don81603
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Clunking On Lift-off

Fri Jan 27, 2006 12:53 am

As we all know, there's a slight clunking sound just after lift-off, and I've asked a few people what exactly it is, and each person gives me a different answer, but the 2 most likely ones are:

1/ The landing gear being retracted, and
2/ The lugguage/cargo shifting slightly due to the angle of accent.

Can anyone elaborate?
Eagles may soar, but weasels don't get sucked into jet engines.
 
Matt72033
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RE: Clunking On Lift-off

Fri Jan 27, 2006 1:15 am

Quoting Don81603 (Thread starter):
1/ The landing gear being retracted, and

thats the most likely!!
depending on aircraft, most larger airlliners use containers for baggage that are locked down into the cargo bay which will hold it still!

the first clunk you hear is generally the gear going up!
then you'll get the whirring of the flaps being retracted! the 744's leading edge slats are very noisy as they are air operated!
 
jamesbuk
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RE: Clunking On Lift-off

Fri Jan 27, 2006 1:17 am

Hi

I'm very sure on this and what it is, the wheels are connected to the bogey and the silver piston. just after take off the bogey makes a clunk from swinging round and the silver piston makes a clunk from extending and hittin the stopper.

Rgds --James--
You cant have your cake and eat it... What the hells the point in having it then!!!
 
don81603
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RE: Clunking On Lift-off

Fri Jan 27, 2006 1:19 am

Thanks, that's kind of what I suspescted. The grinding sound of the flaps/slats retracting I'd figured out from looking at the wing when I heard the sound. Pretty cool to see the parts in action, really.
Eagles may soar, but weasels don't get sucked into jet engines.
 
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Starlionblue
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RE: Clunking On Lift-off

Fri Jan 27, 2006 1:48 am

Quoting Matt72033 (Reply 1):
the first clunk you hear is generally the gear going up!

Actually, as Jamesbuk says, the first clunk (on non bogey geared planes) tends to be when the weight comes off the wheels the struts extend and smash as they stop at the max extension postion. If you're sitting over the wing in a CRJs this sounds like the bottom of the plane falling off with a messy crash, followed by the gear entering the wells, which is like a giant hand hitting the fuse from below. Scares the hell out of white knucklers. Cue me saying: "Did you hear that? That didn't sound good!" Big grin
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
texfly101
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RE: Clunking On Lift-off

Fri Jan 27, 2006 2:58 am

During final assembly when a plane's landing gear is being cycled during functional test (it's up on jacks at that point with the landing gear hanging free), the cycling of the gear being tucked into the wheel well and the doors closing make very loud "clunking noises" as their mechanisms hit their stops or resting points. This is the retraction mechanism at work doing its job. So to hear that on takeoff is a very good sound actually. It is not cargo shifting. Listening for it and then mentally resting at ease is what I do when I fly. The slats and flaps actuators are driven off servos and the sound of those operating along with the associated clunks of the surfaces fitting into their prescribed positions are something that I also listen for and mentally check off as the airplane both takes off and lands. The one noise that we don't hear during flight is the sound of the rudder being swung back and forth. To hear it (and see it) swing back and forth and hit against its stops during functional tests really brings a big slamming noise that is quite impressive. It has made me jump sitting at my desk on the other side of a wall in my cube. I always get up then and go out on the mezzanine and watch the airplane run thru its paces sitting on jacks. Always an interesting sight...cheers and have fun with the sights and sounds during flying
 
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HAWK21M
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RE: Clunking On Lift-off

Fri Jan 27, 2006 3:13 am

Depending on what type.
Most likely the Gear Retraction in Up & locked position.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
Matt72033
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RE: Clunking On Lift-off

Fri Jan 27, 2006 3:32 am

Quoting Starlionblue (Reply 4):
Actually, as Jamesbuk says, the first clunk (on non bogey geared planes) tends to be when the weight comes off the wheels the struts extend and smash as they stop at the max extension postion.

can honestly say ive not heard that before!
 
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Starlionblue
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RE: Clunking On Lift-off

Fri Jan 27, 2006 3:35 am

Quoting Matt72033 (Reply 7):
Quoting Starlionblue (Reply 4):
Actually, as Jamesbuk says, the first clunk (on non bogey geared planes) tends to be when the weight comes off the wheels the struts extend and smash as they stop at the max extension postion.

can honestly say ive not heard that before!

It's mostly apparent on planes with no belly hold (regionals) and if you sit over the wing of a 747.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
474218
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RE: Clunking On Lift-off

Fri Jan 27, 2006 3:47 am

If the clunking noise is right at lift off it is the landing gear piston (lower portion of the main landing gear) extending (because the weight of the aircraft has been removed) and it has contacted the internal stops on the landing gear cylinder (the upper portion of the main landing gear). The piston, axles, trucks, wheels and tires weigh several thousand pounds, so when the weight of the aircraft is removed it extends with some force. The landing gear is a big shock absorber filled with oil and air which dampened the shock when landing and has to support the weight of the aircraft when its on the ground.
 
jamesbuk
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RE: Clunking On Lift-off

Fri Jan 27, 2006 3:57 am

Quoting 474218 (Reply 9):
474218

Exactly what i said just in a more technical term!  Wink

Rgds --James--
You cant have your cake and eat it... What the hells the point in having it then!!!
 
Matt72033
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RE: Clunking On Lift-off

Fri Jan 27, 2006 5:08 am

Quoting 474218 (Reply 9):
The piston, axles, trucks, wheels and tires weigh several thousand pounds, so when the weight of the aircraft is removed it extends with some force

but the aircrafts weight isnt removed suddenly is it? its fairly gradual really isnt it
 
Okie
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RE: Clunking On Lift-off

Fri Jan 27, 2006 5:56 am

Quoting Matt72033 (Reply 11):
but the aircrafts weight isnt removed suddenly is it? its fairly gradual really isnt it

True to some extent, except that the aircraft goes airborne faster than the oleo's will respond to dampen the extension. Even a short amount of travel will make a pretty good clunk when the oleo's hit the stops.
I suspect if you greased one off the tarmac then you would not hear the clunk as loudly but on the other hand you might hear multiple clunking passing over expansion joints while the oleo at the end of its travel.

Okie
 
474218
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RE: Clunking On Lift-off

Fri Jan 27, 2006 6:13 am

Quoting Matt72033 (Reply 11):
but the aircrafts weight isnt removed suddenly is it? its fairly gradual really isnt it

I re-read my post and could not find the word "suddenly". When the weight is removed from the wheels the piston bottoms out with some force, and you can hear it in the cabin as a "clunk". By the way the word isnt is spelled "isn't".
 
Matt72033
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RE: Clunking On Lift-off

Fri Jan 27, 2006 6:20 am

Quoting 474218 (Reply 13):
I re-read my post and could not find the word "suddenly". When the weight is removed from the wheels the piston bottoms out with some force, and you can hear it in the cabin as a "clunk". By the way the word isnt is spelled "isn't"

but if weight is removed gradually then the piston won't bottom out with as much force!

please do not correct my spelling or grammar! the fact that i missed one apostrophe is niether here nor there!
 
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Starlionblue
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RE: Clunking On Lift-off

Fri Jan 27, 2006 6:33 am

Quoting Matt72033 (Reply 14):
Quoting 474218 (Reply 13):
I re-read my post and could not find the word "suddenly". When the weight is removed from the wheels the piston bottoms out with some force, and you can hear it in the cabin as a "clunk". By the way the word isnt is spelled "isn't"

but if weight is removed gradually then the piston won't bottom out with as much force!

please do not correct my spelling or grammar! the fact that i missed one apostrophe is niether here nor there!

The clunk is there and quite noticeable on some planes whether you have noticed it or not.

Furthermore, neither is spelled neither, not niether. And the first word in a sentence should be capitalized.  Wink
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Matt72033
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RE: Clunking On Lift-off

Fri Jan 27, 2006 6:39 am

Quoting Starlionblue (Reply 15):
Furthermore, neither is spelled neither, not niether. And the first word in a sentence should be capitalized.

see my post above! i honestly couldnt care less!
 
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Starlionblue
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RE: Clunking On Lift-off

Fri Jan 27, 2006 7:22 am

Quoting Matt72033 (Reply 16):
Quoting Starlionblue (Reply 15):
Furthermore, neither is spelled neither, not niether. And the first word in a sentence should be capitalized.

see my post above! i honestly couldnt care less!

But your fun reactions make the teasing worth it. Big grin
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
2H4
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RE: Clunking On Lift-off

Fri Jan 27, 2006 7:27 am



Starlion....should I mention he forgot an apostrophe in his last post?  Wink




2H4


Intentionally Left Blank
 
don81603
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RE: Clunking On Lift-off

Fri Jan 27, 2006 7:43 am

Quoting 2H4 (Reply 18):
Starlion....should I mention he forgot an apostrophe in his last post?

And a capitalization...
 Wink
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Jetlagged
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RE: Clunking On Lift-off

Fri Jan 27, 2006 10:51 am

Quoting Matt72033 (Reply 14):
but if weight is removed gradually then the piston won't bottom out with as much force!

The point is the wheels are off the ground before the struts bottom out, so they hit the end-stops with a bang. The wheel and strut assembly is very heavy, so even though it is moving quite slowly the force when it hits the mechanical stop is large.

Secondly, the question is about the clunking sound just after lift-off. The gear won't start retracting for a few seconds after lift-off (i.e. once positive rate of climb is seen and called by the pnf), so it will be several more seconds before the wheels are locked up. The strut bumps happen just after lift-off, before gear is even selected up.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
SFOMB67
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RE: Clunking On Lift-off

Fri Jan 27, 2006 1:17 pm

Also, when the gear retracts into the w/w and the door closes, the door will generally create a thump + it is immediately quieter. I would imagine each aircraft type is slightly different generating this noise.
Not as easy as originally perceived
 
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Jetlagged
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RE: Clunking On Lift-off

Fri Jan 27, 2006 3:41 pm

Quoting Sfomb67 (Reply 21):
Also, when the gear retracts into the w/w and the door closes, the door will generally create a thump + it is immediately quieter. I would imagine each aircraft type is slightly different generating this noise.

Again, this will happen quite a few seconds after lift-off, not immediately after it as referred to by the question.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
speedracer1407
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RE: Clunking On Lift-off

Fri Jan 27, 2006 5:20 pm

I've heard and felt this clunk many times, and if the original poster is referring to the clunk that happens right at the moment of liftoff, it's most certainly the gear thunking to it's fully-extended position, as others have insisted. Usually, gear retraction is a series of clucks and grinds many seconds after liftoff.

Strange thing, though, on a recent NW DC-9 flight, during both powerback and landing, the thrust reverser buckets opened with a HUGE clunk that shook the plane on its roll axis, likely becuase they opened a fraction of a second separate from eachother. I've never felt this on MD-80s.

O
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HAWK21M
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RE: Clunking On Lift-off

Sat Jan 28, 2006 12:40 am

Quoting Jetlagged (Reply 20):
The point is the wheels are off the ground before the struts bottom out, so they hit the end-stops with a bang

Isn't there a Snubber valve built in the Strut like the B737.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
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Jetlagged
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RE: Clunking On Lift-off

Sat Jan 28, 2006 1:56 am

Quoting HAWK21M (Reply 24):
Isn't there a Snubber valve built in the Strut like the B737.

Every design will be different. I can't say I've noticed such bumps after lift-off on a 737, maybe that's why.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
iairallie
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RE: Clunking On Lift-off

Sat Jan 28, 2006 4:28 am

Quoting Don81603 (Thread starter):
2/ The lugguage/cargo shifting slightly due to the angle of accent.

The luggage/cargo should not shift significantly. It is held in place with cargo nets. Shifting cargo would cause weight and balanced problems.
Enough about flying lets talk about me!
 
aogdesk
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RE: Clunking On Lift-off

Sat Jan 28, 2006 8:47 am

Perhaps it could be the tool bag of the mechanic that worked in the MLG wheel well just prior to departure falling onto the strut as the gear doors open???

Purely hypothetical. 100%  Wink
 
jamesbuk
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RE: Clunking On Lift-off

Sat Jan 28, 2006 8:50 am

Hi

Many of you on here have said that the it must be the wheels retracting ( i cant be bothered to quote) well in the original post it says straight after lift off which im guessing is the first 5 seconds, an average airplane would gain about 200 feet in the first 5 seconds of flight, how many times have you ever spotted retraction in that time!!

It must be when the cylinders hit the stoppers!

Rgds --James--
You cant have your cake and eat it... What the hells the point in having it then!!!
 
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HAWK21M
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RE: Clunking On Lift-off

Wed Feb 15, 2006 2:35 pm

Quoting Jamesbuk (Reply 28):
It must be when the cylinders hit the stoppers

BTW what Type Aircraft was this Post related to.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
don81603
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RE: Clunking On Lift-off

Fri Feb 17, 2006 1:24 pm

Quoting HAWK21M (Reply 29):
BTW what Type Aircraft was this Post related to.

I've noticed it on all commercial aircraft, some more so than others. 73X to a lesser extent, and the DC-9's are the noisiest. Almost sounds like a Motley Crue pyro blast  Smile
Eagles may soar, but weasels don't get sucked into jet engines.
 
Silver1SWA
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RE: Clunking On Lift-off

Fri Feb 17, 2006 3:40 pm

The initial "clunk" that I notice comes right at lift off. Obviously this is way before the gear is retracted so it is not the sound of the gear entering the bay etc. It is, as mentioned above, the sound of the struts extending to their stopping points after the wheels lose contact with the ground.
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
jamesbuk
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RE: Clunking On Lift-off

Fri Feb 17, 2006 8:25 pm

Quoting HAWK21M (Reply 29):
BTW what Type Aircraft was this Post related to.

Im guessing any with a retracting gear?

Rgds --James--
You cant have your cake and eat it... What the hells the point in having it then!!!

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