gearup
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Bent Wing 747!

Mon Mar 08, 2004 10:44 am

Check out this photo by Oliver Brunke. I guess the downwards bend in the wings is due to the heavy fuel load, the a/c is headed to Hong Kong. Any comments on this?

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Photo © Oliver Brunke


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BA
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RE: Bent Wing 747!

Mon Mar 08, 2004 10:50 am

That's not unusual at all.

When the wings are full of fuel, they do bend downward. This happens on all aircraft. Some you will see it more noticable such as on the 747 because it has a big wing and carries a lot of fuel.

Nothing to worry about. Wings are made to flex. If they didn't, they'd snap all the time.

Regards
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wilco
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RE: Bent Wing 747!

Mon Mar 08, 2004 10:53 am

the best part is when the heavies rotate and you can actually see the wing go from sagging to the exact opposite.
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QantasA332
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RE: Bent Wing 747!

Mon Mar 08, 2004 10:57 am

Downward wing bending due to fuel-laden wings is actually structurally beneficial (while it lasts, of course). This is because it counteracts the large, upward wing bending present in flight, and thus lessens the strain on the wing.

Cheers,
QantasA332
 
wilco
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RE: Bent Wing 747!

Mon Mar 08, 2004 11:01 am

For you photonuts... it would be great to see:

a head-on shot of a 747 on the ground, fully loaded, wings bent downward
NEXT TO A PICTURE OF
a head-on shot off a 747 in the air, max lift, wings bent upward

This would be extraordinarily cooler if it was a similarly scaled photo (i.e. if you overlayed the two pics the fuselages matched in size)....

I'm probably asking way too much since a head-on air-to-air shot is so rare.
"Ever seen a grown man naked?"
 
KKMolokai
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RE: Bent Wing 747!

Mon Mar 08, 2004 11:04 am

Wow! That's freaky ... never noticed that before!!
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andrewuber
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RE: Bent Wing 747!

Mon Mar 08, 2004 11:14 am

I flew on a United 744 from SFO-ORD, and I was amazed at the wing flex on takeoff. I was in business class, right on the leading edge, and it was cool watching that big wing bounce up and down on takeoff roll, then it seemed to curve up a good four or five feet when we rotated. Amazing!

I looked through the D/B, and found these pics:
Fully Loaded:

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Photo © Carlos Borda


Empty, but on ground:

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Photo © Peter Unmuth - VAP


Flexing up while landing:

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Photo © Ryan C. Umphrey



I wonder exactly how much that wing flexes in "normal use". I've been on the Heavy tour at Everett, and they have pictures on the wall of a 747 wing in testing - it was bent probably 40 degrees up before it shattered!!

Drew
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kalakaua
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RE: Bent Wing 747!

Mon Mar 08, 2004 11:22 am

This is most obvious on the Lockheed C-5 Galaxy. One may think it's wings are anhedral, when in fact, in flight they are cathedral. The wings droop down because of the weight of the fuel.

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andz
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RE: Bent Wing 747!

Mon Mar 08, 2004 2:08 pm

Actually I would hope that the wing flexes upwards BEFORE rotation, as that is a sign that lift is occurring and the damned thing will actually fly!



[Edited 2004-03-08 06:09:56]
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Mr.BA
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RE: Bent Wing 747!

Mon Mar 08, 2004 2:10 pm

I've read before that when the B747 wings are fully fueled up it's not advisable to open the over-wing door. For you might not be able to close it again due to the weight of the wings hanging on the fuselage of the aircraft causing some distortion to it!
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CanadianNorth
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RE: Bent Wing 747!

Mon Mar 08, 2004 2:15 pm

Quite amazing how much wings can bend before they give out... I suppose its alot smarter to have them flex like that otherwise when you get a decent load on there it would probably be down to one good bump and you'd be reaching for the rum while buddy there was saying a round of hail marys...




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Airbus_A340
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RE: Bent Wing 747!

Mon Mar 08, 2004 2:16 pm

Hi there Kalakaua, thanks for pointing that out. I was taught that aircraft with anhedral wings are set as such to purposely de-stabalize the aircraft to help it turn as there is so much weight. These sort of aircraft have anhedral as opposed to dihedral because it would be impractical as it would be extremely hard to manouver with!

Airbus_A340
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VC-10
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RE: Bent Wing 747!

Mon Mar 08, 2004 10:45 pm



This is the VC10 structral test airframe undergoing a proof load test - equivalent to 2.5 G manoevre @ 296,000lbs, 1,000 Ft altitude and 330 Knts. The Wip tip deflection is over 8 Ft.

[Edited 2004-03-08 14:46:41]
 
FredT
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RE: Bent Wing 747!

Tue Mar 09, 2004 3:39 am

The C5 has anhedral to counter the lateral stability inherent in high wing designs. "Cathedral"? Perhaps you're looking for "dihedral"?

Andz,
the wings will not flex before they are generating lift. They will not generate lift until they are at an angle of attack, and they're not at much of an angle of attack until rotation. Alas, no wing bending until rotation, and no vortices either which is beneficial if you are in a light and want to use the runway after a heavy.

Cheers,
Fred
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kalakaua
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RE: Bent Wing 747!

Tue Mar 09, 2004 9:57 am

It can be called "cathderal" as well.
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theflcowboy
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RE: Bent Wing 747!

Tue Mar 09, 2004 10:56 am

I saw a thing on some TV show, I think it was TLC, that the 747 wing can bend 26 feet up and down from whatever they deem to be the center. And then when it breaks, it breaks outside of the inner engine so that if it ever did, you would still have 3 working engines.
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liamksa
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RE: Bent Wing 747!

Tue Mar 09, 2004 12:21 pm

I've heard the wingspan of the B744 grows with a full fuel load due to the droop of the wings and angle of the winglets. Anyone know if this is true?

Wing bending moments:

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AJ
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RE: Bent Wing 747!

Tue Mar 09, 2004 12:39 pm

Liamska, that is true due to the mounting angle of the winglets, as the wings bend down the winglets splay outwards.

Conducting the walkaround on the -400 gave a good indication of the bending. When lightly fuelled (30,000kg was the min fuel for dispatch) it was hard to see in to engines 1 and 4, but fully fuelled they were easy to inspect!

Re the C-5....it has anhedral designed into it that remains in flight.
 
musang
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RE: Bent Wing 747!

Wed Mar 10, 2004 3:45 am

Kalakaua - if you can produce a photo of a C-5 showing dihedral/cathedral at any stage of the operation, I'd be very interested!

Thanks - Musang.
 
FredT
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RE: Bent Wing 747!

Wed Mar 10, 2004 4:31 am

My bad in part, cathedral appears to be an older word for anhedral. I'll doublecheck once I have my aviation dictionaries with me. Never bring your private library to work as you might just need it for important things.  Big grin

However, I would advise using anhedral if you want to be understood. Despite a few years in aviation, I have only heard cathedrals mentioned in religious context until now...

Cheers,
Fred
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kalakaua
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RE: Bent Wing 747!

Wed Mar 10, 2004 5:50 am

Anhedral can be called also "Cat-hedral." Not cath-edral. My professor was an old man, who preferred the old ways. Sorry for the confusion.

I'll just stick to DI-hedral and AN-heral.

[Edited 2004-03-09 21:52:48]
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kalakaua
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RE: Bent Wing 747!

Wed Mar 10, 2004 6:03 am

Here's the best photo I could find with the C-5 having dihedral wings in flight.

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Photo © Gerhard Plomitzer

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FredT
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RE: Bent Wing 747!

Wed Mar 10, 2004 6:49 am

Kalakaua,
you might want to take a closer look at the perspective in that photo. E g, the angle between the wing and an imaginary line between two of the left and right main gear tires. Still anhedral.

BTW, if someone doesn't call me on writing stability when I meant instability above, I'll get worried about the state of this forum! Big grin

Cheers,
Fred

[Edited 2004-03-09 22:51:59]
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N243NW
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RE: Bent Wing 747!

Wed Mar 10, 2004 7:11 am

I've heard the wingspan of the B744 grows with a full fuel load due to the droop of the wings and angle of the winglets. Anyone know if this is true?


Yes, it is. When the 744's wing is full of fuel, the outer portions bend down and the winglets are angled further outward, increasing the wing span by 19 inches (48 centimeters).
-N243NW Big grin
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kalakaua
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RE: Bent Wing 747!

Wed Mar 10, 2004 9:28 am

FredT, but, as you see, the wing bent upwards...
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Beefmoney
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RE: Bent Wing 747!

Wed Mar 10, 2004 12:21 pm

Kalakaua;
If you took that C-5 in the photo and looked at it straight on from the front, you would see that the wings are still angled downwards, and hence still have anhedral. Its just the fact that you are looking at the C-5 from the ground while it is 500 feet in the air that makes it look like the wings are bent upwards.
 
kalakaua
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RE: Bent Wing 747!

Wed Mar 10, 2004 12:32 pm

Argh. I'll ask my professor, "Old Man" Tracy Doryland. He is a retired Navy pilot, and he himself says the wings are dihedral in flight.  Pissed
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AJ
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RE: Bent Wing 747!

Wed Mar 10, 2004 12:33 pm

If it's not dihedral at liftoff, it isn't going to happen later!

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kalakaua
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RE: Bent Wing 747!

Wed Mar 10, 2004 1:02 pm

I'll just shut-up. My battle is lost. I won't bother.

"The anhedral is required to keep the aircraft from becoming too stable! Large transports have both a high wing and a considerable amount of wing sweep, both of which create a large amount of effective dihedral. To counteract this large amount of dihedral, some geometric anhedral is required. Otherwise the aircraft would be overly stable, making turns extremely difficult, and an aircraft that can only fly in one direction isn't much use to anyone."

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liamksa
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RE: Bent Wing 747!

Wed Mar 10, 2004 2:31 pm

The C5 has anhedral to counter the lateral stability inherent in high wing designs.

Fred, this sentence is fine isn't it? Same reason as for the 146 - or am I losing my marbles too?!
 
QantasA332
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RE: Bent Wing 747!

Wed Mar 10, 2004 2:57 pm

"The C5 has anhedral to counter the lateral stability inherent in high wing designs"...Fred, this sentence is fine isn't it?

Yes, it most certainly is. To clarify: high-winged aircraft (such as, of course, the C5) have a large effective dihedral, making them very stable laterally -- too much so in some cases. If this is the case, anhedral helps simply by reducing some of that dihedral and thus decreasing stability.

Cheers,
QantasA332
 
MITaero
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RE: Bent Wing 747!

Wed Mar 10, 2004 4:04 pm

Is the C-5 wing swept much? Sweep increases effective dihedral, so I'm just curious.
 
QantasA332
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RE: Bent Wing 747!

Wed Mar 10, 2004 5:38 pm

Is the C-5 wing swept much? Sweep increases effective dihedral, so I'm just curious.

Yes, the C5's wing has relatively high amount of speep, which, as you said, also contributes to effective dihedral. I only mentioned the fact that a high wing leads to large effective dihedral above for the sake of simplicity, and because a high wing was the only aspect being discussed.

Cheers,
QantasA332
 
manzoori
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RE: Bent Wing 747!

Wed Mar 10, 2004 9:49 pm

Another shot of the C-5 in flight showing Anhedral

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Photo © Art Brett - AirTeamImages



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Rez
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FredT
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RE: Bent Wing 747!

Thu Mar 11, 2004 4:33 am

Liamksa,
d'oh! I'll just shut up now and refrain from posting until the course I am taking is over and I have had a week of sleep.  Big grin

Cheers,
Fred
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lehpron
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RE: Bent Wing 747!

Thu Mar 11, 2004 10:16 am

"Nothing to worry about. Wings are made to flex. If they didn't, they'd snap all the time"

That assumes the force would be great enough to kill the wing, if it did not flex so much and still able to fly, would a not-so-flexing wing be something to worry about?
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Starlionblue
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RE: Bent Wing 747!

Sun Mar 14, 2004 12:24 am

Probably... A wing cannot be built strong enough not to flex without an unacceptable (and unnecessary) increase in weight.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
SlamClick
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RE: Bent Wing 747!

Sun Mar 14, 2004 12:59 am

MrBA You wrote:

I've read before that when the B747 wings are fully fueled up it's not advisable to open the over-wing door. For you might not be able to close it again due to the weight of the wings hanging on the fuselage of the aircraft causing some distortion to it!

This cannot be true, at least not for the reasons given. Simply put, the wings don't "hang" on the fuselage. The fuselage rests on the wings.

I assume that we are talking about on-the-ground. (Otherwise, there are lots of good reasons for not opening the overwing in flight!) The wing structure carries through under the floor of the fuselage, a separate structure from the tube that carries the passengers. On the ground, the weight is carried by the main landing gear. The fuselage rests on top of that, presumably with very little in the way of stress loads. The fuel in the part of the wing outboard of the landing gear puts tensile loads (in the area of the landing gear) on top the wing and compression loads on the bottom. The fuselage weight, resting between the main gear on most aircraft offset that somewhat. The 747 has inboard "body" landing gear to carry some of that weight, but none of it hangs from the fuselage.

If you picture the sideview of the plane, you might imagine the weight of passengers and cargo carried aft of the wing producing a bending load in the area of the wing carry-through. This might be what (if anything) would tend to distort the door opening.

Slam
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Click


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AJ
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RE: Bent Wing 747!

Sun Mar 14, 2004 7:24 pm

Click, it is true. It has happened more than once on our 747-400s. One experience I saw first hand required defuelling of the outer tanks in order to shut doors 3, which had been open for airing!
 
air2gxs
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RE: Bent Wing 747!

Sun Mar 14, 2004 11:46 pm

SlamClick,

I assure that it is true. When I worked for PanAm there were several warnings about opening R3/L3 while fueled for flight. The door opens fine, but will not go overcenter to lock. Happened several times at the gate. Had to defuel until it would lock.
 
Klaus
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RE: Bent Wing 747!

Mon Mar 15, 2004 1:33 am

Sounds logical... even the wing box would flex a little under the changed load, and as long as the upper fuselage is directly mounted to the wing box it will flex as well. If the door mechanism doesn´t have enough flexible play to compensate, some difficulties seem plausible...

Is that effect known from other models as well?
 
galaxy5
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RE: Bent Wing 747!

Mon Mar 15, 2004 8:32 am

The C-5 with its wing span of 222 feet, is a high mounted, high lift wing, anhedral by design with a 25 degree swept wing. The wing does flex inflight approx 16 feet up or down. however with ALDCS active the wing flex is kept to a minimum to prevent fatigue.
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Mr.BA
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RE: Bent Wing 747!

Mon Mar 15, 2004 10:02 am

Thanks Slamclick... good post on how the weight is distributed! Thanks!

Mr.BA
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MD-90
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RE: Bent Wing 747!

Wed Mar 17, 2004 2:52 am

Probably... A wing cannot be built strong enough not to flex without an unacceptable (and unnecessary) increase in weight.

True for large transports, of course, but there are a few smaller aircraft that have almost no wing flex. The Berkut (no longer in kit production) that I was once extremely interested in building has a carbon fiber and foam core wing. It is extremely stiff and turbulence is felt more in flight because it just runs straight through the chop, almost entirely without wing flex to soften the ride.

Of course, they do bend a little, but very, very little. Very strong +10/-3.5G wings, as I recall.

 
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Starlionblue
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RE: Bent Wing 747!

Wed Mar 17, 2004 3:16 am

So they do bend, even if only a little  Big grin
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mrwayne
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RE: Bent Wing 747!

Wed Mar 17, 2004 6:17 am

slamclick you are wrong

MRBA you are wright,

The door open over wing would bend the air frame due to the weight of the fuel on board.

well done you have some good knowledge !

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