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Bending Wings On B787

Grantcv From United States of America, joined Apr 2005, 429 posts, RR: 0
Posted (8 years 1 month 2 weeks 5 days 7 hours ago) and read 2650 times:

It seems from Boeing's recent 787 images that the wings will really flex upwards in flight. I have noticed a similar thing when aboard a 772, but this seems more pronounced. Why is this? What aerodynamic benefit is there?
I am assuming this won't be evident when the plane is on the ground much as it isn't with the 777.

21 replies: All unread, jump to last

NAV20 From Australia, joined Nov 2003, 9165 posts, RR: 37
Reply 1, posted (8 years 1 month 2 weeks 5 days 7 hours ago) and read 2612 times:

All wings flex under load, Grantcv. They're designed to do so, same as the springs in the chair you're sitting in.

An aeroplane with rigid wings would be like a concrete armchair - and just about as heavy Smile

"Once you have flown, you will walk the earth with your eyes turned skywards.." - Leonardo da Vinci

DfwRevolution From , joined Dec 1969, posts, RR:
Reply 2, posted (8 years 1 month 2 weeks 5 days 7 hours ago) and read 2602 times:

Quoting Grantcv (Thread starter):
Why is this?

Nature of composite wings: much more pronounced flex.

Quoting Grantcv (Thread starter):
What aerodynamic benefit is there?

I'm not an aerodynamics expert, so I'm vulnerable here, but I would suspect there is benefit to be derrived. I'd guess (and that's it: a guess) that some wingtip vorticies would be reduced by such "bending" (dihedral?). The 787 looks remarkeably like a bird in-flight, and winglets work by a simmilar process on a smaller scale

http://www.csinews.net/images_antarctica/bird-flying-small.jpg

http://www.boeing.com/commercial/7e7/k63304-3.html

KDTWFlyer From United States of America, joined Jun 2004, 807 posts, RR: 1
Reply 3, posted (8 years 1 month 2 weeks 5 days 7 hours ago) and read 2581 times:

I wonder if the ease of flex because of the composites will lessen the effects of turbulence on the plane a little.

NW B744 B742 B753 B752 A333 A332 A320 A319 DC10 DC9 ARJ CRJ S340

Flybyguy From United States of America, joined Jun 2004, 1791 posts, RR: 1
Reply 4, posted (8 years 1 month 2 weeks 5 days 7 hours ago) and read 2581 times:

Possibly, Boeing has designed the 787 with thinner wings to optimize high altitude cruise efficiency. Thinner wings have less drag and unfortunately less structural support, therefore more pronounced wing flex.

"Are you a pretender... or a thoroughbred?!" - Professor Matt Miller

Ruscoe From Australia, joined Aug 1999, 1415 posts, RR: 2
Reply 5, posted (8 years 1 month 2 weeks 5 days 7 hours ago) and read 2557 times:

When I was at the Australian Airshow at Avalon this year had a chance to talk to one of the Boeing reps. He told me the wings will flex 16 feet (4m) in flight.
Looking at that through the bigger windows might just scare a few inexperienced fliers!

Ruscoe

MasseyBrown From United States of America, joined Dec 2002, 4752 posts, RR: 7
Reply 6, posted (8 years 1 month 2 weeks 5 days 7 hours ago) and read 2555 times:

Quoting DfwRevolution (Reply 2):
The 787 looks remarkeably like a bird in-flight,

Nice observation; I thought that, too. The bend of the wingtips looks like the flex in an eagle's feathers in one of the illustrations.

Consilivm: Cave ne nothi te vexant

Grantcv From United States of America, joined Apr 2005, 429 posts, RR: 0
Reply 7, posted (8 years 1 month 2 weeks 5 days 6 hours ago) and read 2544 times:

Quoting Grantcv (Thread starter):
All wings flex under load, Grantcv. They're designed to do so, same as the springs in the chair you're sitting in.

An aeroplane with rigid wings would be like a concrete armchair - and just about as heavy

I know that, but the flex is much more pronounced here. Same thing on the 777 - when the plane in in the air, the wings bend up quite a bit. The first time I flew aboard a 777, I was amazed to see how much they were bending up. The latest issue of Aviation Week & Space Technology refers to the dihedral wing noting that they will bend more than any other wing. I am wondering why this is a good thing - there must be an areodynamic benefit to a dihedral wing.

Jet-lagged From United States of America, joined Mar 2002, 852 posts, RR: 0
Reply 8, posted (8 years 1 month 2 weeks 5 days 5 hours ago) and read 2461 times:

Good question for the Technical Forum.

Trent900 From United Kingdom, joined Dec 2003, 419 posts, RR: 0
Reply 9, posted (8 years 1 month 2 weeks 5 days ago) and read 2361 times:

Quoting Ruscoe (Reply 5):
Looking at that through the bigger windows might just scare a few inexperienced fliers!

I should think if flying through heavy turbulence there will be a noticable up and down movement at the wing tip. What will nervous passengers think about this? My dad said the 737NG is bad enough, and for shortish wings they flex a lot.

D.

Glom From United Kingdom, joined Apr 2005, 2803 posts, RR: 10
Reply 10, posted (8 years 1 month 2 weeks 4 days 23 hours ago) and read 2274 times:

Quoting Grantcv (Reply 7):
there must be an areodynamic benefit to a dihedral wing.

It makes the aircraft stable in the role. If the aircraft tries to roll a bit to one side, the dihedral causes to role back the other way creating stable equilibrium. Military fast jets have anhedral, which makes the aircraft unstable in the role. This is because it makes the aircraft very readily maneuverable.

Quoting Ruscoe (Reply 5):
Looking at that through the bigger windows might just scare a few inexperienced fliers!

I was impressed by the wing flex on the 777 last time I flew on one. I find it more comforting to see a flexible wing than a rigid wing that is likely to snap.

JetBlue From United States of America, joined Sep 2004, 388 posts, RR: 5
Reply 11, posted (8 years 1 month 2 weeks 4 days 21 hours ago) and read 2173 times:

Quoting Ruscoe (Reply 5):
Looking at that through the bigger windows might just scare a few inexperienced fliers!

When I was on the MD-11, the wings appeared to shake and bend at the tip a lot more than on the 777. And the 777's wing bends more, as a whole, I would say.

Despite the high wing flex, the 777 appears to stay "in shape" during turbulence a lot more than other planes of similar size.

jetBlue

We know for you it's not just a seat on a flight to a place. It's a seat on a flight to your life.

Mrocktor From United States of America, joined Jan 2005, 1647 posts, RR: 50
Reply 12, posted (8 years 1 month 2 weeks 4 days 20 hours ago) and read 2097 times:

The wing flexes because it is less rigid then typical airliner wings. It is less rigid because it was designed to be less rigid. It was designed to be less rigid because that way it is lighter.

You can design a rigid composite wing, you can design a flexible metal wing and you sure as hell can design a rigid wing with as much dihedral as you like.

The 787 wing flex is the result of reducing weight on the wing structure. It is only practical with advanced structural analysys, computational fluid dynamics and flight control system capabilities.

If a rigid wing could be made as light as a flexible one, all wings would be rigid. Much less trouble that way...

mrocktor

Glom From United Kingdom, joined Apr 2005, 2803 posts, RR: 10
Reply 13, posted (8 years 1 month 2 weeks 4 days 20 hours ago) and read 2055 times:

Would a high degree of wing flex have an adverse effect on lift?

Gigneil From United States of America, joined Nov 2002, 16215 posts, RR: 88
Reply 14, posted (8 years 1 month 2 weeks 4 days 20 hours ago) and read 2050 times:

Quoting KDTWFlyer (Reply 3):
I wonder if the ease of flex because of the composites will lessen the effects of turbulence on the plane a little.

This is supposed to be a major benefit of the 787.

N

Areopagus From United States of America, joined Sep 2001, 1357 posts, RR: 1
Reply 15, posted (8 years 1 month 2 weeks 4 days 14 hours ago) and read 1868 times:

from the Seattle Post-Intelligencer:

The 787's wings will also be composite. Passengers seated next to the large windows on the 787 will notice those wings bent upward in flight more than they would be on the 777, Gillette said.

The 777 is a much larger plane. But because composites are stronger than aluminum, Boeing is giving the 787 the same wingspan as that of the 777-200, but with about 20 percent less surface area. As a result, the wing will flex more during flight.

Boeing hopes to have a large model of the 787 with its wings bent upward for display at the Paris Air Show in June.

Ken777 From United States of America, joined Mar 2004, 7528 posts, RR: 5
Reply 16, posted (8 years 1 month 2 weeks 4 days 14 hours ago) and read 1818 times:

I think that the head on illustration of the 787 was given a lot of wing flex to make it more dramatic - the other illustrations didn't show that much flex.

I'm always amazed at the flex in the wings of a 744 - watch them change on both take offs and landings. I think the 380's will be rather impressive also when it's fully loaded.

Squirrel83 From , joined Dec 1969, posts, RR:
Reply 17, posted (8 years 1 month 2 weeks 4 days 14 hours ago) and read 1802 times:

With a more flexible wing wouldn't that create more turbulence?

MrComet From Ireland, joined Mar 2005, 498 posts, RR: 8
Reply 18, posted (8 years 1 month 2 weeks 4 days 14 hours ago) and read 1769 times:

I am not sure about the aerodynamics either but I imagine that some bending would give a similar advantage as wing tips ....i.e. it is harder for the high pressure air below the wing to bleed into the low pressure area. Please correct me if I am mistaken.

The dude abides

Gaut From Belgium, joined Dec 2001, 344 posts, RR: 2
Reply 19, posted (8 years 1 month 2 weeks 4 days 14 hours ago) and read 1739 times:

Quoting Ken777 (Reply 16):
I'm always amazed at the flex in the wings of a 744 - watch them change on both take offs and landings. I think the 380's will be rather impressive also when it's fully loaded.

According to Airbus.com: "During take-off, the wing will flex upwards by over 4 meters"

«Horum omnium fortissimi sunt Belgae.»

DfwRevolution From , joined Dec 1969, posts, RR:
Reply 20, posted (8 years 1 month 2 weeks 4 days 13 hours ago) and read 1734 times:

Quoting Squirrel83 (Reply 17):
With a more flexible wing wouldn't that create more turbulence?

No, think about it as the shock-absorbers on your car. The ability for your shocks to stretch up and down dapens the bumps in the road. Likewise, a non-rigid wing transfers the energy absorbed from hitting up/downdrafts into wing flex.... rather than transfering that energy to your seat.

Trent900 From United Kingdom, joined Dec 2003, 419 posts, RR: 0
Reply 21, posted (8 years 1 month 2 weeks 4 days 2 hours ago) and read 1540 times:

Quoting Ken777 (Reply 16):
I think the 380's will be rather impressive also when it's fully loaded.

The 380's wings did flex upwards by about 4 meters during the take-off. This is noticable if you look closely at film footage during its take-off run, the wings seem to straiten out.

D.

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