A380 Landing Gear

[PIGDOG]

I noticed the A380 landing gear all seem to tilt forward. Does anyone know the reason for this?

I know the A340 centre main gear is the same but the outboard gear tilts backwards.

[r304ndy]

On the A340-500/600, the landing gear has to be in the dipped position to avoid fouling the centre doors as they open prior to gear retraction. Once the doors are fully opened, the gear is then signalled to move to the trail position before folding forward and up into the bay.

[used2flyboeing]

As a best practice - "toes down" truck orientation is to be avoided .. this is because if you draw a free body diagram of the post and gear you will see that this orientation contributes to landing gear strut "windup" & "springback" loading which binds the inner & outer cylinders - IE side loads the hell out of the post causing premature strut bearing failures & ladder crecking.& creates wierd dynamics. The only reason to do it is to correct the touch down wheel geometry so as to put all wheels that touch down first on the same longitudinal centerline in the vicinity of the centroid. As with a big swept wing aircraft, the swept wing & body gears are oriented in different locations about the centroid - possibly the body gear forward of the centroid & the wing gears aft of the centroid -& -therfore not on the same centerline - but all will have to contact the earth on landing in concert. Using a toeup & toes down configuration is a trick to solve this problem - exploiting the truckbeam length to put the trailing wheels of the leading trucks "toes up" will place them inline with the trailing trucks nose wheels "toes down" configuration" - otherwise - the airplane on landing will experiance an abrupt pitching moment on landing due to whatever truck touches down first as a result of being either fore or aft of the centerline.

[Tallbloke]

used2flyboeing, I am sure I have misunderstood something, in the last sentence of your post you mention a pitching moment occuring, dependent on which truck touches down first, whether it is behind or infront of the centroid. Would not the rearmost trucks always touch down first if the aircraft is pitched nose up?

[mustafagander]

used2etc.

I don't think so - check the B767 MLG. Very toes down isn't it? No other wheels to consider. Boeing claims they tilt that way to fit into the wells. Not a bad reason you must admit.

This wheels all in a line stuff might possibly happen in a perfectly flown, perfectly trimmed, perfectly on speed a/c on a perfectly level runway in a perfectly stable airmass with any wind exactly down the runway. Otherwise I think it's a nonsense. I bet a close look at the geometry of the situation will show that the wheels need to point the way they do to fit in.

[used2flyboeing]

Any landing gear designer would tell you that they "have to put the trucks in some sort of orientation" hence the truck tilt actuator & usually in a toesup position. Airbus & Boeing do use the actuator to position the trucks to fit in the wheel well - as well. THe 777-300 with the semi-levered gear positioner - acts as a landing gear snubber on landing to1) reduce body stress on landing for longer structures life & landing comfort, 2) raise the airplane up prior to takeoff to increase aft body clearance margins to maximize takeoff alpha and hence performance & 3) position truck for stowage. I was addressing why the landing gear on the A340-500/600 was a mixture of toesup & toesdown configurations - again because the body & wing gear are not on the same centerline & exploiting truck beam length to put the wheel where they need to be. Landing gear designers prefer the toeups configuration because of the springback loads generated - again - draw a freebody diagram for yourself & check it out ! I dont think the 767 is a toes down configuration - I dont think they would do a config like that unless they had to because of landing gear stress ..

Tallbloke - if you place the landing gear before or aft of the centroid - the airplane will experiance a pitching moment or heaving fore or aft depending on where the moment of inertia is in relation to the touch down gear ( IE the fulcrum). Not a good thing - some modern fly-by-wire systems use the INS inputs to the PFC to wash in elevator to cancel this phenomenon as a function of pitch rate on landing .. but - better not to have the gear placement problem in the first place ..

[mustafagander]

used2etc..

Have you seen a B767 in flight with the gear extended?

[mono]

Got to agree with Gander.

767 IS toes down.

[supercarb]

THe 777-300 with the semi-levered gear positioner - acts as a landing gear snubber on landing to1) reduce body stress on landing for longer structures life & landing comfort, 2) raise the airplane up prior to takeoff to increase aft body clearance margins to maximize takeoff alpha and hence performance

A330/340 MLG works in a similar manner.