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Questions and Answers

What is a limitation of the pitot type inlet?

  • Inlet turbulence at low airspeed and high angles of attack (correct)
  • Inefficient airflow into the compressor
  • Inability to be used on pod-mounted engines
  • High pressure drop

    • Why might a pitot type inlet require a departure from a circular cross section?

  • Due to the shape of the compressor
  • Due to the type of aircraft
  • Due to the size of the engine
  • Due to the proximity to the ground when the wing is flexed (correct)

    • What is a benefit of the pitot type inlet on single-engine aircraft?

  • Limited engine power
  • High pressure drop
  • Turbulent airflow into the compressor
  • Smooth airflow into the compressor (correct)

    • What is a characteristic of subsonic inlet ducts?

    <p>Divergent shape</p> Signup and view all the answers

    What is the effect of the divergent shape of subsonic inlet ducts?

    <p>Increase in static pressure</p> Signup and view all the answers

    What is another name for subsonic inlet ducts?

    <p>Inlet diffuser</p> Signup and view all the answers

    Where are some of the most common locations to mount engine inlets?

    <p>In the wing, on the engine, on the fuselage, and within the fuselage</p> Signup and view all the answers

    What was the advantage of the in-wing design for early commercial and military aircraft?

    <p>It streamlined the turbojet engines</p> Signup and view all the answers

    What materials are typically used to construct inlet ducts?

    <p>Aluminium alloy and/or composites such as carbon fibre and Kevlar</p> Signup and view all the answers

    Where are the inlet ducts typically mounted on most multi-turbojet and turbofan aircraft?

    <p>Directly onto the front of the engine</p> Signup and view all the answers

    Why did the in-wing design become impractical with the introduction of high-bypass turbofan engines?

    <p>It was not suitable for the new engine design</p> Signup and view all the answers

    What is the typical method of attaching turbofan inlets to the engine?

    <p>Bolting</p> Signup and view all the answers

    What is the purpose of the spill valve in the movable spike inlet?

    <p>To dump unwanted ram air overboard at high speed</p> Signup and view all the answers

    What is the primary function of the movable wedge in the inlet?

    <p>To control the air flow velocity</p> Signup and view all the answers

    At what speed does the compression provided by the engine become relatively minor?

    <p>At three times the speed of sound</p> Signup and view all the answers

    What is the purpose of the divergent area in the inlet?

    <p>To slow air velocity</p> Signup and view all the answers

    What happens to the air velocity at the inlet during supersonic flight?

    <p>It slows down to subsonic speeds</p> Signup and view all the answers

    What is the function of the dump valve during subsonic flight?

    <p>To act as an air scoop</p> Signup and view all the answers

    What is the purpose of the movable vane in a particle separator?

    <p>To create a venturi and sudden turn in the engine inlet</p> Signup and view all the answers

    What is the result of the inertia of sand and ice particles in a particle separator?

    <p>They cannot follow the sharp curve of the inlet</p> Signup and view all the answers

    How do individual filter elements in a particle separator work?

    <p>By imparting a swirling motion to the incoming air</p> Signup and view all the answers

    What is the advantage of divided entry inlets on single-engine aircraft?

    <p>They avoid using long inlet type ducts</p> Signup and view all the answers

    What happens when an aircraft with a divided entry inlet yaws?

    <p>A loss of ram pressure occurs on one side of the inlet</p> Signup and view all the answers

    What happens to the foreign particles in a particle separator?

    <p>They are thrown to the outside of the chamber</p> Signup and view all the answers

    What is the benefit of engine-mounted inlet ducts?

    <p>They reduce internal skin friction</p> Signup and view all the answers

    What is a common material used in the construction of inlets?

    <p>Aluminium alloy</p> Signup and view all the answers

    Where are the inlet ducts mounted on some multi-engine jet aircraft?

    <p>On the fuselage</p> Signup and view all the answers

    What shape does the inlet duct take in some fuselage-mounted inlets?

    <p>S-shaped</p> Signup and view all the answers

    What is a limitation of single-entry pitot type inlets at high speeds?

    <p>They form shock waves at the inlet lip</p> Signup and view all the answers

    Where are the inlet ducts mounted on single-engine and some twin-engine military aircraft?

    <p>On the fuselage</p> Signup and view all the answers

    Study Notes

    Engine Inlet Configurations

    • Engine-mounted inlet ducts provide short, efficient inlets with minimal internal skin friction.
    • Inlet ducts can be mounted directly onto the front of the engine or form part of the fuselage, engine pylon, or stub wing structure.

    Inlet Construction on Fuselage

    • Inlet ducts may be constructed from aluminum alloy and/or composites such as carbon fiber and Kevlar.
    • Inlets forming part of the aft fuselage may have a long "S" shaped duct.
    • Some multi-engine jet aircraft have engines mounted on the aft fuselage, with inlet ducts mounted directly onto the front of the engine.

    Inlet Construction Within Fuselage

    • Single-engine and some twin-engine military aircraft have engines mounted within the fuselage.
    • Inlet ducts may be mounted in the nose, under the fuselage, or on both sides of the fuselage.
    • Inlet ducts may form part of the fuselage structure.

    Effects of Inlet Configurations

    • The ideal air inlet for a turbojet engine is a single, short, pitot type circular inlet, which makes full use of ram effect and suffers minimal loss of ram pressure with changes in aircraft attitude.
    • However, as sonic speed is approached, its efficiency begins to fall due to the formation of a shock wave at the inlet lip.

    Inlet Types and Locations

    • Inlet ducts have been designed to accommodate new airframe/engine combinations and variations in engine mounting locations.
    • Common locations for engine inlets include:
      • In the wing
      • On the engine
      • On the fuselage
      • Within the fuselage

    Inlet Construction in Wing

    • Some early commercial and military aircraft had engines installed in the wings, with inlet ducts constructed from aluminum alloy and built into the wing.
    • This design has become impractical with the introduction of high-bypass turbofan engines.

    Inlet Construction on Engine

    • Most multi-turbojet and turbofan aircraft have inlet ducts mounted directly onto the front of the engine.
    • Inlets are constructed from aluminum alloy and/or composites such as carbon fiber and Kevlar.
    • Turbofan inlets are typically bolted to the forward flange of the inlet case or fan case.

    Single-Entry (Pitot) Type Duct

    • This type of inlet results in the minimum pressure drop, but the engine tends to suffer from inlet turbulence, especially at low airspeed and/or high angles of attack (AOA).
    • The pitot type inlet can be used for engines mounted in pods, wings, or other flying surfaces.
    • The inlet may require a departure from the circular cross-section due to the area of the surface.

    Subsonic Inlet Ducts

    • Inlet ducts such as those found on business and commercial jet aircraft are of fixed geometry and have a divergent shape.
    • The divergent duct progressively increases in diameter from front to back, arriving at the compressor at a slightly increased static pressure.
    • This duct is sometimes referred to as an inlet diffuser due to its effect on pressure.

    Moveable Spike Inlet

    • This type of inlet provides a similar function of convergence, divergence, and shock wave formation.
    • It also has a spill valve to dump unwanted ram air overboard at high speed.
    • Many high-performance aircraft have an excess of mass flow at cruising speeds.

    Divided Entry Inlets

    • Divided entry inlets are used on single-engine aircraft to avoid using long inlet type ducts.
    • The twin divided inlet ducts merge into the wing leading edges on each side of the fuselage.
    • The airflow may remain divided until it reaches the engine compressor or merge smoothly before reaching the engine.
    • The disadvantage of the divided type of inlet is that when the aircraft yaws, a loss of ram pressure occurs on one side of the inlet, causing an uneven distribution of airflow into the compressor.

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