Gas Turbine Engine Inlet Design

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Questions and Answers

What is the advantage of an engine-mounted inlet?

Improved engine performance at supersonic speeds

Increased ram pressure

Enhanced air flow at low altitudes

Reduced skin friction (correct)

What materials are inlets constructed from?

Copper and bronze

Aluminium alloy and composites (correct)

Fibreglass and plywood

Steel and titanium

On which part of the fuselage are inlet ducts mounted in some multi-engine jet aircraft?

Nose of the fuselage

Aft fuselage (correct)

Tail section

Under the fuselage

What type of inlet is ideal for an aircraft flying at subsonic or low supersonic speeds?

Single-entry pitot type Signup and view all the answers

What happens to the efficiency of a single-entry pitot type inlet as sonic speed is approached?

It falls due to the formation of a shock wave Signup and view all the answers

What is the primary purpose of allowing air to diffuse in the front portion of the duct?

To provide a uniform pressure and minimal turbulence to the engine Signup and view all the answers

At what point does the compressor reach its aerodynamic design point and produces its optimum compression and fuel economy?

When the aircraft reaches its desired cruising speed Signup and view all the answers

What happens to the inlet pressure when the aircraft begins to move forwards?

It increases due to the ramming of air into the inlet Signup and view all the answers

What is the main difference between a turbofan inlet and a turbojet inlet?

The turbofan inlet discharges only a portion of its air into the gas generator Signup and view all the answers

At what speed range does ram recovery normally begin to occur in most aircraft?

Mach 0.1 to Mach 0.2 Signup and view all the answers

What is the function of the spill valve in a movable spike inlet?

To dump unwanted ram air overboard at high speeds Signup and view all the answers

What happens to the compression provided by the engine as aircraft speed increases?

It becomes relatively minor Signup and view all the answers

What is the purpose of the wedge in a movable spike inlet?

To provide a controlled sonic shock wave Signup and view all the answers

At what speed can a pressure ratio of 50:1 be achieved?

Three times the speed of sound Signup and view all the answers

What happens to the dump valve in subsonic flight?

It is reversed to act as an air scoop Signup and view all the answers

What is the effect of increasing aircraft speed on ram compression?

It increases the compression ratio Signup and view all the answers

What is the purpose of a convergent-divergent inlet duct in a supersonic aircraft?

To slow down airflow to subsonic speed at the face of the engine Signup and view all the answers

What happens to air at supersonic flow rates in a duct?

It is compressed to create a shock wave Signup and view all the answers

What is the function of a movable restrictor in a supersonic inlet duct?

To vary the geometry of the inlet Signup and view all the answers

What is the air velocity behind the final shock wave in a supersonic diffuser type inlet?

Mach 0.8 Signup and view all the answers

What happens to sand and ice particles when they enter the engine inlet with a movable vane?

They are separated from the combustion air due to their inertia Signup and view all the answers

What is the purpose of the helical vanes in a particle separator?

To create a swirling motion and separate dirt particles Signup and view all the answers

What happens to the foreign particles in a particle separator?

They are blown overboard by compressor bleed air Signup and view all the answers

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

They avoid using long inlet type ducts Signup and view all the answers

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

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

Study Notes

Inlet Construction

Engine-mounted inlet ducts can be short and efficient 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.
Inlets are constructed from aluminium alloy and/or composites such as carbon fibre and Kevlar.

Inlet Construction on Fuselage

Multi-engine jet aircraft may have inlet ducts mounted on the aft fuselage.
Inlets forming part of the aft fuselage may have a long "S" shaped duct.

Inlet Construction Within Fuselage

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

Single-Entry (Pitot) Type Duct: ideal for subsonic or low supersonic speeds, uses ram effect to increase air inlet pressure.
Inlet pressure increases add significantly to the mass airflow as the aircraft reaches its cruising speed.
Turbofan inlet is similar to the turbojet except that it discharges only a portion of its air into the gas generator.

Ram Pressure Recovery

Ram pressure recovery occurs when the aircraft begins to move forward, air is rammed into the inlet, and ram recovery takes place.
The resultant increase in inlet pressure cancels the drop in pressure in the inlet, and conditions return to ambient.
Ram recovery normally begins to occur at speeds between Mach 0.1 and Mach 0.2 in most aircraft.

Supersonic Inlets

Convergent-Divergent (C-D) inlet duct is required on all supersonic aircraft to slow the airflow to subsonic speed at the face of the engine.
A movable restrictor is often employed to form a C-D shape of variable proportion.
Supersonic diffuser type inlet provides a means of creating both a shock wave formation to reduce air velocity and a variable C-D shape.

Movable Spike Inlet

The movable spike inlet provides a means of creating both a shock wave formation to reduce air velocity and a variable C-D shape.

Divided Entry Inlets

Divided entry inlets are used on single-engine aircraft to avoid using long inlet type ducts.
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.

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Description

Explore the design and construction of inlet ducts in gas turbine engines, including engine-mounted inlet and inlet construction on fuselage.