Airbus Lover
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Tilted Main Gears

Wed Dec 11, 2002 4:30 pm

I have wondered for a long time and finally I remembered to ask...

Now what are tilted bogies for while landing? The Airbus widebodies' seem to tilt at great angle (ie the A330/340) and while I notice the 777s dont tilt that much and they seem 'stiffer' than Airbus'. Airbus ones look like really flexy and all... Are they tilted so the landings are smoother?

On take offs almost all planes like the 747 767 and Airbuses etc tilt their gear as they rotate... But I noticed that on the 777 when taking off the main gears seem to be 'hard' on and the last wheels on the row of 3 will stay on the ground. If you get what I mean, what is this for?

Thanks for the clarification.
 
FredT
Posts: 2166
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RE: Tilted Main Gears

Wed Dec 11, 2002 5:54 pm

Added suspension travel length -> smoother landing.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Staffan
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RE: Tilted Main Gears

Thu Dec 12, 2002 6:53 am

I believe it also helps position the boogies correctly to be able to fit them in the gear bays when retracting the gear.

Staffan
 
Klaus
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Staffan

Thu Dec 12, 2002 7:46 am

Staffan: I believe it also helps position the boogies correctly to be able to fit them in the gear bays when retracting the gear.

No. In many (most?) cases, the tilt will be changed before retraction
 
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CCA
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RE: Tilted Main Gears

Thu Dec 12, 2002 8:00 am

The Gear was designed to be tilted purely to occupy the least amount of space in the fuselage that way it will allow more cargo space.
Now this is the primary reason but with advances in technology, the tilt can be modified without adding weight, the 777 has a flight position and a retract position and I believe the A340-600 has a similar system for the centre gear, which makes for a smoother landing.

The 777 can't tilt its gear like the 74' wing gear as the gear would become too long and would have to be placed further out on the wing. The 777 gears are only one foot less apart than the 747, but are a lot taller due to the size of the engines.

Now the A330/340 gear is as you said tilted a lot like the 747, but has exactly the same problems as the 777, so what the 330 and 340 do is incorporate a shortening link which pulls the inner cylinder of the strut into the outer as the gear retracts thereby shortening the length of the gear and allowing the gear to be tilted and leave enough room for a centre gear in between. If the shortening link breaks which it has (CX A330) when the gear retracts it hits the landing gear doors due to being full length.

Now on these pic's you can see the wing gear is tilted to take up the minimum fwd/aft space. I'll have to get back to you as my connection is a bit slow at the moment but there are some perfect pic's here on airliners.net to show what I'm babbling on about.


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Photo © Alan Tsui
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Photo © Staffan Hardie


P1 in A330, A340, A346, B742, B744, B748.
 
Staffan
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RE: Tilted Main Gears

Thu Dec 12, 2002 8:56 am

Hey that's my photo  Big grin

Klaus, I'm not sure if we are talking about the same thing, if you look in the photos you can see that the boogies are tilted backwards the same way during retraction as they would be before a landing or after a takeoff. I'm not sure if this is what you mean or if you are suggesting that the boogies aren't in the backward tilting position for retraction?

Staffan
 
Klaus
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Staffan

Thu Dec 12, 2002 12:02 pm

Staffan: Hey that's my photo

And a good one!  Big thumbs up


Staffan: Klaus, I'm not sure if we are talking about the same thing, if you look in the photos you can see that the boogies are tilted backwards the same way during retraction as they would be before a landing or after a takeoff.

For the 747 that may very well be the case... But it doesn´t seem to be for the A330/340 (and for several Boeings as well, as far as I remember).

Staffan: I'm not sure if this is what you mean or if you are suggesting that the boogies aren't in the backward tilting position for retraction?

Just have a look at this picture:


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Photo © Florian Kondziela




There´s also the QuickTime movie at the Airbus Site about assembly of the first A340-600. One of the sequences shows the testing of MLG retraction. And the wing MLG bogies appear to straighten out right before they enter the wheel wells. I don´t think the bogies could fit into the rather narrow wheel wells at all if they retained their tilt during retraction.

The center bogie of the 340-500/600s even tilts "the other way" during retraction.


That´s still nothing compared to the XB-70 "Valkyrie": It uses all three available axes of rotation while folding its MLGs.

http://www.labiker.org/xb70.html

Just scroll down to the description of the "Normal main gear extension sequence".

Talk about "landing gear origami"...! Big grin
 
Staffan
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RE: Tilted Main Gears

Thu Dec 12, 2002 4:11 pm

Ok, I see what you mean now. Hadn't noticed, but it seems as what CCA said, that it's done for space reasons involving the CLG. Not sure if the 767, since it only has a slight tilt forward, changes this during retraction. Any clues?

Staffan
 
AJ
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RE: Tilted Main Gears

Thu Dec 12, 2002 8:39 pm

Nope, the 767 gear remains tilted:

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Photo © John Davies

 
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CCA
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RE: Tilted Main Gears

Fri Dec 13, 2002 1:43 pm

Klaus,
Thanks, that's the perfect photo to show what I was trying to explain.
It also shows I was incorrect and that all the gear on the 330/340 have a flight and retract position, but I'm beginning to think that the gear has a fixed tilt, pulling the front up, and as the gear retracts the shortening link action pulls the center of the gear up thereby untilting the gear.

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Photo © Peter Unmuth - Vienna Aviation Photography
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Photo © Philippe noret



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Photo © Florian Kondziela
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Photo © Stephan Tophoven



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Photo © Ismael Jorda
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Photo © Shaun Grist



I confirmed with a mate at QF the 767 gear is the same as the 747 and remains in a constant tilt position.


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Photo © Florian Kondziela

P1 in A330, A340, A346, B742, B744, B748.
 
Klaus
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CCA

Fri Dec 13, 2002 3:00 pm

CCA: but I'm beginning to think that the gear has a fixed tilt, pulling the front up, and as the gear retracts the shortening link action pulls the center of the gear up thereby untilting the gear.

That sounds plausible indeed. Maybe someone with first-hand knowledge can comment.
 
cdfmxtech
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RE: Tilted Main Gears

Fri Dec 13, 2002 3:11 pm

B747/B757/B767 - One tilt mode
B777 - Three tilt modes
 
Airbus Lover
Topic Author
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RE: Tilted Main Gears

Sat Dec 14, 2002 11:44 pm

Wow, thats very informative. Thanks people!

However, more comments are welcome!
 
ra-85154
Posts: 601
Joined: Tue Sep 04, 2001 10:16 pm

RE: Tilted Main Gears

Mon Dec 16, 2002 7:49 pm

Hi
The way the gears are tilted on the Tupolev TU-134 and 154 I think was designed to make the (rearward) retraction easier as well Smile

tilting

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Photo © Paul Morley



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Photo © Philippe Bleus



retraction

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Photo © STUART PRINCE



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Photo © Olaf Juergensmeier


regards
Martijn


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