Pipe purpose?

[rosenblad]

Hi!
Can anyone tell me the purpose of the pipe sticking out in the middle of the engine exhaust on Ryanair's later aircraft types? As a retired aircraft engineer with experience from SAS DC-9 aircraft I have never seen it before. I have tried searching the web, but no luck!

I tried posting my question under the Ground & Other Ops Forums/Questions thread but noone seems to bother. Maybe this is a better place?

Best Wishes,
Tom

[barit1]

On some engine types, such a pipe would be a bearing sump vent.

What a/c type are you looking at?

[PA28pilot]

Hi Tom,

There's a picture showing the "aft fairing drain tube", 7th photo down here (http://www.b737.org.uk/powerplant.htm#Misc_Photos).

Is this the pipe you mean?

Regards,
PA28pilot

[HiFli]

Assists in noise reduction and heat dissipation.

[3bars]

Barit1 has hit the nail on the head... vent for the main bearings

Next!!!

[HiFli]

B1 & 3b, Rtfq. Exhaust, Ryanair,b738.

[rosenblad]

Hi!

Thanks guys! The pipe in question is precisely what I thought, "the Aft Fairing Drain Tube for any hydraulic fluid, oil or fuel that may collect in there" as stated beside the photo. I should have known you techies were the best choice!:D And yes, I should have mentioned that it was a Boeing 738 as well!

Best Wishes,
Tom

[3bars]

'B1 & 3b, Rtfq. Exhaust, Ryanair,b738.'

Hifli - I did, and from my experience as a type rated engineer on said airplane for said company, answered it!

I believe this is the pipe in question, which shrouds the main bearingshttp://tbn1.google.com/images?q=tbn:RhLB_MNeoRPkoM:http://www.dc8.org/photos/images/dc8-exhaust_sm.jpg (http://www.dc8.org/photos/images/dc8-exhaust_sm.jpg)

[CV880]

GE and CFM use a centreline oil vent or breather system which exhausts through the cone fairing on the rear bearing housing. On earlier engines like the CF6-50 it was hidden inside the exhaust nozzle but modern designs tend to have protruding fairings that are obvious. This arrangement keeps the cowlings clean as any oil vapour exits in the engine exhaust stream. If you look at earlier RR and PW engines the cowls were covered in oil because they breathed through a gearbox vent that allowed any vapour to impinge on the cowls. The early RB211 was particularly bad as the breather outlet was about mid height on the left fan cowl and the oil slick clearly visible especially with painted cowls. RR eventually came up with an extension to the outlet to keep the vapour away from the cowls.

[FE Hoppy]

Rosenblad

I think you're looking at the wrong bit. The aft fairing drain tube is the thin one sticking out of the pylon rather than the centre of the engine as you originally said.

[rosenblad]

Hi FE Hoppy!

You are right! The pipe in question is the one clearly shown in the photo in the entry bu 3bars. Not the upper one from the fairing.

Best Wishes,
Tom

[barit1]

A bit of enlightenment for the multitude:

In order to help keep the lube oil from escaping the bearing sumps, a bit of air is "borrowed" from an early stage of the compressor and applied to the outside of a sump seal. Some air leaks past the seal into the sump, and in the process prevents oil from escaping.

But this air must now be vented - often through a centrifugal air-oil separator. This may be built right into the engine main shaft, and thus it's most practical to route the air out through the pipe that rosenblad noticed. :ok:

[rosenblad]

Hi barit1!

Thank you for that information! Suddenly the shape and position of the pipe became very clear indeed!

Best Wishes,
Tom