A380 takeoff vibration

[Cybersquatter]

Hi everybody

I've dipped in and out of PPRuNe as a reader on and off for a year or two, so here I am with my maiden post :) I just wanted to solicit the experts' opinion on something that I've been pondering.

I've done a LOT of domestic/short haul flights (weekly for several years), so there's not much that scares me when it comes to routine turbulence/takeoff/landing issues - but when on an Emirates A380 taking off from Hong Kong last month, I really did get a bit worried.

It's hard to describe, but as the aircraft approached the takeoff roll, or possibly when it was mid-roll, the aircraft started doing what I can only describe as groaning and vibrating in a very serious way. The vibrating and groaning seemed to continue until approximately lift-off time. The cabin crew didn't look overly concerned, but I suppose they're trained not to :)

I just wondered if anyone could shed any light on what it might be - I'm still in one piece, so I'm not worried - just curious. My amateur's guess was that the tail had struck the ground, but reading around suggests that would have caused the aircraft to turn around and perform an emergency landing at Hong Kong.

Any experts able to offer their insights? Sorry for not using all the right codes and jargon, but I'm just a layman :8

[grounded27]

Each aircraft makes it's own unique noise and vibrations for that matter. Engines, hydraulic components, flexing of the aircraft and other environmental noises depending on where you are seated. If the aircraft did not reject T/O or perform an air turnback I would assume with confidence that your experience was a normal one.

[Espada III]

Try taking off on an A340. For the first few seconds after T/O there is significant vibration, but it all calms down fairly quickly.

[D120A]

Wheel shimmy in the undercarriage?

[moleytt]

You can add the B744 to the list. My recent experience to Dubai and back had noisy vibrations on both take off rolls, so much so my wife asked me if it was okay. I told her it was just vibration resonances that rattled the overhead lockers and other stuff.

Moley

[Dubaian]

I've noticed it on many different types of aircraft. Could it be wheel imbalance? Not noticeable when the full weight of the plane is on the tyres but showing up at take-off when the weight comes off? Just a thought...

[CV880]

Out of balance wheels is definitely a probable cause. Tyres can get flat spotted eg, during a strong crosswind landing, throwing the wheel assembly out of balance. As the weight comes off the wheels on lift off the out of balance can shake the landing gear until the pilot selects gear up when the spinning wheels are brought to a halt by automatic brake application. If it is the nose tyres the pilots report it pretty quick as they feel it but the main gear tends to go unreported.

[SpringHeeledJack]

The first few times I flew on the MD-11 the vibration experienced during the first 30 seconds after leaving the runway caused this intrepid traveller concern until this buffeting was accepted as part of the characteristics of said aircraft. I surmised that it was the effect of the air rushing past the wheels and doors as the were being retracted.



SHJ

[CV880]

SHJ, yes highly likely.
The MD11, DC10-30/-40, A340, B747 and A380 all have 1 or 2 main landing gears attached to the fuselage hence any vibration is transmitted more readily to the passenger cabin than an aircraft with only wing mounted gears.
The MD11 and A340 have larger diameter tyres than a 747 (don't know about an A380) so any out of balance due to tyre flat spotting is exaggerated.
The A340-200/-300 does not have brakes on the centre landing gear so the tyres spin fast until nearly fully retracted so any vibration will continue a bit longer.