Armadillo1
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777X high lift system

Sun Jul 28, 2019 9:16 am

[twoid][/twoid]is there any pics with good angle of view?

looks like they drop 787-style high-speed aileron and move to A350-style 2 sections inboard flaps, but i cant understand complex-looking outboard part with big row of fairing.
 
OldAeroGuy
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Re: 777X high lift system

Mon Jul 29, 2019 11:58 pm

All 777's have an all speed Flaperon that was adapted for the 787.

All 777's have a double slotted inboard flap.

All 777's have a single slotted outboard flap. A major difference for the 777-9 is that the outboard flap has been divided in two inboard and outboard segments. This has required four outboard flap supports and fairings rather than the two supports/fairings used on prior 777's.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
LH707330
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Re: 777X high lift system

Tue Jul 30, 2019 12:17 am

OAG, thanks for that explanation, I'd wondered why they had more canoes than other designs.
 
Armadillo1
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Re: 777X high lift system

Tue Jul 30, 2019 6:57 am

looks like 777X have single-slotted inboard flaps.
http://www.boeingphotostore.com/perl/op ... 1c0fbcdeff
inboard aileron still on render.

and the question still WHY they did two outboard small sections.
asymmetric folding issue?
 
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Starlionblue
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Re: 777X high lift system

Tue Jul 30, 2019 7:54 am

Armadillo1 wrote:
looks like 777X have single-slotted inboard flaps.
http://www.boeingphotostore.com/perl/op ... 1c0fbcdeff
inboard aileron still on render.

and the question still WHY they did two outboard small sections.
asymmetric folding issue?


Do you mean why they didn't make the fold farther inboard?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Armadillo1
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Re: 777X high lift system

Tue Jul 30, 2019 8:20 am

no i mean why they did two section with 4 fairing instead of 1 outboard flaps section.
A350 still looks more simple and effective, with no inboard aileron and continuous flaps
 
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Starlionblue
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Re: 777X high lift system

Tue Jul 30, 2019 8:25 am

I don't know. The only things I can think of are either cheaper maintenance because the sections are easier to handle, or that with two sections they can be extended differentially.

The A350 has 4 ailerons just like the 777. The inboard ones are just not very far inboard.

A continuous flap section is an elegant solution, but with both ailerons far out on the span you need a stiffer wing to mitigate aileron reversal. It's all compromises.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Armadillo1
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Re: 777X high lift system

Tue Jul 30, 2019 8:28 am

can you appoint me inboard aileron on this picture?
Image
 
hitower3
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Re: 777X high lift system

Tue Jul 30, 2019 9:11 am

[quote="Armadillo1"]can you appoint me inboard aileron on this picture?

Dear Armadillo,

I could guess that he meant that the ailerons on the A350 are split. Of course, both of these ailerons (two on each side) are located outside of the outer flaps, so it's a very different design than the high speed (inner) ailerons/flaperons found on many Boeing aircraft.

Best regards,
hendric
 
StTim
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Re: 777X high lift system

Tue Jul 30, 2019 9:14 am

There must be significant benefit to the 777X to split the outer flaps into two sections - adding additional flap tracks is not good for the overall aerodynamics so the benefit must be somewhere....
 
hitower3
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Re: 777X high lift system

Tue Jul 30, 2019 9:34 am

StTim wrote:
There must be significant benefit to the 777X to split the outer flaps into two sections - adding additional flap tracks is not good for the overall aerodynamics so the benefit must be somewhere....


Dear StTim,
I could imagine that the splitting of aerodynamic devices on wings (slats, flaps, ailerons, spoilers) could be related to wing bending.
To illustrate, take a sheet of paper that we would call a "wing".
Now bend it alongside one long side to form a "flap".
Then put the "wing" into a curved shape to simulate a load-induced wing flex. You will notice that the "flap" will now move with difficulty.
Finally, you cut the flap along the chord direction to split it into several smaller flaps. You will notice that the flaps now can move much easier.

Another motivation to split flaps etc. could be redundancy. In case of failure of one device, the remaining devices will ensure proper maneuvrability.

Best regards,
Hendric
 
Armadillo1
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Re: 777X high lift system

Tue Jul 30, 2019 9:36 am

hitower3 wrote:
Armadillo1 wrote:
can you appoint me inboard aileron on this picture?


Dear Armadillo,

I could guess that he meant that the ailerons on the A350 are split. Of course, both of these ailerons (two on each side) are located outside of the outer flaps, so it's a very different design than the high speed (inner) ailerons/flaperons found on many Boeing aircraft.

Best regards,
hendric

thank you, not come in mind it can be called "inboard".
Image
(and even three section on A380)
Image
where its used not for high speed issue only
https://aviation.stackexchange.com/ques ... s-per-wing
One of the examples of using this is in Airbus's Safety First magazine (July 2012), where they use the flexibility of having three ailerons to tune out lateral accelerations in the rear of the aircraft changing the gains of each of the controls. By being able to move the centre aileron a fraction after the inner aileron, they managed to avoid these initial shifts during flight testing of the A380.

https://www.skybrary.aero/bookshelf/books/2275.pdf
 
StTim
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Re: 777X high lift system

Tue Jul 30, 2019 10:09 am

I think we are confusing Flaps and Ailerons.

The 777X is does have a split on the outer flap that I do not think was there for the 777. This may well be a factor due to the different design philosophy on Boeing wings which leads to a more flexible wing and so as hitower3 postulates the change may be necessary to allow ease of movement.

On ailerons - the stiffer Airbus wings allow just out board devices as you do not get roll reversal. The Boeing wing has both outboard and the flaperon inboard because of the potential for roll reversal.
 
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Starlionblue
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Re: 777X high lift system

Tue Jul 30, 2019 11:08 am

Armadillo1 wrote:
hitower3 wrote:
Armadillo1 wrote:
can you appoint me inboard aileron on this picture?


Dear Armadillo,

I could guess that he meant that the ailerons on the A350 are split. Of course, both of these ailerons (two on each side) are located outside of the outer flaps, so it's a very different design than the high speed (inner) ailerons/flaperons found on many Boeing aircraft.

Best regards,
hendric

thank you, not come in mind it can be called "inboard".


Which is why I said it is "not very far inboard"... It is technically the inboard aileron though. :)

And while we're being technical, they are flaperons like the 777 ones.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
FriscoHeavy
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Re: 777X high lift system

Tue Jul 30, 2019 4:57 pm

Armadillo1,

Please proofread your sentences before posting gibberish.
Whatever
 
WIederling
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Re: 777X high lift system

Tue Jul 30, 2019 6:00 pm

StTim wrote:
There must be significant benefit to the 777X to split the outer flaps into two sections - adding additional flap tracks is not good for the overall aerodynamics so the benefit must be somewhere....


segment length limited via (not) coping with (large) wing flex ?
Murphy is an optimist
 
hitower3
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Re: 777X high lift system

Wed Jul 31, 2019 12:40 pm

StTim wrote:
(...)
On ailerons - the stiffer Airbus wings allow just out board devices as you do not get roll reversal. The Boeing wing has both outboard and the flaperon inboard because of the potential for roll reversal.


Dear StTim,

I have one question about "roll reversal" and the need for inbord ailerons/flaperons: Why would this roll reversal occur only at higher speed, creating the need for inbord ailerons, and not at low speed too?

Hendric
 
Armadillo1
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Re: 777X high lift system

Wed Jul 31, 2019 12:59 pm

https://en.wikipedia.org/wiki/Control_reversal
Another manifestation of the problem occurs when the amount of airflow over the wing becomes so great that the force generated by the ailerons is enough to twist the wing itself, due to insufficient torsional stiffness of the wing structure. For instance when the aileron is deflected upwards in order to make that wing move down, the wing twists in the opposite direction. The net result is that the airflow is directed down instead of up and the wing moves upward, opposite of what was expected. This form of control reversal is often lumped in with a number of "high speed" effects as compressibility.


As i understand,
Outer aileron deflection can cause wing twist to increase or decrease AoA.
at high speed a little aileron deflection angle can cause big force, and you have less safety cap.
Also, at high speed plane flies with small AoA and, for example, if wing twist cause 1 degree change, difference between 4 and 3 big enough.

upd: ok, actually for airliners AoA is about 8-9 degree at cruise, but still bigger at low speed.
 
StTim
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Re: 777X high lift system

Wed Jul 31, 2019 1:56 pm

hitower3 wrote:
StTim wrote:
(...)
On ailerons - the stiffer Airbus wings allow just out board devices as you do not get roll reversal. The Boeing wing has both outboard and the flaperon inboard because of the potential for roll reversal.


Dear StTim,

I have one question about "roll reversal" and the need for inbord ailerons/flaperons: Why would this roll reversal occur only at higher speed, creating the need for inbord ailerons, and not at low speed too?

Hendric


Hi, I am not an expert on this abut here is a good place to start. As you can see having a more flexible wing design philosophy is more likely to lead to this situation.

https://en.wikipedia.org/wiki/Control_reversal
 
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Starlionblue
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Re: 777X high lift system

Wed Jul 31, 2019 6:04 pm

Armadillo1 wrote:
https://en.wikipedia.org/wiki/Control_reversal
Another manifestation of the problem occurs when the amount of airflow over the wing becomes so great that the force generated by the ailerons is enough to twist the wing itself, due to insufficient torsional stiffness of the wing structure. For instance when the aileron is deflected upwards in order to make that wing move down, the wing twists in the opposite direction. The net result is that the airflow is directed down instead of up and the wing moves upward, opposite of what was expected. This form of control reversal is often lumped in with a number of "high speed" effects as compressibility.


As i understand,
Outer aileron deflection can cause wing twist to increase or decrease AoA.
at high speed a little aileron deflection angle can cause big force, and you have less safety cap.
Also, at high speed plane flies with small AoA and, for example, if wing twist cause 1 degree change, difference between 4 and 3 big enough.

upd: ok, actually for airliners AoA is about 8-9 degree at cruise, but still bigger at low speed.


8-9 degrees AoA in cruise would be almost stalling at cruise mach numbers. It's more like 4-5 degrees. 2-3 degrees of pitch angle plus the angle of incidence.

The only time you see AoA much over 8-9 in level flight is with the first notch of flap, which is mostly slats.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
GalaxyFlyer
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Re: 777X high lift system

Sun Aug 04, 2019 1:03 am

The Boeing experience, admittedly long ago, with the B-47 was the first with large degree of aeroelasticity and at high speed would have control, reversal to the point right inputs created left roll. Each plane was different, crews dove to around 420; put in toll controls, noted the reversal and were limited to 10 knots below reversal speed. The B-52 used all spoilers. The advantages of aero elastic wings drove the inboard/outboard design.

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