15.3 Inlet Flashcards
(49 cards)
What is total head pressure
Pressure of air when brought to rest in front of the wings and intakes
What is compression
Intakes increase in pressure within the intake at increasing forward speeds
What is recovery
Regain as much of the ram air velocity as possible and convert it into pressure at the face of the engine
What is intake momentum drag?
As forward speed increases, thrust decreases.
What is ram ratio
The ratio of the total pressure at the inlet to the compressor, to static pressure the entrance to the air intake
What is the intake or air inlet
The structure that directs the airflow to the engine, usually a divergent duct
What is the engine inlet
The point at which the airflow passes from the air inlet into the engine
What is subsonic
Any velocity where all the airflow around a body is below Mach 1
What is transonic
Typically velocity between 0.8 and 1.4
What is the name of the inlet as it gets gradually wider
Divergent
What happens to pressure as it moves through a divergent duct
Increases static pressure
What is the first component of a gas turbine engine
The inlet, it should be as straight and smooth as possible
For air to flow smoothly though a compressor what is the optimum speed range at the compressor inlet
Between 0.4 and 0.7
How are intakes designed to slow down the airflow?
By converting Kinetic energy into pressure energy
What is the most efficient subsonic inlet configuration
Pitot type quasi-circular diffuser
Why type of inlet lip must be avoided for high speed flight
Thicker or larger radius lips
What is restricted if a crosswind exceeds a certain velocity
Restricted from applying full power until they have reached a specified ground speed
What is the most practical transonic inlet
A pitot type design up to Mach 1.5
At transonic speeds what is the inlet designed to do
To keep the shock wave out
How does a transonic inlet keep the shockwave out
By using a normal shock diffuser to decelerate the supersonic airflow efficiently to the speed needed for the compressor
What is supercritical condition?
Should the engine require more air than the inlet can provide a pressure drop will occur in the inlet which mean it will swallow the shock wave.
Airflow hitting the compressor will still be supersonic which isn’t good for the compressor
Due to the physical effects of air flowing into and through the inlet, energy loss or ram recovery can be affected by what o
- Frictional losses due to fuselage air/skin friction
- Frictional losses due to the intake duct walls
- Turbulence losses due to structures or components in the intake
- Turbo props cause drag and turbulence losses due to the spinner and blade roots
- When the aircraft yaws, a loss of ram pressure will exist on one side
What can normal duct inefficiencies of 1% cause
Thrust loss of between 1% - 4%
Which intake designs are most efficient
- Pitot: 96-99% efficient
- Wing root: 87-95% efficient
- Side: 80-89% efficient
- turbo prop annular (dart): 74-82% efficient
