747 takeoff

[AdamC]

Recently whilst on a 747-400, both outbound and return there was a rather loud bang from below (Both legs I was sat over the wing, 46A and 48J) - The noise didn't really bother me, I'd heard about it somewhere before (Youtube video I think).

Can anybody tell me what that bang is? - My first guess would be the gear, but I'm not too sure..

Thanks :)

[JEM60]

Correct. Gear and geardoors, happens every time. Perfectly normal.

[Phil Squares]

The bang you hear is the nose gear oleo extending on rotation. If it is slightly over serviced it will tend to do that. Nothing to worry about at all. Perfectly normal.

[perkin]

The bang you hear is the nose gear oleo extending on rotation

And likewise the main gear? Its quite noticeable on the 737, not sure about the 747 as I've never had the pleasure of flying in one.

I believe there is often also a slight judder/vibration which can be caused when the main gear wheels stop rotating just after take-off.

[jet2impress]

Its the same on the 757 too. You will notice this with most large jets I believe.

[PAXboy]

As the aircraft rotates (lifts off), the springs on the landing gear naturally extend to their greatest extent. Given the strength of the springs, there is a bit of bang as they reach the end of their travel. The same would happen if your car suddenly left the road on a hump-back bridge!

Only diff - in your car you would not have time to notice the bang as you worried about the heck was going to happen next!!! Sitting in your seat as (something like) 350 tons is lifted off the springs, you notice the 'bang' but it is a nice bang!

[AdamC]

Thanks, I assumed it was perfectly normal anyway, mainly because an emergency didn't follow haha.

I've only noticed it on 747, not on any other aircraft and I've flown on my fair share of 738's!

[pacer142]

I've noticed it on some 737s but not others.

[perkin]

I've noticed it on every 737 I've been on (and thats a fair few now) including from the front few rows of a 739, the double bump from the main gear is quite apparent even at the front...not been as obvious on the Babybus though...

[stevef]

No springs in modern landing gear, I'm afraid: rapid strut extension on rotation is due to the pressure of the oleo nitrogen charge as it is no longer supporting the load.

[PAXboy]

Thanks for giving the nitty gritty, stevef, I had stuck with plain language and should have put the >'< around - springs. :}

[skiesfull]

Most likely from the main gear doors, if you were over the wing on a -400. Unlikely to hear the nose-gear 'bottoming' before retraction, from seats over the wing.

[BelArgUSA]

Any highly qualified/current Microsoft Airlines veteran 747 captain here...?
Come on, please help. You gentlemen do know better -
xxx
Everyone knows that there are 3 reasons - (sometimes more) -
One "klonk" for the doors closing.
Another "klonk" when wing gear (outer gear) tilts up for retraction positioning.
And one other "klonk" for the gear full down or up (extension/retraction).
That is for the 100-200-300-SPs...
In the 400s, the "klonks" sound more like "bang-boom" -
At least if you sit on seats 45A or 45K.
My FOM indicates that the sounds are within Annex 16/3 noise limits.
xxx
And extra "klonks" if I let that darn F/O land (he logs 2 or more landings)...
:E
Happy contrails

[PAXboy]

BelArgUSA I am not sure which answer best suits:


Do your parents know that you are playing with the internet?
Don't the doors also make a Klonk when they OPEN to allow the gear to retract? That is because the doors are in multiple sections.
Congratulations, you ARE the number one 747 nerd in PPRuNe!:}

[skiesfull]

Whoa there, PAXboy! BelArgUsa is 64 yrs and in the twilight zone of knowing everything, but remembering nothing! At 65 he will be eligible for 'The Home for the Bewildered and Incontinent'! -so go easy on him.

AdamC "one should only turn left on boarding an aircraft" - so buy a first class ticket and the only noises you will hear will be the popping of Champagne corks and your own gentle snoring!

[Final 3 Greens]

Any highly qualified/current Microsoft Airlines veteran 747 captain here...?

Well I did once land a 737 on an aircraft carrier using MSFS.

It was easy, just set the wind to 130 knots down the deck and hovered to a nice gentle touchdown.

You pilots are overpaid :}, flying is easy ;)