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threefourthree
Topic Author
Posts: 149
Joined: Tue Nov 06, 2007 8:23 pm

Wings Flex Up Or Down. Which Is Better?

Sun Jul 20, 2008 1:59 am

I'm doing an assignment on paper planes about distance, ailerons, winglets and wings up or down. I remember reading somewhere that when the wings flex up they give better lift?

Is that true? and if possible can you explain why or direct me somewhere.
 
Mir
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Joined: Mon Jan 05, 2004 3:55 am

RE: Wings Flex Up Or Down. Which Is Better?

Sun Jul 20, 2008 2:06 am

Wings flex because of the weight of the fuselage, and the flex will always be up.

You're probably referring to dihedral (wings sit at an upwards angle) vs. anhedral (wings sit at a downward angle). This has to do with stability,and in a paper airplane that isn't all that stable to begin with, dihedral is going to be preferable.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
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Starlionblue
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RE: Wings Flex Up Or Down. Which Is Better?

Sun Jul 20, 2008 4:00 am

What Mir is saying is that "flex" refers to the bending, while anhedral/dihedral refer to the mounting angle.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
MD-90
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RE: Wings Flex Up Or Down. Which Is Better?

Sun Jul 20, 2008 6:45 am



Quoting Mir (Reply 1):
Wings flex because of the weight of the fuselage, and the flex will always be up.

Well, unless a thunderstorm flips your airliner inverted.
 
Mir
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RE: Wings Flex Up Or Down. Which Is Better?

Mon Jul 21, 2008 2:05 am



Quoting MD-90 (Reply 3):
Well, unless a thunderstorm flips your airliner inverted.

In which case I'd say you have more pressing problems than your wings flexing the wrong way.  scared 

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
AA737-823
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RE: Wings Flex Up Or Down. Which Is Better?

Tue Jul 22, 2008 12:36 am

Dihedral increases stability, as the lift vector points more toward the Center of Lift (and typically on a low-wing airplane, the CG as well). This has an affect of "centering" the airplane.
 
LY744
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RE: Wings Flex Up Or Down. Which Is Better?

Tue Jul 22, 2008 2:00 am



Quoting AA737-823 (Reply 5):
Dihedral increases stability, as the lift vector points more toward the Center of Lift

The lift vector points the same direction regardless of dihedral/anhedral. What does change is the aircraft's behaviour in a roll-induced sideslip: with a dihedral the dipped wing is going to have the higher AOA and therefore more lift, acting to oppose the roll.


LY744.
Pacifism only works if EVERYBODY practices it
 
atlturbine
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Joined: Sat Aug 23, 2008 11:03 pm

RE: Wings Flex Up Or Down. Which Is Better?

Tue Aug 26, 2008 2:55 am

Modern aircraft certified in transport & normal catagories are designed to withstand approximately 3.5 positive (wings bend up) & 1.5 negitive (wings bend down) G forces. If you are in a non aerobatic airplane wings bending down would be a very bad situation.

During the certfication process on the 777 Boeing demonstrated an approximate wing bend of 19 feet in the up direction at the tip. That was over 150% of the design load limit.
To the World you might be One Person but to One Person you might be the World
 
411A
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RE: Wings Flex Up Or Down. Which Is Better?

Tue Aug 26, 2008 4:56 am

Maximum allowed wing flex (as measured at the tip), up/down, in feet, prior to skin deformation.

DC-6B ..... 6 up / 6 down

B707 ..... 12 up / 10 down.
 
atlturbine
Posts: 79
Joined: Sat Aug 23, 2008 11:03 pm

RE: Wings Flex Up Or Down. Which Is Better?

Tue Aug 26, 2008 11:59 am

Video of the 777 static wing test. Listen to that Boom when they FINALLY give!!

http://www.youtube.com/watch?v=pe9PVaFGl3o
To the World you might be One Person but to One Person you might be the World
 
SlamClick
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Joined: Sun Nov 23, 2003 7:09 am

RE: Wings Flex Up Or Down. Which Is Better?

Tue Aug 26, 2008 4:07 pm

Under positive G-load flexing up is preferred.
Under negative G-load, flexing down seems to work better.

Since we haven't heard from the o/p since July 19 can we infer that the subject is of no further interest to him?
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
threefourthree
Topic Author
Posts: 149
Joined: Tue Nov 06, 2007 8:23 pm

RE: Wings Flex Up Or Down. Which Is Better?

Wed Aug 27, 2008 8:13 am

I'm still checking back, I was surprised someone replied a month after. Finished the assignment, got 20/22. Just the concept of it is a bit silly. People were doing things like which battery lasted longer, do plants grow better with music, etc etc.

Thanks for the replies  Smile

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