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toddy333
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Posts: 77
Joined: Fri Jun 11, 2004 5:19 am

Remembering Back To A Flight I Took....

Sun Jun 13, 2004 8:19 am

October last year i flew LHR-J'burg, Cape Town-LHR with Virgin Atlantic both ways... on the way there a lovely new -600 (its 1st ever visit to J'burg!...all the ground crew at the airport were taking photos for ages!) but on the way back a seemingly much older -300.... and on rotation from cape town, i felt a feeling i have never felt before, maybe it is common and happens on every take off, but i have never realised or felt it before!..so, then, just from the point of rotation to the first few seconds of flight, maybe 4 seconds, was the most awful juderring, about five or six 'jerks' that sounded (all i can describe, along with the vibration, as loud "dur dur dur dur dur" sounds!
is this normal? i cannot recall this happening on any other flight i have been on?
 
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VirginFlyer
Posts: 5571
Joined: Sun Sep 10, 2000 12:27 pm

RE: Remembering Back To A Flight I Took....

Mon Jun 14, 2004 10:13 am

Toddy333 - this could have been due to the retraction of the undercarriage. When something is spinning, it has what is called rotational inertia. Simply put, this means it will resist a rotation of its axis of rotation. If you can't picture this, take a bicycle wheel, hold onto the axle, have someone spin it up, then try to tilt it. Anyway, when the undercarriage retracts, you have this inertial effect, which causes a vibration in the undercarriage. I find that it is particulalrly noticable if you are sitting close to the main wheel wells. It is perfectly normal, and nothing to worry about (although it spooked me the first time I heard it).

Perhaps this is what you felt?

V/F
It is not for him to pride himself who loveth his own country, but rather for him who loveth the whole world. The earth is but one country, and mankind its citizens. —Bahá'u'lláh
 
dl757md
Posts: 1483
Joined: Mon May 24, 2004 9:32 am

RE: Remembering Back To A Flight I Took....

Mon Jun 14, 2004 10:45 am

VirginFlyer IMHO I think what Toddy333 was experiencing was actually the truck tilt actuators positioning the main gear trucks (bogies) in their in-air attitude. This would correspond with the time period of the first 4 seconds after rotation.

The gear would not be initiated up at rotation as the mains are still on the ground.

Also, the rotational inertia you reference is not likely to produce vibration. This force resists planar changes of a rotating mass but it is a smooth force which would only result in vibrations if a wheel bearing was failing.
The vibration in the undercarriage during gear retraction that you talked about is actually caused by braking of the main gear wheels. When the landing gear handle is selected to "up", hydraulic pressure is ported to the brakes to stop the main wheels from spinning before they enter the wheel wells. This results in exactly the vibrations you've mentioned.

Dl757md
757 Most beautiful airliner in the sky!
 
ZKSUJ
Posts: 6884
Joined: Tue May 18, 2004 5:15 pm

RE: Remembering Back To A Flight I Took....

Mon Jun 14, 2004 7:22 pm

Toddy333-
It happened to me too, but on an SQ 744 from SIN-ZRH in 2001. There was a loud shuddering sound and the aircraft shook a little. Also, the Baggage compartment above me opened up by itself.(maybe it was just someone not closing it properly). Anyway, it turned out to be a good flight, especially the descent over the alps.

SUJ
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Remembering Back To A Flight I Took....

Wed Jun 16, 2004 11:28 pm

How pleasant it must be to take such a flight and only encounter five or six jerks.
Happiness is not seeing another trite Ste. Maarten photo all week long.

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