Module 15.3 Inlet Flashcards
Engine inlets are what kind of duct and what do they do?
Divergent ducts. This increases the RAM recovery.
When the aircraft is stationary, all the suction is done by what?
What does this mean?
The engine, meaning there’s no RAM effect.
If there is no RAM effect at the inlet, what does this mean for air pressure?
Air pressure at the inlet will be lower than ambient air pressure.
The engine inlet of a turbine engine is designed to do what?
Provide a relatively distortion-free airflow to the inlet of the compressor.
What do many engines use to straighten the airflow and direct it into the first stages of the compressor?
Inlet Guide Vanes (IGV)
What is needed to avoid compressor stall?
A uniform and steady airflow.
Is the air-inlet duct is considered an engine part or airframe part?
An airframe part.
What can inefficiencies of the inlet duct result in?
Performance losses through other components of the engine.
What is used to prevent Foreign Object Damage (FOD) getting into the engine when the aircraft is stationary?
Screens
What happens to thrust as aircraft speed increases?
It decreases
What does RAM recovery compensate for?
Losses caused by reduced thrust due to the increase of speed.
What is RAM recovery?
The process of converting the kinetic energy of incoming air (RAM effect) into potential (static) energy at the engine inlet.
The inlet must be able to recover as much what from the free air stream?
Total pressure.
What does the added pressure at the inlet increase?
The pressure and airflow to the engine (RAM recovery).
What is an air pressure drop at the inlet caused by?
Friction of air along both sides of the duct and by the bends in the duct system.
What does an engine with low flow rates turning the airflow’s nacelle need to be?
Smaller
On turbofan engines, what must the duct have
A straight section to ensure smooth airflow.
What is the configuration to the entrance of the duct dictated by?
Location of the engine and the airspeed, altitude, and attitude the aircraft is designed to operate at.
What two effects can ice have on an engine?
Disturbed air flow that reduces the performance.
Pieces of ice can damage fan blades or inlet vanes.
What do turboprops do to prevent ice build up?
Warm oil from the engine oil reservoir together with a small amount of hot air.
Where is hot air taken from to provide anti-icing protection for the inlet?
From the compressor or diffuser.
How is hot air used to protect against ice?
It’s sprayed in a high-pressure pattern to heat all the surfaces where ice is likely to form.
At what temperatures can ice form on the inlet?
5 °C in dry air and at 7 °C in moist air.
What are the most common ice protection systems known as?
Thermal systems
Thermal anti-ice systems can be subdivided into what two categories?
Bleed Air and Electrical Heating.
Bleed air ice protection is generally used on what engines?
Those with high mass airflows (turbofan engines).
Where is hot air bled off from in the bleed air anti-ice system?
The engine HP compressor and passes through a pressure regulating bleed valve (anti-icing valve).
Bleed air provides surface heating to which parts of the engine?
Inlet Guide Vanes (IGVs), the spinner and the intake lip.
What are anti-ice valves used to protect against?
Over-pressurisation
How can anti-ice valves be operated?
Automatically via the ice detection system, or manually from the flight deck.
What is done with air used for the intake lip anti-icing?
Ejected overboard through small grills.
What is done with air used for the nose cone and inlet guide vanes
Directed overboard or back into the LP compressor intake.
Which valves provides the anti-ice connection between the compressor and where the air’s sent?
The anti-ice valve.
What happens when the anti-ice valve opens?
The hot air enters the anti-ice duct. The hot air sprays through small holes in the anti-ice duct into the engine cowling.
What safety precaution should their be in place during ground tests of thermal anti-ice systems.
No personnel should be in the test area.
How is the regulator valve controlled?
Solenoid-controlled
Other than anti-ice valves, what other valve is found in the anti-ice system?
Solenoid-controlled pressure regulating valves.
All thermal anti-ice valves have what?
A manual override function.
When is the manual override function of anti-ice valve used?
When there is a valve or system failure.
What is the anti-ice system linked to?
Electronic Engine Control (EEC) as part of a Full Authority Digital Engine Control (FADEC) system.
Once the flight crew makes the choice to turn on anti-icing, what does the Electronic Engine Control (EEC) do?
Controls the flow of hot air to the engine inlet.
What is used as anti-icing on smaller turboprop and turboshaft engines?
Electric heat strip systems, which are classed as electro-thermal anti-icing systems.
Where are electric heat strip anti-ice systems located?
At the lip of the nacelle inlet.
What does a divided duct do?
Takes air from either side of the fuselage.
What are two types of divided duct?
Wing-root inlet or scoop
Which type of divided duct is often used
Scoops
Where are divided inlet side scoops placed and why?
As far forward as possible to permit a gradual bend toward the compressor inlet.
Why are a series of turning vanes sometimes placed in the side-scoop inlet?
To assist in straightening the incoming airflow.
What is a disadvantage to a divided inlet arrangement?
Some sudden flight manoeuvres can cause an imbalance in ram air pressure between the two ducts. This can result in slight power loss.
Through all flight conditions, what must be done to the velocity of the airflow as it enters the air-inlet duct?
It must be reduced through the duct before the airflow enters the compressor.
How are inlet ducts designed to decrease velocity and increase static pressure before air gets to the compressor?
They are designed to function as diffusers.
With supersonic flight aircraft, what does the fwd portion of the duct do?
It acts as a diffuser by progressively decreasing in the area in the downstream direction. This decreases the velocity of the airflow to Mach 1.0.
Pressure is also increased
With supersonic flight aircraft, what does the aft portion of the duct do?
It increases in area as this part must act as a subsonic diffuser. This decreases air velocity further and increases pressure further.
What do stronger shockwaves do?
Produce larger changes in the properties of the air or gas. E.g. slow the air down more.
Where are shockwaves created?
In the supersonic flow of the air entering the duct.
what do shockwaves result in?
The diffusion of the airflow, which, in turn, decreases the velocity of the airflow.
