KarelXWB wrote:

Boeing demonstrates the 777X folding wingtip mechanism:

https://youtu.be/q0hEZDLsiF8

Aviation Week editors recently saw a demonstration of the folding wingtip at Boeing’s Everett, Washington plant. The target time for extending and/or retracting the wingtip is 20 sec. Listen closely when it reaches the selected position to hear the locking mechanisms engage.

Intersting, so it's becoming reality. Honestly, I thought it would end similar to the proposal they made years ago ... no airline ordered this feature at that time.

N14AZ wrote:

KarelXWB wrote:

Boeing demonstrates the 777X folding wingtip mechanism:

https://youtu.be/q0hEZDLsiF8

Aviation Week editors recently saw a demonstration of the folding wingtip at Boeing’s Everett, Washington plant. The target time for extending and/or retracting the wingtip is 20 sec. Listen closely when it reaches the selected position to hear the locking mechanisms engage.

Intersting, so it's becoming reality. Honestly, I thought it would end similar to the proposal they made years ago ... no airline ordered this feature at that time.

I believe it's now a standard feature for the 777X, not optional...

frigatebird wrote:

N14AZ wrote:

KarelXWB wrote:

Boeing demonstrates the 777X folding wingtip mechanism:

https://youtu.be/q0hEZDLsiF8

Intersting, so it's becoming reality. Honestly, I thought it would end similar to the proposal they made years ago ... no airline ordered this feature at that time.

I believe it's now a standard feature for the 777X, not optional...

Yes. The current folding wings are also much simpler as it is just the wingtip. The previous option never taken up was the last 21' of the wing and included flight control surfaces.

N14AZ wrote:

KarelXWB wrote:

Boeing demonstrates the 777X folding wingtip mechanism:

https://youtu.be/q0hEZDLsiF8

Aviation Week editors recently saw a demonstration of the folding wingtip at Boeing’s Everett, Washington plant. The target time for extending and/or retracting the wingtip is 20 sec. Listen closely when it reaches the selected position to hear the locking mechanisms engage.

Intersting, so it's becoming reality. Honestly, I thought it would end similar to the proposal they made years ago ... no airline ordered this feature at that time.

Yes, that was more complex, mechanism included some of the flaps and slats if I am not mistaken.

Dutchy wrote:

N14AZ wrote:

KarelXWB wrote:

Boeing demonstrates the 777X folding wingtip mechanism:

https://youtu.be/q0hEZDLsiF8

Intersting, so it's becoming reality. Honestly, I thought it would end similar to the proposal they made years ago ... no airline ordered this feature at that time.

Yes, that was more complex, mechanism included some of the flaps and slats if I am not mistaken.

It was something like this.

The previous iteration was to get a Group V aircraft into Group IV gates. There were enough 747 Classic-sized (Group V) gates around that the time that operators determined they didn't need the extra weight and maintenance expense/hassle.

This iteration is to get a Group VI aircraft into Group V gates. Most airports have no or few Group VI gates; the only Group VI aircraft out there are the A380 and the rare 747-8. By contrast the entire industry has standardized around the Group V 777-300ER. A Group VI 777 would have been a difficult sell to almost everyone.

Edit: Mixed up my Groups (gate) and Categories (approach spacing).

Dutchy wrote:

N14AZ wrote:

KarelXWB wrote:

Boeing demonstrates the 777X folding wingtip mechanism:

https://youtu.be/q0hEZDLsiF8

Intersting, so it's becoming reality. Honestly, I thought it would end similar to the proposal they made years ago ... no airline ordered this feature at that time.

Yes, that was more complex, mechanism included some of the flaps and slats if I am not mistaken.

It was much heavier, too.

KarelXWB wrote:

Boeing demonstrates the 777X folding wingtip mechanism:

https://youtu.be/q0hEZDLsiF8

So what are we seeing here?
Apparently it is some sort of test set-up, but what exactly is being tested? It seems the (non-flight-worthy) frame around the wingtip is doing the actual actuation. Perhaps up-lock/down lock system? Or is the frame applying a pre-determined load profile to the in-wing actuation system during the actuation schedule?
Just curious. Can't wait see the real thing!

PW100 wrote:

So what are we seeing here?
Apparently it is some sort of test set-up, but what exactly is being tested? It seems the (non-flight-worthy) frame around the wingtip is doing the actual actuation. Perhaps up-lock/down lock system? Or is the frame applying a pre-determined load profile to the in-wing actuation system during the actuation schedule?
Just curious. Can't wait see the real thing!

http://aviationweek.com/new-civil-aircr ... ng-wingtip says:

The rig will “unearth any deficiencies or parts of the design that we need to beef up,” says 777X Vice President and General Manager Bob Feldmann. “We have spent a lot of time trying to take risk out of that folding-wingtip system. We built the rig to try to get it done early, and we forced Liebherr to produce a prototype so early that they had not even got the final design nailed down. We did this so we could get parts in here and start testing to see how the control system works, where there is play and where there is not, and how the specification did in defining that system.” Given major problems with the wingtip will require an aircraft-on-ground team for fixes, Feldmann says “we want it to be bulletproof.”

So it seems to mostly be about testing the control system as well as the mechanical aspects. The text or the video aren't clear if the loads are varied as the test rig operates.

I'm just wondering how reliable these foldable wing tips will be, problems extending the wing tips after pushback or retracting before taxi in can quickly become a hassle. Hopefully Delta will order some haha.

DL777200LR wrote:

I'm just wondering how reliable these foldable wing tips will be, problems extending the wing tips after pushback or retracting before taxi in can quickly become a hassle. Hopefully Delta will order some haha.

The folding wing tip will certainly be a simpler mechanism than, for example, the landing gear. Is there any good reason to suspect it will be any more problematic? Regards. -ir

DL777200LR wrote:

I'm just wondering how reliable these foldable wing tips will be, problems extending the wing tips after pushback or retracting before taxi in can quickly become a hassle. Hopefully Delta will order some haha.

My posting just above yours says:

Given major problems with the wingtip will require an aircraft-on-ground team for fixes, Feldmann says “we want it to be bulletproof.”

And Feldmann is Boeing's VP for the 77X program, so it seems they understand the concern and are addressing it.

How does de-ice ops work with the folding tip ? Or is this a fair wx ops only device ?

We tend not to move flaps until we need to for ice. How does the tip work ?

zeke wrote:

How does de-ice ops work with the folding tip ? Or is this a fair wx ops only device ?

We tend not to move flaps until we need to for ice. How does the tip work ?

With the tip upright, ice and snow accumulation would be minimal. That said, you could de-ice with tips folded and then unfold them pior to takeoff.

Can this be something for the A388 in the future? Many here at A.net talks about it needs longer wings.

Boeing will use 6 test planes:

Boeing plans to build four 777-9Xs for the flight-test program, plus a fatigue-test-airframe, while two aircraft will be built for the 777-8X test program. Rollout of the first 777-9X is due in late 2018, with all four test aircraft expected to be engaged in the flight program by mid-2019.

http://aviationweek.com/commercial-avia ... ter-boeing

olle wrote:

Can this be something for the A388 in the future? Many here at A.net talks about it needs longer wings.

It's over-winged as it is. And extending the wings might raise clearance issues during takeoff. Anyway, looks as if A380 production will end within the next few years.

DocLightning wrote:

olle wrote:

Can this be something for the A388 in the future? Many here at A.net talks about it needs longer wings.

It's over-winged as it is. And extending the wings might raise clearance issues during takeoff. Anyway, looks as if A380 production will end within the next few years.

If the A380 for example takes off with wingtips folded and unfolds while airborn, that could be a solution, it hardly needs more lift on take off, but fuel reduction on the way.

Should I call you an optimist, hoping that the A380 will fail, or a pessimist regretting the soon to come death of the A380.

IMO we will see the A380 in production for quite a few more years.

Given major problems with the wingtip will require an aircraft-on-ground team for fixes, Feldmann says “we want it to be bulletproof.”

Interesting.

I thought they might have tried to make it a non MMEL item for flights under X km. Obviously not.


Re the A380, the A380 wing has too much wing area and too short a span. Adding span will improve aspect ratio (lowering induced drag), but also increase wetted area and thus zero-lift drag. Like composites, moveable wingtips are not a panacea.

PW100 wrote:

KarelXWB wrote:

Boeing demonstrates the 777X folding wingtip mechanism:

https://youtu.be/q0hEZDLsiF8

So what are we seeing here?
Apparently it is some sort of test set-up, but what exactly is being tested? It seems the (non-flight-worthy) frame around the wingtip is doing the actual actuation. Perhaps up-lock/down lock system? Or is the frame applying a pre-determined load profile to the in-wing actuation system during the actuation schedule?
Just curious. Can't wait see the real thing!

My first reaction was the same, but I reckon the wingtip is doing its own actuation and the yellow frame is "following" it... presumably because the yellow bit carries a bunch of sensors or is there to prevent things going out of control.

If you look carefully there's a kind of sensor with fingers from the wingtip and the frame being kept at a certain distance from each other.

DocLightning wrote:

zeke wrote:

How does de-ice ops work with the folding tip ? Or is this a fair wx ops only device ?

We tend not to move flaps until we need to for ice. How does the tip work ?

With the tip upright, ice and snow accumulation would be minimal. That said, you could de-ice with tips folded and then unfold them pior to takeoff.

Wouldn't the hinge be precisely the bit you worry about with icing? I would expect that you would have to de-ice the hinge before unfolding... so you might have to recommence de-icing after that.

mjoelnir wrote:

If the A380 for example takes off with wingtips folded and unfolds while airborn, that could be a solution, it hardly needs more lift on take off, but fuel reduction on the way.

That would be the moment of maximum lift and most possible force on the mechanism - I doubt that's a smart way to do things.

SomebodyInTLS wrote:

mjoelnir wrote:

If the A380 for example takes off with wingtips folded and unfolds while airborn, that could be a solution, it hardly needs more lift on take off, but fuel reduction on the way.

That would be the moment of maximum lift and most possible force on the mechanism - I doubt that's a smart way to do things.

Flaps and slats are moved at the same time. And again the A380 doe not need more lift at take off.

The actuator would have to be much bigger/stronger and thus heavier. As the wingtip deployed downwards it would start to create lift - acting against the actuator.

For the 777X version the actuator only has to lift the weight of the wingtip against gravity.

I would think this would make in flight actuation much more difficult.

StTim wrote:

The actuator would have to be much bigger/stronger and thus heavier. As the wingtip deployed downwards it would start to create lift - acting against the actuator.

For the 777X version the actuator only has to lift the weight of the wingtip against gravity.

I would think this would make in flight actuation much more difficult.

All problems with a technical solution. The movement of the wing tip device could first turn while unlocking to a lift neutral position and than lift up. On the downward movement it would be lift neutral and turn while locking to produce lift again. The turning could be the locking and unlocking movement.

I do not say it will be done, or should be done, but if it is necessary to do it, than there will be found a technical solution.

StTim wrote:

The actuator would have to be much bigger/stronger and thus heavier. As the wingtip deployed downwards it would start to create lift - acting against the actuator.

For the 777X version the actuator only has to lift the weight of the wingtip against gravity.

I would think this would make in flight actuation much more difficult.

I'm am unaware of any intention for this to be used in flight. The folding wing tips are for taxiway and gate clearance issues. In fact I'd be amazed if the wingtips could fold in flight, as it would be proper to design the mechanism so that it can't fold while lift is being generated even if the system is activated.

XT6Wagon wrote:

StTim wrote:

The actuator would have to be much bigger/stronger and thus heavier. As the wingtip deployed downwards it would start to create lift - acting against the actuator.

For the 777X version the actuator only has to lift the weight of the wingtip against gravity.

I would think this would make in flight actuation much more difficult.

I'm am unaware of any intention for this to be used in flight. The folding wing tips are for taxiway and gate clearance issues. In fact I'd be amazed if the wingtips could fold in flight, as it would be proper to design the mechanism so that it can't fold while lift is being generated even if the system is activated.

I was talking about the propsed A380 folding wintip - well propsed above, and compaing it to the simpler 777X which as you say is for deployment on the taxiway.

Anything relating to the A380 is clearly nothing to do with this topic. Time to talk about the the 77X.

SomebodyInTLS wrote:

DocLightning wrote:

zeke wrote:

How does de-ice ops work with the folding tip ? Or is this a fair wx ops only device ?

We tend not to move flaps until we need to for ice. How does the tip work ?

With the tip upright, ice and snow accumulation would be minimal. That said, you could de-ice with tips folded and then unfold them pior to takeoff.

Wouldn't the hinge be precisely the bit you worry about with icing? I would expect that you would have to de-ice the hinge before unfolding... so you might have to recommence de-icing after that.

There must be a lot of info out there about how to deal with this. The previous design for the original 777 was said to have leveraged the design from the A-6 Intruder. I'm sure those a/c spent enough time sitting on the carrier deck and/or flying through rain that they accumulated ice.

Here's a pic of the A-6 wing fold I found on Google ( ref: http://tailspintopics.blogspot.com/2014 ... ences.html ):

IslandRob wrote:

DL777200LR wrote:

I'm just wondering how reliable these foldable wing tips will be, problems extending the wing tips after pushback or retracting before taxi in can quickly become a hassle. Hopefully Delta will order some haha.

The folding wing tip will certainly be a simpler mechanism than, for example, the landing gear. Is there any good reason to suspect it will be any more problematic? Regards. -ir

Probably not, but certainly there will be cases were it will not fold up, so it can't use the assigned gate and doesn't fold back down so it will have to be repaired. There probably will be cases were the mechanism will be activated during flight and that could be potential dangerous at low speeds. So it will be one more thing to fail, nothing more.

Ailerons, flaps, slots, slats, extenders, spoilers etc, and all of a sudden another moving part on a wing is a boogie man. Come on, folks.

frmrCapCadet wrote:

Ailerons, flaps, slots, slats, extenders, spoilers etc, and all of a sudden another moving part on a wing is a boogie man. Come on, folks.

Exactly. A failure of any one of those things can cause a flight to be canceled (or worse), and no one here obsesses about them. The folding tip is likely simpler (and less mission critical) than any of the other wing components you listed. -ir

So how would they route the bleed air duct in regards to leading edge Anti-ice?

UAL916 wrote:

So how would they route the bleed air duct in regards to leading edge Anti-ice?

If the tip has ice protection features, I suspect they'd be simple heaters. It's not clear to me that's actually needed though, since the lift generated by the tip is relatively small and there are alternative options like derating in icing conditions.

If it does have a bleed air duct or any kind of anti-ice on the tip, you can design the mating ends of the ducts with flanges that butt together and seal in the latched position - face sealing against a high-temp O-ring, for example. That would be far from the most complicated automatically mating air connector I've seen.

frmrCapCadet wrote:

Ailerons, flaps, slots, slats, extenders, spoilers etc, and all of a sudden another moving part on a wing is a boogie man. Come on, folks.

A flap mechanism failure means the flap stops extending in and out as it should. A wingtip mechanism failure could mean the end of your wing effectively "breaks off"... there's a difference!

(N.B. I don't literally mean breaks *off*, but the effect would be the same - sudden loss of a chunk of lift on one side. And if the failure is rapid enough, then maybe it really would be broken off...)

"So how would they route the bleed air duct in regards to leading edge Anti-ice?"

There is no anti-ice on the raked wing tip (and the outboard slat) for the 773ER. The same will apply for the 777X.

"The folding tip is likely simpler (and less mission critical) than any of the other wing components you listed. -ir"

A good analogy for the folding tip, in terms of mechanical complexity, is the main landing gear door. A folding tip actuation failure is less problematic than the gear door since it occurs on the ground rather than in flight.

N14AZ wrote:

KarelXWB wrote:

Boeing demonstrates the 777X folding wingtip mechanism:

https://youtu.be/q0hEZDLsiF8

Aviation Week editors recently saw a demonstration of the folding wingtip at Boeing’s Everett, Washington plant. The target time for extending and/or retracting the wingtip is 20 sec. Listen closely when it reaches the selected position to hear the locking mechanisms engage.

Intersting, so it's becoming reality. Honestly, I thought it would end similar to the proposal they made years ago ... no airline ordered this feature at that time.

The earlier proposal was much more complex, because it included an aileron. This one doesn't, and it is not optional. The first one was.

Amiga500 wrote:

Given major problems with the wingtip will require an aircraft-on-ground team for fixes, Feldmann says “we want it to be bulletproof.”

Interesting.

I thought they might have tried to make it a non MMEL item for flights under X km. Obviously not.


Re the A380, the A380 wing has too much wing area and too short a span. Adding span will improve aspect ratio (lowering induced drag), but also increase wetted area and thus zero-lift drag. Like composites, moveable wingtips are not a panacea.

I'm tempted to ask "So why are they being used on the 777X?".

Clearly as the extension is at the very tip of the wing, the benefit gained from the increased aspect ratio far outweighs the fractional increase in wetted area.

That is why the 777X has them.
And why the A380 would benefit.
The A380's issue is that of even worse clearance margin on take-off and landing - something the 777X will also have to deal with to a much lesser extent

Rgds

SomebodyInTLS wrote:

frmrCapCadet wrote:

Ailerons, flaps, slots, slats, extenders, spoilers etc, and all of a sudden another moving part on a wing is a boogie man. Come on, folks.

A flap mechanism failure means the flap stops extending in and out as it should. A wingtip mechanism failure could mean the end of your wing effectively "breaks off"... there's a difference!

(N.B. I don't literally mean breaks *off*, but the effect would be the same - sudden loss of a chunk of lift on one side. And if the failure is rapid enough, then maybe it really would be broken off...)

I'm pretty sure failure of a flap to extend would be worse. At a minimum, I know the area of the inboard flaps is far larger than the folding wingtip, and the flaps are optimized more for lift than drag, while the wingtip is optimized for drag. Actually, my understanding was the raked winglet design does more to reduce lift induced drag than it does to generate lift directly.

Also, short of a major screw up in the structural analysis or a critical flutter problem that manages to sneak through flight testing, failure in flight should be less likely for the wingtip, as it doesn't need to move in flight. It gets cross pinned in place on the ground, and they don't take off unless the pins are detected in their latched positions.

Don't get me wrong I am not anti this system but it does bring additional moving parts and they all have the potential to fail.

If a flap were to break away on the final approach I do this that would be unrecoverable. I have not heard of that - but flaps failing to extend or failing to retract are relatively common. As I understand it on these the systems work such that if one side jams the other also stops meaning that asymmetric deployment does not happen.

For the wing tip it will only deploy and retract (for want of a better phrase) on the ground.

Regarding the final point looking at the wingtips of the plans I fly on you do see the wing tip bend upwards in flight as a result of the lift they are creating. They also move most during turbulence. Thus there is going to be some stress on the hinges and locking pins. I am absolutely sure this will be ok and we will not get failures in flight. But they better do a damned good job as an inflight failure would be difficult to handle.

StTim wrote:

Regarding the final point looking at the wingtips of the plans I fly on you do see the wing tip bend upwards in flight as a result of the lift they are creating. They also move most during turbulence. Thus there is going to be some stress on the hinges and locking pins. I am absolutely sure this will be ok and we will not get failures in flight. But they better do a damned good job as an inflight failure would be difficult to handle.

Actually, if it were to break off in flight I think the effect would be negligible. These are mainly to increase efficiency; the amount of lift they contribute is negligible. If one broke off it would cause a sudden yaw and probably a tendency to bank, but it would be easily controllable. The biggest hit would be increased drag (which is why the yaw.)

The wing has to survive 150% of max load. With the wingtip extended. As for movement in flight, that is what that great big locking click is supposed to prevent.

I don't understand people being so concerned with the reliability of this folding mechanism. Naval aircraft have had folding wings over 70 years while subjecting the mechanisms to far more stress than an airliner, and many of those used far more complicated systems than this while folding much greater portions of the wings. While it is a McD legacy product, Boeing currently have a Navy plane, the F/A-18, in production right now with folding wings.

I remember reading elsewhere that Boeing was going to certify the plane with the wingtips in either position so it wouldn't be an AOG situation if the mechanism failed. Depending on which was considered the more desirable failure (tips stuck up or stuck down), you could engineer the system to default to one or the other.

Ya, I thought that's what was said previously as well - losing one in flight would not be fatal.

tjh8402 wrote:

I don't understand people being so concerned with the reliability of this folding mechanism. Naval aircraft have had folding wings over 70 years while subjecting the mechanisms to far more stress than an airliner, and many of those used far more complicated systems than this while folding much greater portions of the wings. While it is a McD legacy product, Boeing currently have a Navy plane, the F/A-18, in production right now with folding wings.

I remember reading elsewhere that Boeing was going to certify the plane with the wingtips in either position so it wouldn't be an AOG situation if the mechanism failed. Depending on which was considered the more desirable failure (tips stuck up or stuck down), you could engineer the system to default to one or the other.

That opinon seems to be in contrast to what Boeing's VP for the 77X said ( ref: #2009, viewtopic.php?t=558021&view=unread#p19161431 ).

He says they will be treating the failure as an AOG situation.

Revelation wrote:

tjh8402 wrote:

I don't understand people being so concerned with the reliability of this folding mechanism. Naval aircraft have had folding wings over 70 years while subjecting the mechanisms to far more stress than an airliner, and many of those used far more complicated systems than this while folding much greater portions of the wings. While it is a McD legacy product, Boeing currently have a Navy plane, the F/A-18, in production right now with folding wings.

I remember reading elsewhere that Boeing was going to certify the plane with the wingtips in either position so it wouldn't be an AOG situation if the mechanism failed. Depending on which was considered the more desirable failure (tips stuck up or stuck down), you could engineer the system to default to one or the other.

That opinon seems to be in contrast to what Boeing's VP for the 77X said ( ref: #2009, viewtopic.php?t=558021&view=unread#p19161431 ).

He says they will be treating the failure as an AOG situation.

I can't find the citation but I remember reading that somewhere. it may be a design goal that was changed as it was a while ago. If that's the case, I would think the easiest thing would be to make it such that gravity, hydraulic pressure, or some other natural mechanism causes the wings to default to an unfolded position, similar to air brakes defaulting to "set" and requiring action to release. That way, if there's a failure of the actual power mechanism, it keeps them down rather than up. The biggest challenge with that would be that you would probably want to secure the tips as soon as possible after folding to make sure they didn't unfold in a tight space. Either way, it's proven system in far more complicated and challenging applications that Boeing has experience making (albeit not designing) so I don't see it being a huge issue.

tjh8402 wrote:

I don't understand people being so concerned with the reliability of this folding mechanism. Naval aircraft have had folding wings over 70 years while subjecting the mechanisms to far more stress than an airliner, and many of those used far more complicated systems than this while folding much greater portions of the wings. While it is a McD legacy product, Boeing currently have a Navy plane, the F/A-18, in production right now with folding wings.

I remember reading elsewhere that Boeing was going to certify the plane with the wingtips in either position so it wouldn't be an AOG situation if the mechanism failed. Depending on which was considered the more desirable failure (tips stuck up or stuck down), you could engineer the system to default to one or the other.

I think quite a few people are overly concerned, but that doesn't mean there is no concern at all. I'm certain Boeing have a very high degree of confidence in their ability to make the design structurally sound. They should also have a high degree confidence in being able to make it reliable, but it will only be so if they do their full diligence in the design and testing.

A commercial aircraft will actually have higher reliability expectations than a naval aircraft. Not that warfare is less critical, but that the Navy has to be and is prepared to deal with worse situations than a stuck actuator. The Navy's experience also has not been trouble free:
https://theaviationist.com/2014/02/19/u ... ded-wings/

tjh8402 wrote:

I don't understand people being so concerned with the reliability of this folding mechanism. Naval aircraft have had folding wings over 70 years while subjecting the mechanisms to far more stress than an airliner, and many of those used far more complicated systems than this while folding much greater portions of the wings. While it is a McD legacy product, Boeing currently have a Navy plane, the F/A-18, in production right now with folding wings.

I remember reading elsewhere that Boeing was going to certify the plane with the wingtips in either position so it wouldn't be an AOG situation if the mechanism failed. Depending on which was considered the more desirable failure (tips stuck up or stuck down), you could engineer the system to default to one or the other.

Military is always a different kettle of fish...

Very different criteria, very different risk.

Just look how long composites were in use on primary structures there before they finally made it to 787. That was, what? 40 years? 50?

(Google is surprisingly bad at helping me on this one...)

SomebodyInTLS wrote:

tjh8402 wrote:

I don't understand people being so concerned with the reliability of this folding mechanism. Naval aircraft have had folding wings over 70 years while subjecting the mechanisms to far more stress than an airliner, and many of those used far more complicated systems than this while folding much greater portions of the wings. While it is a McD legacy product, Boeing currently have a Navy plane, the F/A-18, in production right now with folding wings.

I remember reading elsewhere that Boeing was going to certify the plane with the wingtips in either position so it wouldn't be an AOG situation if the mechanism failed. Depending on which was considered the more desirable failure (tips stuck up or stuck down), you could engineer the system to default to one or the other.

Military is always a different kettle of fish...

Very different criteria, very different risk.

Just look how long composites were in use on primary structures there before they finally made it to 787. That was, what? 40 years? 50?

(Google is surprisingly bad at helping me on this one...)

While I get what you're saying, I do think composites are a poor example, as commercial builders are concerned with the economies of scale and mass production, whereas high end military products can be boutique buys and usually involve smaller pieces. It's much less of a production challenge to build composite empennages for F-15s than it is for planes the size of a 787, much less the 777 (recall that supposedly one of Boeings challenges for the 777x was designing an autoclave large enough to make the wings).

I'd also point out that military aircraft made primarily of composite structures are still relatively new. From what I can tell, the first mass produced (so no F117s or F22s) military jets to be made primarily of composites were 4.5 generation planes like the Euro canard twins, and those only entered service this century, even if their first flights were a long time before. As best I can tell, the F-35 is actually the most ordered composite military aircraft and is currently the third most produced behind the Typhoon and F-22 Raptor.

There's also a huge difference between mastering something groundbreaking like composite construction and a mechanism and action that's been in regular use since the second world war.

The folding wingtip will come with the 777-8/9 and there is no reason it should not work. If they do not fold on arrival the frame will need an A380 gate or remote stand. I assume the frame will be able to fly with the tips folded. If the failure rate is similar to inoperable flaps it should be good.
I think there is no reason to worry that Boeing will not solve all technical problems regarding such a system.