Landing gear tilt angle difference between a B777 200LR & 300ER
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Landing gear tilt angle difference between a B777 200LR & 300ER
This is purely academic.
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
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
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
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
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.
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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.
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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
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
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.
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
Last edited by ACMS; 1st Jun 2017 at 08:28.
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(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?
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.
The same geometry applies regardless of how many wheels there are on the bogie.
(b) Is the toe down capability something that all/most aircraft with 4 wheel bogies have?
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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:
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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.
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.
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.
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.
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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.
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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.
"SEMI-levered". Stiff for takeoff, floppy for landing, so to speak...
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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.
Last edited by JammedStab; 23rd Jun 2017 at 15:41.
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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?
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?
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