudeTroposphere, Stratosphere, Mesosphere, Thermosphere
- 6Troposphere0-11 km AMSL (above mean sea level)
- 7Stratosphere11-50 km AMSL
- 8How are temperature and altitude related in the troposphere and why?Temperature decreases with increasing altitude because warmer near surface due to low altitude water and CO2 absorbing heat radiated from surface
- 9Boundary between troposphere and stratosphereTropopause
- 10Which layer of atmosphere does most flight happen and why?Stratosphere- mainly laminar flow here, so smooth flight
- 11How are temperature and altitude related in the stratosphere and why?Temperature increases with increasing altitude because much less water at lower levels so absorptivity from ground is lower, so not that high temperatures at the bottom. Also, ozone levels increase over this region, increasing absorption from ultraviolet radiation
- 12Mesosphere50-80 km AMSL
- 13Boundary between stratosphere and mesosphereStratopause
- 14How are temperature and altitude related in the mesosphere and why?Temperature decreases with increasing altitude due to decreasing levels of solar heating and increasing cooling by CO2 radiating emission
- 15Thermosphere80-800 km AMSL
- 16How are temperature and altitude related in the thermosphere and why?Temperature increases rapidly up until around 100 km and the constant from above 100 km; density and pressure are very low. This 100 km line (the Karman line) considered edge of space
- 17Altitude of typical low Earth orbitAround 300 km or higher
- 18ExosphereEverything else outside the 4 main layers of atmosphere- forms boundary with empty space
- 19Reference pressure P₀(defined at ground/sea level)
1013.25 hPa = 101325 Pa - 20Reference temperature, T₀15ᵒc = 288.15 K
- 21Reference density, ρ₀1.225 kg m⁻³
- 22Temperature profile for iᵗʰ layerT(z) = Tᵢ + λᵢ (z - hᵢ)
- 23Temperature profile for troposphereT(z) = T₀ + λ₀ z
- 24What is temperature lapse (or lag) rate?Rate of change of temperature with altitude
- 25Hydrostatic equationdp/dz = - ρg
- 26What complications arise with using the hydrostatic equation to address variation of pressure with altitude?Both ρ and g vary with height. ρ can be calculated using p/ RT, and the temperature profile equation. For convenience, we use the same g₀ everywhere.
- 27What is geopotential height? And which is high, geopotential or true?Height which accounts for variation of gravity due to latitude and altitude- geopotential height is higher than true height
- 28Equation relating true and geopotential height
- 29Speed of sound in a perfect gascₛ = √ (γ p/ρ) = √ (γRT)
where γ is ratio of specific heats at constant pressure and volume (cp/ cv), 1.4 for air - 30GlidingAircraft is propelled by using half its weight to counter aerodynamic drag and other half is support by aerodynamic lift forces
- 31Glide ratioMeasure of horizontal distance covered per unit altitude decrease
- 32SoaringGain altitude in presence of rising air (e.g. thermals, lee waves or orographic lift)
- 33Wing reference area, S or Sᵣₑ?Projected area of planform, bounded by the leading and trailing edges and the wing tips
- 34Wing span, bDistance from one wing tip to the other
- 35Wing aspect ratio, ARNon-dimensional quantity which defines slenderness of a wing (i.e. wing's span to mean geometric chord ratio)
b²/ S - 36What is a fuselage?Essentially an aerodynamic shell within which the crew, payload and aircraft subsystems are housed. Also serves as main structural component on which wings and stabilisers are mounted. (also powerplant (e.g. business jets) and undercarriage (e.g. military transport) also mounted for some configurations)
- 37What are some of the common parameters which influence dimensions and cross sectional shape of the fuselage?Volume and dimensions required to house payload and crew, most aerodynamically efficient shape, how structural weight could be minimised- as a rule of thumb, length to diameter ratios usually more aerodynamically efficient yet heavier, while circular cross sections are ideal when cabin pressurisation is used.
- 38Taper ratioDefined as variation of wing's chord length, c along its span- for trapezoidal wing platforms with linear variation of chord length from root to tip, taper, λ, is:
λ = cₜᵢₚ/ cᵣₒₒₜ
= tip chord length/ root cord length - 39SweepA swept-wing encounters oncoming airflow at an oblique rather than normal angle. Amount fo sweep typically quotes as quarter-chord sweep angle, given by angle between wing's quarteer-chord line and aircraft's lateral y-axis. For unswept wing, Λ = 0, backward swept Λ > 0 and forward swept Λ < 0
- 40Benefits of sweep• delaying onset of supersonic flow over top of wing’s surface
• for low speed aircraft sometimes used to help ensure
stability in flight and good flying qualities (like in hang gliders) - 41Drawbacks of sweepTends to degrade wing’s aerodynamic performance and typically increases structural weight
- 42DihedralDefined as angle between plane of wing and horizontal, where Γ > 0 (wing tips higher from ground than roots) whereas anhedral (Γ < 0) refers to tips being closer to ground than roots
- 43Benefits and drawbacks of dihedral• provides additional ground clearance for wing tips and any under-wing mounted engines or ordnance
• adds to the vehicle’s lateral stability
• sometimes when designer wants less laterally stable aircraft, anhedral is used to destabilise - 44NACA 4-series• 1st digit: max. camber (hundredths of chord, e.g. 2 for 2% of c)
• 2nd digit: location of max. camber (tenths of chord)
• 3rd and 4th digits: max. thickness (hundredths of chord) - 45NACA 5-series• 1st digit x 3/2: deisgn lift coeff. (tenths)
• 2 digit / 2: location of max. camber along chord chord L.E. (hundredths of chord)
• 3rd digit (either a 0 or 1): defines use of reflex
• 4th and 5th digits: max. thickness (hundredths of chord) - 46ReflexTrailing edge curves slightly up in an S-shape camber line
- 47NACA 6-series• 1st digit: identifies the series (6)
• 2nd digit: location of min. pressure (tenths of chord)
• 3rd digit: design lift coeff. (tenths)
• 4th and 5th digits: max thickness (hundredths of chord) - 48TwistAerodynamic feature added to aircraft wings to adjust lift distribution along the wing
- 49Geometric twistAerofoil sections set at different angles of attack along wing span. Increase in AoA from root to tip is called wash-in, while reduction in AoA is called wash-out
- 50Aerodynamic twistUsing different aerofoil sections, with different sectional characteristics, along the wing’s span
- 51What are stablisers?Lifting surfaces (wings) typically placed at tail-end of vehicle- contributes to stability and acts as mounting point for aerodynamic control surfaces. Generally about 20-30% of wing size.
- 52Where should vertical stabilisers be placed?Aft of vehicle's centre of gravity to ensure weathercock (directional) stability
- 53Where are horizontal stabilisers usually placed?Mounted on the fuselage or on the fin if a tailplane or else could be located on front of aircraft (called a canard)
- 542 classes of propulsion systemsPower-producing engines and thrust-producing engines
- 55How do power-producing engines work?Deliver power via a rotating shaft to a propeller
- 56How do thrust-producing engines work?Produce a thrust force by increasing momentum of a fluid, typically on-coming airflow
- 57How does a reciprocating or piston engine work?Relies on piston attached to a crankshaft compressing fuel-air mixture which is in turn ignited. High-pressure gases generated by combustion push piston out of cylinder and further rotate crankshaft. Mounting several pistons onto a crankshaft such that they operate out of phase to one another allows cycle to sustain itself, producing continuous shaft power.
- 585 stages of gas turbine• Inlet/ Intake: capture free-stream air and slow it down to efficient conditions
• Compressor: compress air slowing to down, increasing temp and pressure
• Combustion chamber: mixes air with fuel (typically kerosene) and ignites; temperature and pressure increase a lot
• Turbine: extracts energy from high temp and pressure gas driving compressor and shaft (temp and pressure are reduced)
• Nozzle: allows gases to expand to ambient - 59How does a turbojet engine work?A gas turbine engine that works by compressing air with an inlet and a compressor (axial, centrifugal, or both), mixing fuel with the compressed air, burning the mixture in the combustor, and then passing the hot, high-pressure air through a turbine and a nozzle. The compressor is powered by the turbine, which extracts energy from the expanding gas passing through it. The engine converts internal energy in the fuel to kinetic energy in the exhaust, producing thrust. Typically used for aircraft operating and high altitudes and speeds (inefficient at low airspeeds)
- 60How do afterburners work?Used if additional thrust is required for some flight stages. Inject fuel directly into the exhaust stream and burns it using this remaining oxygen. This heats and expands the exhaust gases further, and can increase the thrust of a jet engine by 50% or more. Often used by fighter aircraft to reduce takeoff distances or reach higher supersonic flight speeds. Greatly increase the fuel consumption.
- 61How do ramjets work?For higher supersonic speed applications, where turbojet engines are limited by the turbine stage inlet temperature. An object moving at high speed through air generates a high-pressure region upstream. Ramjet uses this high pressure in front of the engine to force air through the tube (compressed by inlet by slowing it using series of oblique shock waves), where it is heated by combusting some of it with fuel. It is then passed through a nozzle to accelerate it to supersonic speeds. For hypersonic speeds, slowing the airflow down to subsonic speeds for combustion is not possible, hence a supersonic combustion ramjet, abbreviated as scramjet, is used. While ramjets and scramjets can operate efficiently above M = 3 or 6 respectively, can't operate at static conditions, so need to be coupled with another produslive unit to get up to speed.
- 62UndercarriageLanding gear, ensures aircraft can operate effectively on ground/water. Allows steering and braking. Major source of drag, though most high-speed aircraft use retractable undercarriage.
- 633 distinct control surfaces for most fixed-wing aircraft• Elevator
• Ailerons
• Rudder
- 64Static pressure, PₛThe atmospheric pressure recorded on a body at rest relative to the aircraft
- 65Total pressure, Pₜ(aka pitot pressure or stagnation pressure) The pressure recorded when airflow over the aircraft comes to rest
- 66Pitot-static tube
- 67Bernoulli's equationPₜ = Pₛ + 1/2 ρ v² where 1/2 ρ v² is the dynamic pressure
- 68True airspeed vs. Equivalent airspeedTrue airspeed, V = √ 2(Pₜ - Pₛ)/ρ
Equivalent airspeed = Vᵢ = √ 2(Pₜ - Pₛ)/ρ₀
1/2 ρ V² = 1/2 ρ₀ Vᵢ²
Vᵢ = √(ρ/ρ₀) V = √σ V - 69Relative densityσ = ρ/ρ₀
- 70—
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- Undergraduate Introduction to Aerospace Flashcards on The Flying Environment, created by Paris Hart on 18/01/2021.
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