Module 15.3 Inlets Flashcards
What is used to straighten the airflow and direct it into the first compressor stages?
Inlet Guide Vanes (IGV’s)
What is required to avoid compressor stall?
Uniform and steady airflow
The air inlet duct is considered part of what?
Airframe
What can be said about a divergent duct?
Velocity - Decrease
Pressure - Increase
Temperature - Increase
Turboprop and turboshaft engines have what to prevent FOD ingress?
Screens
Where can the inlets be in a divided entrance duct aircraft?
Wing root or scoop at each side of the fuselage
What is placed in the side scoop inlet to assist in straightening the airflow?
Turning vanes
What is a disadvantage of divided entrance ducts W.R.T. Sudden flight movements?
Imbalances in Ram air pressure causing a slight power loss
What is the purpose of diffusers?
Decrease velocity and increase static pressure
What type of lip do you want at the inlet of a supersonic aircraft?
Sharp lip
What aircraft would round lip inlets be used on?
Subsonic
What occurs to the inlet area of a variable geometry duct with varying speeds?
Inside area changed by a mechanical device
What are the 3 methods of slowing airflow to subsonic levels?
- Vary the area
- Variable airflow bypass
- Shockwave in the airstream
What are the disadvantages of compressor inlet screens?
Loss in inlet duct pressure and are susceptible to icing
When are inlet screens retracted?
After take off or if icing conditions are detected
When would a bell mouth compressor inlet be used?
During engine testing in a test cell
What are the benefits to the bell mouth compressor inlets during testing?
- Very high aerodynamic efficiency
- Duct loss is considered 0
What is considered the best inlet design for turboprop engines?
Ducted arrangement
What is used to deflect ice and dust/dirt away from the intake?
Deflector doors
What is the drawback to two spool engines?
Fan and low pressure compressor are connected. Fan has a limited rotational speed which is slower than the optimum compressor rpm. This means that the low pressure compressor is not at its optimum efficiency
How does the fan prevent FOD ingestion?
Hits the fan and thrown radially outward
How is the inlet lip and fan hub/spinner anti-iced?
Lip - Warm bleed
Fan hub/spinner - Warm bleed or conical spinner
What effects can ice build up cause?
- Engine sucks in ice
- Disturbed airflow
What do turboprops use to anti-ice inlet areas?
Warm oil
If only the cowls require anti-ice what may be used?
Electric heat strips
When can ice form in inlet areas? Temperatures?
- 5℃ in dry condition
- 7℃ in fog/rain conditions
What are the types of anti-ice?
- Bleed air
- Electric heating
What engines is bleed air generally used in?
High-mass airflow
Air bled from the HP compressor is used to anti-ice what?
- IGV’s
- Spinner
- Lip
What is the purpose of the anti-icing valve?
- Prevent over pressurisation
- Limit amount bleed air
The engine anti-ice system uses hot air from what?
- Pneumatic system
- Directly from the engine
When is the manual function of the anti-ice regulator valve used?
Valve or system failure
When the engine is controlled by Electronic Engine Control (EEC), what is it linked with?
Anti-ice
What is the most common type of engine ice protection system?
Thermal system
As aircraft speed increases what happens to the thrust?
Thrust tends to decrease
As the aircraft reaches a certain speed, what compensates for the losses in thrust caused by this increase in speed?
Ram recovery
What is another name for ram recovery?
Total pressure recovery
