Jeffry747 From United States of America, joined Jun 2005, 968 posts, RR: 2 Posted (10 years 7 months 2 weeks 1 day 3 hours ago) and read 4324 times:
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.
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.
N79969 From , joined Dec 1969, posts, RR:
Reply 6, posted (10 years 7 months 2 weeks 23 hours ago) and read 4094 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.
FlySC From United States of America, joined Jan 2004, 136 posts, RR: 0
Reply 8, posted (10 years 7 months 2 weeks 13 hours ago) and read 3988 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.
I do not fail!!! I succede at finding what does not work!!!
Avioniker From United States of America, joined Dec 2001, 1109 posts, RR: 10
Reply 10, posted (10 years 7 months 1 week 1 day 19 hours ago) and read 3766 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, 2612 posts, RR: 25
Reply 11, posted (10 years 7 months 1 week 1 day 2 hours ago) and read 3720 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, 7484 posts, RR: 48
Reply 12, posted (10 years 7 months 6 days 21 hours ago) and read 3651 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.