777x Folding wings

[underfire]

Boeing announced today that the new 777X will have folding wings as the standard.

Pretty interesting news and design.

[DevX]

For carrier based use? :}

[a1rm4n]

Have a look at an earlier thread on this:

http://www.pprune.org/tech-log/499826-777-get-folding-wings.html

The web's abuzz with interesting morsels about this, here's a few I could find:

- A close-up photo of of the hinge on a 777X model:
https://mobile.twitter.com/StratAero/status/403614539645599744/photo/1

- A illustration of the folded winglet:
Folding Wings Will Let Boeing's New 777x Squeeze Into Small Airports (http://gizmodo.com/folding-wings-will-let-boeings-new-777x-squeeze-into-s-1466679208)

From an innovation standpoint I hope it works for them as it will open up the door to many other similar high aspect ratio upgrades for other aircraft. But for me when putting my realistic hat on this has trouble written all over it. This mechanism will be required to operate in the harshest environment yet (so put all the proven on military aircraft claims straight in the bin) - longest moment arm from the a/c CG so worst-case continuous vibration and prolonged exposure to very low temperatures are just a couple of issues that spring to mind. Then what will happen when the aircraft will land, will have been allocated with a gate and the folding mechanism fails so it needs a bigger gate when none is available? Sure the flap drives operate to such conditions but don't forget that they are developed according to stringent safety-critical standards. This device will not be safety-critical so good luck to Boeing and in particular the operators that use them in airports that don't have A380 gates.

Let's see how it pans out but for sure it has already been a success in one area and that's the marketing hype it has created for the 777X as Boeing had planned. Just bear in mind that a much more complex version of this concept (including fuel tank volume) was originally developed as a retrofit option for the original 777 and dropped because of lack of interest. This is of course a different case to the 777X that is simpler in comparison but requires it to operate in 777-sized gates. However, it's still worth remembering the facts.

[CCA]

They have already done testing for contaminants involving sand, cold weather, snow, deicing fluid and whatever else they could come up with plus strong winds. Apparently looking at less than 20sec to fold/unfold & lock. Stronger than published winds may slow the process but won't stop it.

It can also be removed quickly and covered under the CDL like a winglet if dinged.

[Mozella]

" ..............................longest moment arm from the a/c CG so worst-case continuous vibration and prolonged exposure to very low temperatures are just a couple of issues that spring to mind. Then what will happen when the aircraft will land, will have been allocated with a gate and the folding mechanism fails so it needs a bigger gate when none is available? .............

If it were up to you, I suppose airliners would have fixed landing gear. Failure to fold is a LOT less concerning than when the retractable gear fails to extend. Just think how long those struts stay tucked up in the wheel wells under continuous vibration and prolonged exposure to very low temperatures. It's a wonder we don't have a dozen belly landings per day. Oh the humanity.

Yes, distance from the wing fold to the A/C cg is a factor, but the further the better from a design point of view. Long distance from the wing fold to the cg, low g limit and a thick airfoil section are three factors which the 777x would have going for it.

Contrast that with something like the FA-18 which has a rather thin wing and a very high g limit (tricky to design). Or, consider several sub-sonic U.S. Navy aircraft where a large percentage of the span folds; i.e. A-3, A-6, S-3 (also a design challenge)

Folding wing technology isn't new and I guarantee you that if and when a 777x is built, the design engineers working on the wing fold mechanism will spend many many hours studying existing Navy aircraft in spite of your advice that they toss experience with previous successful military aircraft in the bin.

Furthermore, a wing fold failure when approaching the gate won't be the end of the world. What do you think airlines do when a wide-body diverts to or makes an emergency landing at an airport not equipped to handle large aircraft? Pop the slides, evacuate the passengers and crew, and then burn the thing on the spot........... hardly.

Folding wing aircraft may or may not be the future of high efficiency airliners. But if it's determined to be a good idea, building the wing fold mechanism won't be a particularly high hurdle.

[Wizofoz]

Then what will happen when the aircraft will land, will have been allocated with a gate and the folding mechanism fails so it needs a bigger gate when none is available?

Then it's just landed at an airport it couldn't have used AT ALL if the wings didn't fold.

[Volume]

Folding wing aircraft may or may not be the future of high efficiency airliners. But if it's determined to be a good idea, building the wing fold mechanism won't be a particularly high hurdle.But at the same time, the benefit would not be significant as well. I am sure it can be done, and sooner or later it will even be a reliable system. But for sure it will add weight and complexity (remember the old DC-3 design philosophy by Ed Heinemann...), it will add new failure scenarios, it will add another source for trouble. The question remains, will it ever pay off compared to a simple state of the art winglet design with practically zero maintenance cost? I seriously doubt that it is the most clever way to gain 1-2% in efficiency, that can probably be done much easier elsewhere.

P.S. I just found the following Statement from Boeing:
“We are spending a lot of effort to make sure we have a a simple design,” he said, “to have a simple and very reliable mechanism, like a landing gear door.”Hopefully not! Check the long list of SB and AD dealing with Landing Gear Door Trouble...

[SADDLER]

If it were up to you, I suppose airliners would have fixed landing gear. Failure to fold is a LOT less concerning than when the retractable gear fails to extend. Just think how long those struts stay tucked up in the wheel wells under continuous vibration and prolonged exposure to very low temperatures. It's a wonder we don't have a dozen belly landings per day. Oh the humanity.

Yes, distance from the wing fold to the A/C cg is a factor, but the further the better from a design point of view. Long distance from the wing fold to the cg, low g limit and a thick airfoil section are three factors which the 777x would have going for it.

Contrast that with something like the FA-18 which has a rather thin wing and a very high g limit (tricky to design). Or, consider several sub-sonic U.S. Navy aircraft where a large percentage of the span folds; i.e. A-3, A-6, S-3 (also a design challenge)

Folding wing technology isn't new and I guarantee you that if and when a 777x is built, the design engineers working on the wing fold mechanism will spend many many hours studying existing Navy aircraft in spite of your advice that they toss experience with previous successful military aircraft in the bin.

Furthermore, a wing fold failure when approaching the gate won't be the end of the world. What do you think airlines do when a wide-body diverts to or makes an emergency landing at an airport not equipped to handle large aircraft? Pop the slides, evacuate the passengers and crew, and then burn the thing on the spot........... hardly.

Folding wing aircraft may or may not be the future of high efficiency airliners. But if it's determined to be a good idea, building the wing fold mechanism won't be a particularly high hurdle.

At last, someone with an ounce of wit.

[CCA]

The problem is the 777-300ER wing is already at the max width for code E, sticking a blended winglet on a 300ER will take it to code F (you'd have to cut the span down to fit a blended winglet on thereby wiping out any gains), so to get the wing they need they have to go wider and once out there you might as well have a 10 foot folding wingtip as a folding winglet is pointless.

[tdracer]

a1rm4n and Volume, I don't think you appreciate just how big a deal even 1% fuel burn is on a big, long range airplane such as the 777. 1% fuel burn is a ton or more of fuel per flight (depending of course on the flight length, but remember the 777 is designed to be a long-range airplane). That is a whole lot of fuel over the 20+ year life of a 777. And even if it adds 1,000 lb. to the aircraft empty weight (it won't), it'll still be able to carry 1,000 extra lbs. payload per flight since it won't need to takeoff with that fuel.


As for complexity, hydraulically actuated movable surfaces are a feature on nearly every commercial jetliner ever built, and they've been hugely reliable.


The original 777 folding wing concept was well inboard of what's being used for the 777X and far more complex. Among other things, there were various movable aerodynamic surfaces outboard of the fold - not so with the 777X. In the highly unlikely event that the folding wingtip fails in-flight, it's only a couple percent of the total wing area and the aircraft will fly just fine (although I'm sure there will be plenty of "I thought we were going to die" stories in the news afterwards :ugh:.) As for not having a gate if the wings fail to fold after landing, I seem to remember something most airports have on hand called "air stairs". And as Saddler and CCA have pointed out, if the airport doesn't have a gate that can handle a 777X if the wings fail to fold, they couldn't handle the 777X if the wings weren't designed to fold.

[Volume]

With respect to the “to have a simple and very reliable mechanism, like a landing gear door.” statement, this (http://avherald.com/h?article=47409a70&opt=0) yesterdays (non)event gives you an idea of what I am talking about. And you have to save 1% of fuel on quite a number of flight to compensate for the cost of such (non)events, including a cancelled flight with 100% of unsatisfied customers and 60% of dumped fuel.
For sure 1% fuel burn is a number for long range aircraft, but a drop of 0.1% in dispatch reliability is as well!
Folding wings are definitively something possible, but they come at the price of a few more reasons why a flight might be delayed or cancelled, they come at the price of additional maintenance cost and additional weight. Time will tell whether they pay off in the long term. I seriously doubt, that they are the most favourable design feature of the 777X.

[zlin77]

Not forgetting that the original 777was offered with a folding wing, an option that none of the early customers opted for...

[Mozella]

(http://avherald.com/h?article=47409a70&opt=0)".........................this (http://avherald.com/h?article=47409a70&opt=0) yesterdays (non)event gives you an idea of what I am talking about. And you have to save 1% of fuel on quite a number of flight to compensate for the cost of such (non)events, including a cancelled flight with 100% of unsatisfied customers and 60% of dumped fuel."

With very few exceptions, the wings are folded and locked before take off, not after. So, unlike a landing gear malfunction after take off, I certainly don't see where anyone is going to dump fuel on account of flying an aircraft with folding wings.

That's not to say that the occasional U.S. Marine aviator hasn't taken off with the wings folded and been forced to dump fuel, but that practice is strongly discouraged; at least it was in the Navy. Plus ex U.S. Marines aren't allowed to fly airliners anymore ever since the Flight Attendant's Union decided that the plots could no longer force them to "DROP AND GIVE ME TEN YOU MAGGOT" when the coffee was cold.

I have folded and extended the wings countless times on various Navy aircraft and while I'm sure that nothing is 100% reliable, I can't ever recall a wing fold malfunction. I do remember a time or two when the indicator system failed to confirm the wings were locked, but a quick visual confirmation is all that is required before take off. I'm sure the 777x will have that provision.

[DaveReidUK]

I seriously doubt, that they are the most favourable design feature of the 777XNobody is claiming that they are.

It's the 1% fuel saving that's the "favourable design feature" - the folding wingtips are simply the means of achieving that while retaining airport compatibility.