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Curious Engine Noise On DC-8s

Jeffry747 From United States of America, joined Jun 2005, 961 posts, RR: 2
Posted (7 years 10 months 4 weeks 15 hours ago) and read 2595 times:

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I've often noticed on Douglas DC-8s at the UPS hub in Louisville, KY,that the CFM56 engines emit a very loud and deep bass noise on start up. Anyone know what causes this? Iv'e only heard the noise come from CFM56 engines.

C'mon Big B, FLY!

13 replies: All unread, jump to last

Lamedianaranja From Venezuela, joined Nov 2004, 1246 posts, RR: 23
Reply 1, posted (7 years 10 months 4 weeks 15 hours ago) and read 2574 times:

And what are the holes for under the nose? Might they cause the noise?

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Jeffry747 From United States of America, joined Jun 2005, 961 posts, RR: 2
Reply 2, posted (7 years 10 months 4 weeks 15 hours ago) and read 2557 times:

The foward facing inlets are for the air conditioning ram air system, and the "slots" on the side are the air system heat exhaust

C'mon Big B, FLY!

Broke From United States of America, joined Apr 2002, 1322 posts, RR: 4
Reply 3, posted (7 years 10 months 4 weeks 12 hours ago) and read 2446 times:

What I think you are hearing is the combustion section of the engine during the start sequence. I have heard similar sounds, that you have described, on the DC-8-70's and on L-1011's.

Air2gxs From , joined Dec 1969, posts, RR:
Reply 4, posted (7 years 10 months 4 weeks 12 hours ago) and read 2415 times:

Quoting Jeffry747 (Thread starter):
CFM56 engines emit a very loud and deep bass noise on start up

The engine has either fuel nozzles or fuel injectors. If fuel nozzles are installed, you will hear (and feel) that deep rumble at start-up. If the engines have injectors installed, the engine will not produce that rumble. You know, I may have it backwards, but either way, it's the type of fuel delivery into the combustor that makes the noise.

Hirisk From United States of America, joined Jan 2004, 223 posts, RR: 0
Reply 5, posted (7 years 10 months 4 weeks 11 hours ago) and read 2370 times:

i love that rumble.like it even more then the boom from the JT8D's on mad dogs when they start.

happy contrails

N79969 From , joined Dec 1969, posts, RR:
Reply 6, posted (7 years 10 months 4 weeks 11 hours ago) and read 2365 times:

Interesting question. I have wondered about the same sound from those exact airplanes. It is very distinct. Interestingly, I have never heard that from any other CFM56 powered airplane-- neither the 737 or A320.

Pilotpip From United States of America, joined Sep 2003, 3082 posts, RR: 12
Reply 7, posted (7 years 10 months 4 weeks 9 hours ago) and read 2316 times:

Every now and then you'll hear it out of a 737. However, the DC-8 has a great sound when it starts. That's the highlight of my night on the ramp.

DMI

FlySC From United States of America, joined Jan 2004, 136 posts, RR: 0
Reply 8, posted (7 years 10 months 4 weeks 2 hours ago) and read 2259 times:

I work on the UPS ramp at CAE and I have to say it is amazing to stand about 20-30 ft away from that engine when it is starting up. It just kind of shakes your body. Starting up the DC-8 is really noisy because of the engines and the airstart equipment that we use.
Fly Safely,
Jason D.

I do not fail!!! I succede at finding what does not work!!!

Jetjack74 From United States of America, joined Jul 2003, 7336 posts, RR: 52
Reply 9, posted (7 years 10 months 3 weeks 1 day 8 hours ago) and read 2038 times:

Quoting Lamedianaranja (Reply 1):
And what are the holes for under the nose? Might they cause the noise?

The 707 has the same ram-air inlet under the fuselage, on the belly, same function

Made from jets!

Avioniker From United States of America, joined Dec 2001, 1109 posts, RR: 11
Reply 10, posted (7 years 10 months 3 weeks 1 day 8 hours ago) and read 2037 times:

You'll hear the same noise from the CF-6 as well. It's caused by the turbulence created when the fuel is first introduced and the flow isn't yet smooth through the cans and turbine section.
Common in GE designs.

One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533

Jetlagged From United Kingdom, joined Jan 2005, 2452 posts, RR: 17
Reply 11, posted (7 years 10 months 3 weeks 15 hours ago) and read 1991 times:

Quoting Jetjack74 (Reply 9):
The 707 has the same ram-air inlet under the fuselage, on the belly, same function

The air conditioning inlets on the 707 are located in the engine pylons (well 3 out of the 4). The much smaller ducts you see in the centre-wing section of many airliners are for the ram air cooling of the pack heat exchangers. This air doesn't enter the cabin.

The glass isn't half empty, or half full, it's twice as big as it needs to be.

Jetjack74 From United States of America, joined Jul 2003, 7336 posts, RR: 52
Reply 12, posted (7 years 10 months 2 weeks 6 days 9 hours ago) and read 1922 times:

Quoting Jetlagged (Reply 11):
The air conditioning inlets on the 707 are located in the engine pylons (well 3 out of the 4)

On the early JT3/4 engines straight-pipes, they're on all four. Interestingly, the 720/B's and AA's 323B/C's have only 2 on both inboard engines. Sorry, my explanation was mistaken concerning the underside inlets. I was equating the the 2 nozzles under the nose of the DC8 with the nozzles under the centre wing section of the 707. But the DC8-50/61 have the same turbocompressor inlets on the underside of the nacelles.

Made from jets!

JETPILOT From United States of America, joined May 1999, 3130 posts, RR: 32
Reply 13, posted (7 years 10 months 1 week 6 days 20 hours ago) and read 1807 times:

The inlets on the nose of the DC8 are for the turbo compressors to pressurize the cabin. There is also an inlets to cool the heat exhangers on the air aonditioning pacs.

On the 70 series the pressurization comes from air bled off the engines, and the turbocompressors are removed and the openings plugged.

On the 50/62/63 series the turbocompressors are still installed and are spun up for an overspeed test just before engine start, and they make an awesome sound.

Respect
JET

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