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"Growling" Turbofans (DC-10)  
User currently offlineJebtha From United States of America, joined Aug 2000, 18 posts, RR: 0
Posted (14 years 4 months 1 week 9 hours ago) and read 3554 times:

What is the source of the distinctive 'growl' heard on DC-10's at takeoff power? Is it a characteristic of some high-bypass turbofans and not others? Back when I lived in Minneapolis I always knew when a NWA DC-10 was outbound over my place (near Hennepin Ave bridge) from the growl, and of course it can be heard from inside the plane as well. It seems that the sound is loudest when one is forward of the engines (that is, after the plane passes overhead, the jet noise reverts to the usual low frequency roar). The sound fades during climb, due to changing air pressure or airspeed or power setting?

Recently I have heard the same sound from on board in two other aircraft -- a UAL 777 and a NWA 757, though I don't remember noticing it on 757's before. I have never heard the growl from the ground with any other aircraft type.

My guess would be it has something to do with the fan impinging on 'low speed' air at a high power setting..?

24 replies: All unread, jump to last
 
User currently offlineJt8dthunder From , joined Dec 1969, posts, RR:
Reply 1, posted (14 years 4 months 1 week 2 hours ago) and read 3184 times:

Your not the only one who hearts this low, very distinct hum. I can Boeing 777's taxiing from where I live just from the type of noise. The DC-10 makes this noise to but it doesn't carry as far as does the 777's engines, maybe cause the fan diameter is shorter. This humming seems to be produced during any increase in power, especially from idle to taxi or from idle to take-off power settings.

User currently offlineJebtha From United States of America, joined Aug 2000, 18 posts, RR: 0
Reply 2, posted (14 years 4 months 6 days 15 hours ago) and read 3102 times:

Thanks for the answer -- we might be hearing the same thing, but the noise I'm trying to describe is quite loud and sustained from the time the engines spool up to takeoff power through the early climb phase. It is by far the loudest component of noise I hear from an approaching DC10 (or MD-11?) that's climbing out.

Inside the cabin it might better be described as a buzzing sound, accompanied by some 'musical' overtones. Similar to a small two-stroke engine running full throttle without a muffler.

Anyway, thanks again.


User currently offlineExPratt From United States of America, joined Mar 2000, 311 posts, RR: 0
Reply 3, posted (14 years 4 months 5 days 17 hours ago) and read 3073 times:

The growl, which some people have referred to as a buzz, is from the tips of the fan blades going transonic. It is most noticeable on the CF6 engines, but can also be heard on the JT9Ds and to a lesser extent the RB211s.

User currently offlineRichie From Switzerland, joined Dec 1999, 143 posts, RR: 0
Reply 4, posted (14 years 4 months 5 days 9 hours ago) and read 3041 times:

Experts call that the GE whine... As ExPRatt sais, the CF6 series turbofans have this specific noise characteristic.

User currently offlineCapt_smith From United States of America, joined May 2000, 65 posts, RR: 0
Reply 5, posted (14 years 4 months 5 days 8 hours ago) and read 3057 times:

Perhaps these sounds are related to my previous posts re: the characteristic "thrumming" or howling sound that I continue to notice on low speed Airbus A320s coming into the final approach. I hear the sound also during it's take off, too. I always can identify the approach of an American West A320 approaching or leaving Port Columbus International.



User currently offlineCapt_smith From United States of America, joined May 2000, 65 posts, RR: 0
Reply 6, posted (14 years 4 months 5 days 8 hours ago) and read 3030 times:

capt_smith sends this photo.



Click for large version
Click here for full size photo!

Photo © Chris Coduto



User currently offlineTn283 From , joined Dec 1969, posts, RR:
Reply 7, posted (14 years 4 months 4 days 17 hours ago) and read 3014 times:

The loudest and most distinctive growling turbofan is definitely the GE TF-39 which is on the C-5 galaxy. If you sit in front of the wing on board, you will need earplugs. I invite you to go to www.TheAviationZone.com and go to "media." There are some engine sounds in there and the TF-39 is one of them. The engine also has the most unusual idle sound I have ever heard. It sounds exactly like a tractor trailer truck tire when traveling at highway speeds.

User currently offlineTn283 From , joined Dec 1969, posts, RR:
Reply 8, posted (14 years 4 months 4 days 16 hours ago) and read 2987 times:

Ok, I'm sorry. I brain dupmed and advertised a web page in my last message. Won't happen again.

User currently offlineJebtha From United States of America, joined Aug 2000, 18 posts, RR: 0
Reply 9, posted (14 years 4 months 4 days 15 hours ago) and read 2987 times:

That's it, TN283. The runup and flyby sounds are excellent examples of the growl or buzz.

Thanks to all for your replies.


User currently offlineCapt_smith From United States of America, joined May 2000, 65 posts, RR: 0
Reply 10, posted (14 years 4 months 4 days 8 hours ago) and read 3001 times:

Could all these sounds that we are discussing be basically the same thing? I have now noticed this loud buzz on the md-80. I don't know the engine variant, but the buzz became very obvious as the engines reached maximum power on take-off roll. At idle, I did notice a slight slow "beat" (from 2 engines toghether?) As the throttles were advanced, the beat became faster and faster until the engines were at highest power. This beat then became the loud buzz we have been talking about. This, I believe, is the similar to what happens when an old mechanical siren is switched on. It has a disc which winds up faster and faster until the sound increases in pitch, and maybe this is a little bit analogous to the "tips going transonic" as mentioned above. What do you all think? The funny thing is that this is only heard on SOME engines!

User currently offlineTn283 From , joined Dec 1969, posts, RR:
Reply 11, posted (14 years 4 months 4 days 5 hours ago) and read 2979 times:

Whether or not the engine makes the growling sound depends on the sound insulation around the fan which many newer engines are incorporating and also the materials the fan blades are made of. The old regime, which is the JT9-D, CF-6, RB11, and TF-39 are much louder than the newer models. The smaller turbofans such as the JT3-D (TF-33 for you military types), and the JT8-D make the same sound but at a much higher frequency due to the size. The rythmic beat you heard during idle has nothing to do with the take-off growl. The growl does come from the fan blades going transonic.

User currently offlineTn283 From , joined Dec 1969, posts, RR:
Reply 12, posted (14 years 4 months 4 days 5 hours ago) and read 2968 times:

While were on this subject, is it not the most incredible sound in the world? I get chills when I'm out on the line and a big Galaxy is rolling down the runway. There's nothing quite like it in the world.

User currently offlineWilcharl From United States of America, joined Jun 2000, 1168 posts, RR: 3
Reply 13, posted (14 years 4 months 3 days 4 hours ago) and read 2958 times:

the rhytmic thumping you hear is noticble when the engine rpm is out of sync causing it to resonate (if i remember the proper term from physics) the other sound we hear on high by pass turbo fans is common on the 717-200 if you sit in the last row by the engine you get that wondeful sound you would normaly only hear on a widebody.. what is scarry is sitting in row 1 .. the 717 is completely quiet up there.. all you can hear is a slight air rush over the plane

User currently offlineAdam84 From United States of America, joined Jul 1999, 1400 posts, RR: 2
Reply 14, posted (14 years 4 months 2 days 12 hours ago) and read 2955 times:

I love this sound. I think it is more noticeble on JT9Ds, and the GE-CF6's of DC-10-10's. I was on a CO DC-10-30 with GE CF6's and it wasnt as audible as it is on NW DC-10-40's or Hawaiian DC-10-10's. I dont know, just my personal observation.

User currently offlineSaluki777 From , joined Dec 1969, posts, RR:
Reply 15, posted (14 years 3 months 2 weeks 5 days 7 hours ago) and read 2895 times:

All I know, when we were flying back to Chicago from Honolulu last spring on a United DC10, when the engines spooled up for takeoff, there was the usual noise of increased power, then the usual "jet roar" suddenly changed to a more subdued "hum". It was so uplifting, flying over Waikiki and hearing just a hum from the engines, all the while powering up at 100% thrust.

User currently offlineDL727-200adv From United States of America, joined Sep 2000, 150 posts, RR: 0
Reply 16, posted (14 years 3 months 2 weeks 5 days 5 hours ago) and read 2902 times:

Aboard a Delta 767-300 equipped with GE CF-6’s I observed an almost deafening sound, which sounded like a motorcycle engine revved wide open coming from the #1 engine. The sound began as soon as the engine spooled up on takeoff and continued through most of the climb out but diminished & then disappeared as the aircraft accelerated. I was seated in seat A several rows in front of the wing. It sounded as if the #2 engine was not making this sound though I cannot be sure. As soon as the 767’s airspeed decreased on approach the sound could be heard once again through landing. I have flown on many CF-6 equipped 767’s over the years and never heard such a noise before or since. This flight was a short hop from CVG to ATL. Strangely several days after this flight a friend of mine was talking about how “loud” a particular United DC-10’s #2 engine sounded during his recent flight from ORD to IAD. He described the exact same sound I had observed. I assume this must be a characteristic of the GE CF-6 even though I’d never observed it before or since? I don’t know if this matches the “growling” sound that the original poster was talking about, but does anybody know why this would be observed occasionally on CF-6 equipped aircraft?

DL727-200adv


User currently offlineAdam84 From United States of America, joined Jul 1999, 1400 posts, RR: 2
Reply 17, posted (14 years 3 months 2 weeks 4 days 1 hour ago) and read 2859 times:

I have also noticed that you cant hear the noise if you are behind the wing. Unless you are sitting in the last row of a DC-10 where you can hear a little bit of it from the #2 engine. The CO DC-10 I flew on with CF6 engines, In IAH i didnt notice the noise on the runway but right after we lifted of, it got loud for a second then quieted. Then in HNL I heard alittle bit of a buzz on takeoff but none once we started climbing.

User currently offlineEWR Spotter From United States of America, joined Aug 2000, 63 posts, RR: 0
Reply 18, posted (14 years 3 months 2 weeks 3 days 21 hours ago) and read 2864 times:

I have also noticed and questioned about this sound to a few of my friends. None of them knew what it was but I always know when a DC-10 is approaching. Some days EWR uses 29 for landings and all the aircraft pass right over my house. Back when Continental had many DC-10's that was all you heard. Even if you didn't see any plane yet you knew what type was headed your way. Now they are getting rid of their DC-10's   and replacing them with 767 and 777's.

User currently offlineBruce From United States of America, joined May 1999, 5066 posts, RR: 15
Reply 19, posted (14 years 3 months 2 weeks 1 day 4 hours ago) and read 2823 times:

I have also noticed a very distinct noise on the L-1011.

It was very unique just as the engines were spooled up until the "hum" got drowned out by the roar but there was still a distinct "buzz" in the roar.

Is this the same sound - or can someone comment on the L-1011's sound?



Bruce Leibowitz - Jackson, MS (KJAN) - Canon 50D/100-400L IS lens
User currently offlineFanoftristars From United States of America, joined Jul 2000, 1615 posts, RR: 5
Reply 20, posted (14 years 3 months 1 hour ago) and read 2792 times:

I have only heard this sound on the L1011 and Delta's 767-300. I have not heard it on the 762s, but every flight I have had on the L1011 I have heard that loud buzz as we climbed and it slowly fades away. So, is everyone in agreement that it is the fan blades going supersonic or could it be something else? This seems like the most logical explination. The L1011 also has a beautiful Moo that comes from its RB211s when they are spooling up for takeoff, or taxiing when the pilots use small amounts of thrust to "follow the lead in line." It is also quite noticeable when they first start the engins and run them up. The MOOOOO turns to a beautiful jet noise. I have a video that I taped of the L1011 on takeoff. I was seated in 10c? You can clearly hear the moo and then the buzz as we took off.


"FLY DELTA JETS"
User currently offlineRayChuang From United States of America, joined Jun 2000, 8034 posts, RR: 5
Reply 21, posted (14 years 2 months 3 weeks 6 days 5 hours ago) and read 2755 times:

I spent a day at SFO at the end of Runway 1R today (and got a sunburn for it   ) and I did notice when the engines on the DC-10-30's that NW flies rev up to full power, they is a very pronounced low-frequency "rumble" you can hear until the plans goes away from you. Mind you, it's not like the higher-pitched (and quite loud) "roar" of the JT8D engines on the 737-200 and MD-80 models.

You can also hear that rumble on Boeing 757's with both the P&W PW2037 and Rolls-Royce RB.211-535E4 engines.


User currently offlineUAL747 From , joined Dec 1969, posts, RR:
Reply 22, posted (14 years 2 months 3 weeks 6 days ago) and read 2743 times:

I live on one of the approach paths for DAL and tonight I saw an ERJ and a CRJ fly over. The sound of their engines was great. Sort of like a vacuum cleaner on steriods.

User currently offlineAKelley728 From United States of America, joined Dec 1999, 2194 posts, RR: 5
Reply 23, posted (14 years 2 months 2 weeks 5 days 13 hours ago) and read 2686 times:

Hey guys, thanks for clearing up a mystery for me.

A couple of weeks ago I flew on a DC-10 for the first time, believe it or not. It was on a Continental DC-10-30, from IAH to EWR.

I was fortunate enough to sit in 4A (BusinessFirst section). Knowing the CO has had a few incidents with the CF6s on the DC-10s lately, my eyes were glued on the left-hand engine during taxi and takeoff roll.

I first noticed the 'buzz' right after we took off. Needless to say, I was a little bit scared. The sound started dying off after a minute or two, and my heart beat returned to normal.

Now that I know that this is a normal sound, I'll be looking out for it the next time I'm on a DC-10!





User currently offlineAKelley728 From United States of America, joined Dec 1999, 2194 posts, RR: 5
Reply 24, posted (14 years 2 months 2 weeks 5 days 13 hours ago) and read 2692 times:

Tn283:

I read in a recent AW&ST that they are planning to re-engine the C-5 Galaxy with derated (50,000 lb) versions of the GE CF680-C2.

I'm sure it'll be a sad day for you when the last TF39 goes!


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