Kukkudrill
Topic Author
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Wing Anhedral

Sat Dec 24, 2005 8:18 pm

Many high-wing aircraft are designed with downward sloping wings (anhedral). If I have this right anhedral makes an aircraft unstable in the roll, which might be useful for a Harrier but not, presumably, an An-124. What then are the compensating advantages of anhedral? And why is it more common to high-wing jets (BAe 146, An-124, Il-76, C-17) than to high-wing prop planes (C-130, G-222, ATR-42 etc)?

Thanks for any info,
Charles
Make the most of the available light ... a lesson of photography that applies to life
 
Buzz
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RE: Wing Anhedral

Sat Dec 24, 2005 9:05 pm

Hi Charles, Buzz here. It's been a long time, but maybe i can describe it...
for example on the C-141, it has anhedral because the high wing and everything else slung underneath would provide too much roll stability. So Lockheed "tuned" the structure so the airplane would be better balance in roll, pitch , and yaw.
That's all i can recall on the topic.
I don't know why the turboprop aircraft have a fairly level wing, with a little dihedral (looking at the Dash 8 series)... prop clearance doesn't seem to be an issue: if you had a MLG that did't extend.... And the prop tips on a DC-3 kick up enough gravel to require the occasional blending. So there's aerodynamics factored in.
g'nite and Merry Christmas
 
Matt72033
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RE: Wing Anhedral

Sat Dec 24, 2005 9:50 pm

i think the lateral stability lost having an anhedral wing is regained to a certain extent by having a high wing with a low C of G
 
Grbld
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RE: Wing Anhedral

Sun Dec 25, 2005 12:46 am

Quoting Matt72033 (Reply 2):
i think the lateral stability lost having an anhedral wing is regained to a certain extent by having a high wing with a low C of G

It's actually the other way around.

Like Buzz says, a high wing aircraft needs anhedral wings because otherwise it's way too hard to put in a bank. Roll stability would be too great and you'd need too much force to roll the aircraft.

Grbld
 
Matt72033
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RE: Wing Anhedral

Sun Dec 25, 2005 1:11 am

Quoting Grbld (Reply 3):
It's actually the other way around.

so in effect....a high wing with low C of G provides too much lateral stability?
anhedral is used to make it unstable, allowing it to be manouvered?
 
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Jetlagged
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RE: Wing Anhedral

Sun Dec 25, 2005 1:29 am

Anhedral on high wings is usually required when the wings are swept back. Sweepback increases roll stability. Turboprops tend not to have swept wings, so don't have anhedral normally.

It's not so much that aircraft like the C141 couldn't be rolled without anhedral, more that they would need a lot of aileron to maintain bank, which is not normally the case and would give them undesirable handling qualities.

A more interesting question is why aircraft like the Tu-134 and Tu-154 have low wings with anhedral. Perhaps Tupolev preferred to design aircraft with very little lateral stability? Anyone know the real reason?
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
LeanOfPeak
Posts: 496
Joined: Thu Oct 21, 2004 2:18 am

RE: Wing Anhedral

Sun Dec 25, 2005 1:37 am

------- [Oops] --------

[Edited 2005-12-24 17:39:06]
 
LeanOfPeak
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RE: Wing Anhedral

Sun Dec 25, 2005 1:38 am

Dihedral is used to increase lateral stability.

There are three ways to increase lateral stability:

  • Dihedral
  • High Wing
  • Wing Sweep


As high-wing transport aircraft generally possess a very high wing and substantial wing sweep, they have, assuming zero dihedral, a great deal of natural lateral stability. The primary problem here is that a design with lateral stability in great excess compared to its directional stability will exhibit a phenomenon called Dutch roll.

In order to tame the excessive lateral stability and the accompanying Dutch roll, anhedral is used.
 
Matt72033
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Joined: Sat May 14, 2005 10:03 pm

RE: Wing Anhedral

Sun Dec 25, 2005 2:28 am

Quoting LeanOfPeak (Reply 7):
There are three ways to increase lateral stability:



Dihedral

High Wing

Wing Sweep

add to that list a high keel surface
 
LeanOfPeak
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Joined: Thu Oct 21, 2004 2:18 am

RE: Wing Anhedral

Sun Dec 25, 2005 2:38 am

OK, among the ways to increase lateral stability are these three...
 
Kukkudrill
Topic Author
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Joined: Thu Dec 30, 2004 10:11 pm

RE: Wing Anhedral

Sun Dec 25, 2005 6:59 am

Thanks for the replies!

Charles
Make the most of the available light ... a lesson of photography that applies to life
 
flyf15
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Joined: Tue May 18, 1999 11:10 am

RE: Wing Anhedral

Sun Dec 25, 2005 12:28 pm

Anyone know why the Falcon series of business jets (especially the Falcon 50 it seems) appear to have anhedral?
 
LeanOfPeak
Posts: 496
Joined: Thu Oct 21, 2004 2:18 am

RE: Wing Anhedral

Sun Dec 25, 2005 3:14 pm

The Falcons seem to have very close to a planar wing, especially when deflected by lift, with what appears to be a hint of inverted gull (Anhedral inboard, dihedral outboard).

Most of the anhedral I see on the Falcons is in the horizontal stabilizer.
 
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Starlionblue
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RE: Wing Anhedral

Sun Jan 01, 2006 5:18 am

Quoting Jetlagged (Reply 5):
A more interesting question is why aircraft like the Tu-134 and Tu-154 have low wings with anhedral. Perhaps Tupolev preferred to design aircraft with very little lateral stability? Anyone know the real reason?

Maybe, and I'm just speculating here, this has to do with the unusual main landing gear arrangement on the Tu-154. And they certainly look cool! Big grin
"There are no stupid questions, but there are a lot of inquisitive idiots."

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