Definition of Total Head pressure
Pressure of the air when brought to rest in front of the wings and intakes.
Definition of recovery
To regain as much of the ram air velocity as possible, and convert it into pressure at the face of the engine.
Definition of intake momentum drag
As forward speed increases, thrust decreases. Momentum of the air passing into the engine in relation to the forward speed of the aircraft.
Definition of ram ratio
Ratio of total pressure at the inlet to the compressor, to the static pressure at the entrance to the air intake.
What two parts make up the air intake?
The intake nose and inlet duct.
What is an inlet duct that gets wider, known as?
Divergent.
What is the job of the intake nose?
Smooth the airflow to prevent disturbances.
What should air intakes be (in general) ?
- As straight as possible.
- As smooth as possible.
- Designed to decelerate the airflow.
What does the inlet duct convert in-flight?
Kinetic energy of the air stream into pressure energy.
What is the most efficient inlet type for subsonic aircraft?
The pitot type quasi-circular diffuser. 😂
How is the inlet lip designed to reduce the risk of flow separation?
It’s well-rounded, has a thicker radius and thin lips for high speed flight.
What is nose suction?
A suction effect from a drop in pressure in front of the inlet, acting in the direction of engine thrust.
What is the ‘super-critical condition’ in supersonic inlets?
Where airflow demand is greater than the inlet can provide, resulting in shockwaves and turbulence that affect the flow into the compressor.
What are the five types of intake loss?
- Frictional losses due to skin friction.
- Frictional losses at the intake duct walls.
- Turbulence losses due to structures in the intake.
- Turboprop drag and turbulence from the spinner and blade roots.
- Divided intake suffers losses due to boundary layer problems, and loss of ram pressure on one side when yawing.
What are the efficiency percentages of the different intake designs?
- Pitot, 96-99% efficient.
- Wing root, 87-95% efficient.
- Side, 80-89% efficient.
- Turbo Prop annular, 74-82% efficient.
How does a ‘normal shockwave inlet’ function?
Employs a single normal shockwave at the front of the inlet to slow the air to subsonic velocity.
Not suitable for higher speed supersonic flight.
How does an oblique shockwave inlet function?
This design employs an external oblique shock wave to slow the supersonic airflow before the normal shock occurs.
How does a variable supersonic inlet function?
Equipped with actuated panels that change angle based on Mach number. Usually, higher Mach number means more closure of the intake.
What are the two negative effects of ice on engine intakes?
- Disturbed airflow that can affect performance and cause compressor stall.
- Physical damage.
What do engines have to prevent ice buildup?
A thermal anti ice system on each engine.
What are the requirements of the anti ice system? (4)
- Reliable
- No weight penalty
- No loss of power
- Ease of maintenance.
What are the two types of heating system for the INTAKE?
Bleed air and electrical heating.
What are the two types of spinner ice protection?
Hot oil and rubber spike.
Where is bleed air bled from?
The HP compressor.
