lehpron
Posts: 6846
Joined: Tue Jul 10, 2001 3:42 am

Why Do Planes Bend?

Wed Aug 01, 2001 4:00 am

I've always figured that the materials used for planes were fairly stong enough for the liftime requirement.

I remember reading an issue of PopSci (4/98?) where the story was on the now-cancelled HSCT. NASA put a canard in front to prevent the body from bending when the plane rolls on T/O. I also remember watching "The Ultimate Guide to Planes" on the discovery channel where they said that the wing lifts by bending up into the loss of pressure when the plane moves.

*Exactly how does that work and should this bending be allowed to happen?

*If we resist the elasticity, will we loose lift in the process?

*What if we extend the length (not span) of a wing to the nose, would that solve both problems?

I hope these aren't trivial, I'd like to learn something.
The meaning of life is curiosity; we were put on this planet to explore opportunities.
 
XFSUgimpLB41X
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Joined: Fri Aug 25, 2000 1:18 am

RE: Why Do Planes Bend?

Wed Aug 01, 2001 5:49 am

In turbulence, the 747's wings pretty much flap. Flexibility improves the strength of the aircraft.
Chicks dig winglets.
 
456
Posts: 315
Joined: Mon Feb 26, 2001 4:20 am

RE: Why Do Planes Bend?

Wed Aug 01, 2001 6:24 am

I saw a documentary on the television about the development of an 777, and one issue was that the wings were tested for a whole day by 'flapping'. Also saw that a wing can bend to the floor (!!) WITHOUT breaking of the fuselage.
You can see it as well on some explosions or accidents with airplanes, that the wings MOST of time are NOT broken, and are intact to the fuselage.
Wings are really flexible (must though, for the fuel tanks, as well for iron fatigue (sorry if this is improper english))
 
Guest

RE: Why Do Planes Bend?

Wed Aug 01, 2001 8:03 am

I guess bending is better than snapping?? LOL  Smile/happy/getting dizzy
 
lehpron
Posts: 6846
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RE: Why Do Planes Bend?

Wed Aug 01, 2001 4:43 pm

XFSUgimpLB41X posted:

"Flexibility improves the strength of the aircraft,"

When a read this, a pix of a flimsy, rubber airplane pops in my head. The wings lift the plane as well as itself to the point as if the forward view has the plane smiling (or grinning) on T/O.

I guess I have a hard time visualizing to myself that if a wing or any part of a plane can warp so easily it can still be strong enough to do anything.

A little more clairity would help, what if the wings were looped around and connected to the tailplane, would it still bend? Would it give similar lift? I know the drag would be less since the votices would be guided to the middle as if it were a forward swept wing.
The meaning of life is curiosity; we were put on this planet to explore opportunities.
 
jwenting
Posts: 9973
Joined: Mon Apr 23, 2001 10:12 pm

RE: Why Do Planes Bend?

Wed Aug 01, 2001 7:09 pm

If a structure cannot bend, it cannot dissipate forces acting on it, which leads to point-stresses and thus thus greater risk at hairfractures and ultimately failure.
Therefore a measure of flexibility is designed into a structure to allow it to absorb forces acting on it, spreading the load over a greater part of the structure.
I wish I were flying
 
air2gxs
Posts: 1443
Joined: Mon Jun 18, 2001 1:29 pm

RE: Why Do Planes Bend?

Wed Aug 01, 2001 7:22 pm

They bend, but do not break.

 
Gregg
Posts: 313
Joined: Sun Jun 18, 2000 12:49 pm

RE: Why Do Planes Bend?

Thu Aug 02, 2001 5:59 am

If planes did not bend, they would break. (If they weren't too heavy to lift off the ground.) You need to have flexibility in large structures. Even tall buildings bend in the wind.

 
Guest

RE: Why Do Planes Bend?

Thu Aug 02, 2001 10:39 am

It better bend or it will break. Flexible is much too rigid, in aviation you have to be fluid.
- Verne Jobst
Cheers, Max
 
Notar520AC
Posts: 1517
Joined: Sat Jul 21, 2001 6:53 am

RE: Why Do Planes Bend?

Tue Aug 07, 2001 11:52 am

Wings on advanced commercial airliners are usually made as shock absorbers, very helpful in turbulence.

-Notar520AC
BMW - The Ultimate Driving Machine
 
lapa_saab340
Posts: 391
Joined: Tue Aug 07, 2001 8:42 pm

RE: Why Do Planes Bend?

Tue Aug 07, 2001 9:25 pm

Looks like Jwenting pretty much covered the first question  Smile/happy/getting dizzy

All structures will deform to a certain degree under loading. In the case of buildings, bridges and such structures, the deformations are more subtle and you won't notice them with the naked eye. In the case of an airplane wing, the deformation is large enough for you to be able to see it. If you wanted a stiffer wing you could make one, and you wouldn't lose any lift doing so, but you'd have a needlessly heavier wing, your ride would be bumpier in turbulence, and you would also run into the problems Jwenting mentioned earlier.

If you were to extend the chord (the width of the wing) and reduce your wingspan, you'd get a very inefficient wing, as a lot more air from the bottom of the wing would be able to spill over the wingtip to the top. This causes loss of lift near the tips (and don't have a wide wing anymore to begin with!) and you also get an increase in drag, which means you burn more fuel!

I hope this helped!

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