Landing Gear's Tilt Angle

[ThomasIp]

Hello guys, I found out the landing gear or the bogie of A310, A380, A350-900, and B767 are tilted forward. But most of the other aircraft like the A350-1000, B777, B787 or A330 are all tilted backward.
Some of my engineer's friend said the forward tilting will absolve the impact better but may damage the body gear steering actuator, but why don't the new 787 and A330neo have this feather?
Thank you very much!

[eckhard]

Apparently it has something to do with the way the bogie fits into the wheel-well.

I’ve never really understood why this is so important. The 747 for example, has a tilting mechanism on the wing gear that straightens the bogie before retraction. In case of malfunction, it would be a reason not to retract the gear.

Maybe the designers of the 767 figured that it would be cheaper/simpler to omit the tilting mechanism and leave the gear “toe-down” when extended.

[YOUNGBUCK]

As Eckhard says its to do with fitting the gear in the bay. A330 uses a shortening mechanism in the leg to also aid the gear fitting in the bay; a pitch trimming actuator ensures the rear wheels touch the runway first as well as giving a greater angle during aircraft rotation angle for take off.
Other aircraft use truck tilt actuators to tilt the truck aft when the weight of the aircraft is off the ensure rear tires make contact first.

As for impact damage, I cannot say. However I do not believe the any steering actuators would be damaged as they are in the nose gear.

[spannersatcx]

777, 747 all have main gear steering actuators.

[PeetPeet]

Sounds like you're getting into the world of bogie/truck positioning.


'Tilt' of the landing gear, i.e. the rake angle is something different. Most main gears have a slight negative rake for passive stability, while nosegear has a positive rake for active stability.


On gears with 4 or 6 wheel bogies/trucks depending whether you're an Airbus or a Boeing, the angle the bogie 'flies at' is known as the bias angle.


Landing gear bays have very tight clearances, ALL the space is used by design. Depending on the airframe space-claim decisions, and whether the bogie/truck positioner can work in tension, compression, or both, a bias angle is defined to be optimal for stowage of the landing gear by the landing gear design team.


Another consideration is bogie/truck dynamic reactions on landing - a bogie gear may oscillate about centre very rapidly on a hard impact landing, so a toe-down angle or toe-up angle might be preferred depending on your bogie pitch trimmer performance.


Toe down can be better because you get the load spread over all 4/6 tyres sooner on landing, and all brakes can all start working straight away.


Conversely, the A330 toes-up bogie pitch mechanism actually works during rotation, and supposedly helps to achieve a lower minimum unstick speed because it gives a couple of degrees extra angle of attack before the tail touches the deck.


Hope that helps!

[kklun]

Apparently it has something to do with the way the bogie fits into the wheel-well.

I’ve never really understood why this is so important. The 747 for example, has a tilting mechanism on the wing gear that straightens the bogie before retraction. In case of malfunction, it would be a reason not to retract the gear.

Maybe the designers of the 767 figured that it would be cheaper/simpler to omit the tilting mechanism and leave the gear “toe-down” when extended.
At first, i have the same idea as you ,until i detaily look at the landing gear of 767
Here is my observation ,the 767’s landing gear still have a pitch trimmer actuator.This means the gear is not “left” down, instead, it is forced down by the actuator on purpose

[kklun]

As Eckhard says its to do with fitting the gear in the bay. A330 uses a shortening mechanism in the leg to also aid the gear fitting in the bay; a pitch trimming actuator ensures the rear wheels touch the runway first as well as giving a greater angle during aircraft rotation angle for take off.
Other aircraft use truck tilt actuators to tilt the truck aft when the weight of the aircraft is off the ensure rear tires make contact first.

As for impact damage, I cannot say. However I do not believe the any steering actuators would be damaged as they are in the nose gear.
There is a steering actuator on 777,747,380’ main landing gear