Main Landing Gear Positioning ??

[billt460]

Something I wondered about. Below are 2 short videos showing the outboard main landing gear position on both a Airbus A-380, as well as a Boeing 747-400 just before touchdown. The outboard main landing gear trucks on the 747 are positioned with the front wheels high. While the A-380 is just the opposite, and pitched downward.

These are the 2 biggest and heaviest airliners currently in service. I was wondering why the difference? Is the position of these gear trucks adjustable by the pilot, depending on landing weight? Or is it by design for positioning the gear in the wheel wells?

 

[4wd]

Something I wondered about. Below are 2 short videos showing the outboard main landing gear position on both a Airbus A-380, as well as a Boeing 747-400 just before touchdown. The outboard main landing gear trucks on the 747 are positioned with the front wheels high. While the A-380 is just the opposite, and pitched downward.

These are the 2 biggest and heaviest airliners currently in service. I was wondering why the difference? Is the position of these gear trucks adjustable by the pilot, depending on landing weight? Or is it by design for positioning the gear in the wheel wells?

I can’t open any YT videos from this site …
No issues otherwise …

 

[mk378]

I would think that they just pivot freely so all the tires can stay on the runway though the plane may be partly flying and pitched forward or backward. Taking off involves rotating the nose up a lot.

It couldn't carry any weight until both ends are on the ground. If it were locked in place the tires on the one axle that is touching would have an excessive load.

 

[Thermo1223]

I am pretty sure the angles are hydraulically controlled and based on weight on landing and such. Everything is controlled based on the airplanes configuration.

 

[tcp71]

I would think it's to keep all the wheels from having to touch down at the same time. Maybe that moment of friction where the tires are spinning up would cause too much airspeed deceleration if it happens all at once. This way the deceleration forces are spread out wider. Pure speculation here.

 

[billt460]

But why the opposite angle between the two? All aircraft flare in a nose up position.

 

[Astro14]

It’s simply a design philosophy thing. Large airliners typically have the Main trucks tilted. The outboard, wing, gear on a 747, the main gear on a 777 and the main gear on an A330, are all tilted upwards.

The main gear on the 767, are tilted slightly downwards, much like the A380.

The tilt is hydraulic, it is the same angle for every landing, and it is not controllable by the Pilot any more than the angle of the gear extension is controlled by the pilot. The gear is either down and locked, in transit, or up and locked.

When the gear is down and locked, that tilt angle is set hydraulically for the landing. The same hydraulic pressure is applied on takeoff, it’s just that during the takeoff for all the gear is all held Horizontally by the aircraft weight.

The upward tilt of the landing gear does make the aircraft easier to land, which begs the question why have a downward tilt?

Obviously, the engineers at both Boeing and Airbus felt that the nose down tilt angle was necessary for some engineering reason on some of their aircraft.

I just don’t know what that is.

It’s easy to get a safe landing in a 767, however, it is very challenging to get a glass smooth landing in the 767, whereas such landings are much easier in the 747–400.

 

[4wd]

Good look at the gear

 

[WobblyElvis]

I think it's more about the design of the structure where the wheels retract up into. Put the equipment in the cheapest/easiest positions and make the gear conform to what room is left.

 

[Astro14]

Good look at the gear

Ouch! The gear is probably fine, however.

 

[billt460]

Ouch! The gear is probably fine, however.

It's amazing how that gear can take that much abuse..... Not to mention the tires!

 

[FowVay]

They're not hydraulically controlled. They angle either forward or rearward based on the way they retract into the gear housing. The reason they angle forward or backward is because the truck attachment is off-center. There is no hydraulic actuator that makes the gear lean forward or backward. They do have pitch dampers that are nothing more than shock absorbers in place to prevent oscillation.

 

[BusyLittleShop]

Heavies employ the long travel suspension so they can absorb a touchdown 'g' loading of 2.6, or as a touchdown rate of descent exceeding 600 feet per minute (fpm), for landing weights up to the certified maximum... stay within the travel to stay safe... bottom out the travel and you begin to loose control and you risk structural damage...

 

[Astro14]

They're not hydraulically controlled. They angle either forward or rearward based on the way they retract into the gear housing. The reason they angle forward or backward is because the truck attachment is off-center. There is no hydraulic actuator that makes the gear lean forward or backward. They do have pitch dampers that are nothing more than shock absorbers in place to prevent oscillation.

My flight manual says, “hydraulically tilted into flight position” on gear extension.

I just did a walk around a couple days ago, and snapped a picture of a 757–200 hydraulic landing gear tilt actuator. I was standing just behind the main landing gear, and you can see all the dried deicing fluid and salt from the weather in Newark.

You’ll notice the small cylinder with hydraulic lines going in and out.

That’s the actuator. Not a spring, a hydraulic actuator.

 

[FowVay]

I try to keep up with all that I've worked but honestly, I haven't done a landing gear for a 757 in over 15 years.

Thanks for the photo. The only aircraft that I was certain used a bogie beam actuator was the 777. I guess I misspoke because several large jets apparently use this method.

 

[Astro14]

No worries. When you said that, I wondered if I was remembering it wrong, so I looked it up in the Flight manual, and then waited until I had a photo to be able to share.

On the 757 and 767 it’s hydraulic.

I honestly don’t remember how it’s done on the 747.

I am not type rated in the 777, so I can’t speak to that airplane.

 

[Dborch41]

As mentioned earlier, the angle of the MLG bogie, whether tilted forward or aft, when fully extended is primarily dependent on wheel well clearance. The 747 is a perfect example, getting all four of those rather large structures tucked up into very limited space requires quite a bit of clever mechanical origami.

 

[Nmr1981]

No worries. When you said that, I wondered if I was remembering it wrong, so I looked it up in the Flight manual, and then waited until I had a photo to be able to share.

On the 757 and 767 it’s hydraulic.

I honestly don’t remember how it’s done on the 747.

I am not type rated in the 777, so I can’t speak to that airplane.

I enjoy the aviation threads on here very much thanks for the insight. What additional requirements do you need to get type rated in a particular aircraft? Is this something you can request or do you get voluntold they are going to train you on something new? Is it similar to learning to drive a sports car to a minivan or race car to a pickup?

 

[2.7ecoboostFordBronco]

I honestly don’t remember how it’s done on the 747.

It’s also hydraulic.

 

[Astro14]

It’s also hydraulic.

View attachment 323522

Thank you. I remember the body gear steering, which was clearly hydraulically operated.

Enabled by the engineer on the 747–100/200 and automatic on the 747–400.

But I couldn’t remember the truck tilt.