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Why Do Planes Bend?  
User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Posted (13 years 3 weeks 3 days 12 hours ago) and read 1934 times:

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.
10 replies: All unread, jump to last
 
User currently offlineXFSUgimpLB41X From United States of America, joined Aug 2000, 4194 posts, RR: 37
Reply 1, posted (13 years 3 weeks 3 days 10 hours ago) and read 1856 times:

In turbulence, the 747's wings pretty much flap. Flexibility improves the strength of the aircraft.


Chicks dig winglets.
User currently offline456 From Netherlands, joined Feb 2001, 328 posts, RR: 1
Reply 2, posted (13 years 3 weeks 3 days 10 hours ago) and read 1843 times:

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))


User currently offlineAmericawest123 From , joined Dec 1969, posts, RR:
Reply 3, posted (13 years 3 weeks 3 days 8 hours ago) and read 1828 times:

I guess bending is better than snapping?? LOL  Smile/happy/getting dizzy

User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 4, posted (13 years 3 weeks 3 days ago) and read 1796 times:

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.
User currently offlineJwenting From Netherlands, joined Apr 2001, 10213 posts, RR: 18
Reply 5, posted (13 years 3 weeks 2 days 21 hours ago) and read 1786 times:

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
User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 6, posted (13 years 3 weeks 2 days 21 hours ago) and read 1782 times:

They bend, but do not break.



User currently offlineGregg From United States of America, joined Jun 2000, 327 posts, RR: 0
Reply 7, posted (13 years 3 weeks 2 days 10 hours ago) and read 1762 times:

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.



User currently offlineMax Power From , joined Dec 1969, posts, RR:
Reply 8, posted (13 years 3 weeks 2 days 6 hours ago) and read 1751 times:

It better bend or it will break. Flexible is much too rigid, in aviation you have to be fluid.
- Verne Jobst
Cheers, Max


User currently offlineNotar520AC From United States of America, joined Jul 2001, 1606 posts, RR: 4
Reply 9, posted (13 years 2 weeks 4 days 4 hours ago) and read 1706 times:

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

-Notar520AC



BMW - The Ultimate Driving Machine
User currently offlineLAPA_SAAB340 From Spain, joined Aug 2001, 390 posts, RR: 4
Reply 10, posted (13 years 2 weeks 3 days 19 hours ago) and read 1705 times:

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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