Aircraft Performance Fundamentals
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Questions and Answers

Which factor is NOT typically identified as governing the performance of an aircraft?

  • Ceiling height
  • Payload capacity
  • Aircraft color (correct)
  • Cruising speed

What is a key performance measure that describes how long an aircraft can operate before needing to land?

  • Range
  • Payload
  • Endurance (correct)
  • Cruising speed

Designers often need to optimize aircraft performance. What is typically a primary consideration in this optimization?

  • Achieving minimum performance criteria (correct)
  • Reducing overall size of the aircraft
  • Using the most advanced materials
  • Maximizing all performance measures equally

Which of the following performance measures refers to the aircraft's ability to carry weight?

<p>Payload (C)</p> Signup and view all the answers

Which of the following performance aspects is involved in atmospheric modeling?

<p>Take-off performance (B)</p> Signup and view all the answers

What is the total take-off distance required for the aircraft to reach take-off speed at a screen height of 35 ft?

<p>1482 m (D)</p> Signup and view all the answers

What is the weight (W) of the aircraft given a total weight of 59,000 kg?

<p>578,790 N (B)</p> Signup and view all the answers

Which of the following contributes to the total drag coefficient C_D at lift-off?

<p>Both total parasitic drag and induced drag (B)</p> Signup and view all the answers

Calculate the aspect ratio (AR) given the wingspan (b) of 32 m and the wing area (S) of 115 m².

<p>8.9 (A)</p> Signup and view all the answers

What is the total thrust provided by the twin turbofans at lift-off (T_LOF)?

<p>140 kN (D)</p> Signup and view all the answers

What formula represents the lift (L) generated by an aircraft in relation to its properties?

<p>$L = \rho V^2 S C_L$ (A)</p> Signup and view all the answers

What does the variable $s_{STOP}$ represent in the context of aircraft performance?

<p>The distance required for the aircraft to decelerate to a stop (C)</p> Signup and view all the answers

How does the aircraft's take-off mass (W) affect the distance required for take-off according to the equations provided?

<p>Increases stopping distance in relation to $\mu$ and $C_D$. (C)</p> Signup and view all the answers

In the formula $s_{STOP} = \int_{V_1}^{0} \frac{1}{2g} \frac{W}{\rho S(\mu C_L - C_D)} V^2 dV$, which variable primarily affects the aircraft's deceleration?

<p>$\mu$ (coefficient of friction) (C)</p> Signup and view all the answers

Which parameter decreases the stopping distance for an aircraft according to the derived formula for $s_{STOP}$?

<p>Increasing the coefficient of lift ($C_L$) (D)</p> Signup and view all the answers

What is the importance of the decision speed V1 in the context of take-off performance?

<p>It signifies the point at which the aircraft must become airborne. (A)</p> Signup and view all the answers

What is the effect of the variable $BFL$ (Brake Force Length) as indicated in take-off performance measures?

<p>It describes the minimum distance required for stopping safely during take-off. (C)</p> Signup and view all the answers

What does the term $\rho$ represent in the context of the equations outlined for an aircraft?

<p>The air density (B)</p> Signup and view all the answers

What happens to air density ($\rho$) when humidity increases?

<p>Air density decreases. (B)</p> Signup and view all the answers

At what altitude does the tropopause exist at the equator?

<p>17 km (A)</p> Signup and view all the answers

In which layer of the atmosphere does temperature increase due to UV absorption?

<p>Stratosphere (C)</p> Signup and view all the answers

What is the approximate temperature at the mesopause?

<p>-85°C (B)</p> Signup and view all the answers

What are jet streams characteristically known for?

<p>High steady winds. (A)</p> Signup and view all the answers

What does the International Standard Atmosphere (ISA) model define?

<p>Typical conditions for aircraft operation up to ~30 km. (B)</p> Signup and view all the answers

How does pressure change with altitude in the troposphere?

<p>Pressure decreases exponentially. (B)</p> Signup and view all the answers

What is the significance of the ionization of oxygen and nitrogen in the thermosphere?

<p>It releases photons visible as aurorae. (B)</p> Signup and view all the answers

What is the value of the minimum drag during climb, $D_{min}$, given the parameters?

<p>101.385 kN (C)</p> Signup and view all the answers

What is the formula used to calculate the maximum climb angle $\gamma_{max}$?

<p>$\gamma_{max} = \sin^{-1}\left(\frac{T - D_{min}}{W}\right)$ (C)</p> Signup and view all the answers

In a steady climb, which equation describes the relationship between thrust, drag, and weight?

<p>Thrust - Drag = Weight sin(θ) (D)</p> Signup and view all the answers

What is the primary purpose of improving climb angle during take-off?

<p>To avoid obstacles and minimize noise (D)</p> Signup and view all the answers

What does the variable $V_c$ represent in the context of climb rate?

<p>Climb Velocity (B)</p> Signup and view all the answers

What is the calculated chord length, c, for the given wingspan and wing planform area?

<p>1.23 m (A)</p> Signup and view all the answers

What is the approximate Reynolds number, Re, at sea level with the given parameters?

<p>2.113 × 10^6 (C)</p> Signup and view all the answers

At an altitude of 1,000 ft, what is the interpolated air density, ρ?

<p>1.1896 kg/m3 (A)</p> Signup and view all the answers

What formula is used to interpolate the dynamic viscosity, µ, at 1,000 ft?

<p>µ = (µ2 - µ1) * (h - h1) / (h2 - h1) + µ1 (B)</p> Signup and view all the answers

What does the Mach number relate to in relation to static pressure?

<p>It represents the relative difference between total and ambient static pressure. (A)</p> Signup and view all the answers

Which expression is used to calculate the equivalent airspeed for subsonic speeds?

<p>$VEAS = a_0 imes rac{5(1 + (q/P_s)^{1/3.5} - 1)}{1}$ (C)</p> Signup and view all the answers

What is the value of dynamic viscosity, µ, at 1,000 ft after interpolation?

<p>1.7734 × 10^-5 kg/m-s (C)</p> Signup and view all the answers

What parameter does 'q' represent in the expression for equivalent airspeed?

<p>Dynamic pressure (A)</p> Signup and view all the answers

Flashcards

Aircraft Performance

The ability of an aircraft to perform its intended task effectively, often measured by factors like payload, ceiling, speed, range, endurance, and efficiency.

Design and Operational Factors

The factors related to how an aircraft's design and operation influence its ability to perform. This includes factors like wing shape, engine power, weight, and environmental conditions.

Evaluating Aircraft Performance

Evaluating an aircraft's performance typically involves analyzing several key metrics, such as payload, ceiling, speed, range, endurance, and operational costs.

Atmospheric Modelling

A model representing atmospheric conditions, influencing the aerodynamic forces acting on an aircraft. It factors in pressure, temperature, and density to predict how the plane will perform at different altitudes.

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Take-Off Performance

The ability of an aircraft to take off and climb safely under specific conditions, often measured by takeoff distance, climb rate, and time to reach a predetermined altitude.

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Troposphere

The region of the atmosphere where almost all weather occurs, extending from the Earth's surface to about 7 km at the poles and 17 km at the equator.

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Tropopause

The boundary between the troposphere and the stratosphere. Its altitude varies depending on latitude, typically around 7 km at the poles and 17 km at the equator.

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Stratosphere

The second major layer of the atmosphere, extending from the tropopause to about 50 km above the Earth's surface. It contains the ozone layer, which absorbs harmful ultraviolet radiation from the sun.

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Stratopause

The boundary between the stratosphere and the mesosphere. Located approximately 50 km above the Earth's surface.

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Mesosphere

The third major layer of the atmosphere, extending from the stratopause to about 80-85 km above the Earth's surface. Most meteors burn up in this layer.

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Mesopause

The boundary between the mesosphere and the thermosphere, located around 80-85 km above the Earth's surface.

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Thermosphere

The outermost layer of the atmosphere, extending from the mesopause to outer space. It is characterized by extremely high temperatures due to the absorption of solar radiation.

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Thermopause

The boundary between the thermosphere and outer space, located at around 500-600 km above the Earth's surface. It's where the atmosphere practically ends.

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Reynolds Number

A measure of the relative size of an object to the surrounding fluid, often air. It helps determine if fluid flow is laminar or turbulent.

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Mach Number

The speed of an object relative to the speed of sound in the surrounding air.

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a0

The speed of sound in air at standard sea level conditions.

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q

The ratio of dynamic pressure to static pressure. It represents the kinetic energy of the airflow.

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Equivalent Airspeed

The speed at which an aircraft would have the same dynamic pressure as if it was flying at sea level standard conditions.

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Reynolds Number & Altitude

The density of air decreases with altitude causing the Reynolds Number to reduce.

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Altitude Affects

Air density and viscosity changes with altitude. This impacts the Reynolds Number and Mach Number of aircraft.

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VEAS Formula

The formula used to calculate Equivalent Airspeed (VEAS) using the Mach number and the ratio of dynamic pressure to static pressure.

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Total Take-off Distance

The total distance an aircraft needs to reach its take-off speed at a specified height above the ground.

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Take-off Speed (V2)

The speed at which the aircraft becomes airborne, typically the speed at which lift equals weight.

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Lift-off Speed (VLOF)

The speed at which the aircraft begins its climb after lift-off.

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Thrust

The force generated by the engines to propel the aircraft forward.

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Drag

The resistance the aircraft encounters while moving through the air.

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Stopping Distance (SSTOP)

The distance required for an aircraft to decelerate from a specific speed, V1, to a complete stop.

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Drag Force (D)

The drag force acting on the aircraft, which opposes its motion through the air.

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Lift Force (L)

The lift force acting on the aircraft, which is generated by the wings and keeps it in the air.

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Lift Coefficient (CL)

The coefficient of lift, which describes the efficiency of the wings in generating lift.

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Drag Coefficient (CD)

The coefficient of drag, which describes the resistance the aircraft experiences from the air.

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Weight (W)

The weight of the aircraft, which acts downwards due to gravity.

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Air Density (ρ)

The density of the air, which affects the amount of lift and drag generated.

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Decision Speed (V1)

The decision speed, a critical speed in the takeoff process where the pilot must commit to continue the takeoff or abort it.

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Climb Rate

The rate at which an aircraft climbs vertically, expressed as speed in meters per second (m/s).

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Climb Angle

The angle between the aircraft's flight path and the horizontal plane, measured in degrees.

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Weight

The force of gravity acting on an aircraft, pulling it downwards.

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Study Notes

Course Content - Semester A

  • Thrust Needed for Flight
  • Basic Principles of Operation
  • Types of Gas Turbine Engines
  • Intakes
  • Compressors
  • Combustion Chambers
  • Turbines
  • Exhaust Systems
  • Performance
  • Off-Design Performance
  • Gas Turbine Cooling Systems

Aircraft Performance Tutorial 1: Atmospheric Modelling & Effects

  • Density:
    • Decreases with altitude.
  • Piston engine aircraft usually operate in the troposphere.

Aircraft Performance Tutorial 1: Aircraft Flight Profile

  • Aircraft typically follow a flight profile with seven different phases.
  • Take-off, climbing, cruising, descent, approach, landing, taxi.
  • These phases, affect an aircraft's performance characteristics;
  • Performance measures are dependent on the characteristics of the atmosphere.

Aircraft Performance Tutorial 1: Aircraft Performance Measures

  • Good aircraft performance maximises these factors:
    • Payload (A to B movement).
    • Ceiling (highest achievable altitude).
    • Speed (time taken).
    • Range (distance flown).
    • Endurance (length of flight time).
    • Aerodynamic/Propulsion efficiency (cost to run).
  • Aircraft designers optimise for most important performance criteria for the aircraft's task.

Aircraft Performance Tutorial 2: Take-off Performance

  • Ground Run: Lift has to be greater than weight. Thrust has to overcome drag.
  • During ground run, thrust has to be greater than the drag.
  • Directional Control During Ground Run:- Nose wheel at low speeds, rudder at high speeds.
  • Rotation Speed (VR) - Airspeed at which the aircraft begins to rotate for take-off.
  • Lift-Off Speed (VLOF) - Airspeed at which the aircraft leaves the ground.
  • Stall Speed (Vs) - Airspeed at which the lift generated by a wing equals the weight of the aircraft.
  • Decision Speed (V1) - Airspeed in the case of engine failure, at which the pilot can safely stop the aircraft.
  • Minimum Control Speed (VMC) - Minimum speed after lift-off, at which directional control can be provided by the rudder.

Aircraft Performance Tutorial 2: Drag

  • Drag (D) = Parasitic drag (Dp) + Induced drag (Di)
  • Parasitic drag (Dp) is a result of aerodynamic friction when an object moves through a fluid, V increases, then Dp increases
  • Induced drag (Di) is a result of the increasing amount of lift generated during take-off ground run

Aircraft Performance Tutorial 2: Induced Drag

  • Induced drag coefficient (CDi)
  • e = Oswald efficiency number (a correction factor, which represents the change in drag with lift for a 3D wing)
  • AR = Wing aspect ratio (b²/S) Where, b = wingspan, S = wing area
  • Cd= CD,P + CDi

Aircraft Performance Tutorial 2: Ground Effect

  • Increase of lift and reduction of induced drag for aircraft close to a surface.

Aircraft Performance Tutorial 2: Take-off Distance/Ground Run Distance

  • Take-off Distance = Ground run distance + Airborne distance to screen height.
  • Ground Run Distance equation: S = (W/gpSCt(CL - CD)) ln(1 + (pS(µCL-CD)V²/2(T-µW))

Aircraft Performance Tutorial 3: Climb Performance

  • Climb Angle (γ): Climb angle is the angle of climb in percentage, (γ)=asin((T-D)/W)
  • Climb Rate (Vc): Rate of climb is defined as the vertical speed of an aircraft (indicated on the vertical speed indicator, VSI).

Aircraft Performance Tutorial 3: Altitude Effects & Minimum Drag Velocity

  • Minimum drag velocity (Vmin)
  • Speed for max angle of climb (Vx)
  • Minimum Drag Velocity and Speed for max angle of climb (Vx) relationship
  • The effects of altitude to changes in lift-to-drag ratio (Cl/Cd) and speed.

Aircraft Performance Tutorial 3: Maximum Climb Angle

  • Given a fuel and engine efficiency, there is a limiting angle for climb.

Aircraft Performance Tutorial 3: Altitude Ceiling

  • Absolute ceiling: Aircraft is unable to climb any further because thrust equals the total drag.
  • Service ceiling: Rate of climb is limited for an aircraft.

Aircraft Performance Tutorial 3: Step & Zoom Climbs

  • Step climb: Aircraft can climb at different rates at different altitudes to save fuel.
  • Zoom climb: A high-speed maneuver that quickly transfers the kinetic energy (airspeed) to potential energy (altitude)

Aircraft Performance Tutorial 4: Cruise Performance

  • Lift = Weight for steady level flight
  • Thrust = Drag for steady level flight.

Aircraft Performance Tutorial 4: Aircraft Drag Polar

  • Coefficient of drag (CD): a + b (CL)^2
  • Induced drag (CDi): e (CL)^2 / (𝝿 AR)
  • Parasitic drag (CDp): CD0
  • Total drag, Cd= (CD,p )+ (CD,i)

Aircraft Performance Tutorial 4: Aircraft Stall Speed

  • Stall speed equation; Vs =√(2W / (ρ0S CLmax))

Aircraft Performance Tutorial 4: Equivalent Stall Speed

  • Equivalent Stall Speed VEAS,S = √2W/(psSCLmax) or Vs/ √(ρs/ρ0)
  • Equivalent stall speed is calculated at sea level.

Aircraft Performance Tutorial 5: Range and Endurance

  • Aircraft range:
    • Ground distance an aircraft can fly using a specified amount of fuel.
  • Aircraft Endurance:
    • Amount of time a given aircraft can stay in the air on a specified amount of fuel.
  • Specific Range calculation.
  • Breguet equation to calculate the range and endurance.
  • Factors to consider for range and endurance.

Aircraft Performance Tutorial 5: Calculating Range

  • Thrust-rated aircraft:
    • Calculation for maximum range from Breguet equation: R = (V/c₁)(C₁/CD)(lnW₁\W₂)

Aircraft Performance Tutorial 5: Calculating Endurance

  • Thrust-rated aircraft:
    • Calculation for maximum endurance from equation: E = (1/c₁)(C₁/CD)(lnW₁\W₂)

Thrust-Speed Curves

  • Turbofan engines have an upper and lower thrust/speed curves.

Various Engine Technologies

  • Turbojet engines
  • Turboprop engines
  • Turboshaft engines
  • Turbofan engines
  • Ram-jet engine
  • Turbo-ramjet engine
  • Open rotors

Aircraft Engine Intake Design

  • Intake shape to minimise losses
  • Consider airflow around other components
  • Provide good airflow distribution across whole compressor
  • Design for various atmospheric conditions
  • De-Icing
  • Bird strike

Aircraft Engine Combustion Chambers

  • Types
    • Multiple Cans
    • Can-Annular
    • Annular Throughflow
    • Annular Reverse Flow
  • Considerations
    • Flame stability and ignition
    • Temperature gradients, including hot spots
    • Design for minimal loss factors (e.g., pressure, cooling).
    • Fuel/air ratios.
    • Reduced carbon dioxide emissions.

Aircraft Engine Propulsion System

  • Newton's Third Law of Motion
  • Principles of operation and design of different propulsion systems (propellers, turbojets)
  • Relationships between thrust, power and speed

Note: Content for pages 675-685 are not included in the provided text.

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