Kukkudrill From Malta, joined Dec 2004, 1123 posts, RR: 4 Posted (10 years 5 months 1 week 14 hours ago) and read 18495 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,
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Buzz From United States of America, joined Nov 1999, 697 posts, RR: 20
Reply 1, posted (10 years 5 months 1 week 13 hours ago) and read 18499 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.
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Jetlagged From United Kingdom, joined Jan 2005, 2620 posts, RR: 25
Reply 5, posted (10 years 5 months 1 week 8 hours ago) and read 18461 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?
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LeanOfPeak From United States of America, joined Oct 2004, 509 posts, RR: 1
Reply 7, posted (10 years 5 months 1 week 8 hours ago) and read 18460 times:
Dihedral is used to increase lateral stability.
There are three ways to increase lateral stability:
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.
Starlionblue From Greenland, joined Feb 2004, 17661 posts, RR: 65
Reply 13, posted (10 years 5 months 5 hours ago) and read 18195 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!
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