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OldAeroGuy
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777X Wing Tip Fold Operational Issues?

Thu Dec 25, 2014 4:44 pm

In a side discussion on this thread, Airbus Considers Ending A380 Production - Part 3 (by American 767 Dec 17 2014 in Civil Aviation), several respected A.net members raised questions about the 777X folding tip operation.

Although this topic has been discussed previously, members thoughts on the topic may have matured/changed so perhaps another look would be in order.

As background, the link from Aspire provides a Boeing document summary of the folding tip system:

http://www.aspireaviation.com/wp-con.../12/777X-airport-compatibility.pdf

Any new or revised thoughts?
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
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rotating14
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RE: 777X Wing Tip Fold Operational Issues?

Thu Dec 25, 2014 4:50 pm

Without having to scroll through 250 posts, what exactly is the question/issue that you are bringing up?
 
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par13del
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RE: 777X Wing Tip Fold Operational Issues?

Thu Dec 25, 2014 5:12 pm

Well it appears the decision on the wing span is a done deal, without knowing all the finances I say fix the wing and be done with it, say money on weight and additional equipment on the a/c.
If the size above already exist and is officially recognized - Cat F - either join the club along with whatever limitations it brings or design something that sits below.
I do not question the technology, it just adds one additional item to be checked by all and sundry, also gets more folks involved where they really do not have to be, now we have Cat F failure mode.

Is the improvement with the additional span the only way to go, not wider (front to back)?
 
OldAeroGuy
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RE: 777X Wing Tip Fold Operational Issues?

Thu Dec 25, 2014 5:27 pm

Issues raised in the prior thread:

- Airplane Category based on tip fold failure, rather than normal operation.

- Ability be Code E on taxiway and Code F on runway.

- Potential for airport operational disruption due to tip fold/unfold time.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
mjoelnir
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RE: 777X Wing Tip Fold Operational Issues?

Thu Dec 25, 2014 6:40 pm

Quoting par13del (Reply 2):
Is the improvement with the additional span the only way to go, not wider (front to back)?

Yes it is the right way to go.
 
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777222LR
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RE: 777X Wing Tip Fold Operational Issues?

Thu Dec 25, 2014 7:53 pm

I've often wondered the issue with having the larger wingspan of the 777X if there is already that much wingspan out there. Remember when they wanted to do this with the 777-200 to make it fit into DC-10 slots?

Can someone enlighten me on the reasoning they are doing this with the 777X? What is the weight penalty?
 
tommy1808
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RE: 777X Wing Tip Fold Operational Issues?

Thu Dec 25, 2014 7:58 pm

Quoting 777222LR (Reply 5):
What is the weight penalty?

my guess: zero or better than zero. If winglets/raked wingtips/whatever other wingtipdevice they'd come up with could have the same effect with lower weight, they would be using those.
Since the tip has no control surfaces, it is much simpler and lighter to build than the old 777 classic ones.

Best regards
Thomas
Well, there is prophecy in the bible after all: 2 Timothy 3:1-6
 
kaitak744
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RE: 777X Wing Tip Fold Operational Issues?

Thu Dec 25, 2014 9:25 pm

This discussion has little merit. Folding wingtips have been used on far more complicated military applications for over half a century. The folding tip on the 777X is nothing compared to those.
 
tommy1808
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RE: 777X Wing Tip Fold Operational Issues?

Thu Dec 25, 2014 9:36 pm

Quoting kaitak744 (Reply 7):
The folding tip on the 777X is nothing compared to those.

It still will fail to move ... Boeing is aming for a failure rate of 1:1000 for deployment and 1:10.000 for folding Iirc (means I could be an order of magnitude off). And if they don't fold, the plane is going to need a cat. F ready way off the runway. I don't think that will be much of a problem, I suspect all airports that get to see the 77X would be able to handle a occasional A380 flight anyways.

Best regards
Thomas
Well, there is prophecy in the bible after all: 2 Timothy 3:1-6
 
OldAeroGuy
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RE: 777X Wing Tip Fold Operational Issues?

Thu Dec 25, 2014 10:14 pm

Quoting tommy1808 (Reply 8):
It still will fail to move ... Boeing is aming for a failure rate of 1:1000 for deployment and 1:10.000 for folding Iirc (means I could be an order of magnitude off).

You are off by an order of magnitude. See page 17 of the presentation linked in the thread starter. It's 1:10,000 for failure to retract and 1:100,000 for failure to deploy.

Quoting kaitak744 (Reply 7):
Folding wingtips have been used on far more complicated military applications for over half a century. The folding tip on the 777X is nothing compared to those.

A big difference is cycles. Military aircraft with wing fold fly 1/10 or fewer cycles compared to commercial airplanes.

Plus the military airplanes have mechanics close at hand if the wing fold fails to cycle properly. You don't see airline mechanics standing around the end of an airport runway.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
tommy1808
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RE: 777X Wing Tip Fold Operational Issues?

Thu Dec 25, 2014 10:42 pm

Quoting OldAeroGuy (Reply 9):
You are off by an order of magnitude

thank you for correcting  

best regards
Thomas
Well, there is prophecy in the bible after all: 2 Timothy 3:1-6
 
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par13del
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RE: 777X Wing Tip Fold Operational Issues?

Thu Dec 25, 2014 11:03 pm

Quoting OldAeroGuy (Reply 9):
A big difference is cycles. Military aircraft with wing fold fly 1/10 or fewer cycles compared to commercial airplanes.

If we get the military involved we can probably ask why they decided to decrease the length of the wing fold, probably something to do with weapons load but I don't know.
Compare the A6-Intruder and the F-18 and you can see the big difference in wing fold.
 
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DocLightning
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RE: 777X Wing Tip Fold Operational Issues?

Thu Dec 25, 2014 11:57 pm

It strikes me that tying retraction automatically to spoiler activation (which is triggered by pressure on the gear) might help with high-speed exit usage.
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par13del
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RE: 777X Wing Tip Fold Operational Issues?

Fri Dec 26, 2014 12:14 am

Quoting DocLightning (Reply 12):
(which is triggered by pressure on the gear) might help with high-speed exit usage.

First thing came to my mind on this was a hard landing, bounce and go around initiated with the wing folding.
Recall an issue with something else activated by tire pressure, need to research in case the memory is failing.
 
Max Q
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RE: 777X Wing Tip Fold Operational Issues?

Fri Dec 26, 2014 1:25 am

Don't think tying wing fold operation to other flight controls is a good idea, I had thought integrating it with flap operation might work but its probably better to have an independent control.



This is touched on briefly in the pdf but not described, anyone yet have an idea what this control will actually look like ?
The best contribution to safety is a competent Pilot.


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roseflyer
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RE: 777X Wing Tip Fold Operational Issues?

Fri Dec 26, 2014 1:49 am

I think too many people think that a retractable wing tip extension is more complicated that it is. It is a very small section of wing without that large of loading on it. People seem to think it might be failure prone, but how often does a flap or spoiler fail to retract? The wing tip is no more complicated than a two position ground spoiler. Parts of the wing have been actuated since before the jet age.

I don't see why airport category would be significantly impacted.
If you have never designed an airplane part before, let the real designers do the work!
 
OldAeroGuy
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RE: 777X Wing Tip Fold Operational Issues?

Fri Dec 26, 2014 4:16 am

I believe the original 777 fold control concept (circa 1990) was a broad lever mounted on the edge of the glare shield. With the tips folded, the lever was above the glare shield and appropriately marked to be noticeable. Moving the lever down to align with the glare shield took it out of the pilots' field of view and extended the tips. (But it's been 25 years and my memory hasn't improved with age.)

I suspect that a similar concept would used on the 777X.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
captainstefan
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RE: 777X Wing Tip Fold Operational Issues?

Fri Dec 26, 2014 4:30 am

Quoting Roseflyer (Reply 15):
I don't see why airport category would be significantly impacted.

Because this kind of incident becomes even more of an issue:

https://www.youtube.com/watch?v=s8u8893oN1o

The wingspan difference between folded and unfolded of the 777X of 20'8", or 10'4" on each side. That can easily be the difference between safely taxiing on most existing widebody-capable ramps/taxiways and knocking the snot out of an RJ, or worse.
Long Live the Tulip!
 
INFINITI329
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RE: 777X Wing Tip Fold Operational Issues?

Fri Dec 26, 2014 6:12 am

Quoting OldAeroGuy (Reply 3):
Potential for airport operational disruption due to tip fold/unfold time.

Non-issue i don't think it will take more than 30 seconds to fold down or up
 
mmo
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RE: 777X Wing Tip Fold Operational Issues?

Fri Dec 26, 2014 7:59 am

Quoting infiniti329 (Reply 18):
Non-issue i don't think it will take more than 30 seconds to fold down or up


In Boeing data that has been released, the complete process will take 20 seconds.

Quoting OldAeroGuy (Reply 16):





I believe the original 777 fold control concept (circa 1990) was a broad lever mounted on the edge of the glare shield. With the tips folded, the lever was above the glare shield and appropriately marked to be noticeable. Moving the lever down to align with the glare shield took it out of the pilots' field of view and extended the tips. (But it's been 25 years and my memory hasn't improved with age.)

I suspect that a similar concept would used on the 777X.

Reading some Boeing documents, I get the impression it will not be a lever but more of a switch. There are references to having it as a permanent data field on the EICAS. And of course, it will obviously be linked into the electronic checklist.
If we weren't all crazy we'd all go insane!
 
strfyr51
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RE: 777X Wing Tip Fold Operational Issues?

Fri Dec 26, 2014 10:05 am

Quoting par13del (Reply 2):
Well it appears the decision on the wing span is a done deal, without knowing all the finances I say fix the wing and be done with it, say money on weight and additional equipment on the a/c.
If the size above already exist and is officially recognized - Cat F - either join the club along with whatever limitations it brings or design something that sits below.
I do not question the technology, it just adds one additional item to be checked by all and sundry, also gets more folks involved where they really do not have to be, now we have Cat F failure mode.

Is the improvement with the additional span the only way to go, not wider (front to back)?

*******************************************************************************************************************************************
Here's the problem with what you're saying.. Airport Gates, Even International gates here in the USA are NOT just going to get larger.
At SFO where I was a Maintenance Supervisor It was not Unusual to show up for work and find 10-12 744,777 and the occasional A340 sitting on the G concourse alone.wingtip to wingtip.
So overreaching the Gate envelope is only going to make the airport LESS efficient and result in remote parking and Loading aircraft with Busses
and who would want That?? Boeing KNEW what the gate restraints were and even though they wanted a much longer wing?
They made a compromise and the retractable tip is it. It's worked pretty well in Naval Aviation over the years.
No Reason it can't in civilian Aviation.
 
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Faro
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RE: 777X Wing Tip Fold Operational Issues?

Fri Dec 26, 2014 10:32 am

What about recurrent freeze-thaw cycles with wet wingfold mechanisms and freezing rain? Won't this decrease fatigue life compared to the rest of the airframe? Will the mechanisms has more frequent inspection intervals?


Faro
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AirlineCritic
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RE: 777X Wing Tip Fold Operational Issues?

Fri Dec 26, 2014 11:34 am

That was an interesting read, thanks for posting.

This is the first time I see such a detailed plan regarding the folding wing tips. The link was also otherwise interesting, recommended people go through it.

I just have one question on this:

Quote:
Boeing to confirm with ICAO/FAA that clearances currently required could be reduced for an aircraft under tow

Do we think this is likely? Are there precedents?
 
nomadd22
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RE: 777X Wing Tip Fold Operational Issues?

Fri Dec 26, 2014 1:25 pm

Quoting Faro (Reply 21):
What about recurrent freeze-thaw cycles with wet wingfold mechanisms and freezing rain? Won't this decrease fatigue life compared to the rest of the airframe? Will the mechanisms has more frequent inspection intervals?

It shouldn't be any different than with any of the moving control surfaces. Probably less critical since the folding mechanism doesn't move and isn't likely to fail in flight.
Anon
 
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Stitch
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RE: 777X Wing Tip Fold Operational Issues?

Fri Dec 26, 2014 4:13 pm

Quoting Faro (Reply 21):
What about recurrent freeze-thaw cycles with wet wingfold mechanisms and freezing rain? Won't this decrease fatigue life compared to the rest of the airframe? Will the mechanisms has more frequent inspection intervals?
Quoting nomadd22 (Reply 23):
It shouldn't be any different than with any of the moving control surfaces. Probably less critical since the folding mechanism doesn't move and isn't likely to fail in flight.

You can also use materials that are more resistant to corrosion and have longer fatigue lives (Titanium, for example).
 
INFINITI329
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RE: 777X Wing Tip Fold Operational Issues?

Fri Dec 26, 2014 9:41 pm

Folding wings and wingtips are not new, we've been doing it since the 1930s.. I don't understand what all the hoopla is about
 
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DocLightning
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RE: 777X Wing Tip Fold Operational Issues?

Fri Dec 26, 2014 10:46 pm

Quoting captainstefan (Reply 17):
Because this kind of incident becomes even more of an issue:

https://www.youtube.com/watch?v=s8u8893oN1o

Ah yes, F-HPJD. I flew on her this summer. We did not smack any RJs, though. She was also the frame that hit the severe turbulence a month or so ago and injured some people aboard.

Quoting infiniti329 (Reply 25):
Folding wings and wingtips are not new, we've been doing it since the 1930s.. I don't understand what all the hoopla is about

It's never been done in a large jet transport before. It introduces operational issues in both figuring out how pilots are going to remember to make it part of their routine and also in the fact that you now have an aircraft that switches from Class E to Class F, which raises issues under normal operations, let alone with a fold failure.

I am sure that even if the whole mechanism failed and the wingtip departed the aircraft in flight, the aircraft would still stay controllable. But less lethal issues that are still very costly (like taking off an RJ's tailfin) can still arise.
-Doc Lightning-

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ArmitageShanks
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RE: 777X Wing Tip Fold Operational Issues?

Fri Dec 26, 2014 11:47 pm

Quoting OldAeroGuy (Thread starter):
members thoughts on the topic may have matured/

Don't patronize me, DAD.
 
OldAeroGuy
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RE: 777X Wing Tip Fold Operational Issues?

Sat Dec 27, 2014 1:55 am

Quoting Armitageshanks (Reply 27):
Quoting OldAeroGuy (Thread starter):members thoughts on the topic may have matured/
Don't patronize me, DAD.

Well, I did say thoughts have matured with no comments about personalities. And after all, I am the OLDAeroguy.

Why take it so personally?
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
Max Q
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RE: 777X Wing Tip Fold Operational Issues?

Sat Dec 27, 2014 7:18 am

Quoting infiniti329 (Reply 25):
Folding wings and wingtips are not new, we've been doing it since the 1930s.. I don't understand what all the hoopla is about

What 'hoopla' is that ?



I think it's just being discussed.
The best contribution to safety is a competent Pilot.


GGg
 
mmo
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RE: 777X Wing Tip Fold Operational Issues?

Sat Dec 27, 2014 8:41 am

Quoting DocLightning (Reply 26):
It introduces operational issues in both figuring out how pilots are going to remember to make it part of their routine and also in the fact that you now have an aircraft that switches from Class E to Class F, which raises issues under normal operations, let alone with a fold failure.

If you read my previous post, you would have had the answer to your question. The "operational issues" as you state are really minor. The folding wing mechanism will be part of the electronic checklist, the status of the folding wings will be a permanent display on the upper EICAS. As for the Class E to Class F that is easily resolved. In the event of a failure to retract, as a last resort a remote spot with buses to offload the paxs will always work. Most large, major international airports will have the space and the failure to retract will not be determined until the crew has vacated the active runway. It will require some coordination, but it is not a major issue.
If we weren't all crazy we'd all go insane!
 
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Horstroad
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RE: 777X Wing Tip Fold Operational Issues?

Sat Dec 27, 2014 8:04 pm

Quoting kaitak744 (Reply 7):
This discussion has little merit. Folding wingtips have been used on far more complicated military applications for over half a century. The folding tip on the 777X is nothing compared to those.

In military aviation efficiency is not as important. flying around an extra 500 or 1000 kg or more over the lifetime of a commercial aircraft is to be compared to the disadvantages of a bigger wingspan.
 
michi
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RE: 777X Wing Tip Fold Operational Issues?

Sat Dec 27, 2014 11:19 pm

There is a gross misunderstanding of weight in general. Since new aircraft did not hit the promised weight target with the first frames of a totally new airplane, total weight (gross weight, empty weight, whatever weight) is focused on to much.

Total weight of course is important. The less the better it seems.

However it is quite helpful to consider the location/position of the weight on the airframe. Wing bending for example is not only a function of lift and wing construction, but also a function of weight distribution. Having a weight on the wing far away from the fuselage might help to save some weight on the general wing construction.

Having a wing tip folding mechanism might "increase" the gross weight by the mechanism itself. But it might safe more weight in total due to a "lighter" wing construction.

Cheers,

Michi
 
kalvado
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RE: 777X Wing Tip Fold Operational Issues?

Sun Dec 28, 2014 12:29 am

Quoting michi (Reply 32):

However it is quite helpful to consider the location/position of the weight on the airframe. Wing bending for example is not only a function of lift and wing construction, but also a function of weight distribution. Having a weight on the wing far away from the fuselage might help to save some weight on the general wing construction.

Having a wing tip folding mechanism might "increase" the gross weight by the mechanism itself. But it might safe more weight in total due to a "lighter" wing construction.


Well, given that winglets - another example of extra aerodynamic weight on a wingtip - require strengthened wing structure and save fuel only with longer cruise phase, your argument looks a bit artificial.
And based on that example, I have hard time imagining extra ballast at wingtip resulting in any savings for wing structure,,,
 
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Starlionblue
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RE: 777X Wing Tip Fold Operational Issues?

Sun Dec 28, 2014 1:39 am

Quoting kalvado (Reply 33):
Quoting michi (Reply 32):

However it is quite helpful to consider the location/position of the weight on the airframe. Wing bending for example is not only a function of lift and wing construction, but also a function of weight distribution. Having a weight on the wing far away from the fuselage might help to save some weight on the general wing construction.

Having a wing tip folding mechanism might "increase" the gross weight by the mechanism itself. But it might safe more weight in total due to a "lighter" wing construction.


Well, given that winglets - another example of extra aerodynamic weight on a wingtip - require strengthened wing structure and save fuel only with longer cruise phase, your argument looks a bit artificial.
And based on that example, I have hard time imagining extra ballast at wingtip resulting in any savings for wing structure,,,

Winglets are a slightly different story, as they do not purely add weight but also change the lift distribution along the span, and thus also the stress pattern on the spars. Also AFAIK the cases where winglets have necessitated a strengthened wing structure have been those where the winglets have been added later in the life of the model, e.g. 737. That's different from, say, the 350 where they are there from the start.

Weight outboard can result in weight savings in other parts of the wing just as michi suggests. For example the weight of the engines and wing fuel decrease wing bending moment, meaning less stress on the spars and allowing a lighter wing.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
michi
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RE: 777X Wing Tip Fold Operational Issues?

Sun Dec 28, 2014 2:59 pm

Quoting kalvado (Reply 33):
Well, given that winglets - another example of extra aerodynamic weight on a wingtip - require strengthened wing structure and save fuel only with longer cruise phase, your argument looks a bit artificial.
And based on that example, I have hard time imagining extra ballast at wingtip resulting in any savings for wing structure,,,

It might look artificial in the beginning. But with a new design it might help to reduce the overall weight, as Starlionblue pointed out quite well.

One more thing. MZFW (Max. Zero Fuel Weight) is a structural limit. Imagine an airplane where you put more and more load into the fuselage. The weak spot will be at the wing root, as gravity pulls the fuselage down. The wings will "pivot" around the wing landing gears. If you have some more weight outside the wing, this would help and counteract the fuselage weight.
The concept behind this is the same that applies on cantilever bridges. Wikipedia has a nice article:

http://en.wikipedia.org/wiki/Cantilever_bridge

This picture explains it quite well:

http://en.wikipedia.org/wiki/Cantile...:Cantilever_bridge_human_model.jpg


Cheers,

Michi
 
StTim
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RE: 777X Wing Tip Fold Operational Issues?

Sun Dec 28, 2014 8:13 pm

One thing I understand is that to be de-iced the tips will need to be deployed - meaning that the 777X would need to be at a Cat F location.
 
kalvado
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RE: 777X Wing Tip Fold Operational Issues?

Sun Dec 28, 2014 10:36 pm

Quoting Starlionblue (Reply 34):

Weight outboard can result in weight savings in other parts of the wing just as michi suggests. For example the weight of the engines and wing fuel decrease wing bending moment, meaning less stress on the spars and allowing a lighter wing.

Good point about winglet lift generation.

Quoting michi (Reply 35):

One more thing. MZFW (Max. Zero Fuel Weight) is a structural limit. Imagine an airplane where you put more and more load into the fuselage. The weak spot will be at the wing root, as gravity pulls the fuselage down. The wings will "pivot" around the wing landing gears. If you have some more weight outside the wing, this would help and counteract the fuselage weight.


Now I am a bit more confused - I thought strength of a wing is determined by 2g MTOW maneuver requirement?
And wingtip weight will not offset body weight - if the body is 100 tons, each of wingroots still need to carry it's fair share of 50 tons (less ~5% for nose gear). I don't see how remote load would affect load distribution on gear-body arm. Wingtip weight would offset sideways load on the gear by counteracting rotational load, but I am not sure how big of an issue that would be.
 
michi
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RE: 777X Wing Tip Fold Operational Issues?

Mon Dec 29, 2014 1:02 am

Quoting kalvado (Reply 37):
Now I am a bit more confused - I thought strength of a wing is determined by 2g MTOW maneuver requirement?
And wingtip weight will not offset body weight - if the body is 100 tons, each of wingroots still need to carry it's fair share of 50 tons (less ~5% for nose gear). I don't see how remote load would affect load distribution on gear-body arm. Wingtip weight would offset sideways load on the gear by counteracting rotational load, but I am not sure how big of an issue that would be.

I wanted to visualize the whole wing weight distribution. Therefore I added the cantilever bridge human model. A small weight increase near the wingtips will not affect the general static of a wing much. But there still is an effect, which might lead to a total weight equilibrium (new wing with folding mechanism vs. new wing without folding mechanism).

The effect on wing strength with quads is far bigger, because engines normally are "heavy".

It is like always with airplane design. There is no simple rule. Some rules might even do you a "favor". Like the folding wing mechanism, which might end up being not a big penalty at all, but a small gain in efficiency.

Another interesting example for wing weight distribution is the White Knight 2.

Better now?
 
kalvado
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RE: 777X Wing Tip Fold Operational Issues?

Mon Dec 29, 2014 3:04 am

Quoting michi (Reply 38):

I wanted to visualize the whole wing weight distribution. Therefore I added the cantilever bridge human model. A small weight increase near the wingtips will not affect the general static of a wing much. But there still is an effect, which might lead to a total weight equilibrium (new wing with folding mechanism vs. new wing without folding mechanism).

The effect on wing strength with quads is far bigger, because engines normally are "heavy".

It is like always with airplane design. There is no simple rule. Some rules might even do you a "favor". Like the folding wing mechanism, which might end up being not a big penalty at all, but a small gain in efficiency.

Let me twist it the other way: are you saying that adding a few kg of lead ballast somewhere in existing wing may improve efficiency of existing wings by equalizing weight distribution or something along those lines? I have very hard time buying that.
 
LU9092
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RE: 777X Wing Tip Fold Operational Issues?

Mon Dec 29, 2014 3:54 am

Quoting kalvado (Reply 39):
Let me twist it the other way: are you saying that adding a few kg of lead ballast somewhere in existing wing may improve efficiency of existing wings by equalizing weight distribution or something along those lines? I have very hard time buying that.

No. I think what he's saying is that adding weight to the wings by hanging bigger engines off them, filling them with more fuel, or whatever helps to counter the force that causes the wing to bend upward in flight. So all else being equal, heavier engines or more fuel in the wings could allow for a lighter wing structure because the wing doesn't need to be as stiff to resist bending. These factors are considered during design of the plane; since changing the structure of existing wings isn't practical, adding ballast would just be dead weight.
 
OldAeroGuy
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RE: 777X Wing Tip Fold Operational Issues?

Mon Dec 29, 2014 4:02 am

Quoting StTim (Reply 36):
One thing I understand is that to be de-iced the tips will need to be deployed - meaning that the 777X would need to be at a Cat F location.

Do you have a reason the tip must be unfolded to be de-iced? De-icing non-planar winglets is similar to de-icing a folded tip.

Quoting kalvado (Reply 37):
Now I am a bit more confused - I thought strength of a wing is determined by 2g MTOW maneuver requirement?

Not necessarily. Unless MTOW = MZFW, reaching MTOW implies some fuel is being carried in the wing for most airplanes. This fuel weight will relieve wing bending moments since it's reaction is opposite to wing lift. The critical wing loading case may occur closer to MZFW than MTOW.

See Replies 35 & 40

[Edited 2014-12-28 20:04:59]

[Edited 2014-12-28 20:07:22]
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
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Starlionblue
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RE: 777X Wing Tip Fold Operational Issues?

Mon Dec 29, 2014 4:22 am

Quoting OldAeroGuy (Reply 41):

Quoting StTim (Reply 36):
One thing I understand is that to be de-iced the tips will need to be deployed - meaning that the 777X would need to be at a Cat F location.

Do you have a reason the tip must be unfolded to be de-iced? De-icing non-planar winglets is similar to de-icing a folded tip.

Might depend on how the mechanism looks when exposed. Will it accept being splashed with fluid?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
OldAeroGuy
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RE: 777X Wing Tip Fold Operational Issues?

Mon Dec 29, 2014 4:28 am

Quoting Starlionblue (Reply 42):
Might depend on how the mechanism looks when exposed. Will it accept being splashed with fluid?

Why not? Every moving control surface on the wing is exposed to de-icing fluid.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
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Starlionblue
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RE: 777X Wing Tip Fold Operational Issues?

Mon Dec 29, 2014 4:47 am

Quoting OldAeroGuy (Reply 43):
Quoting Starlionblue (Reply 42):
Might depend on how the mechanism looks when exposed. Will it accept being splashed with fluid?

Why not? Every moving control surface on the wing is exposed to de-icing fluid.

Good point. Fair dinkum.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
kalvado
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RE: 777X Wing Tip Fold Operational Issues?

Mon Dec 29, 2014 5:01 am

Quoting LU9092 (Reply 40):

No. I think what he's saying is that adding weight to the wings by hanging bigger engines off them, filling them with more fuel, or whatever helps to counter the force that causes the wing to bend upward in flight.

Or you can remove extra weight, trim off extra portion of the wing - and achieve same lighter structure. Yes, most of the weight is there because it needs to be there, that is
I am afraid we're not comparing apples to oranges: yes, a pound on a wingtip is effectively lighter than a pound in the cabin. But it is still a pound of weight.

Quoting OldAeroGuy (Reply 41):

Not necessarily. Unless MTOW = MZFW, reaching MTOW implies some fuel is being carried in the wing for most airplanes. This fuel weight will relieve wing bending moments since it's reaction is opposite to wing lift. The critical wing loading case may occur closer to MZFW than MTOW.

Yes, good point. I would even make it worse: if there is a fuel tank in the wingbox, maximum load would be also affected by the fuel in that tank (and probably that fuel is somehow correlated with ZFW for the flight anyway)
Yet the point is that force at the wingroot is equal to the weight of the body (times g-forces - and I would go without spelling "g-force" every time; and assuming body does not generate lift). Extra weight on outer portion of the wing does not change that (unless that weight is removed from the body, as opposed to just adding it. Then yes, placement does change the deal).
 
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Starlionblue
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RE: 777X Wing Tip Fold Operational Issues?

Mon Dec 29, 2014 5:09 am

Quoting kalvado (Reply 45):
I am afraid we're not comparing apples to oranges: yes, a pound on a wingtip is effectively lighter than a pound in the cabin. But it is still a pound of weight.

It is a pound of weight, but the positioning of your pound of weight is crucial. The pound in the cabin will always mean more stress on the wing, meaning stronger and heavier spars. The pound on the wingtip may mean less stress on the wing, and thus the possibility of shaving weight.

Posit two aircraft, one with wing mounted engines and one with tail mounted engines, and assume said engines are identical. The one with tail mounted engines must have a stiffer wing structure. The one with wing mounted engines will have a lighter wing since the weight of the engines provides bending relief. So by putting the weight on the wing instead of on the fuselage the net effect is a lighter aircraft.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
kalvado
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RE: 777X Wing Tip Fold Operational Issues?

Mon Dec 29, 2014 5:21 am

Quoting Starlionblue (Reply 46):


Posit two aircraft, one with wing mounted engines and one with tail mounted engines, and assume said engines are identical. The one with tail mounted engines must have a stiffer wing structure.

I perfectly agree with that.
But now if we could somehow build similar airplane with engine weight equal to zero, that wing would be even lighter.

My feeling was that the phrase

Quoting michi (Reply 38):
Like the folding wing mechanism, which might end up being not a big penalty at all, but a small gain in efficiency.

meant engineless plane in our example would need more wing structure, than wing-mounted version.
 
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DocLightning
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RE: 777X Wing Tip Fold Operational Issues?

Mon Dec 29, 2014 5:35 am

Quoting mmo (Reply 30):
If you read my previous post, you would have had the answer to your question. The "operational issues" as you state are really minor.

Be that as it may, they still need to be thought through. Boeing certainly agrees that they are minor. Regulators would be out to prove that they aren't so minor.

Quoting Starlionblue (Reply 34):
Winglets are a slightly different story, as they do not purely add weight but also change the lift distribution along the span, and thus also the stress pattern on the spars. Also AFAIK the cases where winglets have necessitated a strengthened wing structure have been those where the winglets have been added later in the life of the model, e.g. 737. That's different from, say, the 350 where they are there from the start.

The raked wingtips will move the center of lift outboard on each wing, too. More so than a winglet. However, they do so while adding less direct weight and wetted area. The mechanism should be pretty light. Probably not more than 25-50kg each wing. The loads out there aren't huge and the spar out there doesn't have to be terribly strong as compared to the inboard spar.

[Edited 2014-12-28 21:36:49]
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Starlionblue
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RE: 777X Wing Tip Fold Operational Issues?

Mon Dec 29, 2014 5:42 am

Quoting kalvado (Reply 47):
But now if we could somehow build similar airplane with engine weight equal to zero, that wing would be even lighter.

Most likely not. The weight of the engine means the wing structure will be lighter.

The crucial bit to understanding this is that in flight, loads on the wing from lift, resulting in upward bending, are way greater than the weight of anything in or on the wing. The wing is holding the entire fuselage aloft, and is much stronger than needed for simply supporting the weight of wing structure, wing fuel and wing-mounted engines on the ground.

Adding more weight to the wing, say with an engine, will thus not necessitate a heavier structure since the wing can already easily support the weight. However since this engine pulls the wing down, it relieves the wing of some bending, meaning weight can be saved.
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