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Wing Anhedral  
User currently offlineKukkudrill From Malta, joined Dec 2004, 1123 posts, RR: 5
Posted (8 years 7 months 1 week 5 days 12 hours ago) and read 15132 times:

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
13 replies: All unread, jump to last
 
User currently offlineBuzz From United States of America, joined Nov 1999, 697 posts, RR: 21
Reply 1, posted (8 years 7 months 1 week 5 days 11 hours ago) and read 15132 times:

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


User currently offlineMatt72033 From United Kingdom, joined May 2005, 1617 posts, RR: 4
Reply 2, posted (8 years 7 months 1 week 5 days 11 hours ago) and read 15129 times:

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

User currently offlineGrbld From Netherlands, joined Dec 2005, 353 posts, RR: 3
Reply 3, posted (8 years 7 months 1 week 5 days 8 hours ago) and read 15108 times:

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


User currently offlineMatt72033 From United Kingdom, joined May 2005, 1617 posts, RR: 4
Reply 4, posted (8 years 7 months 1 week 5 days 7 hours ago) and read 15102 times:

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?


User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2543 posts, RR: 24
Reply 5, posted (8 years 7 months 1 week 5 days 7 hours ago) and read 15094 times:

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.
User currently offlineLeanOfPeak From United States of America, joined Oct 2004, 509 posts, RR: 1
Reply 6, posted (8 years 7 months 1 week 5 days 7 hours ago) and read 15093 times:

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

[Edited 2005-12-24 17:39:06]

User currently offlineLeanOfPeak From United States of America, joined Oct 2004, 509 posts, RR: 1
Reply 7, posted (8 years 7 months 1 week 5 days 7 hours ago) and read 15093 times:

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.


User currently offlineMatt72033 From United Kingdom, joined May 2005, 1617 posts, RR: 4
Reply 8, posted (8 years 7 months 1 week 5 days 6 hours ago) and read 15080 times:

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


User currently offlineLeanOfPeak From United States of America, joined Oct 2004, 509 posts, RR: 1
Reply 9, posted (8 years 7 months 1 week 5 days 6 hours ago) and read 15076 times:

OK, among the ways to increase lateral stability are these three...

User currently offlineKukkudrill From Malta, joined Dec 2004, 1123 posts, RR: 5
Reply 10, posted (8 years 7 months 1 week 5 days 1 hour ago) and read 15044 times:

Thanks for the replies!

Charles



Make the most of the available light ... a lesson of photography that applies to life
User currently offlineFlyf15 From , joined Dec 1969, posts, RR:
Reply 11, posted (8 years 7 months 1 week 4 days 20 hours ago) and read 15009 times:

Anyone know why the Falcon series of business jets (especially the Falcon 50 it seems) appear to have anhedral?

User currently offlineLeanOfPeak From United States of America, joined Oct 2004, 509 posts, RR: 1
Reply 12, posted (8 years 7 months 1 week 4 days 17 hours ago) and read 14982 times:

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.


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17003 posts, RR: 67
Reply 13, posted (8 years 7 months 5 days 3 hours ago) and read 14828 times:

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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