Landing gear tilt angle difference between a B777 200LR & 300ER

[agg_karan]

This is purely academic.
http://i63.tinypic.com/2myvxp1.jpg
As you can see B777 200LR has a truck tilt to -19 DEG capability.
The MLG truck positioner actuator is designed to allow a maximum toes down angle of 19deg on the truck

http://i64.tinypic.com/2ufad6v.jpg
A b777300ER does not have that feature.

Q1) why is there a difference which only applies to 200LR?
Q2) what does this thing do? Why is it installed?

I am fully aware of the main gear differences otherwise with regards to the semi lever gear strut which is exclusive to 300ER. has this got to do with that?

Kindly pardon the curiosity, this is purely academic.
Thankyou & regards

[ACMS]

It's to do with tail strike protection on th long body ER.......giving extra clearance for the tail by making the gear stiff with no toe during rotation. That's why it has semi lever gear struts as well.

[Jet II]

As ACMS said - the 300ER has Semi Lever Gear struts, the 200LR has tilt actuators. The SLG's lock to allow the effective length of the landing gear to increase on rotation to avoid a tailstrike.

[agg_karan]

ACMS & JET II
THANKYOU For your time & reply :)

I still have not understood as to why the 200LR LG has a -19 truck tilt angle 'capability'. I mean which part of flight phase will the tilt be ever reaching minus 19 DEG toe down angle, that was also the doubt :)

THANKYOU once again

[ACMS]

http://www.boeing.com/resources/boeingdotcom/commercial/customers/turkish-airlines/boeing-delivers-first-777-300er-to-turkish-airlines/assets/images/marquee.jpg

777-300ER rotation, note the semi levered gear only trailing wheels on the ground, this increases the tail clearance. The ER doesn't require toe down or indeed want toe down ever.

http://cdn.airplane-pictures.net/images/uploaded-images/2016/6/19/737826as.jpg


Rotation on a 777-200 all 4 wheels on the ground with toe down.

The Toe down is required during times when the nose is high, ( takeoff and landing )
19 deg is the max but it shouldn't get more than about 12 deg or the tail will strike the ground

[agg_karan]

That is just perfect exactly what I was looking for to understand the idea.
THANKYOU and grateful to you

[JammedStab]

The Toe down is required during times when the nose is high, ( takeoff and landing )
19 deg is the max but it shouldn't get more than about 12 deg or the tail will strike the ground

Undestand the SLG stuff, but...

(a) Why is toe down required when the nose is high?
(b) Is the toe down capability something that all/most aircraft with 4 wheel bogies have?

[DaveReidUK]

(a) Why is toe down required when the nose is high?

Consider what the angle between the MLG and the bogie will be immediately following a touchdown in the flare - the bogie is flat on the runway while the aircraft is still pointing skywards.

(b) Is the toe down capability something that all/most aircraft with 4 wheel bogies have?The same geometry applies regardless of how many wheels there are on the bogie.

[skkm]

(b) Is the toe down capability something that all/most aircraft with 4 wheel bogies have?

As explained by the previous reply, by virtue of the obvious geometry with the bogie flat on the ground and the nose airborne, toe down capability is a requirement (except the earlier described 777-300ER on takeoff with the semi-levered gear).

Most aircraft seem to have the gear hang in a toe-up position – two notable exceptions are the 767 and the body gear of the 340-5/600:

http://www.airlinereporter.com/wp-content/uploads/2014/12/IMG_9365.jpg

https://upload.wikimedia.org/wikipedia/commons/7/77/Lufthansa_Airbus_A340-600_on_short_final%2C_Toronto_Pearson_runway_05.jpg

[ACMS]

And the A350-900, in these cases all to do with the geometry of fitting gear retraction into the wheel well.

https://upload.wikimedia.org/wikipedia/commons/thumb/5/54/A7-ALA_%2819397355348%29.jpg/300px-A7-ALA_%2819397355348%29.jpg

[agg_karan]

Ok so to sum up -
1) This extra toe down angle feature is only useful for 'takeoff' phase.
2) I am imagining at Vlof (lift off), it would rather be harmful for a 300ER to 'allow a toe down' as it would not increase the body gear length & not provide desired tail strike protection.
3) for a 200LR a toe down 'exists' because there is no SLG/hydraulic strut actuator & tail strike is not an issue.
4) for 'landing' this toe down has no use or significance. Because both a/c (200LR & 300 ER) bogies approach ground at a tilt (forward wheel pair up & aft wheel pair down)

Are these assumptions correct from what I infer from above discussion?

Thankyou.

[ACMS]

1/ no Landing as well refer to Q4
2/ yes that's why it has a semi levered gear arrangement without Toe down.
3/ yes, the 200 doesn't need the extra tail strike protection so reverts to a typical bogie setup with Toe Down.
4/ on the standard 777-200/200 LR and 300 the Toe Down ensures all 4 wheels will de-rotate and contact the ground quickly after touchdown even with the nose high, for better braking traction etc I guess. This can't happen as quickly on the ER as it has a semi levered ( stiff ) gear bogie with no Toe down.

[JammedStab]

Consider what the angle between the MLG and the bogie will be immediately following a touchdown in the flare - the bogie is flat on the runway while the aircraft is still pointing skywards.

Thanks for the replies. But I am still having trouble understanding this. Google DC-10 landing and L-1011 landing and you will see aircraft on approach with what appears to be no tilt. Was there any problems with those aircraft for takeoff and landing?

Then along came the 747 and there was a huge amount of tilt for the wing gear but my understanding is that this was so that less space was taken up by the gear when retracted. That being said, there is some tilt to the body gear as well but I believe that it is titled back when retracted to once again save space, this time vertically.

[CallmeJB]

4/ on the standard 777-200/200 LR and 300 the Toe Down ensures all 4 wheels will de-rotate and contact the ground quickly after touchdown even with the nose high, for better braking traction etc I guess. This can't happen as quickly on the ER as it has a semi levered ( stiff ) gear bogie with no Toe down.
A quick search of "777-300er landing" will return plenty of images showing touchdowns with the bogies 'toed down' to allow full surface contact while the nose is still in the air.

"SEMI-levered". Stiff for takeoff, floppy for landing, so to speak...

http://cdn.airplane-pictures.net/images/uploaded-images/2010/7/15/95384.jpg

[JammedStab]

Perhaps toes down allows for more effective, immediate braking but some aircraft have the opposite angle ie. toes up. So still a bit of a mystery. Maybe the other types are only for space saving on retraction.

[FullWings]

The -300ER has semi-levered gear for performance reasons as well: there is a decrement if it isn’t working, can’t remember exactly what but in the order of tons...

[agg_karan]

Well the basic doubt was, an a/c whether it's a 200LR or a 300ER would approach the ground at a positive tilt angle (rear wheels down, forward wheels up)

During landing how would it possible for a 200LR to have a negative tilt angle (forward wheel pair down, rear wheel pair gear up) ?

During landing (prior to touchdown) the 200LR would never have a toe down, so just wondering at what phase will this negative truck tilt show up?

[Jet II]

The only time you get negative truck tilt is on Stow and Rotation (see pic at start of thread)

[stilton]

I believe the bogies are only locked for take off.

[Amadis of Gaul]

During landing (prior to touchdown) the 200LR would never have a toe down, so just wondering at what phase will this negative truck tilt show up?

Exactly when needed.

[agg_karan]

JetII - the stow angle is 5 nose down (200LR) however the capability is -19 down. Question was which phase of flight it goes to -19?

What's more surprising is that in both pictures posted by me the only time 'ground' or 'touchdown surface' is shown is when the angle is -19. Rest images only a horizontal line is shown (to exaggerate a medium to differentiate the angle wrt zero datum)

Hence my doubt :)

[underfire]

OT: I see that Boeing is looking to use the semi-lever design for the Max 10 to prevent tailstrike.

[stilton]

How does that work on a single axle bogie ?

[underfire]

Before,they were calling it telescoping, but at Paris, they are calling it a semi-lever or trailing link. Was thinking along the lines of the Embraer E2 landing gear, but not sure with this from Boeing.

737 MAX vice-president and general manager Keith Leverkuhn said in Feb 2017 ."Boeing has been evaluating multiple “good ideas”, including a shift from the 737’s traditional oleo strut to a trailing link landing gear design, A key criteria in the final decision (of the MAX-10) later this year will be the inherent reliability of the landing gear design,"

Keith Leverkuhn said on 2nd May about the -10 MLG: “The design focus is on the upper portion of the gear as it integrates with the actuator. In this area, within the tight confines of the existing wheel well, Boeing’s new design will do some “clever folding using a link mechanism at the top,”

"The lower section of the leg is also modified with an additional shock strut that fits inside the same forging. This moves the contact point aft a little bit. That’s fundamentally what we are doing and yes, it will look like a trailing link gear. We want to make it maintainable, reliable, and we are going to need that gear to get the performance we want out of the -10 but I’m confident in the solution set,”

[Jet II]

JetII - the stow angle is 5 nose down (200LR) however the capability is -19 down. Question was which phase of flight it goes to -19?


Rotation.

On rotation the aircraft rotates around the centre axle which then gives you the 'nose down' scenario - although you will never get to -19 in real life.

[Jet II]

sounds more like an A330 style gear strut mechanism than a 777 SLG.