View Full Version : Nacelle design

4th Feb 2010, 15:17
Can anyone tell me what the purpose of small holes are, that are drilled into the circumference of a nacelle.

On the Citation II with the JT15D engine there are a row of small holes (+/- 3mm) about every 2 cm, the whole circumference, drilled into the nacelle just behind the lip.

I have seen it on other engines too.

Many thanks


Old Smokey
4th Feb 2010, 15:50
Hi Ken, welcome to PPRuNe.:ok:

I'm not familiar with the Citation II or the JT15D engine, but they're probably overboard vents for used hot air after engine cowl de-iceing.


Old Smokey

4th Feb 2010, 22:50
If the holes you mean are on the inside of the nacelle (just fwd of the blades), then they are probably there for noise reduction.

5th Feb 2010, 10:54
Thanks for the replies. I also thought that it might be for the bleed air to escape, but I managed to get a technical manual that says the Nacelle AI heating bleed air is dumped behind the shroud into the bypass duct. There is no mention in the manual about the holes.

Yes the holes are just forward of the blades. I have also about the noise reduction. Thanks that seems to be the answer.

Many thanks for your replies.

5th Feb 2010, 14:22
A picture would help me so I'm only guessing

Originally I had pictured the holes near the inlet lip, a long way in front of the fan blades.

It would make a difference to me whether the holes are through holes into the hollow area of the inlet nacelle. If so they would affect the AI flow and increase the temperature on the inner skin near the holes. This could be to address run-back ice accumulation at this specific area in order to provide some protection against ice ingestion damage to the fan blade tips.

A lot more could be said about this, but since the purpose of the holes is only a guess .....