MLG Orientation.

[denachtenmai]

Sorry if this is in the wrong place but I have been looking at the photo's
of the VC10's arrival at Bruntingthorpe and a question occurs.
In these pic's. the MLG bogie is orientated so as the trailing wheels touch first, as do the 747, Vulcan/ Victor et al, but the latest generation,cf A380, seem to have the front wheels first, does anyone have an explanation?

[JammedStab]

Doesn't the A340-600 have both types with the centre gear angled different than the two main gear legs. Looks kind of odd.

[flyboyike]

I can think of other differences between the VC10/Vulcan/Victor/Insertwhateverprehistoricairplaneyouwanthere and the A380. I guess I hadn't focused on the MLG orientation somehow.

[TURIN]

I can think of other differences between the VC10/Vulcan/Victor/Insertwhateverprehistoricairplaneyouwanthere and the A380. I guess I hadn't focused on the MLG orientation somehow.

That's because the 380 is so damned fugly you daren't look too close.

[CV880]

Simply put the angle of the bogie or truck is determined by the requirement to fit the retracted gear into the smallest space possible especially on aircraft like the B747 and A380 with 4 main gears. See the following-
707, DC8, DC10, MD11, L1011, A300, A310 all had main landing gears installed vertically with the bogies held 90 degrees to the main strut.
767 has a nose down tilt to the bogie but the 757 is level.
The 747 wing landing gear bogie is at an extreme angle so it goes into the wheel well across ship and not fore and aft thus reducing the length of the wheel well required.
The 777 has a nose up tilt to the bogie when the gear is down but transitions to a nose down tilt during retraction to make it fit into the wheel well with the long bogie parallel to the centreline.
The CV880 had a slight nose up tilt but the larger CV990 had a nose down tilt. Convair's explanation for the difference was it was simply a clever change in geometry to enable the 10 inch longer main gear on the 990 to be squeezed into the same space whilst being attached to the wing at the same point as the 880.
The A340-500/-600 has a centre gear with nose down bogie tilt and the wing gears with nose up tilt purely a result of having to squeeze a 4 wheel bogie into the space previously occupied by a 2 wheel landing gear on the A340-200/-300.

[DaveReidUK]

Simply put the angle of the bogie or truck is determined by the requirement to fit the retracted gear into the smallest space possible

Not necessarily. The truck angle with the gear deployed doesn't always correspond to the angle with the gear stowed.

[oceancrosser]

Slight correction CV880, the 757 has a slight nose up gear tilt, opposite direction to the 767.

[oceancrosser]

Slight correction CV880, the 757 has a slight nose up gear tilt, opposite direction to the 767.

Well visible in this picture:

Photos: Boeing 757-24Q Aircraft Pictures | Airliners.net

[PJ2]

CV880;

Nice post.

If I may add two items for the A330/A343/A345/A346; their main gears also tilt to provide greater tail clearance during the rotation and flare manouevres.

The trucks are hydraulically driven by a "pitch trimmer" to, and held, in the tilted position during takeoff and are leveled during the retraction sequence.

At landing they are again hydraullically held in the tilted position until spoiler deployement. When they "unlock", the airplane can thump down pretty hard at times. "Beating the bogies to the ground" is a challenge on the A330 and A343, less so on the A345. I haven't flown the A346.

In addition to this, the main-gear oleos on these aircraft are mechanically shortened during the retraction process, for the reasons you've outlined - clearance in a small space! But I'm not sure why the body gear on the A345/346 is tilted opposite to the mains. They, and the single-axle A340 design ride a bit higher at initial touchdown, and don't touchdown until the mains are "unlocked" and fully on the runway.

[spannersatcx]

if you look at the 345/6 gear when tilted the rear boggie of the main gears line up with the fwd bogie of the centre gear so that all 6 wheels in line contact more or less at the same time.

it has been discussed on here before about gear tilting why's and wherefore's.

[DozyWannabe]

Originally Posted by TURIN

That's because the 380 is so damned fugly you daren't look too close.

I have to say that where I live I get to see at least two or three of 'em on approach vectors most days and from the ground - subjectively speaking - they look awe-inspiring in flight at that level.

[JammedStab]

I believe that there is something about the 777-300ER gear tilt as well. The earlier 777's had main gear that tilted and the tilt of course started to happen as soon as the aircraft was rotated. So just prior to liftoff, the aircraft would be at say 9 or 10 degrees nose up with all of the main gear wheels still rolling on the runway.

But with the 777-300ER, there is something called the semi-lever gear where somehow, it is designed so that there is no tilt during the rotation. So when the aircraft is in the same 9 or 10 degree rotation attitude, only the aft two wheels for each bogie are still on the ground. Somehow this allows a slightly greater tail clearance because the pivot point of rotation has been moved slightly aft allowing the aircraft to be rotated to a slightly higher pitch attitude. which gives better takeoff performance due to the higher AOA achievable on the ground.

Or so I heard anyways.

[DaveReidUK]

Or so I heard anyways.

You're not wrong.

"Because the vast majority of the weight of the airplane is borne by the lift of the wings at the time of rotation, the semi-levered gear acts as if it were “pushing” down like a longer gear. This allows a higher pitch attitude for the same tail clearance or more clearance for the same pitch attitude. A hydraulic strut provides the energy to provide this increased takeoff performance. Although designed to increase takeoff capability, the system provides increased tail clearance for the same weight and thrust as nonequipped airplanes."

Boeing.com: AERO - Tail Strikes: Prevention

[stilton]

Whatever the design , the bogies with the trailing edge touching first are a lot more forgiving.

[chipsburris]

A3456 CLG Bogie

The A3456 CLG has a hydraulic pitch trimmer that is sequenced to maintain the bogie nose down to enable clearance when opening and closing the bays doors, and then position and hold the bogie in a nose up position for retraction into the bay.