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Distance To Fan On Jet Engines

Mon Dec 20, 2004 3:15 pm

Why is the front fan so far inset into the engine cowling?
Is it just a matter of air intake or there's more to it than that?

Answers appreciated,
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RE: Distance To Fan On Jet Engines

Mon Dec 20, 2004 4:24 pm

Purely a guess here,

1. Noise abatement.

2. FOD Protection.

3. Airflow.

Could be one of the reasons, could be all of them. I have never given it any thought. I will give the books a look to see If I can find an answer for you.
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RE: Distance To Fan On Jet Engines

Mon Dec 20, 2004 7:10 pm

I agree with JetMech on 2 of 3 points.

1. Airflow....The inlet smoothes the airflow into the engine and helps reduce compressor stalls.
2. Noise abatement....The inside of the inlet has thousands of small holes that absorb some of the sound generated by the front of the engine and they also serve as outlet ports for engine anti-ice bleed-air.
3. I don't believe the depth of the inlet has a direct effect on FOD protection. However on the old generation 737 with fans the bottom of the nose ring was flattened to increase it's distance from the ground, i.e.. less FOD. This made it necessary to lengthen the inlet to allow the airflow to straighten out before it entered the engine.


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RE: Distance To Fan On Jet Engines

Mon Dec 20, 2004 7:16 pm

It helps with the airflow into the fan.
Also the cowl is a divergent duct and causes a higher static pressure at the fan, which helps the fan which is trying to suck the air.
A very basic description, hopefully it helps.
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