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Questions and Answers
What is the function of the spill valve in a movable spike inlet?
What is the function of the spill valve in a movable spike inlet?
- To increase air velocity
- To provide a sonic shock wave
- To control fuel flow
- To dump unwanted ram air overboard at high speed (correct)
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?
- Three times the speed of sound
- Supersonic speed
- Subsonic speed
- Twice the speed of sound (correct)
What happens to the air velocity when it enters the divergent area of the inlet?
What happens to the air velocity when it enters the divergent area of the inlet?
- It remains the same
- It decreases (correct)
- It increases
- It becomes supersonic
In subsonic flight, what is the position of the wedge and the dump valve?
In subsonic flight, what is the position of the wedge and the dump valve?
What is the purpose of creating a controlled sonic shock wave at the inlet during supersonic flight?
What is the purpose of creating a controlled sonic shock wave at the inlet during supersonic flight?
What is the advantage of having a high-pressure ratio at high speeds?
What is the advantage of having a high-pressure ratio at high speeds?
What is the main advantage of using a bellmouth inlet?
What is the main advantage of using a bellmouth inlet?
Why are mesh screens often used with bellmouth ducts during ground testing?
Why are mesh screens often used with bellmouth ducts during ground testing?
What is a limitation of using inlet screens on aircraft?
What is a limitation of using inlet screens on aircraft?
What type of installations often use compressor inlet screens?
What type of installations often use compressor inlet screens?
What is a potential issue with using inlet screens on aircraft?
What is a potential issue with using inlet screens on aircraft?
What is a unique feature of some turboprop aircraft inlet separators?
What is a unique feature of some turboprop aircraft inlet separators?
What is the advantage of engine-mounted inlet ducts?
What is the advantage of engine-mounted inlet ducts?
What materials are commonly used to construct inlets?
What materials are commonly used to construct inlets?
Where are inlet ducts typically mounted on multi-engine jet aircraft?
Where are inlet ducts typically mounted on multi-engine jet aircraft?
What is the ideal air inlet configuration for a turbojet engine at subsonic or low supersonic speeds?
What is the ideal air inlet configuration for a turbojet engine at subsonic or low supersonic speeds?
What happens to the efficiency of a single-entry, pitot type circular inlet as sonic speed is approached?
What happens to the efficiency of a single-entry, pitot type circular inlet as sonic speed is approached?
Where are inlet ducts typically mounted on single-engine and some twin-engine military aircraft?
Where are inlet ducts typically mounted on single-engine and some twin-engine military aircraft?
What is the primary purpose of ensuring the engine inlet duct is smooth and clean?
What is the primary purpose of ensuring the engine inlet duct is smooth and clean?
What should be done with curves or bends in the intake duct?
What should be done with curves or bends in the intake duct?
What is a potential consequence of bird strikes or hail on the inlet duct leading edge?
What is a potential consequence of bird strikes or hail on the inlet duct leading edge?
What is a potential cause of damage to internal acoustic lining?
What is a potential cause of damage to internal acoustic lining?
Under what conditions are icing conditions most prevalent?
Under what conditions are icing conditions most prevalent?
What is the importance of a gentle curve in the intake duct?
What is the importance of a gentle curve in the intake duct?
What is the purpose of turning on the anti-icing system before entering icing conditions?
What is the purpose of turning on the anti-icing system before entering icing conditions?
What type of systems are used in some smaller turboprop and turboshaft engines for anti-icing?
What type of systems are used in some smaller turboprop and turboshaft engines for anti-icing?
What is a possible location for electro-thermal anti-icing systems?
What is a possible location for electro-thermal anti-icing systems?
What happens if the anti-ice system is turned on after compressor stalls occur from ice formation?
What happens if the anti-ice system is turned on after compressor stalls occur from ice formation?
When is anti-icing heat required?
When is anti-icing heat required?
What is a limitation of electro-thermal anti-icing systems?
What is a limitation of electro-thermal anti-icing systems?
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Study Notes
Inlet Construction
- Inlet ducts are constructed from aluminum alloy and/or composites like carbon fiber and Kevlar.
- Inlets forming part of the aft fuselage may have a long "S" shaped duct.
Inlet Configurations
- Single-engine and some twin-engine military aircraft have their engines mounted within the fuselage.
- Inlet ducts may be mounted in the nose, under the fuselage, or on both sides of the fuselage.
Effects of Inlet Configurations
- A single, short, pitot type circular inlet is the ideal air inlet for a turbojet engine at subsonic or low supersonic speeds.
- This type of inlet makes full use of ram effect on the air due to forward speed and suffers the minimum loss of ram pressure with changes in aircraft attitude.
Inlet Types
- Moveable spike inlet: has a movable wedge that provides a similar function of convergence, divergence, and shock wave formation.
- Bellmouth inlet: increases aerodynamic drag on the airframe, but it is the most efficient option when there is little or no ram pressure available to force air into the compressor.
Inlet Screens
- The use of compressor inlet screens is usually limited to rotorcraft, turboprops, and ground turbine installations.
- Screens have been tried in high subsonic flight engines, but icing and screen fatigue failure caused so many maintenance problems that the use of inlet screens has for the most part been avoided.
Intake Airflow Distortion
- The engine inlet duct must provide a uniform supply of air to the compressor if the engine is to perform at optimum efficiency.
- Curves or bends in the duct must be minimal and carefully blended to prevent intake drag or resistance.
Inlet Duct Damage
- The inlet duct leading edge is susceptible to damage by bird strikes or hail.
- Damage to internal acoustic lining may be caused by bird strike, stones, and mishandling.
Inlet Duct Anti-ice Systems
- Icing of the engine and the leading edges of the intake duct can occur during flight through clouds containing supercooled water droplets or during ground operation in freezing fog.
- Anti-icing heat is required when visible moisture is present in the form of clouds.
- Some smaller turboprop and turboshaft engines use electric heat strip systems classed as electro-thermal anti-icing systems.
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