What causes the BANG when an airliner lifts off?

I've flown a lot of planes, of different sizes, and I always lift off gently.
When I fly as a passenger on an airliner though, there is a "thud" or even a
"bang" as the main wheels leave the runway. Sometimes this bang is so loud is
frightens passengers, and once it was strong enough (on a 777 departing for
Hong Kong) that I was sure we'd at least blown a tire, if not actually struck
something with the mains. But in the end, it's always OK - just normal. Who
knows what this is? Is it the pusher actuators on the main gear? The
telescoping elements of the main gear bottoming out? Just curious. . .

G Faris

As long as you are sure it isn't the wheels completing their retraction into
the wheel well, then it is probably the struts extending to its
full-extended position. Or it may be the brakes stopping the turn of the
wheels before it starts its retraction. I've flown many hours around the
world and the main "bang" I remember is the retraction of the main wheels.

Marco Leon

"G Farris" wrote in message
...
I've flown a lot of planes, of different sizes, and I always lift off
gently.
When I fly as a passenger on an airliner though, there is a "thud" or even
a
"bang" as the main wheels leave the runway. Sometimes this bang is so loud
is
frightens passengers, and once it was strong enough (on a 777 departing
for
Hong Kong) that I was sure we'd at least blown a tire, if not actually
struck
something with the mains. But in the end, it's always OK - just normal.
Who
knows what this is? Is it the pusher actuators on the main gear? The
telescoping elements of the main gear bottoming out? Just curious. . .

G Faris

"G Farris" wrote in message
...
I've flown a lot of planes, of different sizes, and I always lift off
gently.
When I fly as a passenger on an airliner though, there is a "thud" or even
a
"bang" as the main wheels leave the runway. Sometimes this bang is so loud
is
frightens passengers, and once it was strong enough (on a 777 departing
for
Hong Kong) that I was sure we'd at least blown a tire, if not actually
struck
something with the mains. But in the end, it's always OK - just normal.
Who
knows what this is? Is it the pusher actuators on the main gear? The
telescoping elements of the main gear bottoming out? Just curious. . .


The latter. The gear might "bang" during retraction when it's inserted into
the wells, but it's several seconds later.


--
Matt
---------------------
Matthew W. Barrow
Site-Fill Homes, LLC.
Montrose, CO

I would suspect that it is the suspension unloading. The suspension would
have to be extremely strong to support the loads required. I would suspect
that it is not the smothest (quietest) thing while in motion. It probably
thumps hard when it is loaded up (upon landing) and when it is unloaded(take
off). You probably don't notice it on landing because of everything
stopping its downward motion when it hits the ground. It is probably lost
with all of the other noises associated with impacting a runway. The
suspension probably sticks a little and when it is unloaded and effected by
vibrations, it falls to its full extended position on takeoff.

Just and educated guess.

Just an opinion...

If the sound is really right at lift off, maybe it's the wheels trucks
dropping back. They are designed to hang back-end down. I could imagine that
they thump if the lift of is quick enough.

--
-------------------------------
Travis
"Kevin Chandler" wrote in message
...
I would suspect that it is the suspension unloading. The suspension would
have to be extremely strong to support the loads required. I would
suspect
that it is not the smothest (quietest) thing while in motion. It probably
thumps hard when it is loaded up (upon landing) and when it is
unloaded(take
off). You probably don't notice it on landing because of everything
stopping its downward motion when it hits the ground. It is probably lost
with all of the other noises associated with impacting a runway. The
suspension probably sticks a little and when it is unloaded and effected
by
vibrations, it falls to its full extended position on takeoff.

Just and educated guess.

In article ,
says...

Just an opinion...

If the sound is really right at lift off, maybe it's the wheels trucks
dropping back. They are designed to hang back-end down. I could imagine that
they thump if the lift of is quick enough.

--


I was thinking something like that too - except in some large airliners,
like the 777, they do not "drop" into that position, but they are pushed by
hydraulic actuators.

The sound I'm referring to really is immediately after lift-off. It is far too
early for the gear retraction - in fact, this make a distinct noise as well,
but several seconds later.

Thanks to all who replied - I'm still not sure I know exactly what this
noise is, but at least everyone is thinking along similar lines. . .

G Faris

G Farris wrote:

I was thinking something like that too - except in some large airliners,
like the 777, they do not "drop" into that position, but they are pushed by
hydraulic actuators.

Yes, but the first thing that happens during the 777 retract sequence
is that the actuators tilt the gear.

I've heard the sound you're referring to as well, I think. I'm wondering
if the 777 has some kind of automatic wheel spin brake.