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Questions and Answers
What is a limitation of the pitot type inlet?
What is a limitation of the pitot type inlet?
Why might a pitot type inlet require a departure from a circular cross section?
Why might a pitot type inlet require a departure from a circular cross section?
What is a benefit of the pitot type inlet on single-engine aircraft?
What is a benefit of the pitot type inlet on single-engine aircraft?
What is a characteristic of subsonic inlet ducts?
What is a characteristic of subsonic inlet ducts?
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What is the effect of the divergent shape of subsonic inlet ducts?
What is the effect of the divergent shape of subsonic inlet ducts?
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What is another name for subsonic inlet ducts?
What is another name for subsonic inlet ducts?
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Where are some of the most common locations to mount engine inlets?
Where are some of the most common locations to mount engine inlets?
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What was the advantage of the in-wing design for early commercial and military aircraft?
What was the advantage of the in-wing design for early commercial and military aircraft?
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What materials are typically used to construct inlet ducts?
What materials are typically used to construct inlet ducts?
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Where are the inlet ducts typically mounted on most multi-turbojet and turbofan aircraft?
Where are the inlet ducts typically mounted on most multi-turbojet and turbofan aircraft?
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Why did the in-wing design become impractical with the introduction of high-bypass turbofan engines?
Why did the in-wing design become impractical with the introduction of high-bypass turbofan engines?
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What is the typical method of attaching turbofan inlets to the engine?
What is the typical method of attaching turbofan inlets to the engine?
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What is the purpose of the spill valve in the movable spike inlet?
What is the purpose of the spill valve in the movable spike inlet?
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What is the primary function of the movable wedge in the inlet?
What is the primary function of the movable wedge in the inlet?
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At what speed does the compression provided by the engine become relatively minor?
At what speed does the compression provided by the engine become relatively minor?
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What is the purpose of the divergent area in the inlet?
What is the purpose of the divergent area in the inlet?
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What happens to the air velocity at the inlet during supersonic flight?
What happens to the air velocity at the inlet during supersonic flight?
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What is the function of the dump valve during subsonic flight?
What is the function of the dump valve during subsonic flight?
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What is the purpose of the movable vane in a particle separator?
What is the purpose of the movable vane in a particle separator?
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What is the result of the inertia of sand and ice particles in a particle separator?
What is the result of the inertia of sand and ice particles in a particle separator?
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How do individual filter elements in a particle separator work?
How do individual filter elements in a particle separator work?
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What is the advantage of divided entry inlets on single-engine aircraft?
What is the advantage of divided entry inlets on single-engine aircraft?
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What happens when an aircraft with a divided entry inlet yaws?
What happens when an aircraft with a divided entry inlet yaws?
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What happens to the foreign particles in a particle separator?
What happens to the foreign particles in a particle separator?
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What is the benefit of engine-mounted inlet ducts?
What is the benefit of engine-mounted inlet ducts?
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What is a common material used in the construction of inlets?
What is a common material used in the construction of inlets?
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Where are the inlet ducts mounted on some multi-engine jet aircraft?
Where are the inlet ducts mounted on some multi-engine jet aircraft?
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What shape does the inlet duct take in some fuselage-mounted inlets?
What shape does the inlet duct take in some fuselage-mounted inlets?
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What is a limitation of single-entry pitot type inlets at high speeds?
What is a limitation of single-entry pitot type inlets at high speeds?
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Where are the inlet ducts mounted on single-engine and some twin-engine military aircraft?
Where are the inlet ducts mounted on single-engine and some twin-engine military aircraft?
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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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